8635( 3) - 07/28/00 15:22 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8635 Version: 3 Check-in Date: 10-Apr-2000 09:39:37 1.Proposal Title: A test of pulsation and diffusion theory for subluminous B stars ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 9 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Ulrich Heber Universitat Erlangen-Nurnberg CoI: Dr. Ralf Napiwotzki Dr. Remeis-Sternwarte N CoI: Dr. Darragh O'Donoghue South African Astronomical Observatory N CoI: Dr. Chris Koen South African Astronomical Observatory N CoI: Dr. Dave Kilkenny South African Astronomical Observatory N CoI: Dr. Tony Lynas-Gray Dept. of Astrophysics, Oxford N CoI: Prof. Dr. Gilles Fontaine Dept. Physique, Univ. Montreal N CoI: Dr. Stephane Charpinet CFHT Corp. N CoI: Dr. Pierre Chayer Johns Hopkins Univ., Baltimore N CoI: Dr. Sabine Moehler Dr. Remeis-Sternwarte N ------------------------------------------------------------------------------------ 5. Abstract The recent discovery of radial and nonradial mode pulsations in nearly 20 sdB stars makes it possible to use asteroseismology to probe the internal structure of these stars and discern their evolutionary status; this is needed for reasons as diverse as understanding the late stages of stellar evolution and the calibration of the observed ultraviolet upturn in giant elliptical galaxies as an age indicator. Central to any asteroseismological study is an identification of the pulsation driving mechanism; evidence to date suggests that this is due to the recently discovered heavy metal opacity. The necessary metal abundance has to be maintained by diffusive equilibrium between gravitational settling and radiative levitation. Abundance analyses of high resolution optical spectra have, however, revealed that the surface iron abundance is not discriminating between pulsating and non-pulsating sdB stars. We propose to extend the abundance analyses of three pulsating sdB stars and two non-pulsating sdB stars to chemical elements unobservable from the ground using echelle UV spectra; this would enable diffusion/pulsation calculations to be tested by searching for significant differences in their surface abundance patterns. The targets are chosen to cover the full range of sdB gravities since \logg\ is the dominant parameter for both diffusion and pulsation. ------------------------------------------------------------------------------------ 8635( 3) - 07/28/00 15:22 - [ 2] Observations Description ------------------------ We will obtain short-slit (0.2* 0.06) medium dispersion Echelle ultraviolet spectroscopy for five sdB stars (3 pulsating, 2 non-pulsatingfootnoteThe brightest sdB star, HD 149382 (V=8.95, see table 1), another obvious target for the proposal, can be observed with STIS through a ND filter only which results in an inefficient observing strategy..) in the E140M and E230M mode. For PG 1605+072 we shall use the 0.2* 0.2 aperture because its spectral lines are somewhat broadened by rotation (v sin i=39km/s). These modes cover the range 1150--2400 Angstrom\ which contains many lines of doubly and triply ionized iron group elements (i.e. C II/III, IV, N III/IV/V, P III/IV, S III/IV/V, Ca III, Ti III/IV, V IV, Cr III/IV, Mn III/IV, Fe III/IV, Co III, Ni III/IV, Zn III) suitable for spectroscopic analysis (see B82a, b). It is important to cover the full spectral range in order to measure lines of different strength and stage of ionization per chemical element. The lines of doubly ionized iron group elements fall predominantly in the NUV regime whereas triply ionized iron group elements have their lines mainly in the FUV. For an accurate abundance analysis it is important to verify that ionization equilibria are fulfilled. We aim for an (optimum) S/N of 30 at the central wavelengths given in the table to get abundances of the required accuracy. We used the STIS exposure time calculator (using the HST standard star Feige 110) to determine the exposure times necessary to achieve a S/N ~ 30 at 1900Angstrom\ and 1300Angstrom. The fluxes of the three pulsators are derived from a low resolution IUE spectrum of PG 1605+072 (SWP28351) and scaled by the relative visual brightness for the other pulsators. IUE spectra for the non-pulsators are available (SWP14295, SWP24551). Interstellar reddening is negligible since the targets are at high galactic latitudes. The guide star aquisition takes 6 min., the point source acquisition 6 min., peak-up into the small aperture another 6 min., and the guide star reacquisition 5 min. The first MAMA exposure in each visit requires an overhead of 8 min. Feige 48 and PG 1219+534 are in the continuous viewing zone. However, since the CVZ window for PG 1219+534 occurs only once per cycle (about 20 orbits long) it is unclear whether we can make use of it. Therefore, 2 orbits are required for PG1605+072, 4 orbits PG 1219+534 and 3 for Feige 48. If the CVZ opportunity arises, 3 orbits are sufficient for PG 1219+534. 