7614( 8) - 04/24/98 16:56 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7614 Version: 8 Check-in Date: 24-Apr-1998 16:54:44 1.Proposal Title: C and N Production and Pollution Mechanisms in Low-Metallicity Extragalactic HII Regions - Part 2 ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO/CAR 7 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Henry A. Kobulnicky UNIVERSITY OF MINNESOTA CoI: Evan Skillman University of Minnesota N ------------------------------------------------------------------------------------ 5. Abstract We propose a simple test to differentiate between several hypotheses describing carbon and nitrogen production in low- metallicity extra-galactic HII regions. Our primary goal is to obtain FOS UV spectra to measure directly the nebular carbon abundance in four dwarf galaxies with similar metallicity (O/H), but very different N abundances. By holding O/H constant, we avoid uncertainties due to the possible effects of metallicity-dependent stellar yields or C depletion. We will be able to address 1) whether the large scatter in N/O at a given metallicity is the result of short term, localized N pollution from the winds of massive stars, 2) whether the C/O ratio also exhibits a large scatter at a given metallicity that might be expected if C pollution also occurs or is delayed relative to N, and 3) the extent to which N and C production are coupled, as expected if they are both produced mostly in intermediate mass stars. The results of this program will have repercussions for primordial abundance, chemical evolution, and other studies using Delta(element1)/Delta(element2) type relations. FOS spectra from 1600 Angstrom to 6800 Angstrom with the same 1" 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. We will measure the UV lines O III LambdaLambda1661 -- 1666 and C III LambdaLambda1907 -- 1909 simultaneously, which will enable us to measure the C++/O++ ratios with relatively little uncertainty. ------------------------------------------------------------------------------------ 7614( 8) - 04/24/98 16:56 - [ 2] Observations Description ------------------------ We have obtained high quality, multi-position, ground-based spectroscopic data of the primary target NGC 4861 which can be used to determine the electron densities, temperatures, nitrogen abundances, and 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 1600 Angstrom to 6800 Angstrom . G190H contains the crucial O III LambdaLambda1661 -- 1666 and C III LambdaLambda1907 -- 1909 lines used to determine the C++/O++ ratios virtually unaffected by reddening uncertainties. (A detection of N III LambdaLambda1748 -- 1754 would be a bonus, but is probably unlikely given the results of Garnett Etal. (1995).) 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 our ground based spectroscopic mapping of Lambda4363 will be assumed. Exposure times have been estimated for the 1" round aperture using theoretical emissivities relative to HBeta. HBeta fluxes are from our ground- based spectroscopy or data from the literature, mostly Campbell, Terlevich & Melnick (1986). Exposure estimates are also guided by the experience of Garnett Etal. (1995) who observed similar objects. We estimate exposure times of 1200 sec to detect O III Lambda1666 at the 8:1 level in NGC 4861, assuming a Lambda1700 continuum flux 12 times that at HBeta. We have scaled exposure times accordingly for the other galaxies based on HBeta flux with adjustments for different amounts reddening. Exposure times for the other gratings were chosen to obtain at least a signal to noise of 6:1 for the weakest crucial lines in each grating: C II Lambda2326 for the G270 grating, O II Lambda3727 for G400H. Nominal 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 4861 already exist in the archives and will facilitate target acquisition and aperture placement. We are acquiring ground based imaging for the other sources to aid in slit placement. We have applied for additional ground- based spectroscopic mapping and imaging that will allow us to precisely locate regions of highest nebulosity and avoid the contamination by the stellar continuum. Total number of orbits requested is based on use of a 3-stage (40 min overhead) acquisition strategy used in our Cycle 5 observations of NGC 5253, which will be necessary to acquire the regions of highest nebular surface brightness. Real Time Justification ----------------------- None The proposed observations are part of the PI's Ph.D. thesis on elemental abundance pollution in starbursts (endorsement