Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 2450c Report Date: 09-May-96:17:08 Version: ********** Check-in Date: ********** 1.Proposal Title: UV-SPECTROSCOPY OF THE UNIQUE HOT RCRB STAR V348 SGR ------------------------------------------------------------------------------------ 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 Prof. K. Hunger KIEL UNIVERSITY FRG 431-880-4110 DIRECTOR ------------------------------------------------------------------------------------ 7. Abstract V348 is a unique object: it is classified as i) the hottest known RCrB star (with Teff=20000K); ii) a very-late Wolf-Rayet type (WC10) central star of a planetary nebula; iii) a hydrogen-deficient star whose photospheric composition resembles those of extreme helium stars. This unusual combination opens the possibility to attack the following problems concerning late phases of stellar evolution: a) formation of planetaries with He-enriched central stars; b) formation of RCrB stars and extreme helium stars, c) mass loss processes and the RCrB phenomenon. In the present proposal, the following problems shall be addressed: i) position of V348 Sgr in the HR-diagram ii) chemical composition of the photosphere iii) mass-loss rate of V348 Sgr. The final aim is to determine the mass of the original H-rich shell and to derive the time when the nebular was expelled (onset of superwind). ------------------------------------------------------------------------------------ 8. Scientific Key Words: STARS: CHEMICALLY PECULIAR STAR; SPECTRAL ANALYSIS 1.5 ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 2.20 par: 0 10. Num targs pri: 1 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: HRS ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 2450c PI: Prof. K. Hunger Proposal Title: UV-SPECTROSCOPY OF THE UNIQUE HOT RCRB STAR V348 SGR ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Dr. J. P. Kaufmann BERLIN TECHNICAL UNIVERSITY FRG X Dr. D. Kilkenny SOUTH AFRICAN ASTRONOMICAL S AFRICA OBSERVATORY P.I. K. Hunger KIEL UNIVERSITY FRG X Dr. N. K. Rao INDIAN INSTITUTE OF ASTROPHYSICS INDIA Dr. L. Houziaux LIEGE UNIVERSITY BELGIUM X Dr. J. Manfroid LIEGE UNIVERSITY BELGIUM X Mme. F. Nemry LIEGE UNIVERSITY BELGIUM X Dr. K. Nandy ROYAL OBSERVATORY, EDINBURGH UK X Dr. P. W. Hill ST ANDREWS, UNIVERSITY OF UK X Dr. C. S. Jeffery ST ANDREWS, UNIVERSITY OF UK X Mr. D. Pollacco ST ANDREWS, UNIVERSITY OF UK X Dr. R.E.S. Clegg LONDON, UNIVERSITY COLLEGE UK X Dr. J. S. Drilling LOUISIANA STATE UNIVERSITY USA Dr. W.-R. Hamann KIEL UNIVERSITY FRG X Dr. U. Heber KIEL UNIVERSITY FRG X Dr. A. Heck STRASBOURG OBSERVATORY FRANCE X Dr. D. Klinglesmith NASA, GODDARD USA Dr. A. E. Lynas-Gray OXFORD, UNIVERSITY OF UK X Dr. D. Schoenberner KIEL UNIVERSITY FRG X Dr. H. J. Walker NASA, AMES USA ------------------------------------------------------------------------------------ 3. Description of proposed observations. Drilling et al. (1984) and Schoenberner and Heber (1986) compared IUE low- resolution spectra of MV Sgr and V348 Sgr with those of the well-studied extreme helium stars HD 124448 and BD +10D 2179. All four stars are found to have similare IUE spectra, suggesting that the photosphere of V348 Sgr is observable with HST. Accordingly, it is proposed that the ST High-Resolution Spectrograph (HRS) be used to obtain ultraviolet spectroscopy of V348 Sgr at maximum light. Coordinates of V348 Sgr taken from Allen et al. (1982) are alpha(1950) = 18h37m18.2s, delta(1950) = -22D57'20". These are used for Anglo Australian Telescope acquisition and are claimed to be accurate to 2 - 3 arcseconds. While a high coordinate precision is desirable for HST observations, especially in view of the variable magnitude, these should suffice if it can be confirmed from groundbased photometry that V348 Sgr is at maximum light at the time of HST observations. The HRS operates in acquisition mode using a 2 x 2 arcsecond aperture. It is not possible to use the Wide Field Camera/Planetary Camera as V348 Sgr would be too bright; the N2 mirror will give a count rate in the recommended range and the standard acquisition time (5 minutes) will result. Scientific spectra to be obtained with the HRS are as follows: 1. Low resolution spectrum in the wavelength range 120 nm - 148.8 nm. 2. Low resolution spectrum in the wavelength range 141.2 nm - 170 nm. 3. Medium resolution spectrum in the wavelength range (280.7 nm - 285.3 