Resultados de investigación

The phenomenon of limb-darkening is relevant to many topics in astrophysics, including the analysis of light curves of eclipsing binaries, optical interferometry, measurement of stellar diameters, line profiles of rotating stars, gravitational microlensing, and transits of extrasolar planets. Multiple parametric limb-darkening laws have been presented, and there are many available sources of theoretical limb-darkening coefficients (LDCs) calculated using stellar model atmospheres. The power-2 limb-darkening law allows a very good representation of theoretically predicted intensity profiles, but few LDCs are available for this law from spherically symmetric model atmospheres. We therefore present such coefficients in this work. We computed LDCs for the space missions Gaia, Kepler, TESS, and CHEOPS and for the passbands uvby, UBVRIJHK, and SDSS ugriz, using the PHOENIX-COND spherical models. We adopted two methods to characterise the truncation point, which sets the limb of the star: the first (M1) uses the point where the derivative dI(r)/dr is at its maximum --- where I(r) is the specific intensity as a function of the normalised radius r --- corresponding to {mu}_cri_, and the second (M2) uses the midpoint between the point {mu}_cri_ and the point located at {mu}_cri-1_. The LDCs were computed adopting the Levenberg-Marquardt least-squares minimisation method, with a resolution of 900 equally spaced {mu} points, and covering 823 model atmospheres for a solar metallicity, effective temperatures of 2300 to 12000K, logg values from 0.0 to 6.0, and microturbulent velocities of 2km/s. As our previous calculations of LDCs using spherical models included only 100{mu} points, we also updated the calculations for the four-parameter law for the passbands listed above, and compared them with those from the power-2 law. Comparisons between the quality of the fits provided by the power-2 and four-parameter laws show that the latter presents a lower merit function, chi^2^, than the former for both cases (M1 and M2). This is important when choosing the best approach for a particular science goal., We computed LDCs for the power-2 law using specific intensities from spherical model atmospheres, as such results were only previously available for a small range of stellar parameters. To this end, we used the phoenix-cond models for Te values from 2300K to 12000K, log g values from 0.0 to 6.0, solar metallicity, V_{xi}_=2.0km/s, and with 900 {mu} points. We also computed LDCs for the four-parameter law, which supersede our previous calculations based on only 100 {mu} points. For both laws, we computed coefficients for the uvby, UBVRIJHK; and SDSS ugriz passbands, and for the Gaia, Kepler, TESS, and CHEOPS photometric systems., Financial support from the Severo Ochoa grant CEX2021-001131-S funded by MCIN/AEI/ 10.13039/501100011033, No

Radial velocities (RVs) measured from high-resolution stellar spectra are routinely used to detect and characterise orbiting exoplanet companions. The different lines present in stellar spectra are created by several species, which are non-uniformly affected by stellar variability features such as spots or faculae. Stellar variability distorts the shape of the spectral absorption lines from which precise RVs are measured, posing one of the main problems in the study of exoplanets. In this work we aim to study how the spectral lines present in M dwarfs are independently impacted by stellar activity. We use CARMENES optical spectra of six active early- and mid-type M dwarfs to compute line-by-line RVs and study their correlation with several well-studied proxies of stellar activity. We are able to classify spectral lines based on their sensitivity to activity in five M dwarfs displaying high levels of stellar activity. We further use this line classification to compute RVs with activity-sensitive lines and less sensitive lines, enhancing or mitigating stellar activity effects in the RV time series. For specific sets of the least activity-sensitive lines, the RV scatter decreases by ~2 to 5 times the initial one, depending on the star. Finally, we compare these lines in the different stars analysed, finding the sensitivity to activity to vary from star to star. Despite the high density of lines and blends present in M dwarf stellar spectra, we find that a line-by-line approach is able to deliver precise RVs. Line-by-line RVs are also sensitive to stellar activity effects, and allow for an accurate selection of activity- insensitive lines to mitigate activity effects in RV. However, we find stellar activity effects to vary in the same insensitive lines from star to star., Tables containing information about the sensitivity to activity of the different lines, one table for each of the six stars studied in this work. Each table includes the central wavelength of the line as measured in the spectral template used, the scatter of the line RV, and the Pearson's correlation coefficient R obtained for the correlation between the line RV and the three activity indicators considered (i.e. three different R values, one per indicator). We note that even though we use the term line, these 'lines' correspond to minima in the spectrum and are the result of blends of true atomic lines or features in molecular bands., Financial support from the Severo Ochoa grant CEX2021-001131-S funded by MCIN/AEI/ 10.13039/501100011033, No

