A near-infrared survey of Miras and the distance to the Galactic Centre

Abstract

We report the results of a near-infrared survey for long-period variables in a field of view of 20 arcmin by 30 arcmin towards the Galactic Centre (GC). We have detected 1364 variables, of which 348 are identified with those reported in Glass et al. (2001). 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 LMC to be 18.45 mag, and the uncertainty in this quantity is included in the systematic error above. We also discuss the large and highly variable extinction. Its value ranges from 1.5 mag to larger than 4 mag in A Ks 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. (2008) for most of our variables and find that they follow rather narrow period-luminosity relations in the 3.6 to 8.0 µm wavelength range.

Spectroscopic signatures of extratidal stars around the globular clusters NGC 6656 (M 22), NGC 3201, and NGC 1851 from RAVE

“…The properties of the GCs studied here are listed in Table 1, taken from Harris (2010Harris ( edition of 1996, except for the Wilson (1975) tidal radius, which is from McLaughlin & van der Marel (2005). The columns contain (1) the cluster name, (2) the right ascension in hours, minutes and seconds (epoch J2000), (3) the declination in degrees, arcminutes and arcseconds, (4) the Galactic longitude in degrees, (5) the Galactic latitude in degrees, (6) the distance from Sun in kiloparsecs (kpc), (7) the distance from Galactic center (kpc), assuming R 0 =8.0 kpc (e.g., Groenewegen et al 2008;Matsunaga et al 2009), (8) the [Fe/H] metallicity, (9) the Heliocentric radial velocity in km s −1 (10) the core radius in arcmin, (11) the King (1966) tidal radius in arcmin, and (11) the Wilson (1975) tidal radius in arcmin from McLaughlin & van der Marel (2005).…”

Standard candles from the Gaia perspective

“…But Gaia will also offer the possibility to exploit other classes of variable stars as standard candles. Examples of "non-classical" standard candles include Long Period Variables (LPVs) (Feast et al 1989;Matsunaga et al 2009), OGLE Small Amplitude Red Giants (OSARGs; Wray et al 2004), eclipsing binaries (Paczyński 1997) and Large Amplitude δ Scuti stars (McNamara 1997).…”

Variable stars in the Galactic center, as revealed by the VVV Survey

“…Our 353 variable stars have been cross-matched with the data found in the literature, namely the Mira search carried out by [3]. 47 counterparts were found, meaning that we have discovered 306 new variables in the region.…”

“…From the first 50 variables that were analyzed, 4 correspond to Miras, 21 to semi-regulars, while the remaining 25 have irregular light curves. The crossmatch with [3] allowed us to have a long time baseline (over 12 years), enough to check for secular variations in their light curves, which are expected for stars in the AGB phase, both in their amplitude and/or periodicity.…”