New catalogue of blue stragglers in open clusters

Ahumada, J. A.; Lapasset, E.

doi:10.1051/0004-6361:20054590

Cited by 158 publications

(263 citation statements)

References 105 publications

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“…D and the location of blue stragglers as delineated by Ahumada & Lapasset (2007) suggest that at most a few Be stars are in the blue-straggler zone while most Be stars are on the red side of the cluster main sequences. As discussed in Sect.…”

Section: Evolution and Agementioning

confidence: 92%

A slitless spectroscopic survey for Hαemission-line objects in SMC clusters

Martayan

Baade

Fabregat³

2010

A&A

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Context.A fair fraction of all single early-type stars display emission lines well before their supergiant phase. Very rapid rotation is necessary for these stars to form rotationally supported decretion disks. However, it is unknown whether and which other parameters may be important. Aims. We assess the roles of metallicity and evolutionary age in the appearance of the so-called Be phenomenon. Methods. Slitless CCD spectra were obtained covering the bulk (about 3 square degrees) of the Small Magellanic Cloud. For Hα line-emission twice as strong as the ambient continuum, the survey is complete to spectral type B2/B3 on the main sequence. About 8120 spectra of 4437 stars were searched for emission lines in 84 open clusters, and 370 emission-line stars were found, among them at least 231 close to the main sequence. For 176 of them, photometry is available from the OGLE database. For comparison with a higher-metallicity environment, the Galactic sample of the photometric Hα survey by McSwain & Gies (2005, ApJS, 161, 118) was used.Results. Among early spectral sub-types, Be stars are more frequent by a factor ∼3-5 in the SMC than in the Galaxy. The distribution with spectral type is similar in both galaxies, i.e., not strongly dependent on metallicity. The fraction of Be stars does not seem to vary with local star density. The Be phenomenon mainly sets in towards the end of the main-sequence evolution (this trend may be more pronounced in the SMC); but some Be stars already form with Be-star characteristics. In small subsamples (such as single clusters), even if they appear identical, the fraction of emission-line stars can deviate drastically from the mean. Conclusions. In all probability, the fractional critical angular rotation rate, Ω/Ω c , is one of the main parameters governing the occurrence of the Be phenomenon. If the Be character is only acquired during the course of evolution, the key circumstance is the evolution of Ω/Ω c , which is not only dependent on metallicity but differently so for different mass ranges. As a result, even if the Be phenomenon is driven basically by a single parameter (namely Ω/Ω c ), it can assume a complex multi-parametric appearance. The large cluster-to-cluster differences, which seem stronger than all other variations, serve as a caveat that this big picture may undergo significant second-order modulations (e.g., pulsations, initial angular momentum, etc.).

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Section: Evolution and Agementioning

confidence: 92%

A slitless spectroscopic survey for Hαemission-line objects in SMC clusters

Martayan

Baade

Fabregat³

2010

A&A

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“…The star HD 13112 (W6) is catalogued as a blue straggler by Ahumada & Lapasset (1995) and was classified as B8 III (sharp hydrogen lines) by McCuskey (1974). The latter could be a hint of a CP nature because of the generally low rotational velocities of these objects which were often misidentified as sharp lined giants (Preston 1974).…”

