A near-infrared survey of Miras and the distance to the Galactic Centre |
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| Authors: | Noriyuki Matsunaga † Takahiro Kawadu Shogo Nishiyama † Takahiro Nagayama Hirofumi Hatano † Motohide Tamura Ian S Glass Tetsuya Nagata |
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| Institution: | Institute of Astronomy, University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan;Department of Astronomy, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan;Department of Astrophysics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan;National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan;South African Astronomical Observatory, PO Box 9, Observatory 7935, South Africa |
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| Abstract: | We report the results of a near-infrared survey for long-period variables in a field of view of 20× 30 arcmin2 towards the Galactic Centre (GC). We have detected 1364 variables, of which 348 are identified with those reported in Glass et al. We present a catalogue and photometric measurements for the detected variables and discuss their nature. We also establish a method for the simultaneous estimation of distances and extinctions using the period–luminosity relations for the JHK s bands. Our method is applicable to Miras with periods in the range 100–350 d and mean magnitudes available in two or more filter bands. While J band means are often unavailable for our objects because of the large extinction, we estimated distances and extinctions for 143 Miras whose H - and K s -band mean magnitudes are obtained. We find that most are located at the same distance to within our accuracy. Assuming that the barycentre of these Miras corresponds to the GC, we estimate its distance modulus to be 14.58 ± 0.02 (stat.) ± 0.11 (syst.) mag , corresponding to 8.24 ± 0.08 (stat.) ± 0.42 (syst.) kpc . We have assumed the distance modulus to the Large Magellanic Cloud to be 18.45 mag, and the uncertainty in this quantity is included in the above systematic error. We also discuss the large and highly variable extinction. Its value ranges from 1.5 mag to larger than 4 mag in  except towards the thicker dark nebulae and it varies in a complicated way with the line of sight. We have identified mid-infrared counterparts in the Spitzer /IRAC catalogue of Ramírez et al. for most of our variables and find that they follow rather narrow period–luminosity relations in the 3.6–8.0 μm wavelength range. |
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| Keywords: | stars: AGB and post-AGB stars: variables: other dust extinction Galaxy: centre Galaxy: structure infrared: stars |
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