1 orbit suffices for BD+25\dg2534, but 2 are needed for CD-24\dg731. begintable captionExpected exposure times begintabularlcrcr Target & Flux at 1300Angstrom\ & exposure & Flux at 1900Angstrom\ & exposure , & erg/cm^2/s/Angstrom & time s & erg/cm^2/s/Angstrom & time s , PG1605+072 & 1.8\cdot 10^- 12 & 2200 & 6.7\cdot 10^-13 & 2800 , Feige 48 & 1.1 \cdot 10^-12 & 5400 & 4.2\cdot 10^-13 & 6000 , PG1219+534 & 1.5 \cdot 10^-12 & 4000 & 5.5\cdot 10^-13 & 4600 , BD+25\dg2534 & 1.9\cdot 10^-11 & 310 & 7.5\cdot 10^-12 & 325 , CD-24\dg731 & 7.2\cdot 10^-12 & 825 & 2.5\cdot 10^-12 & 1000 , endtabular endtable The exposure times are considerably longer than the pulsation periods. Hence the spectra will be averaged ones as the optical spectra are too. Pulsational velocity and temperature variations, however, are estimated to be small. Real Time Justification ----------------------- One target (Feige 48) lies in the continuous viewing zone and can be observed for 96 min. several times in the year. Since it is also the faintest of our programme stars, the S/N will benefit from the longer exposure time. One other target (PG1219+534) lies marginally in the CVZ. However the possibility to observe it during the entire orbit occurs only once per year for about 20 orbits. If we can make use of this opportunity only 3 orbits instead of four are required. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 8635( 3) - 07/28/00 15:22 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 PG1605+072 STAR, SDB, Pulsating RA=16H 08M 03.69S +/- 0.02S, J2000 V = 13.0+/-0.3 Variable DEC=+07D 04' 28.8" +/- 0.3", B-V = -0.23+/-0.03 PLATE-ID=01GB TYPE=B0 F(1300)=1.8e-12 F(1900)=6.7e-13 Coordinate Source: GUIDE_STAR_CATALOG 2 PG1144+615 STAR, SDB, Pulsating RA=11H 47M 14.56S +/- 0.02S, J2000 V = 13.5+/-0.1 Variable DEC=+61D 15' 31.9" +/- 0.3", B-V = -0.25+/-0.03 PLATE-ID=01QZ TYPE=B0 F(1300)=1.1e-12 F(1900)=4.2e-13 Coordinate Source: GUIDE_STAR_CATALOG 3 PG1219+534 STAR, SDB, Pulsating RA=12H 21M 29.14S +/- 0.02S, J2000 V = 13.2+/-0.2 Variable DEC=+53D 04' 36.7" +/- 0.3", B-V = -0.25+/-0.05 PLATE-ID=00LK TYPE=B0 F(1300)=1.5e-12 F(1900)=5.5e-13 Coordinate Source: GUIDE_STAR_CATALOG 4 BD+25D2534 STAR, SDB RA=12H 37M 23.55S +/- 0.02S, J2000 V = 10.54+/-0.05 DEC=+25D 04' 00.3" +/- 0.3", B-V = -0.28+/-0.03 PLATE-ID=038A TYPE=B0 F(1300)=1.9e-11 F(1900)=7.5e-12 Coordinate Source: GUIDE_STAR_CATALOG 5 CD-24D731 STAR, SDB RA=01H 43M 48.39S +/- 0.02S, J2000 V = 11.76+/-0.05 DEC=-24D 05' 09.6" +/- 0.3", B-V = -0.29+/-0.03 PLATE-ID=04JM TYPE=B0 F(1300)=7.2e-12 F(1900)=2.5e-12 Coordinate Source: GUIDE_STAR_CATALOG 8635( 3) - 07/28/00 15:22 - [ 4] Visit: 01 Visit Priority: 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 PG1605+072 STIS/C ACQ F28X50L MIRROR 1 1 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 2 PG1605+072 STIS/F TIME-TA 0.2X0.2 E140M 1425 BUFFER-TIME=140 1 2340 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 3 PG1605+072 STIS/F TIME-TA 0.2X0.2 E140M 1425 BUFFER-TIME=140 1 2850 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 4 PG1605+072 STIS/N TIME-TA 0.2X0.2 E230M 1978 BUFFER-TIME=145 1 2850 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 8635( 3) - 07/28/00 15:22 - [ 5] Visit: 02 Visit Priority: Visit Requirements: CVZ 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 PG1144+615 STIS/C ACQ F28X50L MIRROR 1 1 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 2 PG1144+615 STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 0.6 S CD K 6 Comments: 20, 000 electrons expected ------------------------------------------------------------------------------------------------------------------------------------ 3 PG1144+615 STIS/F TIME-TA 0.2X0.0 E140M 1425 BUFFER-TIME=300 1 3600 S UV-MAM G 6 A ------------------------------------------------------------------------------------------------------------------------------------ 4 PG1144+615 STIS/F