5904( 7) - 12/12/95 08:08 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 5904 Version: 7 Check-in Date: ********** 1.Proposal Title: Primordial Mass Segregation and Main Sequence Age Spreads in Young LMC Clusters ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Stellar Populations GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Philippe Fischer AT&T Bell Laboratories CoI: Stephen Murray University of California Berkeley N CoI: Mario Mateo University of Michigan N CoI: Carlton Pryor Rutgers U. N CoI: Tom Richtler University of Bonn N CoI: Douglas Heggie University of Edinburgh N CoI: Ram Sagar Indian Institute of Astrophysics N ------------------------------------------------------------------------------------ 6. Abstract Most stars form in clusters, but the details of this process remain very poorly understood. A clearer picture of cluster formation is essential to understanding star formation and the spectral, photometric, and chemical evolution of composite stellar systems. By using the high-resolution imaging capabilities of the WFPC2 to study young clusters in the Large Magellanic Cloud, we will make the first tests that will clearly distinguish between the primary competing theories of cluster formation. Images in V and I of the clusters and background fields will yield precise, well-populated luminosity functions and color-magnitude diagrams. While previous studies of LMC clusters have concentrated on determining global mass functions, primordial mass segregation and age spreads are much stronger diagnostics of cluster- formation theories. We will also use these observations to test models of high-mass stars, to improve the Cepheid distance calibration, and, in conjunction with ground-based kinematic data, to determine the initial mass function down to the low-mass cut-off. The measurement of primordial mass segregation will, for the first time, provide the initial conditions for models of cluster dynamical evolution. ------------------------------------------------------------------------------------ 5904( 7) - 12/12/95 08:08 - [ 2] Observations Description ------------------------ We will center the clusters on the PC chip. This will give us the best resolution where the crowding is the highest (i.e., the PC chip will contain the entire core region -- Table 1) and coverage out to 1.6 arcmin (4.1 arcsec/pc) for about half of each cluster with some coverage out to almost 2 arcmin. At 2 arcmin our program clusters have typically declined in surface brightness by over two orders of magnitude (Elson 1991, ApJs, 76, 185). Two bandpasses (V = F555W and I = F814W) are necessary for constructing cluster CMDs and further reducing contamination. A large range of masses is needed for the mass functions in order to maximize our chances of detecting mass segregation. A lower mass limit of 0.75 M_\odot corresponds to V = 25 and I = 24.5 (Schaerer et al. 1993, A&AS, 98, 523). According to the WFPC manual we can get Sigma(V) = Sigma(I) < 0.1 with 4*300s (gain set to 7 e^- /DN). We add 25\ to this to take into account crowding and cosmic rays (based on C. Pryor's experience with cycle 4 images) giving 5*300s in both bandpasses. These exposures will have minimum unsaturated magnitudes of 18.5 for the WF (18.0 for the PC) for a star centered on a pixel. Additionally, we need short exposures 3*5s in both bandpasses to properly measure the upper main sequence and evolved stars. Even though these objects are relatively bright, the existing ground- based data is of insufficient resolution to distinguish merged stellar images (see \S 3). Based on cycle 4 experience we feel it is essential to have a minimum of five exposures for the 300s integrations and three exposures for the 5s integrations, in order to remove cosmic rays. Background fields of 5*300s will be required to correct the luminosity functions for non-cluster members. We do not require the short exposures in the background fields since they are sufficiently uncrowded that our ground-based data will be adequate. With an overhead of 180s per exposure, the total time per cluster is 5940s plus 4800s for each background field. Since all of our targets are in CVZs with multiple intervals, we have 96 minutes of visibility per orbit for nine orbits. Therefore, based on the worksheet, we calculate that each cluster plus background field will take 2 CVZ orbits including guide star acquisition. Our clusters were chosen for their young ages, large brightnesses, smooth light distributions and relatively low background densities. Two of our clusters are known to contain Cepheids. We have ground-based fields for all the clusters which will be used for calibration and for correcting the bright end of the luminosity function. Four cluster will be a sufficient sample size to rigorously test the cluster formation theories and search for inter-cluster variations in IMFs and primordial mass segregation. The clusters chosen vary by about a factor of two in core radii and distance from the center of the LMC (Table 1). The V and I bandpasses were chosen to maximize the efficiency and utility of the observations. They