ASU Nexus for Exoplanet System Science


Arizona State University NExSS – Published Papers
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A Comparison of Stellar Elemental Abundance Techniques and Measurements

Natalie R. Hinkel1, Patrick A. Young1, Michael D. Pagano1, Steven J. Desch 1, Ariel D. Anbar1, Vardan Adibekyan2, Sergi Blanco-Cuaresma3, Joleen K. Carlberg4, 5, Elisa Delgado Mena2, Fan Liu6, Thomas Nordlander7, Sergio G. Sousa2, Andreas Korn7, Pieter Gruyters7, 8, Ulrike Heiter7, Paula Jofr ́e9, Nuno C. Santos2, 10, Caroline Soubiran11

Stellar elemental abundances are important for understanding the fundamental properties of a star or stellar group, such as age and evolutionary history, as well as the composition of an orbiting planet. However, as abundance measurement techniques have progressed, there has been little standardization between individual methods and their comparisons. The purpose of this paper is to better understand the systematic variations between methods and offer recommendations for producing more accurate results in the future.


ALMA Observations of the η Corvi Debris Disc: Inward Scattering of CO-Rich Exocomets by a Chain of 3-30 M Planets?

S. Marino1⋆, M. C. Wyatt1, O. Pani ́c1,2†, L. Matra`1, G. M. Kennedy1, A. Bonsor1, Q. Kral1, W. R. F Dent3, G. Duchene4,5, D. Wilner6, C. M. Lisse7, J.-F. Lestrade8, B. Matthews9

While most of the known debris discs present cold dust at tens of AU, a few young systems exhibit hot dust analogous to the Zodiacal dust. η Corvi is particularly interesting as it is old and it has both, with its hot dust significantly exceeding the maximum luminosity of an in-situ collisional cascade. Previous work suggested that this system could be undergoing an event similar to the Late Heavy Bombardment (LHB) soon after or during a dynamical instability. Here we present ALMA observa- tions of η Corvi with a resolution of 1.′′2 (∼22au) to study its outer belt. The continuum emission is consistent with an axisymmetric belt, with a mean radius of 152au and radial FWHM of 46au, which is too narrow compared to models of inward scattering of an LHB-like scenario…


Resolving Close Encounters: Stability in the HD 5319 and HD 7924 Planetary Systems

Stephen R. Kane

Radial velocity searches for exoplanets have detected many multi-planet systems around nearby bright stars. An advantage of this technique is that it generally samples the orbit outside of inferior/superior conjunction, potentially allowing the Keplerian elements of eccentricity and argument of periastron to be well characterized. The orbital architectures for some of these systems show signs of close planetary encounters that may render the systems unstable as described. We provide an in-depth analysis of two such systems: HD 5319 and HD 7924, for which the scenario of coplanar orbits results in their rapid destabilization. The poorly constrained periastron arguments of the outer planets in these systems further emphasizes the need for detailed investigations. An exhaustive scan of parameter space via dynamical simulations reveals specific mutual inclinations between the two outer planets in each system that allow for stable configurations over long timescales. We compare these configurations with those presented by mean-motion resonance as possible stability sources…


The Habitability of Proxima Centauri b

Martin Turbet1, Jérémy Leconte2, Franck Selsis2, Emeline Bolmont3, Francois Forget1, Ignasi Ribas4, Sean N. Raymond2, and Guillem Anglada-Escudé5

Radial velocity monitoring has found the signature of a M sin i = 1.3 M planet located within the Habitable Zone (HZ) of Proxima Centauri (Anglada-Escudé et al. 2016). Despite a hotter past and an active host star the planet Proxima b could have retained enough volatiles to sustain surface habitability (Ribas et al. 2016). Here we use a 3D Global Climate Model (GCM) to simulate Proxima b’s atmosphere and water cycle for its two likely rotation modes (1:1 and 3:2 spin-orbit resonances) while varying the unconstrained surface water inventory and atmospheric greenhouse effect. Any low-obliquity low-eccentricity planet within the HZ of its star should be in one of the climate regimes discussed here. We find that a broad range of atmospheric compositions allow surface liquid water. On a tidally-locked planet with sufficient surface water inventory, liquid water is always present, at least in the substellar region…


Stellar Companions to the Exoplanet Host Stars HD 2638 and HD 164509

Justin M. Wittrock1, Stephen R. Kane1, Elliott P. Horch2, Lea Hirsch3, Steve B. Howell4, David R. Ciardi5, Mark E. Everett6, Johanna K. Teske7

