M31 Position from radio source (ApJ 1992, 390 L9), verified with
WFPC2 F555W image u2lg0201t_c0f. All exposures are dithered,
with no CR splits. ----- Submission 1 (Mon Apr 25 23:50:18 GMT 2005) -----
Assigned ID: 105
----- Submission 1 (Thu Jan 20 22:17:43 GMT 2005) -----
Phase I Proposal 105 (m31blue_cy14_v4) successfully submitted.
The Compact Disk of Blue Stars Orbiting the M31 Black HoleWe propose ACS/HRC U and B band imaging of the compact cluster of blue stars at the precise center of M31, which hosts the 1.3X10^8 solar-mass nuclear black hole. Analysis of STIS spectra and WFPC2 images suggest that the cluster is actually a disk. Recovering an accurate light distribution of the disk is essential for obtaining a precise estimate of the black hole mass from the STIS spectra, an approach that is attractive as it bypasses modeling the complex structure and dynamics of the M31 double nucleus by using the Keplerian rotation of the blue disk as a direct mass indicator. Dithered ACS/HRC observations in the blue provide the best spatial resolution available from HST, which is ~2X finer than could be obtained by the WFPC2 observations that first elucidated the structure of the blue cluster. The cluster effective radius (barely resolved by WFPC2) is only ~ 0.06'', thus the ultimate resolution and improved S/N offered by re-observation with ACS/HRC are essential to fully understand the disk inclination and radial starlight distribution. Analysis of the "smoothness" of the blue light distribution may also reveal its composition. The low-luminosity of the disk, M(AB)=-5.5 can be produced by only a few hundred A-stars, a small enough number that fluctuation statistics should leave an obvious signature on the light distribution.The observations comprise ACS/HRC observations of the M31 nucleus. The first orbit consists of 8 F435W exposures in two groups obtained with 2X2 0.5 pixel dithers to ensure Nyquist sampling. The two groups are offset by 3.5 pixels in X and Y to reject hot pixels and CCD defects. The remaining three orbits consist of 12 F330W exposures, again obtained in three groups with 2X2 0.5 pixel dithers. In this case the three groups are offset by increments of 0.125 pixels in X and Y both for rejection of hot pixels and CCD defects, but also to improve sampling in the ACS/WFC parallel observations.GALAXIES12false0.0falsefalsefalsefalsefalseSUPPORTEDGALAXYNUCLEUSMu(V)=13.5J200000 42 41.9000+41 16 8.00J2000ACS/HRCImagingNoNoF330WACS/HRCImagingNoNoF435WPOS-TARGDITHER0.0142LINE0.0124falsefalse90.040.0ACS-HRC-DITHER-BOX1false
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false40/Users/lauer/hst/cy14/OP-cache/m31blue_cy14_v4-v01.xml