Determining the Absolute Magnitudes of Galactic-Bulge Red Clump Giants in the Z and Y Filters of the Vista Sky Surveys and the IRAC Filters of the Spitzer Sky Surveys

Abstract

The properties of red clump giants in the central regions of the Galactic bulge are investigated in the photometric $Z$ and $Y$ bands of the infrared VVV (VISTA/ESO) survey and the [3.6],[4.5], [5.8] and [8.0] bands of the GLIMPSE (Spitzer/IRAC) Galactic plane survey. The absolute magnitudes for objects of this class have been determined in these bands for the first time: $M_Z=-0.20\pm 0.04$ and $M_Y=-0.470\pm 0.045$, $M_{[3.6]}=-1.70\pm 0.03$, $M_{[4.5]}=-1.60\pm 0.03$, $M_{[5.8]}=-1.67\pm 0.03$ and $M_{[8.0]}=-1.70\pm 0.03$. A comparison of the measured magnitudes with the predictions of theoretical models for the spectra of the objects under study has demonstrated good mutual agreement and has allowed some important constraints to be obtained for the properties of bulge red clump giants. In particular, a comparison with evolutionary tracks has shown that we are dealing predominantly with the high-metallicity subgroup of bulge red clump giants. Their metallicity is slightly higher than has been thought previously, $[M/H]\simeq 0.40$ ($\mathbf{Z}\simeq 0.038$) with an error of $[M/H]\simeq 0.1$ dex, while the effective temperature is $4250\pm 150$ K. Stars with an age of 9-10 Gyr are shown to dominate among the red clump giants, although some number of younger objects with an age of $\sim 8$ can also be present. In addition, the distances to several Galactic bulge regions have been measured, as D = 8200-8500 pc, and the extinction law in these directions is shown to differ noticeably from the standard one.

18 pages, 12 figures

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