Proposal_Information ! Section 4 Title: HST Imaging and Spectroscopy of the Peculiar LMC H II Region N44C Proposal_Category: GO Scientific_Category: INTERSTELLAR MEDIUM Cycle: 6 Investigators PI_name: Donald R. Garnett PI_Institution: University of Minnesota CoI_Name: Vanessa Galarza CoI_Institution: New Mexico State University Contact: ! Y or N (designate at most one contact) CoI_Name: You-Hua Chu CoI_Institution: University of Illinois Contact: ! Y or N (designate at most one contact) Abstract: ! Free format text (please update) 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. Questions ! Free format text (please update) Observing_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: ! Move appropriate text from Real_Time_Justification Additional_Comments: Fixed_Targets ! Section 5.1 Target_Number: 1 Target_Name: LMC-N44C-STAR2 Alternate_Names: Description: EXT-STAR,Main Sequence O Position: RA=5H 22M 14.00S +/- 0.02S, ! Most common specification format is DEC=-67D 58' 37.0" +/- 0.3", ! RA=0H 0M 0.00S +/- 0S, PLATE-ID=06B0 ! DEC=0D 0' 0.0" +/- 0", ! PLATE-ID=0000 Equinox: J2000 RV_or_Z: V = +260 RA_PM: ! Units are seconds of time per year Dec_PM: ! Units are seconds of arc per year Epoch: Annual_Parallax: Flux: V=14.2,B-V=-0.22,E(B-V)=0.1 ! Include at least V and B-V Comments: Target_Number: 2 Target_Name: LMC-N44C-NEB Alternate_Names: Description: EXT-MEDIUM, HII REGION Position: RA=5H 22M 14.00S +/- 0.02S, ! Most common specification format is DEC=-67D 58' 34.0" +/- 0.3", ! RA=0H 0M 0.00S +/- 0S, PLATE-ID=06B0 ! DEC=0D 0' 0.0" +/- 0", ! PLATE-ID=0000 Equinox: J2000 RV_or_Z: V = +260 RA_PM: ! Units are seconds of time per year Dec_PM: ! Units are seconds of arc per year Epoch: Annual_Parallax: Flux: SURF-LINE(4861)=2.5 E-13, SURF-LINE(5007)=2.3 E-12, SURF-LINE(6563)=7.5 E-13, SURF-LINE(1909)=8+/-4 E-14, E(B-V)=0.1 ! Include at least V and B-V Comments: Peak surface brightness at FOS position, 3 arcsec north of target 1 ! This is a template for a single visit containing a single exposure ! Repeat exposure and visit blocks as needed Visits ! Section 6 Visit_Number: 3 Visit_Requirements: ! Section 7.1 ! Uncomment or copy visit level special requirements needed ! Most of these requirements (including ORIENT) will limit scheduling ! PCS MODE [Fine | Gyro] ! BEFORE ! SEQ WITHIN