GSC coordinates are given in target comment section. Corrected placement of phase information for the first exposure of each visit. ----- Submission 1 (Wed May 14 15:21:10 GMT 2003) ----- Successfully submitted: Wed May 14 15:21:21 GMT 2003 ----- Submission 2 (Wed May 14 16:57:13 GMT 2003) ----- Wind Accretion and State Transitions in the Black Hole Binary Cyg X-1 The black hole binary, Cyg X-1, is generally observed in one of two long duration X-ray states: a low flux, hard spectrum state (most common) and a high flux, soft spectrum state (rare). Models predict that the high/soft state corresponds to a high mass transfer phase in the binary, and since the X-ray source is fueled by accretion from the stellar wind of the supergiant companion, the simple expectation is that the high/soft state results from an increased wind mass loss rate. Alternatively, a decrease in the wind mass loss rate could result in a more ionized and slower wind in the vicinity of the black hole, which would then be more easily accreted by the black hole. The best test of these hypotheses is to observe the UV P Cygni lines of the supergiant that are formed in its wind outflow. We recently used HST/STIS to obtain the first ever high resolution UV spectra of the system while it resided in the unusual high/soft state. Cyg X-1 has now returned to the low/hard state, and here we propose to revisit Cyg X-1 and complete our investigation of the wind - X-ray state connection. The study will determine (1) the mass loss rate and the dynamical (density and velocity) structure of the wind of the supergiant star in both X-ray states, and (2) how the X-ray source ionizes the wind. These spectra will be useful for other investigations and will form an important resource for the entire research community.
Our primary goal is to measure the P Cygni type line profiles in the UV spectrum of Cyg X-1. The main features include N V 1240, Si IV 1400, and C IV 1550, and we need a resolving power of approximately 10,000 in order to measure accurately the wind terminal velocity and profile distortions caused by X-ray ionization. This is best accomplished with STIS using the E140M echelle grating. This set up covers the entire range of interest at somewhat higher resolving power (R=45,000 which we can rebin later to a lower resolution to increase the signal-to-noise ratio). No special calibrations are required. We used this arrangement for two visits to the target in 2002 June when the system was in the high/soft state, and the spectra resulting from 2 orbits exposure time fully meet our S/N requirements. Here we propose to repeat the observations and measure the wind characteristics now that the system has returned to the low/hard state. Based on the historical record, we expect that Cyg X-1 will remain in the low/hard state throughout Cycle 12. The target continues to be monitored by RXTE/ASM, and is currently in the X-ray low/hard state (May 2003). We need to make the observations at the two orbital conjunction phases in order to study the X-ray ionization effects. There is a 1 day window of opportunity every 5.6 day binary orbital period to schedule each visit, and this was readily accomplished in the earlier observations. We will use the code developed by van Loon et al. (2001) to model the observed changes in the shapes of the P Cygni profiles and determine mass loss rates and ionization structure in the wind. We will also measure mass loss rates from complementary optical spectroscopy of the H-alpha emission using the code described in Herrero et al. (1995). We need to obtain the STIS spectra near the two conjunction phases of the binary (phase zero at black hole superior conjunction occurs at HJD 2,451,355.2599 + 5.599829E) during the low/hard state. The low/hard state is generally more common and longer lasting, and we expect it to last for many months. We need the observations between 2003 July and September for ground based coverage, and we would prefer observations between 1:00 and 9:00 UT for simultaneous ground-based coverage from North America. HOT STARS 0 false 0 0 false false false SUPPORTED STAR SUPERGIANT O MXB B-V=0.84+/-0.02,E(B-V)=1.06+/-0.1,TYPE=O9.5Iab, Guide Star Catalog 19H 58M 21.67S +35D 12' 06.1", PLATE-ID=004C F-CONT(1600)=23+/-2e-14 CYG-X-1 GSC2678-00791 J2000 19 58 21.67 +35 12 5.78 J2000 STIS/FUV-MAMA ACCUM Spectroscopic No STIS/FUV-MAMA ACCUM /tmp/OPVisit29471.xml PREFER START TIME BETWEEN 1:00 and 9:00 UT. (Tic-Visit :proposal-id 9840 :visit-id "01" :proposal-version -1 :trans-version "20030422" :date "14-May-2003 12:54:03.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 174416 :tdrss-contact-duration 0 ) (Tic-Obset :proposal-id 9840 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 9840 :visit-id "01" :orbit-number 1 :pcs-time 365 :si-vis-utilization 2640 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3005 :pcs-gap 0 ) (Tic-Orbit :proposal-id 9840 :visit-id "01" :orbit-number 2 :pcs-time 300 :si-vis-utilization 2705 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3005 :pcs-gap 0 ) true /tmp/OPVisit29463.xml /tmp/OPVisit29470.xml PREFER START TIME BETWEEN 1:00 and 9:00 UT. (Tic-Visit :proposal-id 9840 :visit-id "02" :proposal-version -1 :trans-version "20030422" :date "14-May-2003 12:53:46.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 174416 :tdrss-contact-duration 0 ) (Tic-Obset :proposal-id 9840 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 9840 :visit-id "02" :orbit-number 1 :pcs-time 365 :si-vis-utilization 2640 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3005 :pcs-gap 0 ) (Tic-Orbit :proposal-id 9840 :visit-id "02" :orbit-number 2 :pcs-time 300 :si-vis-utilization 2705 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3005 :pcs-gap 0 ) true /tmp/OPVisit29464.xml