! Proposal 5916, submission 1 ! PI: Nicholas B. Suntzeff ! Received Tue Feb 28 14:54:27 EST 1995 ! From: schommer@ctiow7.ctio.noao.edu ! Hubble Space Telescope Cycle 5 (1995) Phase II Proposal Template ! $Id: 5916,v 7.1 1995/11/27 16:50:43 pepsa Exp $ ! ! Refer to the HST Phase II Proposal Instructions to fill this out ! ! Anything after a "!" is ignored, and may be deleted ! ! All keywords with multiple entries are comma delimited except the ! Visit_Requirements and Special_Requirements keywords which can be ! delimited with carriage returns or semi-colons, but not commas ! ! For help call your Program Coordinator: Marc Bremmer ! Phone: 410 338-4458 , E-mail: bremmer@stsci.edu ! ! This partially completed template was generated from a Phase I proposal. ! Date generated: Sat Dec 17 10:16:17 EST 1994 ! Proposal_Information Title: The Oldest Globular Clusters in the Large Magellanic Cloud Proposal_Category: GO Scientific_Category: Stellar Populations Cycle: 5 Investigators PI_name: Nicholas B. Suntzeff PI_Institution: Cerro Tololo Inter-American Observatory CoI_Name: Paul W. Hodge CoI_Institution: Department of Astronomy, FM-20,University of Washington,Seattle, WA 98195 Contact: N CoI_Name: Mario L. Mateo CoI_Institution: Department of Astronomy,834 Dennnison,University of Michigan,Ann Arbor, MI 48109-1090 Contact: N CoI_Name: Edward W. Olszewski CoI_Institution: Steward Observatory,University of Arizona,Tucson, AZ 85721 Contact: N CoI_Name: Robert A. Schommer CoI_Institution: Cerro Tololo Inter-American Observatory- NOAO,P.O. Box 26732,Tucson AZ 85726 Contact: N CoI_Name: Alistair R. Walker CoI_Institution: Cerro Tololo Inter-American Observatory- NOAO,P.O. Box 26732,Tucson AZ 85726 Contact: N Abstract: We propose to obtain deep V(F555W) and I(F814W) images of a sample of the metal-poor globular clusters in the Large Magellanic Cloud (LMC). With these observations we will be able to measure the ages of the clusters, which will allow us to place the formation epoch of the initial population of stars in the LMC in the general context of the formation of the Milky Way Galaxy. Specifically, there is mounting data that the Milky Way Galaxy contains two distinct populations of old metal-poor stars: the initial population is a flattened disk with a small amount of rotation that dominates the Population II in the solar neighborhood; and a second population of the same metallicity, which forms a non-rotating spherical halo with an R**-3.5 density law, and is apparently a few Gyrs younger than the first population. The former population is perhaps associated with a spherical collapse model (Eggen, Lynden-Bell, & Sandage 1962) and the latter with a slower cellular accretion model of Searle & Zinn (1978). If the LMC did not form via an ELS process at the same epoch as our Galaxy, then we might expect that the oldest LMC clusters are younger than the oldest components of our Galaxy. There is some evidence for this derived from ground-based photometry for a few of the LMC clusters. We propose to test whether formation of Pop II LMC clusters was indeed delayed by a few Gyr, and in particular to test whether there is coevality between the (mean) ages of the LMC Pop II clusters and clusters in the outer halo of our Galaxy. Questions Observing_Description: We propose to observe 6 old LMC clusters with the WFPC2 in the HST F555W and F814W (VI equivalent) filters. We request CVZ observations, since a complete set of observations of a single cluster can be fit into the 96 minute