Browsing by Author "Caballero, J. A."
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PublicationA detailed analysis of the Gl 486 planetary system(EDP Sciencies, 2022-09-20) Caballero, J. A.; Gómez Marfil, Emilio; Montes Gutiérrez, David; Tabernero Guzmán, Hugo Martín; otros, ...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. PublicationA nearby transiting rocky exoplanet that is suitable for atmospheric investigation(Amer Assoc Advancement Science, 2021-03-05) Caballero, J. A.; Cifuentes, C.; Cortés Contreras, Miriam; Montes Gutiérrez, DavidSpectroscopy of transiting exoplanets can be used to investigate their atmospheric properties and habitability. Combining radial velocity (RV) and transit data provides additional information on exoplanet physical properties. We detect a transiting rocky planet with an orbital period of 1.467 days around the nearby red dwarf star Gliese 486. The planet Gliese 486 b is 2.81 Earth masses and 1.31 Earth radii, with uncertainties of 5%, as determined from RV data and photometric light curves. The host star is at a distance of ~8.1 parsecs, has a J-band magnitude of ~7.2, and is observable from both hemispheres of Earth. On the basis of these properties and the planet’s short orbital period and high equilibrium temperature, we show that this terrestrial planet is suitable for emission and transit spectroscopy. PublicationA quarter century of spectroscopic monitoring of the nearby M dwarf Gl 514 A super-Earth on an eccentric orbit moving in and out of the habitable zone(EDP Sciencies, 2022-10-28) Caballero, J. A.; Montes Gutiérrez, David; otros, ...Context. Statistical analyses based on Kepler data show that most of the early-type M dwarfs host multi-planet systems consisting of Earth- to sub-Neptune-sized planets with orbital periods of up to ∼250 days, and that at least one such planet is likely located within the habitable zone. M dwarfs are therefore primary targets to search for potentially habitable planets in the solar neighbourhood. Aims. We investigated the presence of planetary companions around the nearby (7.6 pc) and bright (V = 9 mag) early-type M dwarf Gl 514, analysing 540 radial velocities collected over nearly 25 yr with the HIRES, HARPS, and CARMENES spectrographs. Methods. The data are affected by time-correlated signals at the level of 2–3 ms^(−1) due to stellar activity, which we filtered out, testing three different models based on Gaussian process regression. As a sanity cross-check, we repeated the analyses using HARPS radial velocities extracted with three different algorithms. We used HIRES radial velocities and Hipparcos-Gaia astrometry to put constraints on the presence of long-period companions, and we analysed TESS photometric data. Results. We find strong evidence that Gl 514 hosts a super-Earth on a likely eccentric orbit, residing in the conservative habitable zone for nearly 34% of its orbital period. The planet Gl 514 b has minimum mass m_(b) sin i_(b) = 5.2 ± 0.9 M_(⊕), orbital period P_(b) = 140.43 ± 0.41 days, and eccentricity e_(b) = 0.45^(+0.15)_(−0.14). No evidence for transits is found in the TESS light curve. There is no evidence for a longer period companion in the radial velocities and, based on astrometry, we can rule out a ∼0.2 M_(Jup) planet at a distance of ∼3–10 astronomical units, and massive giant planets and brown dwarfs out to several tens of astronomical units. We discuss the possible presence of a second low-mass companion at a shorter distance from the host than Gl 514 b. Conclusions. Gl 514 b represents an interesting science case for studying the habitability of planets on eccentric orbits. We advocate for additional spectroscopic follow-up to get more accurate and precise planetary parameters. Further follow-up is also needed to investigate the presence of additional planetary signals of less than 1 ms^(−1). PublicationAn ultra-short-period transiting super-Earth orbiting the M3 dwarf TOI-1685(EDP Sciencies, 2021-06-08) Caballero, J. A.; Cortés Contreras, Miriam; Montes Gutiérrez, DavidDynamical histories of planetary systems, as well as the atmospheric evolution of highly irradiated planets, can be studied by characterizing the ultra-short-period planet population, which the TESS mission is particularly well suited to discover. Here, we report on the follow-up of a transit signal detected in the TESS sector 19 photometric time series of the M3.0 V star TOI-1685 (2MASS J04342248+4302148). We