Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 3513c Report Date: 09-May-96:18:40 Version: ********** Check-in Date: ********** 1.Proposal Title: NON-LTE ANALYSIS OF THE POPULATION II POST-AGB STARS ROB 162 AND K648 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID STELLAR ASTROPHYSICS GO Sub Category LATE EVOLUTION ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Ulrich Heber INSTITUT F. THEOR. PHYSIK U. GERMANY 49-431-8804104 ------------------------------------------------------------------------------------ 7. Abstract Post-AGB stars in galactic globular clusters are Rosetta stones for our understanding of late phase of stellar evolution of low mass stars. They are also important objects to study the early phases of the chemical evolution of our galaxy because they are amongst very few cluster stars for which the helium abundance can be determined directly. ROB 162 (in NGC 6397) and K 648, the central star of a PN in M 15, are two post-AGB stars in very metal poor clusters. Quantitative optical spectroscopy indicated that these two stars have a very different evolutionary history with respect to dredge-up events of nuclear processed matter. K 648 is strongly enriched in carbon indicating strong dredge-up from interior layers of the progenitor star. ROB 162, on the other hand, does not show any indication for dredge -up from optical spectroscopy. It is proposed to determine C, N and O abundances from UV-spectroscopy with the FOS using appropriate NLTE model atmospheres developed by our group. These cannot be derived from optical spectra and will put important constraints on the dredge-up history of the two stars. In the case of K 648, it gives the unique possibility to study different layers of the progenitor star, since we can compare the photospheric abundance to that of the Planetary Nebula. In the case of ROB 162, these abundances can prove or disprove the absence of dredge-up. If proven, a direct determination the primordial helium abundance results. ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 3.20 par: 0 10. Num targs pri: 2 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: HRS ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 3513c PI: Ulrich Heber Proposal Title: NON-LTE ANALYSIS OF THE POPULATION II POST-AGB STARS ROB 162 AND K648 ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Pi Ulrich Heber INSTITUT F. THEOR. PHYSIK U. F.R.G. X STERNWARTE DER UNI. KIEL Stefan Dreizler INSTITUT F. THEOR. PHYSIK U. F.R.G. X STERNWARTE DER UNI. KIEL Thomas Rauch INSTITUT F. THEOR. PHYSIK U. F.R.G. X STERNWARTE DER UNI. KIEL Klaus Werner INSTITUT F. THEOR. PHYSIK U. F.R.G. X STERNWARTE DER UNI. KIEL ------------------------------------------------------------------------------------ 3. Description of proposed observations. The original proposal applied for GHRS observations (G140L) of two post-AGB stars of population II. Due to the failure of side 1 we changed 3 of the 4 proposed observations to the FOS. The spacecraft time awarded to the project is insufficient in order to complete it. We have decided to observe only one target, K648, because of its scientific merits. Moreover, we want to restrict the observations to some strategic lines of NIII, NIV, CIII, CIV, and OIV which lie in the range 1225 to 1255 Angstroem and 1320 to 1355 Angstroem. The measurement of these lines can be achieved by two spectra taken with the GHRS and grating G160M. This has the advantage over the FOS that it results in spectra of higher resolution than the FOS. The full spectral resolution of G160M will not be necessary and we will bin the data afterwards as appropriate. We aim at a S/N of 20 for the unbinned data. This way is more flexible than the FOS option since it allows an optimum trade-off between S/N and spectral resolution for the spectral analysis by NLTE-model atmospheres. K648 has been observed with HST with PC (GTO proposal No. 1046 in cycle 0). This image will allow to measure coordinates for the target as well as for a suitable offset ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. High resolution optical spectra of ROB 162 have been obtained with the ESO CASPEC spectrograph at the 3.6m telescope and were analysed by means of Non-LTE model atmospheres techniques. Recently, three additonal CASPEC spectra have been obtained, which yield a S/N near 100. These spectra are still under investigation and will allow to improve on the results of Heber and Kudritzki (1986). However, even these spectra do not show any traces of metal lines. Metal lines can only be measured in the UV. Optical spectra of K648 (of about 0.1nm resolution) have been obtained at the Calar Alto observatory using the Cassegrain Twin spectrograph at the 3.5m telescope. These spectra were taken with a very small slit under superb seeing conditions, which is a prerequisite since K 648 is located in a very crowded field close to the center of M15. In addition K648 is surrounded by a compact planetary nebula and photospheric