! Hubble Space Telescope Cycle 6 (1996) Phase II Proposal Template ! $Id: 6627,v 9.1 1996/06/26 19:39:59 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: Karla Peterson ! Phone: 410-338-4774 , E-mail: peterson@stsci.edu ! ! This partially completed template was generated from a Phase I proposal. Proposal_Information ! Section 4 Title: LYMAN-ALPHA LINE CENTER CONTINUUM AS A DIAGNOSTIC OF THE WINDS OF BRIGHT A STARS Proposal_Category: GO Scientific_Category: HOT STARS Cycle: 6 Investigators PI_name: ROSINE LALLEMENT PI_Institution: SERVICE D AERONOMIE DU CNRS CoI_Name: CLAUDE CATALA CoI_Institution: OBSERVATOIRE MIDI-PYRENEES Contact: ! Y or N (designate at most one contact) Abstract: ! Free format text (please update) A relatively high residual continuum has been observed in the middle of the H Lyman alpha line of Sirius A (Cycle 1 GHRS observations) while classical models predict a null flux at line center. From very simplified calculations it appears that the scattering of photospheric Lyman alpha photons by expanding neutral H associated with a wind would produce a line center continuum of the order of what is observed, when the mass loss and the terminal velocity of the wind are similar to those independantly deduced from the small blue shifted absorptions in the magnesium lines also observed with the GHRS. We then suggest that, through appropriate sophisticated radiative transfer models,the H Lyman alpha continuum and line shape of the A type stars can be used as valuable tracers of the winds generated by these stars, otherwise very poorly detectable. This method , however, is restricted to very bright objects for the line bottom to be well detected. We propose to perform high signal-to-noise ratio GHRS observations of two other very bright A-type stars to search for similar characteristics at Lyman alpha, with also a new observation of Sirius A with higher Signal to Noise with the aim of disentangling stellar line asymetries from interstellar absorptions. Questions ! Free format text (please update) Observing_Description: The amount of exposure time is estimated by comparison with the 1991 cycle-1 Sirius results.We make the assumption that the line center to continuum ratio is of the same order for the three targets. A signal to noise of about 10 at line center (1215.6 A) was obtained for Sirius after 28M with the G160M. This implies exposure times of about 110M for Vega and 300M for Fomalhaut. The Echelle spectrum of Sirius requires about 4 times the exposure time of the 1991 observation for the signal-to-noise ratio to be about the same per pixel. Because a better signal-to-noise is necessary in order to detect the changes in the slopes due to the interstellar lines, the exposure time amounts to 300M. For each exposure, the geocorona will appear in emission in the middle of the saturated core of the interstellar line, providing a precise wavelength calibration. Real_Time_Justification: Calibration_Justification: ! Move appropriate text from Real_Time_Justification Additional_Comments: Fixed_Targets ! Section 5.1 Target_Number:1 Target_Name:HD216956 Alternate_Names:Alpha Piscis Austrini Description:STAR Position:RA=22H 57M 39.055S +/- 0.0023S, DEC=-29D 37' 20.10" +/- 0.04" Equinox:J2000 RV_or_Z:V=+7 RA_PM:0.0255 +/- 0.001S ! units are seconds of time per year Dec_PM:-0.165 +/- 0.001" ! Units are seconds of arc per year Epoch:J2000 Annual_Parallax:0.144 +/- 0.007 Flux:V=1.166 +/- 0.019, ! Include at least V and B-V B-V=0.088 +/- 0.011 ! This is a template for a single visit containing a single exposure ! Repeat exposure and visit blocks as needed Visits ! Section 6 Visit_Number:01 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