arXiv subjects

V. Adibekyan

Publications and source records attributed to V. Adibekyan.

At least 73 records · Page 4Linked to original sources

arXiv2022

Examining the orbital decay targets KELT-9 b, KELT-16 b and WASP-4 b, and the transit-timing variations of HD 97658 b

Tidal orbital decay is suspected to occur especially for hot Jupiters, with the only observationally confirmed case of this being WASP-12 b. By examining this effect, information on the properties of the host star can be obtained using the so-called stellar modified tidal quality factor $Q_*'$, which describes the efficiency with which kinetic energy of the planet is dissipated within the star. This can help to get information about the interior of the star. In this study, we aim to improve constraints on the tidal decay of the KELT-9, KELT-16 and WASP-4 systems, to find evidence for or against the presence of this particular effect. With this, we want to constrain each star's respective $Q_*'$ value. In addition to that, we also aim to test the existence of the transit timing variations (TTVs) in the HD 97658 system, which previously favoured a quadratic trend with increasing orbital period. Making use of newly acquired photometric observations from CHEOPS and TESS, combined with archival transit and occultation data, we use Markov chain Monte Carlo (MCMC) algorithms to fit three models, a constant period model, an orbital decay model, and an apsidal precession model, to the data. We find that the KELT-9 system is best described by an apsidal precession model for now, with an orbital decay trend at over 2 $σ$ being a possible solution as well. A Keplerian orbit model with a constant orbital period fits the transit timings of KELT-16 b the best due to the scatter and scale of their error bars. The WASP-4 system is represented the best by an orbital decay model at a 5 $σ$ significance, although apsidal precession cannot be ruled out with the present data. For HD 97658 b, using recently acquired transit observations, we find no conclusive evidence for a previously suspected strong quadratic trend in the data.

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arXiv2022

Planetary system around LTT 1445A unveiled by ESPRESSO: Multiple planets in a triple M-dwarf system

We present radial velocity follow-up obtained with ESPRESSO of the M-type star LTT 1445A (TOI-455), for which a transiting planet b with an orbital period of~5.4 days was detected by TESS. We report the discovery of a second transiting planet (LTT 1445A c) and a third non-transiting candidate planet (LTT 1445A d) with orbital periods of 3.12 and 24.30 days, respectively. The host star is the main component of a triple M-dwarf system at a distance of 6.9 pc. We used 84 ESPRESSO high-resolution spectra to determine accurate masses of 2.3$\pm$0.3 $\mathrm{M}_\oplus$ and 1.0$\pm$0.2 $\mathrm{M}_\oplus$ for planets b and c and a minimum mass of 2.7$\pm$0.7 $\mathrm{M}_\oplus$ for planet d. Based on its radius of 1.43$\pm0.09$ $\mathrm{R}_\oplus$ as derived from the TESS observations, LTT 1445A b has a lower density than the Earth and may therefore hold a sizeable atmosphere, which makes it a prime target for the James Webb Space Telescope. We used a Bayesian inference approach with the nested sampling algorithm and a set of models to test the robustness of the retrieved physical values of the system. There is a probability of 85$\%$ that the transit of planet c is grazing, which results in a retrieved radius with large uncertainties at 1.60$^{+0.67}_{-0.34}$ $\mathrm{R}_\oplus$. LTT 1445A d orbits the inner boundary of the habitable zone of its host star and could be a prime target for the James Webb Space Telescope.