are sufficiently spaced in wavelength to provide good color information. They are a better choice than B and V since, according to the WFPC manual, the system efficiency is a factor of three higher in I than B. Furthermore, the faintest stars we hope to image, 0.75 Msun\ metal-rich main sequence stars, are brighter in I than in B. Real Time Justification ----------------------- We have ground-based imaging data for these clusters. Although shallower than our proposed data, this will be useful for calibration and supplementing the background fields. We will be obtaining radial velocity data for member stars in LMC clusters with the Rutgers Fabry-Perot spectrograph at CTIO in Jan 1995, for improved IMF determination and dynamical modeling. We also have Stroemgren photometry for the clusters which will yield mean metallicity estimates and, therefore, aid in the comparisons to stellar models. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 5904( 7) - 12/12/95 08:08 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 5904( 7) - 12/12/95 08:08 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC1711 STELLAR CLUSTER, RA=4H 50M 37.4S +/- 0.1S, DEC=- 2000 GLOBULAR CLUSTER 69D 59' 6" +/- 1" 2 NGC2004 STELLAR CLUSTER, RA=5H 30M 40.85S +/- 0.1S, DEC=- 2000 GLOBULAR CLUSTER 67D 17' 17" +/- 1" 3 NGC2031 STELLAR CLUSTER, RA=5H 33M 41.0S +/- 0.1S, DEC=- 2000 GLOBULAR CLUSTER 70D 59' 14" +/- 1" 4 NGC2157 STELLAR CLUSTER, RA=5H 57M 34.75S +/- 0.1S, DEC=- 2000 GLOBULAR CLUSTER 69D 11' 47" +/- 1" 5904( 7) - 12/12/95 08:08 - [ 5] Visit: 01 Visit Requirements: PCS MODE FINE 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC1711 WFPC2 IMAGE PC1-FIX F555W 3 300S POS TARG 0.0, 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC1711 WFPC2 IMAGE PC1-FIX F814W 3 300S POS TARG 0.0, 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC1711 WFPC2 IMAGE PC1-FIX F814W 2 300S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC1711 WFPC2 IMAGE PC1-FIX F555W 2 300S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC1711 WFPC2 IMAGE PC1-FIX F555W 2 10S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC1711 WFPC2 IMAGE PC1-FIX F814W 1 10S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC1711 WFPC2 IMAGE PC1-FIX F814W 3 300S POS TARG 80.0,80.0 Comments: For exposure 8 through 11 I would like as large an offset from the previous exposures as is possible without needing to reacquire a guide star. I would like to maintain the relative offsets (0.5 arcsec in x and y) within this set of exposures. ------------------------------------------------------------------------------------------------------------------------------------ 9 NGC1711 WFPC2 IMAGE PC1-FIX F555W 3 300S POS TARG 80.0,80.0 ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC1711 WFPC2 IMAGE PC1-FIX F555W 2 300S POS TARG 79.5,79.5 ------------------------------------------------------------------------------------------------------------------------------------ 11 NGC1711 WFPC2 IMAGE PC1-FIX F814W 2 300S POS TARG 79.5,79.5 ------------------------------------------------------------------------------------------------------------------------------------ 5904( 7) - 12/12/95 08:08 - [ 6] Visit: 02 Visit Requirements: PCS MODE FINE 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC2004 WFPC2 IMAGE PC1-FIX F555W 3 300S POS TARG 0.0, 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC2004 WFPC2 IMAGE PC1-FIX F814W 3 300S POS TARG 0.0, 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC2004 WFPC2 IMAGE PC1-FIX F814W 2 300S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC2004 WFPC2 IMAGE PC1-FIX F555W 2 300S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC2004 WFPC2 IMAGE PC1-FIX F555W 2 10S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC2004 WFPC2 IMAGE PC1-FIX F814W 1 10S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC2004 WFPC2 IMAGE PC1-FIX F814W 3 300S POS TARG 80.0,80.0 Comments: For exposure 8 through 11 I would like as large an offset from the previous exposures as is possible without needing to reacquire a guide star. I would like to maintain the relative offsets (0.5 arcsec in x and y) within this set of exposures. ------------------------------------------------------------------------------------------------------------------------------------ 9 NGC2004 WFPC2 IMAGE PC1-FIX F555W 3 300S POS TARG 80.0,80.0 ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC2004 WFPC2 IMAGE PC1-FIX F555W 2 300S POS TARG 79.5,79.5 ------------------------------------------------------------------------------------------------------------------------------------ 11 NGC2004 WFPC2 IMAGE PC1-FIX F814W 2 300S POS TARG 79.5,79.5 ------------------------------------------------------------------------------------------------------------------------------------ 5904( 7) - 12/12/95 08:08 - [ 7] Visit: 03 Visit Requirements: PCS MODE FINE 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC2031 WFPC2 IMAGE PC1-FIX F555W 3 300S POS TARG 0.0, 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC2031 WFPC2 IMAGE PC1-FIX F814W 3 300S POS TARG 0.0, 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC2031 