#1 A population-based Habitable Zone perspective
Andras Zsom
What can we tell about exoplanet habitability if currently only the stellar properties, planet radius, and the incoming stellar flux are known? The Habitable Zone (HZ) is the region around stars where planets can harbor liquid water on their surfaces. The HZ is traditionally conceived as a sharp region around the star because it is calculated for one planet with specific properties e.g., Earth-like or desert planets , or rocky planets with H2 atmospheres. Such planet-specific approach is limiting because the planets’ atmospheric and geophysical properties, which influence the surface climate and the presence of liquid water, are currently unknown but expected to be diverse.A statistical HZ description is outlined which does not select one specific planet type. Instead the atmospheric and surface properties of exoplanets are treated as random variables and a continuous range of planet scenarios are considered. Various probability density functions are assigned to each observationally unconstrained random variable, and a combination of Monte Carlo sampling and climate modeling is used to generate synthetic exoplanet populations with known surface climates. Then, the properties of the liquid water bearing subpopulation is analyzed.Given our current observational knowledge of small exoplanets, the HZ takes the form of a weakly-constrained but smooth probability function. The model shows that the HZ has an inner edge: it is unlikely that planets receiving two-three times more stellar radiation than Earth can harbor liquid water. But a clear outer edge is not seen: a planet that receives a fraction of Earth’s stellar radiation (1-10%) can be habitable, if the greenhouse effect of the atmosphere is strong enough. The main benefit of the population-based approach is that it will be refined over time as new data on exoplanets and their atmospheres become available.
|
#2 Sifting Through the Noise - Recalculating the Frequency of Earth-Sized Planets Around Kepler-Stars
Ari Silburt, Eric Gaidos, Yanqin Wu
The NASA Kepler space mission has discovered over 4200 exoplanet candidates to date, giving scientists the opportunity to answer such questions like, “what is the probability that a given star in the Milky Way harbours a habitable planet?”. Extracting fine details about these systems however has proven to be a more difficult task than originally anticipated, since most stars in the Kepler field of view are distant, faint, and poorly characterized. In particular, the radii of most Kepler stars are uncertain to 30% or more, which affects precise determination of planet radii. We have revisited the occurrence of Earth-size planets, paying particular attention to the uncertainties in stellar parameters, and introduce the method of “iterative simulation” to infer the planet distribution without resorting to binning. We analyzed a sample of ~76,000 Sun-like stars hosting 430 planet candidates with periods 20-200 days. We restrict to P>20 day planets to infer the “primordial” population, and find that the radius peaks at 2-2.8 Earth radii. Lastly, we calculate the average number of planets per star is 0.46 +/- 0.03 for our range considered, and an occurrence rate of Earth-size planets within the “habitable zone” to be 8.5 +/- 4.5%.
|
#3 The Pale Orange Dot: The Climactic and Spectral Effects of Haze in Archaen Earth’s Atmosphere
Giada Arney, Shawn Domagal-Goldman, Victoria Meadows, Mark Claire
Many exoplanets may have hazy atmospheres, and geochemical evidence suggests Archean Earth had a periodic hydrocarbon haze formed from methane photolysis. We used a coupled 1D climate-photochemical model and a 1D radiative transfer model to examine the effects of this haze on early Earth and analog low pO2 exoplanets. With even substantial fractal hydrocarbon hazes, the globally averaged Archean Earth could have remained above 273 K. The hazes associated with these self-consistent simulations produce strong features for both direct imaging and transit spectroscopy missions: 1.) in direct imaging, a strong, broadband haze absorption feature is seen at short wavelengths, which “reddens” the color of the planet and could be remotely detectable at low spectral resolution; 2.) a sloped transit transmission spectrum similar to Titan’s is seen that masks absorption features from gases at high haze thicknesses. Lastly, we examined how the stellar spectral energy distribution affects hydrocarbon haze formation for planets orbiting several stellar types: the flaring M3.5 dwarf AD Leo, a modeled quiescent M dwarf, a K2V star, and an F2V star. We find that very high or very low UV fluxes are detrimental to hydrocarbon haze formation.
|
#4 The robustness of using near-UV observations to detect and study exoplanet magnetic fields
Jake Turner, Duncan Christie, Robert E. Johnson, Phil Arras
Studying the magnetic fields of exoplanets will allow for the investigation of their formation history, interior structure, rotation period, atmospheric dynamics, moons, and potential habitability. We observed the transits of 16 exoplanets in the near-UV to detect their magnetic fields. It was postulated that the magnetic fields of all our targets could be constrained if their near-UV light curves start earlier than in their optical light curves. We do not observe an early ingress in any of our targets, but determine upper limits on their magnetic field strengths. All our magnetic field upper limits are well below the predicted magnetic field strengths for hot Jupiters. The upper limits we derived assume that there is an absorbing species in the near-UV and cannot be trusted if there is no such species. We simulate the chemistry, radiation transport, and dynamics of the plasma characteristics in the vicinity of a hot Jupiter using the code CLOUDY. Using CLOUDY we have investigated whether there is an absorption species in the near-UV that can exist to cause an observable early ingress. We find that there isn’t a species in the near-UV that can cause an absorption. Therefore, our upper limits cannot be trusted.
|
#5 The Habitable Zones of Pre-Main-Sequence Stars
Ramses Ramirez, Lisa Kaltenegger
The habitable zone (HZ) is the region around a star in which liquid water could exist on a planetary surface. Although most HZ studies focus on the main-sequence, here we argue that the pre-main-sequence HZ provides additional targets. The spatial distribution of liquid water and its change during the pre-main-sequence phase of protoplanetary systems is important for understanding planetary habitability. Such worlds are interesting for future missions because the coolest stars could provide habitable conditions for up to 2.5 billion years post-accretion. Moreover, for a given star type, planetary systems are more easily resolved because of higher pre-main-sequence stellar luminosities, resulting in larger planet-star separation for cool stars than is the case for the traditional main-sequence (MS) habitable zone (HZ). Using 1-D radiative-convective climate and stellar evolutionary models, we calculate pre-main-sequence HZ distances for F1-M8 stellar types. We also show that accreting planets that are later located in the traditional MS HZ orbiting stars cooler than a K5 receive stellar fluxes that exceed the runaway greenhouse threshold, and thus may lose substantial amounts of water. We predict that M-star planets need to initially accrete more water than Earth did or have additional water delivered afterwards to remain habitable.
|
#7 Spacing of Kepler Planets: Sculpting by Dynamical Instability
Bonan (Michael) Pu, Yanqin Wu
We study the orbital architecture of multi-planet systems detected by the Kepler transit mission using N-body simulations. We find the minimum spacing required for systems of similar masses to survive dynamical instability for as long as a billion years is $\sim 10$ mutual Hill radii, if all orbits are circular and coplanar; and $\sim 12$ if planetary orbits have eccentricities $\sim 0.02$ (a value suggested by studies of planet transit-time-variations). In comparison, accounting for transit geometry and sensitivity limits, the observed spacings are tightly clustered around $12$ mutual Hill radii. This apparent coincidence, between the observed spacing and the theoretical stability threshold, leads us to propose that typical planetary systems were formed with even tighter spacing, but most, except for the widest ones, have undergone dynamical instability, and are pared down to a more anemic version of their former selves, with fewer planets and larger spacings. So while the high multiple systems (five or more transiting planets) are primordial systems that remain stable, the single or double planetary systems, abundantly discovered by the Kepler mission, may be the descendants of more closely packed high multiple systems.
|
#9 Effects of Disk Photoevaporation on Planet Migration
Alexander W. Wise, Dr. Sarah E. Dodson-Robinson
The final locations of planets may be influenced by turning points in their migration tracks called “planet traps” (Hasegawa & Pudritz 2013, 2014). We explore a new planet trap caused by photoevaporation of a protoplanetary disk. Near the end of the lifetime of the gas disk, photoevaporation rates on the inner disk begin to exceed viscous accretion rates, initially resulting in a gap being formed at ~1 AU. Disk material inside the gap is quickly drained and then the gap widens until the gas disk is entirely blown away. Using a combination of analytical calculations and numerical simulations, we show that the variations of disk density resulting from this process can affect the migration tracks of planets. In particular, the initial photoevaporative gap at ~1 AU stops planets from migrating inward from the gap until photoevaporation disperses the remaining disk and the planets lose their primary source of migration. This process may explain the apparent pileup of giant exoplanets around 1 AU seen in radial velocity surveys.
|
#10 A Catalog of Transit Timing Posterior Distributions for all Kepler Planet Candidate Events
Benjamin Montet, Juliette Becker, John Johnson
Kepler has ushered in a new era of planetary dynamics, enabling the detection of interactions between multiple planets in transiting systems for hundreds of systems. These interactions, observed as transit timing variations, have been used to find non-transiting companions to transiting systems and to measure masses, eccentricities, and inclinations of transiting planets. Often, physical parameters are inferred by comparing the observed light curve to the result of a photodynamical model, a time-intensive process that often ignores the effects of correlated noise in the light curve. Catalogs of transit timing observations have previously neglected non-Gaussian uncertainties in the times of transit, uncertainties in the transit shape, and short cadence data. Here, we present a catalog of not only times of transit centers, but also posterior distributions on the time of transit for every transit event in the Kepler data, developed through importance sampling of each transit. This catalog allows us to marginalize over uncertainties in the transit shape and incorporate short cadence data, the effects of correlated noise, and non-Gaussian posteriors. Our catalog will enable dynamical studies that reflect accurately the precision of Kepler and its limitations without requiring the computational power to model the light curve completely with every integration.
