Red Clump Stars as a Tracer of Microlensing Optical Depth
نویسنده
چکیده
Zaritsky and Lin have recently suggested that the color magnitude diagram of the Large Magellanic Cloud (LMC) contains evidence of foreground red clump stars. They interpret this as evidence of tidal debris or a dwarf galaxy at a distance of ∼ 35 kpc which may be responsible for the large gravitational microlensing optical depth observed by the MACHO Collaboration. I derive a relationship between the microlensing optical depth of such a foreground population and the observed density of foreground red clump stars. Recent observational determinations for Pop I and Pop II stellar mass functions are used to show that the surface density of foreground red clump stars claimed by Zaritsky and Lin implies a microlensing optical depth in the range τfg = 0.8 − 3.6 × 10 −8 which is only 3-13% of τLMC as determined by the MACHO Collaboration. If the foreground population has a similar star formation history to the LMC, then the implied τfg is only 3-4% of τLMC . Subject headings: dark matter gravitational lensing
منابع مشابه
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We identify a vertical extension of the red clump stars in the color magnitude diagram (CMD) of a section of the Large Magellanic Cloud (LMC). The distribution of stars in this extension is indistinguishable in the U , B, V , and I bands — confirming that the detection is real and placing a strong constraint on models of this stellar population. After subtracting the principal red clump compone...
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