230 research outputs found
The TRENDS High-Contrast Imaging Survey. V. Discovery of an Old and Cold Benchmark T-dwarf Orbiting the Nearby G-star HD 19467
The nearby Sun-like star HD 19467 shows a subtle radial velocity (RV)
acceleration of -1.37+/-0.09 m/s/yr over an 16.9 year time baseline (an RV
trend), hinting at the existence of a distant orbiting companion. We have
obtained high-contrast adaptive optics images of the star using NIRC2 at Keck
Observatory and report the direct detection of the body that causes the
acceleration. The companion, HD 19467 B, is dK=12.57+/-0.09 mag fainter than
its parent star (contrast ratio of 9.4e-6), has blue colors J-K_s=-0.36+/-0.14
(J-H=-0.29+/-0.15), and is separated by 1.653+/-0.004" (51.1+/-1.0 AU).
Follow-up astrometric measurements obtained over an 1.1 year time baseline
demonstrate physical association through common parallactic and proper motion.
We calculate a firm lower-limit of m>51.9^{+3.6}_{-4.3}Mjup for the companion
mass from orbital dynamics using a combination of Doppler observations and
imaging. We estimate a model-dependent mass of m=56.7^{+4.6}_{-7.2}Mjup from a
gyrochronological age of 4.3^{+1.0}_{-1.2} Gyr. Isochronal analysis suggests a
much older age of Gyr, which corresponds to a mass of
m=67.4^{+0.9}_{-1.5}Mjup. HD 19467 B's measured colors and absolute magnitude
are consistent with a late T-dwarf [~T5-T7]. We may infer a low metallicity of
[Fe/H]=-0.15+/-0.04 for the companion from its G3V parent star. HD 19467 B is
the first directly imaged benchmark T-dwarf found orbiting a Sun-like star with
a measured RV acceleration.Comment: Updated to reflect ApJ versio
Fourteen New Companions from the Keck & Lick Radial Velocity Survey Including Five Brown Dwarf Candidates
We present radial velocities for 14 stars on the California & Carnegie Planet
Search target list that reveal new companions. One star, HD 167665, was fit
with a definitive Keplerian orbit leading to a minimum mass for the companion
of 50.3 Mjup at a separation from its host of ~5.5 AU. Incomplete or limited
phase coverage for the remaining 13 stars prevents us from assigning to them
unique orbital parameters. Instead, we fit their radial velocities with
Keplerian orbits across a grid of fixed values for Msini and period, P, and use
the resulting reduced chi-square surface to place constraints on Msini, P, and
semimajor axis, a. This technique allowed us to restrict Msini below the brown
dwarf -- stellar mass boundary for an additional 4 companions (HD 150554, HD
8765, HD 72780, HD 74014). If the combined 5 companions are confirmed as brown
dwarfs, these results would comprise the first major catch of such objects from
our survey beyond ~3 AU.Comment: 29 pages, 14 figures, accepted to Ap
Two Exoplanets Discovered at Keck Observatory
We present two exoplanets detected at Keck Observatory. HD 179079 is a G5
subgiant that hosts a hot Neptune planet with Msini = 27.5 M_earth in a 14.48
d, low-eccentricity orbit. The stellar reflex velocity induced by this planet
has a semiamplitude of K = 6.6 m/s. HD 73534 is a G5 subgiant with a
Jupiter-like planet of Msini = 1.1 M_jup and K = 16 m/s 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), but rises linearly toward low eccentricity for lower amplitude systems (K
> 20 m/s).Comment: 8 figures, 6 tables, accepted, Ap
Retired A Stars and Their Companions IV. Seven Jovian Exoplanets from Keck Observatory
We report precise Doppler measurements of seven subgiants from Keck
Observatory. All seven stars show variability in their radial velocities
consistent with planet-mass companions in Keplerian orbits. The host stars have
masses ranging from 1.1 < Mstar/Msun < 1.9, radii 3.4 < Rstar/Rsun < 6.1, and
metallicities -0.21 < [Fe/H] < +0.26. The planets are all more massive than
Jupiter (Msini > 1 Mjup) and have semimajor axes > 1 AU. We present
millimagnitude photometry from the T3 0.4m APT at Fairborn observatory for five
of the targets. Our monitoring shows these stars to be photometrically stable,
further strengthening the interpretation of the observed radial velocity
variability. The orbital characteristics of the planets thus far discovered
around former A-type stars are very different from the properties of planets
around dwarf stars of spectral type F, G and K, and suggests that the formation
and migration of planets is a sensitive function of stellar mass. Three of the
planetary systems show evidence of long-term, linear trends indicative of
additional distant companions. These trends, together with the high planet
masses and increased occurrence rate, indicate that A-type stars are very
