arXiv subjects

Victor Almendros-Abad

Publications and source records attributed to Victor Almendros-Abad.

7 recordsLinked to original sources

arXiv2026

Tracing star formation across the Rosette nebula using deep Spitzer imaging

We present a deep large-scale infrared survey of young stellar objects in the Rosette Nebula. Our analysis is based on stacked archival Spitzer/IRAC images. The images have been treated with the software DeNeb to remove nebulous emission. Our catalogue contains ~20000 sources with photometry in all 4 IRAC bands from 3.6 to 8.0 microns, complemented with near-infrared and optical data. From this database, we identify YSOs using multi-filter colour-colour criteria. We select 1528 YSOs, from which 1303 are Class II and 225 are Class I. Using this sample, we compile a list of clusters and groups of YSOs in the Rosette region, including previously known ones, plus three newly identified groups. Using our census of YSOs, in combination with the literature, we derive the Class I ratios and disk fractions for clusters in the nebula. The main clusters in the central cavity, NGC 2244 and NGC 2237 are almost devoid of Class I sources, indicating that star formation has ceased in this area. On the other hand, in an annulus around the centre with radii of 11-16 pc, roughly coinciding with the expanding HII front, about 30% of the YSOs are Class I, a clear sign of ongoing star formation. Other groups further out in the cloud also exhibit a high Class I ratio. Similar patterns are seen in the disk fractions. Our results are consistent with possible triggering by the expanding HII region, combined with star formation beyond the ionisation front.

astro-ph.SR↗

arXiv2026

X-shooter survey Across Regions and Ages to probe Disk Evolution (ARADE): Accretion properties in Orion A and their relation with disk masses

We present a homogeneous VLT/X-Shooter study of accretion in young stellar objects spanning the entire Orion A complex. Our sample includes 91 pre-main-sequence stars hosting a protoplanetary disk according to Spitzer photometry, of which 34 have complementary ALMA dust mass measurements. We derived stellar and accretion properties using a self-consistent multi-component fitting procedure. Our sample encompasses spectral types from K3 down to M5, corresponding to stellar masses within $\sim$0.8-0.1 $M_{\odot}$. The accretion-stellar luminosity ($L_{acc}-L_{\star}$) and the mass accretion rate-stellar mass ($\dot{M}_{acc}-M_{\star}$) scaling relations in Orion A are consistent with those of other star-forming regions (SFRs) that span a range of stellar densities, far-ultraviolet (FUV) irradiation fields, and ages, with all regions occupying the same locus in parameter space. For the 34 sources with complementary dust mass measurements, we present the first investigation of the $\dot{M}_{acc}$ and disk mass ($M_{disk}$) correlation in Orion A, recovering a spread consistent with that reported for other regions. Despite our sample spanning nearly five orders of magnitude in local FUV field strength, we find no statistically significant correlation between $\dot{M}_{acc}$ and FUV irradiation. However, by combining our sample with literature measurements in Lupus, the Orion Nebula Cluster, and $σ$ Orionis, we find a tentative population-level decrease of the inferred disk lifetime $t_{\rm disk} =M_{disk}/\dot{M}_{acc}$ toward stronger FUV environments, though large intrinsic scatter and limited sample sizes at intermediate and high FUV fields prevent firm conclusions. The homogeneous $\dot{M}_{acc}$ measurements reported here provide a solid foundation for future studies of accretion and disk evolution across the diverse environments of Orion A and other SFRs.

astro-ph.SR↗

arXiv2025

Internal dynamics and structure of Cepheus OB4. The asymmetric expansion of Berkeley 59

Accurate measurements of young stellar cluster internal dynamics provide crucial insights into their formation. With Gaia, we are now able to trace stellar motions and study the dynamics of star clusters with unprecedented precision, but this requires a reliable list of probable members. We examine a 2 deg-radius region in Cepheus OB4, centered on the young cluster Berkeley 59, to build a reliable candidate member list, enabling the study of the cluster's structure, kinematics, and stellar population. We compiled a catalog of optical and near-infrared photometry, along with precise positions and proper motions from Gaia DR3, for sources in the Cepheus OB4 field. Membership probabilities were determined using a probabilistic random forest algorithm and further refined by requiring HR diagram positions consistent with a young age. From a list of 1030 probable members, we estimate a distance of 1009+-12 pc to Berkeley 59. Masses, extinction, and ages were derived by fitting the spectral energy distributions to atmospheric and evolutionary models, while internal dynamics was analyzed using proper motions relative to the cluster's mean motion. Berkeley 59 exhibits an asymmetric expansion pattern with velocity increasing outward and a preferred motion toward the north. The IMF between 0.4 and 7 MSun follows a single power law (dN/dM \propto M**-alpha), with the slope alpha=2.3+-0.3, consistent with Salpeter's slope and previous studies in the region. The region's median age, estimated from the HR diagram, is 2.9 Myr. The velocity dispersion of Berkeley 59 exceeds the virial velocity dispersion derived from its total mass (650+-30 MSun) and half-mass radius (1.71+-0.13 pc). The 2D motions of a stellar group located about 1 deg north of Berkeley 59 provide further support for the previously proposed triggered star formation scenario. (Abridged)

astro-ph.SR↗

arXiv2024

Variability in SSTc2d J163134.1-240100, a brown dwarf with quasi-spherical mass loss

