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Papers by John Johnson

We report the discovery of a brown dwarf that transits one member of the M+M binary system LHS 63... more We report the discovery of a brown dwarf that transits one member of the M+M binary system LHS 6343 AB every 12.71 days. The transits were discovered using photometric data from the Kelper public data release. The LHS 6343 stellar system was previously identified as a single high-propermotion M dwarf. We use adaptive optics imaging to resolve the system into two low-mass stars with masses 0.370±0.009 M ⊙ and 0.30±0.01 M ⊙ , respectively, and a projected separation of 0. ′′ 55. High-resolution spectroscopy shows that the more massive component undergoes Doppler variations consistent with Keplerian motion, with a period equal to the transit period and an amplitude consistent with a companion mass of M C = 62.9 ± 2.3 M Jup. Based on our analysis of the transit light curve we estimate the radius of the companion to be R C = 0.833 ± 0.021 R Jup , which is consistent with theoretical predictions of the radius of a > 1 Gyr brown dwarf.

The Astrophysical Journal Supplement Series, 2019

We present the discovery of KELT-22Ab, a hot Jupiter from the KELT-South survey. KELT-22Ab transi... more We present the discovery of KELT-22Ab, a hot Jupiter from the KELT-South survey. KELT-22Ab transits the moderately bright (V ∼ 11.1) Sun-like G2V star TYC 7518-468-1. The planet has an orbital period of P = 1.3866529 ± 0.0000027 days, a radius of R P = 1.285 +0.12 −0.071 R J , and a relatively large mass of M P = 3.47 +0.15 −0.14 M J. The star has R = 1.099 +0.079 −0.046 R , M = 1.092 +0.045 −0.041 M , T eff = 5767 +50 −49 K, log g = 4.393 +0.039 −0.060 (cgs) and [m/H] = +0.259 +0.085 −0.083 , and thus, other than its slightly super-solar metallicity, appears to be a near solar twin. Surprisingly, KELT-22A exhibits kinematics and a Galactic orbit that are somewhat atypical for thin disk stars. Nevertheless, the star is rotating quite rapidly for its estimated age, shows evidence of chromospheric activity, and is somewhat metal rich. Imaging reveals a slightly fainter companion to KELT-22A that is likely bound, with a projected separation of 6 (∼1400 AU). In addition to the orbital motion caused by the transiting planet, we detect a possible linear trend in the radial velocity of KELT-22A suggesting the presence of another relatively nearby body that is perhaps non-stellar. KELT-22Ab is highly irradiated (as a consequence of the small semi-major axis of a/R = 4.97), and is mildly inflated. At such small separations, tidal forces become significant. The configuration of this system is optimal for measuring the rate of tidal dissipation within the host star. Our models predict that, due to tidal forces, the semi-major axis of KELT-22Ab is decreasing rapidly, and is thus predicted to spiral into the star within the next Gyr.

The Astrophysical Journal, 2016

We target the thermal emission spectrum of the non-transiting gas giant HD 88133 b with high-reso... more We target the thermal emission spectrum of the non-transiting gas giant HD 88133 b with high-resolution nearinfrared spectroscopy, by treating the planet and its host star as a spectroscopic binary. For sufficiently deep summed flux observations of the star and planet across multiple epochs, it is possible to resolve the signal of the hot gas giant's atmosphere compared to the brighter stellar spectrum, at a level consistent with the aggregate shot noise of the full data set. To do this, we first perform a principal component analysis to remove the contribution of the Earth's atmosphere to the observed spectra. Then, we use a cross-correlation analysis to tease out the spectra of the host star and HD 88133 b to determine its orbit and identify key sources of atmospheric opacity. In total, six epochs of Keck NIRSPEC L-band observations and three epochs of Keck NIRSPEC K-band observations of the HD 88133 system were obtained. Based on an analysis of the maximum likelihood curves calculated from the multi-epoch cross-correlation of the full data set with two atmospheric models, we report the direct detection of the emission spectrum of the non-transiting exoplanet HD 88133 b and measure a radial projection of the Keplerian orbital velocity of 40±15 km s −1 , a true mass of-+ M 1.02 0.28 0.61 J , a nearly face-on orbital inclination of -+ 15 5 6 , and an atmosphere opacity structure at high dispersion dominated by water vapor. This, combined with 11 years of radial velocity measurements of the system, provides the most up-to-date ephemeris for HD 88133.

The Astrophysical Journal, 2016

Stellar companions can influence the formation and evolution of planetary systems, but there are ... more Stellar companions can influence the formation and evolution of planetary systems, but there are currently few observational constraints on the properties of planet-hosting binary star systems. We search for stellar companions around 77 transiting hot Jupiter systems to explore the statistical properties of this population of companions as compared to field stars of similar spectral type. After correcting for survey incompleteness, we find that 47% ± 7% of hot Jupiter systems have stellar companions with semi-major axes between 50 AU-2000 AU. This is 2.9 times larger than the field star companion fraction in this separation range, with a significance of 4.4σ. In the 1 AU-50 AU range, only 3.9 +4.5 −2.0 % of hot Jupiters host stellar companions compared to the field star value of 16.4% ± 0.7%, which is a 2.7σ difference. We find that the distribution of mass ratios for stellar companions to hot Jupiter systems peaks at small values and therefore differs from that of field star binaries which tend to be uniformly distributed across all mass ratios. We conclude that either wide separation stellar binaries are more favorable sites for gas giant planet formation at all separations, or that the presence of stellar companions preferentially causes the inward migration of gas giant planets that formed farther out in the disk via dynamical processes such as Kozai-Lidov oscillations. We determine that less than 20% of hot Jupiters have stellar companions capable of inducing Kozai-Lidov oscillations assuming initial semi-major axes between 1-5 AU, implying that the enhanced companion occurrence is likely correlated with environments where gas giants can form efficiently.

