Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 4263c Report Date: 09-May-96:19:29 Version: ********** Check-in Date: ********** 1.Proposal Title: NLTE SPECTRAL ANALYSIS OF THREE PG1159 STARS: FINDING THE BOUNDARIES OF THE GW VIR INSTABILITY STRIP CYCLE3 MEDIUM ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID HOT STARS GO Sub Category WHITE DWARFS ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Ulrich Heber UNIVERSITAT ERLANGEN-NURNBER GERMANY ------------------------------------------------------------------------------------ 7. Abstract The PG1159 stars form a new class of hydrogen deficient pre white dwarfs (PWD) representing the hottest stage (Teff>=100,000 K) of PWD evolution. First quan- titative spectral analyses have been carried out by the proposers. The proto- type PG1159-035 has been analysed from the HST-FOS spectrum with unprecedented precision. It has been shown that these stars have atmospheres dominated by carbon and helium with a significant amount of oxygen present. Extreme mass loss has removed the H rich and most of the He rich layers. Such a mass loss event has been observed in Lo4. About every other member of the PG1159 stars is a non- radial, multi-periodic g -mode pulsator driven by cyclic ionisation of C and O. Modelling of the pulsations allows the stellar mass to be determined very accurately and the stellar interior to be probed (asteroseismology). A prerequisite for such modelling is a precise determination of the photospheric parameters. We propose to obtain UV observations of three additional PG1159 stars (one pulsator and two non-pulsators) in addition to the (pulsating) prototype in order to trace differences in photospheric parameters and composition. The spectra will be analysed with new highly-sophisticated NLTE line blanketed model atmospheres, which allow the synthetic spectrum to be calculated and line blending of iron group elements to be included self- consistently. The results will allow us to determine the position of the new instability strip (defined by the pulsating PG1159 stars) in the HRD. ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 9.48 par: 0 10. Num targs pri: 3 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: FOS ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 4263c PI: Ulrich Heber Proposal Title: NLTE SPECTRAL ANALYSIS OF THREE PG1159 STARS: FINDING THE BOUNDARIES OF THE GW VIR INSTABILITY STRIP CYCLE3 MEDIUM ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Pi Ulrich Heber UNIVERSITAT ERLANGEN-NURNBERG GERMANY X Stefan Dreizler UNIVERSITAT ERLANGEN-NURNBERG GERMANY X Thomas Rauch UNIVERSITAT KIEL GERMANY X Klaus Werner UNIVERSITAT ERLANGEN-NURNBERG GERMANY X ------------------------------------------------------------------------------------ 3. Description of proposed observations. The Faint Object Spectrograph (FOS) shall be used to perform ultraviolet spectroscopy of three PG1159 stars in exactly the same way as for PG1159-035 (GO- proposal 2741 carried out in cycle 1): 1. PG1520+525 2. PG1707+427 3. PG1424+535 One low resolution spectrum shall be obtained for each of these objects (long slit, 0.25*2 arcsec) with the blue detector and the G130H grating, namely in the wavelength range 115nm-160nm, covering the NV resonance doublet, OV 137.1nm, and several CIV and OVI lines. ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. Optical spectra of high S/N ratio (near 100) have been obtained at the DSAZ 3.5m telescope, covering the wavelength range from 330nm to 700nm at a spectral resolution of 0.2nm. These spectra have been used for a NLTE model atmosphere analysis (Werner, Heber & Hunger 1991; Werner & Heber 1991a). Low resolution IUE spectra are available from the IUE archive, however, these spectra are of insufficient dispersion for the proposed analysis. On the other hand, the targets are too faint to be observed with IUE in the high resolution mode. Therefore, the UV lines of crucial importance for the high precision analysis (see Scientific Justification) can only be observed with HST. ------------------------------------------------------------------------------------ 