0 Assigned ID: 1335 ----- Attempting Submission 1 (Fri Mar 01 00:26:54 GMT 2013) ----- 0 ----- Attempting Submission 1 (Sat Jun 22 10:53:06 GMT 2013) ----- HST Phase II Proposal 13290 (hst2013.apt) successfully submitted. ----- Attempting Submission 2 (Mon Aug 05 10:41:43 GMT 2013) ----- Type Ia supernovae (SN Ia) are the most important standard candles for measuring the expansion history of the universe. The thermonuclear explosion of a white dwarf can explain their observed properties, but neither the progenitor systems nor any stellar remnants have been conclusively identified. Underluminous SN Ia have been proposed to originate from a so-called double-detonation of a white dwarf. After a critical amount of helium is deposited on the surface through accretion from a close companion, the helium is ignited causing a detonation wave that triggers the explosion of the white dwarf itself. The helium star will then be ejected at so large a velocity that it will escape the Galaxy. The predicted properties of this remnant are an excellent match to the so-called hypervelocity star US 708, a hot, helium-rich star moving at more than 750 km/s, sufficient to leave the Galaxy. Here we propose medium-resolution COS spectroscopy to measure the vsini of the hypervelocity He-sdO US 708 for the first time and to search for abundance anomalies caused by pollution through an SN Ia event. This will allow us to test the double-detonation scenario with sdB donor empirically. Using COS in spectroscopic FUV mode with the G140L grating, we aim at taking $2$ orbits of spectroscopy of US\,708 ($V=18.8\,{\rm mag}$) to achieve an S/N of $\sim60$ sufficient to perform a full quantitative spectral analysis. At a resolution of $\sim1\,{\rm \AA}$ we will be able to measure $v_{\rm rot}\sin{i}$ with sufficient accuracy, if it exceeds about $100\,{\rm km\,s^{-1}}$. In addition, we will observe the bright, single He-sdO WD\,0958$-$118 ($V=13.8\,{\rm mag}$) as comparison star. It has similar atmospheric parameters as US\,708, but is a slow rotator. Using the same setup, we will easily achieve an S/N of $>100$ within one orbit splitting the observation into short single exposures to avoid saturation. There are no scheduling constraints and both sources are non-variable. HOT STARS Default false false false false false SUPPORTED STAR SDO This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 STAR SDO This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 COS/FUV Spectroscopic No No G140L 1105 COS/FUV Spectroscopic No No G140L 1105 1374761286345 /home/stephan/APT_21.2/OP-cache/hst2013_cd-v01.xml The scheduling data was generated by CASM 21.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 13290 :visit-id "01" :proposal-version -1 :trans-version "20130502" :date "25-Jul-2013 16:08:04.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 139328 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13290 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13290 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2977 :al-overhead-at-end 0 :internal-dur-at-end 67 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3333 :pcs-gap 0 ) (Tic-Orbit :proposal-id 13290 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 2598 :al-overhead-at-end 0 :internal-dur-at-end 395 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3333 :pcs-gap 0 ) true 2 0 1375699122557 /tmp/OPVisit3170341983426909797.xml The scheduling data was generated by CASM 21.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 13290 :visit-id "02" :proposal-version -1 :trans-version "20130502" :date "05-Aug-2013 12:38:41.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 452544 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13290 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13290 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2934 :al-overhead-at-end 0 :internal-dur-at-end 505 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3267 :pcs-gap 0 ) true 1 0