ESPRESSO at VLT Pepe, F.; Cristiani, S.; Rebolo, R. ...
Astronomy and astrophysics (Berlin),
01/2021, Letnik:
645
Journal Article
Recenzirano
Context.
ESPRESSO is the new high-resolution spectrograph of ESO’s Very Large Telescope (VLT). It was designed for ultra-high radial-velocity (RV) precision and extreme spectral fidelity with the aim ...of performing exoplanet research and fundamental astrophysical experiments with unprecedented precision and accuracy. It is able to observe with any of the four Unit Telescopes (UTs) of the VLT at a spectral resolving power of 140 000 or 190 000 over the 378.2 to 788.7 nm wavelength range; it can also observe with all four UTs together, turning the VLT into a 16 m diameter equivalent telescope in terms of collecting area while still providing a resolving power of 70 000.
Aims.
We provide a general description of the ESPRESSO instrument, report on its on-sky performance, and present our Guaranteed Time Observation (GTO) program along with its first results.
Methods.
ESPRESSO was installed on the Paranal Observatory in fall 2017. Commissioning (on-sky testing) was conducted between December 2017 and September 2018. The instrument saw its official start of operations on October 1, 2018, but improvements to the instrument and recommissioning runs were conducted until July 2019.
Results.
The measured overall optical throughput of ESPRESSO at 550 nm and a seeing of 0.65″ exceeds the 10% mark under nominal astroclimatic conditions. We demonstrate an RV precision of better than 25 cm s
−1
during a single night and 50 cm s
−1
over several months. These values being limited by photon noise and stellar jitter shows that the performance is compatible with an instrumental precision of 10 cm s
−1
. No difference has been measured across the UTs, neither in throughput nor RV precision.
Conclusions.
The combination of the large collecting telescope area with the efficiency and the exquisite spectral fidelity of ESPRESSO opens a new parameter space in RV measurements, the study of planetary atmospheres, fundamental constants, stellar characterization, and many other fields.
X-shooter is the first 2nd generation instrument of the ESO Very Large Telescope (VLT). It is a very efficient, single-target, intermediate-resolution spectrograph that was installed at the ...Cassegrain focus of UT2 in 2009. The instrument covers, in a single exposure, the spectral range from 300 to 2500 nm. It is designed to maximize the sensitivity in this spectral range through dichroic splitting in three arms with optimized optics, coatings, dispersive elements and detectors. It operates at intermediate spectral resolution (R ~ 4000−17 000, depending on wavelength and slit width) with fixed échelle spectral format (prism cross-dispersers) in the three arms. It includes a 1.8″ × 4″ integral field unit as an alternative to the 11′′ long slits. A dedicated data reduction package delivers fully calibrated two-dimensional and extracted spectra over the full wavelength range. We describe the main characteristics of the instrument and present its performance as measured during commissioning, science verification and the first months of science operations.
Observations in extremely large telescopes will rely on adaptive corrections. To reduce the size and complexity of the instruments observing over large fields, the telescope should correct not only ...fast telescope misalignments and guiding errors, but also the bulk of the errors introduced by the atmosphere. This paper describes an optical design with five mirrors, three of them powered, which fulfils this requirement. The optical system is effectively diffraction limited over a field of 10 arcmin, also delivering very good image quality of laser guide stars. In addition, it offers the possibility of installing a large field atmospheric dispersion corrector and the freedom to switch between a large number of foci by changing the focal length. A weak field curvature concentric to the exit pupil eases the design of instrumentation.
Context.
An accurate characterization of the known exoplanet population is key to understanding the origin and evolution of planetary systems. Determining true planetary masses through the radial ...velocity (RV) method is expected to experience a great improvement thanks to the availability of ultra-stable echelle spectrographs.
Aims.
We took advantage of the extreme precision of the new-generation echelle spectrograph ESPRESSO to characterize the transiting planetary system orbiting the G2V star K2-38 located at 194 pc from the Sun with
V
~ 11.4. This system is particularly interesting because it could contain the densest planet detected to date.
Methods.
We carried out a photometric analysis of the available K2 photometric light curve of this star to measure the radius of its two known planets, K2-38b and K2-38c, with
P
b
= 4.01593 ± 0.00050 d and
P
c
= 10.56103 ± 0.00090 d, respectively. Using 43 ESPRESSO high-precision RV measurements taken over the course of 8 months along with the 14 previously published HIRES RV measurements, we modeled the orbits of the two planets through a Markov chain Monte Carlo analysis, significantly improving their mass measurements.
