The 10 parsec sample in the Gaia era Reylé, C.; Jardine, K.; Fouqué, P. ...
Astronomy and astrophysics (Berlin),
06/2021, Letnik:
650
Journal Article
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Odprti dostop
Context.
The nearest stars provide a fundamental constraint for our understanding of stellar physics and the Galaxy. The nearby sample serves as an anchor where all objects can be seen and understood ...with precise data. This work is triggered by the most recent data release of the astrometric space mission
Gaia
and uses its unprecedented high precision parallax measurements to review the census of objects within 10 pc.
Aims.
The first aim of this work was to compile all stars and brown dwarfs within 10 pc observable by
Gaia
and compare it with the
Gaia
Catalogue of Nearby Stars as a quality assurance test. We complement the list to get a full 10 pc census, including bright stars, brown dwarfs, and exoplanets.
Methods.
We started our compilation from a query on all objects with a parallax larger than 100 mas using the Set of Identifications, Measurements, and Bibliography for Astronomical Data database (SIMBAD). We completed the census by adding companions, brown dwarfs with recent parallax measurements not in SIMBAD yet, and vetted exoplanets. The compilation combines astrometry and photometry from the recent
Gaia
Early Data Release 3 with literature magnitudes, spectral types, and line-of-sight velocities.
Results.
We give a description of the astrophysical content of the 10 pc sample. We find a multiplicity frequency of around 27%. Among the stars and brown dwarfs, we estimate that around 61% are M stars and more than half of the M stars are within the range from M3.0 V to M5.0 V. We give an overview of the brown dwarfs and exoplanets that should be detected in the next
Gaia
data releases along with future developments.
Conclusions.
We provide a catalogue of 540 stars, brown dwarfs, and exoplanets in 339 systems, within 10 pc from the Sun. This list is as volume-complete as possible from current knowledge and it provides benchmark stars that can be used, for instance, to define calibration samples and to test the quality of the forthcoming
Gaia
releases. It also has a strong outreach potential.
Abstract
Gaussian process regression is a widespread tool used to mitigate stellar correlated noise in radial velocity (RV) time series. It is particularly useful to search for and determine the ...properties of signals induced by small-sized low-mass planets (Rp < 4 R⊕, mp < 10 M⊕). By using extensive simulations based on a quasi-periodic representation of the stellar activity component, we investigate the ability in retrieving the planetary parameters in 16 different realistic scenarios. We analyse systems composed by one planet and host stars having different levels of activity, focusing on the challenging case represented by low-mass planets, with Doppler semi-amplitudes in the range 1–3 $\rm{\,m\,s^{-1}}$. We consider many different configurations for the quasi-periodic stellar activity component, as well as different combinations of the observing epochs. We use commonly employed analysis tools to search for and characterize the planetary signals in the data sets. The goal of our injection-recovery statistical analysis is twofold. First, we focus on the problem of planet mass determination. Then, we analyse in a statistical way periodograms obtained with three different algorithms, in order to explore some of their general properties, as the completeness and reliability in retrieving the injected planetary and stellar activity signals with low false alarm probabilities. This work is intended to provide some understanding of the biases introduced in the planet parameters inferred from the analysis of RV time series that contain correlated signals due to stellar activity. It also aims to motivate the use and encourage the improvement of extensive simulations for planning spectroscopic follow-up observations.
ABSTRACT
The last decade of direct imaging (DI) searches for sub-stellar companions has uncovered a widely diverse sample that challenges the current formation models, while highlighting the ...intrinsically low occurrence rate of wide companions, especially at the lower end of the mass distribution. These results clearly show how blind surveys, crucial to constrain the underlying planet and sub-stellar companion population, are not an efficient way to increase the sample of DI companions. It is therefore becoming clear that efficient target selection methods are essential to ensure a larger number of detections. We present the results of the COPAINS Survey conducted with SPHERE/VLT, searching for sub-stellar companions to stars showing significant proper motion differences (Δμ) between different astrometric catalogues. We observed 25 stars and detected ten companions, including four new BDs: HIP 21152 B, HIP 29724 B, HD 60584 B, and HIP 63734 B. Our results clearly demonstrate how astrometric signatures, in the past only giving access to stellar companions, can now thanks to Gaia reveal companions well in the sub-stellar regime. We also introduce FORECAST (Finely Optimised REtrieval of Companions of Accelerating STars), a tool which allows to check the agreement between position and mass of the detected companions with the measured Δμ. Given the agreement between the values of the masses of the new sub-stellar companions from the photometry with the model-independent ones obtained with FORECAST, the results of COPAINS represent a significant increase in the number of potential benchmarks for BD and planet formation and evolution theories.
