169 research outputs found
VLT spectra of the companion candidate Cha Ha 5/cc 1
We obtained optical and infrared spectra of Cha Ha 5/cc 1, a faint possibly
sub-stellar companion candidate next to the M6-type brown dwarf candidate Cha
Ha 5 in Cha I, using FORS1 and ISAAC at the VLT. The VRIJHK colors of Cha Ha
5/cc 1 are consistent with either an L-type companion or a K-type background
giant. Our spectra show that the companion candidate actually is a background
star.Comment: IAU 211 Symp. "Brown dwarfs" poster proceedings (in press
Rotational Periods of very Young Brown Dwarfs in ChaI
A photometric monitoring campaign of brown dwarfs in the ChaI star forming
region in the i and R band revealed significant periodic variations of the
three M6.5-M7 type brown dwarf candidates ChaHa2, 3 and 6 (Joergens et al.
2002). These are the first rotational periods for very young (1-5 Myr) brown
dwarfs and among the first rotational periods for brown dwarfs at all. The
relatively long periods of 2.2 to 3.4 days as well as vsini values (Joergens &
Guenther 2001) indicate that our targets are moderately fast rotators in
contrast to very rapidly rotating old brown dwarfs. The periods for the ChaI
brown dwarf candidates provide valuable data points in an as yet, in terms of
rotational characteristic, almost unexplored region of the age-mass diagram. A
comparison with rotational properties of older brown dwarfs indicates that most
of the acceleration during the contraction phase takes place within the first
30 Myr or less of the lifetime of a brown dwarf. We have also determined
periods for the two M5-M5.5 type very low-mass stars B34 and CHXR78C.Comment: Proceeding of poster presentation at the '1st Potsdam Thinkshop on
Starspots', May 2002, Potsdam, German
Results from the Exoplanet Search Programmes with BEST and TEST
Thueringer Landessternwarte Tautenburg (TLS) has started to operate a small
dedicated telescope - the Tautenburg Exoplanet Search Telescope (TEST) -
searching for transits of extrasolar planets in photometric time series
observations. In a joint effort with the Berlin Exoplanet Search Telescope
(BEST) operated by the Institut fuer Planetenforschung of the "Deutsches
Zentrum fuer Luft- und Raumfahrt (DLR)" at the Observatoire de Haute-Provence
(OHP), France, two observing sites are used to optimise transit search. Here,
we give a short overview of these systems and the data analysis. We describe a
software pipeline that we have set up to identify transit events of extrasolar
planets and variable stars in time series data from these and other telescopes,
and report on some first results.Comment: 6 pages, 5 figures, contributed paper to the "Solar and Stellar
Physics Through Eclipses" conference, eds. O. Demircan, S.O. Selam, B.
Albayrak (Turkey, March 2006
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
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