Blue stragglers

Abstract. We present preliminary results of lithium abundances in turnoff stars in the open cluster NGC 2506. Some fifty turnoff stars and a few blue stragglers have been observed using the FLAMES facility on the VLT, during half a night from the French Guaranteed Time on this instrument. 

The lithium abundance, using the Li I 6707 doublet, will be used as a signature of internal mixing to confirm whether or not internal mixing is one of the mechanisms responsible for the existence of blue straggler stars. 

The formation mechanisms that can explain the existence of blue stragglers are still very unclear. The different explanations involve mass-transfer in binary systems, or internal mixing. 

Moreover the proportion of turnoff stars supposed to be future blue stragglers (i.e. the subturnoff-mass blue stragglers) would give an independent estimate of the ratio found by [8] the number of blue stragglers to the number of giant stars. 

Using FLAMES we observed, 45 turnoff stars, 7 giant stars with GIRAFFE (LR2 from 396.4 to 456.7 nm, R 6400 and H15 from 660.6 to 696.5 nm, R 19300). At the same time, 3 stars known as blue stragglers ([1]) were observed by UVES-link R = 47000, and a 200 nm wide spectral range centered around 580 nm. 

Fig. 1. HR diagram of NGC 2506 crosses are the data from [4]. The targets observed with FLAMES-GIRAFFE are indicated by circles (open circles are the outliers in the radial velocities distribution), and the blue stragglers observed with FLAMES-UVES are indicated by double circles.

In the late 1980s, French astrophysicist Hubert Reeves speculated on the origin of mysterious stars called blue stragglers, first identified in 1952. These... 

Hubert Reeves, Atoms of Silence An Exploration of Cosmic Evolution (Cambridge MIT Press, 1984) M. Beech, Blue stragglers as indicators of extraterrestrial civilizations Earth, Moon, and Planets 49 177-186 (1990) Guillermo A. Lemarchand, Detectability of extraterrestrial technological activities. ... 

Rex Saffer and Dave Zurek, Blue stragglers in globular cluster 47 Tucanae, http // oposite.stsci.edu/pubinfo/PR/97/35/a.html... 

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