Proposal_Information Title: HST Observations of Two Ultraluminous Extragalactic Supernova Remnants Proposal_Category: GO Scientific_Category: Interstellar Medium Cycle: 5 Investigators PI_Name: William P. Blair PI_Institution: The Johns Hopkins University CoI_Name: Robert A. Fesen CoI_Institution: Dartmouth College Contact: CoI_Name: Eric M. Schlegel CoI_Institution: Universities Space Research Association Contact: Abstract: High resolution emission-line images of two unusually luminous extragalactic supernova remnants in the galaxies NGC 4449 and NGC 6946 are requested. The observed X-ray and optical fluxes for these two remnants rank them as the brightest known SNRs. They differ by roughly a factor of 10 in age and expansion velocity, and the large luminosities of both are attributable at least in part to interactions with relatively dense interstellar surroundings. HST images will permit accurate angular size measurements which, when combined with expansion velocity information already in hand, will place hard constraints on the sizes and ages of each object. Continuum images will be used to resolve questions regarding the local environment around each object and permit us to access the make-up of the stellar populations in the local vicinity, constraining the mass of the precursor stars. In addition to the image data, we request FOS far--UV (G160L) spectra of the NGC 4449 SNR to complete the spectroscopy of this object begun in an FOS GTO program. A UV spectrum will permit an estimate of the carbon abundance, which will place a hard constraint on the precursor's mass. Questions Observing_Description: FOC Imagery of NGC 4449 SNR: BKW provide an integrated line flux for O III 5007+4959 of 2.0 x 10^-13 ergs cm^-2 s^-1. However, only half of this flux will be passed by the F501N filter. Hence, we estimate a photon flux of 3.0 x 10^-4 phot cm^-2 s^-1 ang^-1 through F501N. Using the formulation in the FOC handbook, ver. 5.0, we find a source rate of 5.4 cts/pix/s assuming the source is 0.05" in diameter (and hence spread over ~9 pixels). Table 6a of the FOC handbook indicates a source rate of <=0.15 cts/pix/s is required in 512 mode (7.0" FoV; 0.014" pixels) to maintain linearity. We assume the addition of F4ND (factor of 39 attenuation) to ensure the peak count rate stays below this threshold (even if extended), yielding a nominal R_s = 0.14 cts/pix/s. Assuming R_b = 0.001 (i.e. some galaxy background above the nominal dark count), the 18 minute exposure should result in S/N>=12. We request a F346M exposure in 512x512 mode to get `u' colors of stars in the 7" region centered on the SNR. This exposure is designed to get at least S/N = 10 for magnitude 23.0 objects, which would correspond to a late O main sequence star at 5 Mpc. (Stars as late as B0 V should still be detected at S/N >= 3.) The The FOC pointings require one orbit, including overheads and ACQs. An F346M (2500s) exposure has been dropped due to TAC-imposed limitations on the number of orbits. WFPC2 Imagery of NGC 6946: To estimate WFPC2 count rates, in the emission-line filters, we use the formula N_el = 2.28 * 10^12 Lambda T_max F(Lambda), where N_el is the number of electrons per sec per unit area being considered, T_max is the filter throughput from the WFPC2 ver. 5.0 handbook, and F is the flux in ergs cm^-2 s^-1 per unit area. We use fluxes from Blair & Fesen, and assume the flux is spread evenly over 1sec point0 square. (Presumably the SNR shell will actually break up into resolvable structure at PC resolution, so this is a conservative estimate of expected counts.) From this calculation we find that exposures of 1400 s (F656N) and 1800 s (F673N) will result in HAlpha, and S\\ II Lambda 6725 PC exposures with