nm). The intention is to study the HeI line at 282.9 nm and the CII doublet 283.671 nm, 283.76 nm. 4. Medium resolution spectrum in the range (292.2 nm - 296.8 nm) for studying the HeI line at 294.5 nm. It is expected that the HRS low-resolution spectra will be adequate for studying the expected strong lines 124.7 nm (CIII), 130 nm (SiIII, SiII), 135.5 nm (CII), 140 nm (SiIV), 155 nm (CIV), 164 nm (HeII). Page 3 ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. High-resolution optical spectra have been obtained with the ESO-CASPEC (see sect. 2) . Direct images and long-slit spectroscopy of the nebula have been obtained at the ESO 2.2 m telescope and the AAT. Infrared photometry is available both from the ground (Kilkenny and Whittet, 1984) and with the IRAS satellite (Walker, 1985). Well-exposed low-resolution spectra (obtained with the Short Wavelength Prime and Long Wavelength Redundant Cameras of IUE) require about 40 minutes of exposure when V348 Sgr is at maximum light (Heck et al., 1982). Unfortunately, low-resolution spectra obtained with IUE are not of an adequate resolution for an abundance analysis, and high-resolution spectra would require prohibitively long exposures. The HST is therefore needed if an ultraviolet spectrum of V348 Sgr is to be obtained at a resolution sufficient for an abundance analysis of the photosphere. IUE spectra suggest that it is only in the ultraviolet (lambda .LE. 300 nm) that there is any chance of obtaining a photospheric spectrum with comparatively little contamination from the chromosphere, nebula or shell. ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. It is estimated from Figure 4-2 in the HRS Handbook the standard time for acquisition (about 5 minutes) can be adopted. Dark counts rates observed in both detectors (D1 and D2) are negligible in comparison with the count rate produced by V348 Sgr at maximum light. Dead-time effects can be neglected, as can scattered light since the echelle is not being used. Both D1 and D2 suffer from granularity and fixed-pattern noise, but D2 is better than D1 and so D2 is selected for this program. Worst blemishes in D2 deviate by 10% from the mean local response; this is a problem for weak line work and the applicants suggest that it be overcome by breaking each exposure into 4 parts (using the FP-SPLIT option) with the central wavelengths being slightly altered in each case. Possible nebular contributions to the ultraviolet spectrum cannot be excluded in the case of V348 Sgr. It is therefore important to measure the background in the science diodes. Exposure times listed in the table below correspond to the exposures requested in section 3; they are based on IUE fluxes observed by Heck et al. (1982) and HRS sensitivity curves. It has been assumed that 1600 counts are needed in each diode for a signal/noise (S/N) of 40, and each exposure is increased by 6% because of the need for background measurements. Continuum IUE flux 1E14 Grating Counts S/N t Lambda (nm) erg/cm/cm/sec/0.1nm diode/sec (min.) 130 2.9 G140L 0.250 30 22 147.5 6.5 G140L 1.800 30 9 283 4.4 G270M 0.260 20 28 293.9 5.5 G270M 0.230 20 31 Page 4 ------------------------------------------------------------------------------------ 7. Data reduction and analysis plans. Reduction and calibration of HRS spectra can be carried out with the program DIPSO (Howarth, 1984). Heber et al. (1984) have identified CIII, 124.7 nm, SiIII 130 nm, CII, 133.5 nm, SiIV, 140 nm and CIV, 155 nm in the low resolution IUE spectrum of V348 Sgr; these are similar to BD+10D 2179 and HD 124448. Accordingly, a scheme for analysing the HRS spectra of V348 Sgr is suggested, assuming they are similar to the IUE high-resolution spectra of BD+10D 2179. The analysis will be carried out in a similar way as that of BD+10D 2179 (Heber, 1983). Details of model atmosphere and line profile calculation can be found in Heber (1983) and Drilling et al. (1984). The ionization equilibria of CII/CIII and SiIII/SiIV will be used to derive the effective temperature. Surface gravity will be determined by matching the line profiles of the pressure-broadened HeI lines, 282.9 nm and 294.5 nm. After having fixed Teff and log g, abundances for C, N, Al, Si, P, Ti, Cr, Mn, Fe and Ni can be determined as demonstrated in the case of BD+10D 2179 (Heber, 1983). Low resolution IUE spectra of V348 Sgr indicate that the CIV resonance line at 155 nm is affected by an