63 research outputs found
The Lick-Carnegie Survey: A New Two-Planet System Around the Star HD 207832
Keck/HIRES precision radial velocities of HD 207832 indicate the presence of
two Jovian-type planetary companions in Keplerian orbits around this G star.
The planets have minimum masses of 0.56 and 0.73 Jupiter-masses with orbital
periods of ~162 and ~1156 days, and eccentricities of 0.13 and 0.27,
respectively. Stromgren b and y photometry reveals a clear stellar rotation
signature of the host star with a period of 17.8 days, well separated from the
period of the radial velocity variations, reinforcing their Keplerian origin.
The values of the semimajor axes of the planets suggest that these objects have
migrated from the region of giant planet formation to closer orbits. In order
to examine the possibility of the existence of additional (small) planets in
the system, we studied the orbital stability of hypothetical terrestrial-sized
objects in the region between the two planets and interior to the orbit of the
inner body. Results indicated that stable orbits exist only in a small region
interior to planet b. However, the current observational data offer no evidence
for the existence of additional objects in this system.Comment: 23 pages, 4 figures, 5 tables, accepted for publication in Ap
Two super-earths orbiting the solar analog HD 41248 on the edge of a 7 : 5 mean motion resonance
J. S. Jenkins, M. Tuomi, R. Brasser, O. Ivanyuk, and F. Murgas, 'Two super-Earths orbiting the solar analog HD 41248 on the edge of a 7:5 mean motion resonance', The Astrophysical Journal, Vol. 771:41 (13 pp), first published online 14 June 2013. The version of record is available online at doi: 10.1088/0004-637X/771/1/41 © 2013. The American Astronomical Society. All rights reserved.There are a growing number of multi-planet systems known to be orbiting their host stars with orbital periods that place them in mean motion resonances (MMRs). These systems are generally in first-order resonances and dynamical studies have focused their efforts on understanding the origin and evolution of such dynamically resonant commensurabilities. Here we report the discovery of two super-Earths that are close to a second-order dynamical resonance orbiting the metal-poor ([Fe/H] = -0.43 dex) and inactive G2V star HD 41428. We analyzed 62 HARPS archival radial velocities for this star that, until now, exhibited no evidence for planetary companions. Using our new Bayesian Doppler signal detection algorithm, we find two significant signals in the data, with periods of 18.357 days and 25.648 days, indicating they could be part of a 7:5 second-order MMR. Both semi-amplitudes are below 3 m s-1 and the minimum masses of the pair are 12.3 and 8.6 M⊕, respectively. Our simulations found that apsidal alignment stabilizes the system, and even though libration of the resonant angles was not seen, the system is affected by the presence of the resonance and could still occupy the 7:5 commensurability, which would be the first planetary configuration in such a dynamical resonance. Given the multitude of low-mass multi-planet systems that will be discovered in the coming years, we expect that more of these second-order resonant configurations will emerge from the data, highlighting the need for a better understanding of the dynamical interactions between forming planetesimals.Peer reviewe
Astrometry and radial velocities of the planet host M dwarf GJ 317: new trigonometric distance, metallicity and upper limit to the mass of GJ 317b
We have obtained precision astrometry of the planet hosting M dwarf GJ 317 in
the framework of the Carnegie Astrometric Planet Search project. The new
astrometric measurements give a distance determination of 15.3 pc, 65% further
than previous estimates. The resulting absolute magnitudes suggest it is metal
rich and more massive than previously assumed. This result strengthens the
correlation between high metallicity and the presence of gas giants around low
mass stars. At 15.3 pc, the minimal astrometric amplitude for planet candidate
GJ 317b is 0.3 milliarcseconds (edge-on orbit), just below our astrometric
sensitivity. However, given the relatively large number of observations and
good astrometric precision, a Bayesian Monte Carlo Markov Chain analysis
indicates that the mass of planet b has to be smaller than twice the minimum
mass with a 99% confidence level, with a most likely value of 2.5 Mjup.
Additional RV measurements obtained with Keck by the Lick-Carnegie Planet
search program confirm the presence of an additional very long period planet
candidate, with a period of 20 years or more. Even though such an object will
imprint a large astrometric wobble on the star, its curvature is yet not
evident in the astrometry. Given high metallicity, and the trend indicating
that multiple systems are rich in low mass companions, this system is likely to
host additional low mass planets in its habitable zone that can be readily
detected with state-of-the-art optical and near infrared RV measurements.Comment: 20 pages of text, 9 Figures, 8 tables. Accepted in ApJ (in press
The Anglo-Australian Planet Search. XXII. Two New Multi-Planet Systems
We report the detection of two new planets from the Anglo-Australian Planet
Search. These planets orbit two stars each previously known to host one planet.
