6623( 9) - 01/07/97 13:04 - [ 0] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6623 Version: 9 Check-in Date: 07-Jan-1997 12:39:29 1.Proposal Title: HST Imaging and Spectroscopy of the Peculiar LMC H II Region N44C ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle INTERSTELLAR MEDIUM GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Donald R. Garnett UNIVERSITY OF MINNESOTA CoI: Vanessa Galarza New Mexico State University N CoI: You-Hua Chu University of Illinois N ------------------------------------------------------------------------------------ 6. Abstract The H II region N44C in the LMC is peculiar in that it exhibits unusually strong nebular recombination emission from He II, indicating a hard radiation field. However, the ionizing star appears to be a normal O star. Stellar atmosphere models from the Munich group suggest that a hot O supergiant could provide the ionizing power, but the observed spectral type is quite uncertain because of contamination of the optical spectrum by strong nebular emission. Other possible mechanisms include fast shocks or an X-ray binary (possibly fossil) ionizing the nebula. We propose to study this peculiar nebula via (1) GHRS+G160L spectroscopy to determine the spectral type of the ionizing star and its physical properties; (2) FOS spectroscopy of the brightest emission knot, to measure high-ionization UV emission lines of nitrogen, carbon, and oxygen. The UV lines will provide diagnostics on the hardness of the ionizing spectrum and whether C and N are enriched in the nebula (which would indicate the influence of an evolved star). (3) WFPC2 imaging in HAlpha, O III, and continuum to study the interaction of the ionizing star with the nebula gas, and to look for filamentary structure indicative of shocks and any additional stellar components not resolved from the ground. Detailed study of this nebula and the associated O star provide a unique test of state-of-the-art atmosphere models for hot stars. ------------------------------------------------------------------------------------ Observations Description ------------------------ We propose the following observations: 1) A GHRS low- resolution spectral scan with grating G140L in 1st order and the Large Science Aperture to classify and study the UV spectrum of the N44C ionizing star. This will cover the spectral range 1200-1750 Angstrom\\ in 2 exposures, including the important spectral features C IV 1550, N IV 1719, N V 1240, He II 1640, and Si IV 1400. The N IV and N V features are sensitive to spectral type for early O stars, while the Si IV feature is very sensitive to stellar luminosity - only in absorption in main sequence O stars, but a strong P Cyg feature in supergiants. With this spectrum we should be able to definitively classify the star ionizing N44C as early or late O, supergiant or main sequence. The star has V = 14.2, B -V = -0.22 (Oey & Massey 1995), and E(B-V) of approximately 0.1. With these values, we estimate exposure times of about 10 minutes for each of the two wavelength settings to obtain a s/n of 20 per pixel. Including overheads and 19 minutes for target acquisition, these observations would require 1 orbit. The GHRS is superior to the FOS for this work because of its better sensitivity below 1600 Angstrom\\ and its higher spectral resolution. 2) FOS UV spectroscopy of the high surface brightness region of the nebula about 3 arcsec north of the O star, which includes the strongest He II emission. We would observe the entire UV spectrum from LyAlpha longward, using FOS/BL + G130H, and FOS/RD + G190H, G270H. We would specifically look for nebular emission from C II 2325 Angstrom, C III 1909 Angstrom, C IV 1550 Angstrom, N III 1750 Angstrom, N IV 1487 Angstrom, N V 1240 Angstrom, O III 1666 Angstrom, and O IV 1402 Angstrom. These lines will provide detailed information on the ionization balance in the nebula as well as C/O and N/O abundance ratios. Short exposures (< 5 min) with G400H and G570H will provide information on optical lines at the same location and on the reddening; the He II 1640/4686 ratio will help pin down the relative reddening in the UV. The nebula at the proposed location has an estimated HBeta flux of 2.5times10^-13 ergs cm^-2 s^-1 (for a 1 arcsec aperture) and a reddening of about 0.1 mag E(B-V). Based on experience from FOS spectroscopy of the high surface brightness H II region N88A in the SMC (program GO-4382, Garnett CoI), we estimate that we will obtain good data on the UV emission lines with exposures of 30 min in G130H, 20 min in G190H, and 10 min in G270H. Including overheads, we would need 1 orbit for FOS/BL + G130H, and 1 orbit for the FOS/RD spectra. Although GHRS is more sensitive blueward of 1600 Angstrom, the GHRS science apertures are not well- matched to the FOS 0.86-arcsec aperture. 