6040( 6) - 11/10/95 09:48 - [ 1]
PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only
ID: 6040
Version: 6
Check-in Date: **********
1.Proposal Title:
Ultra--high angular resolution of O3 stars in the Carina Nebula and in the LMC
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2. Scientific Category 3. Proposal For 4. Cycle
Hot Stars GO 5
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5. Investigators
Contact?
PI: R. Burg Johns Hopkins University
CoI: M. G. Lattanzi Space Telescope Science Institute Y
CoI: N. R. Walborn Space Telescope Science Institute N
CoI: J. E. Pringle Institute of Astronomy N
CoI: J.L. Hershey Space Telescope Science Institute N
CoI: B.J. McLean Space Telescope Science Institute N
CoI: I.N. Evans Space Telescope Science Institute N
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6. Abstract
The upper mass limit for individual stars remains an open question of great
importance in astronomy. Theory is not currently capable of placing a firm upper
mass limit and, therefore, the problem is an observational one. O3 stars in giant
HII regions are the hottest and presumably the most massive Population I stars. Of
the 70 definite and possible members of this class, 59 are in the Magellanic Clouds
(Walborn 1994). The Carina Nebula has the highest concentration of these stars in
the Milky Way and hence provides the most accessible laboratory for the
investigation of the most massive stars. The LMC has the most extreme examples;
i.e., those objects which are candidates for the most massive star. We propose to
use the Fine Guidance Sensor (FGS) in its interferometric mode to investigate a
complete sample of six O3 stars in Carina and three extreme objects in the LMC in
order to establish if these stars are massive single stars or if, like R136a in the
LMC, they are multiple star systems.
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Observations Description
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All of our proposed exposures use the TRANS mode of the astrometer FGS (FGS 3).
As described in the FGS Instrument Handbook (Version 4.0), and in recently
published papers (Bernacca et al. 1993, Lattanzi et al. 1994) this mode samples
the interference fringe produced by the Koester's prism interferometer, the
``heart'' of the Fine Guidance Sensor. There are two Koester's prism
interferometers in each FGS. These are fed by a beam--splitter to give
sensitivity in two orthogonal directions, usually referred to as X and Y axes.
Therefore, each FGS3 TRANS scan produces two fringes which can then be
independently analyzed for signatures other than those characteristic of the
FGS3 standard single star UP69. Indeed, deviations from the single star fringes
are used to measure double, or multiple, stars projected separations. On--sky
separation and position angle are easily derived from these measurements and
telescope attitude data (Bernacca et al. 1993 and references therein). Accurate
V magnitudes are also derived from the same counts used to construct the
fringes and provided by the 4 photomultipliers (two per axis) which detect the
photons from the Koester's prisms (Bucciarelli et al. 1994; Bernacca et al.
1994). Experience with observations very similar to those proposed here
(Bernacca et al. 1993 and 1994; Lattanzi et al. 1994, and references therein)
indicate that the FGS interferometers are capable of measuring separations
smaller than 0.015 arcsec and position angles to better than 1 deg. We request
one visit per target. Following the procedure for the calculation of the
number of orbits given in the Cycle 5 Phase I Proposal Instructions volume,
each visit comprises a guide star acquisition (12 min), the set--up time
(including the selected filter) for TRANS mode (3 min), then the science
exposure. Our science exposure consists of 30 TRANS scans of 2sec point1 on the
sky each (i.e., 1sec point5 per FGS axis) sampled every 0sec point0008 (the
pixel size per axis is 0sec point0006). Since each sample takes a fixed 0.025
sec, the 30 scans take 31.3 min, for a total of 12+3+31.3 = 46.3 min per visit.
This is less than the visibility period per orbit. Therefore, we request one
orbit per target. Recent observations (Lattanzi et al. 1994 and references
therein) show that scans with the same pixel size, and through the PUPIL
element give optimal resolution with minimum scan time. Consecutive scans are
required for three reasons. First, spacecraft jitter can corrupt fringes. With
multiple scans one can identify jitter--corrupted fringes and reject them.
Second, analysis of multiple scans is the only reliable way to check on the
repeatibility of a detection. Finally, multiple scans are co--added to
increase the signal--to-- noise ratio (S/N). This is crucial for best
resolution during the reductions and to allow for any star variability, and
higher background due to diffuse light emission from nebulosity around the
stars. Successful exposures should yield co--added fringes with typical S/N >
60. Two of our targets are too bright to be observed with the PUPIL element and
the neutral density filter (F5ND) is required. This filter as been very little
used with TRANS observations and some degradation of the fringes is expected.
Also, it is necessary to have F5ND fringes of the FGS single star standard
UP69. Routine TRANS mode calibration observations on UP69 run by the STScI do
not foresee the F5ND filter. We have therefore added one calibration orbit on
UP69. Length, pixel size, and number of scans in the calibration visit are the
same as for the science observations. This calibration should be placed as
close in time as possible to the F5ND science observations. Should the STScI
Cycle 5 calibration plan for TRANS mode include the F5ND filter, the
calibrations orbit requested would not be necessary.
Real Time Justification
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None.