The Astrophysical Journal, 2016

The Astrophysical Journal, 2016

Kepler-454 (KOI-273) is a relatively bright (V = 11.69 mag), Sun-like star that hosts a transitin... more Kepler-454 (KOI-273) is a relatively bright (V = 11.69 mag), Sun-like star that hosts a transiting planet candidate in a 10.6 day orbit. From spectroscopy, we estimate the stellar temperature to be 5687±50 K, its metallicity to be [m/H] = 0.32±0.08, and the projected rotational velocity to be v sin i<2.4 km s −1. We combine these values with a study of the asteroseismic frequencies from short cadence Kepler data to estimate the stellar mass to be M 1.028 0.03 0.04-+  , the radius to be 1.066±0.012 R e , and the age to be 5.25 1.39 1.41-+ Gyr. We estimate the radius of the 10.6 day planet as 2.37±0.13 R ⊕. Using 63 radial velocity observations obtained with the HARPS-N spectrograph on the Telescopio Nazionale Galileo and 36 observations made with the HIRES spectrograph at the Keck Observatory, we measure the mass of this planet to be 6.8±1.4 M ⊕. We also detect two additional nontransiting companions, a planet with a minimum mass of 4.46±0.12 M J in a nearly circular 524 day orbit and a massive companion with a period >10 years and mass >12.1 M J. The 12 exoplanets with radii <2.7 R ⊕ and precise mass measurements appear to fall into two populations, with those <1.6 R ⊕ following an Earth-like composition curve and larger planets requiring a significant fraction of volatiles. With a density of 2.76±0.73 g cm −3 , Kepler-454b lies near the mass transition between these two populations and requires the presence of volatiles and/or H/He gas.

Nature, 2015

White dwarfs are the end state of most stars, including the Sun, after they exhaust their nuclear... more 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 atmospheres 1,2 , even though these elements should rapidly settle into the stellar interiors unless they are occasionally replenished 3-5. The abundance ratios of heavy elements in white dwarf atmospheres are similar to rocky bodies in the Solar system 6,7. This and the existence of warm dusty debris disks 8-13 around about 4% of white dwarfs 14-16 suggest that rocky debris from white dwarf progenitors' planetary systems occasionally pollute the stars' atmospheres 17. The total accreted mass can be comparable to that of large asteroids in the solar system 1. 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.

The Astrophysical Journal, 2006

The unusual flux variations of the pre-main-sequence binary star KH 15D have been attributed to o... more The unusual flux variations of the pre-main-sequence binary star KH 15D have been attributed to occultations by a circumbinary disk. We test whether or not this theory is compatible with newly available data, including recent radial velocity measurements, CCD photometry over the past decade, and photographic photometry over the past 50 years. We find the model to be successful, after two refinements: a more realistic motion of the occulting feature and a halo around each star that probably represents scattering by the disk. The occulting feature is exceptionally sharp edged, raising the possibility that the dust in the disk has settled into a thin layer and providing a tool for fine-scale mapping of the immediate environment of a T Tauri star. However, the window of opportunity is closing, as the currently visible star may be hidden at all orbital phases by as early as 2008.

The Astrophysical Journal, 2006

We present spectroscopy of a transit of the exoplanet HD 189733b. By modeling the Rossiter-McLaug... more We present spectroscopy of a transit of the exoplanet HD 189733b. By modeling the Rossiter-McLaughlin effect (the anomalous Doppler shift due to the partial eclipse of the rotating stellar surface), we find the angle between the sky projections of the stellar spin axis and orbit normal to be. This is the third case of a "hot l p Ϫ1Њ .4 ‫ע‬ 1Њ .1 Jupiter" for which l has been measured. In all three cases l is small, ruling out random orientations with 99.96% confidence, and suggesting that the inward migration of hot Jupiters generally preserves spin-orbit alignment. Subject headings: planetary systems-planetary systems: formation-stars: individual (HD 189733)stars: rotation 1 Data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W. M. Keck Foundation.

The Astrophysical Journal, 2008

We present new spectroscopic and photometric observations of the HAT-P-1 planetary system. Spectr... more We present new spectroscopic and photometric observations of the HAT-P-1 planetary system. Spectra obtained during three transits exhibit the Rossiter-McLaughlin effect, allowing us to measure the angle between the sky projections of the stellar spin axis and orbit normal, λ = 3. • 7 ± 2. • 1. The small value of λ for this and other systems suggests that the dominant planet migration mechanism preserves spin-orbit alignment. Using two new transit light curves, we refine the transit ephemeris and reduce the uncertainty in the orbital period by an order of magnitude. We find a upper limit on the orbital eccentricity of 0.067, with 99% confidence, by combining our new radial-velocity measurements with those obtained previously.

The Astrophysical Journal, 2004

We propose that the extraordinary "winking star" KH 15D is an eccentric pre-main-sequence binary ... more We propose that the extraordinary "winking star" KH 15D is an eccentric pre-main-sequence binary that is gradually being occulted by an opaque screen. This model accounts for the periodicity, depth, duration, and rate of growth of the modern eclipses; the historical light curve from photographic plates; and the existing radial velocity measurements. It also explains the rebrightening events that were previously observed during eclipses and the subsequent disappearance of these events. We predict the future evolution of the system and its full radial velocity curve. Given the small velocity of the occulting screen relative to the center of mass of the binary, the screen is probably associated with the binary and may be the edge of a precessing circumbinary disk.

