9228( 2) - 02/14/01 12:47 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9228 Version: 2 Check-in Date: 14-Feb-2001 12:46:21 1.Proposal Title: Ultraviolet Spectroscopy of R Coronae Borealis Stars -- Broad Lines from an Accretion Disc? ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 10 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: David Lambert University of Texas at Austin CoI: Prof. N. Kameswara Rao Indian Institute of Astrophysics N CoI: Assoc. Prof. Geoffrey Clayton Louisiana State University N CoI: Assoc. Prof. Peter L. Cottrell University of Canterbury N ------------------------------------------------------------------------------------ 5. Abstract STIS spectra of three R Coronae Borealis (RCB) stars will provide novel data on hot gas near these stars; such data can be obtained only from HST. RCBs are hydrogen- deficient and fade at unpredictable times as a carbon soot cloud obscures the star. Optical spectra taken when a star has faded reveal an emission line spectrum containing sharp (FWHM ~15 km s^-1) and broad (FWHM ~250 km s^-1) lines. The latter are of much higher excitation than the former. For R CrB, it has been suggested that the broad lines arise from an accretion disk around a compact secondary. These optical lines are visible only during the infrequent extreme fadings of a RCB. Although IUE spectra reveal high-excitation emission lines at maximum light, the IUE spectra lack the spectral resolution to distinguish broad from sharp lines. STIS spectra will resolve the broad-line from a sharp-line component, and, in the case, of R CrB, where repeat visits are requested, be used to search for velocity variations as the companion orbits the RCB. In addition, the line intensity ratios will provide new estimates of the physical conditions of the gas emitting the broad lines. This proposal may help to answer the question -- How are RCBs formed? And this answer may show that, although RCBs are rare, many low mass stars evolve through the RCB on their path to extinction as a white dwarf. ------------------------------------------------------------------------------------ 9228( 2) - 02/14/01 12:47 - [ 2] Observations Description ------------------------ Archived IUE spectra have been examined to estimate line and continuum fluxes. Line fluxes F_line are quoted in erg cm^-2 s^-1. All IUE spectra were at low resolution and, hence, cannot be used to separate sharp from broad emission lines. It is safe to assume from the known membership of the sharp optical lines that the C II, C IV, and C IV lines are broad lines which will be resolved with G140M and G230M. In estimating exposure times with the ETC we have assumed the lines to have a width FWHM = 250 km s^-1. A S/N = 20 is our target. Overheads of 24 min. per orbit assumed. R CrB: Line fluxes are from our scrutiny of the many archived IUE spectra. The C II lines are seen with an apparently variable flux at a mean flux of F_line = 1.2 * 10^-13 requiring 24m for S/N =20 or 1 orbit given the overheads. These lines are expected to be `broad' without a `sharp' component based on our observation of broad N II lines. Two observations in Cycle 10 separated by several months are requested to search for velocity differences. Real Time Justification ----------------------- This program can be performed equally well in decline or at maximum light. The declines happen at irregular intervals but we shall continue monitoring the stars at Mt. John Observatory, as well as continuing to sift reports from amateur observers worldwide. In deep declines, it will likely be necessary to make changes in the acquisition exposures. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9228( 2) - 02/14/01 12:47 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD141527 STAR RA=15H 48M 34.41S +/- 0.0", J2000 V = 5.8 DEC=+28D 09' 24.3" +/- 0.0" B-V = 0.60 F(1335)=1.2e-13 Coordinate Source: HIPPARCOS/TYCHO_CATALOGUE 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. 9228( 2) - 02/14/01 12:47 - [ 4] Visit: 01 Visit Priority: Visit Requirements: BETWEEN 1-DEC-2001 AND 28-FEB-2002 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 HD141527 STIS/C ACQ F25ND3 MIRROR ACQTYPE=POINT 1 0.5 S CD ------------------------------------------------------------------------------------------------------------------------------------ 2 HD141527 STIS/F ACCUM 52X0.2 G140M 1321 1 35 M UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9228( 2) - 02/14/01 12:47 - [ 5] Visit: 02 Visit Priority: Visit Requirements: BETWEEN 1-May-2002 AND 31-JUL-2002 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 ------------------------------------------------------------------------------------------------------------------------------------ 1 HD141527 STIS/C ACQ F25ND3 MIRROR ACQTYPE=POINT 1 0.5 S CD ------------------------------------------------------------------------------------------------------------------------------------ 2 HD141527 STIS/F ACCUM 52X0.2 G140M 1321 1 35 M UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 9228( 2) - 02/14/01 12:47 - [ 6] Summary Form for Proposal 9228 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F25ND3 52X0.2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 1-DEC-2001 AND 28-FEB-2002 BETWEEN 1-May-2002 AND 31-JUL-2002 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G140M ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD141527 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1321 ------------------------------------------------------------------------------------------------------------------------------------