confirm the planetary nature of the transit signal, which has a period of P_(b) = 0.6691403^(+0.0000023)_(−0.0000021) d, using precise radial velocity measurements taken with the CARMENES spectrograph. From the joint photometry and radial velocity analysis, we estimate the following parameters for TOI-1685 b: a mass of M_(b) = 3.78^(+0.63)_(−0.63) Mꙩ, a radius of R_(b) = 1.70^(+0.07)_(−0.07) Rꙩ, which together result in a bulk density of ρ_(b) = 4.21^(+0.95)_(−0.82) g cm^(−3) , and an equilibrium temperature of T_(eq) = 1069^(+16)_(−16) K. TOI-1685 b is the least dense ultra-short-period planet around an M dwarf known to date. TOI-1685 b is also one of the hottest transiting super-Earth planets with accurate dynamical mass measurements, which makes it a particularly attractive target for thermal emission spectroscopy. Additionally, we report with moderate evidence an additional non-transiting planet candidate in the system, TOI-1685 [c], which has an orbital period of P_(c) = 9.02^(+0.10)_(−0.12) d. PublicationAtmospheric characterization of the ultra-hot Jupiter WASP-33b Detection of Ti and V emission lines and retrieval of a broadened line profile(EDP Sciencies, 2022-12-02) Caballero, J. A.; Montes Gutiérrez, David; otros, ...Ultra-hot Jupiters are highly irradiated gas giant exoplanets on close-in orbits around their host stars. The dayside atmospheres of these objects strongly emit thermal radiation due to their elevated temperatures, making them prime targets for characterization by emission spectroscopy. We analyzed high-resolution spectra from CARMENES, HARPS-N, and ESPaDOnS taken over eight observation nights to study the emission spectrum of WASP-33b and draw conclusions about its atmosphere. By applying the cross-correlation technique, we detected the spectral signatures of Ti I, V I, and a tentative signal of Ti II for the first time via emission spectroscopy. These detections are an important finding because of the fundamental role of Ti- and V-bearing species in the planetary energy balance. Moreover, we assessed and confirm the presence of OH, Fe I, and Si I from previous studies. The spectral lines are all detected in emission, which unambiguously proves the presence of an inverted temperature profile in the planetary atmosphere. By performing retrievals on the emission lines of all the detected species, we determined a relatively weak atmospheric thermal inversion extending from approximately 3400 to 4000 K. We infer a supersolar metallicity close to 1.5 dex in the planetary atmosphere, and find that its emission signature undergoes significant line broadening with a Gaussian full width at half maximum of about 4.5 km s^(−1) . Also, we find that the atmospheric temperature profile retrieved at orbital phases far from the secondary eclipse is about 300 to 700 K cooler than that measured close to the secondary eclipse, which is consistent with different day- and nightside temperatures. Moreover, retrievals performed on the emission lines of the individual chemical species lead to consistent results, which gives additional confidence to our retrieval method. Increasing the number of species included in the retrieval and expanding the set of retrieved atmospheric parameters will further advance our understanding of exoplanet atmospheres. PublicationCalibrating the metallicity of M dwarfs in wide physical binaries with F-, G-, and K-primaries -I: High-resolution spectroscopy with HERMES: stellar parameters, abundances, and kinematics(Oxford Univ Press, 2018-09) Montes Gutiérrez, David; González Peinado, R.; Tabernero, H. M.; Caballero, J. A.; Gómez Marfil, Emilio; Alonso Floriano, F. J.; Cortés Contreras, Miriam; González Hernández, J. I.; Klutsch, A.; Moreno Jodar, C.We investigated almost 500 stars distributed among 193 binary or multiple systems made of late-E, G-, or earl y-K-primaries and late-K- or M-dwarf companion candidates, For all of them, we compiled or measured coordinates, J-band magnitudes, spectral types, distances, and proper motions. With these data, we established a sample of 192 physically bound systems. In parallel, we carried out observations with HERMES/Mercator and obtained high-resolution spectra for the 192 primaries and five secondaries. We used these spectra and the automatic STEPAR code for deriving precise stellar atmospheric parameters: T-eff, log g, xi, and chemical abundances for 13 atomic species, including [Fe/H]. After computing Galactocentric space velocities