Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 5305 Report Date: 18-Jul-95:17:07 Version: ********** Check-in Date: ********** 1.Proposal Title: IRON-PEAK ELEMENTS IN HOT SUBDWARFS: CYCLE4 MEDIUM ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID HOT STARS GO Sub Category SUBDWARFS ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Thierry Lanz USRA USA (301) 286 6083 ------------------------------------------------------------------------------------ 7. Abstract Hot evolved subdwarfs are the immediate progenitors of white dwarfs, and are therefore of great importance for our understanding of the late stages of stellar evolution. Recently, significant abundances of heavy metals have been found in some hot DA white dwarfs, formely thought of having hydrogen-pure atmospheres. Iron and nickel now appear to be the major opacity sources in the FUV and EUV spectrum of these white dwarfs as well as in the hot evolved sdO subdwarfs. We will observe one sdO stars to redetermine most accurately its stellar parameters. We will analyze the spectrum using our new most sophisticated NLTE line-blanketed model atmospheres, including the blanketing of tens of thousands of Fe IV, Fe V, Fe VI, Ni IV and Ni V lines. We will derive consistently the abundances of the iron-peak elements. Contrary to the abundances of light elements which are primarily signatures of nucleosynthetic processes, the iron-peak elements may shed light on the relative importance of the individual mixing processes in the photospheres of sdO stars, and give us a better insight on the connection between these subdwarfs and the white dwarfs. ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 3.00 par: 0 10. Num targs pri: 1 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: HRS ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 5305 PI: Thierry Lanz Proposal Title: IRON-PEAK ELEMENTS IN HOT SUBDWARFS: CYCLE4 MEDIUM ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Thierry Lanz 3650 USA Ivan Hubeny 3650 USA Sara R. Heap 2866 USA ------------------------------------------------------------------------------------ 3. Description of proposed observations. We propose to obtain high-resolution spectra for one sdO star with the GHRS and the grating G160M, to cover the range from 1220 to 1450 A, and around the C IV resonance lines, the He II 1640 and the N IV 1718 line. The strongest iron and nickel lines have been identified in BD +75 325 between 1220 and 1460 A; moreover, we will get also the resonance lines N V 1238, 1242, Si IV 1393, 1402, and C IV 1548, 1550, as well as O IV 1338, 1342 and O V 1371. We need the N IV lines to assess the N IV/N V ionization equilibrium, and He II 1640 is the only He line accessible in this wavelength range. The selected star has already been studied from visual and IUE data, so that we know that it has very probably evolved from the EHB. The effective temperature was found to be around 42000 K, somewhat cooler than BD +75 325, and the photosphere appears to moderately enriched in helium (He/H ~= 1), like BD +75 325. We will be able then to investigate the abundance pattern for different effective temperatures. HD 127493 has a sharp-lined spectrum, so that we will benefit of the high spectral resolution. ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. This is not a project that can be done from the ground. Indeed Fe and Ni lines have been indentified only in the FUV spectrum (they are expected to show up also in the EUV, but no comparable data can be recorded in this wavelength range). What can we do with IUE high-resolution data? The limited resolution and the noise makes them of little use beyond the analysis of the strong resonance lines of light metals. Let us argue with two examples: (1) Feibelman & Bruhweiler (1990, ApJ 357, 548) identified Fe VII lines in BD 75 325. Our NLTE theoretical spectra show that the features at 1226.6 and 1239.7 are actually blends of Ni V lines (2) As discussed above, we need a high-resolution (R=25000) to be able show unambiguously the presence of a weak turbulent velocity, or to show that the line profiles have deep cores caused by surface cooling due to line-blanketing. No definite conclusions can be derived from IUE spectra. Our project therefore requires to obtain GHRS spectra at high-resolution with a good signal-to-noise (50 to 100). ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. No special scheduling requirements. ------------------------------------------------------------------------------------ 6. Description of special calibration exposures. No special calibration exposures. ------------------------------------------------------------------------------------ 8. Additional comments or special requests. We plan to obtain also ground-based visual spectra around hydrogen and helium lines for HD 127493 to redetermine the stellar parameters (in particular log g and He/H) as accurately as possible from our NLTE line-blanketed model atmospheres. Page 3 ------------------------------------------------------------------------------------ 9. Description of previous HST work. Results based on HST Science Assessment and Early Release Observations: Heap S.R., et al., 1991, "First results from the GHRS: Spectroscopic determination of the stellar parameters of Melnick 42, an O3f star in the LMC", ApJ 377, L29 Hubeny I., Heap S.R., Altner B., 1991, "First results from the GHRS: Evidence for photospheric turbulence in early O stars", ApJ 377, L33 Boggess A., et al., 1991, "First results from the GHRS: Resolved velocity and density structure in the beta Pic circumstellar gas", ApJ 377, L49 Malumuth E., Neill J.D., Lindler D.J., Heap S.R., 1991, "Coping with the HST's PSF: Crowed field stellar photometry", in The First Year of HST Observations, STScI, p. 249 Results based on GHRS Guaranteed Time Observations Heap S.R., Hubeny I., Lanz T., 1992, "Non-LTE analysis of the early O subdwarf BD +75 325", BAAS 24, 1203 Linsky J., et al., 1993, "The D/H ratio in the LIS towards Capella", ApJ 402, 694 Heap S.R., Ebbets D., Malumuth E., 1993, "HST Imagery of NGC 2440", in Science with the HST, ESO. Malumuth E., Heap S.R., 1993, "UBV Photometry of the 30 Dor Region", in Science with the HST, ESO. Brandt J.C.,Heap S.R., et al., 1993, "GHRS Spectra of 3C 273", AJ 105, 831 ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). By the time that Cycle 4 starts, we expect to have 2 DEC-alpha workstations which we will use for modelling. We also have access to the HRS VAX computer at Goddard, which we will use to store our data and carry out the data analysis. The salaries of both Heap and Hubeny are fully funded by NASA, and so they will work on the program at no cost to the HST General Observer program. ------------------------------------------------------------------------------------ 11. Address Information Name: THIERRY LANZ Category: PI Institution: USRA Address: NASA GODDARD SPACE FLIGHT CENTER CODE 681 City: GREENBELT State: MD Zip Code: 20771 Country: USA Telephone: (301) 286 6083 Telex (or e-mail): LANZ@STARS.GSFC.NASA.GOV ------------------------------------------------------------------------------------ Name: Category: CON Institution: Address: City: State: Zip Code: Country: Telephone: Telex (or e-mail): ------------------------------------------------------------------------------------ TARGET LIST a) Fixed Targets ID = 5305 [ 4] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial |Acqui|FLX| Flux data No | Name | Description | Position |Eqnx | Vel. |Prblm|REF| | | | | | | | | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD127493 A,108 RA = 14H 32M 21.57S +/- 2000.0 1 V=10.03 0.1S, 2 B-V=-0.25 DEC = -22D 39' 24.7" +/- 0.6", PLATE-ID=0189 ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 5305 [ 5] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15 ------------------------------------------------------------------------------------------------------------------------------------ Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 HD127493 HRS ACQ 2.0 MIRROR-N2 SEARCH-SIZE=3 1 1.8S 1 CYCLE 4 / 10.0- BRIGHT=RETURN 121.0 ONBOARD ACQ FOR 20.0 SEQ 10.0-121.0 NO GAP Comments: STEP-TIME=0.2S ------------------------------------------------------------------------------------------------------------------------------------ 20 HD127493 HRS ACQ/ 0.25 MIRROR-N2 SEARCH-SIZE=5 1 5.0S 1 CYCLE 4 PEAKUP ONBOARD ACQ FOR 30.0-121.0 Comments: STEP-TIME=0.2S ------------------------------------------------------------------------------------------------------------------------------------ 30 WAVE HRS ACCUM SC2 G160M 1240 1 30S 1 CYCLE 4 CALIB FOR 31.0 ------------------------------------------------------------------------------------------------------------------------------------ 31 HD127493 HRS ACCUM 0.25 G160M 1240 1 8M 1 CYCLE 4 ------------------------------------------------------------------------------------------------------------------------------------ 