The new planet orbiting HD 142 has a period of 6005\pm427 days, and a minimum
mass of 5.3M_Jup. HD142c is thus a new Jupiter analog: a gas-giant planet with
a long period and low eccentricity (e = 0.21 \pm 0.07). The second planet in
the HD 159868 system has a period of 352.3\pm1.3 days, and m sin i=0.73\pm0.05
M_Jup. In both of these systems, including the additional planets in the
fitting process significantly reduced the eccentricity of the original planet.
These systems are thus examples of how multiple-planet systems can masquerade
as moderately eccentric single-planet systems.Comment: 31 pages, 8 figures, accepted for publication in Ap
A Hot Uranus Orbiting the Super Metal-rich Star HD77338 and the Metallicity - Mass Connection
We announce the discovery of a low-mass planet orbiting the super metal-rich
K0V star HD77338 as part of our on-going Calan-Hertfordshire Extrasolar Planet
Search. The best fit planet solution has an orbital period of 5.7361\pm0.0015
days and with a radial velocity semi-amplitude of only 5.96\pm1.74 m/s, we find
a minimum mass of 15.9+4.7-5.3 Me. The best fit eccentricity from this solution
is 0.09+0.25-0.09, and we find agreement for this data set using a Bayesian
analysis and a periodogram analysis. We measure a metallicity for the star of
+0.35\pm0.06 dex, whereas another recent work (Trevisan et al. 2011) finds
+0.47\pm0.05 dex. Thus HD77338b is one of the most metal-rich planet host stars
known and the most metal-rich star hosting a sub-Neptune mass planet. We
searched for a transit signature of HD77338b but none was detected. We also
highlight an emerging trend where metallicity and mass seem to correlate at
very low masses, a discovery that would be in agreement with the core accretion
model of planet formation. The trend appears to show that for Neptune-mass
planets and below, higher masses are preferred when the host star is more
metal-rich. Also a lower boundary is apparent in the super metal-rich regime
where there are no very low-mass planets yet discovered in comparison to the
sub-solar metallicity regime. A Monte Carlo analysis shows that this, low-mass
planet desert, is statistically significant with the current sample of 36
planets at around the 4.5\sigma\ level. In addition, results from Kepler
strengthen the claim for this paucity of the lowest-mass planets in super
metal-rich systems. Finally, this discovery adds to the growing population of
low-mass planets around low-mass and metal-rich stars and shows that very
low-mass planets can now be discovered with a relatively small number of data
points using stable instrumentation.Comment: 25 pages, 15 figures, 5 tables, accepted for publication in Ap
A detailed analysis of the HD 73526 2:1 resonant planetary system
We present six years of new radial velocity data from the Anglo-Australian and Magellan Telescopes on the HD 73526 2:1 resonant planetary system. We investigate both Keplerian and dynamical ( interacting) fits to these data, yielding four possible configurations for the system. The new data now show that both resonance angles are librating, with amplitudes of 40 degrees and 60 degrees, respectively. We then perform long-term dynamical stability tests to differentiate these solutions, which only differ significantly in the masses of the planets. We show that while there is no clearly preferred system inclination, the dynamical fit with i = 90 degrees provides the best combination of goodness-of-fit and long-term dynamical stability.Peer reviewe
The Lick-Carnegie Exoplanet Survey: A 3.1 M_Earth Planet in the Habitable Zone of the Nearby M3V Star Gliese 581
We present 11 years of HIRES precision radial velocities (RV) of the nearby
M3V star Gliese 581, combining our data set of 122 precision RVs with an
existing published 4.3-year set of 119 HARPS precision RVs. The velocity set
now indicates 6 companions in Keplerian motion around this star. Differential
photometry indicates a likely stellar rotation period of ~94 days and reveals
no significant periodic variability at any of the Keplerian periods, supporting
planetary orbital motion as the cause of all the radial velocity variations.
The combined data set strongly confirms the 5.37-day, 12.9-day, 3.15-day, and
67-day planets previously announced by Bonfils et al. (2005), Udry et al.
