238 research outputs found
High Precision Radial Velocity Measurements in the Infrared: A First Assessment of the RV Stability of CRIRES
High precision radial velocity (RV) measurements in the near infrared are on
high demand, especially in the context of exoplanet search campaigns shifting
their interest to late type stars in order to detect planets with ever lower
mass or targeting embedded pre-main-sequence objects.
ESO is offering a new spectrograph at the VLT -- CRIRES -- designed for high
resolution near-infrared spectroscopy with a comparably broad wavelength
coverage and the possibility to use gas-cells to provide a stable RV
zero-point.
We investigate here the intrinsic short-term RV stability of CRIRES, both
with gas-cell calibration data and on-sky measurements using the absorption
lines of the Earth's atmosphere imprinted in the source spectrum as a local RV
rest frame. Moreover, we also investigate for the first time the intrinsic
stability of telluric lines at 4100 nm for features originating in the lower
troposphere.
Our analysis of nearly 5 hours of consecutive observations of MS Vel, a M2II
bright giant centred at two SiO first overtone band-heads at 4100 nm,
demonstrates that the intrinsic short-term stability of CRIRES is very high,
showing only a slow and fully compensateable drift of up to 60 m/s after 4.5
hours. The radial velocity of the telluric lines is constant down to a level of
approx. +/- 10 m/s (or 7/1000 of one pixel). Utilising the same telluriclines
as a rest frame for our radial velocity measurements of the science target, we
obtain a constant RV with a precision of approx. +/- 20 m/s for MS Vel as
expected for a M-giant.Comment: 12 pages, 6 figures, accepted by A&
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
Metallicity determination of M dwarfs - High-resolution IR spectroscopy
Context. Several new techniques to determine the metallicity of M dwarfs with
better precision have been developed over the last decades. However, most of
these studies were based on empirical methods. In order to enable detailed
abundance analysis, standard methods established for warmer solar-like stars,
i.e. model-dependent methods using fitting of synthetic spectra, still need to
be used. Aims. In this work we continue the reliability confirmation and
development of metallicity determinations of M dwarfs using high- resolution
infrared spectra. The reliability was confirmed though analysis of M dwarfs in
four binary systems with FGK dwarf companions and by comparison with previous
optical studies of the FGK dwarfs. Methods. The metallicity determination was
based on spectra taken in the J band (1.1-1.4 {\mu}m) with the CRIRES
spectrograph. In this part of the infrared, the density of stellar molecular
lines is limited, reducing the amount of blends with atomic lines enabling an
accurate continuum placement. Lines of several atomic species were used to
determine the stellar metallicity. Results. All binaries show excellent
agreement between the derived metallicity of the M dwarf and its binary
companion. Our results are also in good agreement with values found in the
literature. Furthermore, we propose an alternative way to determine the
effective temperature of M dwarfs of spectral types later than M2 through
synthetic spectral fitting of the FeH lines in our observed spectra.
Conclusions. We have confirmed that a reliable metallicity determination of M
dwarfs can be achieved using high-resolution infrared spectroscopy. We also
note that metallicites obtained with photometric metallicity calibrations
available for M dwarfs only partly agree with the results we obtain from
high-resolution spectroscopy.Comment: 18 page
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
Search for extrasolar planets with high-precision relative astrometry
We present our search program for substellar companions using high-precision
relative astronomy. Due to its orbital motion around the star, an unseen
substellar companion would produce a periodic "wobble" of the host star, which
is the astrometric signal of the unseen companion. By measuring the separation
between the components of stellar double and triple systems, we want to measure
this astrometric signal of a possible unseen companion indirectly as a relative
and periodic change of these separations. Using a new observation mode (the
"cube-mode") where the frames were directly saved in cubes with nearly no loss
of time during the readout, an adaptive optics system to correct for
atmospheric noise and an infrared narrow band filter in the near infrared to
suppress differential chromatic refraction (DCR) effects we achive for our
first target (the double star HD 19994) a relative precision for the separation
measurements of about 100...150 micro-arsecond per epoch. To reach a precision
in the micro-arcsec-regime, we use a statistical approach. We take several
thousand frames per target and epoche and after a verification of a Gaussian
distribution the measurement precision can be calculated as the standard
deviation of our measurements divided by the square root of the number of
Gaussian distributed measurements. Our first observed target is the stellar
binary HD 19994 A & B, where the A component has a known radial velocity planet
candidate.Comment: 4 pages, IAUS 249 conferenc
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