Espectroscopía de estrellas FGKM para la explotación científica de la búsqueda de exoplanetas con CARMENES

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, leída el 04-02-2022The increased interest that sparks the search for exoplanets over the last few years has resulted in the design of high-resolution spectrographs such as CARMENES, installed at the 3.5m telescope in the Calar Alto Observatory in Almería (Spain), in order to improve the radial-velocity measurements and, thus, to help detect Earth-type planets around stars other than the Sun. Among these, M dwarfs constitute ideal candidates given their ubiquity in the solar neighbourhood, low temperatures, and low masses, which favours detections by both the radial-velocity and transit techniques. In this context, the determination of stellar atmospheric parameters is an essential step to characterise exoplanet systems and to shed light on their formation and evolution by means of compared planetology, which tries to link the properties of exoplanets with those of their host stars. In particular, the CARMENES instrument, by virtue of its high resolution and simultaneous spectral coverage in the optical and near-infrared wavelength regions, not only provides key information for the analysis of cool stars, but it also opens up the opportunity to revisit classical techniques, such as the equivalent width method and spectral synthesis, to assess the impact of the near-infrared region on the computation of stellar parameters...El creciente interés que despierta la búsqueda de exoplanetas ha conducido en los últimos años al desarrollo de espectrógrafos de alta resolución como CARMENES, instalado en el telescopio de3.5m del observatorio de Calar Alto en Almería (España), con el objetivo de mejorar las medidas de velocidad radial y permitir la detección de planetas de tipo terrestre alrededor de estrellas distintas al Sol. Entre ellas, las estrellas enanas de tipo M constituyen candidatos ideales dada su ubicuidad en el vecindario solar, sus bajas temperaturas y bajas masas, lo que favorece las detecciones mediante las técnicas de velocidad radial y de tránsitos. En este contexto, la determinación de los parámetros atmosféricos estelares es un paso crucial para caracterizar los sistemas de exoplanetas y para arrojar luz sobre su formación y evolución mediante la planetología comparada, que pretende relacionar las propiedades de los exoplanetas con las de sus estrellas anfitrionas. En particular, el instrumento CARMENES, gracias a su alta resolución y su cobertura espectral simultánea en el óptico y el infrarrojo cercano, no solo proporciona información valiosa para el análisis de las estrellas frías, sino que también da la oportunidad de volver a evaluar técnicas clásicas, como el método de las anchuras equivalentes y la síntesis espectral, para estimar el impacto de la región infrarroja cercana en el cálculo de parámetros estelares...Fac. de Ciencias FísicasTRUEunpu

The CARMENES search for exoplanets around M dwarfs Not-so-fine hyperfine-split vanadium lines in cool star spectra

Context. M-dwarf spectra are complex and notoriously difficult to model, posing challenges to understanding their photospheric properties and compositions in depth. Vanadium (V) is an iron-group element whose abundance supposedly closely tracks that of iron, but has origins that are not completely understood. Aims. Our aim is to characterize a series of neutral vanadium atomic absorption lines in the 800-910 nm wavelength region of high signal-to-noise, high-resolution, telluric-corrected M-dwarf spectra from the CARMENES survey. Many of these lines are prominent and exhibit a distinctive broad and flat-bottom shape, which is a result of hyperfine structure (HFS). We investigate the potential and implications of these HFS split lines for abundance analysis of cool stars. Methods. With standard spectral synthesis routines, as provided by the spectroscopy software iSpec and the latest atomic data (including HFS) available from the VALD3 database, we modeled these striking line profiles. We used them to measure V abundances of cool dwarfs. Results. We determined V abundances for 135 early M dwarfs (M0.0 V to M3.5 V) in the CARMENES guaranteed time observations sample. They exhibit a [V/Fe]-[Fe/H] trend consistent with that derived from nearby FG dwarfs. The tight (+/- 0.1 dex) correlation between [V/H] and [Fe/H] suggests the potential application of V as an alternative metallicity indicator in M dwarfs. We also show hints that neglecting to model HFS could partially explain the temperature correlation in V abundance measurements observed in previous studies of samples involving dwarf stars with T-eff less than or similar to 5300 K. Conclusions. Our work suggests that HFS can impact certain absorption lines in cool photospheres more severely than in Sun-like ones. Therefore, we advocate that HFS should be carefully treated in abundance studies in stars cooler than similar to 5000 K. On the other hand, strong HFS split lines in high-resolution spectra present an opportunity for precision chemical analyses of large samples of cool stars. The V-to-Fe trends exhibited by the local M dwarfs continue to challenge theoretical models of V production in the Galaxy