The Astrophysical Journal, 2011

Doppler observations from Keck Observatory have revealed a triple planet system orbiting the near... more Doppler observations from Keck Observatory have revealed a triple planet system orbiting the nearby mid-type K dwarf, HIP 57274. The inner planet, HIP 57274b, is a super-Earth with M sin i = 11.6 M ⊕ (0.036 M Jup), an orbital period of 8.135 ± 0.004 d, and slightly eccentric orbit e = 0.19±0.1. We calculate a transit probability of 6.5% for the inner planet. The second planet has M sin i = 0.4 M Jup with an orbital period of 32.0 ±0.02 d in a nearly circular orbit, and e = 0.05 ± 0.03. The third planet has M sin i = 0.53 M Jup with an orbital period of 432 ±8 d (1.18 years) and an eccentricity e = 0.23 ± 0.03. This discovery adds to the number of super Earth mass planets with M sin i < 12M ⊕ that 1 Based on observations obtained at the Keck Observatory, which is operated by the University of California

The Astrophysical Journal, 2013

We report that Kepler Object of Interest 256 (KOI-256) is a mutually eclipsing post-common envelo... more We report that Kepler Object of Interest 256 (KOI-256) is a mutually eclipsing post-common envelope binary (ePCEB), consisting of a cool white dwarf (M ⋆ = 0.592 ± 0.089M ⊙ , R ⋆ = 0.01345 ± 0.00091 R ⊙ , T eff = 7100±700 K) and an active M3 dwarf (M ⋆ = 0.51±0.16M ⊙ , R ⋆ = 0.540±0.014R ⊙ , T eff = 3450 ± 50 K) with an orbital period of 1.37865 ± 0.00001 days. KOI-256 is listed as hosting a transiting planet-candidate by Borucki et al. and Batalha et al.; here we report that the planetcandidate transit signal is in fact the occultation of a white dwarf as it passes behind the M dwarf. We combine publicly-available long-and short-cadence Kepler light curves with ground-based measurements to robustly determine the system parameters. The occultation events are readily apparent in the Kepler light curve, as is spin-orbit synchronization of the M dwarf, and we detect the transit of the white dwarf in front of the M dwarf halfway between the occultation events. The size of the white dwarf with respect to the Einstein ring during transit (R Ein = 0.00473 ± 0.00055 R ⊙) causes the transit depth to be shallower than expected from pure geometry due to gravitational lensing. KOI-256 is an old, long-period ePCEB and serves as a benchmark object for studying the evolution of binary star systems as well as white dwarfs themselves, thanks largely to the availability of near-continuous, ultra-precise Kepler photometry.

The Astrophysical Journal, 2006

We present a modification to the iodine cell Doppler technique that eliminates the need for an ob... more We present a modification to the iodine cell Doppler technique that eliminates the need for an observed stellar template spectrum. For a given target star, we iterate toward a synthetic template spectrum beginning with an existing spectrum of a similar star. We then perturb the shape of this first-guess template to match the program observation of the target star taken through an iodine cell. The elimination of a separate template observation saves valuable telescope time, a feature that is ideally suited for the quick-look strategy employed by the "Next 2000 Stars" (N2K) planet search program. Tests using Keck/HIRES spectra indicate that synthetic templates yield a short-term precision of 3 m s −1 and a long-term, run-to-run precision of 5 m s −1. We used this new Doppler technique to discover three new planets: a 1.50 M Jup planet in a 2.1375 d orbit around HD 86081; a 0.71 M Jup planet in circular, 26.73 d orbit around HD 224693; and a Saturn-mass planet in an 18.179 d orbit around HD 33283. The remarkably short period of HD 86081b bridges the gap between the extremely short-period planets detected in the OGLE survey and the 16 Doppler-detected hot jupiters 1 Based on observations obtained at the W. M. Keck Observatory, which is operated jointly by the University of California and the California Institute of Technology

The Astrophysical Journal, 2011

We report the discovery of a brown dwarf that transits one member of the M+M binary system LHS 63... more We report the discovery of a brown dwarf that transits one member of the M+M binary system LHS 6343 AB every 12.71 days. The transits were discovered using photometric data from the Kepler public data release. The LHS 6343 stellar system was previously identified as a single high proper motion M dwarf. We use adaptive optics imaging to resolve the system into two low-mass stars with masses 0.370 ± 0.009 M and 0.30 ± 0.01 M , respectively, and a projected separation of 0. 55. High-resolution spectroscopy shows that the more massive component undergoes Doppler variations consistent with Keplerian motion, with a period equal to the transit period and an amplitude consistent with a companion mass of M C = 62.7 ± 2.4 M Jup. Based on our analysis of the transit light curve, we estimate the radius of the companion to be R C = 0.833 ± 0.021 R Jup , which is consistent with theoretical predictions of the radius of a >1 Gyr brown dwarf.