S/N >= 7 per PC pixel. For the continuum filters, we use eq. 6.1 of the handbook and assume a 23rd magnitude BO star. With exposures of 400 s (F555W) and 900 s (F439W) such a star would have ~1300 counts in V and B. While these filters also include some emission lines, the breadth of the filter will ensure that the continuum emission will dominate. The WFPC2 imagery requires 2 orbits including all ACQs and overheads. The F673N exposure has been shortened significantly to fit in alloted time. FOS Spectra of NGC 4449 SNR: We assume the 1.0" (actual 0.86") paired aperture throughout, with STEP-PATT=SINGLE. The target can be acquired with a 3-stage peak-up with FOS/RD and G570H, with the peak-up using the 4900-5150 Angstrom region of the spectrum. This requires nearly one pass. The switch to FOS/BL is buried in an occultation, and observation with G160L proceeds for two orbits. The UV lines intensities for this object are unknown except that C IV Lambda1550 may have been detected by IUE (Blair et al. 1984). By comparing to the LMC and SMC O-rich SNRs observed with IUE (cf. Blair et al. 1989, 1994), we calculate a G160L exposure time that will permit any UV lines present at a similar level to be well detected. We choose FOS/BL and G160L instead of G130H and G190H because the higher resolution is not needed and the full far-UV range can be covered in one grating. The primary disadvantage with this set-up is about 4 times lower throughput at C III Lambda 1909, but if this line is present, it should be strong enough to be well-detected anyway. Using the ``monochromatic" formula from the FOS Handbook, ver. 5.0 (corrected for the missing Lambda), we find that a ~5000 s integration with G160L will detect any O IV Lambda 1400, C IV, C III, or O III Lambda1665 emission to a level (S/N >= 3) of roughly 20. The FOS request amounts to 3 spacecraft orbits. The FOS/RD G780H spectrum of NGC 4449 SNR, an F346M exposure with FOC on the NGC 4449 SNR, and the WPFC2 F502N image of NGC 6946 have been dropped, and other exposure times modified to reconfigure the proposal from its requested 9 orbits down to the TAC allotment of 6 orbits. We have ground-based optical images of both galaxies, and low resolution optical spectroscopy has been published. We have also obtained and analyzed the Rosat data for NGC 6946 (Schlegel 1994) and Einstein data on NGC 4449 (Blair et al. 1983). Rosat PSPC data on NGC 4449 are in the public domain. We have done what we can from the ground, and the improved spatial resolution provided by HST plus the UV sensitivity for the FOS spectra are necessary for a better understanding of these objects. Real_Time_Justification: Calibration_Justification: Additional_Comments: Fixed_Targets Target_Number: 1 Target_Name: NGC6946-SNR Alternate_Names: Description: EXT-MEDIUM,SNR Position: RA=20H 35M 00.6S +/- 0.13S,DEC=60D 11' 30.0" +/- 1.0" Equinox: J2000 RV_or_Z: RA_PM: 0.0 Dec_PM: 0.0 Epoch: Annual_Parallax: 0.0 Flux: F-LINE(5007)=2.5+/-0.5e-14 W-LINE(5007)=7+/-0.5 Comments: Target_Number: 2 Target_Name: NGC4449-SNR Alternate_Names: Description: EXT-MEDIUM,SNR Position: RA=12H 28M 10.94S +/- 0.1S,DEC=44D 06' 47.67" +/- 1" Equinox: J2000 RV_or_Z: RA_PM: 0.0 Dec_PM: 0.0 Epoch: Annual_Parallax: 0.0 Flux: F-LINE(5007)=1.3+/-0.3e-15 W-LINE(5007)=110+/-5 Comments: Solar_System_Targets Generic_Targets Scan_Data Visits Visit_Number: 01 Visit_Requirements: ORIENT 330D TO 30D On_Hold_Comments: Visit_Comments: While PC observes primary target, remainder of WFC chips will survey northern spiral arms of NGC6946. ORIENT is necessary to position WFC chips approximately. Exact ORIENT is not crucial, but all images should be obtained at the same ORIENTtation. Exposure_Number: 1 Target_Name: