6441( 8) - 02/12/97 14:19 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6441 Version: 8 Check-in Date: 12-Feb-1997 14:15:57 1.Proposal Title: The Unknown Stellar Populations in Amorphous Galaxies: NGC 3077 and M82 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle GALAXIES & CLUSTERS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: SHOKO SAKAI JET PROPULSION LABORATORY CoI: Barry Madore Caltech N ------------------------------------------------------------------------------------ 6. Abstract In a ground-based attempt at the Palomar 5m to determine the distances to M81 Group galaxies using the tip of the red giant branch (TRGB) method, we have discovered a population of at least 1700 star--like objects at I = 21--26 mag and V-I = 1.0 mag within and around the amorphous galaxy NGC 3077. Two possible interpretations for these objects are: (1) intermediate-aged asymptotic giant branch stars, or (2) a vast population of globular clusters unresolved from the ground. In either case, this represents the first resolution of the `stellar' population in an amorphous (= Type II irregular) galaxy. These objects are also most likely a product of the encounter of NGC 3077 with M81. HST provides a resolution of 1.8 parsec/pixel at the distance of the M81 group; even modest V + I exposures should be capable of discriminating between globular clusters and stars based on simple radial luminosity profiles. In these same images, the TRGB stars (expected to begin at I ~ 23.7 mag) will be resolved and a direct distance to NGC 3077 will be obtained. For direct comparison, M82 is another amorphous galaxy in this same group. A differential study of the bright stellar populations in two of the nearest examples of these rare forms of tidally--interacting systems can thus be made in a distance--independent way. We plan therefore to image the halo population of M82 also for the first time, searching for its AGB/cluster population, as well as surely measuring the TRGB population. ------------------------------------------------------------------------------------ 6441( 8) - 02/12/97 14:19 - [ 2] Observations Description ------------------------ Two fields for each galaxy are to be chosen such that separate sets of guide stars do not need to be acquired or re-acquired; a simple differential offset of a few arcmin can be made from the first field center without losing lock. If scheduled in the CVZ, after the usual overheads have been extracted (for guidestar acquisition and CR-split readings of paired exposures) we can expect to have 35 minutes of on -target time for each field (70 minutes per orbit). This would optimally be allocated to sets of CR-split 500- second exposures in both F555W and F814W. Using the STScI ``Exposure Time Estimator'' these exposures individually give photometric errors of better than +/-0.05 mag at V and I = 24.0 mag (somewhat below the expected magnitude of the TRGB at the distance of the M81 Group). centerline Tip of the Red Giant Branch Distances With the HST V + I photometry, we should be able to detect the tip of the red giant branch (TRGB) beginning at I ~ 23.8. The TRGB method for determining distances to nearby galaxies has been proven to be as accurate as the Cepheid PL relation and is applicable to all morphological types of galaxies as long as the Population II red giant branch stars are present (Lee et al. 1993). The first--ascent red giant branch marks the core helium flash of low--mass stars which evolve up the red--giant branch. Their luminosity evolution terminates abruptly and forms a discontinuity in the luminosity function. It has been confirmed both theoretically and observationally that this discontinuity in the luminosity function has minimum dispersion in luminosity (of +/-0.1 mag) when observed in the I-band (Da Costa & Armandroff 1990, Lee et al. 1993). With short-- exposure HST V + I images, we will be able to resolve the red giant branch population and determine the distances directly to two of the M81 group galaxies. References \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\medskip Becker, R., Schilke, P. & Henkel, C., 1989, AA, 211, L19 Cottrell, G. A. 1977, MNRAS, 178, 577 Da Costa, G. S. & Armandroff, T. E., 1990, AJ, 100, 162 Freedman, W. L. et al., 1994, ApJ, 427, 628 Gottesman, S. T. & Weliachew, L., 1977, ApJ, 211, 47 Karachensev, I.D., Karachentseva, V.E. & Borgen, F., 1985, MNRAS, 217, 731. Lee, M. G., Freedman, W. L. & Madore, B. F., 1993, ApJ, 417, 553 Loiseau, N., Reuter, H.