(2007), and Mayor et al (2009). The observations also indicate a 5th planet in
the system, GJ 581f, a minimum-mass 7.0 M_Earth planet orbiting in a 0.758 AU
orbit of period 433 days and a 6th planet, GJ 581g, a minimum-mass 3.1 M_Earth
planet orbiting at 0.146 AU with a period of 36.6 days. The estimated
equilibrium temperature of GJ 581g is 228 K, placing it squarely in the middle
of the habitable zone of the star and offering a very compelling case for a
potentially habitable planet around a very nearby star. That a system harboring
a potentially habitable planet has been found this nearby, and this soon in the
relatively early history of precision RV surveys, indicates that eta_Earth, the
fraction of stars with potentially habitable planets, is likely to be
substantial. This detection, coupled with statistics of the incompleteness of
present-day precision RV surveys for volume-limited samples of stars in the
immediate solar neighborhood suggests that eta_Earth could well be on the order
of a few tens of percent. If the local stellar neighborhood is a representative
sample of the galaxy as a whole, our Milky Way could be teeming with
potentially habitable planets.Comment: Accepted for publication in ApJ; 44 pages, 6 figures, 3 table
Two planets around Kapteyn's star: a cold and a temperate super-Earth orbiting the nearest halo red dwarf
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society - Letters. ©: 2014 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.Exoplanets of a few Earth masses can be now detected around nearby low-mass stars using Doppler spectroscopy. In this Letter, we investigate the radial velocity variations of Kapteyn's star, which is both a sub-dwarf M-star and the nearest halo object to the Sun. The observations comprise archival and new HARPS (High Accuracy Radial velocity Planet Searcher), High Resolution Echelle Spectrometer (HIRES) and Planet Finder Spectrograph (PFS) Doppler measurements. Two Doppler signals are detected at periods of 48 and 120 d using likelihood periodograms and a Bayesian analysis of the data. Using the same techniques, the activity indices and archival All Sky Automated Survey (ASAS-3) photometry show evidence for low-level activity periodicities of the order of several hundred days. However, there are no significant correlations with the radial velocity variations on the same time-scales. The inclusion of planetary Keplerian signals in the model results in levels of correlated and excess white noise that are remarkably low compared to younger G, K and M dwarfs. We conclude that Kapteyn's star is most probably orbited by two super-Earth mass planets, one of which is orbiting in its circumstellar habitable zone, becoming the oldest potentially habitable planet known to date. The presence and long-term survival of a planetary system seem a remarkable feat given the peculiar origin and kinematic history of Kapteyn's star. The detection of super-Earth mass planets around halo stars provides important insights into planet-formation processes in the early days of the Milky Way.Peer reviewe
The California Planet Survey III. A Possible 2:1 Resonance in the Exoplanetary Triple System HD 37124
We present new radial velocities from Keck Observatory and both Newtonian and
Keplerian solutions for the triple-planet system orbiting HD 37124. The orbital
solution for this system has improved dramatically since the third planet was
first reported in Vogt et al. 2005 with an ambiguous orbital period. We have
resolved this ambiguity, and the outer two planets have an apparent period
commensurability of 2:1. A dynamical analysis finds both resonant and
non-resonant configurations consistent with the radial velocity data, and
constrains the mutual inclinations of the planets to be less than about 30
degrees. We discuss HD 37124 in the context of the other 19 exoplanetary
systems with apparent period commenserabilities, which we summarize in a table.
We show that roughly one in three well-characterized multiplanet systems has a
apparent low-order period commensuribility, which is more than would naively be
expected if the periods of exoplanets in known multiplanet systems were drawn
randomly from the observed distribution of planetary orbital periods.Comment: 12 pp, emulateapj style, ApJ accepted. v2. Minor edits to update
numbers, fix garbled tex
A high-precision near-infrared survey for radial velocity variable low-mass stars using CSHELL and a methane gas cell
We present the results of a precise near-infrared (NIR) radial velocity (RV) survey of 32 low-mass stars with spectral types K2-M4 using CSHELL at the NASA InfraRed Telescope Facility in the K band with an isotopologue methane gas cell to achieve wavelength calibration and a novel, iterative RV extraction method. We surveyed 14 members of young (≈25-150 Myr) moving groups, the young field star ϵ Eridani, and 18 nearby (<25 pc) low-mass stars and achieved typical single-measurement precisions of 8-15 m s-1with a long-term stability of 15-50 m s-1 over longer baselines. We obtain the best NIR RV constraints to date on 27 targets in our sample, 19 of which were never followed by high-precision RV surveys. Our results indicate that very active stars can display long-term RV variations as low as ∼25-50 m s-1 at ≈2.3125 μm, thus constraining the effect of jitter at these wavelengths. We provide the first multiwavelength confirmation of GJ 876 bc and independently retrieve orbital parameters consistent with previous studies. We recovered RV variabilities for HD 160934 AB and GJ 725 AB that are consistent with their known binary orbits, and nine other targets are candidate RV variables with a statistical significance of 3σ-5σ. Our method, combined with the new iSHELL spectrograph, will yield long-term RV precisions of ≲5 m s-1 in the NIR, which will allow the detection of super-Earths near the habitable zone of mid-M dwarfs
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