arXiv subjects

Sergi Blanco-Cuaresma

Publications and source records attributed to Sergi Blanco-Cuaresma.

At least 19 recordsLinked to original sources

arXiv2026

Gaia FGK Benchmark Stars: Impact of Spectral Resolution on Stellar Abundances

In the era of large Milky Way spectroscopic surveys, calibrating and standardizing stellar parameters and abundance measurements is crucial. The Gaia benchmark stars (GBS) are key references points characterized by well-defined parameters derived from fundamental relations independent of spectroscopy. We analyze 30 GBS with spectra data at three different resolutions. Our goal is to evaluate the impact of spectral resolution on the measurements of the stellar parameters and chemical abundances. We also present a line selection suitable for both metal-poor and metal-rich stars. We used R~190000 (R190), R~42000 (R42), R~28 000 (R28), and R190 degraded to R28 (R190-R28) spectral data to measure abundances with synthetic fitting and equivalent widths (EW) methods, testing the needed resolution to obtain consistent results. Our comparative analysis between R28 and R190-R28 shows that gaps in wavelength coverage can lead to discrepancies in the derived stellar parameters, particularly log g. These effects are not primarily driven by resolution, but rather by the limited spectral coverage and line availability. We find overall similar abundance, emphasizing the importance of line selection for spectroscopic studies. However, some elements (e.g, Ti II, Sc II) show larger discrepancies, possibly due to blending that becomes more pronounced as resolution decreases or is HFS-sensitive. Our comparative analysis shows that the abundances for Fe I, Ni I, Ti I, and Si I present less scatter across all resolutions, including R28. Our findings indicate that for some elements, synthetic fitting and the EW method give similar abundances, especially at the highest resolution. However, we also find that the highest resolution is not always essential for chemical abundance measurements. Our results provide practical guidelines for upcoming large surveys to reconstruct the chemical history of the Milky Way.

astro-ph.SR↗

arXiv2026

The high-altitude, inner-disc, and chemically peculiar open cluster UBC 1052

Out of all the discovered open clusters (OCs) that are located in the inner part of the Galaxy, only a small fraction has been observed with high-resolution spectroscopy. An intriguing population of inner-disc OCs at relatively high altitudes ($Z$) from the Galactic plane remains poorly studied. There are few reliable detections of such OCs, and their occurrence rate, dynamical origin and survival mechanism remain uncertain. We perform a detailed spectroscopic analysis of UBC 1052, located at a cylindrical galactocentric radius $R_{GC} = 6.1$ kpc and $Z = 340$ pc, which stands out as the oldest and highest-|$Z$| inner-disc OC studied at high resolution to date. We used FLAMES/VLT to acquire high signal-to-noise ratio UVES spectra of four red clump (RC) members ($G\sim14$ mag). From them we derived high-precision radial velocities ($v_{r}$) and local thermodynamic equilibrium chemical abundances for 23 elements through a strict line-by-line differential analysis, achieving a median precision in [X/H] of $\simeq0.06$ dex for each star. The four RC stars have fully compatible chemical abundances, with [X/H] dispersions among them <$0.03$ dex for 20 elements. We also acquired GIRAFFE spectra of other candidate members and derived their $v_{r}$. We find that UBC 1052 has an age of $2.25\pm0.25$ Gyr, a distance of $3.11\pm0.07$ kpc, an extinction $A_{V} =1.23$ mag, a mean radial velocity of $34.0\pm0.6$ $km$ ${s}^{-1}$, and a slightly super-solar [Fe/H] = $0.05\pm0.01$ dex. Such relatively low [Fe/H] at its $R_{GC}$ suggests that UBC 1052 is a rare candidate for an inward-migrated OC in the inner disc. Its detailed abundance pattern (e.g. [Ba/Zr] and [Nd/Y]) shows some interesting features that appear to be unique in the current census of OCs studied at high resolution, making it an interesting object for potential strong chemical-tagging searches for already dispersed member stars. [Abridged]

