5903( 5) - 11/22/95 13:00 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 5903 Version: 5 Check-in Date: ********** 1.Proposal Title: The Origin and Nature of UV Bright Stars in Globular Clusters ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Stellar Populations GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Francesco Ferraro Osservatorio Astronomico di Bologna CoI: Guido De Marchi Osservatorio Astronomico of Teramo N CoI: Francesco Paresce STScI N CoI: Ben Dorman NASA/GSFC N CoI: Robert O'Connell University of Virginia N CoI: Robert Rood University of Virginia N CoI: Jonathan Whitney University of Virginia N CoI: Noella da Cruz University of Virginia N CoI: Carla Cacciari Osservatorio Astronomico of Bologna N CoI: Flavio Fusi Pecci Osservatorio Astronomico of Bologna N ------------------------------------------------------------------------------------ 6. Abstract We have been allocated telescope time to study two globular clusters in optical and UV filters. The clusters, M80 and M13, have blue horizontal-branch (HB) tails extending to V magnitudes equal to or fainter than the main sequence turnoff. The WFPC2 will be used to image the central regions of these clusters in far-UV, mid-UV and near UV broadband filters, and in the V filter to provide a longer baseline. The object of this investigation is twofold: (a) to explore the HB mass distribution in clusters with blue HB tails (BT clusters) and investigate the relationship between the HB mass distribution and the clusters' structural and dynamical properties and (b) to gain further samples of blue straggler stars (BS) in the cores of such clusters. These observations will indiecrtly probe the mass loss process close to the tip of the red giant branch. The bluest stars to be observed are also very similar to the stars that are probably responsible for the UV upturn in elliptical galaxies. The clusters to be observed have different surface brightness profiles but very similar HB morphology. The near- and mid-UV images will be able to detect blue stragglers in the cluster cores, the production of which is also likely to be related to dynamical processes within the clusters. ------------------------------------------------------------------------------------ 5903( 5) - 11/22/95 13:00 - [ 2] Observations Description ------------------------ We will image fields in the cluster centers in the F160BW, F255W, and F336W ultraviolet passbands. A short exposure in the Visual band F555W is also required to provide a long wavelength baseline for the HB observations and to allow the calculation of integrated 16 -V and 25-V colors. Short exposures in the B band (F439W) have also been requested for both clusters, which will facilitate comparisons between our results and previous ground-based work. The V observations will also allow the detection of spurious cool sources arising from the redleak in the F336W passband. From 15 or so possible targets known from previous satellite missions to be bright in integrated UV light we have been approved time for 2 clusters with similar metallicity (Fe/H ~ -1.5). NGC 6093 (= M80) (E(B-V)=0.20, V_0( HB) ~ 15.20) is very blue according to ANS observations, although there is reason to suspect the exact value of the UV colors. M80 is interesting because it does not show the color gradients seen in similar clusters. Our observations will show whether it does indeed provide a counterexample to the relationship between the existence of a BT and the production of core BSS. NGC 6205 (= M13) (E(B-V)=0.02, V_0( HB) ~ 14.90) has optical HB morphology that is virtually identical to M80, but its concentration is somewhat lower and it is rather oblate in shape. Complementary observations suggest a bimodal distribution in rotation. Intercomparison between the two clusters and with dense core clusters observed in other HST programs should clarify how dynamical properties affect stellar populations. The exposure times have been calculated in order to reach approximately S/N=10 at V ~ V_0( HB)+5.5 mag in the bands F160BW and F255W for a B0 star (corresponding to an EHB star at the faint end of the BT), and 1 mag below the turnoff in the bands F336W and F555W for a G0 star (for a proper detection and photometry of the BSS which can be found at the turnoff luminosity level). The parameters used for the S/N (or exposure time) calculation are those specified in the WFPC2 Handbook, Version 2.0 May 1994 with the algorithm (S/N)^2=I^2/(I+B) since our observations are not background- dominated. The signal I has been convolved with the PSF over a 3 by 3 pixel region from Tab. 5.1 and 5.2 of the Handbook, and correspondingly the background B has been considered over a 9 pixel square area. All exposures will be split into 4 separate images, shifted by 1 pixel, for the twofold purpose of (1) mapping the PSF for a better photometric accuracy, and (2) avoiding the blooming in the V images (no blooming is expected in the ultraviolet bands). Real Time Justification ----------------------- DO WE NEED THIS?? The flight of Astro-2 containing the Ultraviolet Imaging Telescope (UIT) was launched on 3rd March 1995. It is scheduled to observe NGC 6205. Its observations will provide supporting data for the outer regions of the cluster not seriously affected by the crowding issues in the center. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 5903( 5) - 11/22/95 13:00 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 5903( 5) - 11/22/95 13:00 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6093 STELLAR CLUSTER, RA=16H 17M 2.5S +/- 0.1S, DEC=- 2000 SURF(V)=15.38 +/- 0.1 GLOBULAR CLUSTER 22D 58' 30.0" +/- 1" E(B-V)=0.20 Comments: Above flux value refers to the central magnitude of the cluster, for ACQ purpose only. For individual stars see observing description. 2 NGC6205 STELLAR CLUSTER, RA=16H 41M 41.5S +/- 0.1S, 2000 SURF(V)=16.77 +/- 0.1 GLOBULAR CLUSTER DEC=+36D 27' 37.0" +/- 1" E(B-V)=0.02 Comments: Above flux value refers to the central magnitude of the cluster, for ACQ purpose only. For individual stars see observing description. 5903( 5) - 11/22/95 13:00 - [ 5] Visit: 01 Visit Requirements: 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 NGC6093 WFPC2 IMAGE PC1-FIX F160BW 1 2000S ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC6093 WFPC2 IMAGE PC1-FIX F439W ATD-GAIN=15 1 30S END ORBIT ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC6093 WFPC2 IMAGE PC1-FIX F439W ATD-GAIN=15 1 30S ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC6093 WFPC2 IMAGE PC1-FIX F336W ATD-GAIN=15 1 1200S ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC6093 WFPC2 IMAGE PC1-FIX F255W CR-SPLIT=0.5 1 600S ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC6093 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15, CR 1 50S -SPLIT=0.5 ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC6093 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15, CR 1 4S -SPLIT=0.5 ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC6093 WFPC2 IMAGE PC1-FIX F160BW 1 2000S POS TARG 0.467, 0.467 ------------------------------------------------------------------------------------------------------------------------------------ 9 NGC6093 WFPC2 IMAGE PC1-FIX F336W ATD-GAIN=15 1 1200S POS TARG 0.467, 0.467 ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC6093 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15, CR 1 50S POS TARG 0.467, 0.467 -SPLIT=0.5 ------------------------------------------------------------------------------------------------------------------------------------ 11 NGC6093 WFPC2 IMAGE PC1-FIX F255W 1 300S POS TARG 0.467, 0.467 ------------------------------------------------------------------------------------------------------------------------------------ 12 NGC6093 WFPC2 IMAGE PC1-FIX F255W 1 300S POS TARG 0.467, 0.467 ------------------------------------------------------------------------------------------------------------------------------------ 5903( 5) - 11/22/95 13:00 - [ 6] Visit: 02 Visit Requirements: 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 NGC6205 WFPC2 IMAGE PC1-FIX F255W CR-SPLIT=0.5 1 100S POS TARG 0.467, 0.467 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC6205 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15, CR 1 16S POS TARG 0.467, 0.467 -SPLIT=0.5 ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC6205 WFPC2 IMAGE PC1-FIX F160BW 1 300S POS TARG 0.467, 0.467 ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC6205 WFPC2 IMAGE PC1-FIX F160BW 1 300S POS TARG 0.467, 0.467 ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC6205 WFPC2 IMAGE PC1-FIX F336W ATD-GAIN=15, CR 1 300S POS TARG 0.467, 0.467 -SPLIT=0.5 ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC6205 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15, CR 1 2S POS TARG 0.467, 0.467 -SPLIT=0.5 ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC6205 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15, CR 1 16S -SPLIT=0.5 ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC6205 WFPC2 IMAGE PC1-FIX F160BW CR-SPLIT=0.5 1 600S ------------------------------------------------------------------------------------------------------------------------------------ 9 NGC6205 WFPC2 IMAGE PC1-FIX F255W CR-SPLIT=0.5 1 100S ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC6205 WFPC2 IMAGE PC1-FIX F336W ATD-GAIN=15, CR 1 300S -SPLIT=0.5 ------------------------------------------------------------------------------------------------------------------------------------ 11 NGC6205 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15, CR 1 2S -SPLIT=0.5 ------------------------------------------------------------------------------------------------------------------------------------ 12 NGC6205 WFPC2 IMAGE PC1-FIX F439W ATD-GAIN=15, CR 1 30S END ORBIT -SPLIT=0.5 ------------------------------------------------------------------------------------------------------------------------------------ 5903( 5) - 11/22/95 13:00 - [ 7] Summary Form for Proposal 5903 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ATD-GAIN=15 CR-SPLIT=0.5 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Stellar Populations ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements END ORBIT POS TARG 0.467, 0.467 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F160BW F439W F336W F255W F555W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC6093 NGC6205 ------------------------------------------------------------------------------------------------------------------------------------