Using the multi-object adaptive optics demonstrator RAVEN to observe metal-poor stars in and towards the Galactic Centre

Abstract

The chemical abundances for five metal-poor stars in and towards the Galactic\nbulge have been determined from H-band infrared spectroscopy taken with the\nRAVEN multi-object adaptive optics science demonstrator and the IRCS\nspectrograph at the Subaru 8.2-m telescope. Three of these stars are in the\nGalactic bulge and have metallicities between -2.1 < [Fe/H] < -1.5, and high\n[alpha/Fe] ~+0.3, typical of Galactic disk and bulge stars in this metallicity\nrange; [Al/Fe] and [N/Fe] are also high, whereas [C/Fe] < +0.3. An examination\nof their orbits suggests that two of these stars may be confined to the\nGalactic bulge and one is a halo trespasser, though proper motion values used\nto calculate orbits are quite uncertain. An additional two stars in the\nglobular cluster M22 show [Fe/H] values consistent to within 1 sigma, although\none of these two stars has [Fe/H] = -2.01 +/- 0.09, which is on the low end for\nthis cluster. The [alpha/Fe] and [Ni/Fe] values differ by 2 sigma, with the\nmost metal-poor star showing significantly higher values for these elements.\nM22 is known to show element abundance variations, consistent with a\nmulti-population scenario (i.e. Marino et al. 2009, 2011; Alves-Brito et al.\n2012) though our results cannot discriminate this clearly given our abundance\nuncertainties. This is the first science demonstration of multi-object adaptive\noptics with high resolution infrared spectroscopy, and we also discuss the\nfeasibility of this technique for use in the upcoming era of 30-m class\ntelescope facilities.\n