Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999hst..prop.8286o&link_type=abstract
HST Proposal ID #8286
Astronomy and Astrophysics
Astronomy
Hst Proposal Id #8286 Galaxy Structure And Dynamics
Scientific paper
We propose to measure precise absolute proper motions for four dwarf spheroidal satellites of the Milky Way using spectroscopically-confirmed background QSOs to define a zero- velocity reference frame. Three epochs within the 2 years separating 3 HST cycles will yield systemic tangential velocities of UMi, Car, Scl, {and For} to +/- 78 kms {+/- 130 kms}. These are worst-case velocity precisions and they are likely to be 2* smaller. With 2-3 QSOs per galaxy and 3 observations per QSO field we will have a clear understanding of the systematic errors that could affect the astrometry. We will test whether the halo contains a small number of massive streams containing several dwarf galaxies, or whether the individual halo dwarfs are traveling along independent orbits. HST is essential to achieving the high precisions needed to conclusively compare the projected orbital motions of the individual galaxies; even with our conservative uncertainties, we are competitive with the best ground-based efforts with only a 2 year baseline. We will also use our results to improve our estimate of the mass of the Galaxy interior to 100 kpc.
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