Person: Charbonneau, David
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Charbonneau, David
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Publication Absence of a Thick Atmosphere on the Terrestrial Exoplanet LHS 3844b(Springer Science and Business Media LLC, 2019-08-19) Kreidberg, Laura; Hu, Renyu; Schaefer, Laura; Deming, Drake; Stevenson, Kevin B.; Dittmann, Jason; Vanderburg, Andrew; Berardo, David; Guo, Xueying; Stassun, Keivan; Crossfield, Ian; Charbonneau, David; Loeb, Abraham; Ricker, George; Seager, Sara; Vanderspek, Roland; Koll, Daniel; Morley, Caroline; Latham, DavidThe majority of terrestrial planets in the Galaxy orbit small stars with radii less than 60% that of the Sun1,2. Theoretical models predict that these planets are more vulnerable to at- mospheric escape and collapse than their counterparts orbiting Sun-like stars3–5. To deter- mine whether a thick atmosphere has survived, one approach is to search for signatures of atmospheric heat redistribution in a planet’s thermal phase curve6–9. This technique was previously applied to the super-Earth 55 Cancri e, which showed an offset hot spot indicative of atmosphere heat circulation10. Here we report a phase curve measurement for the exo- planet LHS 3844b, a 1.3 R⊕ world in an 11-hour orbit around a small, nearby star. This is the first such measurement for a planet smaller than 1.6 Re, the size marking the transition from rocky to gaseous worlds11. The phase variation is symmetric and has a large amplitude, implying a dayside brightness temperature of 1040±40 K and a nightside temperature con- sistent with zero K (1σ confidence). The data are best fit by a bare rock model with a low Bond albedo (< 0.2 at 2σ confidence), or a tenuous atmosphere with surface pressure below 0.1 bar. These results support theoretical predictions that hot terrestrial planets orbiting small stars may not retain substantial atmospheres.Publication A rocky planet transiting a nearby low-mass star(Springer Nature, 2015) Berta-Thompson, Zachory K.; Irwin, Jonathan; Charbonneau, David; Newton, Elisabeth R; Dittmann, Jason Adam; Astudillo-Defru, Nicola; Bonfils, Xavier; Gillon, Michaël; Jehin, Emmanuël; Stark, Antony; Stalder, Brian; Bouchy, Francois; Delfosse, Xavier; Forveille, Thierry; Lovis, Christophe; Mayor, Michel; Neves, Vasco; Pepe, Francesco; Santos, Nuno C.; Udry, Stéphane; Wünsche, AnaëlM-dwarf stars – hydrogen-burning stars that are smaller than 60 per cent of the size of the Sun – are the most common class of star in our Galaxy and outnumber Sun-like stars by a ratio of 12:1. Recent results have shown that M dwarfs host Earth-sized planets in great numbers1,2: the average number of M-dwarf planets that are between 0.5 to 1.5 times the size of Earth is at least 1.4 per star3. The nearest such planets known to transit their star are 39 parsecs away4 , too distant for detailed follow-up observations to measure the planetary masses or to study their atmospheres. Here we report observations of GJ 1132b, a planet with a size of 1.2 Earth radii that is transiting a small star 12 parsecs away. Our Doppler mass measurement of GJ 1132b yields a density consistent with an Earth-like bulk composition, similar to the compositions of the six known exoplanets with masses less than six times that of the Earth and precisely measured densities5−11. Receiving 19 times more stellar radiation than the Earth, the planet is too hot to be habitable but is cool enough to support a substantial atmosphere, one that has probably been considerably depleted of hydrogen. Because the host star is nearby and only 21 per cent the radius of the Sun, existing and upcoming telescopes will be able to observe the composition and dynamics of the planetary atmosphere.Publication The Rotation and Galactic Kinematics of Mid M Dwarfs in the Solar Neighborhood(American Astronomical Society, 2016) Newton, Elisabeth R; Irwin, Jonathan; Charbonneau, David; Berta-Thompson, Zachory K.; Dittmann, Jason Adam; West, Andrew A.Rotation is a directly observable stellar property, and it drives magnetic field generation and activity through a magnetic dynamo. Main-sequence stars with masses below approximately 0.35 ${M}_{\odot }$ (mid-to-late M dwarfs) are fully convective, and are expected to have a different type of dynamo mechanism than solar-type stars. Measurements of their rotation rates provide insight into these