3) Narrow-band imaging in F502N and F656N, to study the detailed structure of N44C at high spatial resolution with WFPC2. This will allow us to look for features that might indicate the presence of shocks, such as sharp shell-like structures and/or filaments, and provide more detailed information on some of the peculiar features seen in the ground-based images (see Fig. 1). N44C has a peak surface brightness of 7.5times10^-13 erg cm^-2 s^-1 arcsec^-2 in HAlpha and 2.3times10^ -12 erg cm^-2 s^-1 arcsec^-2 in O III 5007 A. Short (2 min) exposures in F555W and F675W will also be taken to look for previously unresolved companions to the N44C ionizing star and to do photometry for the brighter stars in the WFPC2 field. One orbit will be required to obtain all the WFPC2 images, accounting for overheads. A total of four orbits is thus required to obtain all of the proposed observations. N44C has a significant number of CVZ orbits available in Cycle 6, and we considered using the opportunity. However, because of the significant overhead involved in instrument switches (e.g., 50-55 minutes to switch from FOS/BL to FOS/RD), we determined that there was little spacecraft time to be saved by asking for CVZ for these observations. Real Time Justification ----------------------- We have supporting ground-based longslit spectroscopy of N44C from CTIO, over the wavelength range 3300-7500 Angstrom. The long slit was oriented N-S and includes both Stars 1 and 2 and the nebular position to be observed with the FOS. An example is shown in Figure 2. These spectra will be used to estimate physical conditions (T_e, N_e) and reddening across the nebula including the region to be observed with the FOS, complementing the data to be obtained with the FOS. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS __Diagnosti Email: , ------------------------------------------------------------------------------------ 6623( 9) - 01/07/97 13:04 - [ 1] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 LMC-N44C- EXT-STAR,Main Sequence RA=5H 22M 14.00S +/- 0.02S, DEC= J2000 V = +260 V = 14.2 STAR2 O -67D 58' 37.0" +/- 0.3", PLATE- B-V = -0.22 ID=06B0 E(B-V) = 0.1 2 LMC-N44C-NEB EXT-MEDIUM, HII REGION RA=5H 22M 14.00S +/- 0.02S, DEC= J2000 V = +260 SURF-LINE(4861)=2.5e-13 -67D 58' 34.0" +/- 0.3", PLATE- SURF-LINE(5007)=2.3e-12 ID=06B0 SURF-LINE(6563)=7.5e-13 SURF-LINE(1909)=8+/-4e-14 E(B-V) = 0.1 Comments: Peak surface brightness at FOS position, 3 arcsec north of target 1 6623( 9) - 01/07/97 13:04 - [ 2] Visit: 03 Visit Requirements: On Hold Comments: Additional Comments: Guide stars are available for this configuration. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 LMC-N44C-ST HRS ACQ 2.0 MIRROR-N1 BRIGHT=RETURN,SEARCH-SIZE=3 1 18 S ONBOARD ACQuisition FOR AR2 2-8 Comments: STEP-TIME = 2 sec; 14th mag. G star 7 arcsec south ------------------------------------------------------------------------------------------------------------------------------------ 2 LMC-N44C-ST HRS ACCUM 2.0 G140L 1345 FP-SPLIT=STD,STEP-PATT=DEF, 1 761.6 S AR2 SPYBAL=DEF ------------------------------------------------------------------------------------------------------------------------------------ 3 LMC-N44C-ST HRS ACCUM 2.0 G140L 1620 FP-SPLIT=STD,STEP-PATT=DEF, 1 652.8 S AR2 SPYBAL=DEF ------------------------------------------------------------------------------------------------------------------------------------ 4 LMC-N44C-NE FOS/BL ACCUM 1.0 G400H 1 360 S B Comments: Small angle offset from GHRS position ------------------------------------------------------------------------------------------------------------------------------------ 5 LMC-N44C-NE FOS/BL ACCUM 1.0 G130H 1 1500 S B Comments: Reconfigure to FOS/RD follows ------------------------------------------------------------------------------------------------------------------------------------ 6 LMC-N44C-NE FOS/RD ACCUM 1.0 G270H 1 650 S B ------------------------------------------------------------------------------------------------------------------------------------ 7 LMC-N44C-NE FOS/RD ACCUM 1.0 G570H 1 110 S B ------------------------------------------------------------------------------------------------------------------------------------ 8 LMC-N44C-NE FOS/RD ACCUM 1.0 G190H 1 1200 S B ------------------------------------------------------------------------------------------------------------------------------------ 9 LMC-N44C-NE WFPC2 IMAGE WF2-FIX F656N CR-SPLIT=NO 3 700 S B ------------------------------------------------------------------------------------------------------------------------------------ 10 LMC-N44C-NE WFPC2 IMAGE WF2-FIX F675W 2 80 S B ------------------------------------------------------------------------------------------------------------------------------------ 11 LMC-N44C-NE WFPC2 IMAGE WF2-FIX F502N CR-SPLIT=NO 3 700 S B ------------------------------------------------------------------------------------------------------------------------------------ 12 LMC-N44C-NE WFPC2 IMAGE WF2-FIX F547M 2 80 S B ------------------------------------------------------------------------------------------------------------------------------------ 6623( 9) - 01/07/97 13:04 - [ 3] Visit: 53 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 ------------------------------------------------------------------------------------------------------------------------------------ 30 LMC-N44C-ST FOS/BL ACQ/PEA 4.3 G190H SEARCH-SIZE-X=1,SEARCH-SIZE-Y=3, 1 5 S ONBOARD ACQ FOR 31 AR2 K SCAN-STEP-Y=1.23 ------------------------------------------------------------------------------------------------------------------------------------ 31 LMC-N44C-ST FOS/BL ACQ/PEA 1.0 G190H SEARCH-SIZE-X=6,SEARCH-SIZE-Y=2, 1 5 S ONBOARD ACQ FOR 32 AR2 K SCAN-STEP-Y=0.602, SCAN-STEP-X=0.602 ------------------------------------------------------------------------------------------------------------------------------------ 32 LMC-N44C-ST FOS/BL ACQ/PEA 0.5 G190H SEARCH-SIZE-X=3,SEARCH-SIZE-Y=3, 1 5 S ONBOARD ACQ FOR 33 AR2 K SCAN-STEP-Y=0.29,SCAN-STEP-X=0.29 ------------------------------------------------------------------------------------------------------------------------------------ 33 LMC-N44C-ST FOS/BL ACQ/PEA 0.3 G190H SEARCH-SIZE-X=4,SEARCH-SIZE-Y=4, 1 5 S ONBOARD ACQ FOR 42-45 AR2 K SCAN-STEP-Y=0.11,SCAN-STEP-X=0.11 ------------------------------------------------------------------------------------------------------------------------------------ 42 LMC-N44C-NE FOS/BL ACCUM 1.0 G130H 1 1740 S B Comments: Small angle offset (3AS) from target 1; Reconfigure to FOS/RD follows ------------------------------------------------------------------------------------------------------------------------------------ 43 LMC-N44C-NE FOS/RD ACCUM 1.0 G190H 1 1300 S B ------------------------------------------------------------------------------------------------------------------------------------ 44 LMC-N44C-NE FOS/RD ACCUM 1.0 G570H 1 180 S B ------------------------------------------------------------------------------------------------------------------------------------ 45 LMC-N44C-NE FOS/RD ACCUM 1.0 G400H 1 360 S B ------------------------------------------------------------------------------------------------------------------------------------ 6623( 9) - 01/07/97 13:04 - [ 4] Summary Form for Proposal 6623 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS FOS/BL FOS/RD WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM IMAGE ACQ/PEAK ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BRIGHT=RETURN SEARCH-SIZE=3 SPYBAL=DEF STEP-PATT=DEF CR-SPLIT=NO SCAN-STEP-Y=1.23 SCAN-STEP-X=0.602 SCAN-STEP-X=0.29 SCAN-STEP-X=0.11 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category INTERSTELLAR MEDIUM ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQuisition FOR 2-8 ONBOARD ACQ FOR 31 ONBOARD ACQ FOR 32 ONBOARD ACQ FOR 33 ONBOARD ACQ FOR 42-45 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N1 G140L G400H G130H G270H G570H G190H F656N F675W F502N F547M ------------------------------------------------------------------------------------------------------------------------------------ Target Names LMC-N44C-STAR2 LMC-N44C-NEB ------------------------------------------------------------------------------------------------------------------------------------