|
#11 Precise Planetary Masses, Radii and Orbital Eccentricities of Sub-Neptunes from Transit Timing
Daniel Jontof-Hutter, Jason Rowe, Eric Ford, Jack Lissauer, Daniel Fabrycky
Kepler’s bounty of sub-Neptunes enables us to study a regime in planetary size and mass that includes a transition from rocky planets to those with substantial envelopes of volatiles— either ices or gases. Characterizing these planets’ masses and radii can probe this transition.There is a small sample of exoplanets with known masses and radii, mostly hot Jupiters whose radii are known from transit depths, and whose masses are determined from radial velocity spectroscopy (RV). In the absence of detectable RV, observed transit timing variations (TTVs) probe perturbations between planets that pass close to one another or are near resonance, and hence dynamical fits can measure planetary masses and eccentricities, particularly in compact multi-planet systems.The precision in measuring the radius of a transiting planet rests on the uncertainty in the stellar radius, typically ~10% for targets with spectral follow-up. With TTVs, however, solutions for the orbital eccentricity can, alongside spectra and the transit light curve, tightly constrain the stellar density and radius, permitting useful planetary density determinations. Here we show the wide range of sizes in planets with measured masses from 5-10 Earth masses; from super-earth size and likely rocky, to sub-saturn size with volumes dominated by light gases.
|
#12 Dynamical stability of imaged planetary systems in formation: Application to HL Tau
Daniel Tamayo, A.H.M.J. Triaud, K. Menou, H. Rein
A recent ALMA image revealed several concentric gaps in the protoplanetary disk surrounding the young star HL Tau. We consider the hypothesis that these gaps are carved by planets, and present a general framework for understanding the dynamical stability of such systems over typical disk lifetimes, providing estimates for the maximum planetary masses. We argue that the locations of resonances should be significantly shifted in disks as massive as estimated for HL Tau, and that theoretical uncertainties in the exact offset, together with observational errors, imply a large uncertainty in the dynamical state and stability in such disks. An important observational avenue to breaking this degeneracy is to search for eccentric gaps, which could implicate resonantly interacting planets. Unfortunately, massive disks should also induce swift pericenter precession that would smear out any such eccentric features of planetary origin. This motivates pushing toward more typical, less massive disks. For a nominal non-resonant model of the HL Tau system with five planets, we find a maximum mass for the outer three bodies of approximately 2 Neptune masses. In a resonant configuration, these planets can reach at least the mass of Saturn. The inner two planets’ masses are unconstrained by dynamical stability arguments.
|
#13 Eccentricity Excitation of Giant Planets: Shedding Light on the Eccentricity Valley
David Tsang, Neal Turner, Andrew Cumming
We show that the first order (non-co-orbital) corotation torques are significantly modified by entropy gradients in a non-barotropic protoplanetary disk. Such non-barotropic torques can dramatically alter the balance that, for barotropic cases, results in the net eccentricity damping for giant gap-clearing planets embedded in the disk. We demonstrate that stellar illumination can heat the gap enough for the planet’s orbital eccentricity to instead be excited. We also discuss the “Eccentricity Valley” noted in the known exoplanet population, where low-metallicity stars have a deficit of eccentric planets between ~0.1 and ~1 AU compared to metal-rich systems. We show that this feature in the planet distribution may be due to the self-shadowing of the disk by a rim located at the dust sublimation radius ~0.1 AU, which is known to exist for several T Tauri systems. In the shadowed region between ~0.1 and ~1 AU, lack of gap insolation allows disk interactions to damp eccentricity. Outside such shadowed regions stellar illumination can heat the planetary gaps and drive eccentricity growth for giant planets. We suggest that the self-shadowing does not arise at higher metallicity due to the increased optical depth of the gas interior to the dust sublimation radius.
|
#14 Accessing the fundamental properties of young stars
Ian Czekala
Mass is the fundamental property that determines a star’s fate. In particular, the masses of young stars are of great relevance to many astrophysical problems, including star and planet formation. We have developed a novel approach that combines optical/near infrared high resolution spectroscopy and spatially resolved sub-millimeter spectral line imaging to derive the fundamental properties of a young star: mass, temperature, and radius. By applying our technique to a sample of pre-main sequence stars, we are mapping out a dynamically-calibrated Hertzsprung-Russell diagram for the express purpose of evaluating pre-main sequence evolutionary models.
|
#15 Gravitational Instabilities in Circumbinary Protoplanetary Disks: Numerical 3D Hydrodynamics Study
Karna Desai, Thomas Steiman-Cameron, Scott Michael, Kai Cai, Richard Durisen
We present a 3D hydrodynamical study of gravitational instabilities (GIs) in a circumbinary protoplanetary disk around a Solar mass star and a brown dwarf companion. GIs can play an important, and at times dominant, role in driving the structural evolution of protoplanetary disks. Although circumbinary disks have been discovered, GIs have not been explored in detail in these systems. The reported simulations were performed employing CHYMERA, a radiative 3D hydrodynamics code developed by the Indiana University Hydrodynamics Group. The simulations include disk self-gravity and radiative cooling governed by realistic dust opacities. We examine the role of GIs in modulating the thermodynamic state of the disks, and determine the strengths of GI-induced density waves, non-axisymmetric density structures, and associated mass inflow and outflow, and gravitational torques. One of the goal of this study is to determine whether presence of the companion might cause the disk to fragment. Results are compared with a parallel simulation of a fiducial protoplanetary disk without the presence of the brown dwarf binary companion.
|
#16 Formation of Misaligned Hot Jupiters in Stellar Binaries
Kassandra Anderson, Natalia Storch, Dong Lai
Motivated by observed hot Jupiter systems with high stellar spin-orbit misalignment, we examine the dynamics of the stellar spin axis in planetary systems where the host star has a distant (100 - 1000 AU) inclined stellar companion. In this scenario, planets can undergo Kozai-Lidov oscillations and migrate inward, while the stellar spin axis is torqued by the planet, and evolves in a complex, and often chaotic manner. Understanding the spin-orbit dynamics is helpful for understanding the formation histories of hot Jupiters, and could help differentiate between various proposed migration mechanisms. We describe the complex dynamics that the stellar spin axis undergoes, and show that the final distribution of spin-orbit misalignment angles depends strongly on both the stellar spin properties and planet mass.
|
#17 Planet Formation in Binary Systems - how Solid is the 1 km Barrier?
Kedron Silsbee, Roman Rafikov
Observations of planets at separations greater than 1 AU in tight binary systems, as well as close-in planets in circumbinary configurations, present a challenge to theories of planet formation. Cores of giant planets are commonly thought to form via coagulation of planetesimals. This mechanism is viable if relative velocities between planetesimals are low enough that collisions lead to sticking rather than fragmentation. In binary systems, gravity from the companion excites planetesimal eccentricity, leading to destructive collisions. We developed an analytic model of planetesimal dynamics incorporating gas drag and gravity from both the binary companion and an eccentric disk, which predicts planetesimal orbital dynamics. We coupled these results with a model for collisional outcomes to determine disk parameters and locations in the disk favorable for planet formation, in both circumprimary and circumbinary systems. We find in situ formation is possible even in dynamically difficult circumprimary systems such as HD 196885, assuming that planetesimals grew in a massive low eccentricity protoplanetary disk aligned with the binary orbit. In situ formation of the Kepler circumbinary systems is harder, requiring kilometer sized initial planetesimals even under the most generous disk assumptions.
|
#18 The Mass-Radius-Eccentricity Distribution of Near-Resonant Transiting Exoplanet Pairs Detected by Kepler
Megan Shabram, Eric Ford, Daniel Jontof-Hutter
We characterize the mass-radius-eccentricity distribution of transiting planets near mean motion resonances using Transit Timing Variations (TTV) observations from NASA’s Kepler mission.Kepler’s precise measurements of transit times (Mazeh et al. 2014; Rowe et al. 2015) constrain the planet-star mass ratio, eccentricity and pericenter directions for hundreds of planets. Strongly-interacting planetary systems allow TTVs to provide precise measurements of masses and orbital eccentricities separately (e.g., Kepler-36, Carter et al. 2012). In addition to these precisely characterized planetary systems, there are several systems harboring at least two planets near a mean motion resonance (MMR) for which TTVs provide a joint constraint on planet masses, eccentricities and pericenter directions (Hadden et al. 2015). Unfortunately, a near degeneracy between these parameters leads to a posterior probability density with highly correlated uncertainties. Nevertheless, the population encodes valuable information about the distribution of planet masses, orbital eccentricities and the planet mass-radius relationship. We characterize the distribution of masses and eccentricities for near-resonant transiting planets by combining a hierarchical Bayesian model with an analytic model for the TTV signatures of near-resonant planet pairs (Lithwick & Wu 2012). By developing a rigorous statistical framework for analyzing the TTV signatures of a population of planetary systems, we significantly improve upon previous analyses. For example, our analysis includes transit timing measurements of near-resonant transiting planet pairs regardless of whether there is a significant detection of TTVs, thereby avoiding biases due to only including TTV detections.