An important aspect of searching for exoplanets is understanding the binarity of the host stars. It is particularly important because nearly half of the solar-like stars within our own Milky Way are part of binary or multiple systems. Moreover, the presence of two or more stars within a system can place further constraints on planetary formation, evolution, and orbital dynamics. As part of our survey of almost a hundred host stars, we obtained images at 692 nm and 880 nm bands using the Differential Speckle Survey Instrument (DSSI) at the Gemini-North Observatory. From our survey, we detect stellar companions to HD 2638 and HD 164509. The stellar companion to HD 2638 has been previously detected, but the companion to HD 164509 is a newly discovered companion. The angular separation for HD 2638 is 0.512 ± 0.002′′ and for HD 164509 is 0.697 ± 0.002′′. This corresponds to a projected separation of 25.6 ± 1.9 AU and 36.5 ± 1.9 AU, respectively…


A Catalog of Kepler Habitable Zone Exoplanet Candidates

Stephen R. Kane1, Michelle L. Hill1, James F. Kasting2, Ravi Kumar Kopparapu3, Elisa V. Quintana4, Thomas Barclay4, Natalie M. Batalha4, William J. Borucki4, David R. Ciardi5, Nader Haghighipour6, Natalie R. Hinkel1,7, Lisa Kaltenegger8, Franck Selsis9, Guillermo Torres10

The NASA Kepler mission has discovered thousands of new planetary candidates, many of which have been confirmed through follow-up observations. A primary goal of the mission is to determine the occurrance rate of terrestrial-size planets within the Habitable Zone (HZ) of their host stars. Here we provide a list of HZ exoplanet candidates from the Kepler Data Release 24 Q1-Q17 data vetting process. This work was undertaken as part of the Kepler Habitable Zone Working Group. We use a variety of criteria regarding HZ boundaries and planetary sizes to produce complete lists of HZ candidates, including a catalog of 104 candidates within the optimistic HZ and 20 candidates with radii less than two Earth radii within the conservative HZ. We cross-match our HZ candidates with the Data Release 25 stellar properties and confirmed planet properties to provide robust stellar parameters and candidate dispositions. We also include false positive probabilities recently calculated by Morton et al. (2016) for each of the candidates within our catalogs to aid in their validation…


Spectroscopic Characterization of HD 95086 b with the Gemini Planet Imager

Robert J. De Rosa1, Julien Rameau2, Jenny Patience3, James R. Graham1, Ren ́e Doyon2, David Lafreni`ere2, Bruce Macintosh4, Laurent Pueyo5, Abhijith Rajan3, Jason J. Wang1, Kimberly Ward-Duong3, Li-Wei Hung6, J ́eroˆme Maire7, Eric L. Nielsen8,4, S. Mark Ammons9, Joanna Bulger10, Andrew Cardwell11, Jeffrey K. Chilcote7, Ramon L. Galvez12, Benjamin L. Gerard13, Stephen Goodsell14,15, Markus Hartung12, Pascale Hibon16, Patrick Ingraham17, Mara Johnson-Groh13, Paul Kalas1,8, Quinn M. Konopacky18, Franck Marchis8, Christian Marois19,13, Stanimir Metchev20,21, Katie M. Morzinski22, Rebecca Oppenheimer23, Marshall D.
Perrin5, Fredrik T. Rantakyro ̈12, Dmitry Savransky25, Sandrine Thomas13

We present new H (1.5–1.8μm) photometric and K1 (1.9–2.2μm) spectroscopic observations of the young exoplanet HD 95086 b obtained with the Gemini Planet Imager. The H-band magnitude has been significantly improved relative to previous measurements, whereas the low resolution K1 (λ/δλ ≈ 66) spectrum is featureless within the measurement uncertainties, and presents a mono- tonically increasing pseudo-continuum consistent with a cloudy atmosphere. By combining these new measurements with literature L′ photometry, we compare the spectral energy distribution of the planet to other young planetary-mass companions, field brown dwarfs, and to the predictions of grids of model atmospheres.


The Catalog of Earth–Like Exoplanet Survey Targets (CELESTA): A Database of Habitable Zones Around Nearby Stars

Colin Orion Chandler1, Iain McDonald2, Stephen R. Kane1

Locating planets in circumstellar Habitable Zones is a priority for many exoplanet surveys. Space–based and ground–based surveys alike require robust toolsets to aid in target selection and mission planning. We present the Catalog of Earth–Like Exoplanet Survey Targets (CELESTA), a database of Habitable Zones around 37,000 nearby stars. We calculated stellar parameters, includ- ing effective temperatures, masses, and radii, and we quantified the orbital distances and periods corresponding to the circumstellar Habitable Zones. We gauged the accuracy of our predictions by contrasting CELESTA’s computed parameters to observational data. We ascertain a potential re- turn on investment by computing the number of Habitable Zones probed for a given survey duration. A versatile framework for extending the functionality of CELESTA into the future enables ongoing comparisons to new observations, and recalculations when updates to Habitable Zone models, stellar temperatures, or parallax data become available. We expect to upgrade and expand CELESTA using data from the Gaia mission as the data becomes available.


