8255( 3) - 09/13/99 15:30 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8255 Version: 3 Check-in Date: 12-Feb-1999 14:15:27 1.Proposal Title: Stellar Populations in the Closest Large Low Surface Brightness Galaxy ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 8 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Patricia Knezek The Johns Hopkins University CoI: Dr. Bryan Miller Leiden University N CoI: Dr. Erwin de Blok University of Melbourne N CoI: Prof. Stacy McGaugh University of Maryland N ------------------------------------------------------------------------------------ 5. Abstract We propose to observe the closest known large low surface brightness (LSB) galaxy, UGC 2302, in order to resolve for the first time the massive stars and tip of the red giant branch in such a system. Large LSBs represent an extreme star formation environment, both locally within their disks, and on a larger scale, often residing in underdense regions of the universe. Resolving the underlying stellar component of such a galaxy can provide critical information on how stars form and evolve in low metallicity, yet gas-rich environments. The combination of this data with planned near-infrared, abundance and molecular gas studies, existing optical UBVRI and Halpha data, and a VLA HI map, will allow comparison between the abundance and distribution of stars, star formation, and neutral gas in unprecedented detail for disk LSBs. In addition, determination of the characteristics of even the brightest stars in this galaxy will provide a key calibration of the relative contribution o f the brightest main sequence, gia nt, and supergiant stars to the optical and near- infrared colors. This calibration can then be applied to determining the underlying stellar populations of other massive LSB galaxies using broad-band filters. ------------------------------------------------------------------------------------ 8255( 3) - 09/13/99 15:30 - [ 2] Observations Description ------------------------ Deep WFPC2 images through filters F555W and F814W will be used to study the stellar populations and star formation history of UGC 2302, the closest large LSB spiral. The F555W and F814W bandpasses are chosen since they have good transformations to the Johnson/Cousins V and I system, which is the standard for observing old stellar populations. The Cycle 4 TAC strongly recommended these filters for galaxy population studies. The galaxy will be centered in the PC to get the highest spatial resolution in the crowded central region. (1 PC pixel=10.5 pc^2 at the distance of UGC 2302, assuming H_0 = 75 km s^-1 Mpc^-1.) One of the primary goals of this project is to detect the tip of the Red Giant Branch (TRGB). The TRGB for old stellar populations is at M_I=-4, (V\.-\.I)~ 1.5, in the color-magnitude diagram. Therefore, for an assumed distance to UGC 2302 of (m-M)_0~31, the TRGB will have I~27 and our detection limit (S/N~3) will need to be I~27.5. The WFPC2 exposure time calcu lator (ETC) suggests that we can r each this limit in ~\.14, 000 sec, or about 5 orbits. We have assumed that objects are centered in the corner of a PC pixel and we have accounted for loss of S/N due to multiple readouts. However, experience with HST imaging of extragalactic globular clusters (Miller et al.\ 1997, AJ, 114, 2381) suggests that the ETC tends to underestimate actual exposure times. Therefore, we feel that 6 orbits in F814W will yield the desired senstivity. An equal amount of exposure time is needed in F555W in order to determine (V-I) colors. Therefore, our project requires 12 orbits. Because there are difficulties with scheduling 12 continuous orbits, we will do the observations in three visits of 4 orbits each. We request that the second visit be approximately 6 days after the first visit (+/- 1 day), and the third visit follow the second by approximately 17 days (+/- 2 days). This will allow us to make an initial search for possible variable stars (e.g. Cepheids), as was suggested by th e TAC. We have chosen this timing separation to try to get the best spread in Cepheid periods, while excluding (1) the short period Cepheids, which may be too faint to detect in one exposure, and (2) the longest period variables, which are likely to be rare. The long exposures will be CR-SPLIT for removal of cosmic rays. In addition, we will sub-pixel dither to improve cosmic ray and hot pixel removal, increase the spatial resolution, and increase the photometric sensitivity by ~\.0.5 mag. This will maximize our chances of being able to detect the TRGB and brighter stars. To make efficient use of HST we will also take images in parallel with STIS. By imaging through both the clear aperture and the longpass filter, we can measure colors similar to (B-I) for the detected objects (Gregg & Minniti 1997, PASP, 109, 1062). Because of the wide filters these images will be very deep, V~30 in 16, 000 sec. The offset field of STIS will give us a better handle on background/foreground contamination in the WFPC2 im ages. Also, we will look for an ex tended halo of RGB stars at ~\.25 kpc from the galaxy. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 8255( 3) - 09/13/99 15:30 - [ 3] Data Distribution Paper Products: NO Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 8255( 3) - 09/13/99 15:30 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 UGC2302 GALAXY, LSB RA=02H 49M 9.0S +/- 0.1S, J2000 V = 1104 V = 13.51 DEC=02D 7' 39.2" +/- 0.3", PLATE E(B-V) = 0.06 -ID=04YH V-I = 0.70 8255( 3) - 09/13/99 15:30 - [ 5] Visit: 01 Visit Priority: Visit Requirements: PCS MODE FINE 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 UGC2302 WFPC2 IMAGE PC1 F555W ATD-GAIN=7,CR-SPLIT=0.5 1 2400 S PAR 2 WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY STIS/C ACCUM 50CCD MIRROR 1 2600 S CD Comments: parallel ------------------------------------------------------------------------------------------------------------------------------------ 3 UGC2302 WFPC2 IMAGE PC1 F555W ATD-GAIN=7,CR-SPLIT=0.5 1 2600 S PAR 4 WITH 3 POS TARG 0.50, 0.25 ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY STIS/C ACCUM 50CCD MIRROR 1 2700 S CD Comments: parallel ------------------------------------------------------------------------------------------------------------------------------------ 5 UGC2302 WFPC2 IMAGE PC1 F814W ATD-GAIN=7,CR-SPLIT=0.5 1 2600 S PAR 6 WITH 5 ------------------------------------------------------------------------------------------------------------------------------------ 6 ANY STIS/C ACCUM F28X50L MIRROR 1 2700 S CD P Comments: parallel ------------------------------------------------------------------------------------------------------------------------------------ 7 UGC2302 WFPC2 IMAGE PC1 F814W ATD-GAIN=7,CR-SPLIT=0.5 1 2600 S PAR 8 WITH 7 POS TARG -0.5,-0.25 ------------------------------------------------------------------------------------------------------------------------------------ 8 ANY STIS/C ACCUM F28X50L MIRROR 1 2700 S CD P Comments: parallel ------------------------------------------------------------------------------------------------------------------------------------ 8255( 3) - 09/13/99 15:30 - [ 6] Visit: 02 Visit Priority: Visit Requirements: PCS MODE FINE SAME ORIENT AS 01 AFTER 01 BY 5 D TO 7 D On Hold Comments: Additional Comments: Visit timing to search for potential Cepheids, as suggested by TAC. Scheduling 5-7 days after visit 1 would be best, but this can be relaxed by +/- 2 days if a serious scheduing conflict arises. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 9 UGC2302 WFPC2 IMAGE PC1 F555W ATD-GAIN=7,CR-SPLIT=0.5 1 2400 S PAR 10 WITH 9 ------------------------------------------------------------------------------------------------------------------------------------ 10 ANY STIS/C ACCUM 50CCD MIRROR 1 2600 S CD Comments: parallel ------------------------------------------------------------------------------------------------------------------------------------ 11 UGC2302 WFPC2 IMAGE PC1 F555W ATD-GAIN=7,CR-SPLIT=0.5 1 2600 S PAR 12 WITH 11 POS TARG 0.25, 0.5 ------------------------------------------------------------------------------------------------------------------------------------ 12 ANY STIS/C ACCUM 50CCD MIRROR 1 