expanding envelope. This line can be used to determine the mass-loss rate. The comoving frame method (Hamann et al., 1982) will be used to estimate the mass-loss rate. ------------------------------------------------------------------------------------ 8. Additional comments or special requests. Photometric monitoring of V348 Sgr for more than fifty years suggests that it spends approximately half of the time at maximum light. Deep obscurational minima, however,can occur abruptly and at unpredictable times. As it is necessary to observe V348 Sgr with the HST at maximum light, so that ultraviolet photospheric spectra will be obtained, it is suggested that HST time be scheduled as though observations were not time-critical; the chance that V348 Sgr would be at maximum light, and remain there during the scheduled observations, is about 50%. The applicants further suggest that HST time be scheduled during the months when V348 Sgr is observable from the ground (April to August inclusive). It would then be possible to conduct nightly monitoring of V348 Sgr, from the South African Astronomical Observatory (SAAO) in advance of HST observations. Should it transpire that V348 Sgr is unlikely to be at maximum at the time of HST observations, a postponement could be requested and the HST time used for another program. ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). Computer resources: i) Starlink computer at the University College London, at the University of Oxford and at the University of St. Andrews will be used to reduce the HRS spectra. ii) CRAY X-MP 216 of the "Rechenzentrum der Universitaet Kiel" will be used to compute model atmospheres. ------------------------------------------------------------------------------------ 11. Address Information Name: KURT HUNGER Category: PI Institution: INST.F. THEOR. PHYSIK UND STERNWA Address: OLSHAUSENSTRASSE 40 City: KIEL D-2300 State: Zip Code: Country: F.R. GERMANY Telephone: Telex (or e-mail): ------------------------------------------------------------------------------------ TARGET LIST a) Fixed Targets ID = 2450c [ 5] ------------------------------------------------------------------------------------------------------------------------------------ 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 V348-SGR STAR; TYPE=RCRB RA = 18H 40M 19.923S +/- 2000 V = 174 1 V = 12.3 +/- 0.3 0.013S, 2 F-CONT(1300) = 2.9 +/- 0.3 E-14 DEC = -22D 54' 28.63" +/- 3 F-CONT(1475) = 6.5 +/- 0.6 E-14 0.2", 4 F-CONT(2830) = 4.4 +/- 0.5 E-14 PLATE-ID=067T 5 F-CONT(2939) = 5.5 +/- 0.6 E-14 ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 2450c [ 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 V348-SGR HRS ACQ 2.0 MIRROR-N2 FAINT=700 1 144.5S 2 1 ONBOARD ACQ FOR 2- BRIGHT=8000 3 5 MAP=END-POINT 4 SEARCH-SIZE=5 5 Comments: STEP-TIME=0.5S ------------------------------------------------------------------------------------------------------------------------------------ 2 V348-SGR HRS ACCUM 2.0 G140L 1200- STEP-PATT=5 1 24.5M 30 2 1 1488 ------------------------------------------------------------------------------------------------------------------------------------ 3 V348-SGR HRS ACCUM 2.0 G140L 1478- STEP-PATT=5 2 12.25M 30 3 1 1766 ------------------------------------------------------------------------------------------------------------------------------------ 4 V348-SGR HRS ACCUM 2.0 G270M 2807- STEP-PATT=5 2 15.5M 20 4 1 2853 ------------------------------------------------------------------------------------------------------------------------------------ 5 V348-SGR HRS ACCUM 2.0 G270M 2922- STEP-PATT=5 2 16M 20 5 2 2968 ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 2450c [ 7] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FAINT=700 BRIGHT=8000 MAP=END-POINT SEARCH-SIZE=5 STEP-PATT=5 ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 2.20 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category STELLAR ASTROPHYSICS ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category LATE EVOLUTION ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 2-5 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N2 G140L G270M ------------------------------------------------------------------------------------------------------------------------------------ Target Names V348-SGR ------------------------------------------------------------------------------------------------------------------------------------