6021( 4) - 09/27/95 09:32 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6021 Version: 4 Check-in Date: ********** 1.Proposal Title: A Test for Abundance Enrichment by Massive Stars in the Wolf-Rayet Galaxy NGC 5253 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Interstellar Medium GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Henry A. Kobulnicky University of Minnesota CoI: Evan Skillman University of Minnesota N ------------------------------------------------------------------------------------ 6. Abstract We propose to obtain UV and optical spectra with the FOS to measure nebular abundances in NGC 5253, a Wolf-Rayet starburst galaxy that exhibits anomalous N/O ratios attributed to pollution from massive star winds. The primary focus of this program is to measure the relative carbon, nitrogen, and oxygen abundances in NGC 5253. We seek to establish the extent of short-term, localized abundance enhancements due to massive star populations, and evaluate C abundance measurements as a new tool for probing the chemical evolution history of starburst galaxies. Multiple FOS spectra over the wavelength range from 1600Angstrom\ to 6800Angstrom\ obtained through the same aperture will allow us to measure several ionization species and minimize uncertainties caused by unknown interstellar reddening and ionization correction factors that have plagued other UV spectroscopic studies. Specifically, we will measure the UV lines O III LambdaLambda1661 -- 1666, C III LambdaLambda1907 -- 1909, and N III LambdaLambda1748 -- 1754 simultaneously, which will enable us to measure the N^++/O^++, and C^++/O^++ ratios with very little uncertainty. This will allow us to confirm the N/O enhancement by measuring the favored ionic species of nitrogen (N^++), and test the claim that C is also enhanced in this region. ------------------------------------------------------------------------------------ 6021( 4) - 09/27/95 09:32 - [ 2] Observations Description ------------------------ Adequate ground-based spectra exist for NGC5253 which can be used to determine the electron densities, temperatures, nitrogen abundances, and crude line ratios for exposure time estimates. To minimize error introduced by applying extinction corrections and temperature estimates from ground- based spectra which employed different slit size and placement, we intend to obtain spectra using four gratings covering the range 1600Angstrom\\ to 6800Angstrom . G190H contains the crucial O III LambdaLambda1661 -- 1666, N III LambdaLambda1748 -- 1754 and C III LambdaLambda1907 -- 1909 lines used to determine the N^++/O^++ and C^++/O^++ ratios virtually unaffected by reddening uncertainties. The G270H grating contains the C II Lambda2326 line useful for constraining the ionization correction factor (ICF) carbon. Grating G400H contains the higher Balmer series lines for one determination of the reddening and the O II Lambda3727 line for determining the oxygen ICF. Grating G570H contains HAlpha and HBeta for establishing the reddening correction, and O III Lambda4959 and O III Lambda5007 lines to be used in determining the oxygen abundance. (An electron temperature from ground based Lambda4363 measurements will be assumed.) centerlineTable 1 centerlineLine Flux and Integration Time Estimates begintabbing XXXXXXXXXXLine \\= XXXXXXF (erg s^-1 cm^-2 arcsec^-1 \\= XXXXGrating \\= XXXXExp. Time (s) Line \\> F (erg s^-1 cm^-2 arcsec^-1) \\> Grating \\> Exp. Time (s) , HBeta Lambda4861 \\> 4times10^-13 \\> G570H \\> 300 , N III Lambda1750 \\> 4times10^-15 \\> G190H \\> 3600 , C II Lambda2326 \\> 7times10^-15 \\> G270H \\> 900 , O II Lambda3727 \\> 4times10^-13 \\> G400H \\> 300 , O III Lambda4959 \\> 6times10^-13 \\> G570H \\> 300 , endtabbing Exposure times have been estimated using theoretical emissivities relative to HBeta, or, where possible, the ground-based spectroscopy of Walsh & Roy (1989). We estimate exposure times of 3600 sec (2 orbits) to detect N III Lambda1750 at the 5Sigma level. Previous attempts to measure this line (Garnett Etal\\ 1994) achieved only upper limits, but if the N enhancements derived from optical data are accurate, we will detect this line. Exposure times for the other gratings were chosen to obtain at least a signal to noise of 5:1 for the weakest crucial lines in each grating: C II Lambda2326 for the G270 grating, O II Lambda3727 for G400H. Exposure times for G570H were selected with the goal of measuring the O III Lambda4959 and Lambda5007 lines in order to have a secondary estimate of the oxygen abundance in addition to