mechanisms, but few rotation periods are available for these stars at field ages. Using photometry from the MEarth Project, we measure rotation periods for 387 nearby, mid-to-late M dwarfs in the northern hemisphere, finding periods from 0.1 to 140 days. The typical rotator has stable, sinusoidal photometric modulations at a semi-amplitude of 0.5%–1%. We find no period–amplitude relation for stars below 0.25 ${M}_{\odot }$ and an anticorrelation between period and amplitude for higher-mass M dwarfs. We highlight the existence of older, slowly rotating stars without Hα emission that nevertheless have strong photometric variability. We use parallaxes, proper motions, radial velocities, photometry, and near-infrared metallicity estimates to further characterize the population of rotators. The Galactic kinematics of our sample is consistent with the local population of G and K dwarfs, and rotators have metallicities characteristic of the solar neighborhood. We use the W space velocities and established age–velocity relations to estimate that stars with P < 10 days have ages of on average <2 Gyr, and that those with P > 70 days have ages of about 5 Gyr. The period distribution is dependent on mass: as the mass decreases, the slowest rotators at a given mass have longer periods, and the fastest rotators have shorter periods. We find a lack of stars with intermediate rotation periods, and the gap between the fast and slow rotators is larger for lower masses. Our data are consistent with a scenario in which these stars maintain rapid rotation for several gigayears, then spin down quickly, reaching periods of around 100 days by a typical age of 5 Gyr.Publication Calibration of the MEarth Photometric System: Optical Magnitudes and Photometric Metallicity Estimates for 1802 Nearby M-dwarfs(American Astronomical Society, 2016) Dittmann, Jason Adam; Irwin, Jonathan; Charbonneau, David; Newton, Elisabeth RThe MEarth Project is a photometric survey systematically searching the smallest stars nearest to the Sun for transiting rocky planets. Since 2008, MEarth has taken approximately two million images of 1844 stars suspected to be midto-late M dwarfs. We have augmented this survey by taking nightly exposures of photometric standard stars and have utilized this data to photometrically calibrate the MEarth system, identify photometric nights, and obtain an optical magnitude with 1.5% precision for each M dwarf system. Each optical magnitude is an average over many years of data, and therefore should be largely immune to stellar variability and flaring. We combine this with trigonometric distance measurements, spectroscopic metallicity measurements, and 2MASS infrared magnitude measurements in order to derive a color-magnitude-metallicity relation across the mid-to-late M dwarf spectral sequence that can reproduce spectroscopic metallicity determinations to a precision of 0.1 dex. We release optical magnitudes and metallicity estimates for 1567 M dwarfs, many of which did not have an accurate determination of either prior to this work. For an additional 277 stars without a trigonometric parallax, we provide an estimate of the distance assuming solar neighborhood metallicity. We find that the median metallicity for a volume limited sample of stars within 20 parsecs of the Sun is [Fe/H] = −0.03 ± 0.008, and that 29 / 565 of these stars have a metallicity of [Fe/H] = −0.5 or lower, similar to the low-metallicity distribution of nearby G-dwarfs. When combined with the results of ongoing and future planet surveys targeting these objects, the metallicity estimates presented here will be important in assessing the significance of any putative planet-metallicity correlation.Publication A 1.9 Earth Radius Rocky Planet and the Discovery of a Non-Transiting Planet in the Kepler-20 System(American Astronomical Society, 2016) Buchhave, Lars A.; Dressing, Courtney D.; Dumusque, Xavier; Rice, Ken; Vanderburg, Andrew; Mortier, Annelies; Lopez-Morales, Mercedes; Lopez, Eric; Lundkvist, Mia S.; Kjeldsen, Hans; Affer, Laura; Bonomo, Aldo S.; Charbonneau, David; Cameron, Andrew Collier; Cosentino, Rosario; Figueira, Pedro; Fiorenzano, Aldo F. M.; Harutyunyan, Avet; Haywood, Raphaelle; Johnson, John; Latham, David; Lovis, Christophe; Malavolta, Luca; Mayor, Michel; Micela, Giusi; Molinari, Emilio; Motalebi, Fatemeh; Nascimbeni, Valerio; Pepe, Francesco; Phillips, David; Piotto, Giampaolo; Pollacco, Don; Queloz, Didier; Sasselov, Dimitar; Ségransan, Damien; Sozzetti, Alessandro; Udry, Stéphane; Watson, ChrisKepler-20 