5 research outputs found
Few-mode fibers and AO-assisted high resolution spectroscopy: coupling efficiency and modal noise mitigation
NIRPS (Near Infra-Red Planet Searcher) is an AO-assisted and fiber-fed
spectrograph for high precision radial velocity measurements that will operate
in the YJH-bands. While using an AO system in such instrument is generally
considered to feed a single-mode fiber, NIRPS is following a different path by
using a small multi-mode fiber (more specifically called "few-mode fiber").
This choice offers an excellent trade-off by allowing to design a compact
cryogenic spectrograph, while maintaining a high coupling efficiency under bad
seeing conditions and for faint stars. The main drawback resides in a much more
important modal-noise, a problem that has to be tackled for allowing 1m/s
precision radial velocity measurements. We study the impact of using an AO
system to couple light into few-mode fibers. We focus on two aspects: the
coupling efficiency into few-mode fibers and the question of modal noise and
scrambling. We show first that NIRPS can reach coupling >= 50% up to magnitude
I=12, and offer a gain of 1-2 magnitudes over a single-mode solution. We
finally show that the best strategy to mitigate modal noise with the AO system
is among the simplest: a continuous tip-tilt scanning of the fiber core.Comment: 10 pages, 5 figures. Proceeding of the AO4ELT5 conferenc
Atmospheric characterization of Proxima b by coupling the Sphere high-contrast imager to the Espresso spectrograph
Context. The temperate Earth-mass planet Proxima b is the closest exoplanet
to Earth and represents what may be our best ever opportunity to search for
life outside the Solar System. Aims. We aim at directly detecting Proxima b and
characterizing its atmosphere by spatially resolving the planet and obtaining
high-resolution reflected-light spectra. Methods. We propose to develop a
coupling interface between the SPHERE high-contrast imager and the new ESPRESSO
spectrograph, both installed at ESO VLT. The angular separation of 37 mas
between Proxima b and its host star requires the use of visible wavelengths to
spatially resolve the planet on a 8.2-m telescope. At an estimated
planet-to-star contrast of ~10^-7 in reflected light, Proxima b is extremely
challenging to detect with SPHERE alone. However, the combination of a
~10^3-10^4 contrast enhancement from SPHERE to the high spectral resolution of
ESPRESSO can reveal the planetary spectral features and disentangle them from
the stellar ones. Results. We find that significant but realistic upgrades to
SPHERE and ESPRESSO would enable a 5-sigma detection of the planet and yield a
measurement of its true mass and albedo in 20-40 nights of telescope time,
assuming an Earth-like atmospheric composition. Moreover, it will be possible
to probe the O2 bands at 627, 686 and 760 nm, the water vapour band at 717 nm,
and the methane band at 715 nm. In particular, a 3.6-sigma detection of O2
could be made in about 60 nights of telescope time. Those would need to be
spread over 3 years considering optimal observability conditions for the
planet. Conclusions. The very existence of Proxima b and the SPHERE-ESPRESSO
synergy represent a unique opportunity to detect biosignatures on an exoplanet
in the near future. It is also a crucial pathfinder experiment for the
development of Extremely Large Telescopes and their instruments (abridged).Comment: 16 pages, 7 figures, revised version accepted to A&
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