18 research outputs found
Discovery of a Transiting Planet Near the Snow-Line
In most theories of planet formation, the snow-line represents a boundary
between the emergence of the interior rocky planets and the exterior ice
giants. The wide separation of the snow-line makes the discovery of transiting
worlds challenging, yet transits would allow for detailed subsequent
characterization. We present the discovery of Kepler-421b, a Uranus-sized
exoplanet transiting a G9/K0 dwarf once every 704.2 days in a near-circular
orbit. Using public Kepler photometry, we demonstrate that the two observed
transits can be uniquely attributed to the 704.2 day period. Detailed light
curve analysis with BLENDER validates the planetary nature of Kepler-421b to >4
sigmas confidence. Kepler-421b receives the same insolation as a body at ~2AU
in the Solar System and for a Uranian albedo would have an effective
temperature of ~180K. Using a time-dependent model for the protoplanetary disk,
we estimate that Kepler-421b's present semi-major axis was beyond the snow-line
after ~3Myr, indicating that Kepler-421b may have formed at its observed
location.Comment: 14 pages, 10 figures, 3 tables. Accepted in Ap
Crossing the Brown Dwarf Desert Using Adaptive Optics: A Very Close L-Dwarf Companion to the Nearby Solar Analog HR 7672
We have found a very faint companion to the active solar analog HR 7672 (HD
190406; GJ 779; 15 Sge). Three epochs of high resolution imaging using adaptive
optics (AO) at the Gemini-North and Keck II Telescopes demonstrate that HR
7672B is a common proper motion companion, with a separation of 0.79" (14 AU)
and a 2.16 um flux ratio of 8.6 mags. Using follow-up K-band spectroscopy from
Keck AO+NIRSPEC, we measure a spectral type of L4.5+/-1.5. This is the closest
ultracool companion around a main sequence star found to date by direct
imaging. We estimate the primary has an age of 1-3 Gyr. Assuming coevality, the
companion is most likely substellar, with a mass of 55-78 Mjup based on
theoretical models. The primary star shows a long-term radial velocity trend,
and we combine the radial velocity data and AO imaging to set a firm
(model-independent) lower limit of 48 Mjup. In contrast to the paucity of brown
dwarf companions at <~4 AU around FGK dwarfs, HR 7672B implies that brown dwarf
companions do exist at separations comparable to those of the giant planets in
our own solar system. Its presence is at variance with scenarios where brown
dwarfs form as ejected stellar embryos. Moreover, since HR 7672B is likely too
massive to have formed in a circumstellar disk as planets are believed to, its
discovery suggests that a diversity of physical processes act to populate the
outer regions of exoplanetary systems.Comment: Astrophysical Journal, in pres
The TRENDS High-contrast Imaging Survey. II. Direct Detection of the HD 8375 Tertiary
We present the direct imaging detection of a faint tertiary companion to the single-lined spectroscopic binary HD 8375 AB. Initially noticed as an 53 m s^–1 yr^–1 Doppler acceleration by Bowler et al., we have obtained high-contrast adaptive optics observations at Keck using NIRC2 that spatially resolve HD 8375 C from its host(s). Astrometric measurements demonstrate that the companion shares a common proper-motion. We detect orbital motion in a clockwise direction. Multiband relative photometry measurements are consistent with an early M-dwarf spectral type (~M1V). Our combined Doppler and imaging observations place a lower-limit of m ≥ 0.297 M_☉ on its dynamical mass. We also provide a refined orbit for the inner pair using recent radial velocity measurements obtained with the High Resolution Echelle Spectrometer. HD 8375 is one of many triple-star systems that are apparently missing in the solar neighborhood
The TRENDS High-contrast Imaging Survey. I. Three Benchmark M Dwarfs Orbiting Solar-type Stars
We present initial results from a new high-contrast imaging program dedicated to stars that exhibit long-term Doppler radial velocity accelerations (or "trends"). The goal of the TRENDS (TaRgetting bENchmark-objects with Doppler Spectroscopy) imaging survey is to directly detect and study the companions responsible for accelerating their host star. In this first paper of the series, we report the discovery of low-mass stellar companions orbiting HD 53665, HD 68017, and HD 71881 using NIRC2 adaptive optics (AO) observations at Keck. Follow-up imaging demonstrates association through common proper motion. These comoving companions have red colors with estimated spectral types of K7-M0, M5, and M3-M4, respectively. We determine a firm lower limit to their mass from Doppler and astrometric measurements. In the near future, it will be possible to construct three-dimensional orbits and calculate the dynamical mass of HD 68017 B and possibly HD 71881 B. We already detect astrometric orbital motion of HD 68017 B, which has a projected separation of 13.0 AU. Each companion is amenable to AO-assisted direct spectroscopy. Further, each companion orbits a solar-type star, making it possible to infer metallicity and age from the primary. Such benchmark objects are essential for testing theoretical models of cool dwarf atmospheres
Discovery of the Transiting Planet Kepler-5B