Water Loss from Terrestrial Planets Orbiting Ultracool Dwarfs: Implications for the Planets of TRAPPIST-1

E. Bolmont1⋆, F. Selsis2,3, J. E. Owen4†, I. Ribas5, S. N. Raymond2,3, J. Leconte2,3,
& M. Gillon6

Ultra cool dwarfs (UCD;Teff <∼3000K) cool to settle on the main sequence after ∼1Gyr. For brown dwarfs, this cooling never stops. Their habitable zone (HZ) thus sweeps inward at least during the first Gyr of their lives. Assuming they possess water, planets found in the HZ of UCDs have experienced a runaway greenhouse phase too hot for liquid water prior to entering the HZ. It has been proposed that such planets are desiccated by this hot early phase and enter the HZ as dry worlds. Here we model the water loss during this pre-HZ hot phase taking into account recent upper limits on the XUV emission of UCDs and using 1D radiation-hydrodynamic simulations. We address the whole range of UCDs but also focus on the planets recently found around the 0.08 M dwarf TRAPPIST-1.


Expanding the Catalog: Considering the Importance of Carbon, Magnesium, and Neon in the Evolution of Stars and Habitable Zones

Amanda Truitt1 & Patrick A. Young1

Building on previous work, we have expanded our catalog of evolutionary models for stars with variable composition; here we present models for stars of mass 0.5 – 1.2 M , at scaled metallicities of 0.1 – 1.5 Z , and specific C/Fe, Mg/Fe, and Ne/Fe values of 0.58 – 1.72 C/Fe , 0.54 – 1.84 Mg/Fe and 0.5 – 2.0 Ne/Fe , respectively. We present 528 new stellar main sequence models, and we calculate the time-dependent evolution of habitable zone boundaries for each based on mass, temperature, and luminosity. We also reintroduce the 2 Gyr “Continuously Habitable Zone” (CHZ2) as a useful tool to help gauge the habitability potential for a given planetary system.


A New Analysis of the Exoplanet Hosting System HD 6434

Natalie R. Hinkel1,2, Stephen R. Kane1, Genady Pilyavsky2, Tabetha S. Boyajian3, David J. James4, Dominique Naef5, Debra A. Fischer4, Stephane Udry5

The current goal of exoplanetary science is not only focused on detecting but characterizing planetary systems in hopes of understanding how they formed, evolved, and relate to the Solar System. The Transit Ephemeris Refinement and Monitoring Survey (TERMS) combines both radial velocity (RV) and photometric data in order to achieve unprecedented ground-based precision in the fundamental properties of nearby, bright, exoplanet-hosting systems. Here we discuss HD 6434 and its planet, HD 6434b.


Evidence for Reflected Light from the Most Eccentric Exoplanet Known

Stephen R. Kane1, Robert A. Wittenmyer2,3, Natalie R. Hinkel1,4, Arita Roy5,6, Suvrath Mahadevan5,6, Diana Dragomir7, Jaymie M. Matthews8, Gregory W. Henry9, Abhijit Chakraborty10, Tabetha S. Boyajian11, Jason T. Wright5,6, David R. Ciardi12, Debra A. Fischer11, R. Paul Butler13, C.G. Tunney2,3, Brad D. Carter14, Hugh R.A. Jones15, Jeremy Bailey2,3, Simon J. O’Toole16

Planets in highly eccentric orbits form a class of objects not seen within our Solar System. The most extreme case known amongst these objects is the planet orbiting HD 20782, with an orbital period of 597 days and an eccentricity of 0.96. Here we present new data and analysis for this system as part of the Transit Ephemeris Refinement and Monitoring Survey (TERMS).


The Elemental Abundances of 518 FGK Stars and Planetary Implications

Michael Pagano1, Patrick A. Young1, Priya Challa2

We present the elemental abundances of 518 stars including 18 planet hosting stars. We look particularly at the elements C, O, Mg, and Si to try and use stellar abundances to help constrain first-order exo-planetary mineralogy. We find that 9.45% of our sample had a C/O ratio above 0.80 which can be used to start to predict carbide planets. 18.9% of the sample had a Mg/Si ratio below 1 and no stars above 2, but some that were approaching this magnesium dominated regime.