|
#19 Chaotic Dynamics of Stellar Spin Driven by Planets Undergoing Lidov-Kozai Oscillations
Natalia I. Storch, Dong Lai, Kassandra R. Anderson
Many exoplanetary systems containing hot Jupiters are found to possess significant misalignment between the spin axis of the host star and the planet’s orbital angular momentum axis. A possible channel for producing such misaligned hot Jupiters involves Lidov-Kozai oscillations of the planet’s orbital eccentricity and inclination driven by a distant binary companion. In a recent work (Storch, Anderson & Lai 2014), we have shown that a proto-hot Jupiter undergoing Lidov-Kozai oscillations can induce complex, and often chaotic, evolution of the spin axis of its host star. Here we discuss several aspects of this complex evolution. We show that the chaotic spin behavior arises due to overlaps in a set of secular spin-orbit resonances. We discuss how the existence of these resonances affects several aspects of the evolution of the system in the presence of dissipative tides within the planet. These effects include bifurcation of the final spin-orbit misalignment angle, and a novel phenomenon we term “adiabatic resonance advection”, in which the spin-orbit angle becomes trapped in a resonance and advected with it to higher misalignment.
|
#20 On the Origin and Evolution of the Kepler-36 System
Thomas Rimlinger, Douglas Hamilton, Derek Richardson
The Kepler-36 system features two exoplanets orbiting a sunlike star in a 7:6 mean-motion orbital resonance at distances of approximately 0.1 AU. The inner planet, a super-Earth with an estimated density of 6.8 g/cc, is significantly denser than the outer sub-Neptune (rho = 0.86 g/cc) [Carter et al. 2012]. This statistically anomalous configuration deviates from the predictions of traditional planetary evolution theories. We explore origin scenarios for this unusual system using numerical integrations with HNDrag, a sophisticated N-body code. In our model, the outer gas giant migrates inwards early in the star’s lifetime, pushing the inner planet ahead and driving accretion of rocky bodies. Such accretion substantially increases the inner planet’s density. To model the accretionary events, we incorporate collisions (modeled as impulses) of different magnitudes onto the inner planet. We also simulate a circumstellar gas disk that damps the planets’ semimajor axes and eccentricities. Our results indicate that it is possible to capture into the 7:6 resonance with this model. In addition, we investigate the extent of the parameter space that permits such a capture as well as its statistical likelihood.
|
#21 Hot Jupiter Atmospheres Revealed with HST/WFC3
Laura Kreidberg
Detailed characterization of exoplanets has begun to yield constraints on their atmospheric properties that rival our knowledge of the Solar System planets. These measurements provide unique insight into planet formation and evolution because atmospheres are a rich record of protoplanetary disk chemistry. In this talk, I will present new constraints on hot Jupiter atmospheric composition and thermal structure from an intensive Hubble Space Telescope observational campaign. I will discuss the importance of synthesizing multiple observational techniques - emission spectroscopy, transmissionspectroscopy, and phase curves - to obtain robust constraints onexoplanet atmospheric chemistry and physics. This intensive observational approach will lay the foundation for characterizing the atmospheres of potentially habitable planets.
|
#22 Colour-Magnitude Diagrams for Transiting Exoplanets
Amaury Triaud
Colour-Magnitude diagrams have been used for about a century to study stellar populations and led to immense advances in stellar evolution.Now similar diagrams can assembled for transiting exoplanets. I will show how to constitute one, even in the absence of GAIA’s parallaxes. More importantly I will present how they can be used to infer properties about the current populations of hot Jupiters and Neptunes, how they compare to directly imaged exoplanets and brown dwarfs.Some interpretations can be made on individual planets too and will show a couple of examples.Then, I will describe how useful they are to choose between planets, notably to decide which objects should receive significant characterisation efforts in the presence of only partial information about the atmospheric properties of these planets.Finally, I may venture into theoretical aspects about these diagrams, what can be prepared from models, how to study young and old planets.
|
#24 Multiband nulling coronography
Brian A. Hicks, Richard G. Lyon, Mark Clampin, Peter Petrone III, Matthew R. Bolcar, Udayan Mallik
Contrast, separation, and radiometric properties of exoplanetary systems place stringent requirements on the space-based 10-meter class telescope and starlight suppression system that will be needed for detecting and studying Earth 2.0. A nulling interferometer (“nuller”) is a coronagraphic suppression system that can be used with arbitrary telescope apertures (unobscured, obscured, segmented, sparse) and designed to access multiple spectroscopic absorption features of oxygen and water. Efforts are underway to evolve such a nuller that achieves high-order starlight suppression with low sensitivity to instabilities, full off-axis discovery space, and high throughput - all with a single nuller. An overview of these efforts will be presented outlining some of the design and testing milestones that have been achieved so far.
|
#25 KMTNet: A Cold Exoplanet Census Through a Global Microlensing Survey
Calen B. Henderson
The unique sensitivity of gravitational microlensing to low-mass planets near and beyond the snow line makes it an indispensable tool for understanding the distribution and formation mechanisms of exoplanets. The Korean Microlensing Telescope Network (KMTNet) consists of three 1.6m telescopes each with a 4 square-degree field of view and will be dedicated to monitoring the Galactic Bulge in order to detect exoplanets via gravitational microlensing. With its relatively large aperture, large field of view, high (~10-minute) cadence, and near-complete longitudinal coverage of the Galactic Bulge for 8 months a year, KMTNet is expected to increase the the annual detection rate of exoplanets via microlensing by a factor of ~5 over current ground-based surveys, pushing down to the mass of Earth for bound and unbound planets. I will summarize the predicted yields of KMTNet’s survey based on detailed simulations, highlighting its sensitivity to low-mass planets and its expected haul of free-floating planets. I will also describe the prospects for characterization of the exoplanetary systems KMTNet will detect, focusing on the variety of techniques current and future high-resolution facilities such as VLT, GMT, and JWST can use to measure the flux from the host stars and ultimately derive planet masses.
|
#26 Characterizing Transiting Exoplanet Atmospheres with Gemini/GMOS: First Results
Catherine Huitson, Jean-Michel Desert, Jacob Bean, Jonathan Fortney, Kevin Stevenson, Marcel Bergmann
We present the first results from a 4-year ground-based survey of nine transiting exoplanet atmospheres. The program uses the Multi-Object Spectrograph (GMOS) on both Gemini north and south to repetitively measure transit lightcurves of individual exoplanets at high spectrophotometric precision. I will present the first results from this program. We attain photometric precisions per spectral bin of 200-600 ppm. Such precision enables us to construct transmission spectra of hot Jupiters. These transmission spectra reveal the dominant upper-atmosphere absorbers in the optical bandpass. Our overarching goal is to understand the prevalence and formation of high altitude clouds and hazes, and other important atmospheric constituents.
|
#27 First exoplanet transit observations with SOFIA
Daniel Angerhausen, & the SOFIA exoplanet team
We present the first two successful exoplanet transit observations with the Stratospheric Observatory for Infrared Astronomy (SOFIA) as a demonstration of SOFIA’s capabilities in this field. The first observation in cycle one was a transit of the hot Jupiter HD 189733 b, where we obtained two simultaneous primary transit lightcurves in the B and z ′ bands. The second observation was a transit of GJ 1214 b observed in cycle two, where we leveraged SOFIA’s full potential by observing three optical and one infrared channel simultaneously with the HIPO, FPI and FLITECAM instruments. Previous theoretical studies have shown that SOFIA has some unique advantages over other - in particular ground-based - platforms in this field, which we are now finally able to test in practise. The HD 189733 b transit observation with HIPO on SOFIA showed that absolute photometry close to the photon noise limit is possible in the optical. We are currently working on the cycle 2 data on GJ 1214 b which also includes one important IR band and plan to show these results at the conference. We will present a detailed description of our data reduction, in particular the correlation of observational systematic effects with various in-flight parameters unique to the airborne observing environment.
|
#28 Statistical Eclipses of Kepler Long Cadence Sub-Saturn Planet Candidates
Holly Sheets, Drake Deming
We present the results of our work to detect secondary eclipses of sub-Saturn planet candidates in Kepler’s long cadence data and to determine their average albedo. Our method is inherently statistical in nature: we scale and combine photometric data for groups of planets to infer their average eclipse depths, and to greatly increase the signal-to-noise. We have modified our method for averaging short cadence light curves of multiple planet candidates (2014, ApJ, 794, 133), and have applied it to long cadence data. We transform the phase of the individual candidates to match a reference candidate, such that the light curves add constructively, and we account for the broadening of the eclipse due to the 30 minute cadence. In the short cadence data, we found that a group of close-in sub-Saturn candidates (1 to 6 Earth radii) was more reflective than typical hot Jupiters. With the larger number of candidates available in long cadence, we improve the resolution in radius and consider groups of candidates with radii between 1 and 2, 2 and 4, and 4 and 6 Earth radii.