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arXiv2022

Characterization of the HD 108236 system with CHEOPS and TESS. Confirmation of a fifth transiting planet

The HD108236 system was first announced with the detection of four small planets based on TESS data. Shortly after, the transit of an additional planet with a period of 29.54d was serendipitously detected by CHEOPS. In this way, HD108236 (V=9.2) became one of the brightest stars known to host five small transiting planets (R$_p$<3R$_{\oplus}$). We characterize the planetary system by using all the data available from CHEOPS and TESS space missions. We use the flexible pointing capabilities of CHEOPS to follow up the transits of all the planets in the system, including the fifth transiting body. After updating the host star parameters by using the results from Gaia eDR3, we analyzed 16 and 43 transits observed by CHEOPS and TESS, respectively, to derive the planets physical and orbital parameters. We carried out a timing analysis of the transits of each of the planets of HD108236 to search for the presence of transit timing variations. We derived improved values for the radius and mass of the host star (R$_{\star}$=0.876$\pm$0.007 R$_{\odot}$ and M$_{\star}$=0.867$_{-0.046}^{+0.047}$ M$_{\odot}$). We confirm the presence of the fifth transiting planet f in a 29.54d orbit. Thus, the system consists of five planets of R$_b$=1.587$\pm$0.028, R$_c$=2.122$\pm$0.025, R$_d$=2.629$\pm$0.031, R$_e$=3.008$\pm$0.032, and R$_f$=1.89$\pm$0.04 [R$_{\oplus}$]. We refine the transit ephemeris for each planet and find no significant transit timing variations for planets c, d, and e. For planets b and f, instead, we measure significant deviations on their transit times (up to 22 and 28 min, respectively) with a non-negligible dispersion of 9.6 and 12.6 min in their time residuals. We confirm the presence of planet f and find no significant evidence for a potential transiting planet in a 10.9d orbital period, as previously suggested. Full abstract in the PDF file.

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arXiv2022

TOI-969: a late-K dwarf with a hot mini-Neptune in the desert and an eccentric cold Jupiter

The current architecture of a given multi-planetary system is a key fingerprint of its past formation and dynamical evolution history. Long-term follow-up observations are key to complete their picture. In this paper we focus on the confirmation and characterization of the components of the TOI-969 planetary system, where TESS detected a Neptune-size planet candidate in a very close-in orbit around a late K-dwarf star. We use a set of precise radial velocity observations from HARPS, PFS and CORALIE instruments covering more than two years in combination with the TESS photometric light curve and other ground-based follow-up observations to confirm and characterize the components of this planetary system. We find that TOI-969 b is a transiting close-in ($P_b\sim 1.82$ days) mini-Neptune planet ($m_b=9.1^{+1.1}_{-1.0}$ M$_{\oplus}$, $R_b=2.765^{+0.088}_{-0.097}$ R$_{\oplus}$), thus placing it on the {lower boundary} of the hot-Neptune desert ($T_{\rm eq,b}=941\pm31$ K). The analysis of its internal structure shows that TOI-969 b is a volatile-rich planet, suggesting it underwent an inward migration. The radial velocity model also favors the presence of a second massive body in the system, TOI-969 c, with a long period of $P_c=1700^{+290}_{-280}$ days and a minimum mass of $m_{c}\sin{i_c}=11.3^{+1.1}_{-0.9}$ M$_{\rm Jup}$, and with a highly-eccentric orbit of $e_c=0.628^{+0.043}_{-0.036}$. The TOI-969 planetary system is one of the few around K-dwarfs known to have this extended configuration going from a very close-in planet to a wide-separation gaseous giant. TOI-969 b has a transmission spectroscopy metric of 93, and it orbits a moderately bright ($G=11.3$ mag) star, thus becoming an excellent target for atmospheric studies. The architecture of this planetary system can also provide valuable information about migration and formation of planetary systems.