Direct Imaging of an Asymmetric Debris Disk in the HD 106906 Planetary System

Paul G. Kalas1, Abhijith Rajan2, Jason J. Wang1, Maxwell A. Millar-Blanchaer5, Gaspard Duchene1,3,4, Christine Chen12, Michael P. Fitzgerald6, Ruobing Dong1, James R. Graham1, Jennifer Patience2, Bruce Macintosh10, Ruth Murray-Clay8, Brenda Matthews15, Julien Rameau14, Christian Marois15, Jeffrey Chilcote5, Robert J. De Rosa1, Rene ́ Doyon14, Zachary H. Draper15, Samantha Lawler15, S. Mark Ammons9, Pauline Arriaga6, Joanna Bulger27, Tara Cotten20, Katherine B. Follette10, Stephen Goodsell11, Alexandra Greenbaum23, Pascale Hibon11, Sasha Hinkley28, Li-Wei Hung6, Patrick Ingraham25, Quinn Konapacky26, David Lafreniere14, James E. Larkin6, Douglas Long12, Je ́roˆme Maire5, Franck Marchis16, Stan Metchev29,30,31, Katie M. Morzinski17, Eric L. Nielsen10, 16, Rebecca Oppenheimer18, Marshall D. Perrin12, Laurent Pueyo12, Fredrik T. Rantakyro ̈11, Jean-Baptiste Ruffio10, Leslie Saddlemyer15, Dmitry Savransky19, Adam C. Schneider22, Anand Sivaramakrishnan12, Re ́mi Soummer12, Inseok Song20, Sandrine Thomas25, Gautam Vasisht24, Kimberly Ward-Duong2, Sloane J. Wiktorowicz7, Schuyler G. Wolff23,12

We present the first scattered light detections of the HD 106906 debris disk using Gemini/GPI in the infrared and HST/ACS in the optical. Our observations reveal a near edge-on debris disk that has a central cleared region with radius ∼50 AU, and an outer extent >500 AU. We hypothesize that HD 106906b could be dynamically involved in the perturbation of the primary’s disk, and investigate whether or not there is evidence for a circumplanetary dust disk or cloud that is either primordial or captured from the primary. We show that both the existing optical properties and near-infrared colors of HD 106906b are weakly consistent with this possibility, motivating future work to test for the observational signatures of dust surrounding the planet.


Chandra Characterization of X-ray Emission in the Young F-Star Binary System HD 113766

C.M. Lisse1, D.J. Christian2, S.J. Wolk3, H.M. Günther4, C.H. Chen5, C.A. Grady6

Using Chandra we have obtained imaging X-ray spectroscopy of the 10-16 Myr old F-star binary HD 113766. We individually resolve the 1.4ʺ separation binary components for the first time in the X-ray and find a total 0.3–2.0 keV luminosity of 2.2×1029 erg/sec.We find emission from the easternmost, infrared-bright, dusty member HD 113766A to be only ~10% that of the western, infrared- faint member HD 113766B. There is no evidence for a 3rd late-type stellar or sub-stellar member of HD113766 with Lx > 6×1025 erg s-1 within 2′ of the binary pair. The emission is soft for both stars, kTApec = 0.30 to 0.50 keV, suggesting X-rays produced by stellar rotation and/or convection in young dynamos, but not accretion or outflow shocks which we rule out. At 1028–1029 erg s-1 luminosity, astrobiologically important effects, like dust warming and X-ray photolytic organic synthesis, are likely for any circumstellar material in the HD 113766 systems.


IRTF/SPEX Observations of the HR 4796A Cometary Ring System

C.M. Lisse1, M.L. Sitko2, M. Marengo3, R. J. Vervack Jr.1, Y.R. Fernandez4

We have utilized the SpeX 0.8 – 5.0 μm spectrometer at the NASA/IRTF 3m telescope to obtain new moderate-resolution (R ~1000) near-infrared observations of the HR 4796A debris disk system. Compared to the 30 other stars in our Near InfraRed Debris disk Survey (NIRDS, Lisse et al. 2017), HR 4796A demonstrates a uniquely linear red excess flux increasing with wavelength from 1 to 5 μm.We conclude that the HR 4796A ring consists of a belt of comets that have been actively emitting gas and large, reddish dust at ~100K, roughly the temperature at which amorphous water ice crystallization/CO2 sublimation-driven cometary activity is seen in our Solar System.