|
#29 Models of exoplanet evaporation
James Owen
Given the numerous exoplanets discovered at close separations to their parents stars, where the stellar UV & X-ray radiation fields can heat the upper layers of the planets atmosphere to 1e4 K, evaporation is bound to occur. I will discuss evaporation in the hydrodynamic limit which can be driven by either the EUV or X-ray radiation, and the associated mass-loss rates. I will argue that evaporation of close-in exoplanets does not occur in `energy limited’ sense where PdV work dominates the energy loss, but that radiative cooling and recombinations are dominant energy sinks. Finally, I will present the results of multi-dimensional calculations and discuss the role planetary and stellar magnetic fields play in exoplanet evaporation, along with the long term impact of evaporation on exoplanets.
|
#30 Photometric Variability of Y Dwarfs
Jesica Trucks, Kevin Hardegree-Ullman, Michael Cushing
Variability in the light curves of brown dwarfs allows us to study the dynamics of ultracool atmospheres. The coolest class of brown dwarfs, the Y dwarfs, has only recently begun to be explored. We have initiated a warm Spitzer program to characterize the variability of Y dwarfs in order to help constrain the models of ultracool brown dwarfs. We have observed fourteen Y dwarfs in two epochs at 3.6 and 4.5 microns. I will discuss the initial results from this campaign.
|
#31 Target Selection for the TESS Survey
Joey Rodriguez
The goal of the TESS mission is to discover small, rocky planets transiting bright stars. Because the mission will be bandwidth-limited, we must create a pre-launch catalog of target stars to observe. We have constructed a compiled catalog of stars from which to select TESS targets. The catalog contains all dwarf stars in the sky with spectral types F5 and later, and I < 12, along with selected sets of fainter M stars. Provisions are being made to augment the target list with stars that fall outside the nominal spectral type and magnitude limits, and to permit dynamic updating of the catalog to accommodate new survey data being released (e.g. GAIA).
|
#32 Improved Parameters for Transiting Exoplanets
Knicole Colon, Joseph Rodriguez, Karen Collins, Joshua Pepper, KELT Team
The KELT (Kilodegree Extremely Little Telescope) survey has been searching for transiting planets for several years and is now producing many exciting results. Discoveries from KELT include the most irradiated brown dwarf known (KELT-1b), several planets with extremely bright host stars (V < 9), a Saturn-mass planet with a long-period outer companion (KELT-6b), and several highly-inflated planets. These discoveries would not be possible without contributions from members of the extensive KELT follow-up network. Through the network we have acquired follow-up observations not only of KELT planets but also of several transiting planets recently discovered by other surveys like SuperWASP. We perform a rigorous analysis of these planets using AstroImageJ (Collins et al., in prep) and EXOFAST (Eastman et al., 2013). EXOFAST produces a global fit of each system, through a simultaneous MCMC analysis of photometric and spectroscopic data. With this analysis we robustly improve the parameters for these planets. We also discuss the utility of the KELT follow-up network for non-exoplanet science.
|
#33 Systematics-insensitive periodic signal search with K2
Ruth Angus, Daniel Foreman-Mackey, John Johnson
Systematic features in K2 light curves, caused by decreased spacecraft pointing precision, pollute the periodograms of long-cadence asteroseismic targets. We develop a method to produce periodograms of K2 light curves that are insensitive to pointing-induced systematics. By modelling light curves as a combination of the systematic trends shared across all stars, as well as a sum of sine and cosine functions over a grid of frequencies, we are able to model the systematics and signals of interest simultaneously. This systematics-insensitive method produces periodograms free from systematic features and, crucially, removes the 6-hour thruster firing signal. We demonstrate that the quality of the resulting periodograms are such that we can detect asteroseismic oscillations in giants, measure stellar rotation periods and detect short-period exoplanets without the need for any detrending. In addition, we develop a method for increasing the detectability of exoplanets orbiting evolved stars, based on their oscillation frequencies.
|
#34 Re-characterization of a gravity-darkened and precessing planetary system PTFO 8-8695
Shoya Kamiaka, Kento Masuda, Yuxin Xue, Yasushi Suto, Tsubasa Nishioka, Risa Murakami, Koichiro Inayama, Madoka Saitoh, Michisuke Tanaka, and Atsunori Yonehara
PTFO 8-8695 is an exoplanetary system consisting of a T-Tauri star and a hot Jupiter, whose transits were observed in 2009 and 2010.Its light curves at the two different epochs show an unexpected time-variability.The host star rotates so rapidly that the strong signature of gravity darkening is expected.Moreover, planet is so close to the star that strong torque between rotational bulge and planet induces the mutual precession of stellar spin and planetary orbital axes.These two features of PTFO 8-8695 are supposed to explain the observed light curve variability at different epochs.Barnes et al. (2013) analyzed light curves and characterized this system on the basis of the above model.While they are successful in modelling the transit lightcurves nicely, the assumption of stellar synchronous rotation to planetary orbital motion that they adopted seems unphysical from the viewpoint of tidal evolution of the system.Therefore we re-analyzed this system without synchronous condition, and found that a variety of solutions are possible to current data.In my talk, we also discuss how to distinguish them by future observations.
|
#35 Transits from the DEdicated MONitor of EXotransits (DEMONEX): Transits of XO-4b
Steven Villanueva Jr., Scott Gaudi, Jason Eastman
The DEdicated MONitor of EXotransits (DEMONEX) was a 20 inch robotic and automated telescope to monitor bright stars hosting transiting exoplanets to discover new planets and improve constraints on the properties of host stars and known planets. We present results for XO-4 containing 6 new transits from the DEMONEX telescope, including 3 full and 3 partial transits, of the planet XO-4b combined with archival light curves and archival radial velocity measurements to derive the host star mass and radius, the planet mass and radius, and a refined period. We test the effects of including various detrend parameters, Mass-Radius relations, and Rossiter-McLaughlin models. We include archival Rossiter-McLaughlin measurements to confirm model dependent measurements of the stellar spin-planetary orbit alignment of XO-4b.
|
#36 Hot and Heavy: Transiting Brown Dwarfs
Thomas Beatty
There are currently ten known transiting brown dwarfs, seven of which orbit single main-sequence stars. These systems give us one of the only ways in which we may directly measure the mass and radius of a brown dwarf, which in turn provides strong constraints on theoretical models of brown dwarf interiors and atmospheres. In addition, the transiting brown dwarfs allow us to forge a link between our understanding of transiting hot Jupiters, and our understanding of the field brown dwarf population. I will discuss recent observational results for the transiting brown dwarf KELT-1b, and suggest how more of these important systems may be discovered in the future.
|
#37 Pre-Transit Absorption Around HD 189733b and an Estimate of the Planetary Magnetic Field
Wilson Cauley, Seth Redfield, Adam Jensen
Magnetic fields are a fundamental property of exoplanets, offering protection from stellar winds and, for Hot Jupiter exoplanets, mediating star-planet interactions. We present a robust detection of a time-resolved pre-transit, as well as in-transit, absorption signature around the hot Jupiter exoplanet HD 189733b using high spectral resolution observations of several hydrogen Balmer lines. The line shape of the pre-transit feature and the shape of the time series absorption provide the strongest constraints on the morphology and physical characteristics of extended structures around an exoplanet. The pre-transit absorption feature occurs 125 minutes before the predicted optical transit, a projected linear distance to the stellar disk of 7.2 planetary radii. The absorption strength observed in the Balmer lines indicates an optically thick, but physically small, geometry. We model this signal as the early ingress of a planetary bow shock. If the bow shock is mediated by a planetary magnetosphere, the large standoff distance derived from the model suggests a large planetary magnetic field strength. Better knowledge of exoplanet magnetic field strengths is crucial to understanding the role these fields play in planetary evolution and the potential development of life on planets in the habitable zone.
|
#38 Emission and Phase Curves from 3D Exoplanet Atmospheres
Y. Katherina Feng
Planetary atmospheres are inherently three-dimensional (3D) structures that feature gradients in temperatures and chemical abundances, as well as hot spots, cold spots, and storms. An understanding of atmospheric composition, which comes from interpreting the spectra of 3D atmospheres, impacts theories of planetary formation, so the accurate determination of abundances is crucial in addressing the origins of the solar system and planets in general.The first step in doing so is preparing robust atmospheric models. We have created a flexible new code to create spectra and thermal emission phase curves from arbitrary 3D model atmospheres. We generate spectra using the radiative transfer code DISORT. Our model planets can have any rotation rate, orbital eccentricity, and orbital inclination, adding great freedom to the viewing geometry that will better portray observed orbital configurations. I present our preliminary results.In the future, we will investigate in particular the role of non-equilibrium chemistry in the atmosphere of the most well-studied transiting exoplanet, HD 189773b, which has full-orbit phase curves in many bandpasses from Spitzer.
|
#39 Exoplanets detection by Gravitational Microlensing theory
Roger Anderson Hurtado Mojica, Medardo Fonseca
The Gravitational Microlensing theory is perhaps the most powerful tool for discovering extrasolar low-mass planets at distances of several AU from their host stars. In this work are shown the basics of Microlensing theory by modeling the lenses as point masses. Some simulations of critical and caustic curves are made, as well as image formation and the magnification curves for a binary lens system, in order to explain why with this technique it is possible to find exoplanets even at separations of few AU using ground-based telescopes. Also are explored the lensing properties of two lens which do not lie in the same plane, the lens equation and the magnification curves in this case are compared with those produced by a binary lens system that lie in the same plane.
