9417( 2) - 02/14/02 13:39 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9417 Version: 2 Check-in Date: 14-Feb-2002 13:37:47 1.Proposal Title: New Clues to the Origin of the Extreme Helium Stars ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 11 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: David Lambert University of Texas at Austin CoI: Prof. N. Kameswara Rao Indian Institute of Astrophysics N CoI: Dr. Simon Jeffery Armagh Observatory N CoI: Dr. Gajendra Pandey University of Texas at Austin N ------------------------------------------------------------------------------------ 5. Abstract The extreme helium stars (EHes) are H-poor supergiants whose origins are not yet understood despite thorough analyses of optical spectra. This proposal seeks STIS echelle spectra for 7 stars from which novel data on their chemical compositions will be obtained to pin down key abundances. First, even the EHe's initial metallicity is uncertain; certain abundance ratios - e.g., Ca/S, Ti/S, and Fe/S - imply alterations of surface abundances among elements from Na to Ni resulting from fractionation or diffusive separation, possibly the result of winnowing of dust grains from gas. The zinc abundance measurable only from UV spectra will be a powerful clue to the true metallicity because it is known not to be removed by such winnowing. Second, elements affected by the s-process, the last of the major nucleosynthetic processes for which surface abundances are unknown for EHes, will be studied. The new abundances will be used to probe the evolutionary origins of these peculiar stars by comparisons with theoretical scenarios involving a merger of white dwarfs or a final He-shell flash in a low mass white dwarf, and with observed abundances for R Coronae Borealis stars that would seem to be close relatives of the EHes. Spectrophotometric observations of EHes obtained with GO 8603 will give accurate estimates of effective temperature and surface gravity that will be used in our abundance determinations. ------------------------------------------------------------------------------------ 9417( 2) - 02/14/02 13:39 - [ 2] Observations Description ------------------------ The spectroscopic goal of the proposal is the determination of the Zn, Y, Zr and La abundances from lines of Zn, ii at 2062.0, 2025.5, 2099.9, 2102.2, 2502.0 and 2558.0 Angstrom, Y, iii at 2206.0, 2327.3 and 2414.6 Angstrom, Zr, iii at 1937.2, 1940.2, 1941.1, 1946.6, 2002.6, 2007.5, 2026.7, 2060.8, 2159.2, 2420.7, and 2444.6 Angstrom and La, iii at 2297.7, 2379.4, 2476.6, and 2651.50 Angstrom for EHes with effective temperatures 9000 <= T_ eff <= 20000 K. There are many Fe, ii and Fe, iii lines in the region, especially around the Zr, iii lines. These will provide a check on optical Fe abundances. The stars are sharp -lined with rather crowded spectra such that use of E230M is appropriate. The single secondary setting Lambda = 2269 Angstrom will give both Zn, ii lines as well as Y, iii, Zr, iii, and La, iii lines. These Y, Zr, and La lines have reliable theoretical gf-values (Brage et al. 1998, ApJ, 496, 1051; Sikstr"om et al. 1999, A&A, 343, 297; Biemont, E. et al. 1999, J. Phys. B., At. Mol. Opt. Phys., 32, 3409). Our synthetic spectra show that E230M spectra at a S/N ~eq 60 will suffice to detect the Y, Zr, and La lines unless the Y, Zr, and La abundances are greatly underabundant relative to the Fe abundance determined from optical spectra. An overabundance of Y and Zr is expected, and seen in the RCBs. Exposure times in all cases are estimated using fluxes provided by IUE archival spectra; continuum fluxes are given below in the usual units of ergs cm^-2 s^-1 AA^-1. The stars, if variable, are only slightly so. A typical overhead of 24 minutes has been considered: 6 minutes each for guide star acquisition, target acquisition, peak-up, and MAMA overheads. Overhead will be less for the repeat orbits. `Visibility' per orbit runs from 52 -- 57 minutes. Then, there is 28 -- 33 minutes for useful exposure on target on the first