6476( 7) - 06/19/96 10:31 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6476 Version: 7 Check-in Date: 19-Jun-1996 10:28:17 1.Proposal Title: A study of circumstellar material formed in a hydrogen-deficient environment ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle HOT STARS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: John Drilling Louisiana State University CoI: James Hecht Aerospace Corporation N CoI: Simon Jeffery University of St Andrews N CoI: Geoffrey Clayton University of Colorado N ------------------------------------------------------------------------------------ 6. Abstract Observing time is requested to obtain low-resolution UV spectra of the hot R CrB star V348 Sgr at maximum light and deep into the ascending portion of its light curve. These spectra will be used along with simultaneous optical spectrophotometry to determine the nature of newly-formed circumstellar material around this star. V348 Sgr is the only object for which an accurate extinction curve for freshly ejected dust can be determined entirely from observation to wavelengths shorter than 2500 Angstrom. An intriguing possibility is the that signature of fullerenes may be identifiable in the extinction curve obtained from these observations. ------------------------------------------------------------------------------------ 6476( 7) - 06/19/96 10:31 - [ 2] Observations Description ------------------------ Strategy has been change to observe the target three times for one orbit each. The reason for this is that, although the observation we just got of V348 Sgr is a good one, we did not get it at maximum light as planned, but one magnitude below maximum. Since the scientific goal of the proposal is to obtain the extinction curve of V348 Sgr, failure to obtain a spectrum at maximum light will be disasterous. Executing Visit 1 at maximum light would be a waste, since the maximum practical signal-to-noise is obtainable in one orbit, whereas executing Visit 2 two more times would give us twice the chance of obtaining the spectrum at maximum light and hopefully an additional spectrum during a minimum, which will improve the accuracy of the extinction curve. Original description: We require low resolution spectra of V348 Sgr covering the entire space ultraviolet accessible to HST, including well- exposed images covering the region of the 2500Angstrom\\ absorption bump, and as close to Ly-Alpha as possible. These must be obtained when the star reaches V=13.5 following an absorption event, and following its subsequent return to maximum (V=12.2). Since 2500Angstrom\\ lies at the upper and lower limits of gratings G160L and G270H respectively, the most efficient way to obtain the desired observations when V348 Sgr reaches V=13.5 is to obtain an exposure with the G270H grating during the first of two adjacent orbits. We can fulfill the conditions for fast target acquisition with the 1 arcsec aperture, and so will be able to expose for 30 minutes, giving a minimum S:N (7 Angstrom) ~20:1. During the second orbit we shall expose for 41 minutes with the G160L grating to obtain similar S:N. A third orbit will be required to obtain the spectrum after V348 Sgr has returned to maximum light. Shorter exposures with both gratings (G270H and G160L) will be made which will provide S:N>~100:1. Visit & Grating & Lambda(Angstrom) & Flux(10^-16) & ct s^-1diode^-1 &Expo. (m)& S/N (7Angstrom) & Orbits Visit 1 & G270H & 2500 & 4 & 0.07 & 30 & 20 & 1 & G160L & 2500 & 4 & 0.09 & 41 & 20 & 1 Visit 2 & G270H & 2500 & 300 & 23 & 10 & 100 & & G160L & 2500 & 300 & 18 & 14 & 100 & 1 Total Orbits = 3 Real Time Justification ----------------------- The first observations must be made as a target of opportunity since they require V348 Sgr to be obscured by 1.3 magnitudes of dust. The lead time cannot be longer than four weeks. The second observations should be scheduled between four and six weeks later, after the star has returned to maximum light. A network of groundbased observers will be established to monitor V348 Sgr for light declines. The average time between minima for V348 Sgr is about 200 days, so the probability of obtaining the observations is high (>50\\%). Ground-based observations will be coordinated with the HST observations. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6476( 7) - 06/19/96 10:31 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6476( 7) - 06/19/96 10:31 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 V348-SGR STAR RA=18H 40M 19.93S +/- 0.05", 2000 V=+174 V = 13.5+/-1.0 DEC=-22D 54' 28.63" +/- 0.5", B = 13.8+/-1.0 PLATE-ID = 067T F(2500)=4+/-2e-16 Comments: Target measured in GSC by Ron Downes 2 V348-SGR- STAR RA=18H 40M 21.01S +/- 0.05", 2000 V=+174 V = 15.4+/-1.0 OFFSET DEC=-22D 54' 23.6" +/- 0.5", B = 1.4+/-1.0 PLATE-ID = 067T Comments: Target position measured in GSC by Ron Downes. Target magnitude measured from Sky Survey by Ron Downes. 6476( 7) - 06/19/96 10:31 - [ 5] Visit: 01 Visit Requirements: ON HOLD SCHED 100% On Hold Comments: Target of Opportunity 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 V348-SGR-OF FOS/BL ACQ/BIN 4.3 MIRROR 1 7.5 S ONBOARD ACQ FOR 20-30 FSET ARY ------------------------------------------------------------------------------------------------------------------------------------ 20 V348-SGR FOS/BL ACCUM 1.0-PAI G270H 2500 1 8 M R-A ------------------------------------------------------------------------------------------------------------------------------------ 30 V348-SGR FOS/BL ACCUM 1.0-PAI G160L 2500 1 10.33 M R-A ------------------------------------------------------------------------------------------------------------------------------------ 6476( 7) - 06/19/96 10:31 - [ 6] Visit: 02 Visit Requirements: ON HOLD SCHED 100% On Hold Comments: TARGET OF OPPORTUNITY 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 V348-SGR-OF FOS/BL ACQ/BIN 4.3 MIRROR 1 7.5 S ONBOARD ACQ FOR 20-30 FSET ARY ------------------------------------------------------------------------------------------------------------------------------------ 20 V348-SGR FOS/BL ACCUM 1.0-PAI G270H 2500 1 8 M R-A ------------------------------------------------------------------------------------------------------------------------------------ 30 V348-SGR FOS/BL ACCUM 1.0-PAI G160L 2500 1 10.33 M R-A ------------------------------------------------------------------------------------------------------------------------------------ 6476( 7) - 06/19/96 10:31 - [ 7] Visit: 03 Visit Requirements: SCHED 100% 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 V348-SGR-OF FOS/BL ACQ/BIN 4.3 MIRROR 1 7.5 S ONBOARD ACQ FOR 20-30 FSET ARY ------------------------------------------------------------------------------------------------------------------------------------ 20 V348-SGR FOS/BL ACCUM 1.0-PAI G270H 2500 1 8 M R-A ------------------------------------------------------------------------------------------------------------------------------------ 30 V348-SGR FOS/BL ACCUM 1.0-PAI G160L 2500 1 10.33 M R-A ------------------------------------------------------------------------------------------------------------------------------------ 6476( 7) - 06/19/96 10:31 - [ 8] Summary Form for Proposal 6476 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/BL ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/BINARY ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category HOT STARS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ON HOLD SCHED 100% ONBOARD ACQ FOR 20-30 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G270H G160L ------------------------------------------------------------------------------------------------------------------------------------ Target Names V348-SGR-OFFSET V348-SGR ------------------------------------------------------------------------------------------------------------------------------------