promising targets for direct imaging surveys.Comment: PASP Accepted, final submission awaiting comments from the communit
Five planets and an independent confirmation of HD 196885Ab from Lick Observatory
We present time series Doppler data from Lick Observatory that reveal the
presence of long-period planetary companions orbiting nearby stars. The typical
eccentricity of these massive planets are greater than the mean eccentricity of
known exoplanets. HD30562b has Msini = 1.29 Mjup, with semi-major axis of 2.3
AU and eccentricity 0.76. The host star has a spectral type F8V and is metal
rich. HD86264b has Msini = 7.0 Mjup, arel = 2.86 AU, an eccentricity, e = 0.7
and orbits a metal-rich, F7V star. HD87883b has Msini = 1.78 Mjup, arel = 3.6
AU, e = 0.53 and orbits a metal-rich K0V star. HD89307b has Msini = 1.78 Mjup,
arel = 3.3 AU, e = 0.24 and orbits a G0V star with slightly subsolar
metallicity. HD148427b has Msini = 0.96 Mjup, arel = 0.93 AU, eccentricity of
0.16 and orbits a metal rich K0 subgiant. We also present velocities for a
planet orbiting the F8V metal-rich binary star, HD196885A. The planet has Msini
= 2.58 Mjup, arel = 2.37 AU, and orbital eccentricity of 0.48, in agreement
with the independent discovery by Correia et al. 2008.Comment: 12 figures, 8 tables, accepted Ap
A High Eccentricity Component in the Double Planet System Around HD 163607 and a Planet Around HD 164509
We report the detection of three new exoplanets from Keck Observatory. HD
163607 is a metal-rich G5IV star with two planets. The inner planet has an
observed orbital period of 75.29 0.02 days, a semi-amplitude of 51.1
1.4 \ms, an eccentricity of 0.73 0.02 and a derived minimum mass of
\msini = 0.77 0.02 \mjup. This is the largest eccentricity of any known
planet in a multi-planet system. The argument of periastron passage is 78.7
2.0; consequently, the planet's closest approach to its parent
star is very near the line of sight, leading to a relatively high transit
probability of 8%. The outer planet has an orbital period of 3.60 0.02
years, an orbital eccentricity of 0.12 0.06 and a semi-amplitude of 40.4
1.3 \ms. The minimum mass is \msini = 2.29 0.16 \mjup. HD 164509 is
a metal-rich G5V star with a planet in an orbital period of 282.4 3.8
days and an eccentricity of 0.26 0.14. The semi-amplitude of 14.2
2.7 \ms\ implies a minimum mass of 0.48 0.09 \mjup. The radial velocities
of HD 164509 also exhibit a residual linear trend of -5.1 0.7 \ms\ per
year, indicating the presence of an additional longer period companion in the
system. Photometric observations demonstrate that HD 163607 and HD 164509 are
constant in brightness to sub-millimag levels on their radial velocity periods.
This provides strong support for planetary reflex motion as the cause of the
radial velocity variations.Comment: 10 pages, 8 figures, accepted to Ap
The California Planet Survey II. A Saturn-Mass Planet Orbiting the M Dwarf Gl649
We report precise Doppler measurements of the nearby (d = 10.34 pc) M dwarf
Gl649 that reveal the presence of a planet with a minimum mass Msini = 0.328
Mjup in an eccentric (e = 0.30), 598.3 day orbit. Our photometric monitoring
reveals Gl649 to be a new variable star with brightness changes on both
rotational and decadal timescales. However, neither of these timescales are
consistent with the 600-day Doppler signal and so provide strong support for
planetary reflex motion as the best interpretation of the observed radial
velocity variations. Gl649b is only the seventh Doppler-detected giant planet
around an M dwarf. The properties of the planet and host-star therefore
contribute significant information to our knowledge of planet formation around
low-mass stars. We revise and refine the occurrence rate of giant planets
around M dwarfs based on the California Planet Survey sample of low-mass stars
(M* < 0.6 Msun). We find that f = 3.4^{+2.2}_{-0.9}% of stars with M* < 0.6
Msun harbor planets with Msini > 0.3$ Mjup and a < 2.5 AU. When we restrict our
analysis to metal-rich stars with [Fe/H] > +0.2 we find the occurrence rate is
10.7^{+5.9}_{-4.2}%.Comment: 8 pages, 4 figures, 3 tables, PASP accepte
The Dynamical Mass and Three-Dimensional Orbit of HR7672B: A Benchmark Brown Dwarf with High Eccentricity
The companion to the G0V star HR7672 directly imaged by Liu et al. (2002) has
moved measurably along its orbit since the discovery epoch, making it possible
to determine its dynamical properties. Originally targeted with adaptive optics
because it showed a long-term radial velocity acceleration (trend), we have
monitored this star with precise Doppler measurements and have now established
a 24 year time baseline. The radial velocity variations show significant
