6607( 7) - 04/02/97 15:48 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6607 Version: 7 Check-in Date: 02-Apr-1997 15:23:26 1.Proposal Title: The Origin and Nature of UV Bright stars in Globular Clusters II ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle STELLAR POPULATIONS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Francesco Ferraro OSSERVATORIO ASTORNOMICO DI BOLOGNA CoI: Robert S. Hill Laboratory for Astronomy and Solar N Physics, NASA/Goddard Space Flight Center CoI: Wayne Landsman Laboratory for Astronomy and Solar N Physics, NASA/Goddard Space Flight Center CoI: Flavio Fusi Pecci Osservatorio Astronomico of Bologna N CoI: Carla Cacciari Osservatorio Astronomico of Bologna N CoI: Ben Dorman Laboratory for Astronomy and Solar N Physics, NASA/Goddard Space Flight Center CoI: Robert O'Connell University of Virginia N CoI: Robert Rood University of Virginia N ------------------------------------------------------------------------------------ 6. Abstract We propose an investigation of the UV-bright stellar populations of NGC 1904, NGC 6254, and NGC 5904. These are Galactic globular clusters that are known to be bright at far-UV wavelengths, with the two known to possess extended blue HB tails. These observations will complement data obtained during Cycle 5 and during the UIT Astro-1 flight in December 1990. The object of this investigation is twofold: (a) to explore the relationship between the HB mass distribution in clusters with blue HB tails (BT clusters) to the clusters' structural and dynamical properties and (b) to gain further samples of blue straggler stars in the cores of such clusters. These observations will allow a probe of the variation in mass loss processes close to the tip of the red giant branch. The clusters have been selected as follows: NGC 1904 and NGC 6254 are similar in HB morphology to NGC 6205 for which we have scheduled Cycle 5 observations, and are both more centrally concentrated. In addition, UIT observations indicate a deficit of blue HB stars in the core of NGC1904. NGC 5904 has similar metallicity and concentration to both NGC 1904 & NGC 6254, and was observed by the ANS to be brighter in the far-UV than its optical HB morphology suggests. Our original target list contained also NGC 6266, which has a larger continuous range in HB colour than any other cluster, extending from the red to the blue extreme, and would have provided information about a cluster with high HB mass dispersion. However the exposure times that we derived in Phase 1 using the WFPC2 Exposure Time Calculator provided by the STScI resulted significantly underestimated because of an error in the ETC. As a result of that, we decided to drop NGC 6266, which is highly reddened and requires long exposure times, in order to obtain acceptably good photometric quality on the other 3 clusters. ------------------------------------------------------------------------------------ 6607( 7) - 04/02/97 15:48 - [ 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. The V observations will also allow the detection of spurious cool sources arising from the redleak in the F336W passband. We propose to spend four orbits each on NGC 1904 and NGC 6254, and three orbits on NGC 5904. The exposure times have have been calculated in order to reach approximately S/N=50 at V=Vo(HB)+4.5 mag in the filter F555W for a G0 star, and S/N=30 in the bands F160BW, F255W, and F336W for a B0, A0, and F0 star respectively. In the Woods filter, a part from the error in the WFPC2 ETC mentioned above, we have some reason to believe, from the exposure times used by the WFPC2 IDT for NGC6681 and their reported accuracy, that the S/N is overestimated for a given exposure because of the variability of the PSF due to chromatic aberration. We are also aware that the contamination in the UV renders the calibration uncertain at the few \\\\% level. We have thus increased our S/N requirement where this is possible, aiming to get data that are limited by other sources of error than photometric uncertainties. In this way we plan to measure with the best possible accuracy EHB stars down to the faint end of the BT and BSS which can be found at the turnoff luminosity level. Note that in the case of NGC 1904 we have not requested the the mid-UV F255W exposures requested for the other clusters in order to avoid duplication with GO 6095. Whenever possible, the exposures will be dithered on 2 or 3 positions (default values) for the twofold purpose of (1) mapping the PSF for a better photometric accuracy, and (2) identifying and cleaning from CR events and other blemishes. Multiple exposures will also help in avoiding the blooming in the V images (no blooming is expected in the ultraviolet bands). The detailed observing strategy aims at using the available time with the maximum possible efficiency. Real Time Justification ----------------------- None. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 6607( 7) - 04/02/97 15:48 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC1904 STELLAR CLUSTER, RA=5H 24M 10.6S +/- 0.1S,DEC=- J2000 SURF(V) = 16.18+/-0.1 GLOBULAR CLUSTER 24D 31' 27.0" +/- 1" B-V = 0.64 E(B-V) = 0.01 2 NGC6254 STELLAR CLUSTER, RA=16H 57M 8.9S +/- 0.1S,DEC=- J2000 SURF(V) = 17.70+/-0.1 GLOBULAR CLUSTER 04D 5' 58.0" +/- 1" B-V = 0.89 E(B-V) = 0.28 3 NGC5904 STELLAR CLUSTER, RA=15H 18M 33.8S +/- J2000 SURF(V) = 16.05+/-0.1 GLOBULAR CLUSTER 0.1S,DEC=02D 4' 58.0" +/- 1" B-V = 0.71 E(B-V) = 0.03 Comments: Above flux values refer to the integrated cluster, for ACQ purposes only. For individual stars see observing description. 