the UV Lambda1661, Lambda1666 lines. This duplication will enable a strong check on the amount of reddening in the UV. HST UV images of NGC 5253 already exist in the archives and will facilitate target acquisition and aperture placement. Real Time Justification ----------------------- None None Calibration Justification ------------------------- Additional Comments ------------------- Should be scheduled in cooperation with a related proposal, proposal number 6001 (Roy etal), for best efficiency. This file is intended to be merged with 6001 to achieve a 12-orbit, 2-visit schedule file. Targets list in this file is same as 6001, for completeness, though not all targes are observed in this visit. ------------------------------------------------------------------------------------ 6021( 4) - 09/27/95 09:32 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6021( 4) - 09/27/95 09:32 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 STAR-OFFSET STAR RA=13H 39M 51.945S +/- J2000 V = 14.5+/-0.5 B-V = 0.5+/-0.5 0.01S,DEC=-31D 39' 02.94" +/- 0.1" 2 NGC5253-UV1 EXT-MEDIUM, HII REGION RA-OFF=4.03S+/- 0.01S,DEC- J2000 V = +400 SURF(V) = 18.4+/-0.2 B-V = 0.0+/-0 A(V) OFF=35.93"+/- 0.1",FROM 1 = 0.9+/-0 Comments: Object in the galaxy is a stellar cluster 3 NGC5253-UV2 EXT-MEDIUM, HII REGION RA-OFF=4.08S+/- 0.01S,DEC- J2000 V = +400 SURF(V) = 18.8+/-0.2 B-V = 0.0+/-0 A(V) OFF=31.54"+/- 0.1",FROM 1 = 0.9+/-0 Comments: Object in the galaxy is a stellar cluster 4 NGC5253-UV3 EXT-MEDIUM, HII REGION RA-OFF=3.63S+/- 0.01S,DEC- J2000 V = +400 SURF(V) = 18.4+/-0.2 B-V = 0.0+/-0 A(V) OFF=33.70"+/- 0.1",FROM 1 = 0.9+/-0 Comments: Object in the galaxy is a stellar cluster 5 NGC5253-HII- EXT-MEDIUM,HII REGION, RA-OFF=4.061S+/- 0.01S,DEC- J2000 V = 400 SURF(V) = 18.4+/-0.2 B-V = 0.0+/-0 A(V) 1 OFF=37.31"+/- 0.1",FROM 1 = 0.9+/-0 Comments: Object in the galaxy is location in an HII region suspected to be N enriched 6 NGC5253-HII- EXT-MEDIUM,HII REGION, RA-OFF=4.007S+/- 0.01S,DEC- J2000 V = 400 SURF(V) = 18.4+/-0.2 B-V = 0.0+/-0 A(V) 2 OFF=39.13"+/- 0.1",FROM 1 = 0.9+/-0 Comments: Object in the galaxy is location in an HII region far from the N enriched location 6021( 4) - 09/27/95 09:32 - [ 5] Visit: 02 Visit Requirements: PCS MODE FINE On Hold Comments: Additional Comments: To be merged into same visit with Roy etal (6001) NGC 5253 observations to get centered on to offset star without peak up exposures. From there, continue with offsets to the two targets in HII region. Entire visit is on FOS/RD. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 51 NGC5253-HII FOS/RD ACCUM 1.0 G190H 1 3600S MIN DUR 90% MAX DUR 110% -1 ------------------------------------------------------------------------------------------------------------------------------------ 52 NGC5253-HII FOS/RD ACCUM 1.0 G400H 1 300S MIN DUR 90% MAX DUR 110% -1 ------------------------------------------------------------------------------------------------------------------------------------ 53 NGC5253-HII FOS/RD ACCUM 1.0 G570H 1 400S MIN DUR 90% MAX DUR 110% -1 ------------------------------------------------------------------------------------------------------------------------------------ 54 NGC5253-HII FOS/RD ACQ 4.3 MIRROR 1 60S MIN DUR 90% MAX DUR 100% -2 ------------------------------------------------------------------------------------------------------------------------------------ 61 NGC5253-HII FOS/RD ACCUM 1.0 G190H 1 2500S -2 ------------------------------------------------------------------------------------------------------------------------------------ 62 NGC5253-HII FOS/RD ACCUM 1.0 G400H 1 300S -2 ------------------------------------------------------------------------------------------------------------------------------------ 63 NGC5253-HII FOS/RD ACCUM 1.0 G570H 1 300S -2 ------------------------------------------------------------------------------------------------------------------------------------ 6021( 4) - 09/27/95 09:32 - [ 6] Summary Form for Proposal 6021 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/RD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ACQ ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Interstellar Medium ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PCS MODE FINE MIN DUR 90% MAX DUR 110% MIN DUR 90% MAX DUR 100% ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G190H G400H G570H MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC5253-HII-1 NGC5253-HII-2 ------------------------------------------------------------------------------------------------------------------------------------