viewing window. By squeezing in one cluster per orbit with only a single filter change during an orbit, we can use HST at a very high efficiency. We will observe each cluster as: 3x500s + 2x30s (V) and 3x600s + 3x20s(I). The observations will be taken with the clusters centered on the PC. The extreme crowding in the cluster+field requires images which are not undersampled. We have calculated the estimated exposure times as follows: The average magnitude for the LMC horizontal branch is ~19.3 (Suntzeff, etal 1992, Table 6). The difference in magnitude between the horizontal branch and the main-sequence turnoff for the average Galactic globular cluster is Delta V^TO_HB=3.55+/-0.09 (Buonanno etal 1989). We estimate that we must reach 2.5 magnitudes below the turnoff with ~0.1 mag accuracy in (V-I) to measure a reliable age, implying an error of about 0.07 in each color at V=25.3. Using the data in the WFPC2 Handbook (version 2.0 1994), and assuming F0 spectral type, V_sky=22.0, read noise of 5.2e-, dark of 0.016e- s^-1, quantization noise equivalent of 3.3e-, and and average sharpness factor of 0.05 for the PC (Table 6.4), we find we will reach S/N=6 in 600s in I and and S/N=8 in 500s in V. With 3 exposures per color, we will reach an error of 0.12 mag in (V-I), and 0.07 in V. According to Table 2.2, with 7e- DN^-1, a 500s exposure with the PC will saturate at V~18.4. To allow a tie-in with ground-based observations, we will also obtain short exposures of 2x30s in V and 3x20s in I which will saturate at about V~15.5. The shorter exposures will allow us to construct a cmd of the whole red giant branch region, and give us candidate stars for future spectroscopic work. (Even the brightest stars in these crowded and compact clusters cannot be measure reliably from ground based telescopes.) We have used the WFPC2 Handbook to calculate read times and exposures. If we instead use the information in the Phase I proposal instructions, the total time per cluster is slightly greater than one orbit. If this is the actual case, we would reduce the number of shorter exposures to fit a cluster into a single orbit. The main uncertainty in this calculation is what we should use for the effective sky brightness in the bar region of the LMC. From Bothun & Thompson (1988), the central surface brightness of the LMC is sigma_B = 21.2 with color B-V = 0.52. The implied surface brightness of sigma_V = 20.7 must be a significant overestimate for our purposes, because it is only the faint stellar component below V~25 which will appear as a ``diffuse'' sky. We can roughly estimate the effective surface brightness of the stars fainter than ~25 by merging the deep luminosity function for LMC field stars (at 4 degrees NW of the LMC center; Butcher 1977) with the shallower luminosity function of the LMC bar (1.4 degrees from the center ; Hardy etal 1984). We extrapolate to V=25.5 and then calculate the fraction of the surface brightness in the bar regions which are due to stars fainter than this limit. Our worst case estimate for the surface brightness for the faint stars is sigma_V~21.8 in the central regions measured by Bothun & Thompson, and at worse sigma_V~22.3 in the regions at 0.5-1 degrees, which are the typical positions of the inner LMC clusters under consideration here. The natural sky background is sigma_V~23 (Table 6.3 in the WFPC2 Handbook). If we combine both the natural and LMC faint star background, we end up with sigma_V~22. Real_Time_Justification: The CVZ requirement is justified