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arXiv2022

Detection of barium in the atmospheres of the ultra-hot gas giants WASP-76b and WASP-121b

High-resolution spectroscopy studies of ultra-hot Jupiters have been key in our understanding of exoplanet atmospheres. Observing into the atmospheres of these giant planets allows for direct constraints on their atmospheric compositions and dynamics while laying the groundwork for new research regarding their formation and evolution environments. Two of the most well-studied ultra-hot Jupiters are WASP-76b and WASP-121b, with multiple detected chemical species and strong signatures of their atmospheric dynamics. We take a new look at these two exceptional ultra-hot Jupiters by reanalyzing the transit observations taken with ESPRESSO at the Very Large Telescope and attempt to detect additional species. To extract the planetary spectra of the two targets, we corrected for the telluric absorption and removed the stellar spectrum contributions. We then exploited new synthetic templates that were specifically designed for ultra-hot Jupiters in combination with the cross-correlation technique to unveil species that remained undetected by previous analyses. We add a novel detection of Ba+ to the known atmospheric compositions of WASP-76b and WASP-121b, the heaviest species detected to date in any exoplanetary atmosphere, with additional new detections of Co and Sr+ and a tentative detection of Ti+ for WASP-121b. We also confirm the presence of Ca+, Cr, Fe, H, Li, Mg, Mn, Na, and V on both WASP-76b and WASP-121b, with the addition of Ca, Fe+, and Ni for the latter. Finally, we also confirm the clear asymmetric absorption feature of Ca+ on WASP-121b, with an excess absorption at the bluer wavelengths and an effective planet radius beyond the Roche lobe. This indicates that the signal may arise from the escape of planetary atmosphere.

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arXiv2022

The KOBE experiment: K-dwarfs Orbited By habitable Exoplanets. Project goals, target selection and stellar characterization

The detection of habitable worlds is one of humanity's greatest endeavors. So far, astrobiological studies show that one of the most critical components for life development is liquid water. Its chemical properties and its capacity to dissolve and hence transport other substances makes this constituent a key piece in the development of life. As a consequence, looking for life as we know it is directly related to the search for liquid water. For a remote detection of life in distant planetary systems, this means looking for planets in the so-called habitable zone. In this sense, K-dwarf stars are the perfect hosts. Contrary to G-dwarfs, the habitable zone is closer, thus making planet detection easier using transit or radial velocity techniques. Contrary to M-dwarfs, the stellar activity is much smaller, hence having a smaller impact in both the detectability and in the true habitability of the planet. Also, K-dwarfs are the quietest in terms of oscillations, and granulation noise. Despite this, there is a dearth of planets in the habitable zone of K-dwarfs due to a lack of observing programs devoted to this parameter space. In response to a call for Legacy Programs of the Calar Alto observatory, we have started the first dedicated and systematic search for habitable planets around K-dwarfs, the K-dwarfs Orbited By habitable Exoplanets (KOBE). This survey is monitoring the radial velocity of 50 carefully pre-selected K-dwarfs with the CARMENES instrument along 5 semesters with an average of 90 data points per target. Based on planet occurrence rates convolved with our detectability limits, we expect to find $1.68\pm 0.25$ planets per star in the KOBE sample and in half of the sample we expect to find one of those planets within the habitable zone. In this paper, we describe the project motivation, goals and target selection and preliminary stellar characterization.

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arXiv2022

HD 23472: A multi-planetary system with three super-Earths and two potential super-Mercuries