astro-ph.GA↗

arXiv2026

AstroConcepts: A Large-Scale Multi-Label Classification Corpus for Astrophysics

Scientific multi-label text classification suffers from extreme class imbalance, where specialized terminology exhibits severe power-law distributions that challenge standard classification approaches. Existing scientific corpora lack comprehensive controlled vocabularies, focusing instead on broad categories and limiting systematic study of extreme imbalance. We introduce AstroConcepts, a corpus of English abstracts from 21,702 published astrophysics papers, labeled with 2,367 concepts from the Unified Astronomy Thesaurus. The corpus exhibits severe label imbalance, with 76% of concepts having fewer than 50 training examples. By releasing this resource, we enable systematic study of extreme class imbalance in scientific domains and establish strong baselines across traditional, neural, and vocabulary-constrained LLM methods. Our evaluation reveals three key patterns that provide new insights into scientific text classification. First, vocabulary-constrained LLMs achieve competitive performance relative to domain-adapted models in astrophysics classification, suggesting a potential for parameter-efficient approaches. Second, domain adaptation yields relatively larger improvements for rare, specialized terminology, although absolute performance remains limited across all methods. Third, we propose frequency-stratified evaluation to reveal performance patterns that are hidden by aggregate scores, thereby making robustness assessment central to scientific multi-label evaluation. These results offer actionable insights for scientific NLP and establish benchmarks for research on extreme imbalance.

cs.CL↗

arXiv2025

Survival of satellites during the migration of a Hot Jupiter

We investigate the origin and stability of extrasolar satellites orbiting close-in gas giants, focusing on whether these satellites can survive planetary migration within a protoplanetary disk. To address this question, we used Posidonius, an N-Body code with an integrated tidal model, which we expanded to account for the migration of a gas giant within a disk. Our simulations include tidal interactions between a $1M_\odot$ star and a $1M_{Jup}$ planet, as well as between the planet and its satellite, while neglecting tides raised by the star on the satellite. We adopt a standard equilibrium tide model for the satellite, planet, and star, and additionally explore the impact of dynamical tides in the convective regions of both the star and planet on satellite survival. We examine key parameters, including the initial satellite-planet distance, disk lifetime (proxy for the planet's final orbital distance), satellite mass, and satellite tidal dissipation. For simulations incorporating dynamical tides, we explore three different initial stellar rotation periods. We find that satellite survival is rare if the satellite has nonzero tidal dissipation. Survival is only possible for initial orbital distances of at least 0.6 times the Jupiter-Io separation and for planets orbiting beyond about 0.1 AU. Satellites that fail to survive are either 1) tidally disrupted, as they experience orbital decay and cross the Roche limit, or 2) dynamically disrupted, where eccentricity excitation drives their periastron within the Roche limit. Satellite survival is more likely for low tidal dissipation and higher satellite mass. Given that satellites around close-in planets appear unlikely to survive planetary migration, our findings suggest that if such satellites do exist, another process should be invoked. In that context, we also discuss the claim of the existence of a putative satellite around WASP-49 A b.

astro-ph.EP↗

arXiv2024

INDUS: Effective and Efficient Language Models for Scientific Applications

Large language models (LLMs) trained on general domain corpora showed remarkable results on natural language processing (NLP) tasks. However, previous research demonstrated LLMs trained using domain-focused corpora perform better on specialized tasks. Inspired by this insight, we developed INDUS, a comprehensive suite of LLMs tailored for the closely-related domains of Earth science, biology, physics, heliophysics, planetary sciences and astrophysics, and trained using curated scientific corpora drawn from diverse data sources. The suite of models include: (1) an encoder model trained using domain-specific vocabulary and corpora to address NLP tasks, (2) a contrastive-learning based text embedding model trained using a diverse set of datasets to address information retrieval tasks and (3) smaller versions of these models created using knowledge distillation for applications which have latency or resource constraints. We also created three new scientific benchmark datasets, CLIMATE-CHANGE NER (entity-recognition), NASA-QA (extractive QA) and NASA-IR (IR) to accelerate research in these multi-disciplinary fields. We show that our models outperform both general-purpose (RoBERTa) and domain-specific (SCIBERT) encoders on these new tasks as well as existing tasks in the domains of interest. Furthermore, we demonstrate the use of these models in two industrial settings -- as a retrieval model for large-scale vector search applications and in automatic content tagging systems.