in the previous section. We also request that the telescope be ``jogged'' by a small amount between all exposures, to reduce the photometric errors in the WF images where there can be real sensitivity variations across a pixel. We understand that this is possible with no additional loss in observing time. ARW and NBS have been granted 4 nights of observing time with the CTIO 1.5m telescope and imaging CCD in Jan 1995 to being a search for variable stars in the clusters SL244, N1754, N1865, N1898, N1916, N1928, N1939, N2005, and N2019. We had planned to use 4min V and 6min B (Johnson system) exposures on each cluster, cycling through all the clusters for 4 nights (plus photometric standards, and a few Galactic globular clusters for tie-in). However, if we are awarded HST time, we will instead incorporate the CTIO set of F555W (HST V equivalent) and F814W (HST I equivalent) filters into our scheduled ground-based observations and observe in B(Johnson)V(F555W)I(F814W). We have bought the FW555 and FW814 filters for CTIO as part of our HST project 5423 (The Tucana Dwarf Spheroidal Galaxy). We would use the 1.5m images as direct calibrations for the LMC cluster images, and as a direct tie-in with Galactic globular clusters measured with our HST equivalent filters. It is our goal to observe ALL the old clusters in the LMC to measure ages. The outer clusters (Hodge 11, NGC 1466, NGC 1841, NGC 2210, NGC 2257, and Reticulum) are in uncrowded regions of the LMC, and ground- based photometry in good seeing can be used to reach V~25. NGC 2257 has been observed on the ESO NNT telescope by Ferraro, etal (1994, preprint) in BV colors, and they find an age several Gyr younger for the cluster than a typical Galactic globular. The VI observations will be made using the CTIO HST filter (F555W and F814W) to provide a consistent system of colors for all the old LMC colors. Calibration_Justification: Additional_Comments: Fixed_Targets Target_Number: 1 Target_Name: NGC1754 Alternate_Names: SL91 Description: EXT-CLUSTER, GLOBULAR CLUSTER Position: RA=4H 54M 18.6S +/- 1.5S, DEC=-70D 26' 32.1" +/- 8" Equinox: J2000 RV_or_Z: V=+236 Flux: V=15.5+/-0.5 B-V=1.5+/-0.5 E(B-V)=0.08+/-0.03 SURF-BKG(V)=22+/-1 Comments: BV MAGNITUDES ARE ESTIMATED FOR BRIGHTEST CLUSTER MEMBERS. LMC FIELD STARS MAY BE AS BRIGHT AS V=12.5. BRIGHT STAR WITH V=11.0 and V-I=0.9 AT (26"S,19"E) OR PA= 144D (N INTO E) AT R= 32.2" WITH RESPECT TO CLUSTER CENTER. THESE ARE APPROXIMATE COORDINATES, AND NOT FINAL GSSS COORDS. Fixed_Targets Target_Number: 2 Target_Name: NGC1835 Alternate_Names: SL215 Description: EXT-CLUSTER, GLOBULAR CLUSTER Position: RA=5H 05M 06.4S +/- 1.5S, DEC=-69D 24' 16.5" +/- 8" Equinox: J2000 RV_or_Z: V=+188 Flux: V=15.5+/-0.5 B-V=1.5+/-0.5 E(B-V)=0.13+/-0.03 SURF-BKG(V)=22+/-1 Comments: BV MAGNITUDES ARE ESTIMATED FOR BRIGHTEST CLUSTER MEMBERS. LMC BAR FIELD STARS MAY BE AS BRIGHT AS V=12.5. ANY ORIENTATION IS OKAY. THESE ARE APPROXIMATE COORDINATES, AND NOT FINAL GSSS COORDS. Fixed_Targets Target_Number: 3 Target_Name: NGC1898 Alternate_Names: SL350 Description: EXT-CLUSTER, GLOBULAR CLUSTER Position: RA=5H 16M 42.5S +/- 1.5S, DEC=-69D 39' 22.5" +/- 8" Equinox: J2000 RV_or_Z: V=+210 Flux: V=15.5+/-0.5 B-V=1.5+/-0.5 E(B-V)=0.06+/-0.03 SURF-BKG(V)=22+/-1 Comments: BV MAGNITUDES ARE ESTIMATED FOR BRIGHTEST CLUSTER MEMBERS. LMC BAR FIELD STARS MAY BE AS BRIGHT AS V=12.5. MANY BRIGHT STARS IN FIELD. ORIENT SO THAT CENTER OF PC1 TO CORNER OF WF3 IS POINTING N. THESE ARE APPROXIMATE COORDINATES, AND