We report the characterisation of a multi-planetary system composed of five exoplanets orbiting the K-dwarf HD~23472 (TOI-174). In addition to the two super-Earths that were previously confirmed, we confirm and characterise three Earth-size planets in the system using ESPRESSO radial velocity observations. The planets of this compact system have periods of $P_d \sim 3.98\,$, $P_e \sim 7.90\,$, $P_f \sim 12.16\,$, $P_b \sim 17.67,\,$ and $P_c \sim 29.80\,$days and radii of $R_d \sim 0.75\,$ , $R_e \sim 0.82,$, $R_f \sim 1.13\,$, $R_b \sim 2.01,\,$ and, $R_c \sim 1.85\,$ \REarth. Because of its small size, its proximity to planet d's transit, and close resonance with planet d, planet e was only recently found. The planetary masses were estimated to be $M_d =0.54\pm0.22$, $M_e =0.76\pm0.30$, $M_f =0.64_{-0.39}^{+0.46}$, $M_b = 8.42_{-0.84}^{+0.83}$, and $M_c = 3.37_{-0.87}^{+0.92}$ \MEarth. These planets are among the lightest planets, with masses measured using the radial velocity method, demonstrating the very high precision of the ESPRESSO spectrograph. We estimated the composition of the system's five planets and found that their gas and water mass fractions increase with stellar distance, suggesting that the system was shaped by irradiation. The high density of the two inner planets ($ρ_d = 7.5_{-3.1}^{+3.9}$ and $ρ_e = 7.5_{-3.0}^{+3.9}\, \mathrm{g.cm^{-3}}$) indicates that they are likely to be super-Mercuries. This is supported by the modelling of the internal structures of the planets, which also suggests that the three outermost planets have significant water or gas content If the existence of two super-Mercuries in the system is confirmed, this system will be the only one known to feature two super-Mercuries, making it an excellent testing bed for theories of super-Mercuries formation. (Abridged)

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arXiv2022

A CHEOPS-enhanced view of the HD3167 system

Much remains to be understood about the nature of exoplanets smaller than Neptune, most of which have been discovered in compact multi-planet systems. With its inner ultra-short period planet b aligned with the star and two larger outer planets d-c on polar orbits, the multi-planet system HD 3167 features a peculiar architecture and offers the possibility to investigate both dynamical and atmospheric evolution processes. To this purpose we combined multiple datasets of transit photometry and radial velocimetry (RV) to revise the properties of the system and inform models of its planets. This effort was spearheaded by CHEOPS observations of HD 3167b, which appear inconsistent with a purely rocky composition despite its extreme irradiation. Overall the precision on the planetary orbital periods are improved by an order of magnitude, and the uncertainties on the densities of the transiting planets b and c are decreased by a factor of 3. Internal structure and atmospheric simulations draw a contrasting picture between HD 3167d, likely a rocky super-Earth that lost its atmosphere through photo-evaporation, and HD 3167c, a mini-Neptune that kept a substantial primordial gaseous envelope. We detect a fourth, more massive planet on a larger orbit, likely coplanar with HD 3167d-c. Dynamical simulations indeed show that the outer planetary system d-c-e was tilted, as a whole, early in the system history, when HD 3167b was still dominated by the star influence and maintained its aligned orbit. RV data and direct imaging rule out that the companion that could be responsible for the present-day architecture is still bound to the HD\,3167 system. Similar global studies of multi-planet systems will tell how many share the peculiar properties of the HD3167 system, which remains a target of choice for follow-up observations and simulations.

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arXiv2022

Automatic model-based telluric correction for the ESPRESSO data reduction software. Model description and application to radial velocity computation

Ground-based high-resolution spectrographs are key instruments for several astrophysical domains. Unfortunately, the observed spectra are contaminated by the Earth's atmosphere. While different techniques exist to correct for telluric lines in exoplanet atmospheric studies, in radial velocity (RV) studies, telluric lines with an absorption depth of >2% are generally masked, which poses a problem for faint targets and M dwarfs as most of their RV content is present where telluric contamination is important. We propose a simple telluric model to be embedded in the ESPRESSO DRS. The goal is to provide telluric-free spectra and enable RV measurements, including spectral ranges where telluric lines fall. The model is a line-by-line radiative transfer code that assumes a single atmospheric layer. We use the sky conditions and the physical properties of the lines from HITRAN to create the telluric spectrum. A subset of selected telluric lines is used to robustly fit the spectrum through a Levenberg-Marquardt minimization algorithm. When applied to stellar spectra from A0- to M5-type stars, the residuals of the strongest H2O lines are below 2% for all spectral types, with the exception of M dwarfs, which are within the pseudo-continuum. We then determined the RVs from the telluric-corrected ESPRESSO spectra of Tau Ceti and Proxima. We created telluric-free masks and compared the obtained RVs with the DRS RVs. In the case of Tau Ceti, we identified that micro-telluric lines introduce systematics up to an amplitude of 58 cm/s and with a period of one year. For Proxima, the gain in spectral content at redder wavelengths is equivalent to a gain of 25% in photon noise. This leads to better constraints on the semi-amplitude and eccentricity of Proxima d. We showcase that our model can be applied to other molecules, and thus to other wavelength regions observed by other spectrographs, such as NIRPS.

