Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 5734 Report Date: 18-Jul-95:17:54 Version: ********** Check-in Date: ********** 1.Proposal Title: PROBING THE IS GAS OF THE SUPERBUBBLE LMC2 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID INTERSTELLAR MEDIUM GO/CAR 3664 Sub Category ABSORPTION LINES ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Adeline M. Caulet SPACE TELESCOPE EUROPEAN COO GERMANY 49-89-32006-29 ------------------------------------------------------------------------------------ 7. Abstract Supershells are gigantic bubbles of hot gas blown in galactic disks by stellar winds and supernovae. Providing an enormous energy input to the ISM, they have an important effect on local dynamics and on galactic halos. One of them, LMC2 in the Large Magellanic Cloud, has been well studied at radio, optical and X-ray wavelengths. We have shown its optical filaments to be expanding in LMC disk gas. Our recent ROSAT observations reveal that the diffuse X-ray emission covers a larger sky area than the optical filaments do. Did LMC2 burst open in the halo\?. What is the dynamics of the optically invisible IS gas layers within and around LMC2\?. To probe the IS gas of LMC2, we propose to obtain GHRS medium resolution UV spectra of 7 supergiant stars in the LMC2 field. The observational goal is to measure the velocities and strengths of UV IS absorption lines arising in the cold, warm and hot LMC2 gas. HST has the only existing UV spectrograph that can detect individual velocity components of IS hot gas (CIV and NV absorption) in connection with the X- ray diffuse emission seen towards the LMC supershells. The scientific goals are to find a satisfactory model of LMC2 that describes the physical characteristics of the superbubble and the effects of supershell expansion or break-out into the LMC halo. ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 13.23 par: 0 10. Num targs pri: 7 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: HRS ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 5734 PI: Adeline M. Caulet Proposal Title: PROBING THE IS GAS OF THE SUPERBUBBLE LMC2 ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Pi Adeline M. Caulet SPACE TELESCOPE EUROPEAN FRANCE X COORDINATING FACILITY Andrew M. Smith NASA GODDARD SPACE FLIGHT CENTER U.S.A. Wolfgang B. Pietsch MAX PLANCK INSTITUT FOR GERMANY X EXTRATERRESTRIAL PHYSICS Gunter Hasinger MAX PLANCK INSTITUT FOR GERMANY X EXTRATERRESTRIAL PHYSICS ------------------------------------------------------------------------------------ 3. Description of proposed observations. We propose to obtain GHRS medium resolution UV spectra of 7 LMC OB supergiants selected in various parts of the LMC2 field to probe thoroughly the IS gas throughout and around the superbubble cavity. For each star, 2 carousel settings of the G160M grating will center wavelengths 1249.36 and 1561.37 A on detector 2. For each carousel setting, a series of 5 minutes exposures will be made , the number of which depends on the target 's UV flux. Breaking the exposure into 5 minute intervals allows correction for image drift due to variations in the effect of the earth's magnetic field on the detector image stability. Step pattern 4 is chosen to yield 2 substeps and measurements of the background signal. Since target positions are accurately known, onboard acquisition will be employed. The small science aperture will be used. We are concerned with the IS spectra and particularly with absorption line velocities. Consequently, we plan to obtain Pt lamp wavelength calibrations for each carousel position. The carousel settings include IS lines in atoms and ions with ionization potentials ranging from 11eV (CI) to 97 eV (NV). CIV and NV absorption lines will sample gas in conduction fronts between hot gas and the superbubble or funnel walls, coronal gas, and gas in highly ionised regions formed by the UV radiation of hot OB stars. SiII and SII absorption lines will give information on the photoionised gas and clouds which have been compressed by shocks. The CI multiplets will sample the warm neutral gas and cold HI clouds trapped inside LMC2. Page 3 ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. HST has the only existing UV spectrograph (GHRS) that can detect the individual velocity components of IS hot gas (CIV and NV), in connection with the X-ray diffuse emission seen towards the superbubbles in the LMC. There is considerable information about the stars and the ISM in the direction of the LMC supershells. This includes