79 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&
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
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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