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arXiv2022

The Gaia-ESO Public Spectroscopic Survey: Motivation, implementation, GIRAFFE data processing, analysis, and final data products

The Gaia-ESO Public Spectroscopic Survey is an ambitious project designed to obtain astrophysical parameters and elemental abundances for 100,000 stars, including large representative samples of the stellar populations in the Galaxy, and a well-defined sample of 60 (plus 20 archive) open clusters. We provide internally consistent results calibrated on benchmark stars and star clusters, extending across a very wide range of abundances and ages. This provides a legacy data set of intrinsic value, and equally a large wide-ranging dataset that is of value for homogenisation of other and future stellar surveys and Gaia's astrophysical parameters. This article provides an overview of the survey methodology, the scientific aims, and the implementation, including a description of the data processing for the GIRAFFE spectra. A companion paper (arXiv:2206.02901) introduces the survey results. Gaia-ESO aspires to quantify both random and systematic contributions to measurement uncertainties. Thus all available spectroscopic analysis techniques are utilised, each spectrum being analysed by up to several different analysis pipelines, with considerable effort being made to homogenise and calibrate the resulting parameters. We describe here the sequence of activities up to delivery of processed data products to the ESO Science Archive Facility for open use. The Gaia-ESO Survey obtained 202,000 spectra of 115,000 stars using 340 allocated VLT nights between December 2011 and January 2018 from GIRAFFE and UVES. The full consistently reduced final data set of spectra was released through the ESO Science Archive Facility in late 2020, with the full astrophysical parameters sets following in 2022.

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arXiv2022

The HD 93963 A transiting system: A 1.04d super-Earth and a 3.65 d sub-Neptune discovered by TESS and CHEOPS

We present the discovery of two small planets transiting HD 93963A (TOI-1797), a G0\,V star (M$_*$=1.109\,$\pm$\,0.043\,M$_\odot$, R$_*$=1.043\,$\pm$\,0.009\,R$_\odot$) in a visual binary system. We combined TESS and CHEOPS space-borne photometry with data from MuSCAT 2, `Alopeke, PHARO, TRES, FIES, and SOPHIE. We validated and spectroscopically confirmed the outer transiting planet HD 93963 Ac, a sub-Neptune with an orbital period of P$_c \approx$ 3.65 d, reported as a TESS object of interest (TOI) shortly after the release of Sector 22 data. HD 93963 Ac has a mass of M$_c = 19.2 \pm 4.1$ M$_{\oplus}$ and a radius of R$_c = 3.228 \pm 0.059$ R$_{\oplus}$, implying a mean density of $ρ_c=3.1\pm0.7$ gcm$^{-3}$. The inner object, HD 93963 Ab, is a validated 1.04 d ultra-short period (USP) transiting super-Earth that we discovered in the TESS light curve and that was not listed as a TOI, owing to the low significance of its signal (TESS signal-to-noise ratio $\approx$ 6.7, TESS $+$ CHEOPS combined transit depth D$_b=141.5 \pm 8.5$ ppm). We intensively monitored the star with CHEOPS by performing nine transit observations to confirm the presence of the inner planet and validate the system. HD 93963 Ab is the first small (R$_b = 1.35 \pm 0.042$ R$_{\oplus}$) USP planet discovered and validated by TESS and CHEOPS. Unlike planet c, HD 93963 Ab is not significantly detected in our radial velocities (M$_b = 7.8 \pm 3.2$ M$_{\oplus}$). We also discovered a linear trend in our Doppler measurements, suggesting the possible presence of a long-period outer planet. With a V-band magnitude of 9.2, HD 93963 A is among the brightest stars known to host a USP planet, making it one of the most favourable targets for precise mass measurement via Doppler spectroscopy and an important laboratory to test formation, evolution, and migration models of planetary systems hosting ultra-short period planets.