TIME-TA 0.2X0.0 E140M 1425 BUFFER-TIME=300 1 3600 S UV-MAM G 6 A ------------------------------------------------------------------------------------------------------------------------------------ 5 PG1144+615 STIS/N TIME-TA 0.2X0.0 E230M 1978 BUFFER-TIME=260 1 3500 S UV-MAM G 6 A ------------------------------------------------------------------------------------------------------------------------------------ 6 PG1144+615 STIS/N TIME-TA 0.2X0.0 E230M 1978 BUFFER-TIME=260 1 3511 S UV-MAM G 6 A ------------------------------------------------------------------------------------------------------------------------------------ 8635( 3) - 07/28/00 15:22 - [ 6] Visit: 03 Visit Priority: 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 PG1219+534 STIS/C ACQ F28X50L MIRROR 1 1 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 2 PG1219+534 STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 0.5 S CD K 6 Comments: 20, 000 electrons expected ------------------------------------------------------------------------------------------------------------------------------------ 3 PG1219+534 STIS/F TIME-TA 0.2X0.0 E140M 1425 BUFFER-TIME=205 1 2160 S UV-MAM G 6 A ------------------------------------------------------------------------------------------------------------------------------------ 4 PG1219+534 STIS/F TIME-TA 0.2X0.0 E140M 1425 BUFFER-TIME=205 1 3100 S UV-MAM G 6 A ------------------------------------------------------------------------------------------------------------------------------------ 5 PG1219+534 STIS/N TIME-TA 0.2X0.0 E230M 1978 BUFFER-TIME=180 1 3100 S UV-MAM G 6 A ------------------------------------------------------------------------------------------------------------------------------------ 6 PG1219+534 STIS/N TIME-TA 0.2X0.0 E230M 1978 BUFFER-TIME=180 1 3100 S UV-MAM G 6 A ------------------------------------------------------------------------------------------------------------------------------------ 8635( 3) - 07/28/00 15:22 - [ 7] Visit: 04 Visit Priority: 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 BD+25D2534 STIS/C ACQ F28X50L MIRROR 1 0.3 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 2 BD+25D2534 STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 0.1 S CD K 6 Comments: 0.1x0.03 used to reduce counts, 50, 000 electrons expected ------------------------------------------------------------------------------------------------------------------------------------ 3 BD+25D2534 STIS/F ACCUM 0.2X0.0 E140M 1425 1 875 S UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 4 BD+25D2534 STIS/N ACCUM 0.2X0.0 E230M 1978 1 875 S UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 8635( 3) - 07/28/00 15:22 - [ 8] Visit: 05 Visit Priority: 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 CD-24D731 STIS/C ACQ F28X50L MIRROR 1 1 S CD P ------------------------------------------------------------------------------------------------------------------------------------ 2 CD-24D731 STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 0.1 S CD K 6 Comments: 20, 000 electrons expected ------------------------------------------------------------------------------------------------------------------------------------ 3 CD-24D731 STIS/F ACCUM 0.2X0.0 E140M 1425 1 878 S UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 4 CD-24D731 STIS/N ACCUM 0.2X0.0 E230M 1978 1 800 S UV-MAM 6 A ------------------------------------------------------------------------------------------------------------------------------------ 8635( 3) - 07/28/00 15:22 - [ 9] Summary Form for Proposal 8635 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP 0.2X0.2 0.2X0.06 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/FUV-MAMA STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ TIME-TAG ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=140 BUFFER-TIME=145 BUFFER-TIME=300 BUFFER-TIME=260 BUFFER-TIME=205 BUFFER-TIME=180 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CVZ ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR E140M E230M ------------------------------------------------------------------------------------------------------------------------------------ Target Names PG1605+072 PG1144+615 PG1219+534 BD+25D2534 CD-24D731 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1425 1978 ------------------------------------------------------------------------------------------------------------------------------------