0 Assigned ID: 725 ----- Attempting Submission 1 (Fri Apr 10 19:44:21 GMT 2015) ----- 0 ----- Attempting Submission 1 (Thu Jul 23 06:47:09 GMT 2015) ----- We have recently detected strong, steady radio emission from the well-known X-ray source X9 in the globular cluster 47 Tuc. The level of radio emission rules out the previous interpretation of the source as a cataclysmic variable, and instead suggests that it hosts a quiescently accreting stellar-mass black hole. An existing far-UV spectrum shows shows a strong C IV 1550 emission line, but no sign of He II 1640 emission. Narrow-band HST photometry exhibits no Halpha excess (down to an equivalent width limit of >~ -10A) and Chandra X-ray observations show an unusual feature that is likely attributable to O VIII emission. All of this evidence, as well as the unusually high X-ray luminosity of the system, points to X9 being an ultracompact binary in which a stellar-mass black hole accretes material from a white dwarf -- which if confirmed would be the first such system ever discovered. Here, we request HST observations to obtain a broad-band optical spectrum of X9 to confirm or reject the ultracompact nature of the system. The resulting data will also be used to evaluate the optimal strategy for determining the system parameters, in particular the orbital period. The main goal of the observations is to search for emission lines (H, He, C, and O) that will help classify the donor star in this candidate ultra-compact black hole binary. A secondary goal is to measure and model the overall SED of the binary. We will first acquire a bright (V~12.4) red giant that is 17" away and then do an offset to the main target, peaking up sing the 52x0.1E1 aperture. The target object has a nominal V~19.8 but is variable, with the faintest recorded mag at V~21.4; we have chosen a peakup exposure time as a compromise in case the object is fainter than expected, but will not saturate the detector even if brighter than expected. All data are taken in a single 4-orbit visit. Two orbits are used on the G430L grating and two with the G750L grating, with 3 CR-SPLITs in all but the first orbit. We have added fringe flats in occultation to the G750L exposures. To improve wavelength calibration, we have added several GO-WAVECALs around the G430L observations. HOT STARS 12 false false false false SUPPORTED STAR LMXB NO Position is from an HST/ACS F606W image calibrated to ICRS using a large sample of 2MASS stars. X9 V1 J2000 J2000 STAR K III-I NO Position is from an HST/ACS F606W image calibrated to ICRS using a large sample of 2MASS stars. X9 V1 J2000 J2000 STIS/CCD Spectroscopic No No G430L 4300 STIS/CCD Spectroscopic No No G750L 7751 1437633966940 /private/var/folders/x3/0522zlt5035b_55jb8vwn1j00000gn/T/OPVisit5706725340714273318.xml The scheduling data was generated by CASM 23.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 14203 :visit-id "02" :proposal-version -1 :trans-version "20150609" :date "23-Jul-2015 14:46:06.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 4 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 405328 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 14203 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 14203 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3263 :al-overhead-at-end 72 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3596 :pcs-gap 0 ) (Tic-Orbit :proposal-id 14203 :visit-id "02" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3372 :al-overhead-at-end 75 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3596 :pcs-gap 0 ) (Tic-Orbit :proposal-id 14203 :visit-id "02" :orbit-number 3 :pcs-time 222 :si-vis-utilization 3372 :al-overhead-at-end 72 :internal-dur-at-end 225 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3596 :pcs-gap 0 ) (Tic-Orbit :proposal-id 14203 :visit-id "02" :orbit-number 4 :pcs-time 222 :si-vis-utilization 3372 :al-overhead-at-end 0 :internal-dur-at-end 624 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3596 :pcs-gap 0 ) true 4 0