orbit and a few minutes more on repeat orbits. As a representative target, we discuss BD +10^o 2179 for which the IUE fluxes are F_2414 = 2.2 * 10^-12 and F_1940 = 3.2 * 10^-12. According to the ETC, a S/N = 60 is reached in 16 minutes at 2414Angstrom\ and in 42 minutes at 1940 Angstrom. In this case, we request 2 orbits in which we shall exceed slightly the nominal S/N = 60. The sensitivity of the E230M set-up is lower at 1940 Angstrom than at 2414 Angstrom and, thus, an exposure providing S/N ~eq 60 at the shorter wavelength comfortably exceeds the desired S/N at 2414 Angstrom. The 1940 Angstrom region is critical as it provides the Zr, iii lines that are observable to higher temperatures than the Y, iii lines. For the other stars, the orbit requests are given in the observation summary. From the observed IUE fluxes it is seen that if S/N ~eq 60 is achieved at 1940 Angstrom much higher S/N is expected for Zn, ii lines at 2062 -- 2550 Angstrom. In several cases, a S/N = 50 and in one case (FQ Aqr) of 35 at 1940 Angstrom has been adopted as a compromise. The E230M secondary setting of 2269 Angstrom provides all required lines of Zn, ii, Y, iii, Zr, iii, and La, iii in a single setting. Neither primary region (2707Angstrom and 1978 Angstrom) does this. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9417( 2) - 02/14/02 13:39 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 BD+10D2179 STAR, BP, STAR, POST- RA=10H 38M 55.24S +/- 0.2", J2000 V = +155 B-V = -0.17 AGB STAR DEC=10D 3' 48.8" +/- 0.2", PLATE V = 9.93 -ID=027Y TYPE=B4P Coordinate Source: GUIDE_STAR_CATALOG Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1991.25 -0.0008 -0.003 0.0005 2 HD124448 STAR, B3-B5 III-I, RA=14H 14M 58.64S +/- 0.5", DEC= J2000 V = -68 V = 9.99 STAR, POST-AGB STAR -46D 17' 20.1" +/- 0.5", PLATE- B-V = -0.11 ID=02MC TYPE=B3P Coordinate Source: GUIDE_STAR_CATALOG Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1991.25 -0.0007 0.001 0.0006 3 CD-46D11775 STAR, B3-B5 III-I, RA=17H 42M 34.03S +/- 0.2", DEC= J2000 V = 10.7 STAR, POST-AGB STAR -46D 58' 48.6" +/- 0.2", PLATE- B-V = 0.3 ID=061A TYPE=B3P Coordinate Source: GUIDE_STAR_CATALOG Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1991.25 0.0007 -0.003 0.0 4 V2244-OPH STAR, B6-B9.5 III-I, RA=17H 51M 26.77S +/- 0.3", DEC= J2000 V = -20 V = 10.9 STAR, POST-AGB STAR -01D 43' 21.4" +/- 0.3", PLATE- B-V = 0.5 ID=00JP TYPE=B9P Coordinate Source: GUIDE_STAR_CATALOG Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1991.25 0.00003 -0.0086 0.0 5 HD168476 STAR, B6-B9.5 III-I, RA=18H 23M 14.72S +/- 0.5", DEC= J2000 V = -167 V = 9.25 STAR, POST-AGB STAR -56D 37' 43.3" +/- 0.5", PLATE- B-V = 0.01 ID=039U TYPE=B7P Coordinate Source: GUIDE_STAR_CATALOG Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1991.25 0.000005 -0.0091 0.0 6 HD225642 STAR, B3-B5 III-I, RA=19H 45M 17.27S +/- 0.3", J2000 V = 10.18 STAR, POST-AGB STAR DEC=33D 58' 26.6" +/- 0.3", B-V = 0.23 PLATE-ID=02TN TYPE=B4P Coordinate Source: GUIDE_STAR_CATALOG Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1991.25 0.00005 -0.0029 0.0 7 BD+01D4381 STAR, A0-A3 III-I, RA=20H 51M 21.34S +/- 0.2", J2000 V = 16 V = 9.52 STAR, POST-AGB STAR DEC=02D 18' 46.6" +/- 0.2", B-V = 0.1 PLATE-ID=050Y TYPE=A2P Coordinate Source: GUIDE_STAR_CATALOG Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1991.25 0.0001 -0.002 0.0 9417( 2) - 02/14/02 13:39 - [ 4] Visit: 01 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Visit 1 of 1 for BD+10D2179 Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 BD+10D2179 STIS/C ACQ F28X50O MIRROR ACQTYPE=POINT 1 1 S CD II Comments: ACQ for 20 S and less, as estimated from ETC, avoids saturation. ------------------------------------------------------------------------------------------------------------------------------------ 20 BD+10D2179 STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 1 S CD K 5ND Comments: PEAKUP for 25 S and less, as estimated from ETC, avoids saturation. ------------------------------------------------------------------------------------------------------------------------------------ 