6839( 4) - 02/17/97 12:03 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6839 Version: 4 Check-in Date: 17-Feb-1997 12:00:36 1.Proposal Title: WFPC2 Imagery of the Dusty HII Region SMC N88A ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle GALAXIES & CLUSTERS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: CINDY MARIE KURT RICE UNIVERSITY CoI: Reginald Dufour Rice University N ------------------------------------------------------------------------------------ 6. Abstract We are proposing to take WFPC2 imagery through narrow band filters isolating several important emission lines in the H II region N88A in the Small Magellanic Cloud (SMC). This small H II region is unusual in the metal-poor and relatively dust-free ISM environment of the SMC in that it is heavily reddened and shows a peculiar ionization structure compared to other SMC H II regions. We anticipate that this new WFPC2 imagery, combined with previous HST FOS spectra and ground- based data, will permit us to construct an accurate model of the nature of N88A and its associated dust. Such a model may provide basic new information on the production of dust in the metal-poor star-forming ISM environment existing in many irregular galaxies - an environment similar to that in our Galaxy at a much earlier time in its chemical evolution. In addition to the above observations, we propose to take wide band ``V'' and ``B'' images to assess the stellar population in and around the nebula. ------------------------------------------------------------------------------------ 6839( 4) - 02/17/97 12:03 - [ 2] Observations Description ------------------------ The observations involve WFPC2 imagery of a single object, SMC N88A, using the F375N, F487N, F502N, F656N, F673N, F953N, and F547M filters. At alpha=21.03 degrees (D) and delta=- 73D15 degrees, there are two continuous viewing zones (CVZs) available in Cycle 6, and therefore we can take advantage of the optimum observational efficiency of HST by having to acquire our guide star once. The WFPC2 exposure times for N88A through the above filters, covering important nebular diagnostic lines of the nebula, are based on our Cycle 3 FOS spectra of its bright core through a 1 arc second square aperture. To achieve a high and nearly WFPC2-limited S/N in the central region of the nebula (for the wide- field mode, with 0.1'' pixels, where the S/N is that per pixel), we used these FOS fluxes to derive WFPC2 exposure times giving S/N of about 100 in the core region (approximately 10^4 photoelectrons) to define our exposure times for the stronger emission lines (e.g., HBeta, Lambda5007, HAlpha, Lambda9532, and Lambda5500 continuum). While such a high S/N seems excessive, it is necessary for the fainter outer regions of the nebula, where the surface brightness is over two orders of magnitude less. All exposure times will be split for maximum rejection of cosmic rays. Exposure times were calculated using STScI's WWW WFPC2 Exposure Time Calculator program for extended sources for all the filters except F375N (where it didn't seem to work correctly), as well as hand calculations using the QT's in the WFPC2 manual for the various filters (corrected for the small velocity redshift of N88A) and the equation for number of photoelectrons and S/N at the bottom of page 71. For reference, we adopted an HBeta surface brightness of S(HBeta) = 1.29 * 10^-12 ergs cm^-2 arcsec^-2 and relative line ratios (3727/4861/5007/6563/6723/9523) = (0.2/1.0/7.8/3.7/0.04/1.3). To get the following S/N's: (20/100/100/100/20/100) with the filters (F375N /F487N/F502N/F656N/F673N/F953N) will require total net exposure times of about (80/25/3/3/40/25) minutes (for which each will be split, adding up to 5 min gaps). In addition, the F547M continuum filter exposure will be 3 minutes (about 1/10th the F487N exposure). The high surface brightness of N88A and the desire to get maximum spatial resolution of the O III arc structure, leads us to further propose obtaining PC exposures with the F502N, F547M, and F656N filters. We calculate that we can obtain high S/N (>30 per pixel) PC exposures in the PC for O III Lambda5007, continuum, and HAlpha with exposure times of about 10 min, 1 min, & 10 min, with overheads. With a 7.5 min guide star acquision, and up to 10 min overhead on each filter (two CR- SPLIT exposures), the whole process sums out to about 2.8 CVZ orbits. In the remaining time in the third orbit we propose to take two images using the wide band F555W (``V") and F439W (``B") filters to assess the stellar population in and around the nebula. Therefore, we request a total of 3 CVZ orbits. Real Time Justification ----------------------- We are requesting observations in a continuous-viewing-zone (CVZ) to maximize the number of WFPC2 images obtained while minimizing the spacecraft time required. The analysis of the FOS spectra of N88A which were acquired in the Cycle 3 program GO-4382, including a series of photoionization models, have been completed during the summer of 1995 by Dufour and Kurt in collaboration with the program CoIs (D. Garnett, J. Mathis, E. Skillman, S. Torres-Peimbert, and M. Peimbert) and we are currently writing a paper for submission to the Astrophysical Journal following on the initial results already published or in press (Garnett et al. 1995 & Kurt et al. 1995). In addition, we are including IUE NEWSIPS low and high