6457( 6) - 08/01/96 09:30 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6457 Version: 6 Check-in Date: 01-Aug-1996 10:26:03 1.Proposal Title: The Abundance of Interstellar Nitrogen ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle INTERSTELLAR MEDIUM GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: DAVID M. MEYER Northwestern University CoI: U. J. Sofia Villanova University N ------------------------------------------------------------------------------------ 6. Abstract We propose to utilize the sensitivity of the GHRS onboard HST to establish an accurate set of gas-phase nitrogen abundances from high S/N observations of the interstellar N I absorption in six sightlines characterized by low fractional abundances of molecular hydrogen. Similar observations of interstellar oxygen and carbon have recently found ``underabundances'' of these elements with respect to their solar values even after reasonable contributions from dust grains are considered. The total (gas + dust) interstellar O abundance inferred (about 2/3 solar) is remarkably similar to the median value found in nearby B stars. Observations of interstellar nitrogen can potentially provide a better understanding of the observed C and O underabundances since N, unlike C and O, may not be significantly present in dust. Our goal is to determine the abundance of nitrogen in the local ISM to an accuracy capable of discriminating between a solar and a B-star N abundance. Establishing the CNO underabundances as cosmic in nature would be important in understanding similar deficits in the abundance of interstellar boron and krypton in the context of Galactic chemical evolution. On the other hand, a set of nitrogen abundances that are more consistent with dust depletion from a solar standard would also be interesting in terms of reconciling the B-star abundances and understanding how to ``hide'' an appreciable fraction of the N and O in the diffuse ISM\@. ------------------------------------------------------------------------------------ 6457( 6) - 08/01/96 09:30 - [ 2] Observations Description ------------------------ begintableh begintabularccccccccc Name & & Spectral Type & & V & & Log H_total^a & & Log f(H_2 )^b , Gamma Cas (HD 5394) & & B0 IV & & 2.47 & & 20.16 & & <-2.36 , Lambda Ori (HD 36861) & & O8 V & & 3.66 & & 20.83 & & -1.41 , Iota Ori (HD 37043) & & O9 III & & 2.77 & & 20.20 & & -5.21 , Kappa Ori (HD 38771) & & B0.5 Ia & & 2.09 & & 20.52 & & - 4.54 , Delta Sco (HD 143275) & & B0 IV & & 2.32 & & 21.16 & & -1.45 , Kappa Sco (HD 160578) & & B1.5 III & & 2.41 & & 20.36 & & <-5.83 , endtabular beginraggedright, ^alog of the total column density of hydrogen nuclei, H_total = 2H_2 + H I, ^blog of the fractional abundance of hydrogen nuclei in H_2, f(H_2) = 2H_2/H_total, endraggedright endtable The table above lists the attributes of the sightlines in which we plan to obtain high S/N GHRS echelle observations of interstellar nitrogen. All observations will be made using the LSA, in order to take advantage of the maximum throughput, and a sampling strategy of two substeps per diode. The slight (20\\ resolution in the post-COSTAR LSA relative to the SSA will not impact our analysis. The N I observations will involve wavelength setups with ECH-A near 1160 Angstrom\\ (order 48). Allowing sufficient time for guide star acquisition (8 min), target acquisition (11 min), and the ACCUM exposure overheads (4 min each), our goal is to achieve the highest possible S/N ratio for each of our N I spectra in one orbit per target with the use of the FP- Split option to better assess and remove the effects of fixed pattern noise. For our faintest UV target, Lambda Ori, we can attain an ECH-A spectrum of N I with a S/N ratio of 300 in two 12 min FP-Split exposures that fill the visibility window. In the case of our brightest target, Gamma Cas, two FP-Split exposures each of 14 min duration will result in a S/N ratio of 500 at 1160 Angstrom\\@. We will take these multiple FP-Split exposures of each star at slightly different wavelength settings to assist in the fixed pattern noise removal. Data of this quality will insure that we obtain accurate (better than 5Sigma) abundances of interstellar nitrogen in all of our targeted sightlines. Our exposure estimates account for the ECH-A blaze efficiency and are based on the post-COSTAR LSA throughput given in the GHRS Cycle 6 Handbook. The proposers are very experienced in making such calculations as well as reducing and analyzing high S/N GHRS data. Real Time Justification ----------------------- None. None. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6457( 6) - 08/01/96 09:30 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6457( 6) - 08/01/96 09:30 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD5394 STAR, BE RA=00H 56M 42.52S +/- 0.03S, J2000 V = 2.47 DEC=+60D 43' 00.3" +/- 0.5" B-V = -0.15 2 HD36861 STAR, OE RA=05H 35M 08.22S +/- 0.03S, J2000 V = 3.66 DEC=+09D 56' 02.6" +/- 0.5" B-V = -0.18 3 HD37043 STAR, GIANT O RA=05H 35M 25.94S +/- 0.03S, J2000 V = 2.77 DEC=-05D 54' 35.6" +/- 0.5" B-V = -0.24 4 HD38771 STAR, B0-B2 III-I RA=05H 47M 45.38S +/- 0.03S, J2000 V = 2.06 DEC=-09D 40' 10.8" +/- 0.5" B-V = -0.17 5 HD143275 STAR, B0-B2 V-IV RA=16H 00M 20.01S +/- 0.03S, J2000 V = 2.32 DEC=-22D 37' 18.0" +/- 0.5" B-V = -0.12 6 HD160578 STAR, B0-B2 III-I RA=17H 42M 29.28S +/- 0.03S, J2000 V = 2.41 DEC=-39D 01' 48.1" +/- 0.5" B-V = -0.22 6457( 6) - 08/01/96 09:30 - [ 5] Visit: 01 Visit Requirements: 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 HD5394 HRS ACQ 2.0 MIRROR-A1 BRIGHT=RETURN,SEARCH-SIZE=3 1 