-P., Wielebinski, R. & Klein, U., 1988, AA, 200, L1 Madore, B. F. & Freedman, W. L., 1995, AJ, 109, 1645 Madore, B. F., Freedman, W. L. & Lee, M. G., 1993, AJ, 106, 2243 O'Connell, R.W., Gallagher, J.S., Hunter, D.A., & Colley, W.N., 1995, ApJ, 446, L10 Price, J. S. & Gullixson, C. A., 1989, ApJ, 337, 658 Sandage, A. & Brucato, R., 1979, AJ, 84, 472 Thronson, H. A., Wilson, C. & Ksir, A., 1991, MNRAS, 252, 543 van der Hulst, J. M., 1979, AA, 75, 97 Real Time Justification ----------------------- The M81 Group is a high--dec target and it makes most sense to schedule these observations in the Continuous Viewing Zone (CVZ). There are 29 orbits available as CVZ time for the RA and DEC of the M81 Group ( HST Cycle 6: Phase I Proposal Instructions Manual, 1995 Version 5.0, p 54) . During each of those orbits there are 96 minutes of target visibility. Discovery observations were made in April 1995 using the Palomar 5m. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6441( 8) - 02/12/97 14:19 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: IPAC 100-22 Caltech Pasadena CA 91125 Ship Via: UPS Email: shoko@ipac.caltech.edu ------------------------------------------------------------------------------------ 6441( 8) - 02/12/97 14:19 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC3077-POS1 GALAXY,AMORPHOUS RA=10H 3M 0.0S +/- 0.1S,DEC=68D J2000 B = 26 IRREGULAR 40' 53.5" +/- 0.5" V = 25 I = 24 20 NGC3077-POS2 GALAXY,AMORPHOUS RA=10H 3M 20.0S +/- 0.1S,DEC=68D J2000 B = 26 IRREGULAR 40' 13.5" +/- 0.5" V = 25 I = 24 30 M82-POS1 GALAXY,AMORPHOUS RA=9H 56M 06.4S +/- 0.1S,DEC=69D J2000 B = 26 IRREGULAR 43' 47.5" +/- 1.0" V = 25 I = 24 40 M82-POS2 GALAXY,AMORPHOUS RA=9H 56M 30.0S +/- 0.1S,DEC=69D J2000 B = 26 IRREGULAR 43' 50.0" +/- 1.0" V = 25 I = 24 6441( 8) - 02/12/97 14:19 - [ 5] Visit: 01 Visit Requirements: CVZ 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 NGC3077-POS WFPC2 IMAGE PC1-FIX F555W 1 500 S 1 ------------------------------------------------------------------------------------------------------------------------------------ 15 NGC3077-POS WFPC2 IMAGE PC1-FIX F555W 1 500 S 1 ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC3077-POS WFPC2 IMAGE PC1-FIX F814W 1 500 S 1 ------------------------------------------------------------------------------------------------------------------------------------ 25 NGC3077-POS WFPC2 IMAGE PC1-FIX F814W 1 500 S 1 ------------------------------------------------------------------------------------------------------------------------------------ 30 NGC3077-POS WFPC2 IMAGE PC1-FIX F555W 1 500 S 2 ------------------------------------------------------------------------------------------------------------------------------------ 35 NGC3077-POS WFPC2 IMAGE PC1-FIX F555W 1 500 S 2 ------------------------------------------------------------------------------------------------------------------------------------ 40 NGC3077-POS WFPC2 IMAGE PC1-FIX F814W 1 500 S 2 ------------------------------------------------------------------------------------------------------------------------------------ 45 NGC3077-POS WFPC2 IMAGE PC1-FIX F814W 1 500 S 2 ------------------------------------------------------------------------------------------------------------------------------------ 6441( 8) - 02/12/97 14:19 - [ 6] Visit: 02 Visit Requirements: CVZ 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 ------------------------------------------------------------------------------------------------------------------------------------ 50 M82-POS1 WFPC2 IMAGE PC1-FIX F555W 1 500 S ------------------------------------------------------------------------------------------------------------------------------------ 55 M82-POS1 WFPC2 IMAGE PC1-FIX F555W 1 500 S ------------------------------------------------------------------------------------------------------------------------------------ 60 M82-POS1 WFPC2 IMAGE PC1-FIX F814W 1 500 S ------------------------------------------------------------------------------------------------------------------------------------ 65 M82-POS1 WFPC2 IMAGE PC1-FIX F814W 1 500 S ------------------------------------------------------------------------------------------------------------------------------------ 70 M82-POS2 WFPC2 IMAGE PC1-FIX F555W 1 500 S ------------------------------------------------------------------------------------------------------------------------------------ 75 M82-POS2 WFPC2 IMAGE PC1-FIX F555W 1 500 S ------------------------------------------------------------------------------------------------------------------------------------ 80 M82-POS2 WFPC2 IMAGE PC1-FIX F814W 1 500 S ------------------------------------------------------------------------------------------------------------------------------------ 85 M82-POS2 WFPC2 IMAGE PC1-FIX F814W 1 500 S ------------------------------------------------------------------------------------------------------------------------------------ 6441( 8) - 02/12/97 14:19 - [ 7] Summary Form for Proposal 6441 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category GALAXIES & CLUSTERS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CVZ ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC3077-POS1 NGC3077-POS2 M82-POS1 M82-POS2 ------------------------------------------------------------------------------------------------------------------------------------