Red Clump Morphology as Evidence Against a New Intervening Stellar Population as the Primary Source of Microlensing Toward the LMC

Abstract

We examine the morphology of the color-magnitude diagram (CMD) for core helium-burning (red clump) stars to test the recent suggestion by Zaritsky & Lin (1997) that an extension of the red clump in the Large Magellanic Cloud (LMC) toward brighter magnitudes is due to an intervening population of stars that is responsible for a significant fraction of the observed microlensing toward the LMC. Using our own CCD photometry of several fields across the LMC, we confirm the presence of this additional red clump feature, but conclude that it is caused by stellar evolution rather than a foreground population. We do this by demonstrating that the feature (1) is present in all our LMC fields, (2) is in precise agreement with the location of the blue loops in the isochrones of intermediate age red clump stars with the metallicity and age of the LMC, (3) has a relative density consistent with stellar evolution and LMC star formation history, and (4) is present in the Hipparcos CMD for the solar neighborhood where an intervening population cannot be invoked. Assuming there is no systematic shift in the model isochrones, which fit the Hipparcos data in detail, a distance modulus of ${\mu }_{LMC}=18.3$ provides the best fit to our dereddened CMD.

21 pages LaTex (aaspp4.sty), including three tables and 9 figures (1 is .ps, 8 are .gif). Accepted for publication by Astronomical Journal on March 16, 1998. One error corrected and major revisions now lead to an even stronger argument for the stellar evolutionary origin of features in the LMC color magnitude diagram, claimed by others to be an intervening stellar population and major source of microlensing optical depth toward the LMC

References in corpus (10)

• A Prescription for Building the Milky Way's Halo from Disrupted Satellites
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• Stellar Populations in Three Outer Fields of the LMC
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• Proceedings of the Bonn/Bochum-Graduiertenkolleg Workshop 'The Magellanic Clouds and Other Dwarf Galaxies'

Cited by in corpus (20)

• K-Band Calibration of the Red Clump Luminosity
• A secondary clump of red giant stars: why and where
• Astrometry with Hubble Space Telescope: A Parallax of the Fundamental Distance Calibrator RR Lyrae
• The Rotation Curve of the Large Magellanic Cloud and the Implications for Microlensing
• A Tidally-Stripped Stellar Component of the Magellanic Bridge
• Self-Lensing Models of the LMC
• Is Galactic Dark Matter White ?
• The Origin of the Microlensing Events Observed Towards the LMC and the Stellar Counterpart of the Magellanic Stream
• Zeroing the Stellar Isochrone Scale: The Red Giant Clump Luminosity at Intermediate Metallicity
• The MACHO Project Hubble Space Telescope Follow-Up: Preliminary Results on the Location of the Large Magellanic Cloud Microlensing Source Stars
• A New Giant Branch Clump Structure In the Large Magellanic Cloud
• Microlens Parallax Asymmetries Toward the LMC
• Constraints on Intervening Stellar Populations Toward the Large Magellanic Cloud
• Magellanic Cloud Gravitational Microlensing Results: What Do They Mean?
• The Master Catalogue of stars towards the Magellanic Clouds
• Microlensing in the Small Magellanic Cloud: Lessons from an N-body Simulation
• A New Argument Against An Intervening Stellar Population Toward the LMC
• Population gradients and photometric metallicities in early- and transition-type dwarf galaxies: Clues from the Sculptor group
• Harmonizing the RR Lyrae and Clump Distance Scales - Stretching the Short Distance Scale to Intermediate Ranges?
• Clump stars in the Solar Neighbourhood