1.8 S ONBOARD ACQ FOR 2-3 ------------------------------------------------------------------------------------------------------------------------------------ 2 HD5394 HRS ACCUM 2.0 ECH-A48 1161.0 FP-SPLIT=STD,STEP-PATT=6 1 806.4 S ------------------------------------------------------------------------------------------------------------------------------------ 3 HD5394 HRS ACCUM 2.0 ECH-A48 1161.5 FP-SPLIT=STD,STEP-PATT=6 1 806.4 S ------------------------------------------------------------------------------------------------------------------------------------ 6457( 6) - 08/01/96 09:30 - [ 6] Visit: 02 Visit Requirements: 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 ------------------------------------------------------------------------------------------------------------------------------------ 4 HD36861 HRS ACQ 2.0 MIRROR-N1 BRIGHT=RETURN,SEARCH-SIZE=3 1 1.8 S ONBOARD ACQ FOR 5-6 Comments: STEP-TIME=0.2S ------------------------------------------------------------------------------------------------------------------------------------ 5 HD36861 HRS ACCUM 2.0 ECH-A48 1161.0 FP-SPLIT=STD,STEP-PATT=6 1 691.2 S ------------------------------------------------------------------------------------------------------------------------------------ 6 HD36861 HRS ACCUM 2.0 ECH-A48 1161.5 FP-SPLIT=STD,STEP-PATT=6 1 691.2 S ------------------------------------------------------------------------------------------------------------------------------------ 6457( 6) - 08/01/96 09:30 - [ 7] Visit: 03 Visit Requirements: 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 ------------------------------------------------------------------------------------------------------------------------------------ 7 HD37043 HRS ACQ 2.0 MIRROR-A1 BRIGHT=RETURN,SEARCH-SIZE=3 1 1.8 S ONBOARD ACQ FOR 8-9 ------------------------------------------------------------------------------------------------------------------------------------ 8 HD37043 HRS ACCUM 2.0 ECH-A48 1161.0 FP-SPLIT=STD,STEP-PATT=6 1 691.2 S ------------------------------------------------------------------------------------------------------------------------------------ 9 HD37043 HRS ACCUM 2.0 ECH-A48 1161.5 FP-SPLIT=STD,STEP-PATT=6 1 748.8 S ------------------------------------------------------------------------------------------------------------------------------------ 6457( 6) - 08/01/96 09:30 - [ 8] Visit: 04 Visit Requirements: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 HD38771 HRS ACQ 2.0 MIRROR-A1 BRIGHT=RETURN,SEARCH-SIZE=3 1 1.8 S ONBOARD ACQ FOR 11-12 ------------------------------------------------------------------------------------------------------------------------------------ 11 HD38771 HRS ACCUM 2.0 ECH-A48 1161.0 FP-SPLIT=STD,STEP-PATT=6 1 691.2 S ------------------------------------------------------------------------------------------------------------------------------------ 12 HD38771 HRS ACCUM 2.0 ECH-A48 1161.5 FP-SPLIT=STD,STEP-PATT=6 1 748.8 S ------------------------------------------------------------------------------------------------------------------------------------ 6457( 6) - 08/01/96 09:30 - [ 9] Visit: 05 Visit Requirements: 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 ------------------------------------------------------------------------------------------------------------------------------------ 13 HD143275 HRS ACQ 2.0 MIRROR-A1 BRIGHT=RETURN,SEARCH-SIZE=3 1 3.6 S ONBOARD ACQ FOR 14-15 ------------------------------------------------------------------------------------------------------------------------------------ 14 HD143275 HRS ACCUM 2.0 ECH-A48 1161.0 FP-SPLIT=STD,STEP-PATT=6 1 691.2 S ------------------------------------------------------------------------------------------------------------------------------------ 15 HD143275 HRS ACCUM 2.0 ECH-A48 1161.5 FP-SPLIT=STD,STEP-PATT=6 1 748.8 S ------------------------------------------------------------------------------------------------------------------------------------ 6457( 6) - 08/01/96 09:30 - [ 10] Visit: 06 Visit Requirements: 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 ------------------------------------------------------------------------------------------------------------------------------------ 16 HD160578 HRS ACQ 2.0 MIRROR-A1 BRIGHT=RETURN,SEARCH-SIZE=3 1 3.6 S ONBOARD ACQ FOR 17-18 ------------------------------------------------------------------------------------------------------------------------------------ 17 HD160578 HRS ACCUM 2.0 ECH-A48 1161.0 FP-SPLIT=STD,STEP-PATT=6 1 748.8 S ------------------------------------------------------------------------------------------------------------------------------------ 18 HD160578 HRS ACCUM 2.0 ECH-A48 1161.5 FP-SPLIT=STD,STEP-PATT=6 1 748.8 S ------------------------------------------------------------------------------------------------------------------------------------ 6457( 6) - 08/01/96 09:30 - [ 11] Summary Form for Proposal 6457 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BRIGHT=RETURN SEARCH-SIZE=3 STEP-PATT=6 FP-SPLIT=STD ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category INTERSTELLAR MEDIUM ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 2-3 ONBOARD ACQ FOR 5-6 ONBOARD ACQ FOR 8-9 ONBOARD ACQ FOR 11-12 ONBOARD ACQ FOR 14-15 ONBOARD ACQ FOR 17-18 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-A1 ECH-A48 MIRROR-N1 ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD5394 HD36861 HD37043 HD38771 HD143275 HD160578 ------------------------------------------------------------------------------------------------------------------------------------