STEPAR: an automatic code to infer stellar atmospheric parameters

Context. StePar is an automatic code written in Python 3.X designed to compute the stellar atmospheric parameters T_(eff), log g, [Fe/H], and ξ of FGK-type stars by means of the equivalent width (EW) method. This code has already been extensively tested in different spectroscopic studies of FGK-type stars with several spectrographs and against thousands of Gaia-ESO Survey UVES U580 spectra of late-type, low-mass stars as one of its 13 pipelines. Aims. We describe the code that we tested against a library of well characterised Gaia benchmark stars. We also release the code to the community and provide the link for download. Methods. We carried out the required EW determination of Fe i and Fe ii spectral lines using the automatic tool TAME. StePar implements a grid of MARCS model atmospheres and the MOOG radiative transfer code to compute stellar atmospheric parameters by means of a Downhill Simplex minimisation algorithm. Results. We show the results of the benchmark star test and also discuss the limitations of the EW method, and hence the code. In addition, we find a small internal scatter for the benchmark stars of 9 ± 32 K in T_(eff), 0.00 ± 0.07 dex in log g, and 0.00 ± 0.03 dex in [Fe/H]. Finally, we advise against using StePar on double-lined spectroscopic binaries or spectra with R 15 km s^(−1) , and on stars later than K4 or earlier than F6

The Gaia-ESO public spectroscopic survey: implementation, data products, open cluster survey, science, and legacy

Context. 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, 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. Aims. 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 reviews the overall survey motivation, strategy, Giraffe pipeline data reduction, organisation, and workflow. Methods. We made use of the information recorded and archived in the observing blocks; during the observing runs; in a number of relevant documents; in the spectra and master catalogue of spectra; in the parameters delivered by the analysis nodes and the working groups; in the final catalogue; and in the science papers. Based on these sources, we critically analyse and discuss the output and products of the Survey, including science highlights. We also determined the average metallicities of the open clusters observed as science targets and of a sample of clusters whose spectra were retrieved from the ESO archive. Results. The Gaia-ESO Survey 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. Conclusions. The final catalogue will be released through the ESO archive in the first half of 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

The CARMENES search for exoplanets around M dwarfs: rubidium abundances in nearby cool stars

Due to their ubiquity and very long main-sequence lifetimes, abundance determinations in M dwarfs provide a powerful and alternative tool to GK dwarfs to study the formation and chemical enrichment history of our Galaxy. In this study, abundances of the neutroncapture elements Rb, Sr, and Zr are derived, for the first time, in a sample of nearby M dwarfs. We focus on stars in the metallicity range −0.5 ˷ 0.0 is attained at metallicities higher than solar. These are surprising results, never seen for any other heavy element, and are difficult to understand within the formulation of the s- and r-processes, both contributing sources to the Galactic Rb abundance. We discuss the reliability of these findings for Rb in terms of non-LTE (local thermodynamic equilibrium) effects, stellar activity, or an anomalous Rb abundance in the Solar System, but no explanation is found. We then interpret the full observed [Rb/Fe] versus [Fe/H] trend within the framework of theoretical predictions from state-of-the-art chemical evolution models for heavy elements, but a simple interpretation is not found either. In particular, the possible secondary behaviour of the [Rb/Fe] ratio at super-solar metallicities would require a much larger production of Rb than currently predicted in AGB stars through the s-process without overproducing Sr and Zr. Python libraries Matplotlib, NumPy, SciPy and collection of software packages AstroPy

HORuS transmission spectroscopy and revised planetary parameters of KELT-7 b

We report on the high-resolution spectroscopic observations of two planetary transits of the hot Jupiter KELT-7b (Mp = 1.28 +/- 0.17Mjup, Teq=2028 K) observed with the High Optical Resolution Spectrograph (HORuS) mounted on the 10.4-m Gran Telescopio Canarias (GTC). A new set of stellar parameters are obtained for the rapidly rotating parent star from the analysis of the spectra. Using the newly derived stellar mass and radius, and the planetary transit data of the Transiting Exoplanet Survey Satellite (TESS) together with the HORuS velocities and the photometric and spectroscopic data available in the literature, we update and improve the ephemeris of KELT-7b. Our results indicate that KELT-7 has an angle Lamda = -10.55 +/- 0.27 deg between the sky projections of the star’s spin axis and the planet’s orbital axis. By combining this angle and our newly derived stellar rotation period of 1.38 +/- 0.05 d, we obtained a 3D obliquity Psi = 12.4 +/- 11.7 deg (or 167.6 deg), thus reinforcing that KELT-7 is a well-aligned planetary system. We search for the presence of Halfa, Li i, Na i, Mg i, and Ca ii features in the transmission spectrum of KELT-7b but we are only able to determine upper limits of 0.08–1.4 % on their presence after accounting for the contribution of the stellar variability to the extracted planetary spectrum. We also discuss the impact of stellar variability in the planetary data. Our results reinforce the importance of monitoring the parent star when performing high-resolution transmission spectroscopy of the planetary atmosphere in the presence of stellar activity