Metallicities in M dwarfs: Investigating different determination techniques

Deriving metallicities for solar-like stars follows well-established methods, but for cooler stars such as M dwarfs, the determination is much more complicated due to forests of molecular lines that are present. Several methods have been developed in recent years to determine accurate stellar parameters for these cool stars (T-eff less than or similar to 4000 K). However, significant differences can be found at times when comparing metallicities for the same star derived using different methods. In this work, we determine the effective temperatures, surface gravities, and metallicities of 18 well-studied M dwarfs observed with the CARMENES high-resolution spectrograph following different approaches, including synthetic spectral fitting, analysis of pseudo-equivalent widths, and machine learning. We analyzed the discrepancies in the derived stellar parameters, including metallicity, in several analysis runs. Our goal is to minimize these discrepancies and find stellar parameters that are more consistent with the literature values. We attempted to achieve this consistency by standardizing the most commonly used components, such as wavelength ranges, synthetic model spectra, continuum normalization methods, and stellar parameters. We conclude that although such modifications work quite well for hotter main-sequence stars, they do not improve the consistency in stellar parameters for M dwarfs, leading to mean deviations of around 50-200 K in temperature and 0.1-0.3 dex in metallicity. In particular, M dwarfs are much more complex and a standardization of the aforementioned components cannot be considered as a straightforward recipe for bringing consistency to the derived parameters. Further in-depth investigations of the employed methods would be necessary in order to identify and correct for the discrepancies that remain

Elemental Abundances of the Super-Neptune WASP-107b's Host Star Using High-resolution, Near-infrared Spectroscopy

We present the first elemental abundance measurements of the K dwarf (K7V) exoplanet-host star WASP-107 using high-resolution (R = 45,000), near-infrared (H- and K-band) spectra taken from Gemini-S/IGRINS. We use the previously determined physical parameters of the star from the literature and infer the abundances of 15 elements: C, N, O, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, and Ni, all with precision < 0.1 dex, based on model fitting using MARCS model atmospheres and the spectral synthesis code Turbospectrum. Our results show near-solar abundances and a carbon-to-oxygen ratio (C/O) of 0.50 (+/-0.10), consistent with the solar value of 0.54 (+/-0.09). The orbiting planet, WASP-107b, is a super Neptune with a mass in the Neptune regime (= 1.8 M_Nep) and a radius close to Jupiter's (= 0.94 R_Jup). This planet is also being targeted by four JWST Cycle 1 programs in transit and eclipse, which should provide highly precise measurements of atmospheric abundances. This will enable us to properly compare the planetary and stellar chemical abundances, which is essential in understanding the formation mechanisms, internal structure, and chemical composition of exoplanets. Our study is a proof-of-concept that will pave the way for such measurements to be made for all JWST's cooler exoplanet-host stars.Comment: 19 pages, 8 figures, Accepted to Ap

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

Stellar atmospheric parameters of FGK-type stars from high-resolution optical and near-infrared CARMENES spectra

With the purpose of assessing classic spectroscopic methods on high-resolution and high signal-to-noise ratio spectra in the near-infrared wavelength region, we selected a sample of 65 F-, G-, and K-type stars observed with CARMENES, the new, ultra-stable, double channel spectrograph at the 3.5 m Calar Alto telescope. We computed their stellar atmospheric parameters (T_(eff), log g, ξ, and [Fe/H]) by means of the STEPAR code, a PYTHON implementation of the equivalent width method that employs the 2017 version of the MOOG code and a grid of MARCS model atmospheres. We compiled four Fe I and Fe II line lists suited to metal-rich dwarfs, metal-poor dwarfs, metal-rich giants, and metal-poor giants that cover the wavelength range from 5300 to 17 100 Å, thus substantially increasing the number of identified Fe I and Fe II lines up to 653 and 23, respectively, We examined the impact of the near-infrared Fe and Fen lines upon our parameter determinations after an exhaustive literature search, placing special emphasis on the 14 Gala benchmark stars contained in our sample, Even though our parameter determinations remain in good agreement with the literature values, the increase in the number of Fe l and Fe II lines when the near-infrared region is taken into account reveals a deeper T_(eff) scale that might stem from a higher sensitivity of the near-infrared lines to T_(eff)

KOBEsim: A Bayesian observing strategy algorithm for planet detection in radial velocity blind-search surveys