|
#40 Suborbital Demonstrations of Starshades
Anthony Harness
One of the most exciting prospects for exoplanet science is the ability to directly image and obtain spectra of an Earth-like planet around another star. Spectra are necessary to characterize the planet, truly determine habitability, search for life, and find a true Earth-twin. One proposed technology that will enable this work is the starshade external occulter. The New Worlds Observer team is currently conducting a suite of suborbital tests and demonstrations to develop starshade technology in preparation for a future Earth-finding mission with starshades. Due to the unique architecture of the starshade, testing at a system-level requires unique and unconventional testing platforms such as Zeppelins, dry lake beds, mountaintops, and vertical takeoff vertical landing rockets. I will present results from completed starshade tests and provide an update on ongoing work to demonstrate starshades with astronomical observations. These tests are aimed to demonstrate the high-contrast capability of starshades, help develop the tools needed to plan for future missions, and validate them as a viable astronomical instrument.
|
#41 Planet Hunting with PARAS
Arpita Roy, Suvrath Mahadevan, Abhijit Chakraborty
PARAS is a high-resolution stabilized optical fiber-fed spectrograph meant for the radial velocity detection of exoplanets around bright stars. Located on a 1.2m telescope in Mt. Abu, India, it has a single-shot spectral coverage of 3800-9500 A at a resolution of ~67,000, and uses simultaneous ThAr calibration. The spectrograph was commissioned in 2010 and has since been performing well, producing radial velocities (RVs) at the 1m/s level. I will discuss both the instrumentation and spectral analysis lessons learned from PARAS, and its importance in context of the next-generation of high-precision RV instruments.
|
#42 The KELT-North Transit Survey: Hot Planets around Hot, Bright Stars
Daniel J. Stevens, on behalf of the KELT-North Survey Team
The Kilodegree Extremely Little Telescope (KELT)-North is a small-aperture, wide-angle automated telescope in southern Arizona that has been surveying roughly 40% of the northern sky for transiting planets since 2006. The small aperture and large field-of-view makes the KELT-North telescope most sensitive to hot Jupiters transiting relatively bright (V~8-10) – and thus relatively hot – stars. Roughly half of the over 200,000 dwarf stars we target are hotter than 6250K; such stars pose novel challenges, but also provide unique opportunities. I will present the transiting substellar companions discovered by KELT-North, focusing in detail on a few recent discoveries. I will discuss our plans for determining the frequency and demographics of short-period companions to hot stars from KELT-North; comparison with similar results for cooler stars may provide important constraints on theories of the emplacement and tidal evolution of low-mass stellar companions. Finally, I will speculate on how the lessons learned from KELT-North may inform target selection and survey strategies for future transit surveys, including the TESS mission.
|
#43 Multifractal structures in radial velocity measurements for exoplanets
Fabio Del Sordo
Radial-velocity data are time-series containing the effect of both planets and stellar disturbances: to observe Earth-like planets, one needs to improve the signal-to-noise ratio, i.e. it is central to understand the noise present in the data. Noise is caused by physical processes which operate on different time-scales, oftentimes acting in a non-periodic fashion. I present here an approach to such problem: to look for multifractal structures in the time-series coming from radial velocity measurements, identifying the underlying long-range correlations and fractal scaling properties, connecting them to the underlying physical processes (stellar oscillations, granulation, rotation, magnetic activity). This method has been previously applied to satellite data related to Arctic sea albedo, relevant for identify trends and noise in the Arctic sea ice (Agarwal, Moon, Wettlaufer, 2012). Here we use such analysis for exoplanetary data related to possible Earth-like planets. Moreover, we apply the same procedure to synthetic data from numerical simulation of stellar dynamos, which give insight on the mechanism responsible for the noise. In such way we can therefore raise the signal-to-noise ratio in the data using the synthetic data as predicted noise to be subtracted from the observations.
|
#44 Towards a Galactic Distribution of Exoplanets
Matthew Penny
Gravitational microlensing surveys have comparable sensitivity to planets orbiting stars in both the Galactic bulge and disk. I will show that the distribution of measured and inferred distance estimates to microlensing planet hosts differs substantially from what one would naively expect. I will outline a number of possible solutions to this puzzle, including that planet abundance may depend on a star’s birth environment or perhaps more simply that the distance estimates may be unreliable. I will end by discussing how upcoming microlensing campaigns by Spitzer and K2 will help to resolve this issue.
|
#45 LSST Can Detect Transiting Exoplanets
Michael Lund
The Large Synoptic Survey Telescope (LSST) has been designed in order to satisfy several different scientific objectives that can be addressed by a ten-year synoptic sky survey. However, LSST will also provide a large amount of data that can then be exploited for additional science beyond its primary goals. This includes the potential of using LSST data to search for transiting exoplanets, and in particular to find planets orbiting host stars that are members of stellar populations that have been less thoroughly probed by current exoplanet surveys.
|
#46 Broadening our Horizons on Short-Period Stellar and Substellar Companions with APOGEE
Nicholas Troup, APOGEE RV Variability Team
In its three years of operation, the Sloan Digital Sky Survey (SDSS-III) Apache Point Observatory Galactic Evolution Experiment (APOGEE-1) observed over 14000 stars which have enough (>7) unique, quality radial velocity measurements over a sufficient baseline to attempt Keplerian orbit fits. In this catalog we present the best fit orbital parameters of 1500 systems with significant RV variations from our automated Keplerian orbit fitting pipeline. While many multiplicity and exoplanet surveys have focused on FGK dwarf stars and the solar neighborhood, our sample contains $>500$ evolved stars (log g <3.8), as well as stars across the disk and into the halo. With a radial velocity precision of ~100 m/s, APOGEE can probe systems with close-in companions down to a few Jupiter-masses (10-3 MSun). In particular, our sample is well suited to comb the brown-dwarf desert. Additionally, stellar parameters and chemical abundances will be available for many of the primary stars in our sample, allowing us to further probe the connection between a host star’s abundance and the presence of companions. Finally, we present some of our most interesting systems with detected companions, as well as initial follow-up observations for a subset of these systems.
|
#47 The Habitable-zone Planet Finder Instrument: Pushing the Limits of Exoplanet Detection in the Near-Infrared
Sam Halverson
The Habitable-zone Planet Finder (HPF) is a stabilized, near-infrared (NIR) Doppler velocimeter being developed at Penn State to discover terrestrial-mass planets around cool M dwarfs. HPF consists of a fiber-fed high resolution spectrograph operating in the z/Y/J NIR bands (0.8 - 1.3 microns), where mid-late M-dwarfs are most luminous. I will present an overview of the current state of high precision radial velocity (RV) measurements in the NIR, and discuss the unique design traits of the HPF spectrograph. In particular, I will focus on recent ‘astro-photonic’ systems developed by the Penn State Optical/Infrared instrumentation group. These systems solve or simplify many issues currently limiting the achievable RV measurement precision of existing Doppler instruments.
|
#48 Improve RV Precision through Better Spectral Modeling and Better Reference Spectra
Sharon Xuesong Wang, Jason T. Wright, Ming Zhao
In precise RV work with iodine cells as calibrators, RV extraction from spectra is done through forward modeling, where references spectra are shifted to the proposed RV and convolved with spectral PSF to fit the data. Our work improves both the modeling process (treating contamination, PSF model construction, algorithm, etc.) and the reference spectra (for both iodine gas cell and target stars). We have: (1) removed > 1m/s aliasing signal at harmonics of a sidereal year caused by contamination from Earth’s atmosphere absorption lines; (2) found an independent way of validating the quality of iodine reference spectra, which shows, quite unexpectedly, concerns over their quality and/or a changing gas cell; (3) constructed the core portion of a new RV extraction code (in Python, will be made available on gitHub) which uses advanced maximum likelihood optimizer or Bayesian MCMC for forward modeling, and incorporates Gaussian processes to properly handle spectral noise/distortion and contamination.
|
#49 Implications for the False-Positive Rate in Kepler Planet Systems From Transit Duration Ratios
Robert C. Morehead, Eric B. Ford
Confirming transiting exoplanet candidates through traditional follow-up methods is challenging, especially for faint host stars. Most of Kepler’s validated planets relied on statistical methods to separate true planets from false-positives. Multiple transiting planet systems (MTPS) have been previously shown to have low false-positive rates and over 851 planets in MTPSs have been statistically validated so far (Lissauer et al. 2014; Rowe et al. 2014). We show that the period-normalized transit duration ratio (ξ) offers additional information that can be used to establish the planetary nature of these systems. We briefly discuss the observed distribution of ξ for the Q1-Q16 Kepler Candidate Search. We also utilize ξ to develop a Bayesian statistical framework combined with Monte Carlo methods to determine which pairs of planet candidates in a MTPS are consistent with the planet hypothesis for a sample of MTPSs that include both candidate and confirmed planets. This analysis proves to be efficient and advantageous in that it only requires catalog-level bulk candidate properties and galactic population modeling to compute the probabilities of a myriad of stellar blend scenarios, without needing additional observational follow-up.