for all the primary stars, we performed a kinematic analysis and classified them in different Galactic populations and stellar kinematic groups of very different ages, which match our own metallicity determinations and isochronal age estimations. In particular, we identified three systems in the halo and 33 systems in the young Local Association, Ursa Major and Castor moving groups, and IC 2391 and Hyades superclusters. We finally studied the exoplanet-metallicity relation in our 193 primaries and made a list 13 M-dwarf companions with very high metallicity that can be the targets of new dedicated exoplanet surveys. All in all, our dataset will be of great help for future works on the accurate determination of metallicity of M dwarfS. PublicationCARMENES input catalog of M dwarfs VI. A time-resolved Ca II H&K catalog from archival data(EDP Sciencies, 2021-08-20) Caballero, J. A.; Cortés Contreras, Miriam; Montes Gutiérrez, DavidContext. Radial-velocity (RV) jitter caused by stellar magnetic activity is an important factor in state-of-the-art exoplanet discovery surveys such as CARMENES. Stellar rotation, along with heterogeneities in the photosphere and chromosphere caused by activity, can result in false-positive planet detections. Hence, it is necessary to determine the stellar rotation period and compare it to any putative planetary RV signature. Long-term measurements of activity indicators such as the chromospheric emission in the Ca ii H&K lines (R’_(HK)) enable the identification of magnetic activity cycles. Aims. In order to determine stellar rotation periods and study the long-term behavior of magnetic activity of the CARMENES guaranteed time observations (GTO) sample, it is advantageous to extract R 0 HK time series from archival data, since the CARMENES spectrograph does not cover the blue range of the stellar spectrum containing the Ca ii H&K lines. Methods. We have assembled a catalog of 11 634 archival spectra of 186 M dwarfs acquired by seven different instruments covering the Ca ii H&K regime: ESPaDOnS, FEROS, HARPS, HIRES, NARVAL, TIGRE, and UVES. The relative chromospheric flux in these lines, R’_(HK), was directly extracted from the spectra by rectification with PHOENIX synthetic spectra via narrow passbands around the Ca ii H&K line cores. Results. The combination of archival spectra from various instruments results in time series for 186 stars from the CARMENES GTO sample. As an example of the use of the catalog, we report the tentative discovery of three previously unknown activity cycles of M dwarfs. Conclusions. We conclude that the method of extracting R 0 HK with the use of model spectra yields consistent results for different instruments and that the compilation of this catalog will enable the analysis of long-term activity time series for a large number of M dwarfs. PublicationCARMENES input catalogue of M dwarfs I. Low-resolution spectroscopy with CAFOS(EDP Sciencies, 2015-05) Alonso Floriano, F. J.; Morales, J. C.; Caballero, J. A.; Montes Gutiérrez, David; Klutsch, A.; Mundt, R.; Cortés Contreras, Miriam; Ribas, I.; Reiners, A.; Amado, P. J.; Quirrenbach, A.; Jeffers, S. V.Context. CARMENES is a stabilised, high-resolution, double-channel spectrograph at the 3.5m Calar Alto telescope. It is optimally designed for radial-velocity surveys of M dwarfs with potentially habitable Earth-mass planets. Aims. We prepare a list of the brightest, single M dwarfs in each spectral subtype observable from the northern hemisphere, from which we will select the best planet-hunting targets for CARMENES. Methods. In this first paper on the preparation of our input catalogue, we compiled a large amount of public data and collected low-resolution optical spectroscopy with CAFOS at the 2.2m Calar Alto telescope for 753 stars. We derived accurate spectral types using a dense grid of standard stars, a double least-squares minimisation technique, and 31 spectral indices previously defined by other authors. Additionally, we quantified surface gravity, metallicity, and chromospheric activity for all the stars in our sample. Results. We calculated spectral types for all 753 stars, of which 305 are new and 448 are revised. We measured pseudo-equivalent widths of H α for all the stars in our sample, concluded that chromospheric activity does not affect spectral typing from our indices, and tabulated 49 stars that had been reported to be young stars in open clusters, moving groups, and stellar