142 research outputs found
The multiplicity of planet host stars - New low-mass companions to planet host stars
We present new results from our ongoing multiplicity study of exoplanet host
stars, carried out with the infrared camera SofI at ESO-NTT. We have identified
new low mass companions to the planet host stars HD101930 and HD65216.
HD101930AB is a wide binary systems composed of the planet host star HD101930A
and its companion HD101930B which is a M0 to M1 dwarf with a mass of about
0.7Msun separated from the primary by ~73arcsec (2200AU projected separation).
HD65216 forms a hierarchical triple system, with a projected separation of
253AU (angular separation of about 7arcsec) between the planet host star
HD65216A and its close binary companion HD65216BC, whose two components are
separated by only ~0.17arcsec (6AU of projected separation). Two VLT-NACO
images separated by 3 years confirm that this system is co-moving to the planet
host star. The infrared photometry of HD65216B and C is consistent with a M7 to
M8 (0.089Msun), and a L2 to L3 dwarf (0.078Msun), respectively, both close to
the sub-stellar limit. An infrared spectrum with VLT-ISAAC of the pair
HD65216BC, even though not resolved spatially, confirms this late spectral
type. Furthermore, we present H- and K-band ISAAC infrared spectra of HD16141B,
the recently detected co-moving companion of the planet host star HD16141A. The
infrared spectroscopy as well as the apparent infrared photometry of HD16141B
are both fully consistent with a M2 to M3 dwarf located at the distance of the
planet host star.Comment: MNRAS accepted, 8 pages, 6 figures, and 1 tabl
HD3651B: the first directly imaged brown dwarf companion of an exoplanet host star
In the course of our ongoing multiplicity study of exoplanet host stars we
detected a faint companion located at ~43arcsec (480AU physical projected
separation) north-west of its primary -- the exoplanet host star HD3651 at
11pc. The companion, HD3651B, clearly shares the proper motion of the exoplanet
host star in our four images, obtained with ESO/NTT and UKIRT, spanning three
years in epoch difference. The magnitude of the companion is H=16.75+-0.16mag,
the faintest co-moving companion of an exoplanet host star imaged directly.
HD3651B is not detected in the POSS-II B-, R- and I-band images, indicating
that this object is fainter than ~20mag in the B- and R-band and fainter than
\~19mag in the I-band. With the Hipparcos distance of HD3651 of 11pc, the
absolute magnitude of HD3651B is about 16.5mag in the H band. Our H-band
photometry and the Baraffe et al. (2003) evolutionary models yield a mass of
HD3651B to be 20 to 60MJup for assumed ages between 1 and 10Gyr. The effective
temperature ranges between 800 and 900K, consistent with a spectral type of T7
to T8. We conclude that HD3651B is a brown-dwarf companion, the first of its
kind directly imaged as a companion of an exoplanet host star, and one of the
faintest T dwarfs found in the solar vicinity (within 11pc).Comment: 5 pages, 3 figures, 2 tables, accepted for publication in MNRAS
LETTER
Astrometric proof of companionship for the L dwarf companion candidate GJ 1048B
Gizis et al. (2001) reported a companion candidate of spectral type L1 near
the K2 dwarf GJ 1048 using the Two Micron All-Sky Survey (2MASS). At that time
it was not possible to verify companionship astrometrically using the 2MASS
data alone due to the small proper motion of GJ 1048. We now show that both
objects share the same proper motion by using data from the UK Schmidt
Telescope Near-infrared (IVN) Southern Survey as the first epoch and data from
2MASS as the second epoch. Our technique of subtracting the PSF of the primary
from the SuperCOSMOS I scans of the Southern Survey enables the astrometry of
the companion candidate to be measured directly.Comment: Accepted to A&A 2004/03/14, 3 pages, 4 figure
Astrometric and photometric monitoring of GQ Lup and its sub-stellar companion
Neuhaeuser et al. (2005) presented direct imaging evidence for a sub-stellar
companion to the young T Tauri star GQ Lup. Common proper motion was highly
significant, but no orbital motion was detected. Faint luminosity, low gravity,
and a late-M/early-L spectral type indicated that the companion is either a
planet or a brown dwarf. We have monitored GQ Lup and its companion in order to
detect orbital and parallactic motion and variability in its brightness. We
also search for closer and fainter companions. We have taken six more images
with the VLT Adaptive Optics instrument NACO from May 2005 to Feb 2007, always
with the same calibration binary from Hipparcos for both astrometric and
photometric calibration. By adding up all the images taken so far, we search
for additional companions. The position of GQ Lup A and its companion compared
to a nearby non-moving background object varies as expected for parallactic
motion by about one pixel (2 \pi with parallax \pi). We could not find evidence
for variability of the GQ Lup companion in the K-band (standard deviation being
\pm 0.08 mag), which may be due to large error bars. No additional companions
are found with deep imaging. There is now exceedingly high significance for
common proper motion of GQ Lup A and its companion. In addition, we see for the