|
#50 From Snowflakes to Snowballs: Bypassing the Bouncing Barrier in Planetesimal Formation
Sarah Dodson-Robinson, Stefano Meschiari
Planet searches and debris-disk observations have demonstrated that icy planet formation is an inevitable outcome of Population I star formation. However, theorists have yet to converge on a physical description of the first stage of planet formation–the growth from millimeter-sized grains to pebbles. While micron-sized grains can easily grow into fluffy aggregates by electrostatic sticking, the surface area/mass ratio becomes too high for sticking when the particles reach roughly one millimeter in size. At the average collision speeds for icy regions of the solar nebula, large grains either bounce or fragment. Here we explore collision outcomes at the low and high ends of the collision speed distribution. At extremely low speeds, electrostatic attraction may overcome the rebound energy for colliding millimeter-sized particles. Even a few “lucky” particles that grow to centimeter sizes may provide the seeds for planetesimal formation. At extremely high speeds, the surface layers of icy particles may melt during collisions. If the melted layer can re-freeze within the collision timescale, the two particles may stick together. We have re-formulated the collisional fusion theory of Wettlaufer (2010), which describes icy particles sticking to a meter-sized boulder, to apply to smaller bodies of similar sizes. We demonstrate that both collisional fusion and the growth of “seeds” can provide a pathway toward planetesimal formation.
|
#51 Breaking the barrier: Simulations of rocky planetesimal formation in protoplanetary disks
Alex Richert, Wladimir Lyra (JPL/Caltech)
The meter size barrier is a well-known problem in early planet formation, wherein the pebbles that form from dust in protoplanetary disks are susceptible to destruction on timescales more rapid than known agglomeration mechanisms can account for. The streaming instability, which occurs when dust particles are trapped in gas pressure maxima, may provide a more rapid path to forming the rocky planetesimals which give rise to terrestrial planets, as well as the seeds of gas giants. I report progress in global 3D hydrodynamical+N-body simulations of dust trapping through the streaming instability in a self-gravitating, magnetorotationally active disk.
|
#52 Giant Planet Formation Through Disk Instability: A study on Dust Settling
Debanjan Sengupta, Sarah E. Dodson-Robinson
There are more than one accepted theories for formation of super-massive planets at a distance ranging from around 5 to 20 AU. Although the general consensus leans towards the theory of core accretion, numerical simulation over the past couple of decades has brought alternatives into the picture. One of the most promising alternative is the fragmentation mechanism in which giant planets are formed directly from the contraction of a clump of gas produced by gravitational instability. In our current work we investigate whether grain growth and subsequent settling can affect the stability criteria of the disk at these distances. We develop a Monte Carlo algorithm to study the physics of grain growth and how grains of different sizes are subject to sedimentation. We then calculate a full wavelength dependent opacity with the evolved grain distribution, followed by a thermal profile of the disk using radiative transfer. We take a prototype disk which is hot on the surface and has a quiescent mid-plane, which, because of being less turbulent allows the grains to grow more efficiently. In this context, we examine the gravitational stability of the layered accretion disk experiencing dust-settling and review the possibilities of super-massive planet formation at the range of distances concerned. The whole work is carried out for a high mass and a low mass disk and the stability of the otherwise gravitationally stable low mass disk is investigated. We also present a steady state grain abundance and the opacity profile at different time of disk evolution. We compare that with the standard viscous accretion disk.
|
#53 Vortices in Dead Zones of Protoplanetary Disks
Ryan Miranda, Dong Lai, Heloise Meheut
Dead zones of protoplanetary disks, in which magnetic turbulence is suppressed, are favorable sites for the formation of large-scale vortices. These are produced as a result of the Rossby wave instability, which is triggered in overdense rings formed at dead zone edges. Using two-dimensional hydrodynamic simulations, we show that vortices are self-consistently created and maintained over hundreds of local orbits in the presence of a dead zone, and demonstrate that they may play several important roles in the evolution of disks. They produce waves which can facilitate angular momentum transport, maintaining steady, non-episodic accretion through the dead zone. They can also efficiently trap dust particles, producing large enhancements of the dust-to-gas ratio, which are necessary for planetesimal formation. This results in asymmetric disk morphologies, which are potentially observable with high-resolution sub-millimeter interferometry.
|
#54 Hubble Space Telescope Spectroscopy of WISE Detected Brown Dwarfs
Adam C. Schneider
The coolest brown dwarfs are indispensable touchstones for ultracool model atmospheres and are a vital component of the volume-limited sample of stars and brown dwarfs in the solar neighborhood. In the last few years, the Wide-field Infrared Survey Explorer (WISE) has uncovered hundreds of nearby cool brown dwarfs, including members of the new ‘Y’ spectral class. Using the Wide Field Camera 3 (WFC3) aboard the Hubble Space Telescope (HST), I have extended the spectral coverage for a significant sample of the known late-type T and Y dwarfs to include the Y, J, and H bands and have confirmed the brown dwarf nature of several new discoveries. Here I present our complete sample of late type dwarfs for which we have obtained HST grism observations (23 total). The increased wavelength coverage allows us to 1) search for spectroscopic features predicted to emerge at low effective temperatures (e.g. ammonia bands), 2) construct a smooth spectral sequence across the T/Y boundary, and 3) attempt to derive improved atmospheric property estimates.
|
#55 First Discoveries from the NEOWISE-Reactivation Proper Motion Survey
Jennifer Greco, Adam Schneider, Michael C. Cushing, J. Davy Kirkpatrick
Recent discoveries with data from the Wide-field Infrared Survey Explorer (WISE; 2009-2010) have demonstrated that some of our closest substellar neighbors have gone undetected because of their low temperatures and high proper motions. WISE was reactivated in December 2013 to search for potentially hazardous near Earth objects (NEOWISE-R). Because the purpose was to search for near-Earth objects, the NEOWISE-R data are single frames, not co-added like previous WISE epochs. Nevertheless, these frames give us an additional epoch of data with which to search for nearby objects with large proper motions. When combined with the WISE data, they give us a ~4-7 year epoch difference, 8-14x longer than the baseline in previous WISE proper motion surveys (Luhman 2014, Kirkpatrick et al. 2014). This increase will allow for a significant improvement in the accuracy of proper motion measurements, and will allow identification of sources with proper motions too small to be detected in previous WISE proper motion surveys. We have combined the NEOWISE-R data with the original WISE data to identify missing members of the solar neighborhood using their proper motions. Here, we report the progress of the NEOWISE-R proper motion survey, including the discovery of three new brown dwarfs.
|
#56 Characterizing Retired A Stars
Luan Ghezzi, John Johnson
A complete understanding of the formation and evolution of planetary systems depends on the precise characterization of the planets and their host stars. The stellar mass is particularly important because it might influence the planet occurrence and it is used to constrain the planetary masses, thus providing information about the systems’ architectures. Single FGK stars on the main sequence usually have precise masses estimated from evolutionary tracks, but the results of this method for subgiants and giants have recently been called into question. In this work, we describe the ongoing efforts to precisely constrain the masses of evolved stars using benchmark subgiants and giants from the literature as well as the sample of retired A stars observed by the California Planet Search survey. Different input atmospheric parameters (from excitation and ionization equilibria, spectral synthesis, interferometry and photometry) and methods (evolutionary tracks, asteroseismology and lithium abundances) are used to critically evaluate the stellar masses and its uncertainties. Preliminary results are discussed and suggest that current mass determinations for evolved stars do not present any significant systematic errors.
|
#58 Constraining the Demographics of Exoplanets Using Results from Multiple Detection Methods
Christian Clanton
The results of several exoplanet discovery methods have begun to characterize the underlying population of planets in our galaxy. These studies have provided interesting results, but, individually, are constrained to limited regions of planet parameter space. Synthesizing detection results from multiple methods yields more powerful constraints on the demographics of exoplanets than is afforded by any individual technique, better informing models of planet formation and migration. We discuss the comparison and combination of results from radial velocity and microlensing surveys, demonstrating an ability to derive robust constraints on the frequency of planets orbiting M dwarfs across several orders of magnitude in both planet mass and semimajor axis. We also discuss the combination of microlensing, radial velocity, and direct imaging surveys to constrain the distribution of long-period, giant planets and the implications of the resultant constraints on the population of wide separation, or unbound, planets identified by microlensing.
|
#59 Ultra Precise Environmental Control for High Precision Radial Velocity Measurements
Gudmundur Stefansson
This project centers around the overall development and testing of the environmental control system (ECS) of the Habitable Zone Planet Finder (HPF) - a Near Infrared (NIR) spectrograph which requires a high level of temperature control to prevent mechanical drifts, thermal contraction and expansion, and a high level of vacuum to prevent refractive index changes in the full optical train. I will discuss the design, fabrication and integration of some of the required subsystems for the HPF-ECS, including: a) the design and fabrication of Multi-Layer Insulation (MLI) blankets, Cu thermal straps, and Al heater-panels; b) wiring of the individual ECS subsystems, and c) the installation and monitoring of the HPF thermal enclosure at McDonald Observatory. Lastly, I will discuss the integration of these subsystems with the fully machined HPF vacuum-cryostat, discuss data acquired from a number of (eventual) vacuum thermal pump-down cycles that (will) demonstrate the sub-milliKelvin temperature stability of the instrument.
