arXiv subjects

Jose A. Caballero

Publications and source records attributed to Jose A. Caballero.

26 records · Page 2Linked to original sources

arXiv2009

Reaching the boundary between stellar kinematic groups and very wide binaries. The Washington Double Stars with the widest angular separations

Aims. I look for and characterise very wide binaries and multiple systems with projected physical separations larger than s = 0.1 pc, which is generally believed to be a sharp upper limit to the distribution of wide binay semimajor axes. Methods. I investigated in detail 30 Washington Double Stars with angular separations rho > 1000 arcsec. I discarded 23 of them as probably unbound systems based on discordant astrometry, photometry, spectral types, and radial velocities. The remaining seven systems were subject to a comprehensive data compilation and derivation (multi-wavelength photometry, heliocentric distance, multiplicity, age, mass, metallicity, membership in young kinematic group). Results. Of the seven very wide systems, six have projected physical separations larger than the hypothetical cutoff at s = 0.1 pc; four of them have separations s > 0.2 pc. Although there are two systems in young kinematic groups (namely HD 136654 and BD+32 2572 in the Hyades Supercluster, and AU Mic and AT Mic AB in the beta Pictoris moving group), there is not a clear prevalence of young systems (tau < 1 Ga) among these very wide binaries. Finally, I compare the binding energies of the seven systems with those of other weakly bound systems in the field.

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arXiv2009

From 1000 AU to 1000 pc: high proper-motion stars in the solar neighbourhood, radio sources in the sigma Orionis cluster, and new X-ray stars surrounding Alnilam

The Virtual Observatory is useful. I summarise some of my works where I extensively use the Aladin sky atlas. Topics cover from the search and common proper motion confirmation of very low-mass stars and brown dwarfs in wide (rho > 1000 AU) binaries and multiple systems, to the identification and characterisation of stellar and substellar populations in young open clusters and OB associations at heliocentric distances of up to 1000 pc. I present three practical examples of what one can do with Aladin in one morning: a fruitful proper-motion search of objects with available ugrizJHKs photometry, an analysis of the 21 cm radio sources towards the young sigma Orionis cluster, and a novel study of X-ray young stars surrounding Alnilam in the Orion Belt.

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arXiv2008

Formation, evolution and multiplicity of brown dwarfs and giant exoplanets

This proceeding summarises the talk of the awardee of the Spanish Astronomical Society award to the the best Spanish thesis in Astronomy and Astrophysics in the two-year period 2006-2007. The thesis required a tremendous observational effort and covered many different topics related to brown dwarfs and exoplanets, such as the study of the mass function in the substellar domain of the young sigma Orionis cluster down to a few Jupiter masses, the relation between the cluster stellar and substellar populations, the accretion discs in cluster brown dwarfs, the frequency of very low-mass companions to nearby young stars at intermediate and wide separations, or the detectability of Earth-like planets in habitable zones around ultracool (L- and T-type) dwarfs in the solar neighbourhood.

astro-ph↗

arXiv2008

Stars and brown dwarfs, spatial distribution, multiplicity, X-rays, discs, and the complete mass function of the sigma Orionis cluster

The young sigma Orionis cluster in the Orion Belt is an incomparable site for studying the formation and evolution of high-mass, solar-like, and low-mass stars, brown dwarfs, and substellar objects below the deuterium burning mass limit. The first version of the Mayrit catalogue was a thorough data compilation of cluster members and candidates, which is regularly used by many authors of different disciplines. I show two new applications of the catalogue and advance preliminar results on very wide binarity and the initial mass function from 18 to 0.035 Msol in sigma Orionis. The making-up of a new version of the Mayrit catalogue with additional useful data is in progress.