cs.CL↗

arXiv2024

Drifts of the sub-stellar points of the TRAPPIST-1 planets

Accurate modeling of tidal interactions is crucial for interpreting recent JWST observations of the thermal emissions of TRAPPIST-1~b and c and for characterizing the surface conditions and potential habitability of the other planets in the system. Indeed, the rotation state of the planets, driven by tidal forces, significantly influences the heat redistribution regime. Due to their proximity to their host star and the estimated age of the system, the TRAPPIST-1 planets are commonly assumed to be in a synchronization state. In this work, we present the recent implementation of the co-planar tidal torque and forces equations within the formalism of Kaula in the N-body code Posidonius. This enables us to explore the hypothesis of synchronization using a tidal model well suited to rocky planets. We studied the rotational state of each planet by taking into account their multi-layer internal structure computed with the code Burnman. Simulations show that the TRAPPIST-1 planets are not perfectly synchronized but oscillate around the synchronization state. Planet-planet interactions lead to strong variations on the mean motion and tides fail to keep the spin synchronized with respect to the mean motion. As a result, the sub-stellar point of each planet experiences short oscillations and long-timescale drifts that lead the planets to achieve a synodic day with periods varying from $55$~years to $290$~years depending on the planet.

astro-ph.EP↗

arXiv2024

VELOcities of CEpheids (VELOCE) I. High-precision radial velocities of Cepheids

This first VELOCE data release comprises 18,225 high-precision RV measurements of 258 bona fide classical Cepheids on both hemispheres collected mainly between 2010 and 2022, alongside 1161 additional observations of 164 other stars. The median per-observation RV uncertainty is 0.037 km/s, and some reach 0.002 km/s. Non-variable standard stars characterize RV zero-point stability and provide a base for future cross-calibrations. We determined zero-point differences between VELOCE and 31 literature data sets using template fitting and measured linear period changes of 146 Cepheids. Seventy six spectroscopic binary Cepheids and 14 candidates are identified using VELOCE data alone and are investigated in detail in a companion paper (VELOCE II). Several new insights into Cepheid pulsations were obtained, including: a) the most detailed description of the Hertzsprung progression by RVs; b) the identification of double-peaked bumps in the RV curve; c) clear evidence that virtually all Cepheids feature spectroscopic variability signals that lead to modulated RV variability. We identified 36 such stars, of which 4 also exhibit orbital motion. Linear radius variations depend strongly on pulsation period and a steep increase in slope of the $Δ$R/p versus logP-relation is found near 10d, challenging the existence of a tight relation between Baade-Wesselink projection factors and pulsation periods. We investigated the accuracy of RV time series measurements, v$_γ$, and RV amplitudes published in Gaia's DR3 and determined an average offset of 0.65 \pm 0.11 km/s relative to VELOCE. We recommend adopting a single set of template correlation parameters for distinct classes of large-amplitude variable stars to avoid systematic offsets in v$_γ$ among stars belonging to the same class. Peak-to-peak amplitudes of Gaia RVs exhibit significant (16%) dispersion compared to VELOCE. [abridged]

astro-ph.SR↗

arXiv2024

Psychological Assessments with Large Language Models: A Privacy-Focused and Cost-Effective Approach

This study explores the use of Large Language Models (LLMs) to analyze text comments from Reddit users, aiming to achieve two primary objectives: firstly, to pinpoint critical excerpts that support a predefined psychological assessment of suicidal risk; and secondly, to summarize the material to substantiate the preassigned suicidal risk level. The work is circumscribed to the use of "open-source" LLMs that can be run locally, thereby enhancing data privacy. Furthermore, it prioritizes models with low computational requirements, making it accessible to both individuals and institutions operating on limited computing budgets. The implemented strategy only relies on a carefully crafted prompt and a grammar to guide the LLM's text completion. Despite its simplicity, the evaluation metrics show outstanding results, making it a valuable privacy-focused and cost-effective approach. This work is part of the Computational Linguistics and Clinical Psychology (CLPsych) 2024 shared task.