NGC6946-SNR Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F656N Wavelength: 6563 Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 1400S Special_Requirements: Comments: Exposure_Number: 2 Target_Name: NGC6946-SNR Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F673N Wavelength: 6732 Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 2000S Special_Requirements: EXPAND Comments: Would like any extra time to go into this exposure, but RPS2 balks at EXPAND. Exposure_Number: 3 Target_Name: NGC6946-SNR Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F555W Wavelength: 5407 Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 400S Special_Requirements: Comments: Exposure_Number: 4 Target_Name: NGC6946-SNR Config: WFPC2 Opmode: IMAGE Aperture: PC1 Sp_Element: F439W Wavelength: 4300 Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 900S Special_Requirements: Comments: Visit_Number: 02 Visit_Requirements: On_Hold_Comments: Visit_Comments: Exposure_Number: 11 Target_Name: NGC4449-SNR Config: FOC/96 Opmode: IMAGE Aperture: 512X512 Sp_Element: F501N,F2ND Wavelength: 5010 Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 1080S Special_Requirements: EXPAND Comments: Exposure_Number: 12 Target_Name: NGC4449-SNR Config: FOC/96 Opmode: IMAGE Aperture: 512X512 Sp_Element: F346M Wavelength: 3480 Optional_Parameters: Number_of_Iterations: 1 Time_Per_Exposure: 600S Special_Requirements: Comments: Visit_Number: 03 Visit_Requirements: On_Hold_Comments: Visit_Comments: Exposure_Number: 21 Target_Name: NGC4449-SNR Config: FOS/RD Opmode: ACQ/PEAK Aperture: 4.3 Sp_Element: G570H Wavelength: 4900-5150 Optional_Parameters: SCAN-STEP-X=3.3,SCAN-STEP-Y=1.23,SEARCH-SIZE-X=2,SEARCH-SIZE-Y=6 Number_of_Iterations: 1 Time_Per_Exposure: 4.83S Special_Requirements: ONBOARD ACQ FOR 22 Comments: EXPOSURE TIME from simulator (J. Hayes) Note: Times are 2x Jeff's numbers to improve S/N. WPB 8/16/95 Exposure_Number: 22 Target_Name: NGC4449-SNR Config: FOS/RD Opmode: ACQ/PEAK Aperture: 1.0-PAIR-A Sp_Element: G570H Wavelength: 4900-5150 Optional_Parameters: SCAN-STEP-X=0.602,SCAN-STEP-Y=0.602,SEARCH-SIZE-X=6,SEARCH-SIZE-Y=2 Number_of_Iterations: 1 Time_Per_Exposure: 5.3S Special_Requirements: ONBOARD ACQ FOR 23 Comments: EXPOSURE TIME from simulator (J. Hayes) Note: Times are 2x Jeff's numbers to improve S/N. WPB 8/16/95 Exposure_Number: 23 Target_Name: NGC4449-SNR Config: FOS/RD Opmode: ACQ/PEAK Aperture: 0.5-PAIR-A Sp_Element: G570H Wavelength: 4900-5150 Optional_Parameters: SCAN-STEP-X=0.29,SCAN-STEP-Y=0.29,SEARCH-SIZE-X=3,SEARCH-SIZE-Y=3 Number_of_Iterations: 1 Time_Per_Exposure: 5.8S Special_Requirements: ONBOARD ACQ FOR 24 Comments: EXPOSURE TIME from simulator (J. Hayes) Note: Times are 2x Jeff's numbers to improve S/N. WPB 8/16/95 Exposure_Number: 24 Target_Name: NGC4449-SNR Config: FOS/RD Opmode: ACQ/PEAK Aperture: 0.25-PAIR-A Sp_Element: G570H Wavelength: 4900-5150 Optional_Parameters: SCAN-STEP-X=0.172,SCAN-STEP-Y=0.172,SEARCH-SIZE-X=3,SEARCH-SIZE-Y=3 Number_of_Iterations: 1 Time_Per_Exposure: 5.8S Special_Requirements: ONBOARD ACQ FOR 25 Comments: This is a new step recommended by Tony Keyes. Exposure_Number: 25 Target_Name: NGC4449-SNR Config: FOS/BL Opmode: ACCUM Aperture: 1.0-PAIR Sp_Element: G160L Wavelength: 1800 Optional_Parameters: STEP-PATT=SINGLE Number_of_Iterations: 1 Time_Per_Exposure: 4750S Special_Requirements: EXPAND Comments: Want as much time as possible on this exposure within acquisition constraints. Data_Distribution ! Defaults indicated; change if desired Medium: 8MM Blocking_Factor: 10 Ship_To: PI_Address Ship_Via: UPS Recipient_Email: ! Let us know what you think of this template and software! ! Please send a list of your likes and dislikes to your Program Coordinator