Type Ia supernovae (SNe Ia) are thermonuclear explosions of degenerate white dwarf stars destabilized by mass accretion from a companion star, but the nature of their progenitors remains poorly understood. A way to discriminate between progenitor systems is through radio observations; a non-degenerate companion star is expected to lose material through winds or binary interaction before explosion, and the supernova ejecta crashing into this nearby circumstellar material should result in radio synchrotron emission. However, despite extensive efforts, no type Ia supernova (SN Ia) has ever been detected at radio wavelengths, which suggests a clean environment and a companion star that is itself a degenerate white dwarf star. Here we report on the study of SN 2020eyj, a SN Ia showing helium-rich circumstellar material, as demonstrated by its spectral features, infrared emission and, for the first time in a SN Ia to our knowledge, a radio counterpart. On the basis of our modelling, we conclude that the circumstellar material probably originates from a single-degenerate binary system in which a white dwarf accretes material from a helium donor star, an often proposed formation channel for SNe Ia. We describe how comprehensive radio follow-up of SN 2020eyj-like SNe Ia can improve the constraints on their progenitor systems., SN 2020eyj was first detected on 7 March 2020 UT (modified Julian date (MJD) = 58915.12, at RA=11:11:47.19, DE=29:23:06.5 (J2000). The SN was classified as a SN Ia based on a low-resolution spectrum obtained on 2 April 2020, 25 days after the first detection. We present optical photometry of SN 2020eyj in table 1., Financial support from the Severo Ochoa grant CEX2021-001131-S funded by MCIN/AEI/ 10.13039/501100011033, No

Light from celestial objects interacts with the molecules of the Earth's atmosphere, resulting in the production of telluric absorption lines in ground-based spectral data. Correcting for these lines, which strongly affect red and infrared wavelengths, is often needed in a wide variety of scientific applications. Here we present the template division telluric modeling (TDTM) technique, a method to accurately remove telluric absorption lines in stars that exhibit numerous intrinsic features. Based on the Earth's barycentric motion through the year, our approach is suited to disentangle telluric and stellar spectral components. By fitting a synthetic transmission model, telluric-free spectra are derived. We demonstrate the performance of the TDTM technique in correcting telluric contamination using a high-resolution optical spectral time series of the feature-rich M3.0 dwarf star Wolf 294 obtained with the CARMENES spectrograph. We apply the TDTM approach to the CARMENES survey sample, which consists of 382 targets encompassing 22357 optical and 20314 near-infrared spectra, to correct for telluric absorption. The corrected spectra are co-added to construct template spectra for each of our targets. This library of telluric-free, high signal-to-noise ratio (S/N), high-resolution (R>80000) templates comprises the most comprehensive collection of spectral M dwarf data available to date, both in terms of quantity and quality, and is available at the project's website., In Table C.1, we provide the list of stars included in the spectral template library, which features telluric-free, high S/N optical (VIS) and near-infrared (NIR) CARMENES spectra. The individual observations of each star have been corrected for telluric absorption lines using the TDTM technique. Subsequently, the individual spectra have been coadded to produce a high S/N template spectrum for each star. Details in Table C.1 include the the star identifier, coordinates, spectral type, J magnitude, the number of coadded spectra for each VIS and NIR template, and the S/N of each VIS and NIR template. The template spectra are accessible through the CARMENES GTO Data Archive (http://carmenes.cab.inta-csic.es)., Financial support from the Severo Ochoa grant CEX2021-001131-S funded by MCIN/AEI/ 10.13039/501100011033, No