Section: Stockmentioning

confidence: 99%

Photoelectric search for peculiar stars in open clusters

Paunzen

Netopil

Maitzen³

et al. 2014

A&A

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Context. The chemically peculiar (CP) stars of the upper main sequence are mainly characterized by strong overabundances of heavy elements. Two subgroups (CP2 and CP4) have strong local magnetic fields which make them interesting targets for astrophysical studies. This star group, in general, is often used for the analysis of stellar formation and evolution in the context of diffusion as well as meridional circulation. Aims. In continuation of a long term study of CP stars (initiated in the 1980s), we present new results based on photoelectric measurements for ten open clusters that are, with one exception, younger than 235 Myr. Observations in star clusters are favourable because they represent samples of stars of constant age and homogeneous chemical composition. Methods. The very efficient tool of Δa photometry was applied. It samples the flux depression at 5200 Å typically for CP stars. In addition, it is able to trace emission line Be/Ae and λ Bootis stars. Virtually all CP2 and CP4 stars can be detected via this tool, and it has been successfully applied even in the Large Magellanic Cloud. For all targets in the cluster areas, we performed a kinematic membership analysis. Results. We obtained new photoelectric Δa photometry of 304 stars from which 207 objects have a membership probability higher than 50%. Our search for chemically peculiar objects results in fifteen detections. The stars have masses between 1.7 M and 7.7 M and are between the zero-and terminal-age-main-sequence. We discuss the published spectral classifications in the light of our Δa photometry and identify several misclassified CP stars. We are also able to establish and support the nature of known bona fide CP candidates. Conclusions. It is vital to use kinematic data for the membership determination and also to compare published spectral types with other data, such as Δa photometry. There are no doubts about the accuracy of photoelectric measurements, especially for stars brighter than 10th magnitude. The new and confirmed CP stars are interesting targets for spectroscopic follow-up observations to put constraints on the formation and evolution of CP stars.

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“…These objects are found in star clusters, dwarf galaxies, and in the field. The existence of blue stragglers can probably be explained only by an interaction between two or more stars, and so to understand this phenomenon we study the interaction of stars in stellar systems (see Leonard 1989;Bailyn & Pinsonneault 1995;Sandquist et al 1997;Sills et al 1997;Chen & Han 2004;Ahumada & Lapasset 2007). Ahumada & Lapasset (2007) listed the most frequently cited explainations of the formation of blue stragglers.…”

Section: Introductionmentioning

confidence: 99%

“…The existence of blue stragglers can probably be explained only by an interaction between two or more stars, and so to understand this phenomenon we study the interaction of stars in stellar systems (see Leonard 1989;Bailyn & Pinsonneault 1995;Sandquist et al 1997;Sills et al 1997;Chen & Han 2004;Ahumada & Lapasset 2007). Ahumada & Lapasset (2007) listed the most frequently cited explainations of the formation of blue stragglers. They could be (1) horizontal-branch stars that appear above the main sequence turn-off point; (2) stars of a second or third generation; (3) stars that have extended their main-sequence life because of some internal mixing, which would generate a chemically peculiar blue straggler; (4) stars formed by the collision of two single stars; (5) the result of mass transfer in a close binary system; (6) produced by the merger of the components of a binary system; or (7) the result of a collision between two or more binary systems.…”

Section: Introductionmentioning

confidence: 99%

Explaining the Praesepe blue straggler HD 73666

Fossati¹,

Mochnacki²,

Landstreet³

et al. 2010

A&A

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Aims. The blue straggler phenomenon is not yet well explained by current theory, although evolutionary models of star clusters require a good knowledge of it. We attempt to develop a formation scenario for HD 73666, a blue straggler member of the Praesepe cluster. Methods. We compile the known physical properties of HD 73666 found in the literature, focusing in particular on possible binarity and the abundance pattern. Results. HD 73666 appears to be slowly rotating, have no detectable magnetic field, and have normal abundances, thereby excluding close binary evolution and mass transfer processes. There is no evidence of a hot radiation source. Conclusions. With the use of theoretical results on blue straggler formation present in literature, we are able to conclude that HD 73666 was probably formed by physical collision involving at least one binary system, between 5 and 350 Myr (50 Myr if the star is an intrinsic slow rotator) ago.

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New catalogue of blue stragglers in open clusters

Cited by 158 publications

References 105 publications

A slitless spectroscopic survey for Hαemission-line objects in SMC clusters

A slitless spectroscopic survey for Hαemission-line objects in SMC clusters

Photoelectric search for peculiar stars in open clusters

Explaining the Praesepe blue straggler HD 73666

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