cs.CL↗

arXiv2023

Experimenting with Large Language Models and vector embeddings in NASA SciX

Open-source Large Language Models enable projects such as NASA SciX (i.e., NASA ADS) to think out of the box and try alternative approaches for information retrieval and data augmentation, while respecting data copyright and users' privacy. However, when large language models are directly prompted with questions without any context, they are prone to hallucination. At NASA SciX we have developed an experiment where we created semantic vectors for our large collection of abstracts and full-text content, and we designed a prompt system to ask questions using contextual chunks from our system. Based on a non-systematic human evaluation, the experiment shows a lower degree of hallucination and better responses when using Retrieval Augmented Generation. Further exploration is required to design new features and data augmentation processes at NASA SciX that leverages this technology while respecting the high level of trust and quality that the project holds.

cs.CL↗

arXiv2022

Improving astroBERT using Semantic Textual Similarity

The NASA Astrophysics Data System (ADS) is an essential tool for researchers that allows them to explore the astronomy and astrophysics scientific literature, but it has yet to exploit recent advances in natural language processing. At ADASS 2021, we introduced astroBERT, a machine learning language model tailored to the text used in astronomy papers in ADS. In this work we: - announce the first public release of the astroBERT language model; - show how astroBERT improves over existing public language models on astrophysics specific tasks; - and detail how ADS plans to harness the unique structure of scientific papers, the citation graph and citation context, to further improve astroBERT.

cs.CL↗

arXiv2022

Web accessibility trends and implementation in dynamic web applications

The NASA Astrophysics Data System (ADS), a critical research service for the astrophysics community, strives to provide the most accessible and inclusive environment for the discovery and exploration of the astronomical literature. Part of this goal involves creating a digital platform that can accommodate everybody, including those with disabilities that would benefit from alternative ways to present the information provided by the website. NASA ADS follows the official Web Content Accessibility Guidelines (WCAG) standard for ensuring accessibility of all its applications, striving to exceed this standard where possible. Through the use of both internal audits and external expert review based on these guidelines, we have identified many areas for improving accessibility in our current web application, and have implemented a number of updates to the UI as a result of this. We present an overview of some current web accessibility trends, discuss our experience incorporating these trends in our web application, and discuss the lessons learned and recommendations for future projects.

cs.HC↗

arXiv2021

Building astroBERT, a language model for Astronomy & Astrophysics

The existing search tools for exploring the NASA Astrophysics Data System (ADS) can be quite rich and empowering (e.g., similar and trending operators), but researchers are not yet allowed to fully leverage semantic search. For example, a query for "results from the Planck mission" should be able to distinguish between all the various meanings of Planck (person, mission, constant, institutions and more) without further clarification from the user. At ADS, we are applying modern machine learning and natural language processing techniques to our dataset of recent astronomy publications to train astroBERT, a deeply contextual language model based on research at Google. Using astroBERT, we aim to enrich the ADS dataset and improve its discoverability, and in particular we are developing our own named entity recognition tool. We present here our preliminary results and lessons learned.

cs.CL↗

arXiv2021

On the influence of equilibrium tides on transit-timing variations of close-in super-Earths. I. Application to single-planet systems and the case of K2-265 b

In this work, we investigate the influence of planetary tidal interactions on the transit-timing variations of short-period low-mass rocky exoplanets. For such purpose, we employ the recently-developed creep tide theory to compute tidally-induced TTVs. We implement the creep tide in the recently-developed Posidonius N-body code, thus allowing for a high-precision evolution of the coupled spin-orbit dynamics of planetary systems. As a working example for the analyses of tidally-induced TTVs, we apply our version of the code to the K2-265 b planet. We analyse the dependence of tidally-induced TTVs with the planetary rotation rate, uniform viscosity coefficient and eccentricity. Our results show that the tidally-induced TTVs are more significant in the case where the planet is trapped in non-synchronous spin-orbit resonances, in particular the 3/2 and 2/1 spin-orbit resonant states. An analysis of the TTVs induced separately by apsidal precession and tidally-induced orbital decay has allowed for the conclusion that the latter effect is much more efficient at causing high-amplitude TTVs than the former effect by 2 - 3 orders of magnitude. We compare our findings for the tidally-induced TTVs obtained with Posidonius with analytical formulations for the transit timings used in previous works, and verified that the results for the TTVs coming from Posidonius are in excellent agreement with the analytical formulations. These results show that the new version of Posidonius containing the creep tide theory implementation can be used to study more complex cases in the future. For instance, the code can be used to study multiplanetary systems, in which case planet-planet gravitational perturbations must be taken into account additionally to tidal interactions to obtain the TTVs.

