The Evolution of Blue Stragglers Formed via Stellar Collisions

Ouellette, J. A.

doi:10.1086/300362

Cited by 19 publications

(13 citation statements)

References 45 publications

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“…Sandquist, Bolte and Hernquist (1997) find similar results. However, subsequent convection or meridional circulation can still induce mixing (Leonard & Livio 1995;Lombardi et al 1995), although this was not found to be the case in detailed numerical work by Sills et al (1997) and Ouellette & Pritchet (1998). In summary, "absence of proof is not proof of absence"; if the analogy to blue stragglers is justified, then it appears that the lack of unusual spectral features in the S-stars does not place strong constraints on their origin.…”

Section: The Riddle Of the Young Starsmentioning

confidence: 93%

Stellar processes near the massive black hole in the Galactic center

2005

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Section: The Riddle Of the Young Starsmentioning

confidence: 93%

Stellar processes near the massive black hole in the Galactic center

2005

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“…-Modelling of collisional blue stragglers in globular clusters (Sills & Bailyn 1999): the number and distribution of the stragglers in the colour-magnitude diagrams are determined by the current dynamical state and population of the clusters. More analyses of the formation of, and mixing in, collisional globular-cluster stragglers: Sills et al (1995), Sandquist et al (1997), Ouellette & Pritchet (1998), Lombardi et al (2002). -Discussion of high-resolution spectra of stragglers in M 67 (Shetrone & Sandquist 2000): the abundance of CNO elements may be a better index for distinguishing collisional stragglers from those resulting from mass transfer in close binaries.…”

Section: Theoriesmentioning

confidence: 99%

New catalogue of blue stragglers in open clusters

Ahumada

Lapasset

2006

A&A

158

242

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We present a catalogue of blue-straggler candidates in galactic open clusters. It is based on the inspection of the colour-magnitude diagrams of the clusters, and it updates and supersedes the first version (Ahumada & Lapasset 1995). A new bibliographical search was made for each cluster, and the resulting information is organised into two tables. Some methodological aspects have been revised, in particular those concerning the delimitation of the area in the diagrams where the stragglers are selected. A total of 1887 blue-straggler candidates have been found in 427 open clusters of all ages, doubling the original number. The catalogued stars are classified into two categories mainly according to membership information.

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“…As previously observed, the BSs tend to reside redward of the ZAMS. Ouellette & Pritchet (1998) and Ouellette (2000) simulated different synthetic BS populations using a range of assumptions for their creation scenarios. By comparing the positions of these synthetic populations to those of the real populations in several clusters they deduced the most likely BS formation scenario.…”

Section: Comparison With Stellar Evolutionary Modelsmentioning

confidence: 99%

A Spectroscopic Analysis of Blue Stragglers, Horizontal Branch Stars, and Turnoff Stars in Four Globular Clusters

Marco

Shara

Zurek

et al. 2005

ApJ

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We present a spectroscopic analysis of HST STIS and FOS low-and intermediate-resolution spectroscopy of 55 stars in four globular clusters (47 Tucanae, M3, NGC 6752, and NGC 6397). Stars hotter than T eA ¼ 5750 K and with a signal-to-noise ratio larger than 15 were analyzed with non-local thermodynamic equilibrium model atmospheres, and values for their effective temperatures and gravities were obtained. Using photometric fluxes, we also obtained radii, luminosities, and spectroscopic masses.Twenty-four stars in our sample are blue stragglers ( BSs). Their photometric colors and magnitudes place these BSs above and redward of the clusters' zero-age main sequence: this is consistent with the gravities we find for these stars, which are lower than zero-age main-sequence gravities. A comparison with stellar evolutionary tracks shows that almost all of our BSs are in the Hertzsprung gap. This is contrary to theory, because of the short timescale expected for stars in this evolutionary phase.The mean BS mass is 1.04 M for 14 nonvariable stars, or 1.07 M counting all 24 BSs in our sample. For the nonvariable stars the mean BS masses for individual clusters are 1.73, 1.01, 0.95, and 0.72 M for NGC 6397, NGC 6752, 47 Tuc, and M3, respectively. Adding the variable stars (which improves the statistics but increases the uncertainty), the mean masses become 1.27, 1.05, 0.99, and 0.99 M , respectively. Although there is considerable scatter, the BS spectroscopic masses correlate with both effective temperature and brightness of the stars, as expected.The mean nonvariable turnoff star mass (0.58 M ) is significantly below the values determined for the BSs and below the main-sequence turnoff mass. The mean nonvariable horizontal-branch (HB) star mass is higher than expected (0.79 M ). In particular, several HB stars have masses well above the main-sequence turnoff mass. Some of these HB stars are suspected of actually being BSs, since most of them reside at ambiguous locations on the CMD, making them prone to misclassification.Values and limits to the stellar rotation rates (v sin i) are imposed by fitting weak metal lines, the Ca ii K line wings, or the helium lines for the hotter stars. Five BSs with reasonably constrained rotations show average and median v sin i values of 109 and 100 km s À1, respectively, suggesting v $ 160 km s À1. At least some GC BSs are very rapid rotators, but this information cannot yet constrain their origin as stellar collision or binary mergers because of the lack of clear theoretical predictions. Six extreme HB stars have rotation rates v sin i between 50 and 200 km s À1, which are high for these stars and might indicate a binary origin.De Marco et al. found that four BSs and two HB stars in our sample have Balmer jumps that are too large for the effective temperatures implied by the slopes of their Paschen continua. Two additional HB stars are now identified in the current study as having the same feature. For these stars, the presence of a disk of partly ionized material is suspected, ...

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The Evolution of Blue Stragglers Formed via Stellar Collisions

Cited by 19 publications

References 45 publications

Stellar processes near the massive black hole in the Galactic center

Stellar processes near the massive black hole in the Galactic center

New catalogue of blue stragglers in open clusters

A Spectroscopic Analysis of Blue Stragglers, Horizontal Branch Stars, and Turnoff Stars in Four Globular Clusters

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