ABSTRACT
The class of transiting cold Jupiters, orbiting at ≳0.5–1.0 au, is to-date underpopulated. Probing their atmospheric composition and physical characteristics is particularly valuable, as it ...allows for direct comparisons with the Solar system giant planets. We investigate some aspects of the synergy between Gaia astrometry and other ground-based and space-borne programs for detection and characterization of such companions. We carry out numerical simulations of Gaia observations of systems with one cold transiting gas giant, using Jovian planets around a sample of nearby low-mass stars as proxies. Using state-of-the-art orbit fitting tools, we gauge the potential of Gaia astrometry to predict the time of transit centre Tc for the purpose of follow-up observations to verify that the companions are indeed transiting. Typical uncertainties on Tc will be on the order of a few months, reduced to several weeks for high astrometric signal-to-noise ratios and periods shorter than ∼3 yr. We develop a framework for the combined analysis of Gaia astrometry and radial-velocity data from representative ground-based campaigns and show that combined orbital fits would allow to significantly reduce the transit windows to be searched for, down to about ±2 weeks (2–σ level) in the most favourable cases. These results are achievable with a moderate investment of observing time (∼0.5 nights per candidate, ∼50 nights for the top 100 candidates), reinforcing the notion that Gaia astrometric detections of potentially transiting cold giant planets, starting with Data Release 4, will constitute a valuable sample worthy of synergistic follow-up efforts with a variety of techniques.
ABSTRACT
We present the discovery of a white dwarf companion at ∼3.6 arcsec from GJ 3346, a nearby (π ∼ 42 mas) K star observed with SPHERE@VLT as part of an open time survey for faint companions to ...objects with significant proper motion discrepancies (Δμ) between Gaia DR1 and Tycho-2. Syrius-like systems like GJ 3346 AB, which include a main-sequence star and a white dwarf, can be difficult to detect because of the intrinsic faintness of the latter. They have, however, been found to be common contaminants for direct imaging (DI) searches. White dwarfs have in fact similar brightness to substellar companions in the infrared, while being much brighter in the visible bands like those used by Gaia. Combining our observations with Gaia DR2 and with several additional archival data sets, we were able to fully constrain the physical properties of GJ 3346 B, such as its effective temperature (11 × 103 ± 500 K) as well as the cooling age of the system (648 ± 58 Myr). This allowed us to better understand the system history and to partially explain the discrepancies previously noted in the age indicators for this object. Although further investigation is still needed, it seems that GJ 3346, which was previously classified as young, is in fact most likely to be older than 4 Gyr. Finally, given that the mass (0.58 ± 0.01 M⊙) and separation (85 au) of GJ 3346 B are compatible with the observed Δμ, this discovery represents a further confirmation of the potential of this kind of dynamical signatures as selection methods for DI surveys targeting faint, substellar companions.
ABSTRACT The recently discovered super-Earth Gl 514 b, orbiting a nearby M0.5-1.0 star at 7.6 pc, is one of the best benchmark exoplanets for understanding the potential climate states of eccentric ...planets. The elongated (e = 0.45$^{+0.15}_{-0.14}$) orbit of Gl 514 b, which only partially lies in the Conservative Habitable Zone, suggests a dynamically young system, where the spin-orbit tidal synchronization may not have yet occurred up to the present time. In the present work, we use a seasonal-latitudinal energy balance model, EOS-ESTM, to explore the potential impact of both constrained and unconstrained planetary, orbital, and atmospheric parameters on the Gl 514 b habitability, mapped in terms of surface temperature. We test three distinct CO2-dominated atmospheres by varying the CH4 concentration values (0 per cent, 0.1 per cent, and 1 per cent) and the total surface pressure. As a general trend, we find that habitable conditions are favoured by high-CH4 and high-pressure regimes. Habitability also increases for high-axis obliquities (at least until the appearance of an icebelt), long-rotation periods, and high-ocean fractional coverage. If the ocean fraction is low, then also the argument of periastron becomes relevant. Our results are robust against changes of the continental distribution. Thus, we conclude that Gl 514 b can potentially maintain temperate surface conditions with modest seasonal temperature variations under a wide variety of planetary, orbital, and atmospheric conditions. Despite no transit have been detected yet, the results found in this work should motivate the community to invest time in future observations.