first time an indication for orbital motion (about 2 to 3 mas/yr decrease in
separation, but no significant change in the position angle), consistent with a
near edge-on or highly eccentric orbit. We measured the parallax for GQ Lup A
to be \pi = 6.4 \pm 1.9 mas (i.e. 156 \pm 50 pc) and for the GQ Lup companion
to be 7.2 \pm 2.1 mas (i.e. 139 \pm 45 pc), both consistent with being in the
Lupus I cloud and bound to each other.Comment: A&A in pres
CRIRES-VLT high-resolution spectro-astrometry as a tool in the search of small structures at the cores of Planetary Nebulae
The onset of the asymmetry in planetary nebulae (PNe) occurs during the short
transition between the end of the asymptotic giant branch (AGB) phase and the
beginning of the PN phase. Sources in this transition phase are compact and
emit intensely in infrared wavelengths, making high spatial resolution
observations in the infrared mandatory to investigate the shaping process of
PNe. Interferometric VLTI IR observations have revealed compelling evidence of
disks at the cores of PNe, but the limited sensitivity, strong observational
constraints, and limited spatial coverage place severe limits on the universal
use of this technique. Inspired by the successful detection of proto-planetary
disks using spectro-astrometric observations, we apply here for the first time
this technique to search for sub-arcsecond structures in PNe. Our exploratory
study using CRIRES (CRyogenic high-resolution Infra-Red Echelle Spectrograph)
commissioning data of the proto-PN IRAS 17516-2525 and the young PN SwSt 1 has
revealed small-sized structures after the spectro-astrometric analysis of the
two sources. In IRAS 17516-2525, the spectro-astrometric signal has a size of
only 12 mas, as detected in the Brackett-gamma line, whereas the structures
found in SwSt 1 have sizes of 230 mas in the [Fe III] line and 130 mas in the
Brackett-gamma line. The spectroscopic observations required to perform
spectro-astrometry of sources in the transition towards the PN phase are less
time consuming and much more sensitive than VLTI IR observations. The results
presented here open a new window in the search of the small-sized collimating
agents that shape the complex morphologies of extremely axisymmetric PNe.Comment: 6 pages, 4 figure
Detecting Planets Around Very Low Mass Stars with the Radial Velocity Method
The detection of planets around very low-mass stars with the radial velocity
method is hampered by the fact that these stars are very faint at optical
wavelengths where the most high-precision spectrometers operate. We investigate
the precision that can be achieved in radial velocity measurements of low mass
stars in the near infrared (nIR) Y-, J-, and H-bands, and we compare it to the
precision achievable in the optical. For early-M stars, radial velocity
measurements in the nIR offer no or only marginal advantage in comparison to
optical measurements. Although they emit more flux in the nIR, the richness of
spectral features in the optical outweighs the flux difference. We find that
nIR measurement can be as precise than optical measurements in stars of
spectral type ~M4, and from there the nIR gains in precision towards cooler
objects. We studied potential calibration strategies in the nIR finding that a
stable spectrograph with a ThAr calibration can offer enough wavelength
stability for m/s precision. Furthermore, we simulate the wavelength-dependent
influence of activity (cool spots) on radial velocity measurements from optical
to nIR wavelengths. Our spot simulations reveal that the radial velocity jitter
does not decrease as dramatically towards longer wavelengths as often thought.
The jitter strongly depends on the details of the spots, i.e., on spot
temperature and the spectral appearance of the spot. Forthcoming nIR
spectrographs will allow the search for planets with a particular advantage in
mid- and late-M stars. Activity will remain an issue, but simultaneous
observations at optical and nIR wavelengths can provide strong constraints on
spot properties in active stars.Comment: accepted by ApJ, v2 accepted revision with new precision
calculations, abstract abride
Discovery of a nearby young brown dwarf binary candidate
In near-infrared NaCo observations of the young brown dwarf 2MASS
J0041353-562112, we discovered a companion a little less than a magnitude
fainter than the primary. The binary candidate has a separation of 143 mas, the
spectral types are M6.5 and M9.0 for the two components. Colors and flux ratios
are consistent with the components being located at the same distance
minimizing the probability of the secondary being a background object. The
brown dwarf is known to show Li absorption constraining the age to less than
~200 Myr, and it was suspected to show ongoing accretion, indicating an age as
low as ~10 Myr. We estimate distance and orbital parameters of the binary as a
function of age. For an age of 10 Myr, the distance to the system is 50 pc, the
orbital period is 126 yr, and the masses of the components are ~30 and ~15
MJup. The binary brown dwarf fills a so far unoccupied region in the parameters
mass and age; it is a valuable new benchmark object for brown dwarf atmospheric
and evolutionary models.Comment: 4 pages, 2 figures, accepted by A&
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