associations. Of the 753 stars, two are new subdwarf candidates, three are T Tauri stars, 25 are giants, 44 are K dwarfs, and 679 are M dwarfs. Many of the 261 investigated dwarfs in the range M4.0-8.0V are among the brightest stars known in their spectral subtype. Conclusions. This collection of low-resolution spectroscopic data serves as a candidate target list for the CARMENES survey and can be highly valuable for other radial-velocity surveys of M dwarfs and for studies of cool dwarfs in the solar neighbourhood. PublicationCharged-current inclusive neutrino cross sections in the SuperScaling model(Amer Inst Physics, 2016) Ivanov, M. V.; Megías, G. D.; González Jiménez, R.; Moreno, O.; Bárbaro, M. B.; Caballero, J. A.; Donnelly, T. W.; Antonov, A. N.; Moya de Guerra, Elvira; Udías Moinelo, José ManuelSuperScaling model (SuSA) predictions to neutrino-induced charged-current pi(+) production in the Delta-resonance region are explored under MiniBooNE experimental conditions. The SuSA charged-current pi(+) results are in good agreement with data on neutrino flux-averaged double-differential cross sections. The SuSA model for quasielastic scattering and its extension to the pion production region are used for predictions of charged-current inclusive neutrino-nucleus cross sections. Results are also compared with the T2K experimental data for inclusive scattering. PublicationDetection of Fe and evidence for TiO in the dayside emission spectrum of WASP-33b(EDP Sciencies, 2021-07-07) Cont, D.; Yan, F.; Reiners, A.; Casasayas-Barris, N.; Mollière, P.; Pallé, E.; Henning, Th.; Nortmann, L.; Stangret, M.; Czesla, S.; López-Puertas, M.; Sánchez-López, A.; Rodler, F.; Ribas, I.; Quirrenbach, A.; Caballero, J. A.; Amado, P. J.; Carone, L.; Khaimova, J.; Kreidberg, L.; Molaverdikhani, K.; Montes Gutiérrez, David; Morello, G.; Nagel, E.; Oshagh, M.; Zechmeister, M.Context. Theoretical studies predict the presence of thermal inversions in the atmosphere of highly irradiated gas giant planets. Recent observations have identified these inversion layers. However, the role of different chemical species in their formation remains unclear. Aims. We search for the signature of the thermal inversion agents TiO and Fe in the dayside emission spectrum of the ultra-hot Jupiter WASP-33b. Methods. The spectra were obtained with CARMENES and HARPS-N, covering different wavelength ranges. Telluric and stellar absorption lines were removed with SYSREM. We cross-correlated the residual spectra with model spectra to retrieve the signals from the planetary atmosphere. Results. We find evidence for TiO at a significance of 4.9σ with CARMENES. The strength of the TiO signal drops close to the secondary eclipse. No TiO signal is found with HARPS-N. An injection-recovery test suggests that the TiO signal is below the detection level at the wavelengths covered by HARPS-N. The emission signature of Fe is detected with both instruments at significance levels of 5.7σ and 4.5σ, respectively. By combining all observations, we obtain a significance level of 7.3σ for Fe. We find the TiO signal at K_(p )= 248.0^(+2.0)_(−2.5) km s^(−1), which is in disagreement with the Fe detection at K_(p) = 225.0^(+4.0)_(−3.5) km s^(−1). The Kp value for Fe is in agreement with prior investigations. The model spectra require different temperature profiles for TiO and Fe to match the observations. We observe a broader line profile for Fe than for TiO. Conclusions. Our results confirm the existence of a temperature inversion layer in the planetary atmosphere. The observed K_(p) offset and different strengths of broadening in the line profiles suggest the existence of a TiO-depleted hot spot in the planetary atmosphere. PublicationDetection of the hydrogen Balmer lines in the ultra-hot Jupiter WASP-33b(EDP Sciencies, 2020-12-22) Caballero, J. A.; Montes Gutiérrez, DavidUltra-hot Jupiters (UHJs) are highly irradiated giant exoplanets with extremely high day-side temperatures, which lead to thermal dissociation of most of the molecular species. It is expected that the neutral hydrogen atom is one of the main species in the upper atmospheres of ultra-hot Jupiters. Neutral hydrogen has been detected in several UHJs by observing its Balmer line absorption. Here, we report four transit observations of the ultra-hot Jupiter WASP-33b, performed with the CARMENES and HARPS-North spectrographs, and the detection of the Hα, Hβ, and Hγ lines in the planetary transmission