curvature (change in the acceleration) including an inflection point. We have
also obtained a recent image of HR7672B with NIRC2 at Keck. The astrometry also
shows curvature. In this paper, we use jointly-fitted Doppler and astrometric
models to calculate the three-dimensional orbit and dynamical mass of the
companion. The mass of the host star is determined using a direct radius
measurement from CHARA interferometry in combination with high resolution
spectroscopic modeling. We find that HR7672B has a highly eccentric,
, near edge-on, deg, orbit with
semimajor axis, AU. The mass of the companion is
at the 68.2% confidence level. HR7672B thus resides
near the substellar boundary, just below the hydrogen-fusing limit. These
measurements of the companion mass are independent of its brightness and
spectrum and establish HR7672B as a rare and precious "benchmark" brown dwarf
with a well-determined mass, age, and metallicity essential for testing
theoretical evolutionary models and synthetic spectral models. It is presently
the only directly imaged L,T,Y-dwarf known to produce an RV trend around a
solar-type star.Comment: accepted to Ap
The TRENDS High-contrast Imaging Survey. IV. The Occurrence Rate of Giant Planets around M Dwarfs
Doppler-based planet surveys have discovered numerous giant planets but are incomplete beyond several AU. At larger star–planet separations, direct planet detection through high-contrast imaging has proven successful, but this technique is sensitive only to young planets and characterization relies upon theoretical evolution models. Here we demonstrate that radial velocity measurements and high-contrast imaging can be combined to overcome these issues. The presence of widely separated companions can be deduced by identifying an acceleration (long-term trend) in the radial velocity of a star. By obtaining high spatial resolution follow-up imaging observations, we rule out scenarios in which such accelerations are caused by stellar binary companions with high statistical confidence. We report results from an analysis of Doppler measurements of a sample of 111 M-dwarf stars with a median of 29 radial velocity observations over a median time baseline of 11.8 yr. By targeting stars that exhibit a radial velocity acceleration ("trend") with adaptive optics imaging, we determine that 6.5% ± 3.0% of M-dwarf stars host one or more massive companions with 1 < m/M_J < 13 and 0 < a < 20 AU. These results are lower than analyses of the planet occurrence rate around higher-mass stars. We find the giant planet occurrence rate is described by a double power law in stellar mass M and metallicity F ≡ [Fe/H] such that f(M, F) = 0.039^+0.056)_(-0.028)M^(0.8)^(+1.1)_(-0.9) 10^(3.8±1.2). Our results are consistent with gravitational microlensing measurements of the planet occurrence rate; this study represents the first model-independent comparison with microlensing observations
Retired A Stars and Their Companions: Exoplanets Orbiting Three Intermediate-Mass Subgiants
We report precision Doppler measurements of three intermediate-mass subgiants
from Lick and Keck Observatories. All three stars show variability in their
radial velocities consistent with planet-mass companions in Keplerian orbits.
We find a planet with a minimum mass of 2.5 Mjup in a 351.5 day orbit around HD
192699, a planet with a minimum mass of 2.0 Mjup in a 341.1 day orbit around HD
210702, and a planet with a minimum mass of 0.61 Mjup in a 297.3 day orbit
around HD 175541. Stellar mass estimates from evolutionary models indicate that
all of these stars were formerly A-type dwarfs with masses ranging from 1.65 to
1.85 Msun. These three long-period planets would not have been detectable
during their stars' main-sequence phases due to the large rotational velocities
and stellar jitter exhibited by early-type dwarfs. There are now 9 "retired"
(evolved) A-type stars (Mstar > 1.6 Msun) with known planets. All 9 planets
orbit at distances a \geq 0.78 AU, which is significantly different than the
semimajor axis distribution of planets around lower-mass stars. We examine the
possibility that the observed lack of close-in planets is due to engulfment by
their expanding host stars, but we find that this explanation is inadequate
given the relatively small stellar radii of K giants (Rstar < 32 Rsun = 0.15
AU) and subgiants (Rstar < 7 Rsun = 0.03 AU). Instead, we conclude that planets
around intermediate-mass stars reside preferentially beyond ~0.8 AU, which may
be a reflection of different formation and migration histories of planets
around A-type stars.Comment: 31 pages, 9 figures, 6 tables, ApJ accepted, corrected minor typo
- …