arXiv subjects

Sergio Sánchez-Sanjuán

Publications and source records attributed to Sergio Sánchez-Sanjuán.

4 recordsLinked to original sources

arXiv2026

Massive stars in the SDSS-V survey: New O2 stars in the Large Magellanic Cloud

{O2 stars define the hottest end of the normal O-star sequence, but their identification requires blue-optical nitrogen diagnostics absent from many surveys.} {We reassess three luminous Large Magellanic Cloud (LMC) sources with multi-epoch Sloan Digital Sky Survey V (SDSS-V) spectroscopy obtained with the Baryon Oscillation Spectroscopic Survey (BOSS) spectrographs: \wsi, \lh, and \sk.} {We measure visit-resolved radial velocities and H, He, and N equivalent widths (EWs), compare robust combinations with LMC O2 templates at a common effective resolution, and use OSTAR2002 spectral energy distribution (SED) fits and a Gaia colour--magnitude diagram (CMD) as broad-band checks.} {The weighted $\log|{\rm EW}(\niv~\lambda4058)/{\rm EW}(\niii~\lambda4640)|$ values are $0.64\pm0.29$, $0.48\pm0.23$, and $0.34\pm0.44$ for \wsi, \lh, and \sk. The detection of \nv~$λ\lambda4604,4620$ supports the O2~If$^\ast$ and O2~V--III classifications adopted for \wsi\ and \lh, respectively. For \sk, the uncertain \niv/\niii\ ratio and non-detection of \nv\ motivate O2--3~V--III. Weak \hei~$\lambda4471$ may indicate unresolved later-type contamination in \wsi\ and \sk. The radial velocities of \sk\ show suggestive but non-significant variability. OSTAR2002 fits over 45--55~kK and the Gaia CMD place all three sources in the luminous very-early-O regime; \wsi\ shows a strong mid-infrared (MIR) excess, \lh\ is nearly photospheric, and \sk\ shows only a modest $3$--$8\,μ$m excess.} {The BOSS spectra add \wsi\ and \lh\ to the LMC very-early-O population and identify \sk\ as an additional O2--3 source. These cases show how incomplete blue coverage and ambiguous catalogue associations can conceal the hottest massive stars.}

astro-ph.SR↗

arXiv2026

TESSExtractor: A web-based interactive tool for light-curve visualisation and period estimation using TESS full-frame images

We present a user-friendly web application that allows users to extract, visualise, and interact with TESS light-curves (LCs) from full-frame images. The service works for any star identified in the TIC database or using stellar coordinates. TESSExtractor performs photometry using a circular aperture centred on the object of interest, with a sky annulus for background subtraction. The application also uses cotrending basis vectors provided by TESS to correct photometry for possible systematic effects. The Lomb-Scargle Periodogram is used to obtain periods from the LC. The TESSExtractor's website offers an intuitive interface for scientific and educational purposes and is publicly available at https://www.tessextractor.app. This tool simplifies the analysis of TESS LCs and provides valuable insight for researchers seeking to extract and analyse TESS data for a variety of scientific goals (e.g., stellar rotation, activity, transient detection, asteroseismology, or simply detection of planetary transits or stellar companions, among others). TESS provides insights into our understanding of time-domain astrophysics, and TESSExtractor provides an accessible and intuitive web interface for scientific exploitation of TESS data. We demonstrate that TESSExtractor produces LCs of sufficient quality for both quantitative and morphological time-domain studies.

astro-ph.IM↗

arXiv2026

Dynamical evolution and dissolution timescale of young stellar clusters in the Orion star-forming complex

We present a comprehensive analysis of the Orion star-forming complex (OSFC), combining structural, kinematic, and dynamical information to constrain the present-day state and future evolution of its stellar substructures. Using \textit{Gaia} DR3 astrometry and complementary radial velocities from high-resolution spectroscopic surveys, we derived three-dimensional velocity distributions and structural parameters for 13 young clusters. For the stellar component, we estimated a correction of the present-day mass function for observational incompleteness and calculated the virial state, $α_{\rm vir}$, finding that all clusters are supervirial. Direct $N$-body simulations initialized from the present-day global parameters and evolved for 300~Myr in a Galactic potential suggest a separation of the OSFC clusters into two regimes: seven clusters with $α_{\rm vir}\lesssim 7$ evolve in a Galactic-potential-regulated regime that retains a bound core for $\gtrsim 170$ Myr as long-lived open clusters, whereas six clusters with $α_{\rm vir}\gtrsim 7$ enter an internal-dynamics--dominated regime, dissolving before 120 Myr and rapidly populating the Galactic stellar field. For both regimes, a control test indicates negligible cluster--cluster interactions under current OSFC conditions. Finally, long-lived clusters show low-amplitude modulations in the bound fraction correlated with the Galactic vertical motion, consistent with disk-crossing tidal heating and the temporary recapture of marginal members. These results highlight the OSFC as a natural laboratory where heterogeneous initial conditions give rise to persistent open clusters and dispersing groups.

astro-ph.GA↗

arXiv2024

Kinematic study of the Orion Complex: Analysing the young stellar clusters from big and small structures

In this work, we analysed young stellar clusters with spatial and kinematic coherence in the Orion star-forming complex. For this study, we selected a sample of pre-main sequence candidates using parallaxes, proper motions and positions on the colour-magnitude diagram. After applying a hierarchical clustering algorithm in the 5D parameter space provided by Gaia DR3, we divided the recovered clusters into two regimes: Big Structures and Small Structures, defined by the number of detected stars per cluster. In the first regime, we found 13 stellar groups distributed along the declination axis in the regions where there is a high density of stars. In the second regime, we recovered 34 clusters classified into two types: 14 as small groups completely independent from the larger structures, including four candidates of new clusters, and 12 classified as sub-structures embedded within five larger clusters. Additionally, radial velocity data from APOGEE-2 and GALAH DR3 was included to study the phase space in some regions of the Orion complex. From the Big Structure regime, we found evidence of a general expansion in the Orion OB1 association over a common centre, giving a clue about the dynamical effects the region is undergoing. Likewise, in the Small Structure regime, the projected kinematics shows the ballistic expansion in the $λ$ Orionis association and the detection of likely events of clusters' close encounters in the OB1 association.

astro-ph.GA↗