The Astrophysical Journal, 2010

We report on the discovery and the Rossiter-McLaughlin (R-M) effect of Kepler-8b, a transiting pl... more We report on the discovery and the Rossiter-McLaughlin (R-M) effect of Kepler-8b, a transiting planet identified by the NASA Kepler Mission. Kepler photometry and Keck-HIRES radial velocities yield the radius and mass of the planet around this F8IV subgiant host star. The planet has a radius R P = 1.419 R J and a mass M P = 0.60 M J , yielding a density of 0.26 g cm −3 , one of the lowest planetary densities known. The orbital period is P = 3.523 days and the orbital semimajor axis is 0.0483 +0.0006 −0.0012 AU. The star has a large rotational v sin i of 10.5 ± 0.7 km s −1 and is relatively faint (V ≈ 13.89 mag); both properties are deleterious to precise Doppler measurements. The velocities are indeed noisy, with scatter of 30 m s −1 , but exhibit a period and phase that are consistent with those implied by transit photometry. We securely detect the R-M effect, confirming the planet's existence and establishing its orbit as prograde. We measure an inclination between the projected planetary orbital axis and the projected stellar rotation axis of λ = −26. • 4 ± 10. • 1, indicating a significant inclination of the planetary orbit. R-M measurements of a large sample of transiting planets from Kepler will provide a statistically robust measure of the true distribution of spin-orbit orientations for hot Jupiters around F and early G stars.

The Astrophysical Journal, 2009

We present two exoplanets detected at Keck Observatory. HD 179079 is a G5 subgiant that hosts a h... more We present two exoplanets detected at Keck Observatory. HD 179079 is a G5 subgiant that hosts a hot Neptune planet with M sin i = 27.5 M ⊕ in a 14.48 days, low-eccentricity orbit. The stellar reflex velocity induced by this planet has a semiamplitude of K = 6.6 m s −1. HD 73534 is a G5 subgiant with a Jupiterlike planet of M sin i = 1.1 M Jup and K = 16 m s −1 in a nearly circular 4.85 yr orbit. Both stars are chromospherically inactive and metal-rich. We discuss a known, classical bias in measuring eccentricities for orbits with velocity semiamplitudes, K, comparable to the radial velocity uncertainties. For exoplanets with periods longer than 10 days, the observed exoplanet eccentricity distribution is nearly flat for large amplitude systems (K > 80 m s −1), but rises linearly toward low eccentricity for lower amplitude systems (K > 20 m s −1).

The Astrophysical Journal, 2013

Doppler surveys have shown that the occurrence rate of Jupiter-mass planets appears to increase a... more Doppler surveys have shown that the occurrence rate of Jupiter-mass planets appears to increase as a function of stellar mass. However, this result depends on the ability to accurately measure the masses of evolved stars. Recently, Lloyd called into question the masses of subgiant stars targeted by Doppler surveys. Lloyd argues that very few observable subgiants have masses greater than 1.5 M , and that most of them have masses in the range 1.0-1.2 M. To investigate this claim, we use Galactic stellar population models to generate an all-sky distribution of stars. We incorporate the effects that make massive subgiants less numerous, such as the initial mass function and differences in stellar evolution timescales. We find that these effects lead to negligibly small systematic errors in stellar mass estimates, in contrast to the ≈50% errors predicted by Lloyd. Additionally, our simulated target sample does in fact include a significant fraction of stars with masses greater than 1.5 M , primarily because the inclusion of an apparent magnitude limit results in a Malmquist-like bias toward more massive stars, in contrast to the volume-limited simulations of Lloyd. The magnitude limit shifts the mean of our simulated distribution toward higher masses and results in a relatively smaller number of evolved stars with masses in the range 1.0-1.2 M. We conclude that, within the context of our present-day understanding of stellar structure and evolution, many of the subgiants observed in Doppler surveys are indeed as massive as main-sequence A stars.

The Astrophysical Journal, 2013

We construct high signal-to-noise "template" spectra by co-adding hundreds of spectra of nearby d... more We construct high signal-to-noise "template" spectra by co-adding hundreds of spectra of nearby dwarfs spanning K7 to M4, taken with Keck/HIRES as part of the California Planet Search. We identify several spectral regions in the visible (370-800 nm) that are sensitive to the stellar luminosity and metallicity. We use these regions to develop a spectral calibration method to measure the mass, metallicity, and distance of low-mass stars, without the requirement of geometric parallaxes. Testing our method on a sample of nearby M dwarfs, we show that we can reproduce stellar masses to about 8%-10%, metallicity to ∼0.15 dex, and distance to 11%. We were able to make use of HIRES spectra obtained as part of the radial velocity monitoring of the star KOI-314 to derive a new mass estimate of 0.57 ± 0.05 M , a radius of 0.54 ± 0.05 R , a metallicity, [Fe/H], of −0.28 ± 0.10, and a distance of 66.5 ± 7.3 pc. Using HARPS archival data and combining our spectral method with constraints from transit observations, we are also able to derive the stellar properties of GJ 3470, a transiting planet hosting M dwarf. We estimate a mass of 0.53 ± 0.05 M , a radius of 0.50 ± 0.05 R , a metallicity, [Fe/H], of 0.12 ± 0.12, and a distance of 29.9± 3.7 3.4 pc.

The Astrophysical Journal, 2006

We report the detection of a Jupiter-mass planet in a 6.838 day orbit around the 1.28 M subgiant ... more We report the detection of a Jupiter-mass planet in a 6.838 day orbit around the 1.28 M subgiant HD 185269. The eccentricity of HD 185269b (e ¼ 0:30) is unusually large compared to other planets within 0.1 AU of their stars. Photometric observations demonstrate that the star is constant to AE0.0001 mag on the radial velocity period, strengthening our interpretation of a planetary companion. This planet was detected as part of our radial velocity survey of evolved stars located on the subgiant branch of the H-R diagram-also known as the Hertzsprung gap. These stars, which have masses between 1.2 and 2.5 M , play an important role in the investigation of the frequency of extrasolar planets as a function of stellar mass. Subject headingg s: planetary systems: formation-stars: individual (HD 189269)-techniques: radial velocities 1 Based on observations obtained at the Lick Observatory, which is operated by the University of California.