Context. Ground-based observing time is precious in the era of exoplanet follow-up and characterization, especially in high-precision radial velocity instruments. Blind-search radial velocity surveys thus require a dedicated observational strategy in order to optimize the observing time, which is particularly crucial for the detection of small rocky worlds at large orbital periods. Aims. We developed an algorithm with the purpose of improving the efficiency of radial velocity observations in the context of exoplanet searches, and we applied it to the K-dwarfs Orbited By habitable Exoplanets experiment. Our aim is to accelerate exoplanet confirmations or, alternatively, reject false signals as early as possible in order to save telescope time and increase the efficiency of both blind-search surveys and follow-up of transiting candidates. Methods. Once a minimum initial number of radial velocity datapoints is reached in such a way that a periodicity starts to emerge according to generalized Lomb-Scargle periodograms, that period is targeted with the proposed algorithm, named KOBEsim. The algorithm selects the next observing date that maximizes the Bayesian evidence for this periodicity in comparison with a model with no Keplerian orbits. Results. By means of simulated data, we proved that the algorithm accelerates the exoplanet detection, needing 29-33% fewer observations and a 41-47% smaller time span of the full dataset for low-mass planets (mp < 10 M⊕) in comparison with a conventional monotonic cadence strategy. For 20 M⊕ planets we found a 16% enhancement in the number of datapoints. We also tested KOBEsim with real data for a particular KOBE target and for the confirmed planet HD 102365 b. These two tests demonstrate that the strategy is capable of speeding up the detection by up to a factor of 2 (i.e., reducing both the time span and number of observations by half).14 página

Project goals, target selection, and stellar characterization

The detection of habitable worlds is one of humanitya-s greatest endeavors. Thus far, astrobiological studies have shown that one of the most critical components for allowing life to develop is liquid water. Its chemical properties and its capacity to dissolve and, hence, transport other substances makes this constituent a key piece in this regard. 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 essentially means looking for planets in the so-called habitable zone. In this sense, K-dwarf stars are the perfect hosts to search for planets in this range of distances. Contrary to G-dwarfs, the habitable zone is closer, thus making planet detection easier using transit or radial velocity techniques. Contrary to M-dwarfs, stellar activity is on a much smaller scale, hence, it has a smaller impact in terms of both the detectability and the true habitability of the planet. Also, K-dwarfs are the quietest in terms of oscillations, and granulation noise. In spite of 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 initiated the first dedicated and systematic search for habitable planets around these stars: 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 over five 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 ± 0.25 planets per star in the KOBE sample. Furthermore, in half of the sample, we expect to find one of those planets within the habitable zone. Here, we describe the motivations, goals, and target selection for the project as well as the preliminary stellar characterization. © 2022 EDP Sciences. All rights reserved

Pottery technology of levels IV and III in Kobaederra site (Cortézubi, Bizkaia). Supply and modification of raw material

RESUMEN: El estudio tecnológico del material cerámico requiere de la aplicación de técnicas de análisis arqueométrico que permitan un acercamiento a su mineralogía y composición química, con la fi nalidad de identifi car las etapas de su secuencia de elaboración. Este artículo presenta el análisis tecnológico de la cerámica neolítica documentada en los niveles inferiores del yacimiento de Kobaederra (Cortézubi, Bizkaia), a partir de su análisis mineralógico (petrografía y difracción de rayos X, DRX) y geoquímico (microscopio electrónico de barrido-espectómetro de dispersión de energía, MEB-EDS). Su objetivo es discriminar las potenciales áreas de aprovisionamiento de las materias primas y su modifi cación mediante la adición de desgrasantes. Por último, se discuten las implicaciones de los resultados obtenidos en relación con el resto de las evidencias arqueológicas disponibles para los niveles IV y III de Kobaederra.ABSRTACT: The technological study of ceramic materials requires the application of archaeometric analytical techniques to approach both their mineralogy and chemical composition, with the aim of identifying steps in their production sequence. This paper presents the technological analysis of the Neolithic pottery documented in the lower levels of the Kobaederra site (Cortézubi, Bizkaia) on the basis of their mineralogical (petrography and X-ray diffraction, XRD) and geochemical (SEM-EDS) analysis. Its goal is to discriminate the possible areas of raw materials supply and their modifi cation through the addition of tempers. Finally, the implications of the results in relation to the rest of available archaeological evidences from the IV and the III levels of the Kobaederra site are discussed