267 research outputs found
The multiplicity of exoplanet host stars - New low-mass stellar companions of the exoplanet host stars HD125612 and HD212301
Aims: We present new results from our ongoing multiplicity study of exoplanet
host stars, carried out with SofI/NTT. We provide the most recent list of
confirmed binary and triple star systems that harbor exoplanets.
Methods: We use direct imaging to identify wide stellar and substellar
companions as co-moving objects to the observed exoplanet host stars, whose
masses and spectral types are determined with follow-up photometry and
spectroscopy.
Results: We found two new co-moving companions of the exoplanet host stars
HD125612 and HD212301. HD125612B is a wide M4 dwarf (0.18 Msun) companion of
the exoplanet host star HD125612, located about 1.5 arcmin (~4750 AU of
projected separation) south-east of its primary. In contrast, HD212301B is a
close M3 dwarf (0.35 Msun), which is found about 4.4 arcsec (~230 AU of
projected separation) north-west of its primary.
Conclusions: The binaries HD125612AB and HD212301AB are new members in the
continuously growing list of exoplanet host star systems of which 43 are
presently known. Hence, the multiplicity rate of exoplanet host stars is about
17%.
Based on observations obtained on La Silla in ESO programs 079.C-0099(A),
080.C-0312(A)Comment: 7 pages, 7 figures, 2 tables, A&A in pres
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
Direct detection of exoplanet host star companion Îł Cep B and revised masses for both stars and the sub-stellar object
Context. The star Îł Cep is known as a single-lined spectroscopic triple system at a distance of 13.8 pc, composed of a K1 III-IV primary star with V = 3.2 mag, a stellar-mass companion in a 66-67 year orbit (Torres 2007, ApJ, 654, 1095), and a substellar companion with M_p sin i = 1.7 M_(Jup) that is most likely a planet (Hatzes et al. 2003, ApJ, 599, 1383).
Aims. We aim to obtain a first direct detection of the stellar companion, to determine its current orbital position (for comparison with the spectroscopic and astrometric data), its infrared magnitude and, hence, mass.
Methods. We use the Adaptive Optics camera CIAO at the Japanese 8 m telescope Subaru on Mauna Kea, Hawaii, with the semi-transparent coronograph to block most of the light from the bright primary γ Cep A, and to detect at the same time the faint companion B. In addition, we also used the IR camera Ω Cass at the Calar Alto 3.5 m telescope, Spain, to image γ Cep A and B by adding up many very short integrations (without AO).
Results. γ Cep B is clearly detected on our CIAO and Ω Cass images. We use a photometric standard star to determine the magnitude of B after PSF subtraction in the Subaru image, and the magnitude difference between A and B in the Calar Alto images, and find an average value of K = 7.3 ± 0.2 mag. The separations and position angles between A and B are measured on 15 July 2006 and 11 and 12 Sept. 2006, B is slightly south of west of A.
Conclusions. By combining the radial velocity, astrometric, and imaging data, we have refined the binary orbit and determined the dynamical masses of the two stars in the Îł Cep system, namely 1.40 ± 0.12 M_â for the primary and 0.409 ± 0.018 M_â for the secondary (consistent with being a M4 dwarf). We also determine the minimum mass of the sub-stellar companion to be M_p sin i = 1.60 ± 0.13 M_(Jup)
A lucky imaging multiplicity study of exoplanet host stars
To understand the influence of additional wide stellar companions on planet
formation, it is necessary to determine the fraction of multiple stellar
systems amongst the known extrasolar planet population. We target recently
discovered radial velocity exoplanetary systems observable from the northern
hemisphere and with sufficiently high proper motion to detect stellar
companions via direct imaging. We utilize the Calar Alto 2.2m telescope in
combination with its lucky imaging camera AstraLux. 71 planet host stars have
been observed so far, yielding one new low-mass (0.239 \pm 0.022M\odot) stellar
companion, 4.5 arcsec (227AU of projected separation) northeast of the planet
host star HD185269, detected via astrometry with AstraLux. We also present
follow-up astrometry on three previously discovered stellar companions, showing
for the first time common proper motion of the 0.5 arcsec companion to
HD126614. Additionally, we determined the achieved detection limits for all
targets, which allows us to characterize the detection space of possible
further companions of these stars
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