7477( 6) - 03/01/99 10:41 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7477 Version: 6 Check-in Date: 01-Mar-1999 10:40:52 1.Proposal Title: DUST FORMATION AROUND R CORONAE BOREALIS STARS: WHERE IS THE CO? ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 7 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Geoffrey Clayton Louisiana State University CoI: W. A. Lawson Australian Defence Force Academy N CoI: T. R. Ayres University of Colorado N CoI: J. S. Drilling Louisiana State University N CoI: P. Woitke TU Berlin N ------------------------------------------------------------------------------------ 5. Abstract It has been known for 60 years that the declines of R Coronae Borealis (RCB) stars are caused by circumstellar dust formation. The declines occur suddenly and without warning. No spectroscopic changes have yet been noted near the beginning of the decline, which might be linked to the cooling gas that must be condensing to form the dust. The mechanism of mass loss and dust formation is still a mystery. New observational evidence along with models of the carbon chemistry around RCB stars suggest that dust may condense close to the star. Shocks propagating through the outer atmospheres encourage non-equilibrium conditions where the conditions for carbon nucleation may be present. We propose to use STIS to search for a spectroscopic signature of the dust formation in these enigmatic stars, namely carbon monoxide (CO) emission in the UV. This abundant molecule is thought to be a critical gas coolant, yet CO has never been detected in an RCB star. V854 Cen and RY Sgr are the only two RCB stars with well defined pulsation cycles, linked to the time of dust formation. Spectra of these stars will be obtained at phase 0.0 of their pulsation cycles, 43.2 and 37.8 days, respectively when we know dust is forming. HST is required to obtain the ultraviolet spectra for this program. The program can be carried out equally well when the star is at maximum light or in decline, and there are 8 pulsation cycles of each star per year available for scheduling purposes. ------------------------------------------------------------------------------------ 7477( 6) - 03/01/99 10:41 - [ 2] Observations Description ------------------------ In the FUV region, first-order disperser G140L with the 0.5*52 slit provides high sensitivity and adequate resolving power. The brightest feature is the C II Lambda1335 multiplet. See Figure 1. Its flux density (stronger component) is ~ 4times10^-14 ergs cm^-2 s^-1 AA^-1 (for FWHM~ 1 Angstrom, the approximate resolution of G140L). The C II count rate in that configuration will be ~ 1.4 s^-1. An observation of ~ 73 min duration would yield S/N~ 70 on the C II multiplet, and be capable of securely detecting (5 Sigma level) features at a flux density two orders of magnitude fainter. The observation would be carried out as follows. The initial Guide Star ACQ would require 9 min; a CCD-ACQ, 10 min. The exposure would be started at that point, and continued up to the Earth occultation in the second orbit. Given the 10 min overhead for camera operations, and the 6 min for GS re-ACQ at the beginning of the second orbit, approximately 73 min would be available for the exposure. No PEAKUP likely would be required for the second orbit. It is not clear whether auto-WAVE would be required for these observations. Thus, two orbits would be required for each of the targets. Real Time Justification ----------------------- The pulsational period of V854 Cen is 43.2 days (Lawson et al. 1992) and that of RY Sgr is 37.8 days (Lawson & Cottrell 1990). Therefore, while the observations required for this program are time-critical, there are 8 pulsational cycles for each star per year. Any cycle may be chosen for scheduling purposes. THIS PROGRAM CAN BE ACCOMPLISHED EQUALLY WELL AT MAXIMUM LIGHT OR IN DECLINE. The ephemeris for V854 is: JD (phase=0.5) = 2447422.2 + 43.2N where N is the number of cycles. The ephemeris for RY Sgr is: JD (phase=0.5) = 2433905.39 + 37.78N where N is the number of cycles. The observations for each star should take place at phase 0.5+/- 0.10 (+/-4 days). W. A. Lawson will request simultaneous time at Mt. Stromlo Observatory to obtain high dispersion spectra. We will request service photometry at optical and infrared wavelengths at Mount John University Observatory, New Zealand and Sutherland, South Africa, so that the brightness of the star and infrared excess will be well documented. Calibration Justification ------------------------- Additional Comments ------------------- To get around an RPSS bug I have altered the phase information for both stars. ------------------------------------------------------------------------------------ 7477( 6) - 03/01/99 10:41 - [ 3] Data Distribution Paper Products: Media: ELECTRONIC Blocking Factor: 10 Ship To: *Dept. of Physics and Astronomy*Louisiana State University*Baton Rouge*70803 Ship Via: Email: GCLAYTON@FENWAY.PHYS.LSU.EDU ------------------------------------------------------------------------------------ 7477( 6) - 03/01/99 10:41 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 V854-CEN STAR, POST-AGB STAR, RA=14H 34M 49.43S +/- 0.41S, J2000 V = 7.0 IRREGULAR VARIABLE DEC=-39D 33' 19.7" +/- 0.41", B-V = 0.6 PLATE-ID=0163 F(1335)=1e-14 Comments: This is an irregular variable. The V magnitude can fade by several magnitudes. The flux in the wavelength region of interest will not change significantly. Very accurate coordinates could not be obtained because the star was too bright on the PSS. Coordinates taken from the GSC, which listed the magnitude as 10.89. (DCT) 2 HD180093 STAR, POST-AGB STAR, RA=19H 16M 32.78S +/- 0.05S, J2000 V = 6.5 IRREGULAR VARIABLE DEC=-33D 31' 20.4" +/- 0.05" B-V = 0.6 F(1335)=1e-14 Comments: This is an irregular variable. The V magnitude can fade by several magnitudes. The flux in the wavelength region of interest will not change significantly. Very accurate coordinates could not be obtained because the star was too bright on the PSS. Coordinates taken from Hipparcos Input Catalog (in the GSC), which listed the magnitude as 5.8. GSC star 07427-02655. (DCT) 7477( 6) - 03/01/99 10:41 - [ 5] Visit: 01 Visit Priority: Visit Requirements: PERIOD 43.2D AND ZERO-PHASE JD2447422.2 On Hold Comments: Additional Comments: Visit should take place within +/- 4 Days of phase 0.5 Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 V854-CEN STIS/C ACQ F25ND3 MIRROR 1 0.1 S ONBOARD ACQuisition FOR CD 02 PHASE 0.40 TO 0.60 ------------------------------------------------------------------------------------------------------------------------------------ 2 V854-CEN STIS/F ACCUM 52X0.5 G140L 1425 2 30 M EXPAND PHASE 0.40 TO 0.60 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 7477( 6) - 03/01/99 10:41 - [ 6] Visit: 02 Visit Priority: Visit Requirements: PERIOD 37.78D AND ZERO-PHASE JD2433905.39 On Hold Comments: Additional Comments: Visit should take place within +/- 4 Days of phase 0.5 Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 3 HD180093 STIS/C ACQ F25ND3 MIRROR 1 0.1 S ONBOARD ACQuisition FOR CD 04 PHASE 0.40 TO 0.60 ------------------------------------------------------------------------------------------------------------------------------------ 4 HD180093 STIS/F ACCUM 52X0.5 G140L 1425 2 30 M EXPAND PHASE 0.40 TO 0.60 UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 7477( 6) - 03/01/99 10:41 - [ 7] Summary Form for Proposal 7477 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F25ND3 52X0.5 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PERIOD 43.2D AND ZERO-PHASE JD2447422.2 ONBOARD ACQuisition FOR 02 PHASE 0.40 TO 0.60 EXPAND PHASE 0.40 TO 0.60 PERIOD 37.78D AND ZERO-PHASE JD2433905.39 ONBOARD ACQuisition FOR 04 PHASE 0.40 TO 0.60 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names V854-CEN HD180093 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1425 ------------------------------------------------------------------------------------------------------------------------------------