A revisit to agglomerates of early‐type Hipparcos stars

Caballero, J. A.; Dinís, Luis

doi:10.1002/asna.200811024

Cited by 27 publications

(31 citation statements)

References 161 publications

(203 reference statements)

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“…They are Mayrit 208324 (HD 294271, B5V), Mayrit 1116300 10 (HD 37333, A1Va -but see Naylor 2009), and Mayrit 11238 (σ Ori C, A2V). The star HD 37699, a young B5V star with an envelope at 25.8 arcmin to the cluster centre, seems to be associated to the stellar population near the Horsehead Nebula (Caballero & Dinis 2008).…”

Section: Early-type Starsmentioning

confidence: 99%

HRC-I/ChandraX-ray observations towardsσ Orionis

Caballero

Colombo

López‐Santiago

2010

A&A

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Aims. We investigated the X-ray emission from young stars and brown dwarfs in the σ Orionis cluster (τ ∼ 3 Ma, d ∼ 385 pc) and its relation to mass, the presence of circumstellar discs, and separation to the cluster centre by taking advantage of the superb spatial resolution of the Chandra X-ray Observatory. Methods. We used public HRC-I/Chandra data from a 97.6 ks pointing towards the cluster centre and complemented them with X-ray data from IPC/Einstein, HRI/ROSAT, EPIC/XMM-Newton, and ACIS-S/Chandra together with optical and infrared photometry and spectroscopy from the literature and public catalogues. On our HRC-I/Chandra data, we measured count rates, estimated X-ray fluxes, and searched for short-term variability. We also looked for long-term variability by comparing with previous X-ray observations. Results. Among the 107 detected X-ray sources, there were 70 cluster stars with known signposts of youth, two young brown dwarfs, 12 cluster member candidates, four field dwarfs, and two galaxies with optical-infrared counterpart. The remaining sources were extragalactic. Based on a robust Poisson-χ 2 analysis, nine cluster stars displayed flares or rotational modulation during the HRC-I observations, while eight other stars and one brown dwarf showed X-ray flux variations between the HRC-I and IPC, HRI, and EPIC epochs. We constructed a cluster X-ray luminosity function from O9.5 (about 18 M ) to M6.5 (about 0.06 M ). We found: (i) that early-type stars in multiple systems or with spectroscopic peculiarities tend to display X-ray emission; (ii) that the two detected brown dwarfs and the least-massive star are among the σ Orionis objects with the highest L X /L J ratios; and (iii) that a large fraction of known classical T Tauri stars in the cluster are absent in this and other X-ray surveys. Finally, from a spatial distribution analysis, we quantified the impact of sensitivity degradation towards the HRC-I borders on the detection of faint X-ray sources and concluded that dozens X-ray σ Orionis stars and brown dwarfs still need to be detected.

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Section: Early-type Starsmentioning

confidence: 99%

HRC-I/ChandraX-ray observations towardsσ Orionis

Caballero

Colombo

López‐Santiago

2010

A&A

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“…However, it was not infallible. For example, Caballero & Dinis (2008) show some stars whose astrometric solution got worse with the new reduction. If LP 754-50 were located at the distance to ξ 02 Cap, it would have an absolute J-band magnitude M J = 6.27 ± 0.03 mag, which translates into a theoretical mass M ∼ 0.55 M and an effective temperature typical of an early M dwarf of solar age (Baraffe et al 1998).…”

Section: Wds 15208+3129 (Hd 136654 and Bd+32 2572)mentioning

confidence: 99%

Reaching the boundary between stellar kinematic groups and very wide binaries

Caballero¹

2009

A&A

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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 binary semimajor axes. Methods. I investigated in detail 30 Washington double stars with angular separations of ρ > 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 a young kinematic group). Results. Of the seven very wide systems, six have projected physical separations greater than the hypothetical cutoff at s = 0.1 pc and four 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 β Pictoris moving group), there is no clear prevalence of young systems (τ < 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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“…The population of stars surrounding Alnilam (ǫ Ori) and Mintaka (δ Ori), to the west of the Belt, are older (5-10 Ma) and spread over a wider area than the much denser σ Orionis cluster (Caballero & Solano 2008). Surrounding the Belt, there is another dispersed population of 10-20 Ma-old stars, mostly associated to the Ori OB1 a subgroup association (Jeffries et al 2006; and its agglomerates, such as the 25 Orionis group or the η Orionis overdensity (Briceño et al 2007;Caballero & Dinis 2008).…”

Section: Introductionmentioning

confidence: 99%

Finding the most variable stars in the Orion Belt with the All Sky Automated Survey

2010

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We look for high-amplitude variable young stars in the open clusters and associations of the Orion Belt. We use public data from the ASAS-3 Photometric V -band Catalogue of the All Sky Automated Survey, infrared photometry from the 2MASS and IRAS catalogues, proper motions, and the Aladin sky atlas to obtain a list of the most variable stars in a survey area of side 5 deg centred on the bright star Alnilam (ǫ Ori) in the centre of the Orion Belt. We identify 32 highly-variable stars, of which 16 had not been reported to vary before. They are mostly variable young stars and candidates (16) and background giants (8), but there are also field cataclysmic variables, contact binaries, and eclipsing binary candidates. Of the young stars, which typically are active Herbig Ae/Be and T Tauri stars with Hα emission and infrared flux excess, we discover four new variables and confirm the variability status of another two. Some of them belong to the well known σ Orionis cluster. Besides, six of the eight giants are new variables, and three are new periodic variables.

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A revisit to agglomerates of early‐type Hipparcos stars

Cited by 27 publications

References 161 publications

HRC-I/ChandraX-ray observations towardsσ Orionis

HRC-I/ChandraX-ray observations towardsσ Orionis

Reaching the boundary between stellar kinematic groups and very wide binaries

Finding the most variable stars in the Orion Belt with the All Sky Automated Survey

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