9053( 2) - 02/08/01 14:21 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9053 Version: 2 Check-in Date: 08-Feb-2001 14:20:48 1.Proposal Title: The Late Evolution of Low-Mass Stars: a Deep UV Color-Magnitude Diagram of M32 ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 10 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Thomas Brown Catholic University of America CoI: Charles W. Bowers Goddard Space Flight Center N CoI: Randy A. Kimble Goddard Space Flight Center N CoI: Allen V. Sweigart Goddard Space Flight Center N CoI: Henry C. Ferguson Space Telescope Science Institute N ------------------------------------------------------------------------------------ 5. Abstract We propose to construct a deep far-UV color-magnitude diagram (CMD) of the hot stellar population in the center of M32 (NGC221). Our previous Cycle 7 near-UV STIS observations of the M32 core resolved 8000 stars in a single bandpass. While these observations provided no color information, they nonetheless showed conclusively that hot (T_eff > 8500 K) horizontal branch (HB) stars exist in M32. Moreover, the near-UV luminosity function showed a surprising lack of post- asymptotic giant branch (post-AGB) stars, indicating that they evolve much more rapidly than expected from canonical theory. Obtaining color information is the vital next step to extending this analysis. A CMD for a statistically large sample of evolved stars in M32 will provide fundamental information on post-red giant branch evolution that is not obtainable from Galactic globular clusters (because of too few stars) or from the Galactic field (because distance uncertainties dominate the errors). We aim to address the following questions: 1) Do hot HB stars have high helium abundance, as predicted by some models of elliptical galaxy chemical evolution? 2) How does the rate of post-AGB evolution differ from theoretical expectations, and what does this tell us about mass-loss on the AGB? 3) What is the mass and temperature distribution on the HB of M32? 4) What are the relative lifetimes of the HB and post-HB phases? ------------------------------------------------------------------------------------ 9053( 2) - 02/08/01 14:21 - [ 2] Observations Description ------------------------ Our observing strategy is fairly simple. The M32 nucleus is bright enough to enable a brief (10 sec) CCD acquisition, after which we will do an offset, to place the field so that it coincides with the position and orientation (modulo 90 degrees) of our earlier near-UV observations (program 7557). Although the M32 nucleus has a sharp bright peak, the galaxy is very red and is completely safe for the MAMA detectors; this is confirmed by previous FOC F175W and F275W observations of the same region, and by the STIS near-UV imaging. These new STIS observations will utilize the FUVMAMA with the F25SRF2 filter. The choice of F25SRF2 over F25QTZ is not trivial. In the F25QTZ filter, the sky counts are much lower than in the F25SRF2, but the throughput is also greatly reduced, with the reduction primarily at the shortest wavelengths; the F25SRF2 provides the better temperature lever when combined with the near-UV observations. We performed simulations with our own code and with the STScI Exposure Time Calculator; for our science, the gains made with the F25SRF2 filter outweigh the disadvantage of the increased sky background. Note that unresolved cooler populations comprise a diffuse background that must be added to the ``sky'' background in these calculations. The sky in the F25SRF2 filter varies dramatically over the course of an orbit (with day and night and the presence of the tropical OI bands), and so we will use a series of short exposures. These exposres can then be selected according to sky brightness, and summed to create images that will maximize the signal-to-noise ratio for both the bright and faint evolutionary phases. We have estimated the sky variation in this filter with archival imaging in the same mode. Note that the far-UV detector ``glow'' (where the dark rate is increased locally by an order of magnitude) is not a problem for these observations, because it is small compared to the other background sources. This glow would be more apparent in the F25QTZ mode. To remove those portions of each orbit that have the brightest sky, we could theoretically use TIMETAG mode instead of a series of short exposures, but the extant data in this bandpass shows occasional instances of very high sky rate, making it difficult to determine an appropriate BUFFER-TIME, so we chose ACCUM mode with short exposures (taking advantage of the STIS ability to dump the buffer in parallel to observations). Small changes in the position for each visit (via POS-TARGs) will be used to remove hot and defective pixels in the data reduction. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9053( 2) - 02/08/01 14:21 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 M32-OFFSET GALAXY, DWARF RA=0H 42M 41.72S +/- 0.1S, J2000 E(B-V) = 0.11+/-0.03 ELLIPTICAL DEC=40D 51' 53.52" +/- 0.1", SURF(V) = 11.5+/-0.1 PLATE-ID=0738 F(1400)=2+/-0.2e-15 F(1800)=2+/-0.2e-15 F(2500)=1+/-0.2e-15 Coordinate Source: HST_IMAGE Comments: Our science observations will be at a position approximately 7.7 arcsec south of the M32 core. Target 1, the core, is specified for acquisition, after which an offset will place the STIS field at the offset position. 