We present 44 days of high duty cycle, ultra precise photometry of the 13th magnitude star Kepler-5 (KIC 8191672, T(eff) = 6300 K, log g = 4.1), which exhibits periodic transits with a depth of 0.7%. Detailed modeling of the transit is consistent with a planetary companion with an orbital period of 3.548460 +/- 0.000032 days and a radius of 1.431(-0.052)(+0.041) R(J). Follow-up radial velocity measurements with the Keck HIRES spectrograph on nine separate nights demonstrate that the planet is more than twice as massive as Jupiter with a mass of 2.114(-0.059)(+0.056) M(J) and a mean density of 0.894 +/- 0.079 g cm(-3).NASA's Science Mission DirectorateAstronom
HAT-P-50b, HAT-P-51b, HAT-P-52b, and HAT-P-53b: Three Transiting Hot Jupiters and a Transiting Hot Saturn From the HATNet Survey
We report the discovery and characterization of four transiting exoplanets by
the HATNet survey. The planet HAT-P-50b has a mass of 1.35 M_J and a radius of
1.29 R_J, and orbits a bright (V = 11.8 mag) M = 1.27 M_sun, R = 1.70 R_sun
star every P = 3.1220 days. The planet HAT-P-51b has a mass of 0.31 M_J and a
radius of 1.29 R_J, and orbits a V = 13.4 mag, M = 0.98 M_sun, R = 1.04 R_sun
star with a period of P = 4.2180 days. The planet HAT-P-52b has a mass of 0.82
M_J and a radius of 1.01 R_J, and orbits a V = 14.1 mag, M = 0.89 M_sun, R =
0.89 R_sun star with a period of P = 2.7536 days. The planet HAT-P-53b has a
mass of 1.48 M_J and a radius of 1.32 R_J, and orbits a V = 13.7 mag, M = 1.09
M_sun, R = 1.21 R_sun star with a period of P = 1.9616 days. All four planets
are consistent with having circular orbits and have masses and radii measured
to better than 10% precision. The low stellar jitter and favorable R_P/R_star
ratio for HAT-P-51 make it a promising target for measuring the
Rossiter-McLaughlin effect for a Saturn-mass planet.Comment: Submitted to AJ. 20 pages, 9 figures, 5 tables. Data available at
http://hatnet.org
Kepler Observations of Transiting Hot Compact Objects
Kepler photometry has revealed two unusual transiting companions orbiting an
early A-star and a late B-star. In both cases the occultation of the companion
is deeper than the transit. The occultation and transit with follow-up optical
spectroscopy reveal a 9400 K early A-star, KOI-74 (KIC 6889235), with a
companion in a 5.2 day orbit with a radius of 0.08 Rsun and a 10000 K late
B-star KOI-81 (KIC 8823868) that has a companion in a 24 day orbit with a
radius of 0.2 Rsun. We infer a temperature of 12250 K for KOI-74b and 13500 K
for KOI-81b.
We present 43 days of high duty cycle, 30 minute cadence photometry, with
models demonstrating the intriguing properties of these object, and speculate
on their nature.Comment: 12 pages, 3 figures, submitted to ApJL (updated to correct KOI74
lightcurve
Characterizing the Orbital and Dynamical State of the HD 82943 Planetary System with Keck Radial Velocity Data
We present an updated analysis of radial velocity data of the HD 82943 planetary system based on 10 yr of measurements obtained with the Keck telescope. Previous studies have shown that the HD 82943 system has two planets that are likely in 2:1 mean-motion resonance (MMR), with orbital periods about 220 and 440 days. However, alternative fits that are qualitatively different have also been suggested, with two planets in a 1:1 resonance or three planets in a Laplace 4:2:1 resonance. Here we use χ^2 minimization combined with a parameter grid search to investigate the orbital parameters and dynamical states of the qualitatively different types of fits, and we compare the results to those obtained with the differential evolution Markov chain Monte Carlo method. Our results support the coplanar 2:1 MMR configuration for the HD 82943 system, and show no evidence for either the 1:1 or three-planet Laplace resonance fits. The inclination of the system with respect to the sky plane is well constrained at 20^(+4.9)_(-5.5) degrees, and the system contains two planets with masses of about 4.78 M_J and 4.80 M_J (where M_J is the mass of Jupiter) and orbital periods of about 219 and 442 days for the inner and outer planet, respectively. The best fit is dynamically stable with both eccentricity-type resonant angles θ_1 and θ_2 librating around 0°
LHS6343C: A Transiting Field Brown Dwarf Discovered by the Kepler Mission
We report the discovery of a brown dwarf that transits one member of the M+M
binary system LHS6343AB every 12.71 days. The transits were discovered using
photometric data from the Kelper public data release. The LHS6343 stellar
system was previously identified as a single high-proper-motion M dwarf. We use
high-contrast imaging to resolve the system into two low-mass stars with masses
0.45 Msun and 0.36 Msun, respectively, and a projected separation of 55 arcsec.
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 = 62.8
+/- 2.3 Mjup. Based on an analysis of the Kepler light curve we estimate the
radius of the companion to be R_C = 0.832 +/- 0.021 Rjup, which is consistent
with theoretical predictions of the radius of a > 1 Gyr brown dwarf.Comment: Our previous analysis neglected the dependence of the scaled
semimajor axis, a/R, on the transit depth. By not correcting a/R for the
third-light contamination, we overestimated the mass of Star A, which led to
an overestimate the mass and radius of the LHS6343