detailed studies of the HI emission line gas (Rohlfs et al. 1984), our Fabry-Perot optical observations of the velocities of the LMC2 filaments (Caulet et al. 1982), and our extensive ROSAT survey data of soft X-ray emission arising in the LMC2 region (Hasinger and Pietsch 1991). Therefore, taking into account all this knowledge, the LMC is the best galaxy for supershell detailed studies. A complete study of superbubble dynamics requires the study of all IS superbubble gas phases. Our Fabry-Perot optical data on the visible LMC2 filaments revealed the expansion of the receding portion of LMC2, but could not trace most of the superbubble gas, which is optically invisible. According to the current superbubble models, many UV absorption lines are expected to arise in the expanding envelope, corresponding to the predicted temperature drop from 1.0xE6 K to 1000 K. The wavelengths of these lines lie below the atmospheric cut -off (3000 A), and cannot be observed using spectrographs on ground-based telescopes. Only HST has the sensitivity and resolving power to detect these absorption lines in the UV spectra of background LMC stars selected in the direction of LMC2. The spectrograph onboard IUE cannot do it. ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. We have scheduled a wavelength calibration at each carousel setting. Since the study of the dynamics of the superbubble gas is a major objective of our proposal, we need velocity measurements at least as accurate as those obtained from the ground-based optical velocities. Accuracies of about +/- 3.5 km/s will be sufficient and should be obtainable with on-board Pt lamp calibrations performed at the same carousel settings at which the science data is recorded. ------------------------------------------------------------------------------------ 6. Description of special calibration exposures. OSF Line Number, Instrument, Mode , Special Calibration Requirement 1.0 , HRS , ACCUM, 1 WAVE CAL 2.0 , HRS , ACCUM, 1 WAVE CAL 3.0 , HRS , ACCUM, 1 WAVE CAL 4.0 , HRS , ACCUM, 1 WAVE CAL 5.0 , HRS , ACCUM, 1 WAVE CAL 6.0 , HRS , ACCUM, 1 WAVE CAL 7.0 , HRS , ACCUM, 1 WAVE CAL ------------------------------------------------------------------------------------ 8. Additional comments or special requests. We have determined the coordinates of all targets (astrometry from the GASP plates from STScI). Page 4 ------------------------------------------------------------------------------------ 9. Description of previous HST work. Andrew M. Smith has the following HST programs (as of August 1991): Program No. 1200 (GTO), "Search for Interstellar Molecules in the Spectra of Two B Stars", UNRELATED. Program No. 1201 (GTO), "Physical parameters in the Local Interstellar Medium", UNRELATED. Program No. 3024 (SAT), "Xi Per Interstellar Spectrum", UNRELATED. Observations were made by the GHRS of the cool, neutral gas in the line of sight to Xi Per. Heliocentric velocities and equivalent widths were measured for absorption lines of CI and SI. Synthetic spectra were computed and fitted to the observed CO 2-0 and 3-0 bands in the Fourth Positive System which were resolved by the GHRS into 3 and possibly 4 velocity components. Derived populations of the CI ground state fine structure levels and the CO ground state rotational levels were used to derive the densities of two of these velocity components. The component displaying the strongest C I absorption reveals extraordinarily high pressure (P/k > 4.3xE4 K/cm3). Along the same line of sight, the column densities were determined for neutral and singly ionized atoms using profile information in the form of velocity-dependent apparent column densities. Abundances determined from this analysis are very tightly constrained. GHRS ultraviolet absorption line measurements have become so accurate that the interpretations are now limited by the inaccuracies in atomic f-values and our knowledge of solar abundances. At velocities near 7.5 km/s ordinarily depleted elements are heavily depleted, but for velocities between 7.7 and 20 km/s the depletions decrease by a factor of 2 or more suggesting significant grain modification. At 25 km/s the abundances are nearly solar. "First Results from the GHRS: Interstellar C I, S I, and CO Toward Xi Persei and the Physical Conditions in Diffuse Clouds", Andrew M. Smith, Frederick C. Bruhweiler, David L. Lambert, Blair D. Savage, Jason A. Cardelli, Dennis C. Ebbets, Cheng-Hsuan Lyu, and Yaron Sheffer, Ap.J. Letters, 377, L61, 1991. "First Results from the Goddard High Resolution Spectrograph: Elemental Abundances in the Diffuse Clouds Toward Xi Per", Jason A. Cardelli, Blair D. Savage, Frederick C. Bruhweiler, Andrew M. Smith, Dennis C. Ebbets, Kenneth R. Sembach, and Ulysses J. Sofia, Ap.J. Letters, 377, L57, 1991. "First Results from the Goddard High Resolution Spectrograph: Elemental Abundances as a Function of Velocity in the Neutral Gas Toward Xi Persei", Jason A. Cardelli, Blair D. Savage, Frederick C. Bruhweiler, Andrew M. Smith, Dennis C. Ebbets, Kenneth R. Sembach, and Ulysses J. Sofia, Ap.J. Letters, 377, L53, 1991. ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). Resources for data reduction and analysis are provided by the P.I. institution (ST-ECF) and by GSFC for A. Smith for the HST data, and by the Max-Planck Institute in Garching for the use of the ROSAT survey data (G. Hasinger and W. Pietsch). No funding is requested, since all resources necessary for this project exist already. ------------------------------------------------------------------------------------ 11. Address Information Name: ADELINE M. CAULET Category: PI Institution: SPACE TELESCOPE EUROPEAN COORDINA Address: EUROPEAN SOUTHERN OBSERVATORY KARL-SCHWARZSCHILD STR. 2 D-8046 City: GARCHING BEI MUNCHEN State: Zip Code: Country: GERMANY Telephone: 49-89-32006-291 Telex (or e-mail): ------------------------------------------------------------------------------------ TARGET LIST a) Fixed Targets ID = 5734 [ 5] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial |Acqui|FLX| Flux data No | Name | Description | Position |Eqnx | Vel. |Prblm|REF| | | | | | | | | ------------------------------------------------------------------------------------------------------------------------------------ 3 SK-70111 B, 113 PLATE-ID=06B0, 2000 1 V=11.8, TYPE=B1 IA GSC9167735 RA = 05H 41M 36.93S +/- 2 F(1239)=5.7E-13 HD269993 0.5", 3 F(1549)=4.3E-13 DEC = -70D 00' 52.38" +/- 0.5" ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 5734 [ 6] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15 ------------------------------------------------------------------------------------------------------------------------------------ Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 7 SK-70111 HRS ACQ 2.0 MIRROR-N2 BRIGHT=RETURN 1 5.0S 1 1 ONBOARD ACQ FOR SEARCH-SIZE=5 7.1 CYCLE 4 Comments: STEP-TIME = 0.2S ------------------------------------------------------------------------------------------------------------------------------------ 7.1 SK-70111 HRS ACQ/ 0.25 MIRROR-N2 1 20.4S 1 1 ONBOARD ACQ FOR PEAKUP 8.1-9.1 CYCLE 4 Comments: STEP-TIME = 0.2S ------------------------------------------------------------------------------------------------------------------------------------ 8 WAVE HRS ACCUM SC2 G160M 1249.36 STEP-PATT=4 1 DEF 1 CALIB FOR 8.1 CYCLE 4 SEQ 8.0-8.1 NO GAP ------------------------------------------------------------------------------------------------------------------------------------ 8.1 SK-70111 HRS ACCUM 0.25 G160M 1249.36 STEP-PATT=4 2 1968.0S 10 2 1 CYCLE 4 FP-SPLIT=STD 2419.2S ------------------------------------------------------------------------------------------------------------------------------------ 9 WAVE HRS ACCUM SC2 G160M 1561.37 STEP-PATT=4 1 DEF 1 CALIB FOR 9.1 CYCLE 4 SEQ 9.0-9.1 NO GAP ------------------------------------------------------------------------------------------------------------------------------------ 9.1 SK-70111 HRS ACCUM 0.25 G160M 1561.37 STEP-PATT=4 2 1968.0S 10 3 1 CYCLE 4 FP-SPLIT=STD 2419.2S ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 5734 [ 7] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAKUP ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BRIGHT=RETURN SEARCH-SIZE=5 STEP-PATT=4 FP-SPLIT=STD ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO/CAR ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 13.23 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category INTERSTELLAR MEDIUM ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category ABSORPTION LINES ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 7.1; CYCLE 4; ONBOARD ACQ FOR 8.1-9.1; CALIB FOR 8.1; SEQ 8.0-8.1 NO GAP; CALIB FOR 9.1; SEQ 9.0-9.1 NO GAP; ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N2 G160M ------------------------------------------------------------------------------------------------------------------------------------ Target Names SK-70111 GSC9167735 HD269993 ------------------------------------------------------------------------------------------------------------------------------------