30 BD+10D2179 STIS/N ACCUM 0.2X0.0 E230M 2269 1 1852 S UV-MAM 6 A Comments: 1 orbit ------------------------------------------------------------------------------------------------------------------------------------ 40 BD+10D2179 STIS/N ACCUM 0.2X0.0 E230M 2269 1 2910 S UV-MAM 6 A Comments: 1 orbit ------------------------------------------------------------------------------------------------------------------------------------ 9417( 2) - 02/14/02 13:39 - [ 5] Visit: 02 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Visit 2 of 2 for HD124448 Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 HD124448 STIS/C ACQ F28X50O MIRROR ACQTYPE=POINT 1 1 S CD II Comments: ACQ for 20 S and less, as estimated from ETC, avoids saturation. ------------------------------------------------------------------------------------------------------------------------------------ 20 HD124448 STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 1 S CD K 5ND Comments: PEAKUP for 25 S and less, as estimated from ETC, avoids saturation. ------------------------------------------------------------------------------------------------------------------------------------ 30 HD124448 STIS/N ACCUM 0.2X0.0 E230M 2269 1 2007 S UV-MAM 6 A Comments: 1 orbit ------------------------------------------------------------------------------------------------------------------------------------ 40 HD124448 STIS/N ACCUM 0.2X0.0 E230M 2269 1 3084 S UV-MAM 6 A Comments: 1 orbit ------------------------------------------------------------------------------------------------------------------------------------ 9417( 2) - 02/14/02 13:39 - [ 6] Visit: 03 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Visit 3 of 3 for CD-46D11775 Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 CD-46D11775 STIS/C ACQ F28X50O MIRROR ACQTYPE=POINT 1 3 S CD II Comments: ACQ for 50 S and less, as estimated from ETC, avoids saturation. ------------------------------------------------------------------------------------------------------------------------------------ 20 CD-46D11775 STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 4 S CD K 5ND Comments: PEAKUP for 68 S and less, as estimated from ETC, avoids saturation. ------------------------------------------------------------------------------------------------------------------------------------ 30 CD-46D11775 STIS/N ACCUM 0.2X0.0 E230M 2269 1 1927 S UV-MAM 6 A Comments: 1 orbit ------------------------------------------------------------------------------------------------------------------------------------ 40 CD-46D11775 STIS/N ACCUM 0.2X0.0 E230M 2269 1 3084 S UV-MAM 6 A Comments: 1 orbit ------------------------------------------------------------------------------------------------------------------------------------ 9417( 2) - 02/14/02 13:39 - [ 7] Visit: 04 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Visit 4 of 4 for V2244-OPH Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 V2244-OPH STIS/C ACQ F28X50O MIRROR 1 3 S CD II Comments: ACQ for 52 S and less, as estimated from ETC, avoids saturation. ------------------------------------------------------------------------------------------------------------------------------------ 20 V2244-OPH STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 4 S CD K 5ND Comments: PEAKUP for 64 S and less, as estimated from ETC, avoids saturation. ------------------------------------------------------------------------------------------------------------------------------------ 30 V2244-OPH STIS/N ACCUM 0.2X0.0 E230M 2269 1 1772 S UV-MAM 6 A Comments: 1 orbit ------------------------------------------------------------------------------------------------------------------------------------ 40 V2244-OPH STIS/N ACCUM 0.2X0.0 E230M 2269 2 2929 S UV-MAM 6 A Comments: 2 orbits ------------------------------------------------------------------------------------------------------------------------------------ 9417( 2) - 02/14/02 13:39 - [ 8] Visit: 05 