7. Data reduction and analysis plans. Data reduction will be carried out using the IRAF+STSDAS program package at the ESA-ECF, Garching. The software will also be installed on the Bamberg node of the German Astronet (DAN). Observed line profiles will be compared to theoretical predictions in order to derive effective temperature, surface gravity, and abundances. The model atmosphere calculations described in the Scientific Justification will be extended further. Numerical calculations are carried out using the Cray YMP/EL computer of the "Rechenzentrum der Universitaet Erlangen- Nuernberg", the Cray YMP of the "Bayerischer Landesvektorrechner in Muenchen" and the Cray X-MP computer of the "Rechenzentrum der Universitaet Kiel". Page 3 ------------------------------------------------------------------------------------ 9. Description of previous HST work. Cycle 1: ID 2741: NLTE SPECTRAL ANALYSIS OF THE PRE WHITE DWARF PG1159-035 We have obtained a FOS spectrum of PG1159-035, the prototype of the PG1159 class. Results of the model atmosphere analysis have yielded the atmospheric parameters with high precision (see section 1 and the line profile fits in Fig. 1 and 2.). This observation is closely related to this proposal, since one of its targets (PG1520+525) is spectroscopically similar to PG1159-035 (in the optical), however, it does not pulsate. The spectrum obtained for ID 2741 (in cycle 1) will serve as a reference spectrum for a differential analysis of the three targets proposed here. Differences among the pulsator--non-pulsator pairs in the UV spectra will help to determine the position of the GW Vir instability strip in the HRD. Cycle 2: ID 3513: Non-LTE analysis of the population II post AGB stars ROB162 and K648 (not related to this proposal) ID 2741: A FOS spectrum with the blue detector, grating G130H and the 0.25"*1.4" aperture has been obtained on May 8, 1992. It has been analysed by comparing the normalized spectrum to synthetic spectra calculated from our NLTE model grid. The effective temperature has been determined with unprecedented accuracy (better than 3%) to be 140,000K (see Fig. 1 and 2 attached to the Scientific justification). Due to better known Teff and the larger number of spectral lines the analysis will give much more reliable abundances that the early results based on optical spectroscopy. ID 3513: The observations are currently in the process of scheduling. ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). Computer resources: i) Micro VAX 3300 + 2 VAX Station 3100 of the DAN node Bamberg ii) Cray YMP/EL of the Universitaet Erlangen-Nuernberg iii) Cray YMP, Landesvektorrechner Muenchen iv) VAX 8550 of the "Rechenzentrum der Universitaet Kiel" v) Cray X-MP of the "Rechenzentrum der Universitaet Kiel" vi) MODCOMP- Unix-Workstation of the Physics Department of Universitaet Kiel Research assistance: Dr. H. Drechsel (system manager of the Bamberg DAN node), Dipl.Ing. G.Jonas (Kiel, data reduction specialist), ------------------------------------------------------------------------------------ 11. Address Information Name: ULRICH HEBER Category: PI Institution: Universitat Erlangen-Nurnberg Address: DR. REMEIS-STERNWARTE ASTRONOMISCHES INSTITUT DER UNIVERSITAET ERLANGEN- City: D-8600 BAMBERG State: Zip Code: Country: GERMANY Telephone: 499519522214 Telex (or e-mail): ------------------------------------------------------------------------------------ TARGET LIST a) Fixed Targets ID = 4263c [ 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 PG1520+525 A,176 RA = 15H 21M 46.542S +/- 2000 1 V = 15.5 +/- 0.2, TYPE=DOZ, E(B- 0.013S, 2 V)=0.00 DEC = +52D 22' 3.85" +/- 3 F-CONT(1370) = 5.4 +/- 1.0 E-13 0.2", 4 F-CONT(1550) = 3.2 +/- 0.6 E-13 PLATE-ID=01RT F-CONT(1240) = 7.5 +/- 1.0 E-13 ------------------------------------------------------------------------------------------------------------------------------------ 2 PG1424+535 A,176 RA = 14H 25M 55.412S +/- 2000 1 V = 16.2 +/- 0.2, TYPE=DOZ, E(B- 0.013S, 2 V)=0.00 DEC = +53D 15' 24.76" +/- 3 F-CONT(1370) = 3.7 +/- 0.7 E-13 0.2", 4 F-CONT(1550) = 2.2 +/- 0.4 E-13 PLATE-ID=01AL