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arXiv2007

Stars and brown dwarfs in the sigma Orionis cluster: the Mayrit catalogue

The young sigma Orionis cluster is an indispensable basis for understanding the formation and evolution of stars, brown dwarfs and planetary-mass objects. Our knowledge of its stellar population is, however, incomplete. I present the Mayrit catalogue, that comprises most of the stars and high-mass brown dwarfs of the cluster. The basis of this work is an optical-near infrared correlation between the 2MASS and DENIS catalogues in a circular area of radius 30 arcmin centred on the OB-type binary sigma Ori AB. The analysis is supported on a bibliographic search of confirmed cluster members with features of youth and on additional X-ray, mid-infrared and astrometric data. I list 241 sigma Orionis stars and brown dwarfs with known features of youth, 97 candidate cluster members (40 are new) and 115 back- and foreground sources in the survey area. The 338 cluster members and member candidates constitute the Mayrit catalogue. This catalogue is a suitable input for studying the spatial ditribution, multiplicity, properties and frequency of discs and the complete mass function of sigma Orionis.

astro-ph↗

arXiv2007

Dynamical parallax of sigma Ori AB: mass, distance and age

The massive OB-type binary sigma Ori AB is in the centre of the very young sigma Orionis cluster. I have computed the most probable distances and masses of the binary for several ages using a dynamical parallax-like method. It incorporates the BVRIH-band apparent magnitudes of both components, precise orbital parameters, interstellar extinction and a widely used grid of stellar models from the literature, the Kepler's third law and a chi^2 minimisation. The derived distance is 334^(+25)_(-22) pc for an age of 3+/-2 Ma; larger ages and distances are unlikely. The masses of the primary and the secondary lie on the approximate intervals 16-20 and 10-12 Msol, respectively. I also discuss the possibility of sigma Ori AB being a triple system at ~385 pc. These results will help to constrain the properties of young stars and substellar objects in the sigma Orionis cluster.

astro-ph↗

arXiv2007

Spatial distribution of stars and brown dwarfs in sigma Orionis

I have re-visited the spatial distribution of stars and high-mass brown dwarfs in the sigma Orionis cluster (~3 Ma, ~360 pc). The input was a catalogue of 340 cluster members and candidates at separations less than 30 arcmin to sigma Ori AB. Of them, 70 % have features of extreme youth. I fitted the normalised cumulative number of objects counting from the cluster centre to several power-law, exponential and King radial distributions. The cluster seems to have two components: a dense core that extends from the centre to r ~ 20 arcmin and a rarified halo at larger separations. The radial distribution in the core follows a power-law proportional to r^1, which corresponds to a volume density proportional to r^(-2). This is consistent with the collapse of an isothermal spherical molecular cloud. The stars more massive than 3.7 Msol concentrate, however, towards the cluster centre, where there is also an apparent deficit of very low-mass objects (M < 0.16 Msol). Last, I demonstrated through Monte Carlo simulations that the cluster is azimuthally asymmetric, with a filamentary overdensity of objects that runs from the cluster centre to the Horsehead Nebula.

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arXiv2006

The widest ultracool binary

Aims: I test the ejection scenario of formation of brown dwarfs and very low-mass stars through the detection of a very wide ultracool binary. Methods: LEHPM 494 (M6.0 +/- 1.0 V) and DENIS-P J0021.0-4244 (M9.5 +/- 0.5 V) are separated by 1.3 arcmin and are high proper motion co-moving ultracool stars. I have used six astrometric epochs spaced 22 years to confirm their common tangential velocity. Results: The angular separation between both low-mass stars keeps constant with an uncertainty less than 0.1 %. I have also derived their most probable heliocentric distance (23 +/- 2 pc), age interval (2-10 Ga) and masses (0.103 +/- 0.006 and 0.079 +/- 0.004 Msol). The pair, with a projected physical separation of 1800 +/- 170 AU, is by far the widest ultracool binary ever found in the field. Conclusions: This serendipitous and simple detection is inconsistent with ultra low-mass formation ejection scenarios and complements current searches of low-mass tight binaries.

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