2 research outputs found
A new wavelength calibration for echelle spectrographs using Fabry-Perot etalons
The study of Earth-mass extrasolar planets via the radial-velocity technique
and the measurement of the potential cosmological variability of fundamental
constants call for very-high-precision spectroscopy at the level of
\updelta\lambda/\lambda<10^{-9}. Wavelength accuracy is obtained by providing
two fundamental ingredients: 1) an absolute and information-rich wavelength
source and 2) the ability of the spectrograph and its data reduction of
transferring the reference scale (wavelengths) to a measurement scale (detector
pixels) in a repeatable manner. The goal of this work is to improve the
wavelength calibration accuracy of the HARPS spectrograph by combining the
absolute spectral reference provided by the emission lines of a thorium-argon
hollow-cathode lamp (HCL) with the spectrally rich and precise spectral
information of a Fabry-P\'erot-based calibration source. On the basis of
calibration frames acquired each night since the Fabry-P\'erot etalon was
installed on HARPS in 2011, we construct a combined wavelength solution which
fits simultaneously the thorium emission lines and the Fabry-P\'erot lines. The
combined fit is anchored to the absolute thorium wavelengths, which provide the
`zero-point' of the spectrograph, while the Fabry-P\'erot lines are used to
improve the (spectrally) local precision. The obtained wavelength solution is
verified for auto-consistency and tested against a solution obtained using the
HARPS Laser-Frequency Comb (LFC). The combined thorium+Fabry-P\'erot wavelength
solution shows significantly better performances compared to the thorium-only
calibration. The presented techniques will therefore be used in the new HARPS
and HARPS-N pipeline, and will be exported to the ESPRESSO spectrograph.Comment: 15 pages, 8 figure
The CORALIE survey for southern extrasolar planets: XVIII. Three new massive planets and two low-mass brown dwarfs at greater than 5 AU separation
Context. Since 1998, a planet-search around main sequence stars within 50~pc
in the southern hemisphere has been carried out with the CORALIE spectrograph
at La Silla Observatory. Aims. With an observing time span of more than 20
years, the CORALIE survey is able to detect long term trends in data with
masses and separations large enough to select ideal targets for direct imaging.
Detecting these giant companion candidates will allow us to start bridging the
gap between radial velocity detected exoplanets and directly imaged planets and
brown dwarfs. Methods. Long-term precise Doppler measurements with the CORALIE
spectrograph reveal radial velocity signatures of massive planetary companions
and brown dwarfs on long-period orbits. Results. In this paper we report the
discovery of new companions orbiting HD~181234, HD~13724, HD~25015, HD~92987
and HD~50499. We also report updated orbital parameters for HD~50499b,
HD~92788b and HD~98649b. In addition, we confirm the recent detection of
HD~92788c. The newly reported companions span a period range of 15.6 to 40.4
years and a mass domain of 2.93 to 26.77 , the latter of
which straddles the nominal boundary between planets and brown dwarfs.
Conclusion. We have reported the detection of five new companions and updated
parameters of four known extrasolar planets. We identify at least some of these
companions to be promising candidates for imaging and further characterisation