12000( 2) - 14-Apr-2009 18:14:29 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 12000 Version: 2 Check-in Time: 14-Apr-2009 18:14:29 STScI Edit Number: 0 Title The Natural Coronagraph of R Coronae Borealis ------------------------------------------------------------------------------------ Type Cycle GO/DD 16 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Geoffrey C. Clayton Louisiana State University and A & M College CoI: Dr. Howard E. Bond Space Telescope Science Institute N CoI: Dr. Orsola De Marco Macquarie University N CoI: Dr. Thomas R. Geballe Gemini Observatory, Northern Operations N CoI: Dr. Ben E. Sugerman Goucher College N ------------------------------------------------------------------------------------ Abstract We propose HST/WFPC2 imaging to take advantage of a recent unique and dramatic fading of the unusual variable star R Coronae Borealis. R CrB has temporarily dropped 9 mag due to formation of a dust cloud above the photosphere in the line of sight. Since the dust does not block the star as seen from other directions, it acts as a "natural coronagraph, " allowing us to explore the nearby circumstellar environment at HST resolution. R Coronae Borealis (RCB) stars are rare hydrogen-deficient carbon-rich supergiants. Evolutionary scenarios proposed to account for their origin include a merger of two white dwarfs (the double-degenerate or DD mode), or a final helium-shell flash in a single PN central star (FF mode). We have recently found a large overabundance of oxygen-18 in several RCB stars, favoring the DD merger scenario; however, the presence of Li in the atmospheres of four RCB stars, including R CrB itself, favors the FF scenario. The presence or absence of circumstellar material, and the morphology of this material if it exists, provide a fossil record of previous evolutionary stages. In particular, we expect to see evidence for an old PN shell in the FF stars, but not in DD merger descendants. Our recent Gemini optical images of R CrB tantalizingly suggest circumstellar material very close to the star, but compromised by ground-based seeing and relatively low S/N. We propose HST/WFPC2 images to confirm this material at higher spatial resolution and signal than attainable from the ground. ------------------------------------------------------------------------------------ Observations Description ------------------------ We will use WFPC2 to carry out direct imaging of the hydrogen-deficient star R CrB, which is currently (April 2009) in a deep minimum, more than 9 mag below its normal brightness. The aim is to study ejecta and possible companion stars in the immediate vicinity of R CrB, which are normally obscured by the wings of the stellar image when the star is at its usual magnitude of ~5.9. We will place the target near the corner of the PC chip (for less degradation by CTE) and take dithered exposures in the broad-band V (F555W) and I (F814W) 12000( 2) - 14-Apr-2009 18:14:29 - [ 2] filters. Short exposures of 7 and 16 sec will reach about 50% of saturation. These will be followed by exposures of 120 sec (F555W) and 160-200 sec (F814W), which will be saturated by factors of ~5 to 8, obscuring a few pixels around the star but reaching more deeply into the immediate surroundings. We are using CLOCKS=YES throughout, since this yields less time lost to overheads. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 12000( 2) - 14-Apr-2009 18:14:29 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 R-CRB STAR, CARBON STAR RA=15H48M34.4149S +/- 0.1", J2000 V = 15 DEC=+28D09'24.30" +/- 0.1" Reference Frame: ICRS Comments: Star is normally at V=5.9, but is currently (April 2009) in a deep minimum at about V=15. ------------------------------------------------------------------------------------------------------------------------------------ 12000( 2) - 14-Apr-2009 18:14:29 - [ 4] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 R-CRB WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=7, CLOCKS=YES, 1 7 S POS TARG -7, -7 CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 2 R-CRB WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=7, CLOCKS=YES, 1 120 S POS TARG -7, -7 CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 3 R-CRB WFPC2 IMAGE PC1-FIX F814W ATD-GAIN=7, CLOCKS=YES, 1 16 S POS TARG -7, -7 CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 4 R-CRB WFPC2 IMAGE PC1-FIX F814W ATD-GAIN=7, CLOCKS=YES, 1 160 S POS TARG -7, -7 CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 5 R-CRB WFPC2 IMAGE PC1-FIX F814W ATD-GAIN=7, CLOCKS=YES, 1 160 S POS TARG -6.77215, CR-SPLIT=NO -6.886075 ------------------------------------------------------------------------------------------------------------------------------------ 6 R-CRB WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=7, CLOCKS=YES, 1 120 S POS TARG -6.77215, CR-SPLIT=NO -6.886075 ------------------------------------------------------------------------------------------------------------------------------------ 7 R-CRB WFPC2 IMAGE PC1-FIX F814W ATD-GAIN=7, CLOCKS=YES, 1 160 S POS TARG -6.658225, CR-SPLIT=NO -6.658225 ------------------------------------------------------------------------------------------------------------------------------------ 8 R-CRB WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=7, CLOCKS=YES, 1 120 S POS TARG -6.658225, CR-SPLIT=NO -6.658225 ------------------------------------------------------------------------------------------------------------------------------------ 9 R-CRB WFPC2 IMAGE PC1-FIX F555W ATD-GAIN=7, CLOCKS=YES, 1 120 S POS TARG -6.886075, CR-SPLIT=NO -6.77215 ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ R-CRB 1 WFPC2 IMAGE PC1-FIX F555W none none none none 1 N/A R-CRB 2 WFPC2 IMAGE PC1-FIX F555W none none none none 1 N/A R-CRB 3 WFPC2 IMAGE PC1-FIX F814W none none none none 1 N/A R-CRB 4 WFPC2 IMAGE PC1-FIX F814W none none none none 1 N/A R-CRB 5 WFPC2 IMAGE PC1-FIX F814W none none none none 1 N/A R-CRB 6 WFPC2 IMAGE PC1-FIX F555W none none none none 1 N/A R-CRB 7 WFPC2 IMAGE PC1-FIX F814W none none none none 1 N/A R-CRB 8 WFPC2 IMAGE PC1-FIX F555W none none none none 1 N/A R-CRB 9 WFPC2 IMAGE PC1-FIX F555W none none none none 1 N/A 12000( 2) - 14-Apr-2009 18:14:29 - [ 5] Summary Form for Proposal 12000 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PC1-FIX ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ATD-GAIN=7, CLOCKS=YES, CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements POS TARG -6.658225, -6.658225, POS TARG -6.77215, -6.886075, POS TARG -6.886075, -6.77215, POS TARG -7, -7 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names R-CRB ------------------------------------------------------------------------------------------------------------------------------------