We report on a search for variability in the young brown dwarf SST1624 (~M7 spectral type, M~0.05Msol), previously found to feature an expanding gaseous shell and to undergo quasi-spherical mass loss. We find no variability on timescales of 1-6hours. Specifically, on these timescales, we rule out the presence of a period with amplitude >1%. A photometric period in that range would have been evidence for either pulsation powered by Deuterium burning or rotation near breakup. However, we see a 3% decrease in the K-band magnitude between two consecutive observing nights (a 10sigma result). There is also clear evidence for variations in the WISE lightcurves at 3.6 and 4.5 microns on timescales of days, with a tentative period of about 6d (with a plausible range between 3 and 7d). The best explanation for the variations over days is rotational modulation due to spots. These results disfavour centrifugal winds driven by fast rotation as mechanism for the mass loss, which, in turn, makes the alternative scenario -- a thermal pulse due to Deuterium burning -- more plausible.

astro-ph.SR↗

arXiv2023

Disks around young planetary-mass objects: Ultradeep Spitzer imaging of NGC1333

We report on a sensitive infrared search for disks around isolated young planetary-mass objects (PMOs) in the NGC1333 cluster, by stacking 70 Spitzer/IRAC frames at 3.6 and 4.5$\,μm$. Our co-added images go >2.3 mag deeper than single-epoch frames, and cover 50 brown dwarfs, 15 of which have M9 or later spectral types. Spectral types >M9 correspond to masses in the giant planet domain, i.e., near or below the Deuterium-burning limit of 0.015 Msol. Five of the 12 PMOs show definitive evidence of excess, implying a disk fraction of 42%, albeit with a large statistical uncertainty given the small sample. Comparing with measurements for higher-mass objects, the disk fraction does not decline substantially with decreasing mass in the sub-stellar domain, consistent with previous findings. Thus, free-floating PMOs have the potential to form their own miniature planetary systems. We note that only one of the six lowest-mass objects in NGC1333, with spectral type L0 or later, has a confirmed disk. Reviewing the literature, we find that the lowest mass free-floating objects with firm disk detections have masses ~0.01 Msol (or ~10 MJup). It is not clear yet whether even lower mass objects harbor disks. If not, it may indicate that ~10 MJup is the lower mass limit for objects that form like stars. Our disk detection experiment on deep Spitzer images paves the way for studies with JWST at longer wavelengths and higher sensitivity, which will further explore disk prevalence and formation of free-floating PMOs.

astro-ph.SR↗

arXiv2022

Stellar population of the Rosette Nebula and NGC 2244: application of the probabilistic random forest

(Abridged) In this work, we study the 2.8x2.6 deg2 region in the emblematic Rosette Nebula, centred at the young cluster NGC 2244, with the aim of constructing the most reliable candidate member list to date, determining various structural and kinematic parameters, and learning about the past and the future of the region. Starting from a catalogue containing optical to mid-infrared photometry, as well as positions and proper motions from Gaia EDR3, we apply the Probabilistic Random Forest algorithm and derive membership probability for each source. Based on the list of almost 3000 probable members, of which about a third are concentrated within the radius of 20' from the centre of NGC 2244, we identify various clustered sources and stellar concentrations, and estimate the average distance of 1489+-37 pc (entire region), 1440+-32 pc (NGC 2244) and 1525+-36 pc (NGC 2237). The masses, extinction, and ages are derived by SED fitting, and the internal dynamic is assessed via proper motions relative to the mean proper motion of NGC 2244. NGC 2244 is showing a clear expansion pattern, with an expansion velocity that increases with radius. Its IMF is well represented by two power laws (dN/dM\propto M^{-α}), with slopes α= 1.05+-0.02 for the mass range 0.2 - 1.5 MSun, and α= 2.3+-0.3 for the mass range 1.5 - 20 MSun, in agreement with other star forming regions. The mean age of the region is ~2 Myr. We find evidence for the difference in ages between NGC 2244 and the region associated with the molecular cloud, which appears slightly younger. The velocity dispersion of NGC 2244 is well above the virial velocity dispersion derived from the total mass (1000+-70 MSun) and half-mass radius (3.4+-0.2 pc). From the comparison to other clusters and to numerical simulations, we conclude that NGC 2244 may be unbound, and possibly even formed in a super-virial state.

astro-ph.GA↗

arXiv2022

Discovery of a brown dwarf with quasi-spherical mass-loss

We report the serendipitous discovery of an elliptical shell of CO associated with the faint stellar object SSTc2d J163134.1-24006 as part of the "Ophiuchus Disk Survey Employing ALMA" (ODISEA), a project aiming to study the entire population of protoplanetary disks in the Ophiuchus Molecular Cloud from 230 GHz continuum emission and $^{12}$CO (J=2-1), $^{13}$CO (J=2-1) and C$^{18}$CO (J=2-1) lines readable in Band-6. Remarkably, we detect a bright $^{12}$CO elliptical shape emission of $\sim$ 3$^{"}$ $\times$ 4$^{"}$ towards SSTc2d J163134.1-24006 without a 230 GHz continuum detection. Based on the observed near-IR spectrum taken with the Very Large Telescope (KMOS), the brightness of the source, its 3-dimensional motion, and Galactic dynamic arguments, we conclude that the source is not a giant star in the distant background ($>$5 - 10 kpc) and is most likely to be a young brown dwarf in the Ophiuchus cloud, at a distance of just $\sim$139 pc. This is the first report of quasi-spherical mass loss in a young brown dwarf. We suggest that the observed shell could be associated with a thermal pulse produced by the fusion of deuterium, which is not yet well understood, but for a sub-stellar object is expected to occur during a short period of time at an age of a few Myr, in agreement with the ages of the objects in the region. Other more exotic scenarios, such as a merger with planetary companions, cannot be ruled out from the current observations.

astro-ph.SR↗