6456( 8) - 06/28/96 10:32 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6456 Version: 8 Check-in Date: 28-Jun-1996 10:27:25 1.Proposal Title: The photospheric iron abundance of UV bright stars in globular clusters ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle STELLAR POPULATIONS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: RALF NAPIWOTZKI UNIVERSITAET ERLANGEN-NUERNBERG CoI: Ulrich Heber Universitaet Erlangen-Nuernberg N CoI: Stefan Haas Universitaet Erlangen-Nuernberg N CoI: Sabine Moehler Landesternwarte Heidelberg N CoI: Stefan Dreizler Universitaet Kiel N CoI: Klaus Werner Universitaet Potsdam N ------------------------------------------------------------------------------------ 6. Abstract UV bright stars can be found in colour-magnitude diagrams of globular clusters, lying above the horizontal branch and to the blue of the giant branch. They are mostly post-AGB stars evolving to white dwarfs. Recent analyses of field pop. II post-AGB stars raised the question if the chemical abundances in their atmospheres are the product of dredge-ups or of a gas -dust-separation. The knowledge of the original metallicities (= metallicity of the globular cluster) of the cluster post- AGB stars will allow to overcome this ambiguity. From the measurement of the iron abundance in these stars it can directly be judged if dust depletion is at work. Existing high -S/N, high resolution optical spectra allow the abundances of lighter elements (C,N,O,Si) to be measured, but no iron lines are present. In the UV, however, lines of iron (Fe III, Fe IV and Fe V) can be used. Highly sophisticated NLTE model atmospheres and accurate atomic data are at hand in order to determine precise iron abundances. Thus a crucial test of the predictions of stellar evolutionary theory for low-mass stars can be performed. We therefore propose high- resolution spectroscopic observations of iron lines (in carefully selected wavelengths regions) in the UV for five post-AGB stars spread out over a large range in T(eff) (20000 K\ldots51000 K). Parallel observations with WFPC2 in the outer regions of the clusters shall collect images in FUV (1600Angstrom), U and V to search for faint blue stars. ------------------------------------------------------------------------------------ 6456( 8) - 06/28/96 10:32 - [ 2] Observations Description ------------------------ We propose observations of two hot UV bright stars (ROA5701 and Barnard 29) with the GHRS with grating G200M in the wavelength range 1865\\ldots 1905 Angstrom\\ and a three additional targets (vZ 1128, PG 2120+062, ROB 162) with grating G160M and central wavelength 1615 Angstrom\\ and 1280 Angstrom\\ (ROB 162), respectively. We aim at a signal-to- noise ratio of ~30. From our experience with the analysis of coadded IUE high resolution spectra of the pop. II central star BD+33 2642 this S/N is adequate for a model atmosphere analysis of the iron lines even at the low abundances expected. From the known temperature and magnitudes (and reddening) of the target objects we calculate fluxes and count rates (0.13, 0.14, 0.19, 0.6 and 0.17 counts/s/diode for ROA 5701, vZ 1128, and Barnard 29, ROB 162 and PG 2120+062, resp.). Including overhead times the exposure time available in two orbits will yield S/N in the range 25\\ldots 30 for the target stars, except for ROB 162 which requires only one orbit. The cluster target stars lie typically about 2 arcmin. from the cluster center. Coordinates have been taken from literature (ROA 5701, Barnard 29, vZ1128, including the earliest papers by von Zeippel, 1908 and Barnard, 1931) or measured recently by Dr. A. Good at ROE (ROB 162). Since they are the UV brightest stars in the clusters and do not lie in the very centers of the cluster, the ``Return to brightest Point'' mode of GHRS will allow a safe target acquisition into the LSA. Parallel exposures As explained in the scientific justification, we plan to take WFPC2 images in U,V and UV (F160BW or F170W) filters in parallel mode to search for faint blue stars. These observations can be taken while exposing the primary targets at no extra cost, and will allow us to construct deep colour- magnitude and colour-colour diagrams. We propose to obtain a combination of short and long exposures in order to recover, without saturation, stars in a wide magnitude range. We plan to use the F606W filter as V filter as it is much more efficient than F555W and can be transformed to Johnson V. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6456( 8) - 06/28/96 10:32 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC5139- STAR,SDO RA=13H 27M 28.89S +/- 0.02S, J2000 V = 13.2+/-0.2 132729- DEC=-47D 22' 48.1" +/- 0.3", F(1900)=2.1+/-0.2e-13 472247 PLATE-ID=00AK 2 NGC6205- STAR,SDO RA=16H 41M 33.74S +/- 0.03S, J2000 V = 13.0+/-0.1 164133+36285 DEC=+36D 26' 07.8" +/- 0.3", F(1900)=2.8+/-0.2e-13 2 PLATE-ID=00CK 3 NGC5272- STAR,SDO RA=13H 42M 16.75S +/- 0.02S, J2000 V = 14.9 133740+28260 DEC=+28D 26' 01.1" +/- 0.2", F(1600)=1.7+/-0.1e-13 1 PLATE-ID=009L Comments: Coordinates from GSC 4 NGC6397- STAR,SDO RA=17H 40M 38.35S +/- 0.02S, J2000 V = 13.2 174038- DEC=-53D 38' 31.6" +/- 0.3", F(1300)=8.0+/-0.5e-13 533832 PLATE-ID=0688 Comments: Coordinates from GSC 5 STAR- STAR,SDO RA=21H 22M 31.73S +/- 0.02S, J2000 V = 14.4+/-0.1 212003+06090 DEC=+06D 21' 56.1" +/- 0.2", F(1600)=2.15+/-0.2e-13 3 PLATE-ID=02V8 Comments: Coordinates from GSC 6456( 8) - 06/28/96 10:32 - [ 4] 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 NGC5139-132 HRS ACQ 2.0 MIRROR-N2 SEARCH-SIZE=3,BRIGHT=RETURN 1 1.8 S ONBOARD ACQ FOR 2 729-472247 Comments: STEP-TIME=0.2S, EXPECT 2500 CNTS ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC5139-132 HRS ACCUM 2.0 G200M 1865-19 8 598.4 S 729-472247 05 ------------------------------------------------------------------------------------------------------------------------------------ 6456( 8) - 06/28/96 10:32 - [ 5] 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 NGC6205-164 HRS ACQ 2.0 MIRROR-N2 SEARCH-SIZE=3,BRIGHT=RETURN 1 1.8 S ONBOARD ACQ FOR 2 133+362852 Comments: STEP-TIME=0.2S, EXPECT 3500 CNTS ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC6205-164 HRS ACCUM 2.0 G200M 1865-19 8 584.8 S 133+362852 05 ------------------------------------------------------------------------------------------------------------------------------------ 6456( 8) - 06/28/96 10:32 - [ 6] Visit: 03 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 NGC5272-133 HRS ACQ 2.0 MIRROR-N2 SEARCH-SIZE=3,BRIGHT=RETURN 1 3.6 S ONBOARD ACQ FOR 2 740+282601 Comments: STEP-TIME=0.4S, EXPECT 2500 CNTS ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC5272-133 HRS ACCUM 2.0 G160M 1600-16 FP-SPLIT=STD 4 1088.0 740+282601 35 ------------------------------------------------------------------------------------------------------------------------------------ 6456( 8) - 06/28/96 10:32 - [ 7] Visit: 04 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 NGC6397-174 HRS ACQ 2.0 MIRROR-N2 SEARCH-SIZE=3,BRIGHT=RETURN 1 1.8 S ONBOARD ACQ FOR 2 038-533832 Comments: STEP-TIME=0.2S, EXPECT 3500 CNTS ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC6397-174 HRS ACCUM 2.0 G160M 1255-12 FP-SPLIT=STD 2 870.4 S 038-533832 90 ------------------------------------------------------------------------------------------------------------------------------------ 6456( 8) - 06/28/96 10:32 - [ 8] Visit: 05 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 STAR-212003 HRS ACQ 2.0 MIRROR-N2 SEARCH-SIZE=3,BRIGHT=RETURN 1 2.7 S ONBOARD ACQ FOR 2 +060903 Comments: STEP-TIME=0.3S, EXPECT 2000 CNTS ------------------------------------------------------------------------------------------------------------------------------------ 2 STAR-212003 HRS ACCUM 2.0 G160M 1600-16 8 571.2 S +060903 35 ------------------------------------------------------------------------------------------------------------------------------------ 6456( 8) - 06/28/96 10:32 - [ 9] Summary Form for Proposal 6456 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SEARCH-SIZE=3 BRIGHT=RETURN FP-SPLIT=STD ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category STELLAR POPULATIONS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 2 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N2 G200M G160M ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC5139-132729-472247 NGC6205-164133+362852 NGC5272-133740+282601 NGC6397-174038-533832 STAR-212003+060903 ------------------------------------------------------------------------------------------------------------------------------------