----- Attempting Submission 1 (Mon Apr 13 23:07:15 GMT 2009) ----- Phase II Proposal 12000 (12000.apt) successfully submitted. ----- Attempting Submission 2 (Tue Apr 14 18:00:43 GMT 2009) ----- APT keeps insisting we have used zero orbits but were allocated one orbit. But, we HAVE used exactly one orbit! So, we are submitting anyway. -- Howard Bond Assigned ID: 3011 ----- Attempting Submission 1 (Wed Apr 08 00:31:59 GMT 2009) ----- 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.

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) 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. ISM AND CIRCUMSTELLAR MATTER 0 false 0.0 0.0 false false false false false SUPPORTED STAR CARBON STAR Star is normally at V=5.9, but is currently (April 2009) in a deep minimum at about V=15. J2000 15 48 34.4100 +28 09 24.20 J2000 WFPC2 Imaging No F555W WFPC2 Imaging No F814W The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. /var/tmp/OPVisit1500.xml 1239731198474 (Tic-Visit :proposal-id 12000 :visit-id "01" :proposal-version -1 :trans-version "20090130" :date "14-Apr-2009 13:46:37.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 403344 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12000 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12000 :visit-id "01" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2700 :al-overhead-at-end 120 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3149 :pcs-gap 0 ) true 1 0