is a solar-type star (V = 12.5) hosting a compact system of five transiting planets, all packed within the orbital distance of Mercury in our own solar system. A transition from rocky to gaseous planets with a planetary transition radius of ~1.6 ${R}_{\oplus }$ has recently been proposed by several articles in the literature. Kepler-20b (${R}_{p}$ ~ 1.9 ${R}_{\oplus }$) has a size beyond this transition radius; however, previous mass measurements were not sufficiently precise to allow definite conclusions to be drawn regarding its composition. We present new mass measurements of three of the planets in the Kepler-20 system that are facilitated by 104 radial velocity measurements from the HARPS-N spectrograph and 30 archival Keck/HIRES observations, as well as an updated photometric analysis of the Kepler data and an asteroseismic analysis of the host star (${M}_{\star }$ = $0.948\pm 0.051$ ${M}_{\odot }$ and ${R}_{\star }$ = $0.964\pm 0.018$ ${R}_{\odot }$). Kepler-20b is a ${1.868}_{-0.034}^{+0.066}$ ${R}_{\oplus }$ planet in a 3.7 day period with a mass of ${9.70}_{-1.44}^{+1.41}$ ${M}_{\oplus }$, resulting in a mean density of ${8.2}_{-1.3}^{+1.5}$ ${\rm{g}}\,{\mathrm{cm}}^{-3}$, indicating a rocky composition with an iron-to-silicate ratio consistent with that of the Earth. This makes Kepler-20b the most massive planet with a rocky composition found to date. Furthermore, we report the discovery of an additional non-transiting planet with a minimum mass of ${19.96}_{-3.61}^{+3.08}$ ${M}_{\oplus }$ and an orbital period of ~34 days in the gap between Kepler-20f (P ~ 11 days) and Kepler-20d (P ~ 78 days).Publication Zodiacal Exoplanets in Time (Zeit) Iii: A Short-Period Planet Orbiting a Pre-Main-Sequence Star in the Upper Scorpius Ob Association(American Astronomical Society, 2016) Mann, Andrew W.; Newton, Elisabeth R; Rizzuto, Aaron C.; Irwin, Jonathan; Feiden, Gregory A.; Gaidos, Eric; Mace, Gregory N.; Kraus, Adam L.; James, David J.; Ansdell, Megan; Charbonneau, David; Covey, Kevin R.; Ireland, Michael J.; Jaffe, Daniel T.; Johnson, Marshall C.; Kidder, Benjamin; Vanderburg, AndrewWe confirm and characterize a close-in (Porb = 5.425 days), super-Neptune sized (5.04+0.34 −0.37 R⊕) planet transiting K2-33 (2MASS J16101473-1919095), a late-type (M3) pre-main sequence (11 Myr-old) star in the Upper Scorpius subgroup of the Scorpius-Centaurus OB association. The host star has the kinematics of a member of the Upper Scorpius OB association, and its spectrum contains lithium absorption, an unambiguous sign of youth (< 20 Myr) in late-type dwarfs. We combine photometry from K2 and the ground-based MEarth project to refine the planet’s properties and constrain the host star’s density. We determine K2-33’s bolometric flux and effective temperature from moderate resolution spectra. By utilizing isochrones that include the effects of magnetic fields, we derive a precise radius (6-7%) and mass (16%) for the host star, and a stellar age consistent with the established value for Upper Scorpius. Follow-up high-resolution imaging and Doppler spectroscopy confirm that the transiting object is not a stellar companion or a background eclipsing binary blended with the target. The shape of the transit, the constancy of the transit depth and periodicity over 1.5 years, and the independence with wavelength rules out stellar variability, or a dust cloud or debris disk partially occulting the star as the source of the signal; we conclude it must instead be planetary in origin. The existence of K2-33b suggests close-in planets can form in situ or migrate within ∼ 10 Myr, e.g., via interactions with a disk, and that long-timescale dynamical migration such as by Lidov-Kozai or planet-planet scattering is not responsible for all short-period planets.Publication Transiting Exoplanet Studies and Community Targets for JWST 's Early Release Science Program(IOP Publishing, 2016) Stevenson, Kevin B.; Lewis, Nikole K.; Bean, Jacob L.; Beichman, Charles; Fraine, Jonathan; Kilpatrick, Brian M.; Krick, J. E.; Lothringer, Joshua D.; Mandell, Avi M.; Valenti, Jeff A.; Agol, Eric; Angerhausen, Daniel; Barstow, Joanna K.; Birkmann, Stephan M.; Burrows, Adam; Charbonneau, David; Cowan, Nicolas B.; Crouzet, Nicolas; Cubillos, Patricio E.; Curry, S. M.; Dalba, Paul A.; de Wit, Julien; Deming, Drake; Désert, Jean-Michel; Doyon, René; Dragomir, Diana; Ehrenreich, David; Fortney, Jonathan J.; García Muñoz, Antonio; Gibson, Neale P.; Gizis, John E.; Greene, Thomas P.; Harrington, Joseph; Heng, Kevin; Kataria, Tiffany; Kempton, Eliza M.