spectrum. The combined Hα transmission spectrum of the four transits has an absorption depth of 0.99±0.05 %, which corresponds to an effective radius of 1.31±0.01 R_(p). The strong Hα absorption indicates that the line probes the high-altitude thermosphere. We further fitted the three Balmer lines using the PAWN model, assuming that the atmosphere is hydrodynamic and in LTE. We retrieved a thermosphere temperature 12200^(+1300)_(−1000) K and a mass-loss rate Ṁ = 10^(11.8)^^(+0.6)__(−0.5) g s^(−1) . The retrieved large mass-loss rate is compatible with the “Balmer-driven” atmospheric escape scenario, in which the stellar Balmer continua radiation in the near-ultraviolet is substantially absorbed by the excited hydrogen atoms in the planetary thermosphere. PublicationErratum: Nuclear effects in neutrino and antineutrino charged-current quasielastic scattering at MINERνA kinematics(Amer Physical Soc, 2015-02-11) Megías, G. D.; Ivanov, M. V.; González Jiménez, R.; Caballero, J. A.; Bárbaro, M. B.; Donnelly, T. W.; Udías Moinelo, José Manuel PublicationEvidence of energy-, recombination-, and photon-limited escape regimes in giant planet H/He atmospheres(EDP Sciencies, 2021-04-23) Lampón, M.; López-Puertas, M.; Czesla, S.; Sánchez-López, A.; Lara, L. M.; Salz, M.; Sanz-Forcada, J.; Molaverdikhani, K.; Quirrenbach, A.; Pallé, E.; Caballero, J. A.; Henning, Th.; Nortmann, L.; Amado, P. J.; Montes Gutiérrez, David; Reiners, A.; Ribas, I.Hydrodynamic escape is the most efficient atmospheric mechanism of planetary mass loss and has a large impact on planetary evolution. Three hydrodynamic escape regimes have been identified theoretically: energy-limited, recombination-limited, and photonlimited. However, no evidence of these regimes had been reported until now. Here, we report evidence of these three regimes via an analysis of a helium I triplet at 10 830 Å and Lyα absorption involving a 1D hydrodynamic model that allows us to estimate hydrogen recombination and advection rates. In particular, we show that HD 209458 b is in the energy-limited regime, HD 189733 b is in the recombination-limited regime, and GJ 3470 b is in the photon-limited regime. These exoplanets can be considered as benchmark cases for their respective regimes. PublicationFinal state interactions in semi-inclusive neutrino-nucleus scattering: Applications to the T2K and MINER nu A experiments.(Amer Physical Soc, 2022-12-19) Franco Patiño, J. M.; González Jiménez, Raúl; Dolan, S.; Barbaro, M. B.; Caballero, J. A.; Megias, G. D.; Udías Moinelo, José ManuelWe present a complete comparison of semi-inclusive nu mu-12C cross section measurements by T2K and MINER nu A collaborations with the predictions from the SuSAv2-MEC model implemented in the neutrino -nucleus event generator GENIE and an unfactorized approach based on the relativistic distorted wave impulse approximation. Results, that include cross sections as function of the final muon and proton kinematics and correlations between both, show that the agreement with data obtained by the relativistic distorted wave impulse approximation approach, that accounts for final-state interactions, matches or improves GENIE-SuSAv2 predictions for very forward angles where scaling violations are relevant. PublicationFinding the most variable stars in the Orion Belt with the All Sky Automated Survey(Wiley-VCH Verlag Gmbh, 2010-03) Caballero, J. A.; Cornide Castro-Piñeiro, Manuel; Castro Rubio, Elisa deWe look for high-amplitude variable young stars in the open clusters and associations of the Orion Belt. We use public data from the ASAS-3 Photometric V -band Catalogue of the All Sky Automated Survey, infrared photometry from the 2MASS and IRAS catalogues, proper motions, and the Aladin sky atlas to obtain a list of the most variable stars in a survey area of side 5 deg centred on the bright star Alnilam (Ƹ Ori) in the centre of the Orion Belt. We identify 32 highly-variable stars, of which 16 had not been reported to vary before. They are mostly variable young stars and candidates (16) and background giants (8), but there are also field cataclysmic variables, contact binaries, and eclipsing binary candidates. Of the young stars, which typically are active Herbig Ae/Be and T Tauri stars with Hα emission and infrared flux excess, we discover four new variables and confirm the variability status of another two. Some of them belong to the well known σ Orionis cluster. Besides, six of the eight giants are