Characterization of members to stellar kinematic groups using chemical tagging

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Física de la Tierra, Astronomía y Astrofísica II (Astrofísica y Ciencias de la Atmósfera), leída el 31-10-2014.Los grupos cinemáticos estelares -supercúmulos, grupos de movimiento y asociaciones estelares- son grupos de estrellas con una cinemática común originalmente definidos por Olin Eggen. Este último sugiere que los grupos de movimiento pueden ser el resultado de la disolución de cúmulos estelares abiertos en la población general de estrellas. En general un cúmulo abierto será desmantelado bajo la acción del potencial gravitacional de la Galaxia. Las estrellas son dispersadas principalmente por dos mecanismos: la rotación diferencial de la galaxia y el calentamiento del disco. Sin embargo, estos grupos se pueden originar también de otras formas. Las sobredensidades en algunas regiones del plano UV de velocidades galácticas pueden ser el resultado de mecanismos a gran escala, debido a la simetría no axial de la Galaxia. Es decir, la presencia de una barra central y de los brazos espirales. Algunos estudios previos muestran la existencia de diferentes grupos de edad localizados en la región de plano de velocidades, donde se sitúan los grupos de movimiento clásicos. De entre estos, cabe resaltar algunos de los más jóvenes, tales como el supercúmulo de las Híades, el grupo de movimiento de la Osa Mayor, la Asociación local o el grupo de movimiento de las Pleiades, el supercúmulo IC 2391, y el grupo de Castor. Una forma de averiguar el origen de estos grupos cinemáticos es realizando un análisis detallado de sus abundancias químicas dado que aquellas estrellas que nacieron en un mismo cúmulo presentan una composición química similar. En esta tesis se analizan dos grupos de movimiento: el supercúmulo de las Híades y el grupo de movimiento de la Osa Mayor. También se han analizado estrellas del cartografiado del Gaia-ESO -GES, Gaia-ESO Survey-, que ha permitido estudiar en detalle las posibilidades del análisis químico en una muestra de gran tamaño. Permitiendo una futura búsqueda de estrellas pertenecientes a grupos de movimiento.El estudio que conforma esta tesis doctoral hace uso de datos espectroscópicos. Se han analizado más de mil espectros echelle de alta resolución -R mayor que 40000- en el visible. La obtención de estos espectros se hizo utilizando distintos instrumentos: FOCES -Observatorio de Calar Alto-, HERMES -Observatorio de La Palma-, TLS-Observatorio de Tautenburg y UVES en el telescopio VLT, Observatorio de La Silla. Se han desarrollado dos códigos StePar y SteAbu que permiten analizar con mucho detalle estrellas de tipo solar. Ambos códigos hacen uso de las intensidades de las líneas espectrales de diversos elementos para caracterizar estas estrellas. StePar es un código automático que permite obtener los parámetros estelares de las estrellas que luego son pasados a SteAbu para calcular las abundancias químicas. Se han calculado las abundancias de 20 elementos químicos diferentes.En cuanto al análisis de abundancias del supercúmulo de las Híades Tabernero et al. 2012, AyA, 547, A13, se muestra que el 46 por ciento son consistentes con haberse originado en un mismo cúmulo. Mientras que en el caso del grupo de la Osa Mayor, Tabernero et al. 2014, AyA, in press, revela que el 66 por ciento de las estrellas son muy probablemente consistentes con un origen común. Estos resultados para ambos grupos estudiados son compatibles con lo que uno puede obtener por comparación con isocronas teóricas de las edades asociadas a estos grupos, además de ser marginalmente distinguibles entre si en cuanto a su composición química. El cartografiado del Gaia-ESO, ha servido como campo de pruebas que ha permitido comprobar como se comportan las abundancias químicas de diferentes elementos para distintos cúmulos abiertos. Siendo posible inferir de ello las posibilidades de detectar posibles miembros de grupos de movimiento en grandes muestras de estrellas.Depto. de Física de la Tierra y AstrofísicaFac. de Ciencias FísicasTRUEunpu