dispersion spectra into the analysis, as well as CTIO 4m longslit CCD spectra of N88A obtained a few years ago. Ultimately, we wish to model the nebular structure from the proposed WFPC2 imagery and then combine our results with those obtained from the ground-based, archival IUE, and HST FOS spectra, as well as IR data published by others, to model the physical state of the ionized gas in detail using a nebular photoionization code. It is also possible that Kurt will obtain imagery of various SMC H II regions at CTIO in late 1996 to study their dust content and extinction. All of this will constitute the bulk of her dissertation for the Ph. D. in Space Physics & Astronomy at Rice University over the next two years. Calibration Justification ------------------------- Additional Comments ------------------- Use of wide band filters F439W and F555W pending approval by STScI. ------------------------------------------------------------------------------------ 6839( 4) - 02/17/97 12:03 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: ------------------------------------------------------------------------------------ 6839( 4) - 02/17/97 12:03 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NEB-012409- EXT-MEDIUM,HII REGION RA=1H 24M 9.2S +/- 0.02S, DEC=- 2000 V = 12.0+/-.1 730917 73D 9' 17" +/- 0.2" E(B-V) = 0.1+/-.1 SURF-LINE(3727)=2.9+/-0.4e-13 SURF-LINE(4861)=13+/-0.5e-13 SURF-LINE(5007)=10+/-1e-12 SURF-LINE(6563)=48+/-0.8e-13 SURF-LINE(6723)=4.6+/-2e-14 SURF-LINE(9523)=17+/-1e-13 Comments: Brightest stars in region have V = 12.0 and B-V = 0.0 . 6839( 4) - 02/17/97 12:03 - [ 5] Visit: 01 Visit Requirements: CVZ 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 NEB-012409- WFPC2 IMAGE WF3-FIX F953N 9523 2 500 S 730917 ------------------------------------------------------------------------------------------------------------------------------------ 2 NEB-012409- WFPC2 IMAGE WF3-FIX F953N 9523 1 400 S 730917 ------------------------------------------------------------------------------------------------------------------------------------ 3 NEB-012409- WFPC2 IMAGE WF3-FIX F547M 5476 1 100 S 730917 ------------------------------------------------------------------------------------------------------------------------------------ 4 NEB-012409- WFPC2 IMAGE WF3-FIX F547M 5476 1 80 S 730917 ------------------------------------------------------------------------------------------------------------------------------------ 5 NEB-012409- WFPC2 IMAGE WF3-FIX F375N 3727 CR-SPLIT=NO 3 1500 S 730917 ------------------------------------------------------------------------------------------------------------------------------------ 6 NEB-012409- WFPC2 IMAGE WF3-FIX F487N 4861 3 500 S 730917 ------------------------------------------------------------------------------------------------------------------------------------ 7 NEB-012409- WFPC2 IMAGE WF3-FIX F502N 5007 2 100 S 730917 ------------------------------------------------------------------------------------------------------------------------------------ 8 NEB-012409- WFPC2 IMAGE WF3-FIX F656N 6563 2 100 S 730917 ------------------------------------------------------------------------------------------------------------------------------------ 9 NEB-012409- WFPC2 IMAGE WF3-FIX F673N 6723 CR-SPLIT=NO 3 800 S 730917 ------------------------------------------------------------------------------------------------------------------------------------ 10 NEB-012409- WFPC2 IMAGE PC1-FIX F547M 5476 1 26 S 730917 ------------------------------------------------------------------------------------------------------------------------------------ 11 NEB-012409- WFPC2 IMAGE PC1-FIX F547M 5476 1 26 S 730917 ------------------------------------------------------------------------------------------------------------------------------------ 12 NEB-012409- WFPC2 IMAGE PC1-FIX F555W 5398 2 60 S 730917 ------------------------------------------------------------------------------------------------------------------------------------ 13 NEB-012409- WFPC2 IMAGE PC1-FIX F502N 5007 2 230 S 730917 ------------------------------------------------------------------------------------------------------------------------------------ 14 NEB-012409- WFPC2 IMAGE PC1-FIX F656N 6563 2 230 S 730917 ------------------------------------------------------------------------------------------------------------------------------------ 15 NEB-012409- WFPC2 IMAGE PC1-FIX F439W 4300 1 230 S 730917 ------------------------------------------------------------------------------------------------------------------------------------ 6839( 4) - 02/17/97 12:03 - [ 6] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 16 NEB-012409- WFPC2 IMAGE PC1-FIX F439W 4300 1 200 S 730917 ------------------------------------------------------------------------------------------------------------------------------------ 6839( 4) - 02/17/97 12:03 - [ 7] Summary Form for Proposal 6839 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category GALAXIES & CLUSTERS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CVZ ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F953N F547M F375N F487N F502N F656N F673N F555W F439W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NEB-012409-730917 ------------------------------------------------------------------------------------------------------------------------------------