Results.
Using ESPRESSO spectra, we derived the stellar parameters,
T
eff
= 5731 ± 66, log
g
= 4.38 ± 0.11 dex, and Fe/H = 0.26 ± 0.05 dex, and thus the mass and radius of K2-38,
M
⋆
= 1.03
−0.02
+0.04
M
⊕
and
R
⋆
= 1.06
−0.06
+0.09
R
⊕
. We determine new values for the planetary properties of both planets. We characterize K2-38b as a super-Earth with
R
P
= 1.54 ± 0.14
R
⊕
and
M
p
= 7.3
−1.0
+1.1
M
⊕
, and K2-38c as a sub-Neptune with
R
P
= 2.29 ± 0.26
R
⊕
and
M
p
= 8.3
−1.3
+1.3
M
⊕
. Combining the radius and mass measurements, we derived a mean density of
ρ
p
= 11.0
−2.8
+4.1
g cm
−3
for K2-38b and
ρ
p
= 3.8
−1.1
+1.8
g cm
−3
for K2-38c, confirming K2-38b as one of the densest planets known to date.
Conclusions.
The best description for the composition of K2-38b comes from an iron-rich Mercury-like model, while K2-38c is better described by a rocky-model with H2 envelope. The maximum collision stripping boundary shows how giant impacts could be the cause for the high density of K2-38b. The irradiation received by each planet places them on opposite sides of the radius valley. We find evidence of a long-period signal in the RV time-series whose origin could be linked to a 0.25–3
M
J
planet or stellar activity.
Fibrate derivatives and HMG-CoA reductase inhibitors modify homeostasis of cholesterol. The aim of this study was to assess in an unselected population whether these hypolipidemic drugs are risk ...factors for cholelithiasis or, conversely, are protective agents. Both sexes, all socioeconomic categories, pregnant women, and cholecystectomized subjects were included. Clinical data collection and gallbladder ultrasonography were both carried out in a double-blind fashion. Fibrate derivatives were predominantly fenofibrate, HMG-CoA reductase inhibitors were simvastatin and pravastatin. On univariate analysis, age (>50 years), sex, and use of fibrates were found to be significantly related to the presence of cholelithiasis. Age, sex, and fibrate treatment remained independently correlated with the presence of gallstones on multivariate analysis. With fibrates, the relative risk for lithiasis was 1.7 (P = 0.04). The HMG-CoA reductase inhibitors were not associated with a protective effect on univariate analysis. Of the lipid-lowering drugs, only fibrate derivatives were found to increase the risk of gallstone formation.
Context. Since 2019, GRAVITY has provided direct observations of giant planets and brown dwarfs at separations of down to 95 mas from the host star. Some of these observations have provided the first ...direct confirmation of companions previously detected by indirect techniques (astrometry and radial velocities). Aims. We want to improve the observing strategy and data reduction in order to lower the inner working angle of GRAVITY in dual-field on-axis mode. We also want to determine the current limitations of the instrument when observing faint companions with separations in the 30–150 mas range. Methods. To improve the inner working angle, we propose a fiber off-pointing strategy during the observations to maximize the ratio of companion-light-to-star-light coupling in the science fiber. We also tested a lower-order model for speckles to decouple the companion light from the star light. We then evaluated the detection limits of GRAVITY using planet injection and retrieval in representative archival data. We compare our results to theoretical expectations. Results. We validate our observing and data-reduction strategy with on-sky observations; first in the context of brown dwarf follow-up on the auxiliary telescopes with HD 984 B, and second with the first confirmation of a substellar candidate around the star Gaia DR3 2728129004119806464. With synthetic companion injection, we demonstrate that the instrument can detect companions down to a contrast of 8 × 10 −4 (Δ Κ = 7.7 mag) at a separation of 35 mas, and a contrast of 3 × 10 −5 (Δ Κ = 11 mag) at 100 mas from a bright primary ( K < 6.5), for 30 min exposure time. Conclusions. With its inner working angle and astrometric precision, GRAVITY has a unique reach in direct observation parameter space. This study demonstrates the promising synergies between GRAVITY and Gaia for the confirmation and characterization of substellar companions.
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