6607( 7) - 04/02/97 15:48 - [ 4] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: OBSERVATIONS CONTAIN FAR UV EXPOSURES: PLEASE ATTEMPT TO SCHEDULE SOON AFTER DECONTAMINATION Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6254 WFPC2 IMAGE PC1-FIX F255W CR-SPLIT=NO 1 1700 S EXPAND MAX DUR 200% ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC6254 WFPC2 IMAGE PC1-FIX F336W ATD-GAIN=15 1 500 S ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC6254 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15 1 30 S ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC6254 WFPC2 IMAGE PC1-FIX F255W CR-SPLIT=NO 1 1700 S POS TARG 0.3535,0.3535 ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC6254 WFPC2 IMAGE PC1-FIX F336W ATD-GAIN=15 1 500 S POS TARG 0.3535,0.3535 ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC6254 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15 1 30 S POS TARG 0.3535,0.3535 ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC6254 WFPC2 IMAGE PC1-FIX F255W CR-SPLIT=NO 1 1700 S POS TARG 0.707,0.707 ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC6254 WFPC2 IMAGE PC1-FIX F336W ATD-GAIN=15 1 500 S POS TARG 0.707,0.707 ------------------------------------------------------------------------------------------------------------------------------------ 9 NGC6254 WFPC2 IMAGE PC1-FIX F160BW CR-SPLIT=NO,DITHER-TYPE=LINE, 1 1100 S DITHER-LINE-STEPS=2 ------------------------------------------------------------------------------------------------------------------------------------ 6607( 7) - 04/02/97 15:48 - [ 5] Visit: 02 Visit Requirements: On Hold Comments: Additional Comments: OBSERVATIONS CONTAIN FAR UV EXPOSURES: PLEASE ATTEMPT TO SCHEDULE SOON AFTER DECONTAMINATION Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC1904 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15,DITHER-TYPE=LINE, 1 100 S DITHER-LINE-STEPS=3 ------------------------------------------------------------------------------------------------------------------------------------ 21 NGC1904 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15,CR-SPLIT=0.5 1 6 S MAX DUR ------------------------------------------------------------------------------------------------------------------------------------ 22 NGC1904 WFPC2 IMAGE PC1-FIX F160BW CR-SPLIT=NO,DITHER-TYPE=LINE, 1 1100 S DITHER-LINE-STEPS=3 ------------------------------------------------------------------------------------------------------------------------------------ 24 NGC1904 WFPC2 IMAGE PC1-FIX F336W ATD-GAIN=15,CR-SPLIT=NO, 1 1100 S DITHER-TYPE=LINE, DITHER-LINE-STEPS=2 ------------------------------------------------------------------------------------------------------------------------------------ 25 NGC1904 WFPC2 IMAGE PC1-FIX F336W ATD-GAIN=15,CR-SPLIT=NO, 1 1100 S DITHER-TYPE=LINE, DITHER-LINE-STEPS=2 ------------------------------------------------------------------------------------------------------------------------------------ 6607( 7) - 04/02/97 15:48 - [ 6] Visit: 03 Visit Requirements: On Hold Comments: Additional Comments: OBSERVATIONS CONTAIN FAR UV EXPOSURES: PLEASE ATTEMPT TO SCHEDULE SOON AFTER DECONTAMINATION Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 30 NGC5904 WFPC2 IMAGE PC1-FIX F255W CR-SPLIT=NO 1 1200 S EXPAND MAX DUR 110% ------------------------------------------------------------------------------------------------------------------------------------ 31 NGC5904 WFPC2 IMAGE PC1-FIX F336W ATD-GAIN=15 1 350 S EXPAND MAX DUR 120% ------------------------------------------------------------------------------------------------------------------------------------ 32 NGC5904 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15,CR-SPLIT=0.5 1 60 S ------------------------------------------------------------------------------------------------------------------------------------ 33 NGC5904 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15 1 30 S ------------------------------------------------------------------------------------------------------------------------------------ 34 NGC5904 WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=15,CR-SPLIT=0.5 1 6 S MAX DUR ------------------------------------------------------------------------------------------------------------------------------------ 35 NGC5904 WFPC2 IMAGE PC1-FIX F160BW 1 500 S ------------------------------------------------------------------------------------------------------------------------------------ 36 NGC5904 WFPC2 IMAGE PC1-FIX F255W CR-SPLIT=NO 1 1200 S POS TARG 0.3535,0.3535 EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 37 NGC5904 WFPC2 IMAGE PC1-FIX F336W ATD-GAIN=15 1 350 S POS TARG 0.3535,0.3535 EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 38 NGC5904 WFPC2 IMAGE PC1-FIX F160BW 1 500 S POS TARG 0.3535,0.3535 ------------------------------------------------------------------------------------------------------------------------------------ 39 NGC5904 WFPC2 IMAGE PC1-FIX F255W CR-SPLIT=NO 1 1200 S POS TARG 0.707,0.707 EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 40 NGC5904 WFPC2 IMAGE PC1-FIX F336W ATD-GAIN=15 1 350 S POS TARG 0.707,0.707 EXPAND ------------------------------------------------------------------------------------------------------------------------------------ 6607( 7) - 04/02/97 15:48 - [ 7] Summary Form for Proposal 6607 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ATD-GAIN=15 DITHER-LINE-STEPS=2 DITHER-LINE-STEPS=3 CR-SPLIT=0.5 DITHER-TYPE=LINE ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category STELLAR POPULATIONS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements EXPAND MAX DUR 200% POS TARG 0.3535,0.3535 POS TARG 0.707,0.707 MAX DUR EXPAND MAX DUR 110% EXPAND MAX DUR 120% POS TARG 0.3535,0.3535 EXPAND POS TARG 0.707,0.707 EXPAND ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F255W F336W F555W F160BW ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC6254 NGC1904 NGC5904 ------------------------------------------------------------------------------------------------------------------------------------