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arXiv2022

Transmission spectroscopy of MASCARA-1b with ESPRESSO: Challenges of overlapping orbital and Doppler tracks

Atmospheric studies at high spectral resolution have shown the presence of molecules, neutral and ionised metals, and hydrogen in the transmission spectrum of ultra-hot Jupiters, and have started to probe the dynamics of their atmospheres. We analyse the transmission spectrum of MASCARA-1b, one of the densest ultra-hot Jupiters orbiting a bright (V=8.3) star. We focus on the CaII H&K, NaI, LiI, H$α$, and KI D1 spectral lines and on the cross-correlated FeI, FeII, CaI, YI, VI, VII, CaH, and TiO lines. For those species that are not present in the stellar spectrum, no detections are reported, but we measure upper limits with an excellent precision ($\sim10$ ppm for particular species). For those species that are present in the stellar spectrum and whose planet-occulted spectral lines induce spurious features in the planetary transmission spectrum, an accurate modelling of the Rossiter-McLaughlin effect (RM) and centre-to-limb variations (CLV) is necessary to recover possible atmospheric signals. In the case of MASCARA-1b, this is difficult due to the overlap between the radial velocities of the stellar surface regions occulted by MASCARA-1b and the orbital track along which the planet atmospheric signal is expected to be found. To try to disentangle a possible planetary signal, we compare our results with models of the RM and CLV effects, and estimate the uncertainties of our models depending on the different system parameters. Unfortunately, more precise measurements of the spin-orbit angle are necessary to better constrain the planet-occulted track and correct for the transit effects in the transmission spectrum with enough precision to be able to detect or discard possible planetary absorptions. Finally, we discuss the possibility that non-detections are related to the low absorption expected for a high surface gravity planet such as MASCARA-1b.

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arXiv2022

The Gaia-ESO Public Spectroscopic Survey: Implementation, data products, open cluster survey, science, and legacy

In the last 15 years different ground-based spectroscopic surveys have been started (and completed) with the general aim of delivering stellar parameters and elemental abundances for large samples of Galactic stars, complementing Gaia astrometry. Among those surveys, the Gaia-ESO Public Spectroscopic Survey (GES), the only one performed on a 8m class telescope, was designed to target 100,000 stars using FLAMES on the ESO VLT (both Giraffe and UVES spectrographs), covering all the Milky Way populations, with a special focus on open star clusters. This article provides an overview of the survey implementation (observations, data quality, analysis and its success, data products, and releases), of the open cluster survey, of the science results and potential, and of the survey legacy. A companion article (Gilmore et al.) reviews the overall survey motivation, strategy, Giraffe pipeline data reduction, organisation, and workflow. The GES has determined homogeneous good-quality radial velocities and stellar parameters for a large fraction of its more than 110,000 unique target stars. Elemental abundances were derived for up to 31 elements for targets observed with UVES. Lithium abundances are delivered for about 1/3 of the sample. The analysis and homogenisation strategies have proven to be successful; several science topics have been addressed by the Gaia-ESO consortium and the community, with many highlight results achieved. The final catalogue has been released through the ESO archive at the end of May 2022, including the complete set of advanced data products. In addition to these results, the Gaia-ESO Survey will leave a very important legacy, for several aspects and for many years to come.