NOT FINAL GSSS COORDS. Fixed_Targets Target_Number: 4 Target_Name: NGC1916 Alternate_Names: SL361 Description: EXT-CLUSTER, GLOBULAR CLUSTER Position: RA=5H 18M 37.66S +/- 1.5S, DEC=-69D 24' 25.6" +/- 8" Equinox: J2000 RV_or_Z: V=+278 Flux: V=15.5+/-0.5 B-V=1.5+/-0.5 E(B-V)=0.18+/-0.03 SURF-BKG(V)=22+/-1 Comments: BV MAGNITUDES ARE ESTIMATED FOR BRIGHTEST CLUSTER MEMBERS. LMC BAR FIELD STARS MAY BE AS BRIGHT AS V=12.5. BRIGHT STAR AT 135"W OF CLUSTER CENTER WITH V=14. ANY ORIENTATION IS OKAY. THESE ARE APPROXIMATE COORDINATES, AND NOT FINAL GSSS COORDS. Fixed_Targets Target_Number: 5 Target_Name: NGC2005 Alternate_Names: SL518 Description: EXT-CLUSTER, GLOBULAR CLUSTER Position: RA=5H 30M 10.4S +/- 1.5S, DEC=-69D 45' 10.1" +/- 8" Equinox: J2000 RV_or_Z: V=+270 Flux: V=15.5+/-0.5 B-V=1.5+/-0.5 E(B-V)=0.012+/-0.03 SURF-BKG(V)=22+/-1 Comments: BV MAGNITUDES ARE ESTIMATED FOR BRIGHTEST CLUSTER MEMBERS. LMC BAR FIELD STARS MAY BE AS BRIGHT AS V=12.5. VERY BRIGHT STAR AT (120"S,20"W) OR PA=189D AND R=121". THESE ARE APPROXIMATE COORDINATES, AND NOT FINAL GSSS COORDS. Fixed_Targets Target_Number: 6 Target_Name: NGC2019 Alternate_Names: SL554 Description: EXT-CLUSTER, GLOBULAR CLUSTER Position: RA=5H 31M 56.8S +/- 1.5S, DEC=-70D 09' 34.0" +/- 8" Equinox: J2000 RV_or_Z: V=+269 Flux: V=15.5+/-0.5 B-V=1.5+/-0.5 E(B-V)=0.12+/-0.03 SURF-BKG(V)=22+/-1 Comments: BV MAGNITUDES ARE ESTIMATED FOR BRIGHTEST CLUSTER MEMBERS. LMC BAR FIELD STARS MAY BE AS BRIGHT AS V=12.5. ANY ORIENTATION IS OKAY. THESE ARE APPROXIMATE COORDINATES, AND NOT FINAL GSSS COORDS. Visits Visit_Number: 1 Visit_Requirements: CVZ Visit_Comments: WOULD LIKE TO ORIENT 109D TO 179D, BUT NO CVZ ZONE THEN. Exposure_Number: 101 Target_Name: NGC1754 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F555W Optional_Parameters: CLOCKS=NO Number_of_Iterations: 2 Time_Per_Exposure: 20S Comments: Exposure_Number: 102 Target_Name: NGC1754 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F555W Optional_Parameters: CLOCKS=NO Number_of_Iterations: 3 Time_Per_Exposure: 500S Comments: Exposure_Number: 103 Target_Name: NGC1754 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F814W Optional_Parameters: CLOCKS=NO Number_of_Iterations: 3 Time_Per_Exposure: 20S Comments: Exposure_Number: 104 Target_Name: NGC1754 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F814W Optional_Parameters: CLOCKS=NO Number_of_Iterations: 3 Time_Per_Exposure: 600S Comments: Visit_Number: 2 Visit_Requirements: CVZ Visit_Comments: ANY ORIENTATION IS OKAY Exposure_Number: 201 Target_Name: NGC1835 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F555W Optional_Parameters: CLOCKS=NO Number_of_Iterations: 2 Time_Per_Exposure: 20S Comments: Exposure_Number: 202 Target_Name: NGC1835 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F555W Optional_Parameters: CLOCKS=NO Number_of_Iterations: 3 Time_Per_Exposure: 500S Comments: Exposure_Number: 203 Target_Name: NGC1835 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F814W Optional_Parameters: CLOCKS=NO Number_of_Iterations: 3 Time_Per_Exposure: 20S Comments: Exposure_Number: 204 Target_Name: NGC1835 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F814W Optional_Parameters: CLOCKS=NO Number_of_Iterations: 3 Time_Per_Exposure: 600S Comments: Visit_Number: 3 Visit_Requirements: CVZ ORIENTation 320D to 40D Visit_Comments: ORIENT -40D to +40D Exposure_Number: 301 Target_Name: NGC1898 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F555W Optional_Parameters: CLOCKS=NO Number_of_Iterations: 