|
#60 Defining the Range of Chemistry for Exoplanet Interiors
John Brewer
To understand how planets formed, how common they may be, or wether or not they might be habitable, we have to accurately characterize the planets we are finding, and for that we need to accurately and precisely characterize the stars around wich they live. Traditionally, high resolution spectroscopic analysis has been the gold standard in precise stellar parameters. However, biases in determining surface gravities combined with correlated errors in effective temperature and metallicity have lead to inaccuracies in radius and metallicity which undermine the planet parameters we are interested in. I have developed a new spectroscopic analysis procedure which yields surface gravities accurate to within 0.05 dex of asteroseismically determined log g. In addition to surface gravity the procedure yields precise temperatures, metallicities, and abundances for 15 elements. I have used the technique to analyze more than 2500 spectra from the California Planet Survey taken since 2005. This dataset is allowing me to look for correlations between refractory abundance patterns and planet radius and evaluate the frequency of systems with exotic compositions such as those dominated by graphite and carbides.
|
#63 The Radiation Environment of Habitable-Zone Planets Orbiting Low-Mass Stars
Robert Loyd
Low-mass stars will host the bulk of habitable-zone planets detected in the coming decades. This is due both to the vastly greater number of these stars and to the deeper and more frequent transits of their habitable-zone planets when compared to solar-mass hosts. However, evaluating the true habitability of these planets is now widely recognized to go well beyond simple estimates of planetary surface temperature. In particular, planets orbiting low-mass stars are exposed to stellar radiation that differs substantially from the Sun’s both in its spectral content and its temporal volatility. To better characterize these radiation environments, our group has begun Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanetary Systems (MUSCLES), a treasury survey of 15 M and K dwarf stars (11 hosting planets). We have constructed panchromatic spectra for all X of the targets observed to date and spectrally characterized Y flares detected in the time-series ultraviolet data. These data describe a space environment for habitable-zone planets orbiting low-mass stars that is substantially different than Earth’s. We describe the key differences and how they might modify the atmospheres of rocky planets through photochemistry and mass loss, with implications for habitability and the detection of “biomarker” molecules.(X and Y to be updated nearer to the conference)
|
#64 Sizing up the Stars
Tabetha Boyajian
This presentation will review the status of our survey to measure the fundamental properties of nearby, main-sequence, K- and M- type stars. Our method exploits high angular resolution observations available from long baseline optical/infrared interferometry to precisely measure angular sizes. This data, combined with parallaxes and flux-calibrated photometry, are used to determine stellar luminosities, linear radii, and effective temperatures. We demonstrate how the data are used to calibrate less-direct methods in determining fundamental stellar properties. The data are also used to identify weaknesses in stellar atmosphere and evolutionary modeling, where observed discrepancies with models compared to observations have implications for the characterization of exoplanet systems.
|
#65 Calibrating the pixel-level Kepler imaging data with a causal data-driven model
Dun Wang, Dan Foreman-Mackey, David W. Hogg, Bernhard Schölkopf
We study the importance of star forming environments on the energetics of forming planetesimals. In the earliest phases of planet formation radioactive decay of species such as 26Al and 60Fe dominates their total energy balance and thus clearly had an important role in the formation of solids in our own Solar System. The concentration of these species could vary by orders of magnitude, depending on their delivery mechanism and richness, geometry and dynamical history of the hosting star cluster. Ultimately, understanding the early evolution of planetesimals could help determine whether a planetary system is more or less likely to form terrestrial planets with active plate tectonics and a protective magnetic field, and thus able to give rise to life. We use an interdisciplinary approach, combining the methodology of star cluster simulations in Astrophysics to planet formation modeling in Geophysics in order to understand the environment in which the Solar System formed and how common planetary systems “like ours” might be. For this symposium I will mainly focus on the geophysical perspective, which investigates the following question: What effect does changing the abundances of initial 26Al and 60Fe abundances have on the evolution of planetesimals?
|
#66 Transit Studies with Small Telescopes: Educational Utility and Implications for Future Detection Surveys
Daniel Polsgrove, Devin Della-Rose, Francis Chun, Kimberlee Gresham, Roger Tippets, Steven Novotny, Samantha Howard, Peter Tarvin, Grant Boehme
We discuss tools, techniques, results and lessons learned from transit studies performed by faculty and cadet undergraduate students with sub-meter class telescopes at the U.S. Air Force Academy (USAFA). Differential photometry was used to analyze transit data on known exoplanets collected with the Academy’s 24” f/8 Cassegrain telescope as well as a 20” f/8 Ritchey-Cretien telescope associated with the Falcon Telescope Network (FTN) – a system of ground-based, automated 20” telescopes to be located at twelve sites on five continents. This ongoing effort is aimed at achieving two primary objectives: (1) providing cadets hands-on experience with space object data collection and analysis relevant to Air Force space operations, and (2) determining the capabilities and limitations of equipment and analytical tools currently available to researchers at USAFA. Results from this research are being used to baseline a potential future exoplanet transit survey designed to take advantage of the FTN’s global distribution and continuous sky coverage. Currently, four of the twelve FTN sites are operational, with the remaining eight under construction; the FTN is expected to reach full operational capability by the end of 2016.
|
#67 Radial Velocity Measurements with Small Telescopes: Educational Utility for Future Exoplanet Researchers
Steven J. Novotny
We present results from a radial velocity study of Tau Bootis b by the Astronomical Research Group and Observatory (ARGO) team at the U.S. Air Force Academy (USAFA). Besides providing future officers with hands-on experience and skills relevant to Air Force missions like satellite operations and space situational awareness, the main purpose of this project was to explore spectroscopic capabilities and limitations using our sub-meter class telescope and commercially available analytical software. Tau Bootis b was chosen as the target object due to its advantageous combination of stellar magnitude (v = 4.5), period (3.3 days) and radial velocity change (~ 1000 m/s, peak-to-peak). Spectral data has been collected over the past year with an eShel spectrograph connected to the Academy’s 24” f/16 Cassegrain telescope, with participants including faculty, cadet undergraduates and a local high school student. We describe the various successes, pitfalls and lessons learned while attempting to determine this well-known system’s orbital characteristics with indigenous observational data and analytical techniques.
|
#68 The Unusual Disintegrating Planet Candidate KIC 125557548b: Additional Evidence for Large Particles in the Escaping Debris
Everett Schlawin, Ming Zhao, Johanna Teske, Terry Herter
The intriguing disintegrating exoplanet candidate KIC 12557548b has evidence for a comet-like tail of dusty debris trailing a small rocky planet. The characterization of this tail can constrain the particle size and lifetime of the planet, which likely comes from a rocky sub-Mercury body. Early dust particle size predictions from the scattering of the comet-like tail pointed towards a dust size of 0.1um. These small particles would produce a much deeper optical transit depth than near-infrared transit depth. We measure a transmission spectrum for KIC 12557548b using the SpeX spectrograph and MORIS imager on the Infrared telescope facility from 0.8um to 2.4um with simultaneous r′ photometry. Our transmission spectrum is flat to within errors, supporting previous findings that KIC 12557548b’s debris is likely composed of larger particles >~0.5um.
|
#69 Testing the origin of compact exoplanetary systems around M dwarfs
Mark Veyette, Philip Muirhead, Andrew Mann
Recent results from NASA’s Kepler mission suggest over 20% of mid-M dwarfs in the solar neighborhood host multiple planets in compact configurations (compact multiples). The origin of these unusual systems is unknown, yet has significant consequences for current theories of planetary formation. TESS will discover numerous compact multiples around nearby M dwarfs. By characterizing the stars that host these systems, we can hope to understand the processes that form them. Recent simulations have found that even moderately carbon-enriched protoplanetary disks may form numerous planets in short-period orbits, suggesting that carbon-rich stars could be the source of compact multiples. We describe an investigation of this theory by developing a method to measure the carbon-to-oxygen ratio C/O in M dwarfs from high resolution (R>25,000), high signal-to-noise (SNR>100), near-infrared spectra. We outline a potential observing program to empirically calibrate these methods via a sample of M dwarfs with widely-separated (5’’-1500’’), but associated, F, G or K-type binary companions and present preliminary results. Once calibrated, we will apply these methods to a survey of nearby M dwarfs, including many stars to be observed by TESS and search for a significant correlation between high C/O and the occurrence of compact multiples.
|
#70 The Transit Transmission Spectrum of a Cold Gas Giant
Paul A. Dalba, P. Muirhead, J. Fortney, M. Hedman, P. Nicholson, M. Veyette
Transit transmission spectroscopy is a powerful technique that utilizes the wavelength dependence of an exoplanet’s transit depth to probe the composition and structure of its atmosphere. While this technique has led to detections of various molecular features in exoplanet atmospheres, it heavily relies on our ability to generate complex models of synthetic atmospheres that match exoplanet observations. Solar system objects are our only “ground truth” for transit transmission spectroscopy. In this work, we utilize observations of Saturn from the Visual and Infrared Mapping Spectrometer on board the Cassini Spacecraft to enhance our ability to use transmission spectroscopy for exoplanet atmosphere characterization. We develop an occultation model that fits for the effects of atmospheric refraction and molecular absorption and produces the first transit transmission spectrum of Saturn. This work will contribute to our understanding of what transmission spectra can and cannot reveal about cold, gaseous exoplanets.