F-CONT(1240) = 5.1 +/- 1.0 E-13 ------------------------------------------------------------------------------------------------------------------------------------ 3 PG1707+427 A,176 RA = 17H 8M 47.697S +/- 2000 1 V = 16.4 +/- 0.4, TYPE=DOZ, E(B- 0.013S, 2 V)=0.00 DEC = +42D 40' 59.95" +/- 3 F-CONT(1370) = 1.5 +/- 0.3 E-13 0.2", 4 F-CONT(1550) = 0.8 +/- 0.2 E-13 PLATE-ID=009J F-CONT(1240) = 2.1 +/- 0.4 E-13 ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 4263c [ 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 PG1520+525 FOS/BL ACQ/ 4.3 MIRROR 1 1.4S 1 CYCLE 3 BINARY ONBOARD ACQ FOR 1.100 ------------------------------------------------------------------------------------------------------------------------------------ 1.1 PG1520+525 FOS/BL ACQ/ 0.25X2. MIRROR TYPE=UP 1 1.4S 1 CYCLE 3 PEAK 0 SPATIAL SCAN ONBOARD ACQ FOR 1.200 ------------------------------------------------------------------------------------------------------------------------------------ 1.2 PG1520+525 FOS/BL ACCUM 0.25X2. G130H 1200- 1 112M 100 4 1 CYCLE 3 0 1600 ------------------------------------------------------------------------------------------------------------------------------------ 2 PG1424+535 FOS/BL ACQ/ 4.3 MIRROR 1 2.0S 1 CYCLE 3 BINARY ONBOARD ACQ FOR 2.100 ------------------------------------------------------------------------------------------------------------------------------------ 2.1 PG1424+535 FOS/BL ACQ/ 0.25X2. MIRROR TYPE=UP 1 2.0S 1 CYCLE 3 PEAK 0 SPATIAL SCAN ONBOARD ACQ FOR 2.200 ------------------------------------------------------------------------------------------------------------------------------------ 2.2 PG1424+535 FOS/BL ACCUM 0.25X2. G130H 1200- 1 100M 80 4 1 CYCLE 3 0 1600 ------------------------------------------------------------------------------------------------------------------------------------ 3 PG1707+427 FOS/BL ACQ/ 4.3 MIRROR 1 4.0S 1 CYCLE 3 BINARY ONBOARD ACQ FOR 3.100 ------------------------------------------------------------------------------------------------------------------------------------ 3.1 PG1707+427 FOS/BL ACQ/ 0.25X2. MIRROR TYPE=UP 1 5.0S 1 CYCLE 3 PEAK 0 SPATIAL SCAN ONBOARD ACQ FOR 3.200 ------------------------------------------------------------------------------------------------------------------------------------ 3.2 PG1707+427 FOS/BL ACCUM 0.25X2. G130H 1200- 1 172M 80 4 1 CYCLE 3 0 1600 ------------------------------------------------------------------------------------------------------------------------------------ Scan Paramters Form Proposal ID: 4263c [ 6] ------------------------------------------------------------------------------------------------------------------------------------ Data ID: 1 Exposure Logsheet lines: 1.100,2.100,3.100 FGS Scan: DWELL Dwell Only: dwell points/line: 7 Seconds per dwell: 1.00 Scan width (arc-secs): 0.0000 Scan length (arc-secs): 0.4000 Angle between sides (degrees) 90.00 Number of lines: 1 Scan rate (arc-sec/sec): 0.0000 PA of first scan line (degrees) 90.000 Scan frame (CEL or S/C): S/C Length Offset (arc-sec): 0.2000 Width Offset (arc-sec): 0. ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 4263c [ 7] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/BL ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/BINARY ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters TYPE=UP ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 9.48 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category HOT STARS ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category WHITE DWARFS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CYCLE 3; ONBOARD ACQ FOR 1.100 SPATIAL SCAN; ONBOARD ACQ FOR 1.200 CYCLE 3 ONBOARD ACQ FOR 2.100 ONBOARD ACQ FOR 2.200 ONBOARD ACQ FOR 3.100 ONBOARD ACQ FOR 3.200 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G130H ------------------------------------------------------------------------------------------------------------------------------------ Target Names PG1520+525 PG1424+535 PG1707+427 ------------------------------------------------------------------------------------------------------------------------------------