We present an adapted version of the code HII-CHI-mistry-UV (Perez-Montero & Amorin, 2017MNRAS.467.1287P) to derive chemical abundances from emission lines in the ultraviolet, for use in narrow line regions (NLR) of Active Galactic Nuclei (AGN). We evaluate different ultraviolet emission line ratios and how different assumptions about the models, including the presence of dust grains, the shape of the incident spectral energy distribution, or the thickness of the gas envelope around the central source, may affect the final estimates as a function of the set of emission lines used. We compare our results with other published recipes for deriving abundances using the same emission lines and show that deriving the carbon-to-oxygen abundance ratio using CIII] {lambda}1909{AA} and OIII] {lambda}1665{AA} emission lines is a robust indicator of the metal content in AGN that is nearly independent of model assumptions, similar to the case of star-forming regions. Moreover, we show that a prior determination of C/O allows for a much more precise determination of the total oxygen abundance using carbon UV lines, as op- posed to assuming an arbitrary relationship between O/H and C/O, which can lead to non-negligible discrepancies., Table 2: List of UV fluxes for the sample of AGN and references. Table 3: Chemical abundances estimated from HCm-UV, using the grid of AGN models for alpha(OX)=-1.2 and the stopping criteria of 98% of free electrons. Dust-free or grain-included models are selected based on their C3C4 value., Financial support from the Severo Ochoa grant CEX2021-001131-S funded by MCIN/AEI/ 10.13039/501100011033, No

Quaoar is a classical trans-Neptunian object (TNO) with an area-equivalent diameter of 1100 km and an orbital semi-major axis of 43.3 astronomical units. Based on stellar occultations observed between 2018 and 2021, an inhomogeneous ring (Q1R, i.e., Quaoar's first ring) has been detected around this body. A new stellar occultation by Quaoar was observed on August 9, 2022, with the aim of improving Quaoar's shape models and the physical parameters of Q1R, while searching for additional material around the body. The occultation provided nine effective chords across Quaoar, pinning down its size, shape, and astrometric position. Large facilities, such as Gemini North and the Canada-France-Hawaii Telescope (CFHT), were used to obtain high acquisition rates and signal-to-noise ratios. The light curves were also used to characterize the Q1R ring (radial profiles and orbital elements). Quaoar's elliptical fit to the occultation chords yields the limb with an apparent semi-major axis of 579.5+/-4.0km, apparent oblateness of 0.12+/-0.01, and area-equivalent radius of 543+/-2km. Quaoar's limb orientation is consistent with Q1R and Weywot orbiting in Quaoar's equatorial plane. The orbital radius of Q1R is refined to a value of 4057+/-6km. The radial opacity profile of the more opaque ring profile follows a Lorentzian shape that extends over 60 km, with a full width at half maximum (FWHM) of ~5km and a peak normal optical depth of 0.4. Besides the secondary events related to the already reported rings, new secondary events detected during the August 2022 occultation in three different data sets are consistent with another ring around Quaoar with a radius of 2520+/-20km, assuming the ring is circular and co-planar with Q1R. This new ring has a typical width of 10km and a normal optical depth of ~0.004. Just as Q1R, it also lies outside Quaoar's classical Roche limit., Light flux of the occulted star plus the occulting object during the stellar occultation for each observer, also the best fitted model and their residuals. objects: ------------------------------------------------------------------- Planet Name H i e a mag deg AU ------------------------------------------------------------------- 50000 Quaoar 2.51 7.990425 0.04154574 43.64120180 -------------------------------------------------------------------, Financial support from the Severo Ochoa grant CEX2021-001131-S funded by MCIN/AEI/ 10.13039/501100011033, No