new variables, and three are new periodic variables. PublicationGestión del Patrimonio Histórico en grandes obras de infraestructura: El modelo geo-arqueológico aplicado en el proyecto de remodelación de la M-30(Consejería de Cultura y Turismo. DGPH. Comunidad de Madrid, 2007) Rus, I.; Bárez, S.; Caballero, J. A.; García Somoza, Pilar; Panera, Joaquin; Rubio-Jara, Susana; Uribelarrea del Val, DavidSe presentan los resultados preliminares del desarrollo de un modelo de gestión del patrimonio arqueológico, paleontológico y geológico para una gran obra de infraestructura, como es el Proyecto de Remodelación de la M-30, actualmente en ejecución. Este modelo se ha planteado y coordinado desde la Dirección General de Patrimonio Histórico de la Comunidad de Madrid en colaboración con el Ayuntamiento de Madrid, promotor de las obras, con el asesoramiento de una Comisión Científica, integrada por investigadores del campo de la Arqueología, la Paleontología y la Geología, asistida por un Equipo técnico multidisciplinar. El principal objetivo del modelo es avanzar en el conocimiento científico de la ocupación humana de Madrid desde la Prehistoria hasta la actualidad, del registro paleontológico, así como de la reconstrucción y evolución física del paisaje, mediante el empleo de sistemas de documentación y conservación del Patrimonio Histórico que hagan compatible la protección e investigación del patrimonio con el desarrollo urbano. PublicationHe I λ 10 830 Å in the transmission spectrum of HD 209458 b(EDP Sciencies, 2019-09) Sanz Forcada, J.; Caballero, J. A.; Labarga Ávalos, F.; Montes Gutiérrez, DavidContext. Recently, the He I triplet at 10 830 Å was rediscovered as an excellent probe of the extended and possibly evaporating atmospheres of close-in transiting planets. This has already resulted in detections of this triplet in the atmospheres of a handful of planets, both from space and from the ground. However, while a strong signal is expected for the hot Jupiter HD 209458 b, only upper limits have been obtained so far. Aims. Our goal is to measure the helium excess absorption from HD 209458 b and assess the extended atmosphere of the planet and possible evaporation. Methods. We obtained new high-resolution spectral transit time-series of HD 209458 b using CARMENES at the 3.5 m Calar Alto telescope, targeting the He I triplet at 10 830 Å at a spectral resolving power of 80 400. The observed spectra were corrected for stellar absorption lines using out-of-transit data, for telluric absorption using the MOLECFIT software, and for the sky emission lines using simultaneous sky measurements through a second fibre. Results. We detect He I absorption at a level of 0.91 ± 0.10% (9σ) at mid-transit. The absorption follows the radial velocity change of the planet during transit, unambiguously identifying the planet as the source of the absorption. The core of the absorption exhibits a net blueshift of 1.8 ± 1.3 km s^(−1) . Possible low-level excess absorption is seen further blueward from the main absorption near the centre of the transit, which could be caused by an extended tail. However, this needs to be confirmed. Conclusions. Our results further support a close relation between the strength of planetary absorption in the helium triplet lines and the level of ionising, stellar X-ray, and extreme-UV irradiation. PublicationIonized calcium in the atmospheres of two ultra-hot exoplanets WASP-33b and KELT-9b(EDP Sciencies, 2019-12-05) Caballero, J. A.; Cortés Contreras, Miriam; Montes Gutiérrez, DavidUltra-hot Jupiters are emerging as a new class of exoplanets. Studying their chemical compositions and temperature structures will improve our understanding of their mass loss rate as well as their formation and evolution. We present the detection of ionized calcium in the two hottest giant exoplanets - KELT-9b and WASP-33b. By using transit datasets from CARMENES and HARPS-N observations, we achieved high-confidence-level detections of Ca II using the cross-correlation method. We further obtain the transmission spectra around the individual lines of the Ca II H&K doublet and the near-infrared triplet, and measure their line profiles. The Ca II H&K lines have an average line depth of 2.02 +/- 0.17% (effective radius of 1.56 R_p) for WASP-33b and an average line depth of 0.78 +/- 0.04% (effective radius of 1.47 R_p) for KELT-9b, which indicates that the absorptions are from very high upper-atmosphere layers close to the