7753( 7) - 10/20/98 14:30 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7753 Version: 7 Check-in Date: 20-Oct-1998 14:28:57 1.Proposal Title: White dwarf companions of Barium and CH peculiar Stars ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO/CAR 7 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Erika Bohm-Vitense University of Washington CoI: Kenneth Carpenter Lasp/Goddard Space Flight Center, Code 681 N CoI: Rich Robinson CSC at Goddard Space Flight Center, Code N 681 CoI: Tom Ake CSC at Goddard Space Flight Center, Code N 681 CoI: Jeff Brown University of Washington N ------------------------------------------------------------------------------------ 5. Abstract In 1980 McClure et al.(ApJ 238, L35) discovered that all Ba stars show radial velocity variations indicative of their binary nature. These authors already suspected that the companions are white dwarfs. White dwarf companions were indeed detected for the Ba star zeta Cap and the mild Ba star zeta Cyg (Boehm-Vitense 1980, ApJ 239, L79) by means of IUE observations. Evidence for a high temperature radiation field was seen in the spectra of the mild Ba stars HR1016, 16Ser and 56UMa. If present, the white dwarf companions are too faint to be seen with IUE. We would like to look for them now with HST. It seems to us to be very important to check whether indeed all Ba stars have white dwarf companions. If so this makes it highly probable that the peculiar abundances are due to mass transfer from a very luminous companion to the present Ba star. After losing its envelope the luminous companion was left as the present white dwarf. This opens up the possibility that other peculiar abundances seen in other peculiar stars like the CH stars or perhaps also the weak G band stars might also be due to mass transfer. On the other hand if the white dwarfs are not found for all Ba stars we may have to look for other processes, that could bring to the surface of these stars material which has experienced the slow neutron capture process. ------------------------------------------------------------------------------------ 7753( 7) - 10/20/98 14:30 - [ 2] Observations Description ------------------------ We would like to observe the target Ba and some subgiant CH peculiar stars with the GHRS and the G140L in the 2" aperture in order to detect the white dwarf companions which are believed to be present. For the population I giants all the white dwarf companions should be observable, because they have not yet had time to cool down below 9500K. The GHRS appears to be the only instrument with which this can be done, because the filters for the WFPC2 have red leaks and so has the FOS. Since the white dwarfs are expected to be fainter by about 10 to 12 magnitudes than the Ba stars the scattered red light of the Ba stars would make it impossible to see the white dwarfs, even though the energy emitted in the UV by the Ba stars is expected to be low enough that it should not cause any problems. In order to make sure of this and to be able to correct for any UV light perhaps emitted by chromospheres of the Ba stars, we will need also observations of standard comparison stars known to have no companions. In this way we can check whether there is any continuous chromospheric emission, which has to be subtracted from the observed flux in order to find the continuum due to the white dwarf companion. (Any chromospheric emission of the Ba stars, continuous or line emission, would also give us a wrong UV signal for a possible white dwarf companion if we would attempt to use the WFPC2). The G140L appears to be sensitive enough to observe these faint stars and also give information about the energy distribution for the white dwarfs, from which their temperatures and ages can be determined. We may want to use the rapid read out method to reduce the noise. During the spare time in the acquisition orbit we will observe the MgII line region with the G270M. This will give us information about the chromospheres of these peculiar stars and possibly about circumstellar material. For the standard stars we need exposure levels comparable to the ones estimated for the Ba stars of about equal brightness in order to see whether the Ba stars show intrinsic excess flux. Real Time Justification ----------------------- IUE studies have been made several years ago to look for these companions. While a few white dwarf companions have been seen most of the Ba stars are too far away for cool white dwarf companions to be detected by IUE. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Paper Products: Media: ELECTRONIC Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 7753( 7) - 10/20/98 14:30 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD65699-B Star, DA RA=7H 59M 05.731S +/- 0.1S, DEC= J2000 V=11 V = 16.1+/-3 -23D 18' 37.65" +/- 0.1" B-V = 0.00+/-0.15 Comments: We want to observe the white dwarf companion to the K2III star, which has V=5.1, B-V=1.12. The WD companion has not yet been seen. (Coordinates are from Hipparcos Input Catalog.) Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 0.000 0.001 0.001 7753( 7) - 10/20/98 14:30 - [ 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 ------------------------------------------------------------------------------------------------------------------------------------ 11 HD65699-B STIS/C ACQ F28X50O MIRROR ACQTYPE=POINT 1 0.1 S ONBOARD ACQUISITION FOR CD II 12-17 Comments: WE WANT TO OBSERVE THE WHITE DWARF COMPANION TO THE K2III STAR, WHICH HAS V=5.11 ------------------------------------------------------------------------------------------------------------------------------------ 12 HD65699-B STIS/C ACQ/PEA 52X0.2 G230MB 2794 1 1.0 S ONBOARD ACQuisition FOR CD K 13-17 ------------------------------------------------------------------------------------------------------------------------------------ 13 HD65699-B STIS/N ACCUM 52X0.2 G230M 2818 2 180 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 14 HD65699-B STIS/F ACCUM 52X0.2 G140L 1425 2 6.0 M UV-MAM A Comments: END ORBIT ------------------------------------------------------------------------------------------------------------------------------------ 15 HD65699-B STIS/F ACCUM 52X0.2 G140L 1425 3 14.0 M UV-MAM A Comments: END ORBIT ------------------------------------------------------------------------------------------------------------------------------------ 16 HD65699-B STIS/F ACCUM 52X0.2 G140L 1425 3 14.0 M UV-MAM A Comments: END ORBIT ------------------------------------------------------------------------------------------------------------------------------------ 17 HD65699-B STIS/F ACCUM 52X0.2 G140L 1425 3 14.0 M UV-MAM A Comments: END ORBIT ------------------------------------------------------------------------------------------------------------------------------------ 7753( 7) - 10/20/98 14:30 - [ 5] Summary Form for Proposal 7753 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50OII 52X0.2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/NUV-MAMA STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO/CAR ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQUISITION FOR 12-17 ONBOARD ACQuisition FOR 13-17 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G230MB G230M G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD65699-B ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 2794 2818 1425 ------------------------------------------------------------------------------------------------------------------------------------