6418( 3) - 01/31/96 11:13 - [ 1]
PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only
ID: 6418
Version: 3
Check-in Date: 31-Jan-1996
11:07:04
1.Proposal Title:
Small-Scale ISM Structure: The Remarkable Sightline Toward Mu Cru
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2. Scientific Category 3. Proposal For 4. Cycle
INTERSTELLAR MEDIUM GO 6
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5. Investigators
Contact?
PI: David M. Meyer Northwestern University
CoI: J. Chris Blades Space Telescope Science Institute N
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6. Abstract
We propose to use the GHRS on HST to accurately measure and compare the interstellar
Zn II, Cr II, Mg I, and C I absorption line profiles toward both members of the
binary Mu Cru. Recent optical observations of Na I at very high spectral resolution
(Deltav = 0.3 km s^-1) toward this system reveal line strength variations in at
least 4 velocity components indicative of ISM structure on scales less than the
projected binary separation of 6600 AU. Based on similar observations toward other
binaries, such structure now appears to be a common feature of the cold diffuse gas
in the local ISM and detectable toward systems with projected separations as small
as 1000 AU. The Mu Cru sightline provides an ideal laboratory to study the nature of
this small-scale ISM structure with high S/N GHRS echelle observations of key
interstellar ions. In particular, comparisons between the optically thin Zn II and
Cr II lines will allow us to assess how the clumpiness of the gas is reflected in
the dust. Observations of the C I fine -structure excitation will provide good
estimates of the pressures in the cold clumps whose small scale lengths suggest high
gas densities in a very diffuse ambient medium. In summary, our proposed GHRS
observations of Mu Cru will provide the first quantitative steps toward
understanding how small- scale structure forms and evolves in the diffuse ISM.
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6418( 3) - 01/31/96 11:13 - [ 2]
Observations Description
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Our goal is to obtain high S/N GHRS echelle observations of the interstellar Zn
II, Cr II, Mg I, and C I absorption line profiles toward both members of the
binary Mu Cru. All observations will be made using the SSA and a sampling
strategy of four substeps per diode in order to maximize the spectral
resolution needed for good profile comparisons. The observations of Zn II
LambdaLambda2026.14, 2062.66, Cr II LambdaLambda2062.23, 2066.16, and Mg I
LambdaLambda2026.48, 2852.96 will involve three ECH-B wavelength setups per
star. Based on the IUE fluxes for Mu Cru and accounting for the effects of the
ECH-B blaze efficiency as well as the reduced SSA throughput on the
sensitivities listed in the Cycle 6 GHRS Handbook, we can achieve spectra of
all of these lines at a S/N ratio of 150 in a total integration time of 39 min.
(3 exposures) on Mu^1 Cru and 160 min. (9 exposures) on Mu^2 Cru. We plan to
use the FP-Split option in all of our exposures in order to better assess and
remove the effects of fixed pattern noise. In the case of C I, the multiplets
centered near 1277 and 1280 Angstrom\\ can both be covered with one ECH-A
wavelength setup per star. Since the oscillator strengths and wavelength
separations of the various J = 0, 1, 2 transitions in these multiplets are
quite different, it will be possible to make an accurate comparison of the C I
fine-structure excitation as a function of velocity in the Mu Cru line
profiles. We can obtain a C I spectrum with a S/N ratio of 150 toward Mu^1 Cru
in a total integration time of 19 min. (1 exposure) and one with a S/N ratio of
100 toward Mu^2 Cru in a time of 64 min. (4 exposures). The C I sensitivity
goal is somewhat lower for Mu^2 Cru because this star is appreciably fainter in
the far- UV and the key component (-9 km s^-1) to be studied is in the Mu^1 Cru
sightline. Allowing for all of the acquisition and exposure overheads
(including the 45 min. GHRS side change from ECH-A to ECH-B which can occur
mostly during occultation), our proposed observations will require 2 orbits on
Mu^1 Cru and 6 orbits on Mu^2 Cru given a visibility window of 57 min. per
orbit.
Real Time Justification
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None. 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: ,
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6418( 3) - 01/31/96 11:13 - [ 3]
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 HD112092 STAR, B0-B2 V-IV RA=12H 54M 35.64S +/- 0.03S, J2000 V = 4.03
DEC=-57D 10' 39.8" +/- 0.5" B-V = -0.17
2 HD112091 STAR, BE RA=12H 54M 36.91S +/- 0.03S, J2000 V = 5.17
DEC=-57D 10' 06.7" +/- 0.5" B-V = -0.12
6418( 3) - 01/31/96 11:13 - [ 4]
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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1 HD112092 HRS ACQ 2.0 MIRROR-N1 BRIGHT=RETURN,S 1 1.8S ONBOARD ACQ FOR 2
EARCH-SIZE=3
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2 HD112092 HRS ACQ/PEA 0.25 MIRROR-N1 SEARCH-SIZE=5 1 5.0S ONBOARD ACQ FOR 3-6
KUP
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3 HD112092 HRS ACCUM 0.25 ECH-A44 1278.7 FP- 2 544.0S
SPLIT=STD,STEP-
PATT=7
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4 HD112092 HRS ACCUM 0.25 ECH-B28 2026.0 FP- 4 652.8S
SPLIT=STD,STEP-
PATT=7
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5 HD112092 HRS ACCUM 0.25 ECH-B27 2063.0 FP- 3 544.0S
SPLIT=STD,STEP-
PATT=7
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6 HD112092 HRS ACCUM 0.25 ECH-B20 2853.0 FP- 2 435.2S
SPLIT=STD,STEP-
PATT=7
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6418( 3) - 01/31/96 11:13 - [ 5]
Visit: 02
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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7 HD112091 HRS ACQ 2.0 MIRROR-N1 BRIGHT=RETURN,S 1 1.8S ONBOARD ACQ FOR 8
EARCH-SIZE=3
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8 HD112091 HRS ACQ/PEA 0.25 MIRROR-N1 SEARCH-SIZE=5 1 5.0S ONBOARD ACQ FOR 9-12
KUP
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9 HD112091 HRS ACCUM 0.25 ECH-A44 1278.7 FP- 4 979.2S
SPLIT=STD,STEP-
PATT=7
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10 HD112091 HRS ACCUM 0.25 ECH-B28 2026.0 FP- 4 870.4S
SPLIT=STD,STEP-
PATT=7
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11 HD112091 HRS ACCUM 0.25 ECH-B27 2063.0 FP- 3 870.4S
SPLIT=STD,STEP-
PATT=7
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12 HD112091 HRS ACCUM 0.25 ECH-B20 2853.0 FP- 2 979.2S
SPLIT=STD,STEP-
PATT=7
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6418( 3) - 01/31/96 11:13 - [ 6]
Summary Form for Proposal 6418
Item Used in this proposal
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Configurations HRS
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Opmodes ACQ ACQ/PEAKUP ACCUM
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Optional Parameters BRIGHT=RETURN SEARCH-SIZE=3 SEARCH-SIZE=5 STEP-PATT=7 FP-SPLIT=STD
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Proposal Category GO
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Scientific Category INTERSTELLAR MEDIUM
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Special Requirements ONBOARD ACQ FOR 2 ONBOARD ACQ FOR 3-6 ONBOARD ACQ FOR 8 ONBOARD ACQ FOR 9-12
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Spectral Elements MIRROR-N1 ECH-A44 ECH-B28 ECH-B27 ECH-B20
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Target Names HD112092 HD112091
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