2700 S CD Comments: parallel ------------------------------------------------------------------------------------------------------------------------------------ 13 UGC2302 WFPC2 IMAGE PC1 F814W ATD-GAIN=7,CR-SPLIT=0.5 1 2600 S PAR 14 WITH 13 ------------------------------------------------------------------------------------------------------------------------------------ 14 ANY STIS/C ACCUM F28X50L MIRROR 1 2700 S CD P Comments: parallel ------------------------------------------------------------------------------------------------------------------------------------ 15 UGC2302 WFPC2 IMAGE PC1 F814W ATD-GAIN=7,CR-SPLIT=0.5 1 2600 S PAR 16 WITH 15 POS TARG -0.25,-0.5 ------------------------------------------------------------------------------------------------------------------------------------ 16 ANY STIS/C ACCUM F28X50L MIRROR 1 2700 S CD P Comments: parallel ------------------------------------------------------------------------------------------------------------------------------------ 8255( 3) - 09/13/99 15:30 - [ 7] Visit: 03 Visit Priority: Visit Requirements: PCS MODE FINE SAME ORIENT AS 01 AFTER 02 BY 16 D TO 18 D On Hold Comments: Additional Comments: Visit timing to search for potential Cepheids, as suggested by TAC. Scheduling 16-18 days after visit 2 would be best, but this can be relaxed by +/- 4 days if a serious scheduing conflict arises. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 17 UGC2302 WFPC2 IMAGE PC1 F555W ATD-GAIN=7,CR-SPLIT=0.5 1 2400 S PAR 18 WITH 17 ------------------------------------------------------------------------------------------------------------------------------------ 18 ANY STIS/C ACCUM 50CCD MIRROR 1 2600 S CD Comments: parallel ------------------------------------------------------------------------------------------------------------------------------------ 19 UGC2302 WFPC2 IMAGE PC1 F555W ATD-GAIN=7,CR-SPLIT=0.5 1 2600 S PAR 20 WITH 19 POS TARG 0.5, 0.5 ------------------------------------------------------------------------------------------------------------------------------------ 20 ANY STIS/C ACCUM 50CCD MIRROR 1 2700 S CD Comments: parallel ------------------------------------------------------------------------------------------------------------------------------------ 21 UGC2302 WFPC2 IMAGE PC1 F814W ATD-GAIN=7,CR-SPLIT=0.5 1 2600 S PAR 22 WITH 21 ------------------------------------------------------------------------------------------------------------------------------------ 22 ANY STIS/C ACCUM F28X50L MIRROR 1 2700 S CD P Comments: parallel ------------------------------------------------------------------------------------------------------------------------------------ 23 UGC2302 WFPC2 IMAGE PC1 F814W ATD-GAIN=7,CR-SPLIT=0.5 1 2600 S PAR 24 WITH 23 POS TARG -0.5,-0.5 ------------------------------------------------------------------------------------------------------------------------------------ 24 ANY STIS/C ACCUM F28X50L MIRROR 1 2700 S CD P Comments: parallel ------------------------------------------------------------------------------------------------------------------------------------ 8255( 3) - 09/13/99 15:30 - [ 8] Summary Form for Proposal 8255 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PC1 50CCD F28X50LP ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 STIS/CCD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ATD-GAIN=7 CR-SPLIT=0.5 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PCS MODE FINE PAR 2 WITH 1 PAR 4 WITH 3 POS TARG 0.50, 0.25 PAR 6 WITH 5 PAR 8 WITH 7 POS TARG -0.5,-0.25 PCS MODE FINE SAME ORIENT AS 01 AFTER 01 BY 5 D TO 7 D PAR 10 WITH 9 PAR 12 WITH 11 POS TARG 0.25, 0.5 PAR 14 WITH 13 PAR 16 WITH 15 POS TARG -0.25,-0.5 PCS MODE FINE SAME ORIENT AS 01 AFTER 02 BY 16 D TO 18 D PAR 18 WITH 17 PAR 20 WITH 19 POS TARG 0.5, 0.5 PAR 22 WITH 21 PAR 24 WITH 23 POS TARG -0.5,-0.5 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W MIRROR F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names UGC2302 ANY ------------------------------------------------------------------------------------------------------------------------------------