planetary Roche lobes. The observed Ca II lines are significantly deeper than the predicted values from the hydrostatic models. Such a discrepancy is probably a result of hydrodynamic outflow that transports a significant amount of Ca II into the upper atmosphere. The prominent Ca II detection with the lack of significant Ca I detection implies that calcium is mostly ionized in the upper atmospheres of the two planets. PublicationLow-resolution spectroscopy and spectral energy distributions of selected sources towards σ Orionis(EDP Sciencies, 2008-11) Caballero, J. A.; Valdivielso, L.; Martín, E. L.; Montes Gutiérrez, David; Pascual, S.; Pérez González, Pablo GuillermoAims. We study in detail nine sources in the direction of the young σ Orionis cluster, which is considered to be a unique site for studying stellar and substellar formation. The nine sources were selected because of their peculiar properties, such as extremely-red infrared colours or excessively strong Hα emission for their blue optical colours. Methods. We acquired high-quality, low-resolution spectroscopy (R ∼ 500) of the nine targets with ALFOSC at the Nordic Optical Telescope. We also re-analysed -band photometry from MIPS/Spitzer and compiled the highest quality photometric dataset available at the ViJHK_s passbands and the four IRAC/Spitzer channels, for constructing accurate spectral energy distributions between 0.55 and 24 μm. Results. The nine targets were classified into: one Herbig Ae/Be star with a scattering edge-on disc; two G-type stars; one X-ray flaring, early-M, young star with chromospheric Hα emission; one very low-mass, accreting, young spectroscopic binary; two young objects at the brown-dwarf boundary with the characteristics of classical T Tauri stars; and two emission-line galaxies, one undergoing star formation, and another whose spectral energy distribution is dominated by an active galactic nucleus. We also discovered three infrared sources associated with overdensities in a cold cloud of the cluster centre. Conclusions. Low-resolution spectroscopy and spectral energy distributions are a vital tool for measuring the physical properties and evolution of young stars and candidates in the σ Orionis cluster. PublicationMagnetism, rotation, and nonthermal emission in cool stars: average magnetic field measurements in 292 M dwarfs(EDP Sciencies, 2022-06-10) Montes Gutiérrez, David; Caballero, J. A.; otros, ...Stellar dynamos generate magnetic fields that are of fundamental importance to the variability and evolution of Sun-like and low-mass stars, and for the development of their planetary systems. As a key to understanding stellar dynamos, empirical relations between stellar parameters and magnetic fields are required for comparison to ab initio predictions from dynamo models. We report measurements of surface-average magnetic fields in 292 M dwarfs from a comparison with radiative transfer calculations; for 260 of them, this is the first measurement of this kind. Our data were obtained from more than 15 000 high-resolution spectra taken during the CARMENES project. They reveal a relation between average field strength, ⟨B⟩, and Rossby number, Ro, resembling the well-studied rotation–activity relation. Among the slowly rotating stars, we find that magnetic flux, Φ_(B), is proportional to rotation period, P, and among the rapidly rotating stars that average surface fields do not grow significantly beyond the level set by the available kinetic energy. Furthermore, we find close relations between nonthermal coronal X-ray emission, chromospheric Hα and Ca H&K emission, and magnetic flux. Taken together, these relations demonstrate empirically that the rotation–activity relation can be traced back to a dependence of the magnetic dynamo on rotation. We advocate the picture that the magnetic dynamo generates magnetic flux on the stellar surface proportional to rotation rate with a saturation limit set by the available kinetic energy, and we provide relations for average field strengths and nonthermal emission that are independent of the choice of the convective turnover time. We also find that Ca H&K emission saturates at average field strengths of ⟨B⟩≈800 G while Hα and X-ray emission grow further with stronger fields in the more rapidly rotating stars. This is in conflict with the coronal stripping scenario predicting that in the most rapidly rotating stars coronal plasma would be cooled to chromospheric temperatures.