Cool M dwarfs within a few tens of parsecs from the Sun are becoming the focus of dedicated observational programs in the realm of exoplanet astrophysics. Gaia, in its all-sky survey of >109 objects, ...will deliver precision astrometry for a magnitude-limited (V = 20) sample of M dwarfs. We investigate some aspects of the synergy between the Gaia astrometric data on nearby M dwarfs and other ground-based and space-borne programs for planet detection and characterization. We carry out numerical simulations to gauge the Gaia potential for precision astrometry of exoplanets orbiting a sample of known dM stars within ∼30 pc from the Sun. We express Gaia detection thresholds as a function of system parameters and in view of the latest mission profile, including the most up-to-date astrometric error model. Our major findings are as follows: (1) it will be possible to accurately determine orbits and masses for Jupiter-mass planets with orbital periods in the range 0.2 P 6.0 yr and with an astrometric signal-to-noise ratio /σAL 10. Given present-day estimates of the planet fraction f
p around M dwarfs, 102 giant planets could be found by Gaia around the sample. Comprehensive screening by Gaia of the reservoir of ∼4 × 105 M dwarfs within 100 pc could result in ∼2600 detections and as many as ∼500 accurate orbit determinations. The value of f
p could then be determined with an accuracy of 2 per cent, an improvement by over an order of magnitude with respect to the most precise values available to-date; (2) in the same period range, inclination angles corresponding to quasi-edge-on configurations will be determined with enough precision (a few per cent) so that it will be possible to identify intermediate-separation planets which are potentially transiting within the errors. Gaia could alert us of the existence of 10 such systems. More than 250 candidates could be identified assuming solutions compatible with transit configurations within 10 per cent accuracy, although a large fraction of these (∼85 per cent) could be false positives; (3) for well-sampled orbits, the uncertainties on planetary ephemerides, separation and position angle will degrade at typical rates of Δ < 1 mas yr−1 and Δ < 2° yr−1, respectively. These are over an order of magnitude smaller than the degradation levels attained by present-day ephemerides predictions based on mas-level precision Hubble Space Telescope/Fine Guidance Sensor astrometry; (4) planetary phases will be measured with typical uncertainties Δλ of several degrees, resulting (under the assumption of purely scattering atmospheres) in phase-averaged errors on the phase function ΔΦ(λ) 0.05, and expected uncertainties in the determination of the emergent flux of intermediate-separation (0.3 < a < 2.0 au) giant planets of ∼20 per cent. Our results help to quantify the actual relevance of the Gaia astrometric observations of the large sample of nearby M dwarfs in a synergetic effort to optimize the planning and interpretation of follow-up/characterization measurements of the discovered systems by means of transit survey programs, and upcoming and planned ground-based as well as space-borne observatories for direct imaging (e.g. Very Large Telescope/Spectro-Polarimetric High-Contrast Exoplanet Research, European Extremely Large Telescope/Planetary Camera and Spectrograph) and simultaneous multiwavelength spectroscopy (e.g. Exoplanet Characterisation Observatory, James Webb Space Telescope).
Context.
The solar telescope connected to HARPS-N has been observing the Sun since the summer of 2015. Such a high-cadence, long-baseline data set is crucial for understanding spurious ...radial-velocity signals induced by our Sun and by the instrument. On the instrumental side, this data set allowed us to detect sub- m s
−1
systematics that needed to be corrected for.
Aims.
The goals of this manuscript are to (i) present a new data reduction software for HARPS-N, (ii) demonstrate the improvement brought by this new software during the first three years of the HARPS-N solar data set, and (iii) release all the obtained solar products, from extracted spectra to precise radial velocities.
Methods.