astro-ph.EP↗

arXiv2021

TOI-257b (HD 19916b): A Warm sub-Saturn Orbiting an Evolved F-type Star

We report the discovery of a warm sub-Saturn, TOI-257b (HD 19916b), based on data from NASA's Transiting Exoplanet Survey Satellite (TESS). The transit signal was detected by TESS and confirmed to be of planetary origin based on radial velocity observations. An analysis of the TESS photometry, the Minerva-Australis, FEROS, and HARPS radial velocities, and the asteroseismic data of the stellar oscillations reveals that TOI-257b has a mass of $M_P=0.138\pm0.023$\,$\rm{M_J}$ ($43.9\pm7.3$\,$M_{\rm \oplus}$), a radius of $R_P=0.639\pm0.013$\,$\rm{R_J}$ ($7.16\pm0.15$\,$R_{\rm \oplus}$), bulk density of $0.65^{+0.12}_{-0.11}$ (cgs), and period $18.38818^{+0.00085}_{-0.00084}$\,$\rm{days}$. TOI-257b orbits a bright ($\mathrm{V}=7.612$\,mag) somewhat evolved late F-type star with $M_*=1.390\pm0.046$\,$\rm{M_{\odot}}$, $R_*=1.888\pm0.033$\,$\rm{R_{\odot}}$, $T_{\rm eff}=6075\pm90$\,$\rm{K}$, and $v\sin{i}=11.3\pm0.5$\,km\,s$^{-1}$. Additionally, we find hints for a second non-transiting sub-Saturn mass planet on a $\sim71$\,day orbit using the radial velocity data. This system joins the ranks of a small number of exoplanet host stars ($\sim100$) that have been characterized with asteroseismology. Warm sub-Saturns are rare in the known sample of exoplanets, and thus the discovery of TOI-257b is important in the context of future work studying the formation and migration history of similar planetary systems.

astro-ph.EP↗

arXiv2021

Determination of spectroscopic parameters for 313 M dwarf stars from their APOGEE Data Release 16 H-band spectra

The scientific community's interest on the stellar parameters of M dwarfs has been increasing over the last few years, with potential applications ranging from galactic characterization to exoplanet detection. The main motivation for this work is to develop an alternative and objective method to derive stellar parameters for M dwarfs using the H-band spectra provided by the Apache Point Observatory Galactic Evolution Experiment (APOGEE). Synthetic spectra generated with \textit{iSpec}, \textit{Turbospectrum}, \textit{MARCS} models atmospheres and a custom made line list including over 1 000 000 water lines, are compared to APOGEE observations, and parameters are determined through $χ^2$ minimization. Spectroscopic parameters ($T_\mathrm{eff}$, $[M/H]$, $\log g$, $v_{mic}$) are presented for a sample of 313 M dwarfs, obtained from their APOGEE H-band spectra. The generated synthetic spectra reproduce observed spectra to a high accuracy level. The impact of the spectra normalization on the results are analyzed as well. Our output parameters are compared with the ones obtained with APOGEE Stellar Parameter and Chemical Abundances Pipeline (ASPCAP) for the same stellar spectrum, and we find that the values agree within the expected uncertainties. Comparisons with other previous near-infrared and optical literature are also available, with median differences within our estimated uncertainties found in most cases. Possible reasons for these differences are explored. The full H-band line list, the line selection for the synthesis, and the synthesized spectra are available for download, as are the calculated stellar parameters.