We report the discovery of a brown dwarf that transits one member of the M+M binary system LHS 63... more We report the discovery of a brown dwarf that transits one member of the M+M binary system LHS 6343 AB every 12.71 days. The transits were discovered using photometric data from the Kelper public data release. The LHS 6343 stellar system was previously identified as a single high-propermotion M dwarf. We use adaptive optics imaging to resolve the system into two low-mass stars with masses 0.370±0.009 M ⊙ and 0.30±0.01 M ⊙ , respectively, and a projected separation of 0. ′′ 55. High-resolution spectroscopy shows that the more massive component undergoes Doppler variations consistent with Keplerian motion, with a period equal to the transit period and an amplitude consistent with a companion mass of M C = 62.9 ± 2.3 M Jup. Based on our analysis of the transit light curve we estimate the radius of the companion to be R C = 0.833 ± 0.021 R Jup , which is consistent with theoretical predictions of the radius of a > 1 Gyr brown dwarf.

The Astrophysical Journal Supplement Series, 2019

We present the discovery of KELT-22Ab, a hot Jupiter from the KELT-South survey. KELT-22Ab transi... more We present the discovery of KELT-22Ab, a hot Jupiter from the KELT-South survey. KELT-22Ab transits the moderately bright (V ∼ 11.1) Sun-like G2V star TYC 7518-468-1. The planet has an orbital period of P = 1.3866529 ± 0.0000027 days, a radius of R P = 1.285 +0.12 −0.071 R J , and a relatively large mass of M P = 3.47 +0.15 −0.14 M J. The star has R = 1.099 +0.079 −0.046 R , M = 1.092 +0.045 −0.041 M , T eff = 5767 +50 −49 K, log g = 4.393 +0.039 −0.060 (cgs) and [m/H] = +0.259 +0.085 −0.083 , and thus, other than its slightly super-solar metallicity, appears to be a near solar twin. Surprisingly, KELT-22A exhibits kinematics and a Galactic orbit that are somewhat atypical for thin disk stars. Nevertheless, the star is rotating quite rapidly for its estimated age, shows evidence of chromospheric activity, and is somewhat metal rich. Imaging reveals a slightly fainter companion to KELT-22A that is likely bound, with a projected separation of 6 (∼1400 AU). In addition to the orbital motion caused by the transiting planet, we detect a possible linear trend in the radial velocity of KELT-22A suggesting the presence of another relatively nearby body that is perhaps non-stellar. KELT-22Ab is highly irradiated (as a consequence of the small semi-major axis of a/R = 4.97), and is mildly inflated. At such small separations, tidal forces become significant. The configuration of this system is optimal for measuring the rate of tidal dissipation within the host star. Our models predict that, due to tidal forces, the semi-major axis of KELT-22Ab is decreasing rapidly, and is thus predicted to spiral into the star within the next Gyr.

The Astrophysical Journal, 2016

We target the thermal emission spectrum of the non-transiting gas giant HD 88133 b with high-reso... more We target the thermal emission spectrum of the non-transiting gas giant HD 88133 b with high-resolution nearinfrared spectroscopy, by treating the planet and its host star as a spectroscopic binary. For sufficiently deep summed flux observations of the star and planet across multiple epochs, it is possible to resolve the signal of the hot gas giant's atmosphere compared to the brighter stellar spectrum, at a level consistent with the aggregate shot noise of the full data set. To do this, we first perform a principal component analysis to remove the contribution of the Earth's atmosphere to the observed spectra. Then, we use a cross-correlation analysis to tease out the spectra of the host star and HD 88133 b to determine its orbit and identify key sources of atmospheric opacity. In total, six epochs of Keck NIRSPEC L-band observations and three epochs of Keck NIRSPEC K-band observations of the HD 88133 system were obtained. Based on an analysis of the maximum likelihood curves calculated from the multi-epoch cross-correlation of the full data set with two atmospheric models, we report the direct detection of the emission spectrum of the non-transiting exoplanet HD 88133 b and measure a radial projection of the Keplerian orbital velocity of 40±15 km s −1 , a true mass of-+ M 1.02 0.28 0.61 J , a nearly face-on orbital inclination of -+ 15 5 6 , and an atmosphere opacity structure at high dispersion dominated by water vapor. This, combined with 11 years of radial velocity measurements of the system, provides the most up-to-date ephemeris for HD 88133.

The Astrophysical Journal, 2016

Stellar companions can influence the formation and evolution of planetary systems, but there are ... more Stellar companions can influence the formation and evolution of planetary systems, but there are currently few observational constraints on the properties of planet-hosting binary star systems. We search for stellar companions around 77 transiting hot Jupiter systems to explore the statistical properties of this population of companions as compared to field stars of similar spectral type. After correcting for survey incompleteness, we find that 47% ± 7% of hot Jupiter systems have stellar companions with semi-major axes between 50 AU-2000 AU. This is 2.9 times larger than the field star companion fraction in this separation range, with a significance of 4.4σ. In the 1 AU-50 AU range, only 3.9 +4.5 −2.0 % of hot Jupiters host stellar companions compared to the field star value of 16.4% ± 0.7%, which is a 2.7σ difference. We find that the distribution of mass ratios for stellar companions to hot Jupiter systems peaks at small values and therefore differs from that of field star binaries which tend to be uniformly distributed across all mass ratios. We conclude that either wide separation stellar binaries are more favorable sites for gas giant planet formation at all separations, or that the presence of stellar companions preferentially causes the inward migration of gas giant planets that formed farther out in the disk via dynamical processes such as Kozai-Lidov oscillations. We determine that less than 20% of hot Jupiters have stellar companions capable of inducing Kozai-Lidov oscillations assuming initial semi-major axes between 1-5 AU, implying that the enhanced companion occurrence is likely correlated with environments where gas giants can form efficiently.

