! +====================+ ! | PED OUTPUT PRODUCT | ! +====================+ ! ! /hal/data1/proposals/6441.prop ! Generated by PREPROCESSOR, version 6.0e ! Date: Mon Feb 12 11:32:19 EST 1996 Proposal_Information Title: The Unknown Stellar Populations in Amorphous Galaxies: NGC 3077 and M82 Proposal_Category: GO Scientific_Category: GALAXIES & CLUSTERS Cycle: 6 Investigators PI_Name: Shoko Sakai PI_Institution: Jet Propulsion Laboratory CoI_Name: Barry Madore CoI_Institution: Caltech Contact: 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. Questions Observing_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: Fixed_Targets Target_Number: 10 Target_Name: NGC3077-POS1 Alternate_Names: UGC5398 Description: GALAXY,AMORPHOUS IRREGULAR, Position: RA=10H 3M 0.0S +/- 0.1S,DEC=68D 40' 53.5" +/- 0.5" Equinox: J2000 RV_or_Z: RA_PM: 0.0 Dec_PM: 0.0 Epoch: Annual_Parallax: 0.0 Flux: B = 26 V = 25 I = 24 Comments: Target_Number: 20 Target_Name: NGC3077-POS2 Alternate_Names: UGC5398 Description: GALAXY,AMORPHOUS IRREGULAR, Position: RA=10H 3M 20.0S +/- 0.1S,DEC=68D 40' 13.5" +/- 0.5" Equinox: J2000 RV_or_Z: RA_PM: 0.0 Dec_PM: 0.0 Epoch: Annual_Parallax: 0.0 Flux: B = 26 V = 25 I = 24 Comments: Target_Number: 30 Target_Name: M82-POS1 Alternate_Names: UGC5322 Description: GALAXY,AMORPHOUS IRREGULAR, Position: RA=9H 56M 06.4S +/- 0.1S,DEC=69D 43' 47.5" +/- 1.0" Equinox: J2000 RV_or_Z: RA_PM: 0.0 Dec_PM: 0.0 Epoch: Annual_Parallax: 0.0 Flux: B = 26 V = 25 I = 24 Comments: Target_Number: 40 Target_Name: M82-POS2 Alternate_Names: UGC5322 Description: GALAXY,AMORPHOUS IRREGULAR, Position: RA=9H 56M 30.0S +/- 0.1S,DEC=69D 43' 50.0" +/- 1.0" Equinox: J2000 RV_or_Z: RA_PM: 0.0 Dec_PM: 0.0 Epoch: Annual_Parallax: 0.0 Flux: B = 26 V = 25 I = 24 Comments: Solar_System_Targets Generic_Targets Scan_Data Visits Visit_Number: 01 Visit_Requirements: CVZ On_Hold_Comments: Visit_Comments: Exposure_Number: 10 Target_Name: NGC3077-POS1 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F555W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 500S Special_Requirements: Comments: Exposure_Number: 15 Target_Name: NGC3077-POS1 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F555W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 500S Special_Requirements: Comments: Exposure_Number: 20 Target_Name: NGC3077-POS1 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F814W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 500S Special_Requirements: Comments: Exposure_Number: 25 Target_Name: NGC3077-POS1 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F814W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 500S Special_Requirements: Comments: Exposure_Number: 30 Target_Name: NGC3077-POS2 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F555W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 500S Special_Requirements: Comments: Exposure_Number: 35 Target_Name: NGC3077-POS2 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F555W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 500S Special_Requirements: Comments: Exposure_Number: 40 Target_Name: NGC3077-POS2 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F814W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 500S Special_Requirements: Comments: Exposure_Number: 45 Target_Name: NGC3077-POS2 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F814W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 500S Special_Requirements: Comments: Visit_Number: 02 Visit_Requirements: CVZ On_Hold_Comments: Visit_Comments: Exposure_Number: 50 Target_Name: M82-POS1 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F555W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 500S Special_Requirements: Comments: Exposure_Number: 55 Target_Name: M82-POS1 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F555W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 500S Special_Requirements: Comments: Exposure_Number: 60 Target_Name: M82-POS1 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F814W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 500S Special_Requirements: Comments: Exposure_Number: 65 Target_Name: M82-POS1 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F814W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 500S Special_Requirements: Comments: Exposure_Number: 70 Target_Name: M82-POS2 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F555W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 500S Special_Requirements: Comments: Exposure_Number: 75 Target_Name: M82-POS2 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F555W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 500S Special_Requirements: Comments: Exposure_Number: 80 Target_Name: M82-POS2 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F814W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 500S Special_Requirements: Comments: Exposure_Number: 85 Target_Name: M82-POS2 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F814W Wavelength: Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 500S Special_Requirements: Comments: Data_Distribution ! Defaults indicated; change if desired Medium: 8MM Blocking_Factor: 10 Ship_To: IPAC 100-22 Caltech Pasadena CA 91125 Ship_Via: UPS Recipient_Email: shoko@ipac.caltech.edu ! Let us know what you think of this template and software! ! Please send a list of your likes and dislikes to your Program Coordinator