-R.; Knutson, Heather; Kreidberg, Laura; Lafrenière, David; Lagage, Pierre-Olivier; Line, Michael R.; Lopez-Morales, Mercedes; Madhusudhan, Nikku; Morley, Caroline; Rocchetto, Marco; Schlawin, Everett; Shkolnik, Evgenya L.; Shporer, Avi; Sing, David K.; Todorov, Kamen O.; Tucker, Gregory S.; Wakeford, Hannah R.The James Webb Space Telescope (JWST) will likely revolutionize transiting exoplanet atmospheric science due to a combination of its capability for continuous, long duration observations and its larger collecting area, spectral coverage, and spectral resolution compared to existing space-based facilities. However, it is unclear precisely how well JWST will perform and which of its myriad instruments and observing modes will be best suited for transiting exoplanet studies. In this article, we describe a prefatory JWST Early Release Science (ERS) Cycle 1 program that focuses on testing specific observing modes to quickly give the community the data and experience it needs to plan more efficient and successful transiting exoplanet characterization programs in later cycles. We propose a multi-pronged approach wherein one aspect of the program focuses on observing transits of a single target with all of the recommended observing modes to identify and understand potential systematics, compare transmission spectra at overlapping and neighboring wavelength regions, confirm throughputs, and determine overall performances. In our search for transiting exoplanets that are well suited to achieving these goals, we identify 12 objects (dubbed “community targets”) that meet our defined criteria. Currently, the most favorable target is WASP-62b because of its large predicted signal size, relatively bright host star, and location in JWST’s continuous viewing zone. Since most of the community targets do not have well-characterized atmospheres, we recommend initiating preparatory observing programs to determine the presence of obscuring clouds/hazes within their atmospheres. Measurable spectroscopic features are needed to establish the optimal resolution and wavelength regions for exoplanet characterization. Other initiatives from our proposed ERS program include testing the instrument brightness limits and performing phase-curve observations. The latter are a unique challenge compared to transit observations because of their significantly longer durations. Using only a single mode, we propose to observe a full-orbit phase curve of one of the previously characterized, short-orbital-period planets to evaluate the facility-level aspects of long, uninterrupted time-series observations.Publication A precise water abundance measurement for the hot Jupiter WASP-43b(IOP Publishing, 2014) Kreidberg, Laura; Bean, Jacob L.; Désert, Jean-Michel; Line, Michael R.; Fortney, Jonathan J.; Madhusudhan, Nikku; Stevenson, Kevin B.; Showman, Adam P.; Charbonneau, David; McCullough, Peter R.; Seager, Sara; Burrows, Adam; Henry, Gregory W.; Williamson, Michael; Kataria, Tiffany; Homeier, DerekThe water abundance in a planetary atmosphere provides a key constraint on the planet's primordial origins because water ice is expected to play an important role in the core accretion model of planet formation. However, the water content of the solar system giant planets is not well known because water is sequestered in clouds deep in their atmospheres. By contrast, short-period exoplanets have such high temperatures that their atmospheres have water in the gas phase, making it possible to measure the water abundance for these objects. We present a precise determination of the water abundance in the atmosphere of the 2 M Jup short-period exoplanet WASP-43b based on thermal emission and transmission spectroscopy measurements obtained with the Hubble Space Telescope. We find the water content is consistent with the value expected in a solar composition gas at planetary temperatures (0.4-3.5 × solar at 1σ confidence). The metallicity of WASP-43b's atmosphere suggested by this result extends the trend observed in the solar system of lower metal enrichment for higher planet