The Astrophysical Journal, 2016

The Astrophysical Journal, 2016

Kepler-454 (KOI-273) is a relatively bright (V = 11.69 mag), Sun-like star that hosts a transitin... more Kepler-454 (KOI-273) is a relatively bright (V = 11.69 mag), Sun-like star that hosts a transiting planet candidate in a 10.6 day orbit. From spectroscopy, we estimate the stellar temperature to be 5687±50 K, its metallicity to be [m/H] = 0.32±0.08, and the projected rotational velocity to be v sin i<2.4 km s −1. We combine these values with a study of the asteroseismic frequencies from short cadence Kepler data to estimate the stellar mass to be M 1.028 0.03 0.04-+  , the radius to be 1.066±0.012 R e , and the age to be 5.25 1.39 1.41-+ Gyr. We estimate the radius of the 10.6 day planet as 2.37±0.13 R ⊕. Using 63 radial velocity observations obtained with the HARPS-N spectrograph on the Telescopio Nazionale Galileo and 36 observations made with the HIRES spectrograph at the Keck Observatory, we measure the mass of this planet to be 6.8±1.4 M ⊕. We also detect two additional nontransiting companions, a planet with a minimum mass of 4.46±0.12 M J in a nearly circular 524 day orbit and a massive companion with a period >10 years and mass >12.1 M J. The 12 exoplanets with radii <2.7 R ⊕ and precise mass measurements appear to fall into two populations, with those <1.6 R ⊕ following an Earth-like composition curve and larger planets requiring a significant fraction of volatiles. With a density of 2.76±0.73 g cm −3 , Kepler-454b lies near the mass transition between these two populations and requires the presence of volatiles and/or H/He gas.

Nature, 2015

White dwarfs are the end state of most stars, including the Sun, after they exhaust their nuclear... more 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 atmospheres 1,2 , even though these elements should rapidly settle into the stellar interiors unless they are occasionally replenished 3-5. The abundance ratios of heavy elements in white dwarf atmospheres are similar to rocky bodies in the Solar system 6,7. This and the existence of warm dusty debris disks 8-13 around about 4% of white dwarfs 14-16 suggest that rocky debris from white dwarf progenitors' planetary systems occasionally pollute the stars' atmospheres 17. The total accreted mass can be comparable to that of large asteroids in the solar system 1. 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.

The Astrophysical Journal, 2006

The unusual flux variations of the pre-main-sequence binary star KH 15D have been attributed to o... more The unusual flux variations of the pre-main-sequence binary star KH 15D have been attributed to occultations by a circumbinary disk. We test whether or not this theory is compatible with newly available data, including recent radial velocity measurements, CCD photometry over the past decade, and photographic photometry over the past 50 years. We find the model to be successful, after two refinements: a more realistic motion of the occulting feature and a halo around each star that probably represents scattering by the disk. The occulting feature is exceptionally sharp edged, raising the possibility that the dust in the disk has settled into a thin layer and providing a tool for fine-scale mapping of the immediate environment of a T Tauri star. However, the window of opportunity is closing, as the currently visible star may be hidden at all orbital phases by as early as 2008.

The Astrophysical Journal, 2006

We present spectroscopy of a transit of the exoplanet HD 189733b. By modeling the Rossiter-McLaug... more We present spectroscopy of a transit of the exoplanet HD 189733b. By modeling the Rossiter-McLaughlin effect (the anomalous Doppler shift due to the partial eclipse of the rotating stellar surface), we find the angle between the sky projections of the stellar spin axis and orbit normal to be. This is the third case of a "hot l p Ϫ1Њ .4 ‫ע‬ 1Њ .1 Jupiter" for which l has been measured. In all three cases l is small, ruling out random orientations with 99.96% confidence, and suggesting that the inward migration of hot Jupiters generally preserves spin-orbit alignment. Subject headings: planetary systems-planetary systems: formation-stars: individual (HD 189733)stars: rotation 1 Data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W. M. Keck Foundation.

The Astrophysical Journal, 2008

We present new spectroscopic and photometric observations of the HAT-P-1 planetary system. Spectr... more We present new spectroscopic and photometric observations of the HAT-P-1 planetary system. Spectra obtained during three transits exhibit the Rossiter-McLaughlin effect, allowing us to measure the angle between the sky projections of the stellar spin axis and orbit normal, λ = 3. • 7 ± 2. • 1. The small value of λ for this and other systems suggests that the dominant planet migration mechanism preserves spin-orbit alignment. Using two new transit light curves, we refine the transit ephemeris and reduce the uncertainty in the orbital period by an order of magnitude. We find a upper limit on the orbital eccentricity of 0.067, with 99% confidence, by combining our new radial-velocity measurements with those obtained previously.

The Astrophysical Journal, 2004

We propose that the extraordinary "winking star" KH 15D is an eccentric pre-main-sequence binary ... more We propose that the extraordinary "winking star" KH 15D is an eccentric pre-main-sequence binary that is gradually being occulted by an opaque screen. This model accounts for the periodicity, depth, duration, and rate of growth of the modern eclipses; the historical light curve from photographic plates; and the existing radial velocity measurements. It also explains the rebrightening events that were previously observed during eclipses and the subsequent disappearance of these events. We predict the future evolution of the system and its full radial velocity curve. Given the small velocity of the occulting screen relative to the center of mass of the binary, the screen is probably associated with the binary and may be the edge of a precessing circumbinary disk.