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arXiv2022

Fundamental physics with ESPRESSO: Constraints on Bekenstein and dark energy models from astrophysical and local probes

Dynamical scalar fields in an effective four-dimensional field theory are naturally expected to couple to the rest of the theory's degrees of freedom, unless some new symmetry is postulated to suppress these couplings. In particular, a coupling to the electromagnetic sector will lead to spacetime variations of the fine-structure constant, $α$. Astrophysical tests of the space-time stability of $α$ are therefore a powerful probe of new physics. Here we use ESPRESSO and other contemporary measurements of $α$, together with background cosmology data, local laboratory atomic clock and Weak Equivalence Principle measurements, to place stringent constraints on the simplest examples of the two broad classes of varying $α$ models: Bekenstein models and quintessence-type dark energy models, both of which are parametric extensions of the canonical $Λ$CDM model. In both cases, previously reported constraints are improved by more than a factor of ten. This improvement is largely due to the very strong local constraints, but astrophysical measurements can help to break degeneracies between cosmology and fundamental physics parameters.

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arXiv2022

Fundamental effective temperature measurements for eclipsing binary stars -- III. SPIRou near-infrared spectroscopy and CHEOPS photometry of the benchmark G0V star EBLM J0113+31

EBLM J0113+31 is moderately bright (V=10.1), metal-poor ([Fe/H]$\approx-0.3$) G0V star with a much fainter M dwarf companion on a wide, eccentric orbit (=14.3 d). We have used near-infrared spectroscopy obtained with the SPIRou spectrograph to measure the semi-amplitude of the M dwarf's spectroscopic orbit, and high-precision photometry of the eclipse and transit from the CHEOPS and TESS space missions to measure the geometry of this binary system. From the combined analysis of these data together with previously published observations we obtain the following model-independent masses and radii: $M_1 = 1.029 \pm 0.025 M_{\odot}$, $M_2 = 0.197 \pm 0.003 M_{\odot}$, $R_1 = 1.417 \pm 0.014 R_{\odot}$, $R_2 = 0.215 \pm 0.002 R_{\odot}$. Using $R_1$ and the parallax from Gaia EDR3 we find that this star's angular diameter is $θ= 0.0745 \pm 0.0007$ mas. The apparent bolometric flux of the G0V star corrected for both extinction and the contribution from the M dwarf ($<0.2$ per cent) is ${\mathcal F}_{\oplus,0} = (2.62\pm 0.05)\times10^{-9}$ erg.cm$^{-2}$.s$^{-1}$. Hence, this G0V star has an effective temperature $T_{\rm eff,1} = 6124{\rm\,K} \pm 40{\rm \,K\,(rnd.)} \pm 10 {\rm \,K\,(sys.)}$. EBLM J0113+31 is an ideal benchmark star that can be used for "end-to-end" tests of the stellar parameters measured by large-scale spectroscopic surveys, or stellar parameters derived from asteroseismology with PLATO. The techniques developed here can be applied to many other eclipsing binaries in order to create a network of such benchmark stars.

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arXiv2022

A novel framework for semi-Bayesian radial velocities through template matching

The detection and characterization of an increasing variety of exoplanets has been in part possible thanks to the continuous development of high-resolution, stable spectrographs, and using the Doppler radial-velocity (RV) method. The Cross Correlation Function (CCF) method is one of the traditional approaches for RV extraction. More recently, template matching was introduced as an advantageous alternative for M-dwarf stars. In this paper, we describe a new implementation of template matching within a semi-Bayesian framework, providing a more statistically principled characterization of the RV measurements. In this context, a common RV shift is used to describe the difference between each spectral order of a given stellar spectrum and a template built from the available observations. Posterior probability distributions are obtained for the relative RV associated with each spectrum, after marginalizing with respect to the continuum. This methodology was named S-BART: Semi-Bayesian Approach for RVs with Template-matching, and it can be applied to HARPS and ESPRESSO. The application of our method to HARPS archival observations of Barnard's star allowed us to validate our implementation against HARPS-TERRA and SERVAL. Then, we applied it to 33 ESPRESSO targets, evaluating its performance and comparing it with the CCF method. We found a decrease in the median RV scatter of \sim 10\% and \sim 4\% for M- and K-type stars, respectively. S-BART yields more precise RV estimates than the CCF method, particularly in the case of M-type stars where a median uncertainty of \sim 15 cm/s is achieved over 309 observations. Further, we estimated the nightly zero point (NZP) of ESPRESSO, finding a weighted NZP scatter below \sim 0.7 m/s. As this includes stellar variability, photon noise, and potential planetary signals, it should be taken as an upper limit of the RV precision attainable with ESPRESSO data.