Because of its proximity and the large size of its black hole, M87 is one of the best targets for studying the launching mechanism of active galactic nucleus jets. Currently, magnetic fields are considered to be an essential factor in the launching and accelerating of the jet. However, current observational estimates of the magnetic field strength of the M87 jet are limited to the innermost part of the jet (<~100r_s_) or to HST-1 (~10^5^r_s_). No attempt has yet been made to measure the magnetic field strength in between. We aim to infer the magnetic field strength of the M87 jet out to a distance of several thousand r_s_ by tracking the distance-dependent changes in the synchrotron spectrum of the jet from high-resolution very long baseline interferometry observations. In order to obtain high-quality spectral index maps, quasi-simultaneous observations at 22 and 43GHz were conducted using the KVN and VERA Array (KaVA) and the Very Long Baseline Arra (VLBA). We compared the spectral index distributions obtained from the observations with a model and placed limits on the magnetic field strengths as a function of distance. The overall spectral morphology is broadly consistent over the course of these observations. The observed synchrotron spectrum rapidly steepens from alpha_22-43GHz_~-0.7 at ~2mas to alpha_22-43GHz_~-2.5 at ~6mas. In the KaVA observations, the spectral index remains unchanged until ~10mas, but this trend is unclear in the VLBA observations. A spectral index model in which nonthermal electron injections inside the jet decrease with distance can adequately reproduce the observed trend. This suggests the magnetic field strength of the jet at a distance of 2-10mas (~900r_s_~4500r_s_ in the deprojected distance) has a range of B=(0.3-1.0G)(z/2mas)^-0.73^. Extrapolating to the Event Horizon Telescope scale yields consistent results, suggesting that the majority of the magnetic flux of the jet near the black hole is preserved out to ~4500r_s_ without significant dissipation., VLBI CLEAN images of M87 in FITS format. This is a multi-epoch (Eight epochs for KaVA and five epochs for VLBA) and multi-frequency (22 and 43GHz) data set for reconstructing the spectral index profiles. When creating the FITS images, data within the (u, v) range of 33-170 mega-lambda has been used for KaVA, and 25-685 mega-lambda for VLBA. All images have been restored to the same beam size of 1.2masx1.2mas (for details, see Sect 3.1 of the paper)., Financial support from the Severo Ochoa grant CEX2021-001131-S funded by MCIN/AEI/ 10.13039/501100011033, No

The large amounts of astrophysical data being provided by existing and future instrumentation require efficient and fast analysis tools. Transfer learning is a new technique promising higher accuracy in the derived data products, with information from one domain being transferred to improve the accuracy of a neural network model in another domain. In this work, we demonstrate the feasibility of applying the deep transfer learning (DTL) approach to high-resolution spectra in the framework of photospheric stellar parameter determination. To this end, we used 14 stars of the CARMENES survey sample with interferometric angular diameters to calculate the effective temperature, as well as six M dwarfs that are common proper motion companions to FGK-type primaries with known metallicity. After training a deep learning (DL) neural network model on synthetic PHOENIX-ACES spectra, we used the internal feature representations together with those 14+6 stars with independent parameter measurements as a new input for the transfer process. We compare the derived stellar parameters of a small sample of M dwarfs kept out of the training phase with results from other methods in the literature. Assuming that temperatures from bolometric luminosities and interferometric radii and metallicities from FGK+M binaries are sufficiently accurate, DTL provides a higher accuracy than our previous state-of-the-art DL method (mean absolute differences improve by 20K for temperature and 0.2dex for metallicity from DL to DTL when compared with reference values from interferometry and FGK+M binaries). Furthermore, the machine learning (internal) precision of DTL also improves as uncertainties are five times smaller on average. These results indicate that DTL is a robust tool for obtaining M-dwarf stellar parameters comparable to those obtained from independent estimations for well-known stars., Teff and [M/H] values for CARMENES stars estimated by the DTL method., Financial support from the Severo Ochoa grant CEX2021-001131-S funded by MCIN/AEI/ 10.13039/501100011033, No

