6784( 10) - 08/29/96 15:46 - [ 0]
PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only
ID: 6784
Version: 10
Check-in Date: 29-Aug-1996
16:43:48
1.Proposal Title:
Ultraviolet Spectral Templates from the Metal-Rich Open Cluster NGC 6791
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2. Scientific Category 3. Proposal For 4. Cycle
STELLAR POPULATIONS GO 6
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5. Investigators
Contact?
PI: Ruth C. Peterson ASTROPHYSICAL ADVANCES
CoI: Elizabeth Green Steward Observatory N
CoI: James Liebert Steward Observatory N
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6. Abstract
The open cluster NGC 6791 is a potential Rosetta Stone for decoding the properties
of metal-rich stars. It is as old or older than any other open cluster and has an
iron abundance about twice solar. In addition to a well-populated red horizontal-
branch (HB), it has several hot HB stars whose membership is supported by radial
velocities, and confirmed in the one case where a proper motion exists. An existing
ground- based spectrum of one blue HB star of type A5 III shows no A- type spectral
peculiarities; its analysis will produce a precise iron abundance for the cluster.
We propose here to acquire ultraviolet spectra (2500 - 3200 Angstrom) for cluster
members on the blue HB for comparison with theoretical spectral- synthesis
calculations. In addition, HST spectra covering 1150 - 2300Angstrom\ will be
obtained for several sdB/sdO stars in NGC 6791 to see whether such stars could
account for the UV upturn seen in some metal-rich systems.
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Observations Description
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We will use FOS/RD, the 0.3 aperture, and the grating covering 2500 --
3200Angstrom, G270H, for two stars on the red end of the blue HB. Exposure
times at 2800Angstrom\\ with this grating are estimated from IUE fluxes of the
field BHB star HD 86986, with V = 8.0, B-V = 0.12, U = 8.3, which is similar to
NGC 6752 II-17 in temperature (but has lower metallicity). According to IUE
observations discussed by Cacciari (1985), HD 86986 has a flux of 1.2 * 10^-12
erg/s/cm^2/Angstrom\\ at 2800Angstrom. We estimate a flux of 1.5 * 10^-15 for a
similar but fainter BHB with V = 15.0, U = 15.7 if unreddened. With the
sensitivity function from Table 1-7, we find 0.80 cts/diode/s. This is reduced
to 86\\% for the 0.5 aperture, and reduced further by 10\\% for the cluster
reddening of E(B- V)=0.05, to yield 0.62 cts/s/diode. Stronger blanketing
suggests a 33% decrease in flux. A S/N = 28 per diode takes ~30min for such a
star. In two orbits, two stars will be observed. For the farUV, the lower setup
time prompts us to use HRS and G140L. In six orbits, four stars may be
observed.
Real Time Justification
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Calibration Justification
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Additional Comments
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Data Distribution
Media: 8MM
Blocking Factor: 10
Ship To: PI_Address
Ship Via: UPS
Email: ,
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6784( 10) - 08/29/96 15:46 - [ 1]
TARGET LIST a) Fixed Targets
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Tar| Target | Target | Target |Coord | Radial | Flux data
No | Name | Description | Position |Eqnx | Vel. |
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2 NGC6791-B2 STAR,HORIZONTAL BRANCH RA-OFF = -10.04S +/- .1S, DEC- 2000 V= -49 V = 17.43+/-0.1
STAR OFF = -264.4" +/- .2", FROM 7, B-V = -0.12+/-0.05
PLATE-ID=037K E(B-V) = 0.13+/-0.02
F-CONT(1600)=6.0+/-0.2e-15
Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec)
1984. 0.0 0.0 0.0
4 NGC6791-B4 STAR,HORIZONTAL BRANCH RA-OFF = +12.94S +/- .1S, DEC- 2000 V= -49 V = 17.75+/-0.1
STAR OFF = -12.2" +/- .2", FROM 7, B-V = -0.19+/-0.05
PLATE-ID=037K E(B-V) = 0.13+/-0.02
F-CONT(1600)=4.5+/-0.2e-15
Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec)
1985. 0.0 0.0 0.0
7 NGC6791- STAR,HORIZONTAL BRANCH RA = 19H 20M 59.96S +/- .1S, DEC 2000 V= -49 V = 15.0+/-0.1
KII17-OFFSET STAR = +37D 46' 3.3" +/- .2", PLATE- B-V = 0.47+/-0.05
ID=037K E(B-V) = 0.13+/-0.02
F-CONT(2800)=1.0+/-0.2e-15
Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec)
1984 0.0 0.0 0.0
6784( 10) - 08/29/96 15:46 - [ 2]
Visit: 01
Visit Requirements: <none>
On Hold Comments: <none>
Additional Comments: <none>
Exposures
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Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special
Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements
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12 NGC6791-B2 FOS/BL ACQ/BIN 4.3 MIRROR 1 20. S ONBOARD ACQ FOR 13
ARY
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13 NGC6791-B2 HRS ACCUM 2.0 G140L 1310-15 FP-SPLIT=STD,STEP-PATT=DEF 3 1523.2
96
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14 NGC6791-B4 FOS/BL ACQ/BIN 4.3 MIRROR 1 20. S ONBOARD ACQ FOR 15,31
ARY
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15 NGC6791-B4 HRS ACCUM 2.0 G140L 1310-15 FP-SPLIT=STD,STEP-PATT=DEF 3 2502.4
96
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31 NGC6791-KII FOS/RD ACQ/BIN 4.3 MIRROR 2800 1 2.8 S ONBOARD ACQ FOR 33
17-OFFSET ARY
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33 NGC6791-KII FOS/RD ACQ/PEA 0.3 MIRROR SCAN-STEP-X=0.17,SCAN-STEP-Y=0.17 1 2.8 S ONBOARD ACQ FOR 34
17-OFFSET K ,SEARCH-SIZE-X=3,SEARCH-SIZE-Y=3
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34 NGC6791-KII FOS/RD ACQ/PEA 0.3 MIRROR SCAN-STEP-X=0.052, 1 20. S ONBOARD ACQ FOR 35-36
17-OFFSET K SCAN-STEP-Y=0.052,SEARCH-SIZE-X=5
,SEARCH-SIZE-Y=5
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35 NGC6791-KII FOS/RD ACCUM 0.3 G270H 2800 1 2590. S
17-OFFSET
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36 NGC6791-KII FOS/RD ACCUM 0.3 G270H 2800 1 2590. S
17-OFFSET
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6784( 10) - 08/29/96 15:46 - [ 3]
Summary Form for Proposal 6784
Item Used in this proposal
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Configurations FOS/BL HRS FOS/RD
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Opmodes ACQ/BINARY ACCUM ACQ/PEAK
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Optional Parameters FP-SPLIT=STD STEP-PATT=DEF SEARCH-SIZE-Y=3 SEARCH-SIZE-Y=5
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Proposal Category GO
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Scientific Category STELLAR POPULATIONS
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Special Requirements ONBOARD ACQ FOR 13 ONBOARD ACQ FOR 15,31 ONBOARD ACQ FOR 33 ONBOARD ACQ FOR 34 ONBOARD ACQ FOR
35-36
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Spectral Elements MIRROR G140L G270H
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Target Names NGC6791-B2 NGC6791-B4 NGC6791-KII17-OFFSET
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