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: __Diagnostic-Sum-Section__ Software-Version (Contro,
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6040( 6) - 11/10/95 09:48 - [ 4]
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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1 HDE269810 EXT-STAR, Giant O RA = 05H 35M 13.93S +/- 0.1S, 2000 V=12.3 +/- 0.1
DEC = -67D 33' 26.7" +/- 1", B-V=-0.23
PLATE-ID=06B0 TYPE=O3III
2 LMC-053705- EXT-STAR, Giant O RA = 05H 37M 05.57S +/- 0.1S, 2000 V=13.1 +/- 0.1
662136 DEC = -66D 21' 35.4" +/- 1", B-V=-0.12
PLATE-ID=06B0 TYPE=O3III
3 LMC-045659- EXT-STAR, Giant O RA= 04H 56M 58.92S +/- 0.1S, DEC 2000 V=12.66 +/- 0.01
662438 = -66D 24' 39.0" +/- 1", PLATE- B-V=-0.11 +/- 0.01
ID=06AF TYPE=O3III
4 HD93129A STAR, Supergiant O RA = 10H 43M 57.30S +/- 0.1S, 2000 V=7.3 +/- 0.1
DEC = -59D 32' 51.2" +/- 1", B-V=0.22
PLATE-ID=ZZZQ
Comments: Target HD93129B is TRANSed together with HD93129A
5 HD93205 STAR, Main Sequence O RA = 10H 44M 33.90S +/- 0.1S, 2000 V=7.8 +/- 0.1
DEC = -59D 44' 15.2" +/- 1", B-V=0.05
PLATE-ID=ZZZQ
6 HD93250 STAR, Main Sequence O RA = 10H 44M 45.13S +/- 0.1S, 2000 V=7.4 +/- 0.1
DEC = -59D 33' 55.0" +/- 1", B-V=0.15
PLATE-ID=ZZZQ
7 HD303308 STAR, Main Sequence O RA = 10H 45M 06.05S +/- 0.1S, 2000 V=8.2 +/- 0.1
DEC = -59D 40' 06.1" +/- 1", B-V=0.13
PLATE-ID=ZZZQ
8 HD93128 STAR, Main Sequence O RA = 10H 43M 54.00S +/- 0.1S, 2000 V=8.8 +/- 0.1
DEC = -59D 32' 56.0" +/- 1", B-V=0.24
PLATE-ID=ZZZQ
9 Mk42 EXT-STAR, Supergiant O RA=05H 38M 42.22S +/- 0.05S, J2000 V=12.7 +/- 0.1
DEC=-69D 05' 55.3" +/- 0.1" B-V=0.0 +/- 0.1
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Visit: 01
Visit Requirements: PCS MODE F
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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1 HDE269810 FGS TRANS 3 PUPIL STEP-SIZE=0.6, 1 1875S
SCANS=30
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Visit: 02
Visit Requirements: PCS MODE F ORIENT 355D TO 5D ON HOLD
On Hold Comments: Waiting for non-HST data
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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1 LMC-053705- FGS TRANS 3 PUPIL STEP-SIZE=0.6, 1 1625S
662136 SCANS=26
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Visit: 03
Visit Requirements: PCS MODE F
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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1 LMC-045659- FGS TRANS 3 PUPIL STEP-SIZE=0.6, 1 1875S
662438 SCANS=30
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Visit: 04
Visit Requirements: PCS MODE F ORIENTation 101D TO 107D
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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1 HD93129A FGS TRANS 3 F5ND STEP-SIZE=1.2, 1 2004.3S
SCANS=17
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2 HD93129A FGS TRANS 3 F5ND STEP-SIZE=1.2, 1 2240.1S
SCANS=19
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Visit: 05
Visit Requirements: PCS MODE F
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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1 HD93205 FGS TRANS 3 F5ND STEP-SIZE=0.6, 1 1812.5S
SCANS=29
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Visit: 06
Visit Requirements: PCS MODE F
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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1 HD93250 FGS TRANS 3 F5ND STEP-SIZE=0.6, 1 1812.5S
SCANS=29
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Visit: 07
Visit Requirements: PCS MODE F
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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1 HD303308 FGS TRANS 3 PUPIL STEP-SIZE=0.6, 1 1812.5S
SCANS=29
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Visit: 08
Visit Requirements: PCS MODE F
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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1 HD93128 FGS TRANS 3 PUPIL STEP-SIZE=0.6, 1 1812.5S
SCANS=29
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Visit: 09
Visit Requirements: ORIENT 297D TO 307D
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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1 Mk42 FGS TRANS 3 PUPIL STEP-SIZE=2, 1 1769.63
SCANS=13
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Summary Form for Proposal 6040
Item Used in this proposal
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Configurations FGS
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Opmodes TRANS
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Optional Parameters STEP-SIZE=0.6 SCANS=30 SCANS=26 SCANS=17 SCANS=19 SCANS=29 SCANS=13
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Proposal Category GO
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Scientific Category Hot Stars
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Special Requirements PCS MODE F PCS MODE F ORIENT 355D TO 5D ON HOLD PCS MODE F ORIENTation 101D TO 107D ORIENT 297D TO
307D
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Spectral Elements PUPIL F5ND
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Target Names HDE269810 LMC-053705-662136 LMC-045659-662438 HD93129A HD93205 HD93250 HD303308 HD93128 Mk42
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