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Variable Blue Stragglers in M67. Zhang Xiao-Bin NAOC. Abstract. - PowerPoint PPT Presentation
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Variable Blue Stragglers in M67
Zhang Xiao-Bin NAOC
Abstract A long-term time-series CCD photometry on variabl
e blue stragglers (BSs) was performed, aiming on the understanding of the properties and physical nature of the BSs based on the comprehensive photometric study. I report here the progress and some results drawn from this project.
Blue stragglers
Bluer and brighter than the turn-off of the stellar population; noticed first by Sandage (1953) in the GC M3;
BSs related: yellow or red stragglers; up and under-loop stars;
Origin: complicated proceedings; many theories: Binary merger; Multiple epochs of star formation; Star-life extend due to internal mixing; Mass-transfer within binary stars; Stellar collisions;
All relying on the complete understanding of the properties and evolutionary status of BSs;
Variable BSs (photometric and/or spectroscopic): the most ideal samples;
BSs in M67 M67: with the age similar to the Sun; extensively ob
served; More than 30 BSs identified; More than 10 BSs are proved to be photometric an
d/or spectroscopic variables; Well-classified photometric variable BSs:
1 RS CVn star: S1082; 2 W Uma systems: S1036 and S1282; 2 oscillation BSs: S1280 and S1284;
The long-term photometry
BATC: Feb. 2001; 85 cm reflector:
Dec. 2003 – Jan. 2004; Dec. 2004 – Jan. 2004;
Complete photometric study has been finished for S1282, S1280 and S1284; physical parameters for the 3 variable BSs are determined, evolutionary status and probable formation mechanism are discussed;
S1036 and S1082; waiting for more observations.
S1282, an example W Uma system discovered early in 1960; orbital and physical
parameters are very uncertain; almost at the turn-off in the CMD
Light curve analysis: Physical parameters:
adopting the distance modulus
of the cluster
Discussions: The primary: un-evolved normal MS star; the
deduced mass matches its position in the CMD (the turn-off mass of M67: 1.25 solar mass);
The secondary: over-radius, over-luminosity, obviously evolved;
Mass transfer and mass ratio inverse undergone; To be a BS…