letter attached). In support of the proposed observations, we have obtained high quality, spectroscopic maps of the primary target NGC 4861 with the Calar Alto 3.5 telescope (Kobulnicky & Skillman 1995). We have proposed similar observations with 4m class telescopes for our other targets in order to match identically the positions of the HST observations, and obtain measurements of the electron temperatures, NII abundances, OII abundances and reddening. We have applied for additional ground -based spectroscopic mapping and imaging that will allow us to precisely locate regions of highest nebulosity for slit placement and avoid the contamination by the stellar continuum. Related to this project on elemental abundance pollution, we have acquired multi-frequency, scaled configuration VLA radio continuum observations of a sample of young starbursts to measure the thermal/non-thermal fractions as an additional ``age'' indicator. These data will help us to ascertain the probability of the ``delayed release'' hypothesis for N and C pollution. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 7614( 8) - 04/24/98 16:56 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 7614( 8) - 04/24/98 16:56 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 41 T1304-386- STAR RA=13H 7M 19.32S +/- 0.05S, DEC= J2000 V = 0 V = 14.8+/-0.6 OFFSET -38D 54' 30.7" +/- 0.2", PLATE- B-V = 0.7 ID=0162 Comments: Offset star for acquisition purposes Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) B1979 0 0 0 42 T1304-386- EXT-MEDIUM, HII REGION RA-OFF=01.87S+/- 0.05S, DEC-OFF= J2000 V = 4200 V = 14.6+/-0.5 POS1 -19.14"+/- 0.2", FROM 41, PLATE- B-V = 0.0 ID=0162 Comments: Target is an x-gal HII region Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) B1979 0 0 0 7614( 8) - 04/24/98 16:56 - [ 5] Visit: 04 Visit Priority: Visit Requirements: PCS MODE FINE AFTER 24-Jun-1996 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 ------------------------------------------------------------------------------------------------------------------------------------ 41 T1304-386-O STIS/C ACQ F28X50L MIRROR 1 2 S ONBOARD ACQ FOR 44 FFSET CD P Comments: ACQ On offset star ------------------------------------------------------------------------------------------------------------------------------------ 44 T1304-386-P STIS/C ACQ F28X50O MIRROR ACQTYPE=DIFFUSE,CHECKBOX=7 1 60 S ONBOARD ACQ FOR 46 OS1 CD II Comments: Acquire on OII emission line to find the region of highest nebular suface brightness in the galaxy. The strong OII 3727 line is redshifted to 3780A for this source, so the line will fall at the half-power point of the F28X50OII bandpass which is centered at 3740 and 80 A wide. ------------------------------------------------------------------------------------------------------------------------------------ 46 T1304-386-P STIS/C ACCUM 52X0.5 G430L 4300 CR-SPLIT=3 1 15 M MAX DUR OS1 CD ------------------------------------------------------------------------------------------------------------------------------------ 47 T1304-386-P STIS/C ACCUM 52X0.5 G750L 7751 CR-SPLIT=3 1 450 S MAX DUR OS1 CD ------------------------------------------------------------------------------------------------------------------------------------ 48 CCDFLAT STIS/C ACCUM 52X0.5 G750L 7751 2 DEF CD ------------------------------------------------------------------------------------------------------------------------------------ 50 T1304-386-P STIS/N ACCUM 52X0.5 G230L 2376 1 2600 S EXPAND OS1 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 52 T1304-386-P STIS/N ACCUM 52X0.5 G230L 2376 1 2600 S EXPAND OS1 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 7614( 8) - 04/24/98 16:56 - [ 6] Summary Form for Proposal 7614 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP F28X50OII 52X0.5 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=DIFFUSE CHECKBOX=7 CR-SPLIT=3 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO/CAR ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PCS MODE FINE AFTER 24-Jun-1996 ONBOARD ACQ FOR 44 ONBOARD ACQ FOR 46 MAX DUR EXPAND ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G430L G750L G230L ------------------------------------------------------------------------------------------------------------------------------------ Target Names T1304-386-OFFSET T1304-386-POS1 CCDFLAT ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 4300 7751 2376 ------------------------------------------------------------------------------------------------------------------------------------