WFPC2 IMAGE PC1-FIX F814W 2 300S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC2031 WFPC2 IMAGE PC1-FIX F555W 2 300S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC2031 WFPC2 IMAGE PC1-FIX F555W 2 10S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC2031 WFPC2 IMAGE PC1-FIX F814W 1 10S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC2031 WFPC2 IMAGE PC1-FIX F814W 3 300S POS TARG 80.0,80.0 Comments: For exposure 8 through 11 I would like as large an offset from the previous exposures as is possible without needing to reacquire a guide star. I would like to maintain the relative offsets (0.5 arcsec in x and y) within this set of exposures. ------------------------------------------------------------------------------------------------------------------------------------ 9 NGC2031 WFPC2 IMAGE PC1-FIX F555W 3 300S POS TARG 80.0,80.0 ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC2031 WFPC2 IMAGE PC1-FIX F555W 2 300S POS TARG 79.5,79.5 ------------------------------------------------------------------------------------------------------------------------------------ 11 NGC2031 WFPC2 IMAGE PC1-FIX F814W 2 300S POS TARG 79.5,79.5 ------------------------------------------------------------------------------------------------------------------------------------ 5904( 7) - 12/12/95 08:08 - [ 8] Visit: 04 Visit Requirements: PCS MODE FINE 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC2157 WFPC2 IMAGE PC1-FIX F555W 3 300S POS TARG 0.0, 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC2157 WFPC2 IMAGE PC1-FIX F814W 3 300S POS TARG 0.0, 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC2157 WFPC2 IMAGE PC1-FIX F814W 2 300S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC2157 WFPC2 IMAGE PC1-FIX F555W 2 300S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC2157 WFPC2 IMAGE PC1-FIX F555W 2 10S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC2157 WFPC2 IMAGE PC1-FIX F814W 1 10S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC2157 WFPC2 IMAGE PC1-FIX F814W 3 300S POS TARG 80.0,80.0 Comments: For exposure 8 through 11 I would like as large an offset from the previous exposures as is possible without needing to reacquire a guide star. I would like to maintain the relative offsets (0.5 arcsec in x and y) within this set of exposures. ------------------------------------------------------------------------------------------------------------------------------------ 9 NGC2157 WFPC2 IMAGE PC1-FIX F555W 3 300S POS TARG 80.0,80.0 ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC2157 WFPC2 IMAGE PC1-FIX F555W 2 300S POS TARG 79.5,79.5 ------------------------------------------------------------------------------------------------------------------------------------ 11 NGC2157 WFPC2 IMAGE PC1-FIX F814W 2 300S POS TARG 79.5,79.5 ------------------------------------------------------------------------------------------------------------------------------------ 5904( 7) - 12/12/95 08:08 - [ 9] Visit: 05 Visit Requirements: PCS MODE FINE 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC1711 WFPC2 IMAGE PC1-FIX F555W 3 300S POS TARG 0.0, 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC1711 WFPC2 IMAGE PC1-FIX F814W 3 300S POS TARG 0.0, 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC1711 WFPC2 IMAGE PC1-FIX F814W 2 300S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC1711 WFPC2 IMAGE PC1-FIX F555W 2 300S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC1711 WFPC2 IMAGE PC1-FIX F555W 2 10S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC1711 WFPC2 IMAGE PC1-FIX F814W 1 10S POS TARG 0.5,0.5 ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC1711 WFPC2 IMAGE PC1-FIX F814W 3 300S POS TARG 80.0,80.0 Comments: For exposure 8 through 11 I would like as large an offset from the previous exposures as is possible without needing to reacquire a guide star. I would like to maintain the relative offsets (0.5 arcsec in x and y) within this set of exposures. ------------------------------------------------------------------------------------------------------------------------------------ 9 NGC1711 WFPC2 IMAGE PC1-FIX F555W 3 300S POS TARG 80.0,80.0 ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC1711 WFPC2 IMAGE PC1-FIX F555W 2 300S POS TARG 79.5,79.5 ------------------------------------------------------------------------------------------------------------------------------------ 11 NGC1711 WFPC2 IMAGE PC1-FIX F814W 2 300S POS TARG 79.5,79.5 ------------------------------------------------------------------------------------------------------------------------------------ 5904( 7) - 12/12/95 08:08 - [ 10] Summary Form for Proposal 5904 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Stellar Populations ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PCS MODE FINE CVZ POS TARG 0.0, 0.0 POS TARG 0.5,0.5 POS TARG 80.0,80.0 POS TARG 79.5,79.5 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC1711 NGC2004 NGC2031 NGC2157 ------------------------------------------------------------------------------------------------------------------------------------