To correct for the instrumental systematics observed in the data reduced with the current version of the HARPS-N data reduction software (DRS version 3.7), we adapted the newly available ESPRESSO DRS (version 2.2.3) to HARPS-N and developed new optimised recipes for the spectrograph. We then compared the first three years of HARPS-N solar data reduced with the current and new DRS.
Results.
The most significant improvement brought by the new DRS is a strong decrease in the day-to-day radial-velocity scatter, from 1.27 to 1.07 m s
−1
; this is thanks to a more robust method to derive wavelength solutions, but also to the use of calibrations closer in time. The newly derived solar radial-velocities are also better correlated with the chromospheric activity level of the Sun in the long term, with a Pearson correlation coefficient of 0.93 compared to 0.77 before, which is expected from our understanding of stellar signals. Finally, we also discuss how HARPS-N spectral ghosts contaminate the measurement of the calcium activity index, and we present an efficient technique to derive an index free of instrumental systematics.
Conclusions.
This paper presents a new data reduction software for HARPS-N and demonstrates its improvements, mainly in terms of radial-velocity precision, when applied to the first three years of the HARPS-N solar data set. Those newly reduced solar data, representing an unprecedented time series of 34 550 high-resolution spectra and precise radial velocities, are released alongside this paper. Those data are crucial to understand stellar activity signals in solar-type stars further and develop the mitigating techniques that will allow us to detect other Earths.
Aims.
We report on ESPRESSO high-resolution transmission spectroscopic observations of two primary transits of the highly irradiated, ultra-hot Jupiter-sized planet, WASP-76b. We investigated the ...presence of several key atomic and molecular features of interest that may reveal the atmospheric properties of the planet.
Methods.
We extracted two transmission spectra of WASP-76b with
R
≈ 140 000 using a procedure that allowed us to process the full ESPRESSO wavelength range (3800–7880 Å) simultaneously. We observed that at a high signal-to-noise ratio, the continuum of ESPRESSO spectra shows ‘wiggles’, which are likely caused by an interference pattern outside the spectrograph. To search for the planetary features, we visually analysed the extracted transmission spectra and cross-correlated the observations against theoretical spectra of different atomic and molecular species.
Results.
The following atomic features are detected: Li
I
, Na
I
, Mg
I
, Ca
II
, Mn
I
, K
I
, and Fe
I
. All are detected with a confidence level between 9.2
σ
(Na
I
) and 2.8
σ
(Mg
I
). We did not detect the following species: Ti
I
, Cr
I
, Ni
I
, TiO, VO, and ZrO. We impose the following 1
σ
upper limits on their detectability: 60, 77, 122, 6, 8, and 8 ppm, respectively.
Conclusions.
We report the detection of Li
I
on WASP-76b for the first time. In addition, we confirm the presence of Na
I
and Fe
I
as previously reported in the literature. We show that the procedure employed in this work can detect features down to the level of ~0.1% in the transmission spectrum and ~10 ppm by means of a cross-correlation method. We discuss the presence of neutral and singly ionised features in the atmosphere of WASP-76b.
ABSTRACT
To push the radial velocity (RV) exoplanet detection threshold, it is crucial to find more reliable RV extraction methods. The least-squares deconvolution (LSD) technique has been used to ...infer the stellar magnetic flux from spectropolarimetric data for the past two decades. It relies on the assumption that stellar absorption lines are similar in shape. Although this assumption is simplistic, LSD provides a good model for intensity spectra and likewise an estimate for their Doppler shift. We present the multi-mask least-squares deconvolution (MM-LSD) RV extraction pipeline that extracts the RV from two-dimensional echelle-order spectra using LSD with multiple tailored masks after continuum normalization and telluric absorption line correction. The flexibility of LSD allows to exclude spectral lines or pixels at will, providing a means to exclude variable lines or pixels affected by instrumental problems. The MM-LSD pipeline was tested on HARPS-N data for the Sun and selected well-observed stars with 5.7 < Vmag < 12.6. For FGK-type stars with median signal-to-noise ratio above 100, the pipeline delivered RV time series with on average 12 per cent lower scatter as compared to the HARPS-N RV extraction pipeline based on the cross-correlation function technique. The MM-LSD pipeline may be used as a standalone RV code, or modified and extended to extract a proxy for the magnetic field strength.
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