Balmer absorptions have for the first time been resolved from the intense nebular Balmer emission as detailed in section 1. These spectra also allow to measure He II, C III and C IV absorption lines with high precision, which will allow the atmospheric parameters and the carbon abundance to be determined from appropriate NLTE model atmospheres. Abundances of other metals can only be obtained from ultraviolet spectra. Ultraviolet spectroscopy of K648 and ROB 162 has been carried out with the IUE satellite. Both stars have been observed in the low resolution mode (about 0.5nm). These spectra have been used to estimate the ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. Page 3 ------------------------------------------------------------------------------------ 7. Data reduction and analysis plans. Data reduction of FOS spectra will be carried out with using IRAF + STSDAS which is presently installed on the MODCOMP computer of the Physics department in Kiel. Observed line profiles will be compared to theoretical predictions in order to derive atmospheric parameters and abundances. To this end, the model atmosphere calculations described in section 1 will be extended. Numerical calculations will be carried out using the Cray X-MP 216 computer of the Rechenzentrum der Universitaet Kiel. ------------------------------------------------------------------------------------ 8. Additional comments or special requests. ------------------------------------------------------------------------------------ 9. Description of previous HST work. a. List HST program numbers and titles, and specify whether they are related to this project or not. ID 2741: Non-LTE spectral analysis of the pre white dwarf PG1159-035 not related to this project b. Summarize the main results obtained from previous related programs. the observations are scheduled for cycle 1, in the long range schedule as of February, c. List publications resulting from the above data (Format: Title, Authors,Journal, Volume, Page, and Year.) ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). Computer resources: i) VAX 8550 of the Rechenzentrum der Universitaet Kiel, MODCOMP computer of the physics department; to be used for data reduction. ii) Cray X-MP 216 of the Rechenzentrum der Universitaet Kiel to be used for Non-LTE model atmosphere calculations. Research assistance: Dipl. Ing. G. Jonas (data reduction specialist). One graduate student will assist the proposers in the spectral analysis. ------------------------------------------------------------------------------------ 11. Address Information Name: ULRICH HEBER Category: PI Institution: INSTITUT F. THEOR. PHYSIK U. STER Address: OLSHAUSENSTR. 40 City: KIEL State: Zip Code: Country: F.R.G. Telephone: +49 4318804103 Telex (or e-mail): 292706 IAPKI D ------------------------------------------------------------------------------------ TARGET LIST a) Fixed Targets ID = 3513c [ 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 K648 A,108,184 RA=21H 29M 59.4175S +/- 2000 1 V = 14.95 +/- 0.2, TYPE=DOZ, E(B- 0.02S, 2 V)=0.08 DEC=+12D 10' 25.987" +/- F-CONT(1300) = 2.25E-13 0.3", PLATE-ID=02V2 ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 3513c [ 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 K648 HRS ACQ 2.0 MIRROR-N2 SEARCH-SIZE=5 1 30.6S 2 1 CYCLE 2 BRIGHT=RETURN ONBOARD ACQ FOR LOCATE=YES 1.100 MAP=END-POINT Comments: STEP TIME = 0.2S ------------------------------------------------------------------------------------------------------------------------------------ 1.1 K648 HRS ACQ/ 2.0 MIRROR-N2 1 20.4S 2 1 CYCLE 2 PEAKUP ONBOARD ACQ FOR 2.000-3.000 Comments: STEP TIME = 0.2S ------------------------------------------------------------------------------------------------------------------------------------ 2 K648 HRS ACCUM 2.0 G160M 1225- FP-SPLIT=FOUR 2 34M 20 2 1 CYCLE 2 1258 ------------------------------------------------------------------------------------------------------------------------------------ 3 K648 HRS ACCUM 2.0 G160M 1317- FP-SPLIT=FOUR 2 32.1M 20 2 1 CYCLE 2 1350 ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 3513c [ 6] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAKUP ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SEARCH-SIZE=5 BRIGHT=RETURN LOCATE=YES MAP=END-POINT FP-SPLIT=FOUR ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 3.20 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category STELLAR ASTROPHYSICS ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category LATE EVOLUTION ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CYCLE 2; ONBOARD ACQ FOR 1.100 ONBOARD ACQ FOR 2.000-3.000; CYCLE 2 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N2 G160M ------------------------------------------------------------------------------------------------------------------------------------ Target Names K648 ------------------------------------------------------------------------------------------------------------------------------------