Testing the chemical tagging technique with open clusters

© ESO 2015. This work was partially supported by the Gaia Research for European Astronomy Training (GREAT-ITN) Marie Curie network, funded through the European Union Seventh Framework Programme [FP7/2007-2013] under grant agreement n. 264895. U.H. and A.J.K. acknowledge support from the Swedish National Space Board (Rymdstyrelsen). I.S.R. gratefully acknowledges the support provided by the Gemini-CONICYT project 32110029. All the software used in the data analysis were provided by the Open Source community.Context. Stars are born together from giant molecular clouds and, if we assume that the priors were chemically homogeneous and well-mixed, we expect them to share the same chemical composition. Most of the stellar aggregates are disrupted while orbiting the Galaxy and most of the dynamic information is lost, thus the only possibility of reconstructing the stellar formation history is to analyze the chemical abundances that we observe today. Aims. The chemical tagging technique aims to recover disrupted stellar clusters based merely on their chemical composition. We evaluate the viability of this technique to recover co-natal stars that are no longer gravitationally bound. Methods. Open clusters are co-natal aggregates that have managed to survive together. We compiled stellar spectra from 31 old and intermediate-age open clusters, homogeneously derived atmospheric parameters, and 17 abundance species, and applied machine learning algorithms to group the stars based on their chemical composition. This approach allows us to evaluate the viability and efficiency of the chemical tagging technique. Results. We found that stars at different evolutionary stages have distinct chemical patterns that may be due to NLTE effects, atomic diffusion, mixing, and biases. When separating stars into dwarfs and giants, we observed that a few open clusters show distinct chemical signatures while the majority show a high degree of overlap. This limits the recovery of co-natal aggregates by applying the chemical tagging technique. Nevertheless, there is room for improvement if more elements are included and models are improved.Unión Europea. FP7Gaia Research for European Astronomy Training (GREAT-ITN) Marie Curie network through the European Union Seventh Framework Programme [FP7]Swedish National Space Board (Rymdstyrelsen)Comisión Nacional de Investigación Científica y Tecnológica (CONICYT), ChileMinisterio de Educación (Chile)Depto. de Física de la Tierra y AstrofísicaFac. de Ciencias FísicasTRUEpu

A detailed analysis of the Gl 486 planetary system

Context. The Gl 486 system consists of a very nearby, relatively bright, weakly active M3.5 V star at just 8 pc with a warm transiting rocky planet of about 1.3 R_(⊕) and 3.0 M_(⊕). It is ideal for both transmission and emission spectroscopy and for testing interior models of telluric planets. Aims. To prepare for future studies, we aim to thoroughly characterise the planetary system with new accurate and precise data collected with state-of-the-art photometers from space and spectrometers and interferometers from the ground. Methods. We collected light curves of seven new transits observed with the CHEOPS space mission and new radial velocities obtained with MAROON-X at the 8.1 m Gemini North telescope and CARMENES at the 3.5 m Calar Alto telescope, together with previously published spectroscopic and photometric data from the two spectrographs and TESS. We also performed near-infrared interferometric observations with the CHARA Array and new photometric monitoring with a suite of smaller telescopes (AstroLAB, LCOGT, OSN, TJO). This extraordinary and rich data set was the input for our comprehensive analysis. Results. From interferometry, we measure a limb-darkened disc angular size of the star Gl 486 at θ_(LDD) = 0.390 ± 0.018 mas. Together with a corrected Gaia EDR3 parallax, we obtain a stellar radius R_(*) = 0.339 ± 0.015 R_(ꙩ). We also measure a stellar rotation period at P_(rot) = 49.9 ± 5.5 days, an upper limit to its XUV (5–920 Å) flux informed by new Hubble/STIS data, and, for the first time, a variety of element abundances (Fe, Mg, Si, V, Sr, Zr, Rb) and C/O ratio. Moreover, we imposed restrictive constraints on the presence of additional components, either stellar or sub-stellar, in the system. With the input stellar parameters and the radial-velocity and transit data, we determine the radius and mass of the planet Gl 486 b at R_(p) = 1.343^(+0.063)_( −0.062) R_(⊕) and M_(p) = 3.00^(+0.13)_(−0.13) M_(⊕), with relative uncertainties of the planet radius and mass of 4.7% and 4.2%, respectively. From the planet parameters and the stellar element abundances, we infer the most probable models of planet internal structure and composition, which are consistent with a relatively small metallic core with respect to the Earth, a deep silicate mantle, and a thin volatile upper layer. With all these ingredients, we outline prospects for Gl 486 b atmospheric studies, especially with forthcoming James Webb Space Telescope (Webb) observations

The Gaia-ESO survey: calibrating the lithium-age relation with open clusters and associations I. Cluster age range and initial membership selections

Context. Previous studies of open clusters have shown that lithium depletion is not only strongly age dependent but also shows a complex pattern with other parameters that is not yet understood. For pre- and main-sequence late-type stars, these parameters include metallicity, mixing mechanisms, convection structure, rotation, and magnetic activity. Aims. We perform a thorough membership analysis for a large number of stars observed within the Gaia-ESO survey (GES) in the field of 20 open clusters, ranging in age from young clusters and associations, to intermediate-age and old open clusters. Methods. Based on the parameters derived from the GES spectroscopic observations, we obtained lists of candidate members for each of the clusters in the sample by deriving radial velocity distributions and studying the position of the kinematic selections in the EW(Li)-versus-Teff plane to obtain lithium members. We used gravity indicators to discard field contaminants and studied [Fe/H] metallicity to further confirm the membership of the candidates. We also made use of studies using recent data from the Gaia DR1 and DR2 releases to assess our member selections. Results. We identified likely member candidates for the sample of 20 clusters observed in GES (iDR4) with UVES and GIRAFFE, and conducted a comparative study that allowed us to characterize the properties of these members as well as identify field contaminant stars, both lithium-rich giants and non-giant outliers. Conclusions. This work is the first step towards the calibration of the lithium–age relation and its dependence on other GES parameters. During this project we aim to use this relation to infer the ages of GES field stars, and identify their potential membership to young associations and stellar kinematic groups of different ages