7750( 1) - 05/31/97 07:33 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7750 Version: 1 Check-in Date: 30-May-1997 17:06:43 1.Proposal Title: Interstellar Cadmium: Probing Galactic Chemical Evolution ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle INTERSTELLAR MATTER GO/CAR 7 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Ulysses J. Sofia Villanova University CoI: David Meyer Northwestern University N ------------------------------------------------------------------------------------ 6. Abstract We propose a study to obtain high quality interstellar abundance data (i.e. S/N ~ 500-1000) for the heavy atom Cd (Z = 48), an element produced mainly by s-process neutron capture in intermediate-to-low mass AGB stars, to explore nucleosynthetic enrichment in the ISM. The only existing ISM measure of Cd, in a sight line characterized by large gas depletions onto dust, yields an abundance consistent with the solar value. However, since Cd should be chemically similar to Zn, an element with a common outer electron shell structure but which is depleted from solar by at least a factor 3 in this sight line, we suspect that Cd must be somewhat depleted onto dust. We believe the apparent solar abundance of Cd reflects the fact that the true ISM reference ( cosmic) abundance is larger than the solar value, reflecting an increase since the formation of the solar system 4.5 billion years ago. This supposition is not unreasonable -- observations of other heavy s-process elements in the atmospheres of some AGB stars show substantial enrichments and so we expect that some heavy s-process element enrichment of the ISM must have occurred. The science proposed here provides an opportunity to determine the degree of post- stellar evolution enrichment, yielding important information on bulk s-process yields and cumulative injection of this material into the ISM over the past 4.5 billion years. Because this program requires S/N values unobtainable with STIS, this represents the last opportunity to do this type of science. ------------------------------------------------------------------------------------ 7750( 1) - 05/31/97 07:33 - [ 2] Observations Description ------------------------ We propose to obtain Ech-B data in the LSA (2 or 4 samples/diode depending on the target brightness) on the Cd II line at Lambda2145.07 Angstrom\\ toward six stars sampling a large range of f(H_2) values (see Fig.3). We use the LSA to maximize the throughput (the 20\\% reduction in resolution over the SSA will have no impact on the science goals). Basic target information is shown in the table below. Since accurate measures of the Cd abundances are desired (i.e. >= 5 -Sigma detection limits), we require high S/N values (500- 1000) at each diode substep. Accounting for guide star acquistion, target ACQ, and exposure overhead times, these values can be obtained in the time remaining in a single orbit (these estimates are based on the post-COSTAR LSA throughput data given in the GHRS Cycle 6 Handbook). The required S/N values will be achieved through analysis of multiple grating position subexposures, each obtained with the FP- SPLIT command. We are well versed in both the development and use of the techniques for obtaining high S/N GHRS data -- Cardelli & Ebbets 1994, ``Attaining High Signal- to-Noise Data with the Goddard High Resolution Spectrograph", in Calibrating the Hubble Space Telescope, (STScI: Baltimore) and Cardelli 1995, ``High S/N Spectroscopy with the GHRS: Methods and Applications", in Calibrating HST in the Post-Costar Era (STScI: Baltimore), in press. begintableh begintabularccccccccc Name & & Spectral Type & & V & & Log H_total^a & & Log f(H_2)^b , Zeta Per (HD 24398) & & B1 Ib & & 2.87 & & 21.20 & & -0.23 , beta^1 Sco (HD 144217A) & & B0.5 V & & 2.63 & & 21.14 & & -1.01 , Epsilon Ori (HD 37128) & & B0 Ia & & 1.70 & & 20.45 & & -3.58 , Kappa Ori (HD 38771) & & B0.5 Ia & & 2.09 & & 20.52 & & -4.54 , 15 Mon (HD 47839) & & O7 V & & 4.65 & & 20.40 & & -4.55 , Tau CMa (HD 57061) & & O9 II & & 4.40 & & 20.70 & & -5.22 , 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 targets proposed here are same as those in the cycle 5 Sn program. The goal here is to build strong continuity in the analysis. In this regard, we will also have a (near) complete set of Kr measures for these stars as well. Since Kr is a noble gas and is not expected to deplete onto dust, it serves as a useful reference standard in this case. Our data (Cardelli & Meyer 1995) show Kr/H to be constant over a large range of f(H_2). Obtaining both Cd and Sn data will allow us to unambiguously determine the degree to which these analogous main s-process elements have been enriched. We had planned on including Cd in the Sn proposal, but did not since we had not yet proved its detectability. Since STIS will be unable to obtain such precise measures of weak lines, this is the last foreseeable opportunity to do this type of science. Real Time Justification ----------------------- NONE NONE Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 7750( 1) - 05/31/97 07:33 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: ------------------------------------------------------------------------------------ 7750( 1) - 05/31/97 07:33 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD24398 STAR, B0-B2 III-I RA=03H 54M 