The Astrophysical Journal, 2011

Doppler observations from Keck Observatory have revealed a triple planet system orbiting the near... more Doppler observations from Keck Observatory have revealed a triple planet system orbiting the nearby mid-type K dwarf, HIP 57274. The inner planet, HIP 57274b, is a super-Earth with M sin i = 11.6 M ⊕ (0.036 M Jup), an orbital period of 8.135 ± 0.004 d, and slightly eccentric orbit e = 0.19±0.1. We calculate a transit probability of 6.5% for the inner planet. The second planet has M sin i = 0.4 M Jup with an orbital period of 32.0 ±0.02 d in a nearly circular orbit, and e = 0.05 ± 0.03. The third planet has M sin i = 0.53 M Jup with an orbital period of 432 ±8 d (1.18 years) and an eccentricity e = 0.23 ± 0.03. This discovery adds to the number of super Earth mass planets with M sin i < 12M ⊕ that 1 Based on observations obtained at the Keck Observatory, which is operated by the University of California

The Astrophysical Journal, 2013

We report that Kepler Object of Interest 256 (KOI-256) is a mutually eclipsing post-common envelo... more We report that Kepler Object of Interest 256 (KOI-256) is a mutually eclipsing post-common envelope binary (ePCEB), consisting of a cool white dwarf (M ⋆ = 0.592 ± 0.089M ⊙ , R ⋆ = 0.01345 ± 0.00091 R ⊙ , T eff = 7100±700 K) and an active M3 dwarf (M ⋆ = 0.51±0.16M ⊙ , R ⋆ = 0.540±0.014R ⊙ , T eff = 3450 ± 50 K) with an orbital period of 1.37865 ± 0.00001 days. KOI-256 is listed as hosting a transiting planet-candidate by Borucki et al. and Batalha et al.; here we report that the planetcandidate transit signal is in fact the occultation of a white dwarf as it passes behind the M dwarf. We combine publicly-available long-and short-cadence Kepler light curves with ground-based measurements to robustly determine the system parameters. The occultation events are readily apparent in the Kepler light curve, as is spin-orbit synchronization of the M dwarf, and we detect the transit of the white dwarf in front of the M dwarf halfway between the occultation events. The size of the white dwarf with respect to the Einstein ring during transit (R Ein = 0.00473 ± 0.00055 R ⊙) causes the transit depth to be shallower than expected from pure geometry due to gravitational lensing. KOI-256 is an old, long-period ePCEB and serves as a benchmark object for studying the evolution of binary star systems as well as white dwarfs themselves, thanks largely to the availability of near-continuous, ultra-precise Kepler photometry.

The Astrophysical Journal, 2006

We present a modification to the iodine cell Doppler technique that eliminates the need for an ob... more We present a modification to the iodine cell Doppler technique that eliminates the need for an observed stellar template spectrum. For a given target star, we iterate toward a synthetic template spectrum beginning with an existing spectrum of a similar star. We then perturb the shape of this first-guess template to match the program observation of the target star taken through an iodine cell. The elimination of a separate template observation saves valuable telescope time, a feature that is ideally suited for the quick-look strategy employed by the "Next 2000 Stars" (N2K) planet search program. Tests using Keck/HIRES spectra indicate that synthetic templates yield a short-term precision of 3 m s −1 and a long-term, run-to-run precision of 5 m s −1. We used this new Doppler technique to discover three new planets: a 1.50 M Jup planet in a 2.1375 d orbit around HD 86081; a 0.71 M Jup planet in circular, 26.73 d orbit around HD 224693; and a Saturn-mass planet in an 18.179 d orbit around HD 33283. The remarkably short period of HD 86081b bridges the gap between the extremely short-period planets detected in the OGLE survey and the 16 Doppler-detected hot jupiters 1 Based on observations obtained at the W. M. Keck Observatory, which is operated jointly by the University of California and the California Institute of Technology

The Astrophysical Journal, 2011

We report the discovery of a brown dwarf that transits one member of the M+M binary system LHS 63... more We report the discovery of a brown dwarf that transits one member of the M+M binary system LHS 6343 AB every 12.71 days. The transits were discovered using photometric data from the Kepler public data release. The LHS 6343 stellar system was previously identified as a single high proper motion M dwarf. We use adaptive optics imaging to resolve the system into two low-mass stars with masses 0.370 ± 0.009 M and 0.30 ± 0.01 M , respectively, and a projected separation of 0. 55. High-resolution spectroscopy shows that the more massive component undergoes Doppler variations consistent with Keplerian motion, with a period equal to the transit period and an amplitude consistent with a companion mass of M C = 62.7 ± 2.4 M Jup. Based on our analysis of the transit light curve, we estimate the radius of the companion to be R C = 0.833 ± 0.021 R Jup , which is consistent with theoretical predictions of the radius of a >1 Gyr brown dwarf.