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Visit 5 of 5 for HD168476 Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 HD168476 STIS/C ACQ F28X50O MIRROR ACQTYPE=POINT 1 1 S CD II Comments: ACQ for 10s and less, as estimated from ETC, avoids saturation. ------------------------------------------------------------------------------------------------------------------------------------ 20 HD168476 STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 1 S CD K 5ND Comments: PEAKUP for 13 S and less, as estimated from ETC, avoids saturation. ------------------------------------------------------------------------------------------------------------------------------------ 30 HD168476 STIS/N ACCUM 0.2X0.0 E230M 2269 1 2088 S UV-MAM 6 A Comments: 1 orbit ------------------------------------------------------------------------------------------------------------------------------------ 40 HD168476 STIS/N ACCUM 0.2X0.0 E230M 2269 1 3165 S UV-MAM 6 A Comments: 1 orbit ------------------------------------------------------------------------------------------------------------------------------------ 9417( 2) - 02/14/02 13:39 - [ 9] Visit: 06 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Visit 6 of 6 for HD225642 Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 HD225642 STIS/C ACQ F28X50O MIRROR ACQTYPE=POINT 1 1 S CD II Comments: ACQ for 23 S and less, as estimated from ETC, avoids saturation. ------------------------------------------------------------------------------------------------------------------------------------ 20 HD225642 STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 2 S CD K 5ND Comments: PEAKUP for 30 S and less, as estimated from ETC, avoids saturation. ------------------------------------------------------------------------------------------------------------------------------------ 30 HD225642 STIS/N ACCUM 0.2X0.0 E230M 2269 1 1874 S UV-MAM 6 A Comments: 1 orbit ------------------------------------------------------------------------------------------------------------------------------------ 40 HD225642 STIS/N ACCUM 0.2X0.0 E230M 2269 1 2975 S UV-MAM 6 A Comments: 1 orbit ------------------------------------------------------------------------------------------------------------------------------------ 9417( 2) - 02/14/02 13:39 - [ 10] Visit: 07 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Visit 7 of 7 for BD+01D4381 Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 BD+01D4381 STIS/C ACQ F28X50O MIRROR ACQTYPE=POINT 1 1 S CD II Comments: ACQ for 21 S and less, as estimated from ETC, avoids saturation. ------------------------------------------------------------------------------------------------------------------------------------ 20 BD+01D4381 STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 1 S CD K 5ND Comments: PEAKUP for 20 S and less, as estimated from ETC, avoids saturation. ------------------------------------------------------------------------------------------------------------------------------------ 30 BD+01D4381 STIS/N ACCUM 0.2X0.0 E230M 2269 1 1852 S UV-MAM 6 A Comments: 1 orbit ------------------------------------------------------------------------------------------------------------------------------------ 40 BD+01D4381 STIS/N ACCUM 0.2X0.0 E230M 2269 2 2929 S UV-MAM 6 A Comments: 2 orbits ------------------------------------------------------------------------------------------------------------------------------------ 9417( 2) - 02/14/02 13:39 - [ 11] Summary Form for Proposal 9417 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50OII 0.2X0.05ND 0.2X0.06 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR E230M ------------------------------------------------------------------------------------------------------------------------------------ Target Names BD+10D2179 HD124448 CD-46D11775 V2244-OPH HD168476 HD225642 BD+01D4381 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 2269 ------------------------------------------------------------------------------------------------------------------------------------