Observing strategy - Galaxy observations

Bulge survey. Here the prime targets are K giants, including the red clump (I=15 typically). These dominate the relevant colour magnitude diagram (CMD) selection. The analysis tests show that S/N=50 is needed to deliver log g, while the typical giant will have S/N=100. Two GIRAFFE setups are needed. Four observing blocks (OBs), to provide iron-peak elements: Fe, Cr, Mn, Co, Ni; alpha elements: Mg, Si, Ca, Ti; proton-capture elements: Sc, V.

Halo/thick disc survey. Primary targets are r=17-18 F stars, with the bluer, fainter F stars probing the halo, brighter, redder F stars probing the thick disc. Sloan Digital Sky Survey (SDSS) photometry shows a clear thick disc/halo transition at 17 ≤ r ≤ 18; 0.2 ≤ g − r ≤ 0.4 – we use the equivalent selection from VISTA. The spectrum analysis tests suggest that minimum S/N=30 for thick disc and halo FG stars delivers: iron-peak elements: Fe, Cr, Mn; alpha elements: Mg (all), Si, Ca, Ti (down to around [M/H]=−1.0); proton-capture elements: Sc. In both cases, this requires 2×HR21, 2×HR10, giving S/N=40 & 30. A single FPOSS setup is used, so fields can be completed in a single semester. In fields crossing known halo streams (e.g. Sgr) we will include stream K-giant candidates.

Outer thick disc fields will have distant F stars as prime targets, like the halo. A well-defined low latitude sample probes 2–4 kpc, more than a radial scale length. In addition, we will allocate 25% of the fibres to brighter candidate K giants, which probe the far outer disc, warp, flare and Mon stream, and will deliver excellent S/N.

Thin disc dynamics. We will target 4–6 fields to I=19 in the Plane to test spiral arm/bar dynamics. These require HR21 for radial velocities (RVs) only. Several thousand RVs per line of sight will be obtained.

Solar Neighbourhood. We also dedicate UVES parallels for the field surveys to an unbiased sample of 5000 FG stars within 2 kpc of the Sun with detailed elemental abundances. UVES580 is adopted.

Page last updated: 05/08/2013