5894( 13) - 12/18/95 11:09 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 5894 Version: 13 Check-in Date: ********** 1.Proposal Title: The hot gaseous halo of the Large Magellanic Cloud ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Interstellar Medium GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Bart Wakker University of Wisconsin CoI: You-Hua Chu University of Illinois Y CoI: Sean Points University of Illinois N CoI: Dominik Bomans Universitaet Bonn N ------------------------------------------------------------------------------------ 6. Abstract We request observing time with the GHRS on HST to help determine the structure and physical parameters of the hot gaseous halo of the Large Magellanic Cloud (LMC). The SMC and LMC are the only galaxies in which such a determination can be done in detail, as confusion along the line-of-sight is much less than in the Milky Way. They are also the only other galaxies near enough to be able to obtain high- resolution spectra of individual stars. Gas at 10^5 K can be detected in the C IV LambdaLambda1548, 1550 UV absorption lines. From such data it is also possible to obtain information on velocities and the depth structure of the halo. Previous work with IUE has shown that 10^5 K gas is present around very hot stars, in some H II regions, in superbubbles and in supergiant shells. However, with IUE it is not possible to determine the existence of a continuous halo surrounding the LMC, since the required probes are too faint. We request observing time for eight probes selected to take into account the distribution 10^6 K gas mapped by ROSAT, while avoiding areas known to produce 10^5 K gas locally. We request a total of ten orbits and plan to use the G160M grating of GHRS, which allows us to reach a signal-to- noise ratio of 20 or higher. This corresponds to a detection limit for N(C IV) of 2x10^13 , within the range of values detected in the Milky Way. ------------------------------------------------------------------------------------ 5894( 13) - 12/18/95 11:09 - [ 2] Observations Description ------------------------ We plan to observe six stars in X-ray dim areas of the LMC, and two in X-ray bright areas. These targets have been selected avoid bright H Alpha emission and supergiant shells. For each target we intend to use the G160M grating over the wavelength range 1533-1566 Angstrom. Standard comb- addition and FP-split will be used to reduce the effects of fixed pattern noise. The spectra will be sampled with 2 sub- steps per diode (Step Pattern 4). We will use the large aperture during our observations. The small loss of resolution relative to the use of the small aperture does not outweigh the loss of a factor two in light. Exposure times are estimated using the description in the post-COSTAR HST GHRS Instrument Handbook (v5.0, May 1994). To determine the stellar fluxes, we constructed a table of unreddened flux ratios f(1550)/f(5500) for several different stellar types, and we determined the reddening for each target. To determine flux ratios, we used IUE Newsletter No. 22, and measured reddened flux ratios for stars of spectral types between O9 and B1, of all luminosity classes. These values were dereddened using the value of E(B-V) given in the Newsletter and the UV extinction model described in the GHRS handbook (Seaton 1979, MNRAS 187, 73p). Since stars of spectral type B0 and especially B1 also have a broad stellar absorption, we used half of the continuum flux to obtain the flux ratios to make sure that we do not underestimate the flux at the wavelength of interest. The reddening of each target was found by subtracting the intrinsic color given by Fitzgerald (1970, AA 4, 234) from the value of \bmv\ given by Rousseau et al. We used E(B-V)=0.12 for the one target with unknown color (Sk-70 69). Given the flux ratio, reddening and visual magnitude, we find the flux at 1550 Angstrom. The table below gives the result. The count rate then follows from the sensitivities in the Handbook. Column 7 gives the resulting integration time to reach a S/N of 20, the minimum value we need to obtain results that can be unambiguously interpreted. The acquisition overhead is substantial (12 minutes for the guide star, 11 minutes for the target), and only 36 out of each 59 minutes in an orbit are available for the actual integration. In one orbit we can reach the desired S/N only for Sk-69 59 and