53 research outputs found
M2K: I. A Jovian mass planet around the M3V star HIP79431
Doppler observations from Keck Observatory reveal the presence of a planet
with Msini of 2.1 Mjup orbiting the M3V star HIP79431. This is the sixth giant
planet to be detected in Doppler surveys of M dwarfs and it is one of the most
massive planets discovered around an M dwarf star. The planet has an orbital
period of 111.7 days and an orbital eccentricity of 0.29. The host star is
metal rich, with an estimated [Fe/H] = +0.4. This is the first planet to emerge
from our new survey of 1600 M-to-K dwarf stars.Comment: 5 figure
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
The NASA-UC Eta-Earth Program: I. A Super-Earth Orbiting HD 7924
We report the discovery of the first low-mass planet to emerge from the
NASA-UC Eta-Earth Program, a super-Earth orbiting the K0 dwarf HD 7924.
Keplerian modeling of precise Doppler radial velocities reveals a planet with
minimum mass M_P sin i = 9.26 M_Earth in a P = 5.398 d orbit. Based on
Keck-HIRES measurements from 2001 to 2008, the planet is robustly detected with
an estimated false alarm probability of less than 0.001. Photometric
observations using the Automated Photometric Telescopes at Fairborn Observatory
show that HD 7924 is photometrically constant over the radial velocity period
to 0.19 mmag, supporting the existence of the planetary companion. No transits
were detected down to a photometric limit of ~0.5 mmag, eliminating transiting
planets with a variety of compositions. HD 7924b is one of only eight planets
known with M_P sin i < 10 M_Earth and as such is a member of an emerging family
of low-mass planets that together constrain theories of planet formation.Comment: ApJ accepted, 10 pages, 10 figures, 4 table
M2K: I. A Jupiter-Mass Planet Orbiting the M3V Star HIP 79431
Doppler observations from Keck Observatory reveal the presence of a planet with M sin i of 2.1 M_(Jup) orbiting the M3V star HIP 79431. This is the sixth giant planet to be detected in Doppler surveys of M dwarfs and it is one of the most massive planets discovered around an M dwarf star. The planet has an orbital period of 111.7 days and an orbital eccentricity of 0.29. The host star is metal rich, with an estimated [Fe/H] = +0.4. This is the first planet to emerge from our new survey of 1600 M-to-K dwarf stars
Prospecting in ultracool dwarfs : Measuring the metallicities of mid- and late-m dwarfs
© 2014. The American Astronomical Society. All rights reserved.Metallicity is a fundamental parameter that contributes to the physical characteristics of a star. The low temperatures and complex molecules present in M dwarf atmospheres make it difficult to measure their metallicities using techniques that have been commonly used for Sun-like stars. Although there has been significant progress in developing empirical methods to measure M dwarf metallicities over the last few years, these techniques have been developed primarily for early- to mid-M dwarfs. We present a method to measure the metallicity of mid- to late-M dwarfs from moderate resolution (R ∼ 2000) K-band (≃ 2.2 μm) spectra. We calibrate our formula using 44 wide binaries containing an F, G, K, or early-M primary of known metallicity and a mid- to late-M dwarf companion. We show that similar features and techniques used for early-M dwarfs are still effective for late-M dwarfs. Our revised calibration is accurate to ∼0.07 dex for M4.5-M9.5 dwarfs with -0.58 <[Fe/H] <+0.56 and shows no systematic trends with spectral type, metallicity, or the method used to determine the primary star metallicity. We show that our method gives consistent metallicities for the components of M+M wide binaries. We verify that our new formula works for unresolved binaries by combining spectra of single stars. Lastly, we show that our calibration gives consistent metallicities with the Mann et al. study for overlapping (M4-M5) stars, establishing that the two calibrations can be used in combination to determine metallicities across the entire M dwarf sequence.Peer reviewe
New X-ray Clusters in the EMSS I: Modifications to the XLF
The complete ensemble of Einstein Imaging Proportional Counter (IPC) X-ray
images has been re-processed and re-analyzed using a multi-aperture source
detection algorithm. A catalog of 772 new source candidates detected within the
central regions of the 1435 IPC fields comprising the Extended Medium
Sensitivity Survey (EMSS) has been compiled. By comparison, 478 EMSS sources
fall within the same area of sky. A randomly-selected subsample of 133 fields
was first examined. We found that most of these sources are either the
summation of two or more lower count rate point sources that fall within the
larger detection apertures or are single point sources, while \leq 2.3% of the
full catalog of sources are extrapolated to be actual distant (z > 0.14)
clusters whose extended X-ray structure kept them from being detected in the
EMSS despite having sufficient total flux.