07.9S +/- 0.03S, J2000 V = 2.87 DEC=+31D 53' 01.0" +/- 0.5" B-V = 0.12 Comments: target previously observed with ghrs-these coordinates come from the hst observing log 2 HD144217 STAR, B0-B2 V-IV RA=16H 05M 26.1S +/- 0.03S, DEC= J2000 V = 2.63 -19D 48' 19.0" +/- 0.5" B-V = -0.07 Comments: target previously observed with ghrs-these coordinates come from the hst observing log 3 HD37128 STAR, B0-B2 III-I RA=05H 36M 12.8S +/- 0.03S, DEC= J2000 V = 1.70 -01D 12' 06.9" +/- 0.5" B-V = -0.19 Comments: target previously observed with ghrs-these coordinates come from the hst observing log 4 HD38771 STAR, B0-B2 III-I RA=05H 47M 45.3S +/- 0.03S, DEC= J2000 V = 2.09 -09D 40' 11.0" +/- 0.5" B-V = -0.17 Comments: target previously observed with ghrs-these coordinates come from the hst observing log 5 HD57061 STAR, SUPERGIANT O RA=07H 18M 42.4S +/- 0.03S, DEC= J2000 V = 4.40 -24D 57' 15.2" +/- 0.5" B-V = -0.15 Comments: target previously observed with ghrs-these coordinates come from the hst observing log 7750( 1) - 05/31/97 07:33 - [ 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 HD24398 HRS ACQ 2.0 MIRROR-A2 BRIGHT=RETURN,SEARCH-SIZE=3 1 1.8 S ONBOARD ACQ FOR 2 Comments: STEP-TIME = 0.2s ------------------------------------------------------------------------------------------------------------------------------------ 2 HD24398 HRS ACCUM 2.0 ECH-B26 2145 FP-SPLIT=STD,STEP-PATT=6 3 6.72 M ------------------------------------------------------------------------------------------------------------------------------------ 7750( 1) - 05/31/97 07:33 - [ 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 ------------------------------------------------------------------------------------------------------------------------------------ 3 HD144217 HRS ACQ 2.0 MIRROR-A2 BRIGHT=RETURN,SEARCH-SIZE=3 1 1.8 S ONBOARD ACQ FOR 4 Comments: STEP-TIME = 0.2s ------------------------------------------------------------------------------------------------------------------------------------ 4 HD144217 HRS ACCUM 2.0 ECH-B26 2145 FP-SPLIT=STD,STEP-PATT=6 3 6.72 M ------------------------------------------------------------------------------------------------------------------------------------ 7750( 1) - 05/31/97 07:33 - [ 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 ------------------------------------------------------------------------------------------------------------------------------------ 5 HD37128 HRS ACQ 2.0 MIRROR-A2 BRIGHT=RETURN,SEARCH-SIZE=3 1 1.8 S ONBOARD ACQ FOR 6 Comments: STEP-TIME = 0.2s ------------------------------------------------------------------------------------------------------------------------------------ 6 HD37128 HRS ACCUM 2.0 ECH-B26 2145 FP-SPLIT=STD,STEP-PATT=7 5 217.6 S ------------------------------------------------------------------------------------------------------------------------------------ 7750( 1) - 05/31/97 07:33 - [ 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 ------------------------------------------------------------------------------------------------------------------------------------ 7 HD38771 HRS ACQ 2.0 MIRROR-A2 BRIGHT=RETURN,SEARCH-SIZE=3 1 1.8 S ONBOARD ACQ FOR 8 Comments: STEP-TIME = 0.2s ------------------------------------------------------------------------------------------------------------------------------------ 8 HD38771 HRS ACCUM 2.0 ECH-B26 2145 FP-SPLIT=STD,STEP-PATT=7 5 217.6 S ------------------------------------------------------------------------------------------------------------------------------------ 7750( 1) - 05/31/97 07:33 - [ 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 ------------------------------------------------------------------------------------------------------------------------------------ 9 HD57061 HRS ACQ 2.0 MIRROR-A2 BRIGHT=RETURN,SEARCH-SIZE=3 1 1.8 S ONBOARD ACQ FOR 10-12 Comments: STEP-TIME = 0.2s ------------------------------------------------------------------------------------------------------------------------------------ 10 HD57061 HRS ACCUM 2.0 ECH-B26 2144 FP-SPLIT=STD,STEP-PATT=6 3 6.72 M ------------------------------------------------------------------------------------------------------------------------------------ 11 HD57061 HRS ACCUM 2.0 ECH-B26 2145 FP-SPLIT=STD,STEP-PATT=6 3 6.72 M ------------------------------------------------------------------------------------------------------------------------------------ 12 HD57061 HRS ACCUM 2.0 ECH-B26 2146 FP-SPLIT=STD,STEP-PATT=6 3 6.72 M ------------------------------------------------------------------------------------------------------------------------------------ 7750( 1) - 05/31/97 07:33 - [ 10] Summary Form for Proposal 7750 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BRIGHT=RETURN SEARCH-SIZE=3 STEP-PATT=6 FP-SPLIT=STD STEP-PATT=7 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO/CAR ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category INTERSTELLAR MATTER ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 2 ONBOARD ACQ FOR 4 ONBOARD ACQ FOR 6 ONBOARD ACQ FOR 8 ONBOARD ACQ FOR 10-12 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-A2 ECH-B26 ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD24398 HD144217 HD37128 HD38771 HD57061 ------------------------------------------------------------------------------------------------------------------------------------