6627( 9) - 06/26/96 15:43 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6627 Version: 9 Check-in Date: 26-Jun-1996 15:40:03 1.Proposal Title: LYMAN-ALPHA LINE CENTER CONTINUUM AS A DIAGNOSTIC OF THE WINDS OF BRIGHT A STARS ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle HOT STARS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: ROSINE LALLEMENT SERVICE D AERONOMIE DU CNRS CoI: CLAUDE CATALA OBSERVATOIRE MIDI-PYRENEES N ------------------------------------------------------------------------------------ 6. Abstract 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. ------------------------------------------------------------------------------------ 6627( 9) - 06/26/96 15:43 - [ 2] Observations 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 ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6627( 9) - 06/26/96 15:43 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD216956 STAR RA=22H 57M 39.055S +/- 0.0023S, J2000 V=+7 V = 1.166+/-0.019 DEC=-29D 37' 20.10" +/- 0.04" B-V = 0.088+/-0.011 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) J2000 0.0255 -0.165 0.144 6627( 9) - 06/26/96 15:43 - [ 4] Visit: 01 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 HD216956 HRS ACQ 2.0 MIRROR-A1 SEARCH-SIZE=3,BRIGHT=RETURN, 1 8.1 S ONBOARD ACQ FOR 20 LOCATE=YES Comments: STEP-TIME=.9S, EXPECT 2000 CTS IN STEP ------------------------------------------------------------------------------------------------------------------------------------ 20 HD216956 HRS ACQ/PEA 0.25 MIRROR-A1 SEARCH-SIZE=5 1 22.5 S ONBOARD ACQ FOR 30 KUP Comments: STEP-TIME=.9S, EXPECT 2000 CTS IN STEP ------------------------------------------------------------------------------------------------------------------------------------ 30 HD216956 HRS ACQ/PEA 0.25 MIRROR-A1 SEARCH-SIZE=5 1 22.5 S ONBOARD ACQ FOR 40-60 KUP Comments: STEP-TIME=.9S, EXPECT 2000 CTS IN STEP ------------------------------------------------------------------------------------------------------------------------------------ 40 HD216956 HRS ACCUM 0.25 ECH-A 1213.75 STEP-PATT=7,FP-SPLIT=STD, 3 1740.8 COMB=FOUR ------------------------------------------------------------------------------------------------------------------------------------ 50 HD216956 HRS ACCUM 0.25 ECH-A 1213.75 STEP-PATT=7,FP-SPLIT=STD, 3 1740.8 COMB=FOUR,SPYBAL=YES ------------------------------------------------------------------------------------------------------------------------------------ 60 HD216956 HRS ACCUM 0.25 ECH-A 1213.75 STEP-PATT=7,FP-SPLIT=STD, 3 1740.8 COMB=FOUR,SPYBAL=YES ------------------------------------------------------------------------------------------------------------------------------------ 6627( 9) - 06/26/96 15:43 - [ 5] Summary Form for Proposal 6627 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAKUP ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SEARCH-SIZE=3 BRIGHT=RETURN LOCATE=YES SEARCH-SIZE=5 COMB=FOUR SPYBAL=YES FP-SPLIT=STD ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category HOT STARS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 20 ONBOARD ACQ FOR 30 ONBOARD ACQ FOR 40-60 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-A1 ECH-A ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD216956 ------------------------------------------------------------------------------------------------------------------------------------