IRTF/SPEX Observations of the Unusual Kepler Light Curve System KIC 8462852

C. M. Lisse1, M. L. Sitko2,3, M. Marengo4

We have utilized the NASA/IRTF 3m SpeX instrument’s high-resolution spectral mode to observe and characterize the near-infrared flux emanating from the unusual Kepler light curve system KIC 8462852. Within the errors of our measurements, this star looks like a normal solar abundance main-sequence F1V to F3V dwarf star without any obvious traces of significant circumstellar dust or gas. We also see no evidence of significant ongoing accretion onto the star nor any stellar outflow away from it. We speculate that KIC 8462852, like the ∼1.4 Gyr old F2V system η Corvi, is undergoing a late heavy bombardment, but is only in its very early stages.


Bayesian analysis of interiors of HD 219134b, Kepler-10b, Kepler-93b, CoRoT-7b, 55 Cnc e, and HD 97658b using stellar abundance proxies

Caroline Dorn1, Natalie R. Hinkel2, and Julia Venturini1

Using a generalized Bayesian inference method, we aim to explore the possible interior structures of six selected exoplanets for which planetary mass and radius measurements are available in addition to stellar host abundances: HD 219134b, Kepler-10b, Kepler- 93b, CoRoT-7b, 55 Cnc e, and HD 97658b. We aim to investigate the importance of stellar abundance proxies for the planetary bulk composition (namely Fe/Si and Mg/Si) on prediction of planetary interiors.


Stellar Activity and Exclusion of the Outer Planet in the HD 99492 System

Stephen R. Kane, Badrinath Thirumalachari, Gregory W. Henry, Natalie R. Hinkel, Eric L.N. Jensen, Tabetha S. Boyajian, Debra A. Fischer, Andrew W. Howard, Howard T. Isaacson, Jason T. Wright

A historical problem for indirect exoplanet detection has been contending with the intrinsic vari- ability of the host star. If the variability is periodic, it can easily mimic various exoplanet signatures, such as radial velocity variations that originate with the stellar surface rather than the presence of a planet. Here we present an update for the HD 99492 planetary system, using new radial veloc- ity and photometric measurements from the Transit Ephemeris Refinement and Monitoring Survey (TERMS).We further include a revised Keplerian orbital solution for the remaining planet, along with a new transit ephemeris.




Relevant Non-NExSS Papers
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MuSCAT: A Multicolor Simultaneous Camera for Studying Atmospheres of Transiting Exoplanets

Norio Naritaa,b,c, Akihiko Fukuid, Nobuhiko Kusakabeb, Masahiro Onitsukab,c, Tsuguru Ryub,c, Kenshi Yanagisawad, Hideyuki Izumiurac,d, Motohide Tamuraa,b,e, Tomoyasu Yamamurof

We report a development of a multi-color simultaneous camera for the 188cm telescope at Okayama Astro- physical Observatory in Japan. The instrument, named MuSCAT, has a capability of 3-color simultaneous imaging in optical wavelength where CCDs are sensitive. The principal purpose of MuSCAT is to perform high precision multi-color transit photometry.We demonstrate relative photometric precisions of 0.101%, 0.074%, and 0.076% in g2′ , r2′ , and zs,2 bands, respectively, for GJ436 with 30 s exposures. The achieved precisions meet our objective, and the instrument is ready for operation.


A Six-Planet System Orbiting HD 219134

Steven S. Vogt, Jennifer Burt, Stefano Meschiari, R. Paul Butler, Gregory W. Henry, Songhu Wang, Brad Holden, Cyril Gapp, Russell Hanson, Pamela Arriagada, Sandy Keiser, Johanna Teske, Gregory Laughlin

We present new, high-precision Doppler radial velocity (RV) data sets for the nearby K3V star HD 219134. The data include 175 velocities obtained with the HIRES Spectrograph at the Keck I Telescope, and 101 velocities obtained with the Levy Spectrograph at the Automated Planet Finder Telescope (APF) at Lick Observatory. Our observations reveal six new planetary candidates.


Comparative Habitability of Transiting Exoplanets

Rory Barnes, Victoria S. Meadows, Nicole Evans

Exoplanet habitability is traditionally assessed by comparing a planet’s semi-major axis to the location of its host star’s “habitable zone,” the shell around a star for which Earth-like planets can possess liquid surface water. We propose a method to compare transiting planets for their potential to support life based on transit data, stellar properties and previously reported limits on planetary emitted flux. Our method mitigates the “eccentricity-albedo degeneracy”, includes a penalty for large-radius planets, uses terrestrial mass-radius relationships, and, when available, constraints on eccentricity to compute a number we call the “habitability index for transiting exoplanets” that represents the relative probability that an exoplanet could support liquid surface water.


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