astro-ph.SR↗

arXiv2020

Agile methodologies in teams with highly creative and autonomous members

The Agile manifesto encourages us to value individuals and interactions over processes and tools, while Scrum, the most adopted Agile development methodology, is essentially based on roles, events, artifacts, and the rules that bind them together (i.e., processes). Moreover, it is generally proclaimed that whenever a Scrum project does not succeed, the reason is because Scrum was not implemented correctly and not because Scrum may have its own flaws. This grants irrefutability to the methodology, discouraging deviations to fit the actual needs and peculiarities of the developers. In particular, the members of the NASA ADS team are highly creative and autonomous whose motivation can be affected if their freedom is too strongly constrained. We present our experience following Agile principles, reusing certain Scrum elements and seeking the satisfaction of the team members, while rapidly reacting/keeping the project in line with our stakeholders expectations.

cs.SE↗

arXiv2020

On the impact of tides on the transit-timing fits to the TRAPPIST-1 system

Transit Timing Variations, or TTVs, can be a very efficient way of constraining masses and eccentricities of multi-planet systems. Recent measurements of the TTVs of TRAPPIST-1 led to an estimate of the masses of the planets, enabling an estimate of their densities. A recent TTV analysis using data obtained in the past two years yields a 34% and 13% increase in mass for TRAPPIST-1b and c, respectively. In most studies to date, a Newtonian N-body model is used to fit the masses of the planets, while sometimes general relativity is accounted for. Using the Posidonius N-body code, we show that in the case of the TRAPPIST-1 system, non-Newtonian effects might be also relevant to correctly model the dynamics of the system and the resulting TTVs. In particular, using standard values of the tidal Love number $k_2$ (accounting for the tidal deformation) and the fluid Love number $k_{2f}$ (accounting for the rotational flattening) leads to differences in the TTVs of TRAPPIST-1b and c similar to the differences caused by general relativity. We also show that relaxing the values of tidal Love number $k_2$ and the fluid Love number $k_{2f}$ can lead to TTVs which differ by as much as a few 10~s on a $3-4$-year timescale, which is a potentially observable level. The high values of the Love numbers needed to reach observable levels for the TTVs could be achieved for planets with a liquid ocean, which, if detected, might then be interpreted as a sign that TRAPPIST-1b and TRAPPIST-1c could have a liquid magma ocean. For TRAPPIST-1 and similar systems, the models to fit the TTVs should potentially account for general relativity, for the tidal deformation of the planets, for the rotational deformation of the planets and, to a lesser extent, for the rotational deformation of the star, which would add up to 7x2+1 = 15 additional free parameters in the case of TRAPPIST-1.

astro-ph.EP↗

arXiv2020

Derivation of parameters for 3748 FGK stars using H-band spectra from APOGEE Data Release 14

The Apache Point Observatory Galactic Evolution Experiment (APOGEE) has observed the H-band spectra of over 200 000 stars with $R\sim22 000$. The main motivation for this work is to test an alternative method to the standard APOGEE pipeline (APOGEE Stellar Parameter and Chemical Abundances Pipeline, ASPCAP) to derive parameters in the Near-InfraRed (NIR) for FGK dwarfs. \textit{iSpec} and \textit{Turbospectrum} are used to generate synthetic spectra matching APOGEE observations and to determine the parameters through $χ^2$ minimization. We present spectroscopic parameters ($T_\mathrm{eff}$, $[M/H]$, $\log g$, $v_{mic}$) for a sample of 3748 main-sequence and subgiant FGK stars, obtained from their APOGEE H-band spectra We compare our output parameters with the ones obtained with ASPCAP for the same stellar spectra, and find that the values agree within the expected uncertainties. A comparison with the optical samples California Planet Survey, HARPS-GTO (High Accuracy Radial Velocity Planet Searcher - Guaranteed Time Observations), and PASTEL, is also available, and median differences below 10 K for $T_\mathrm{eff}$ and 0.2 dex for $[M/H]$ are found. Reasons for these differences are explored. The full H-band line-list, the line selection for the synthesis and the synthesized spectra are available for download, as well as the calculated parameters and their estimated uncertainties.

astro-ph.SR↗