masses.Publication A Disintegrating Minor Planet Transiting a White Dwarf(Springer Nature, 2015) Vanderburg, Andrew; Johnson, John; Rappaport, Saul; Bieryla, Allyson; Irwin, Jonathan; Lewis, John; Kipping, David; Brown, Warren; Dufour, Patrick; Ciardi, David R.; Angus, Ruth; Schaefer, Laura Kay; Latham, David; Charbonneau, David; Beichman, Charles; Eastman, Jason; McCrady, Nate; Wittenmyer, Robert A.; Wright, Jason T.White dwarfs are the end state of most stars, including the Sun, after they exhaust their nuclear fuel. Between 1/4 and 1/2 of white dwarfs have elements heavier than helium in their atmospheres1,2, even though these elements should rapidly settle into the stellar interiors unless they are occasionally replenished3–5. The abundance ratios of heavy elements in white dwarf atmospheres are similar to rocky bodies in the Solar system6,7. This and the existence of warm dusty debris disks8–13 around about 4% of white dwarfs14–16 suggest that rocky debris from white dwarf progenitors’ planetary systems occasionally pollute the stars’ atmospheres17. The total accreted mass can be comparable to that of large asteroids in the solar system1. However, the process of disrupting planetary material has not yet been observed. Here, we report observations of a white dwarf being transited by at least one and likely multiple disintegrating planetesimals with periods ranging from 4.5 hours to 4.9 hours. The strongest transit signals occur every 4.5 hours and exhibit varying depths up to 40% and asymmetric profiles, indicative of a small object with a cometary tail of dusty effluent material. The star hosts a dusty debris disk and the star’s spectrum shows prominent lines from heavy elements like magnesium, aluminium, silicon, calcium, iron, and nickel. This system provides evidence that heavy element pollution of white dwarfs can originate from disrupted rocky bodies such as asteroids and minor planets.Publication Kepler-93b: A Terrestrial World Measured to Within 120 Km, and a Test Case for a New Spitzer Observing Mode(IOP Publishing, 2014) Ballard, Sarah; Chaplin, William J.; Charbonneau, David; Désert, Jean-Michel; Fressin, Francois; Zeng, Li; Werner, Michael W.; Davies, Guy R.; Aguirre, Victor Silva; Basu, Sarbani; Christensen-Dalsgaard, Jørgen; Metcalfe, Travis S.; Stello, Dennis; Bedding, Timothy R.; Campante, Tiago L.; Handberg, Rasmus; Karoff, Christoffer; Elsworth, Yvonne; Gilliland, Ronald L.; Hekker, Saskia; Huber, Daniel; Kawaler, Steven D.; Kjeldsen, Hans; Lund, Mikkel N.; Lundkvist, MiaWe present the characterization of the Kepler-93 exoplanetary system, based on three years of photometry gathered by the Kepler spacecraft. The duration and cadence of the Kepler observations, in tandem with the brightness of the star, enable unusually precise constraints on both the planet and its host. We conduct an asteroseismic analysis of the Kepler photometry and conclude that the star has an average density of 1.652 ± 0.006 g cm–3. Its mass of 0.911 ± 0.033 M ☉ renders it one of the lowest-mass subjects of asteroseismic study. An analysis of the transit signature produced by the planet Kepler-93b, which appears with a period of 4.72673978 ± 9.7 × 10–7 days, returns a consistent but less precise measurement of the stellar density, 1.72$^{+0.02}_{-0.28}$ g cm–3. The agreement of these two values lends credence to the planetary interpretation of the transit signal. The achromatic transit depth, as compared between Kepler and the Spitzer Space Telescope, supports the same conclusion. We observed seven transits of Kepler-93b with Spitzer, three of which we conducted in a new observing mode. The pointing strategy we employed to gather this subset of observations halved our uncertainty on the transit radius ratio RP /R sstarf. We find, after folding together the stellar radius measurement of 0.919 ± 0.011 R ☉ with the transit depth, a best-fit value for the planetary radius of 1.481 ± 0.019 R ⊕. The uncertainty of 120 km on our measurement of the planet's size currently renders it one of the most precisely measured planetary radii outside of the solar system. Together with the radius, the planetary mass of 3.8 ± 1.5 M ⊕ corresponds to a rocky density of 6.3 ± 2.6 g cm–3. After applying a prior on the plausible maximum densities of similarly sized worlds between 1 and 1.5 R ⊕, we find that Kepler-93b possesses an average density within this group.