The formation process of fossil groups (FGs) is still under debate, and, due to the relative rarity of FGs, large samples of such objects are still missing. The aim of the present paper is to increase the sample of known FGs, and to analyse the properties of their brightest group galaxies (BGG) and compare them with a control sample of non-FG BGGs. Based on the large spectroscopic catalogue of haloes and galaxies publicly made available by Tinker, we extract a sample of 87 FG and 100 non-FG candidates. For all the objects with data available in UNIONS (initially the Canada France Imaging Survey, CFIS), in the u and r bands, and/or in an extra r-band processed to preserve all low surface brightness features (rLSB hereby), we made a 2D photometric fit of the BGG with GALFIT with one or two Sersic components. We also analysed how the subtraction of intracluster light contribution modifies the BGG properties. From the SDSS spectra available for the BGGs of 65 FGs and 82 non- FGs, we extracted the properties of their stellar populations with Firefly. To complement our study, we investigated the origin of the emission lines in a nearby FG, dominated by the NGC 4104 galaxy, to illustrate in detail the possible origin of emission lines in the FG BGGs, involving the presence or absence of an AGN. Morphologically, a single Sersic profile can fit most objects in the u band, while two Sersics are needed in the r and rLSB bands, both for FGs and non-FGs. Non-FG BGGs cover a larger range of Sersic index n. FG BGGs follow the Kormendy relation (mean surface brightness versus effective radius) previously derived for almost one thousand brightest cluster galaxies (BCGs) by Chu et al. (2022A&A...666A..54C) while non-FGs BGGs are in majority located below this relation, with fainter mean surface brightnesses. This suggests that FG BGGs have evolved similarly to BCGs, and non-FG BGGs have evolved differently from both FG BGGs and BCGs. All the above properties can be strongly modified by the subtraction of intracluster light contribution. Based on spectral fitting, the stellar populations of FG and non-FG BGGs do not differ significantly. The morphological properties and the Kormendy relation of FG and non-FG BGGs differ, suggesting they have had different formation histories. However, it is not possible to trace differences in their stellar populations or in their large scale distributions., The aim of this paper is to increase the number of known FGs to shed light on their formation process. Here, we increase the sample by 87 FG candidates confirmed spectroscopically, and with a high probability of being real FGs in view of their estimated large halo mass, though the confirmation of the X-ray condition on their X-ray luminosity (LX>10^42^erg/s) is still missing. For the FGs with UNIONS data available (35 in the u band, 25 in the r band and 19 in the rLSB band (r band treated with the Elixir-LSB software), we analyse the morphological properties of their brightest group galaxy (BGG), and compare these properties with those of a control sample of 30 non-FG BGGs., Financial support from the Severo Ochoa grant CEX2021-001131-S funded by MCIN/AEI/ 10.13039/501100011033, No

Studies indicate strong evidence of a scaling relation in the local Universe between the supermassive black hole mass (MBH) and the stellar mass of their host galaxies (M*). They even show similar histories across cosmic times of their differential terms: the star formation rate (SFR) and black hole accretion rate (BHAR). However, a clear picture of this coevolution is far from being understood. We selected an X-ray sample of active galactic nuclei (AGN) up to z=2.5 in the miniJPAS footprint. Their X-ray to infrared spectral energy distributions (SEDs) have been modeled with the CIGALE code, constraining the emission to 68 bands, from which 54 are the narrow filters from the miniJPAS survey. For a final sample of 308 galaxies, we derived their physical properties, such as their M*, SFR, star formation history (SFH), and the luminosity produced by the accretion process of the central BH (LAGN). For a subsample of 113 sources, we also fit their optical spectra to obtain the gas velocity dispersion from the broad emission lines and estimated the MBH. We calculated the BHAR in physical units depending on two radiative efficiency regimes. We find that the Eddington ratios (Edd) and its popular proxy (LX/M*) have a difference of 0.6dex, on average, and a KS test indicates that they come from different distributions. Our sources exhibit a considerable scatter on the M_BH_-M* scaling relation, which can explain the difference between Edd and its proxy. We also modeled three evolution scenarios for each source to recover the integral properties at z=0. Using the SFR and BHAR, we show a notable diminution in the scattering between M_BH_-M*. For the last scenario, we considered the SFH and a simple energy budget for the AGN accretion, and we retrieved a relation similar to the calibrations known for the local Universe. Our study covers 1deg^2^ in the sky and is sensitive to biases in luminosity. Nevertheless, we show that, for bright sources, the link between the differential values (SFR and BHAR) and their decoupling based on an energy limit is the key that leads to the local M_BH_-M* scaling relation. In the future, we plan to extend this methodology to a thousand degrees of the sky using JPAS with an X-ray selection from eROSITA, to obtain an unbiased distribution of BHAR and Eddington ratios., We present the sources and physical parameters derived from our work. The sources also have extra information, e.g., the magnitude in the r band and X-ray luminosities from literature. The physical parameters were obtained through a SED fitting with 68 bands, covering from X-ray to mid-IR. Black hole masses were obtained by fitting the broad line region of the source spectra and using the sigma-BH mass relation., Financial support from the Severo Ochoa grant CEX2021-001131-S funded by MCIN/AEI/ 10.13039/501100011033, No