! Proposal 6656, submission 1 ! PI: Dr. Judith Provencal ! Received Wed Feb 7 15:15:59 EST 1996 ! From: jlp@UDel.Edu ! Hubble Space Telescope Cycle 6 (1996) Phase II Proposal Template ! $Id: 6656,v 5.1 1996/07/16 17:57:46 pepsa Exp $ ! Hubble Space Telescope Cycle 6 (1996) Phase II Proposal Template ! $Id: 6656,v 5.1 1996/07/16 17:57:46 pepsa Exp $ ! ! Refer to the HST Phase II Proposal Instructions to fill this out ! ! Anything after a "!" is ignored, and may be deleted ! ! All keywords with multiple entries are comma delimited except the ! Visit_Requirements and Special_Requirements keywords which can be ! delimited with carriage returns or semi-colons, but not commas ! ! For help call your Program Coordinator: Manning ! Phone: 410-338-4456 , E-mail: manning@stsci.edu ! ! This partially completed template was generated from a Phase I proposal. ! Name of Phase I Proposal: archive-0694.provencal.prop ! Date generated: Fri Dec 22 16:54:35 EST 1995 ! Proposal_Information ! Section 4 Title: Hydrogen, Interstellar Accretion, and Hot Helium Rich White Dwarfs Proposal_Category: GO Scientific_Category: HOT STARS Cycle: 6 Investigators PI_name: Dr. Judith Provencal PI_Institution: University of Delaware CoI_Name: Prof. Harry Shipman CoI_Institution: University of Delaware Contact: ! Y or N (designate at most one contact) Abstract: ! Free format text (please update) The study of white dwarf structure provides valuable insights into the final stages of stellar evolution. Recently, rapid developments in UV spectroscopy have altered our understanding of these simplest of stars. It is now clear that hydrogen (DA) and helium (DB) white dwarfs follow different evolutionary paths. While it appears that once a DA is formed, it remains a DA throughout its evolution, our understanding of DB evolution is particularly sketchy. About 20\% of all DBs contain traces of hydrogen, and we observe a gap in DB distribution between 30,000\ rmK< rmT_eff<45,000\ rmK. Current theory predicts that, at these temperatures, hydrogen floats to the surface, masking the DB white dwarf beneath a thin hydrogen photosphere. In 1992, HST obtained high resolution spectra, centered on 1215\ Angstrom, of the prototype DBV PG1645+325 (GD358), detecting broad shallow absorption wings of hydrogen surrounding the geocoronal emission. Initial results indicate that PG1645+325, rmT_eff=\ 27,000 K, does not have enough hydrogen to have been a DA in the DB gap. We propose a search for hydrogen in hot DB white dwarfs, to test theories of DB evolution and address the question of the uniqueness of PG1645+325. Questions ! Free format text (please update) Observing_Description: The observations will be done with GHRS in ACCUM mode, centered on 1215\ Angstrom, using the small science aperture to reduce geocoronal emission. We have calculated the exposure times of the other targets using previous observations of PG1645+325 as a flux model. The exposure times are calculated to give a signal to noise ratio of ~20 (see table). We have submitted a second proposal addressing carbon pollution and convective dredgeup in the hotter DBs, also motivated by earlier HST observations of PG1645+325. Both these proposals deal with the atmospheric structure of DB white dwarfs, yet we felt we were exploring a different aspect of the problem with each proposal. We opted for individual proposals because we felt we could learn something interesting from each separately. Real_Time_Justification: Calibration_Justification: ! Move appropriate text from Real_Time_Justification Additional_Comments: Fixed_Targets ! Section 5.1 Target_Number: 1 Target_Name: GD190 Alternate_Names: PG1542+182 Description: STAR,DB Position: RA=15H 44M 19.45S +/- 0.030S,DEC=+18D 06' 46.38" +/- 0.40", PLATE-ID=00GM Equinox: J2000 RV_or_Z: RA_PM: 0.001 ! Units are seconds of time per year Dec_PM: -0.113 ! Units are seconds of arc per year Epoch: 1982.384033203 Annual_Parallax: Flux: V=14.72, B-V=-0.10 ! Include at least V and B-V Comments: Target_Number: 2 Target_Name: PG0112+104 Alternate_Names: WD0112+104 Description: STAR, DB Position: RA=01H 14M 37.68S +/- 0.030S,DEC=+10D 41' 05.45" +/- 0.40", PLATE-ID=00GR Equinox: J2000 RV_or_Z: RA_PM: ! Units are seconds of time per year Dec_PM: ! Units are seconds of arc per year Epoch: 1982.7950439453 Annual_Parallax: Flux: V=15.33,B-V=-0.03 ! Include at least V and B-V Comments: Solar_System_Targets ! Section 5.2 Target_Number: Target_Name: Description: Level_1: ! Satellite of Sun Level_2: ! Satellite of Level_1 Level_3: ! Satellite of Level_2 Ephem_Uncert: ! Needed for REQ EPHEM CORR sp req Acq_Uncert: ! Needed for SAVE and USE OFFSET sp reqs Window: Flux: ! Include at least V and B-V Comments: Generic_Targets ! Section 5.3 Target_Number: Target_Name: Description: Criteria: Flux: Comments: Scan_Data ! Appendix B Scan_Number: FGS_Scan: Cont_or_Dwell: Dwell_Points: Dwell_Secs: Scan_Width: Scan_Length: Sides_Angle: Number_Lines: Scan_Rate: First_Line_PA: Scan_Frame: Length_Offset: Width_Offset: ! This is a template for a single visit containing a single exposure ! Repeat exposure and visit blocks as needed Visits ! Section 6 Visit_Number: 1 Visit_Requirements: ! Section 7.1 ! Uncomment or copy visit level special requirements needed ! Most of these requirements (including ORIENT) will limit scheduling ! PCS MODE [Fine | Gyro] ! GUIDing TOLerance ! DROP TO GYRO IF NECESSARY [NO REACQuisition] ! ORIENTation TO ! ORIENTation TO FROM ! ORIENTation TO FROM NOMINAL ! SAME ORIENTation AS ! CVZ ! PARallel ! SCHEDulability ! AFTER [BY [TO ]] ! AFTER ! BEFORE ! BETWEEN AND ! GROUP WITHIN