arXiv subjects

Javier Osses

Publications and source records attributed to Javier Osses.

5 recordsLinked to original sources

arXiv2026

Hot water emission during an outburst in a classical T Tauri star

In this paper, we present observations of an eruptive young star in the Rosette Nebula, identified by the Gaia Science Alerts system using Gaia time series data. We aim to investigate the evolution of the brightness and mass accretion rate of V557 Mon throughout its outburst and subsequent decline. In addition, we trace the evolution of the inner accretion disk during the outburst by monitoring molecular emission features. We compiled multi-band photometric time series from Gaia, ZTF, and several 1 m-class ground-based telescopes and obtained optical and near-infrared spectra at multiple epochs covering the outburst and fading phases. Stellar parameters were derived from quiescent colour/spectra and spectral energy distribution (SED) fitting. We also measured the mass accretion rate and fit models to molecular emission bands. Since late 2024, V557 Mon has undergone a year-long outburst consistent with EXor variability. Based on quiescent photometry, V557 Mon has a spectral type of M1 with an extinction of AV = 1.8+_0.3 mag, consistent with a 0.4-0.5 M_sol star at an age of 2 Myr. Our multi-epoch spectra and u-band photometry indicate a peak accretion rate of 6.3x10^(-7)M_sol/yr during the outburst, roughly 70 times higher than in quiescence. We report the detection of hot water vapour emission bands, together with TiO, VO, and CO emission features. Using ExoMol models, we measured the inner-disk temperature changed from 3000 K to 2000 K during the fading phase of the outburst. We report a recent EXor outburst in a low-mass Class II YSO. Our observations reveal the transient formation of a hot molecular inner disk, traced by variable water vapour emission during the EXor event. A positive correlation is found between the molecular excitation temperature and the overall stellar brightness.

astro-ph.SR↗

arXiv2026

A Bayesian Search for Planet Engulfment Signatures in Solar Analogs

We present a systematic Bayesian search for chemical fingerprints of planet engulfment in 113 solar twins and analogs with high-precision abundance measurements, 45 of which host known or candidate planets or brown-dwarf companions. We constructed a Bayesian framework with three sets of abundance models: random scatter, Galactic chemical evolution, and planet engulfment with bulk Earth or CM chondrite compositions. Through model comparisons, we identified three candidates whose abundance patterns strongly favor planet engulfment over the alternatives, with inferred engulfed masses of about 7.5-33 Earth masses. Our findings correspond to a nominal detection rate of 1-3% for planet-engulfment signatures among solar analogs. This work extends abundance-based engulfment searches beyond the binary-star context and provides a framework for probing star-planet co-evolution with solar analogs, which goes beyond the commonly used abundance-condensation-temperature correlation (Tc slope).

astro-ph.EP↗

arXiv2026

Gaia24ccy: An outburst followed the footsteps of its predecessor

Accretion-driven outbursts in young stellar objects remain poorly understood, largely limited by a statistically small sample of closely followed-up events. This underscores the importance of a thorough exploration of each outbursting object. We studied a peculiar outbursting system, Gaia24ccy, which exhibited two $\Delta g \sim$ 3.8 mag outbursts in 2019 and 2024. The system consists of two unresolved, nearly identical, and rapidly rotating young stars: Gaia24ccy A (1.1419 days) and Gaia24ccy B (1.7898 days). Periodogram analyses just before the onset of the outbursts suggest Gaia24ccy B to be the outbursting component. Unlike any previously known EXor sources, the two outburst profiles show a very similar evolution: both rose at the same rate for the first 15 days, followed by many 'sub-bursts' on the timescale of 10-20 days. The 2019 outburst lasted 145-255 days, while the 2024 outburst persisted for 367 days. We infer the unstable region to lie at $r_{\rm trigger} \simeq 0.019-0.047$ au ($\sim5-12.3 R_\star$). The accreted mass per event $M_{\rm acc}\sim10^{-5} M_\odot$ can be provided by a compact inner-disk reservoir. The photometric rise/decay timescales and the mid-infrared color evolution favor a thermal-viscous trigger in a hot inner disk, while the appearance of rich emission-line spectra indicates concurrent magnetospheric compression - together best described by a hybrid picture. Finally, we explain the reddening of the mid-infrared color observed during the outburst as a consequence of the competing emission from the viscous disk and the photosphere.

astro-ph.SR↗

arXiv2025

VVV-WIT-13: an eruptive young star with cool molecular features

Here we investigate an infrared eruptive source, identified from the decade-long VISTA Variables in the Via Lactea survey (VVV). We named this target after a group of variable sources discovered by VVV, as VVV-WIT-13, with WIT standing for "What Is This?", due to its unique photometric variation behaviour and the mysterious origin of the outburst. This target exhibited an outburst with a 5.7 mag amplitude in the Ks-band, remained on its brightness plateau for 3.5 years, and then rapidly faded to its pre-eruptive brightness afterwards. We aim to reveal the variable nature and outburst origin of VVV-WIT-13 by presenting our follow-up photometric and spectroscopic observations along with theoretical models. We gathered photometric time series in both near- and mid-infrared wavelengths. We obtained near-infrared spectra during the outburst and decaying stages on XSHOOTER/VLT and FIRE/Magellan, and then fitted the detected molecular absorption features using models from ExoMol. We applied 2D numerical simulations to re-create the observables of the eruptive phenomenon. We observe deep AlO absorption bands in the infrared spectra of VVV-WIT-13, during the outburst stage, along with other more common absorption bands (e.g. CO). Our best-fit model suggests a 600 K temperature of the AlO absorption band. In the decaying stage, the AlO bands disappeared, whilst broad blue-shifted H2 lines arose, a common indicator of stellar wind and outflow. The observational evidence suggests that the CO and TiO features originate from an outflow or a wind environment. We find that VVV-WIT-13 is an eruptive young star with instability occurring in the accretion disk. One favoured theoretical explanation of this event is a disrupted gas clump at a distance of 3 au from the source. If confirmed, this would be the first such event observed in real time.

astro-ph.SR↗

arXiv2025

Young Stellar Objects in the Carina nebula: Near-Infrared variability and spectroscopy

We present a catalog of 652 young stellar objects (YSOs) in the Carina star-forming region. The catalog was constructed by combining near-infrared Ks-band variability from the VISTA Variables in the Via Lactea eXtended survey and medium-resolution H-band spectroscopy from APOGEE-2, Sloan Digital Sky Survey IV (SDSS-IV). Variability analysis of 6.35 million sources identified 606 variable stars. The classification of the spectral lines by semisupervised K-means clustering of 704 stars, refined through comparison with known catalogs in literature and visual inspection of the spectra, was performed. Combined with Ks variability, the final catalog contains three groups: Emission-line YSOs, Absorption-line YSOs, and Literature/Variable-identified YSOs. Cross validation with the Gaia DR3 proper motion and distance estimates supports Carina membership for 415 sources. The statistical characterization of YSO variability demonstrated that most Carina members (78%) exhibit variability patterns. Of these, 134 stars show emissions in their spectra, which is consistent with some accretion processes. Analysis of fundamental stellar parameters from StarHorse and Gaia DR3 reveals typical distributions of YSOs, dominated by low-mass 1-4 Msun, solar-metallicity stars with temperatures between 4000 and 6000K. Only a small fraction (4%) of the sources are more massive than 4 Msun, suggesting limited ongoing massive star formation in Carina. This well-characterized catalog also offers a robust training dataset for machine learning applications aimed at predicting YSO behavior.

astro-ph.SR↗