The Astrophysical Journal, 2010

We report on the discovery and the Rossiter-McLaughlin (R-M) effect of Kepler-8b, a transiting pl... more We report on the discovery and the Rossiter-McLaughlin (R-M) effect of Kepler-8b, a transiting planet identified by the NASA Kepler Mission. Kepler photometry and Keck-HIRES radial velocities yield the radius and mass of the planet around this F8IV subgiant host star. The planet has a radius R P = 1.419 R J and a mass M P = 0.60 M J , yielding a density of 0.26 g cm −3 , one of the lowest planetary densities known. The orbital period is P = 3.523 days and the orbital semimajor axis is 0.0483 +0.0006 −0.0012 AU. The star has a large rotational v sin i of 10.5 ± 0.7 km s −1 and is relatively faint (V ≈ 13.89 mag); both properties are deleterious to precise Doppler measurements. The velocities are indeed noisy, with scatter of 30 m s −1 , but exhibit a period and phase that are consistent with those implied by transit photometry. We securely detect the R-M effect, confirming the planet's existence and establishing its orbit as prograde. We measure an inclination between the projected planetary orbital axis and the projected stellar rotation axis of λ = −26. • 4 ± 10. • 1, indicating a significant inclination of the planetary orbit. R-M measurements of a large sample of transiting planets from Kepler will provide a statistically robust measure of the true distribution of spin-orbit orientations for hot Jupiters around F and early G stars.

The Astrophysical Journal, 2009

We present two exoplanets detected at Keck Observatory. HD 179079 is a G5 subgiant that hosts a h... more We present two exoplanets detected at Keck Observatory. HD 179079 is a G5 subgiant that hosts a hot Neptune planet with M sin i = 27.5 M ⊕ in a 14.48 days, low-eccentricity orbit. The stellar reflex velocity induced by this planet has a semiamplitude of K = 6.6 m s −1. HD 73534 is a G5 subgiant with a Jupiterlike planet of M sin i = 1.1 M Jup and K = 16 m s −1 in a nearly circular 4.85 yr orbit. Both stars are chromospherically inactive and metal-rich. We discuss a known, classical bias in measuring eccentricities for orbits with velocity semiamplitudes, K, comparable to the radial velocity uncertainties. For exoplanets with periods longer than 10 days, the observed exoplanet eccentricity distribution is nearly flat for large amplitude systems (K > 80 m s −1), but rises linearly toward low eccentricity for lower amplitude systems (K > 20 m s −1).

The Astrophysical Journal, 2013

Doppler surveys have shown that the occurrence rate of Jupiter-mass planets appears to increase a... more Doppler surveys have shown that the occurrence rate of Jupiter-mass planets appears to increase as a function of stellar mass. However, this result depends on the ability to accurately measure the masses of evolved stars. Recently, Lloyd called into question the masses of subgiant stars targeted by Doppler surveys. Lloyd argues that very few observable subgiants have masses greater than 1.5 M , and that most of them have masses in the range 1.0-1.2 M. To investigate this claim, we use Galactic stellar population models to generate an all-sky distribution of stars. We incorporate the effects that make massive subgiants less numerous, such as the initial mass function and differences in stellar evolution timescales. We find that these effects lead to negligibly small systematic errors in stellar mass estimates, in contrast to the ≈50% errors predicted by Lloyd. Additionally, our simulated target sample does in fact include a significant fraction of stars with masses greater than 1.5 M , primarily because the inclusion of an apparent magnitude limit results in a Malmquist-like bias toward more massive stars, in contrast to the volume-limited simulations of Lloyd. The magnitude limit shifts the mean of our simulated distribution toward higher masses and results in a relatively smaller number of evolved stars with masses in the range 1.0-1.2 M. We conclude that, within the context of our present-day understanding of stellar structure and evolution, many of the subgiants observed in Doppler surveys are indeed as massive as main-sequence A stars.

The Astrophysical Journal, 2013

We construct high signal-to-noise "template" spectra by co-adding hundreds of spectra of nearby d... more We construct high signal-to-noise "template" spectra by co-adding hundreds of spectra of nearby dwarfs spanning K7 to M4, taken with Keck/HIRES as part of the California Planet Search. We identify several spectral regions in the visible (370-800 nm) that are sensitive to the stellar luminosity and metallicity. We use these regions to develop a spectral calibration method to measure the mass, metallicity, and distance of low-mass stars, without the requirement of geometric parallaxes. Testing our method on a sample of nearby M dwarfs, we show that we can reproduce stellar masses to about 8%-10%, metallicity to ∼0.15 dex, and distance to 11%. We were able to make use of HIRES spectra obtained as part of the radial velocity monitoring of the star KOI-314 to derive a new mass estimate of 0.57 ± 0.05 M , a radius of 0.54 ± 0.05 R , a metallicity, [Fe/H], of −0.28 ± 0.10, and a distance of 66.5 ± 7.3 pc. Using HARPS archival data and combining our spectral method with constraints from transit observations, we are also able to derive the stellar properties of GJ 3470, a transiting planet hosting M dwarf. We estimate a mass of 0.53 ± 0.05 M , a radius of 0.50 ± 0.05 R , a metallicity, [Fe/H], of 0.12 ± 0.12, and a distance of 29.9± 3.7 3.4 pc.

The Astrophysical Journal, 2006

We report the detection of a Jupiter-mass planet in a 6.838 day orbit around the 1.28 M subgiant ... more We report the detection of a Jupiter-mass planet in a 6.838 day orbit around the 1.28 M subgiant HD 185269. The eccentricity of HD 185269b (e ¼ 0:30) is unusually large compared to other planets within 0.1 AU of their stars. Photometric observations demonstrate that the star is constant to AE0.0001 mag on the radial velocity period, strengthening our interpretation of a planetary companion. This planet was detected as part of our radial velocity survey of evolved stars located on the subgiant branch of the H-R diagram-also known as the Hertzsprung gap. These stars, which have masses between 1.2 and 2.5 M , play an important role in the investigation of the frequency of extrasolar planets as a function of stellar mass. Subject headingg s: planetary systems: formation-stars: individual (HD 189269)-techniques: radial velocities 1 Based on observations obtained at the Lick Observatory, which is operated by the University of California.