GMOS SV program 57

	Status: in preparation Data link: not yet available Assessment: not yet available

Title:	Dark matter in dSphs
Modes:	Imaging (for mask preparation) Multi-object spectroscopy with narrow slits
Additional instrument verification:	Data reduction pipeline for imaging data and MOS data; mask preparation software; use of 0.25" slits; stability radial velocity measurements.
Telescope verification:	Acquisition and guiding with GMOS for tested mode. Stability of guiding over long periods of time and large hour angles. Stability of the delivered plate scale.
Proposed observing sequence:	Imaging: 4 dithered observations in order to cover the gaps between the CCDs and clean the combined images for bad pixels and cosmic-ray-events. MOS: Not yet available.
OT program file:	Not yet available
Science background:	Proposal is to measure velocities accurate to ~3 km/s for samples (preferably 2 masks) of K giants in local group dwarf galaxies (e.g., M31 dwarf spheroidal And II) with a view to determining velocity dispersions and mass-to-light ratios. Question to be addressed is whether or not these dwarf galaxies have high M/L values as (apparently) the dSph companions to the Milky Way do. If yes, will confirm existence of dark matter in these systems; if no, would suggest Milky Way dSphs are not dynamical equilibrium (as a result of tidal effects). The observations, to be done at the CaII triplet, will also yield abundance information. And I has red giants at I magnitudes brighter than 21.5. 3 km/s RV accuracy obtainable in 3 hrs with R=12000. The velocity dispension is expected to be less than 10 km/s. Southern targets are provided for GMOS-S SV.
Target(s):	dSphs
	Object	RA (J2000)	Dec (J2000)
	And I	00:45	38
	And II	00:30	35
	Phoenix	01:50	-44
	Tucana	22:40	-64
Observing condition constraints:	image quality: 50%-ile sky transparency (clouds): 50%-ile sky transparency (water vapour): Any sky background: 80%-ile max air mass: 1.5
Instrument configuration:	MOS: R1200, 0.25" slitlets
Observing time requirements:	Imaging: 4x2 min MOS: 2-3 hours per galaxy.
SV team member(s) responsible for assessment:	Gary Da Costa; Jeremy Allington-Smith

Last update October 12, 2001; Inger Jørgensen