|
#71 M-dwarf Planet Occurrence Rates out to Several Hundred Days Using the Citizen Science Program Planet Hunters
Joseph Schmitt, Tabetha Boyajian, Ji Wang, Stuart Lynn, Chris Lintott, Matt Giguere, Debra Fischer
Exoplanet science has been revolutionized by the Kepler spacecraft’s discovery of more than 1,000 confirmed planets and thousands more candidates. This has enabled the first population studies of exoplanets, which have begun to shed light on the occurrence rate of planets, a measurement of fundamental importance in exoplanets. We are now working towards calculating an occurrence rate for M-dwarf planets out to several hundred, perhaps even 1000 days, instead of the typical P < 50 days. This is made possible using Planet Hunters, a citizen science project which uses the public to classify Kepler data and identify transits one at a time rather than requiring multiple transits, allowing people to find planets with as few as one or two transits. We present here our current progress.
|
#72 T Dwarf Model Fits at Low Spectral Resolution
Paige Giorla, Emily L. Rice, Stephanie T. Douglas, Gregory N. Mace
Some of the coolest, low mass brown dwarfs are analogs for high mass, hotter planets, since they have overlapping temperatures, masses, and spectral features. We can therefore use brown dwarfs to probe our physical understanding of exoplanet atmospheres. We must first examine if we interpret brown dwarf spectra reliably to understand the physical processes occurring in these substellar objects. Since brown dwarfs have complex spectra that are influenced by gravity, metallicity, and cloud properties, their spectral types possibly do not correlate uniquely to temperature. I investigate this relationship in T dwarfs, the coolest fully-populated brown dwarf spectral class, using synthetic model fits to observed spectra. Using a sample of 154 T dwarfs with near-infrared, low resolution (R~75-200) SpeX Prism spectra, I compare four model grids, which treat cloud parameters differently, to the spectra of these objects. The model fits will elucidate temperature and gravity parameters of the objects, to constrain their atmospheric properties.
|
#73 Age-Rotation-Activity Relation for Kepler Field Stars
Thea Kozakis, James Lloyd, Jose Manuel Olmedo Aguilar, Miguel Chavez, Kevin Covey, Eric Mamajek, Evgenya Shkolnik, Lucianne Walkowicz
A better understanding of stellar activity and age is important when characterizing potentially habitable exoplanets, since the UV activity influences the surface habitability and detectability of biosignatures in the atmosphere [1,2]. Over the past several decades, it has been shown that there is a strong connection between stellar rotation, activity, and age, which has come to be known as the age-rotation-activity relationship. A comprehensive understanding of this relationship will enable more accurate stellar age determination as well as improve our knowledge of magnetic field generation. Here we present the results of an analysis of 19,616 Kepler field stars with known rotation periods and near-UV fluxes, 15,471 with characterized differential rotation. All rotation periods were calculated in [3], and all near-UV fluxes were obtained by the GALEX space telescope. Previous studies of the age-rotation-activity have been conducted with at most hundreds of targets, and exclusively in young stellar clusters.References:[1] Rugheimer S. et al (2015a) submitted. [2] Rugheimer S. et al (2015b), submitted. [3] Reinhold T. et al (2014) A&A, 560, A4
|
#74 Empirical Radius/Temperature Fits for Cool Stars Using Interferometry
Arthur Adams
The radii of transiting exoplanets and boundaries of the HZ depend on the radii and effective temperature of the host stars. Using angular diameter measurements from the CHARA interferometer, Hipparcos parallaxes, and new bolometric fluxes, we now have radii and effective temperatures for 61 nearby late-K and M dwarfs. We derive relations between each of these to both a range of color indices and metallicity. This work expands previous relations with a larger sample, and uses both directly measured photometric colors and synthetic colors from convolution with SEDs, which allows for empirical color-metallicity-radius and color-metallicity-temperature relations for a wide range of available color magnitudes.
|
#75 Characterization of 53 Long-Period Exoplanet Candidates from the Kepler Archival Data
Ji Wang, Allysa Picard, Joey Schmitt, Bo Ma, Debra Fischer
The census is still incomplete for exoplanets at 1 AU and beyond. Detections of these planets provide valuable information on how they form and evolve at large orbital distances. We present 53 long-period planet candidates identified by Planet Hunters based on the Kepler archival data (Q1-Q17). Among them, 24 exhibit only one transit, 15 have two visible transits and 14 have three visible transits. For planet candidates with only one visible transit, we estimate their orbital periods based on transit duration and host star properties. The majority of the planet candidates in this work (75%) have orbital periods that correspond to distances of 1-3 AU from their host stars. We conduct follow-up imaging and spectroscopic observations to validate and characterize planet host stars. We obtain adaptive optics images to search for possible blending sources. We also take high-resolution stellar spectra to estimate stellar properties. This sample of long-period planet candidates, together with a proper assessment of detection efficiency of Planet Hunters, will provide constraint on the occurrence rate of planets at orbital distances around and beyond 1 AU.
|
#76 Particle Flux to Titan: Astrobiological Implications
Julia DeMarines, Dr. David Grinspoon, Dr. Steve Benner
This research explores the habitability of Titan, a large moon of Saturn, and draws from a NASA research initiative titled, “Titan as a Pre-Biotic Chemical System.” Titan is of interest to Astrobiologists due to its similarity to Earth, as it is often referred to as a pre-biotic Earth. However, despite its similarities to Earth, Titan’s environment is too hostile for life as we know it. According to synthetic biologist Dr. Steve Benner, of FfAME Lab in Gainsville, Florida, Titan may not possess enough of key elements (Germanium, Oxygen, Boron, Arsenic, and Molybdenum) that would be necessary for life to survive at its surface temperature of -300º F. These scarce elements entering Titan’s atmosphere via particle flux could increase the habitability of Titan. This research estimates the amount of life sustaining elements brought to Titan, in the form of interplanetary dust particles. Future applications of this research will include particle flux to Phobos, the small carbonaceous moon of Mars, and its resulting impact ejecta.
|
#77 Kepler AutoRegressive Planet Search
Gabriel Caceres
The Kepler AutoRegressive Planet Search (KARPS) project uses statistical methodology associated with autoregressive (AR) processes to model the publicly available Kepler light curve data in order to improve exoplanet transit detection in systems with high stellar variability. We also introduce a planet-search algorithm to detect transits in time-series residuals after application of the AR models. One of the main obstacles in detecting faint planetary transits is the intrinsic stellar variability of the host star. The variability displayed by many stars may have autoregressive properties, wherein later flux values are correlated with previous ones in some manner. Tests of the methods have been made on a subset of Kepler Objects of Interest (KOI) systems. The flux of a typical quiescent Kepler star has an interquartile range (IQR) of ~10 e-/sec, which may improve slightly after modeling, while those with IQR ranging from 20 to 50 e-/sec, have improvements from 20% up to 70%. While the modeling is effective at reducing stellar noise, it also reduces and transforms the transit signal into ingress/egress spikes. To search for transits in these residuals, we develop a new Transit Comb Filter (TCF) that replaces traditional box-finding algorithms, and use it to construct a periodogram.
|
#78 Best Practices for Effective Poster Design
Kimberly M. S. Cartier, Ming Zhao, Thomas G. Beatty, Robert C. Morehead, Daniel Jontof-Hutter
This meta-poster illustrates how good poster design can effectively communicate scientific ideas to a broad professional audience.
|
#79 Precision Photometry of Tight Binary Stars using AO-IFU for Study of Exoplanet Atmosphere
Lamiya Mowla, Ji Wang
Studying exoplanet atmosphere using ground-based facilities requires reference star for calibration. Planet hosting binary stars are self-calibrating systems as the companion star can be used for calibration. We are using Adaptive Optics aided Integral Field Spectrographs to spatially resolve known planet hosting binary stars. Our project will demonstrate the feasibility of the proposed technique.
|
#80 High-contrast hyperspectral imaging with P1640: the first near-IR spectrum of brown dwarf GJ 758 B
Ricky Nilsson, AAron Veicht, Emily Rice, Paige Giorla, Rebecca Oppenheimer
Techniques for direct imaging of thermal emission from substellar companions to young nearby stars have matured to a level allowing multi-epoch and multi-band observations to determine the system’s physical and orbital characteristics. GJ 758 is a Sun-like star located 15.5 pc away, with a 30-40 M_Jup companion (GJ 758 B) at ~29 AU projected separation, imaged in several near-IR photometric bands. Atmospheric modeling has indicated an effective surface temperature of ~600 K (making it the coldest imaged companion of a Sun-like star), and possible presence of methane. Using spectral differential imaging with Project 1640 at the 200-inch Hale telescope at Palomar Observatory, we obtain the first low-resolution (R~30) spectrum of GJ 758 B, covering wavelengths of 969-1797 nm. Preliminary modeling of its spectrum suggests a significantly higher effective temperature than derived from previous photometry, but clearly establishes the presence of methane absorption in its atmosphere.
|