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arXiv2022

Ariel stellar characterisation: I -- homogeneous stellar parameters of 187 FGK planet host stars Description and validation of the method

In 2020 the European Space Agency selected Ariel as the next mission to join the space fleet of observatories to study planets outside our Solar System. Ariel will be devoted to the characterisation of a thousand planetary atmospheres, for understanding what exoplanets are made of, how they formed and how they evolve. To achieve the last two goals all planets need to be studied within the context of their own host stars, which in turn have to be analysed with the same technique, in a uniform way. We present the spectro-photometric method we have developed to infer the atmospheric parameters of the known host stars in the Tier 1 of the Ariel Reference Sample. Our method is based on an iterative approach, which combines spectral analysis, the determination of the surface gravity from {\em Gaia} data, and the determination of stellar masses from isochrone fitting. We validated our approach with the analysis of a control sample, composed by members of three open clusters with well-known ages and metallicities. We measured effective temperature, Teff, surface gravity, logg, and the metallicity, [Fe/H], of 187 F-G-K stars within the Ariel Reference Sample. We presented the general properties of the sample, including their kinematics which allows us to separate them between thin and thick disc populations. A homogeneous determination of the parameters of the host stars is fundamental in the study of the stars themselves and their planetary systems. Our analysis systematically improves agreement with theoretical models and decreases uncertainties in the mass estimate (from 0.21+/-0.30 to 0.10+/-0.02 M_sun), providing useful data for the Ariel consortium and the astronomical community at large.

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arXiv2022

The polar orbit of the warm Neptune GJ436b seen with VLT/ESPRESSO

GJ436b might be the prototype of warm Neptunes that have undergone late migration induced by an outer companion. Precise determination of the orbital architecture of such systems is critical to constraining their dynamical history and evaluating the role of delayed migration in the exoplanet population. To this purpose we analyzed the Rossiter-McLaughlin (RM) signal of GJ436 b in two transits - recently observed with ESPRESSO - using three different techniques. The high level of precision achieved in radial velocity (RV) measurements allows us to detect the deviation from the Keplerian orbit, despite the slow rotation of the M dwarf host (vsini = 272.0+40.0-34.0 m/s), and to measure the sky-projected obliquity ($λ$ = 102.5+17.2-18.5$^{\circ}$). The Reloaded RM technique, which allows the stellar RV field along the transit chord to be analyzed, yields $λ$ = 107.5+23.6-19.3$^{\circ}$ and vsini = 292.9+41.9-49.9 m/s. The RM Revolutions technique, which allows us to fit the spectral profiles from all planet-occulted regions together, yields $λ$ = 114.1+22.8-17.8$^{\circ}$ and vsini = 300.5+45.9-57.0 m/s. The consistent results between these three techniques, and with published results from HARPS/HARPS-N data, confirm the polar orbit of GJ436b and support the hypothesis that its origin lies in Kozai migration. Results from a joint RM Revolutions analysis of the ESPRESSO, HARPS, and HARPS-N datasets ($λ$ = 113.5+23.3-17.3$^{\circ}$; vsini = 293.5+43.7-52.2 m/s) combined with a revised stellar inclination ($i_\star$ = 35.7+5.9-7.6$^{\circ}$ or 144.2+7.6-5.9$^{\circ}$) lead us to constrain the 3D obliquity $Ψ$ to 103.2+12.8-11.5$^{\circ}$.

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