Sk-69 110. For Sk-68 28 and Sk-67 46, the missing time is only 4 and 6 minutes, and the resulting S/N of 19 will still be sufficient. For Sk-67 45 and Sk-69 68 on the other hand, the noise increases by 25%. Scheduling three consecutive orbits, we can combine the two longest integrations with the third and fourth longest and we can achieve the desired S/N for all four stars in two groups of three consecutive orbits. We would then acquire one of the objects midway through the second orbit, and we would need two 6-minute re- acquisitions. The total acquisition overhead in the three orbits would be 2*(23+6) or 58 minutes, leaving 118 minutes of integration time, just what we need. We therefore request one orbit each for four probes, and two combinations of three orbits for the other four probes, for a grand total of 10 orbits. We note that the right ascension and declination of the LMC place it within the Continuous Viewing Zone (CVZ) of HST four times each year. We may use the CVZ to increase the efficiency of our program from 40% to 91%. The sum of the required integration times is 363 minutes. The total required overhead for each star is 26 minutes (12 for guide-star acquisition, 11 for target acquisition, 3 for internal wavelength calibration) or a total of 208 minutes. Within the CVZ, the total required time of 571 minutes can fit in 6 orbits. In the case that our program is scheduled during CVZ time, we can adjust the description of the observation accordingly. Name & type & V &E(B-V)& f_1550 &ct/s/d &T(20)&SN(36) (1) & (2) & (3) & (4) & (5) & (6) &(7) &(8) Priority-1 probes Sk-67 46 & B1 & 12.34 & 0.12 & 3.5x10^-13 & 0.173 & 40 & 19 Sk-67 76 & B0 & 12.42 & 0.17 & 3.1x10^-13 & 0.151 & 46 & 18 Sk-69 59 & B0 & 12.13 & 0.18 & 3.8x10^-13 & 0.183 & 38 & 20 Sk-69 110 & B1 & 11.65 & 0.18 & 4.3x10^-13 & 0.210 & 33 & 21 Sk-70 96 & B1 & 12.67 & 0.12 & 3.1x10^- 13 & 0.152 & 45 & 18 Priority-2 probes (only if CVZ time scheduled) Sk-67 28 & B1 & 12.4 & 0.12 & 3.4x10^-13 & 0.164 & 42 & 19 Sk-67 45 & B1 & 12.97 & 0.09 & 2.3x10^-13 & 0.112 & 62 & 15 Sk-69 68 & B0.5 & 12.6 & 0.21 & 2.5x10^- 13 & 0.122 & 57 & 16 Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- If scheduling permits we may increase the efficiency of our program from 40% to 64%. IUE observing time has been awarded to re-observe the three stars for which we found tentative non-detections. These stars have the following magnitudes and spectral types: 10.6 (a composite spectrum of main type B2Ia), 11.2 (type O9Ib) and 12.4 (type O7Ib). The IUE proposal also includes the brightest two stars known that are not obviously connected with regions containing hot material. These are of magnitude 11.5 (type B0) and 11.9 (type O9). For all five probes we calculated that at least two IUE shifts (16 hours) are needed to obtain a useful spectrum. A total of 10 US1 shifts in the 18th episode were awarded to us. Observing time has been awarded to start a ROSAT HRI survey of the LMC, with Chu as P.I. The HRI observations are more sensitive to point sources. The results will help the removal of point sources from the PSPC images, and improve the diffuse X-ray measurements. ------------------------------------------------------------------------------------ 5894( 13) - 12/18/95 11:09 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: Dr. Bart Wakker*University of Wisconsin*Astronomy Department*475 N Charter St*WI 53706 Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 5894( 13) - 12/18/95 11:09 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 Sk-67.46 EXT-STAR, B0-B2 III-I, RA = 05H 07M 1.63S +/- 0.03S, J2000 TYPE=B1I EXT-MEDIUM, Coronal Gas DEC = -67D 37' 29.7" +/- 0.2", V=12.34 PLATE-ID = 06B0 B-V=-0.06 E(B-V)=0.12 F(1550)=3.5E-13 Comments: Coordinates are from GSC Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1979.193 0.0 0.0 0.0 2 Sk-67.76 EXT-STAR, B0-B2 III-I, RA = 05H 20M 5.81S +/- 0.03S, J2000 TYPE=B0I EXT-MEDIUM, Coronal Gas DEC = -67D 21' 8.9" +/- 0.2", V=12.42 PLATE-ID = 06B0 B-V=-0.13 E(B-V)=0.17 F(1550)=3.1E-13 Comments: Coordinates are from GSC Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1979.193 0.0 0.0 0.0 3 Sk-69.59 EXT-STAR, B0-B2 III-I, RA = 05H 03M 12.79S +/- 0.04S, J2000 TYPE=B0I EXT-MEDIUM, Coronal Gas DEC = -69D 01' 37.2" +/- 0.2", V=12.13 PLATE-ID = 05ZW B-V=-0.12 E(B-V)=0.10 F(1550)=6.8E-13 Comments: Coordinates are from GSC Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1987.064 