84 research outputs found
Multiplicity, kinematics and rotation rates of very young brown dwarfs in ChaI
We have studied twelve very young (1-5Myr) bona fide and candidate brown
dwarfs in the ChaI star forming region in terms of their kinematic properties,
the occurrence of multiple systems among them as well as their rotational
characteristics. Based on high-resolution spectra taken with UVES at the VLT
(8.2m), radial and rotational velocities have been measured. A kinematic study
of the sample showed that their radial velocity dispersion is relatively small
suggesting that they are not ejected during their formation as proposed in
recent formation scenarios. By means of time-resolved UVES spectra, a radial
velocity survey for close companions to the targets was conducted. The radial
velocities of the targets turned out to be rather constant setting upper limits
for the mass Msini of possible companions to 0.1 - 2 M_Jup. These findings hint
at a rather low (<10%) multiplicity fraction of the studied brown dwarfs.
Furthermore, a photometric monitoring campaign of the targets yielded the
determination of rotational periods for three brown dwarf candidates in the
range of 2.2 to 3.4 days. These are the first rotational periods for very young
brown dwarfs and among the first for brown dwarfs at all.Comment: Proceeding of IAU Colloquium No. 211 on Brown Dwarfs, Hawai'i, May
2002 (7 pages, 5 figures
High-Resolution Spectroscopy of the Planetary Host HD 13189: Highly-Evolved and Metal-Poor
We report on the abundances of 13 elements in the planetary host HD 13189, a
massive giant star. Abundances are found to be sub-solar, with [Fe/H] = -0.58
+/- 0.04$; HD 13189 is one of the most metal-poor planetary hosts yet
discovered. Abundance ratios relative to Fe show no peculiarities with respect
to random field stars. A census of metallicities of the seven currently known
planet-harboring giants results in a distribution that is more metal-poor than
the well-known metal-rich distribution of main sequence (MS) planetary hosts.
This finding is discussed in terms of accretion of H-depleted material, one of
the possible mechanisms responsible for the high-metallicity distribution of MS
stars with planets. We estimate the mass of the HD 13189 progenitor to be 3.5
M_sun but cannot constrain this value to better than 2-6 M_sun. A stellar mass
of 3.5 M_sun implies a planetary mass of m sin i = 14.0 +/- 0.8 M_J, placing
the companion at the planet/brown dwarf boundary. Given its physical
characteristics, the HD 13189 system is potentially unique among planetary
systems, and its continued investigation should provide invaluable data to
extrasolar planetary research.Comment: 14 pages, 2 figures; Accepted for publication in ApJ Letter
Exoplanets around G-K Giants
G and K giants are a class of radial velocity (RV) variables. One reason for
this variability are planetary companions which are indicated in time series of
stellar spectra. Since 2004 these spectra in the visual range were obtained
with the high resolution coud\'e \'echelle spectrograph mounted on the 2m
telescope of the Th\"uringer Landessternwarte Tautenburg (TLS) for a northern
sample of 62 very bright K giants. In the South around 300 G and K giants were
observed with HARPS mounted on the 3.6m telescope on La Silla. The TLS sample
contains at least 11 stars (18 %) which show low-amplitude, long-period RV
variations most likely due to planets. This percentage of planet frequency is
confirmed by preliminary results of the HARPS study. Moreover the TLS survey
seems to indicate that giant planets do not favour metal-rich stars, are more
massive, and have longer periods than those found around solar-type host stars.Comment: Part of PlanetsbeyondMS/2010 proceedings
http://arxiv.org/html/1011.660
Angular Diameters and Effective Temperatures of Twenty-five K Giant Stars from the CHARA Array
Using Georgia State University's CHARA Array interferometer, we measured
angular diameters for 25 giant stars, six of which host exoplanets. The
combination of these measurements and Hipparcos parallaxes produce physical
linear radii for the sample. Except for two outliers, our values match angular
diameters and physical radii estimated using photometric methods to within the
associated errors with the advantage that our uncertainties are significantly
lower. We also calculated the effective temperatures for the stars using the
newly-measured diameters. Our values do not match those derived from
spectroscopic observations as well, perhaps due to the inherent properties of
the methods used or because of a missing source of extinction in the stellar
models that would affect the spectroscopic temperatures
EPIC 219388192 b - an inhabitant of the brown dwarf desert in the Ruprecht 147 open cluster
We report the discovery of EPIC 219388192 b, a transiting brown dwarf in a
5.3-day orbit around a member star of Ruprecht-147, the oldest nearby open
cluster association, which was photometrically monitored by K2 during its
Campaign 7. We combine the K2 time-series data with ground-based adaptive
optics imaging and high resolution spectroscopy to rule out false positive
scenarios and determine the main parameters of the system. EPIC 219388192 b has
a radius of =~ and mass of
=~, yielding a mean density of
~. The host star is nearly a Solar twin with
mass =~, radius
=~, effective temperature
=~K and iron abundance [Fe/H]=~dex.
Its age, spectroscopic distance, and reddening are consistent with those of
Ruprecht-147, corroborating its cluster membership. EPIC 219388192 b is the
first brown dwarf with precise determinations of mass, radius and age, and
serves as benchmark for evolutionary models in the sub-stellar regime.Comment: 13 pages, 11 figures, 4 tables, submitted to AAS Journal
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