40 WAVE HRS ACCUM SC2 G160M 1272 1 30S 1 CYCLE 4 CALIB FOR 41.0 ------------------------------------------------------------------------------------------------------------------------------------ 41 HD127493 HRS ACCUM 0.25 G160M 1272 1 8M 1 CYCLE 4 ------------------------------------------------------------------------------------------------------------------------------------ 50 WAVE HRS ACCUM SC2 G160M 1304 1 30S 1 CYCLE 4 CALIB FOR 51.0 ------------------------------------------------------------------------------------------------------------------------------------ 51 HD127493 HRS ACCUM 0.25 G160M 1304 1 8M 1 CYCLE 4 ------------------------------------------------------------------------------------------------------------------------------------ 60 WAVE HRS ACCUM SC2 G160M 1336 1 30S 1 CYCLE 4 CALIB FOR 61.0 ------------------------------------------------------------------------------------------------------------------------------------ 61 HD127493 HRS ACCUM 0.25 G160M 1336 1 8M 1 CYCLE 4 ------------------------------------------------------------------------------------------------------------------------------------ 70 WAVE HRS ACCUM SC2 G160M 1368 1 30S 1 CYCLE 4 CALIB FOR 71.0 ------------------------------------------------------------------------------------------------------------------------------------ 71 HD127493 HRS ACCUM 0.25 G160M 1368 1 9M 1 CYCLE 4 ------------------------------------------------------------------------------------------------------------------------------------ 80 WAVE HRS ACCUM SC2 G160M 1400 1 30S 1 CYCLE 4 CALIB FOR 81.0 ------------------------------------------------------------------------------------------------------------------------------------ 81 HD127493 HRS ACCUM 0.25 G160M 1400 1 10M 1 CYCLE 4 ------------------------------------------------------------------------------------------------------------------------------------ 90 WAVE HRS ACCUM SC2 G160M 1432 1 30S 1 CYCLE 4 CALIB FOR 91.0 ------------------------------------------------------------------------------------------------------------------------------------ 91 HD127493 HRS ACCUM 0.25 G160M 1432 1 9M 1 CYCLE 4 ------------------------------------------------------------------------------------------------------------------------------------ 100 WAVE HRS ACCUM SC2 G160M 1550 1 30S 1 CYCLE 4 CALIB FOR 101.0 ------------------------------------------------------------------------------------------------------------------------------------ 101 HD127493 HRS ACCUM 0.25 G160M 1550 1 11M 1 CYCLE 4 ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 5305 [ 6] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15 ------------------------------------------------------------------------------------------------------------------------------------ Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 110 WAVE HRS ACCUM SC2 G160M 1640 1 30S 1 CYCLE 4 CALIB FOR 111.0 ------------------------------------------------------------------------------------------------------------------------------------ 111 HD127493 HRS ACCUM 0.25 G160M 1640 1 8M 1 CYCLE 4 ------------------------------------------------------------------------------------------------------------------------------------ 120 WAVE HRS ACCUM SC2 G160M 1730 1 30S 1 CYCLE 4 CALIB FOR 121.0 ------------------------------------------------------------------------------------------------------------------------------------ 121 HD127493 HRS ACCUM 0.25 G160M 1730 1 8M 1 CYCLE 4 ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 5305 [ 7] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAKUP ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SEARCH-SIZE=3 BRIGHT=RETURN SEARCH-SIZE=5 ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 3.00 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category HOT STARS ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category SUBDWARFS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CYCLE 4 / 10.0-121.0; ONBOARD ACQ FOR 20.0; SEQ 10.0-121.0 NO GAP CYCLE 4; ONBOARD ACQ FOR 30.0-121.0; CALIB FOR 31.0 CALIB FOR 41.0 CALIB FOR 51.0 CALIB FOR 61.0 CALIB FOR 71.0 CALIB FOR 81.0 CALIB FOR 91.0 CALIB FOR 101.0 CALIB FOR 111.0 CALIB FOR 121.0 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N2 G160M ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD127493 ------------------------------------------------------------------------------------------------------------------------------------