0.0 0.0 0.0 4 Sk-69.110 EXT-STAR, B0-B2 III-I, RA = 05H 20M 33.85S +/- 0.04S, J2000 TYPE=B1 EXT-MEDIUM, Coronal Gas DEC = -69D 32' 35.5" +/- 0.2", V=11.65 PLATE-ID = 05ZW B-V=0.08 E(B-V)=0.16 F(1550)=5.0E-13 Comments: Coordinates are from GSC Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1987.064 0.0 0.0 0.0 5 Sk-70.96 EXT-STAR, B0-B2 III-I, RA = 05H 29M 23.90S +/- 0.04S, J2000 TYPE=B1Ib EXT-MEDIUM, Coronal Gas DEC = -70D 14' 0.9" +/- 0.2", V=12.67 PLATE-ID = 05ZW E(B-V)=0.10 F(1550)=3.6E-13 Comments: Coordinates are from GSC Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1987.064 0.0 0.0 0.0 5894( 13) - 12/18/95 11:09 - [ 5] 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 Sk-67.46 HRS ACQ 2.0 MIRROR-N2 MAP=DEF, SEARCH 1 1.8S ONBOARD ACQ FOR 2 -SIZE=3 Comments: STEP-TIME=0.2S ------------------------------------------------------------------------------------------------------------------------------------ 2 Sk-67.46 HRS ACCUM 2.0 G160M 1539 STEP-PATT=4, 5 403.2S COMB=FOUR, FP- SPLIT=STD, DOPPLER=ON Comments: STEP-TIME=0.2S; Changes required if scheduled in CVZ ------------------------------------------------------------------------------------------------------------------------------------ 5894( 13) - 12/18/95 11:09 - [ 6] 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 Sk-67.76 HRS ACQ 2.0 MIRROR-N2 MAP=DEF, SEARCH 1 1.8S ONBOARD ACQ FOR 2 -SIZE=3 Comments: STEP-TIME=0.2S ------------------------------------------------------------------------------------------------------------------------------------ 2 Sk-67.76 HRS ACCUM 2.0 G160M 1539 STEP-PATT=4, 5 403.2S COMB=FOUR, FP- SPLIT=STD, DOPPLER=ON Comments: STEP-TIME=0.2S; Changes required if scheduled in CVZ ------------------------------------------------------------------------------------------------------------------------------------ 5894( 13) - 12/18/95 11:09 - [ 7] 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 Sk-69.59 HRS ACQ 2.0 MIRROR-N2 MAP=DEF, SEARCH 1 1.8S ONBOARD ACQ FOR 2 -SIZE=3 Comments: STEP-TIME=0.2S ------------------------------------------------------------------------------------------------------------------------------------ 2 Sk-69.59 HRS ACCUM 2.0 G160M 1539 STEP-PATT=4, 5 403.2S COMB=FOUR, FP- SPLIT=STD, DOPPLER=ON Comments: STEP-TIME=0.2S; Changes required if scheduled in CVZ ------------------------------------------------------------------------------------------------------------------------------------ 5894( 13) - 12/18/95 11:09 - [ 8] 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 Sk-69.110 HRS ACQ 2.0 MIRROR-N2 MAP=DEF, SEARCH 1 1.8S ONBOARD ACQ FOR 2 -SIZE=3 Comments: STEP-TIME=0.2S ------------------------------------------------------------------------------------------------------------------------------------ 2 Sk-69.110 HRS ACCUM 2.0 G160M 1539 STEP-PATT=4, 5 403.2S COMB=FOUR, FP- SPLIT=STD, DOPPLER=ON Comments: STEP-TIME=0.2S; Changes required if scheduled in CVZ ------------------------------------------------------------------------------------------------------------------------------------ 5894( 13) - 12/18/95 11:09 - [ 9] 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 Sk-70.96 HRS ACQ 2.0 MIRROR-N2 MAP=DEF, SEARCH 1 1.8S ONBOARD ACQ FOR 2 -SIZE=3 Comments: STEP-TIME=0.2S ------------------------------------------------------------------------------------------------------------------------------------ 2 Sk-70.96 HRS ACCUM 2.0 G160M 1539 STEP-PATT=4, 5 403.2S COMB=FOUR, FP- SPLIT=STD, DOPPLER=ON Comments: STEP-TIME=0.2S; Changes required if scheduled in CVZ ------------------------------------------------------------------------------------------------------------------------------------ 5894( 13) - 12/18/95 11:09 - [ 10] Summary Form for Proposal 5894 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters MAP=DEF SEARCH-SIZE=3 DOPPLER=ON FP-SPLIT=STD COMB=FOUR STEP-PATT=4 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Interstellar Medium ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 2 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N2 G160M ------------------------------------------------------------------------------------------------------------------------------------ Target Names Sk-67.46 Sk-67.76 Sk-69.59 Sk-69.110 Sk-70.96 ------------------------------------------------------------------------------------------------------------------------------------