2 Time_Per_Exposure: 20S Comments: Exposure_Number: 302 Target_Name: NGC1898 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F555W Optional_Parameters: CLOCKS=NO Number_of_Iterations: 3 Time_Per_Exposure: 500S Comments: Exposure_Number: 303 Target_Name: NGC1898 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F814W Optional_Parameters: CLOCKS=NO Number_of_Iterations: 3 Time_Per_Exposure: 20S Comments: Exposure_Number: 304 Target_Name: NGC1898 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F814W Optional_Parameters: CLOCKS=NO Number_of_Iterations: 3 Time_Per_Exposure: 600S Comments: Visit_Number: 4 Visit_Requirements: CVZ Visit_Comments: ANY ORIENTATION OKAY Exposure_Number: 401 Target_Name: NGC1916 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F555W Optional_Parameters: CLOCKS=NO Number_of_Iterations: 2 Time_Per_Exposure: 20S Comments: Exposure_Number: 402 Target_Name: NGC1916 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F555W Optional_Parameters: CLOCKS=NO Number_of_Iterations: 3 Time_Per_Exposure: 500S Comments: Exposure_Number: 403 Target_Name: NGC1916 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F814W Optional_Parameters: CLOCKS=NO Number_of_Iterations: 3 Time_Per_Exposure: 20S Comments: Exposure_Number: 404 Target_Name: NGC1916 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F814W Optional_Parameters: CLOCKS=NO Number_of_Iterations: 3 Time_Per_Exposure: 600S Comments: Visit_Number: 5 Visit_Requirements: CVZ Visit_Comments: WOULD LIKE TO ORIENT 149D TO 229D, BUT NO CVZ ZONE THEN Exposure_Number: 501 Target_Name: NGC2005 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F555W Optional_Parameters: CLOCKS=NO Number_of_Iterations: 2 Time_Per_Exposure: 20S Comments: Exposure_Number: 502 Target_Name: NGC2005 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F555W Optional_Parameters: CLOCKS=NO Number_of_Iterations: 3 Time_Per_Exposure: 500S Comments: Exposure_Number: 503 Target_Name: NGC2005 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F814W Optional_Parameters: CLOCKS=NO Number_of_Iterations: 3 Time_Per_Exposure: 20S Comments: Exposure_Number: 504 Target_Name: NGC2005 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F814W Optional_Parameters: CLOCKS=NO Number_of_Iterations: 3 Time_Per_Exposure: 600S Comments: Visit_Number: 6 Visit_Requirements: CVZ Visit_Comments: ANY ORIENTATION OKAY Exposure_Number: 601 Target_Name: NGC2019 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F555W Optional_Parameters: CLOCKS=NO Number_of_Iterations: 2 Time_Per_Exposure: 20S Comments: Exposure_Number: 602 Target_Name: NGC2019 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F555W Optional_Parameters: CLOCKS=NO Number_of_Iterations: 3 Time_Per_Exposure: 500S Comments: Exposure_Number: 603 Target_Name: NGC2019 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F814W Optional_Parameters: CLOCKS=NO Number_of_Iterations: 3 Time_Per_Exposure: 20S Comments: Exposure_Number: 604 Target_Name: NGC2019 Config: WFPC2 Opmode: IMAGE Aperture: PC1-FIX Sp_Element: F814W Optional_Parameters: CLOCKS=NO Number_of_Iterations: 3 Time_Per_Exposure: 600S Comments: ! Uncomment or copy exposure level special requirements needed ! POSition TARGet , ! SAME POSition AS Data_Distribution Medium: 8MM ! 8MM or 6250BPI or 1600BPI Blocking_Factor: 10 ! 10 or 1 Ship_To: Dr. Nicholas B. Suntzeff NOAO 950 North Cherry Avenue Tucson, AZ 85719 Ship_Via: UPS Recipient_Email: nsuntzeff@noao.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