2 M32-FIELD GALAXY, DWARF RA-OFF=0.05S+/- 0.01S, DEC-OFF=- J2000 E(B-V) = 0.11+/-0.03 ELLIPTICAL 7.6"+/- 0.01", FROM 1, PLATE- SURF(V) = 11.5+/-0.1 ID=0738 F(1400)=2+/-0.2e-15 F(1800)=2+/-0.2e-15 F(2500)=1+/-0.2e-15 Coordinate Source: HST_IMAGE Comments: Target 2, offset from the M32 core, is the location for our science observations. The M32 core should appear approximately 7.7" north of the STIS field center. 9053( 2) - 02/08/01 14:21 - [ 4] Visit: 01 Visit Priority: Visit Requirements: ORIENT 68D TO 72D ORIENT 158D TO 162D ORIENT 248D TO 252D ORIENT 338D TO 342D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 M32-OFFSET STIS/C ACQ 50CCD MIRROR ACQTYPE=DIFFUSE,CHECKBOX=5, 1 10 S CD DIFFUSE-CENTER=FLUX-CENTROID ------------------------------------------------------------------------------------------------------------------------------------ 20 M32-FIELD STIS/F ACCUM F25SRF2 MIRROR 45 300 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9053( 2) - 02/08/01 14:21 - [ 5] Visit: 02 Visit Priority: Visit Requirements: ORIENT 68D TO 72D ORIENT 158D TO 162D ORIENT 248D TO 252D ORIENT 338D TO 342D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 M32-OFFSET STIS/C ACQ 50CCD MIRROR ACQTYPE=DIFFUSE,CHECKBOX=5, 1 10 S CD DIFFUSE-CENTER=FLUX-CENTROID ------------------------------------------------------------------------------------------------------------------------------------ 20 M32-FIELD STIS/F ACCUM F25SRF2 MIRROR 45 300 S POS TARG 0.25, 0.25 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9053( 2) - 02/08/01 14:21 - [ 6] Visit: 03 Visit Priority: Visit Requirements: ORIENT 68D TO 72D ORIENT 158D TO 162D ORIENT 248D TO 252D ORIENT 338D TO 342D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 M32-OFFSET STIS/C ACQ 50CCD MIRROR ACQTYPE=DIFFUSE,CHECKBOX=5, 1 10 S CD DIFFUSE-CENTER=FLUX-CENTROID ------------------------------------------------------------------------------------------------------------------------------------ 20 M32-FIELD STIS/F ACCUM F25SRF2 MIRROR 45 300 S POS TARG 0.25,-0.25 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9053( 2) - 02/08/01 14:21 - [ 7] Visit: 04 Visit Priority: Visit Requirements: ORIENT 68D TO 72D ORIENT 158D TO 162D ORIENT 248D TO 252D ORIENT 338D TO 342D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 M32-OFFSET STIS/C ACQ 50CCD MIRROR ACQTYPE=DIFFUSE,CHECKBOX=5, 1 10 S CD DIFFUSE-CENTER=FLUX-CENTROID ------------------------------------------------------------------------------------------------------------------------------------ 20 M32-FIELD STIS/F ACCUM F25SRF2 MIRROR 45 300 S POS TARG -0.25,-0.25 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9053( 2) - 02/08/01 14:21 - [ 8] Visit: 05 Visit Priority: Visit Requirements: ORIENT 68D TO 72D ORIENT 158D TO 162D ORIENT 248D TO 252D ORIENT 338D TO 342D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 M32-OFFSET STIS/C ACQ 50CCD MIRROR ACQTYPE=DIFFUSE,CHECKBOX=5, 1 10 S CD DIFFUSE-CENTER=FLUX-CENTROID ------------------------------------------------------------------------------------------------------------------------------------ 20 M32-FIELD STIS/F ACCUM F25SRF2 MIRROR 45 300 S POS TARG -0.25, 0.25 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9053( 2) - 02/08/01 14:21 - [ 9] Visit: 06 Visit Priority: Visit Requirements: ORIENT 68D TO 72D ORIENT 158D TO 162D ORIENT 248D TO 252D ORIENT 338D TO 342D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 M32-OFFSET STIS/C ACQ 50CCD MIRROR ACQTYPE=DIFFUSE,CHECKBOX=5, 1 10 S CD DIFFUSE-CENTER=FLUX-CENTROID ------------------------------------------------------------------------------------------------------------------------------------ 20 M32-FIELD STIS/F ACCUM F25SRF2 MIRROR 45 300 S POS TARG 0.25, 0.25 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9053( 2) - 02/08/01 14:21 - [ 10] Visit: 07 Visit Priority: Visit Requirements: ORIENT 68D TO 72D ORIENT 158D TO 162D ORIENT 248D TO 252D ORIENT 338D TO 342D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 M32-OFFSET STIS/C ACQ 50CCD MIRROR ACQTYPE=DIFFUSE,CHECKBOX=5, 1 10 S CD DIFFUSE-CENTER=FLUX-CENTROID ------------------------------------------------------------------------------------------------------------------------------------ 20 M32-FIELD STIS/F ACCUM F25SRF2 MIRROR 45 300 S POS TARG -0.25,-0.25 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9053( 2) - 02/08/01 14:21 - [ 11] Summary Form for Proposal 9053 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 50CCD F25SRF2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=DIFFUSE CHECKBOX=5 DIFFUSE-CENTER=FLUX-CENTROID ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 68D TO 72D ORIENT 158D TO 162D ORIENT 248D TO 252D ORIENT 338D TO 342D POS TARG 0.25, 0.25 POS TARG 0.25,-0.25 POS TARG -0.25,-0.25 POS TARG -0.25, 0.25 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names M32-OFFSET M32-FIELD ------------------------------------------------------------------------------------------------------------------------------------