We then constructed other subsamples specifically selected to contain those
X-ray sources most likely to be clusters. Both a database search and an optical
imaging campaign have found several new distant clusters, setting a firm lower
limit on the number of new clusters in the entire catalog. We estimate that the
original EMSS cluster sample is 72-83% complete. We update the Henry et al.
1992 EMSS distant cluster sample with more recent information, and use the
redshifts and X-ray luminosities for these new EMSS clusters to compute a
revised X-ray Luminosity Function (XLF). The addition of these new high-z,
high-L_X clusters to the EMSS is sufficient to remove the requirement for
``negative'' evolution at high-L_X out to z~0.5. We conclude that the EMSS has
systematically missed clusters of low surface brightness.Comment: Accepted to ApJ, 32 pages, 8 figures, uses emulateapj5.sty, for
associated data table see
http://casa.colorado.edu/~lewisad/research/nemsscatalog.htm
M2K: II. A Triple-Planet System Orbiting HIP 57274
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 \msini\ = 11.6 \mearth (0.036 \mjup), an orbital
period of 8.135 0.004 d, and slightly eccentric orbit .
We calculate a transit probability of 6.5% for the inner planet. The second
planet has \msini\ = 0.4 \mjup\ with an orbital period of 32.0 d in
a nearly circular orbit, and . The third planet has \msini\
= 0.53 \mjup\ with an orbital period of 432 d (1.18 years) and an
eccentricity . This discovery adds to the number of super
Earth mass planets with \msini < 12 \mearth\ that have been detected with
Doppler surveys. We find that 56 % super-Earths are members of
multi-planet systems. This is certainly a lower limit because of observational
detectability limits, yet significantly higher than the fraction of Jupiter
mass exoplanets, %, that are members of Doppler-detected,
multi-planet systems.Comment: 11 figures, submitte to ApJ on Sept 10, 201
The Plasma and Suprathermal Ion Composition (PLASTIC) investigation on the STEREO observatories
The Plasma and Suprathermal Ion Composition (PLASTIC) investigation provides the in situ solar wind and low energy heliospheric ion measurements for the NASA Solar Terrestrial Relations Observatory Mission, which consists of two spacecraft (STEREO-A, STEREO-B). PLASTIC-A and PLASTIC-B are identical. Each PLASTIC is a time-of-flight/energy mass spectrometer designed to determine the elemental composition, ionic charge states, and bulk flow parameters of major solar wind ions in the mass range from hydrogen to iron. PLASTIC has nearly complete angular coverage in the ecliptic plane and an energy range from ∼0.3 to 80 keV/e, from which the distribution functions of suprathermal ions, including those ions created in pick-up and local shock acceleration processes, are also provided
Formation and Evolution of Planetary Systems (FEPS): Properties of Debris Dust around Solar-type Stars
We present Spitzer photometric (IRAC and MIPS) and spectroscopic (IRS low
resolution) observations for 314 stars in the Formation and Evolution of
Planetary Systems (FEPS) Legacy program. These data are used to investigate the
properties and evolution of circumstellar dust around solar-type stars spanning
ages from approximately 3 Myr to 3 Gyr. We identify 46 sources that exhibit
excess infrared emission above the stellar photosphere at 24um, and 21 sources
with excesses at 70um. Five sources with an infrared excess have
characteristics of optically thick primordial disks, while the remaining
sources have properties akin to debris systems. The fraction of systems
exhibiting a 24um excess greater than 10.2% above the photosphere is 15% for
ages < 300 Myr and declines to 2.7% for older ages. The upper envelope to the
70um fractional luminosity appears to decline over a similar age range. The
characteristic temperature of the debris inferred from the IRS spectra range
between 60 and 180 K, with evidence for the presence of cooler dust to account
for the strength of the 70um excess emission. No strong correlation is found
between dust temperature and stellar age. Comparison of the observational data
with disk models containing a power-law distribution of silicate grains suggest
that the typical inner disk radius is > 10 AU. Although the interpretation is
not unique, the lack of excess emission shortwards of 16um and the relatively
flat distribution of the 24um excess for ages <300~Myr is consistent with
steady-state collisional models.Comment: 85 pages, 18 figures, 4 tables; accepted for publication in ApJ
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