5867( 6) - 01/25/96 22:51 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 5867 Version: 6 Check-in Date: 25-Jan-1996 22:48:03 1.Proposal Title: UV spectroscopy of the Low Mass X-ray Binary SCO-X1 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Hot Stars GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Timothy Kallman Laboratory for High Energy Astrophysics CoI: Saequa Vrtilek University of Maryland N CoI: Richard McCray Joint Institute for Laboratory N Astrophysics CoI: Bram Boroson Joint Institute for Laboratory N Astrophysics CoI: Fumiaki Nagase ISAS N CoI: John Raymond Smithsonian Astrophysical Observatory N ------------------------------------------------------------------------------------ 6. Abstract We propose to observe the UV spectrum of SCO-X1 with the GHRS on HST. This will provide a probe into the structure and dynamics of the accretion flow, enable us to test models of the UV emission, and explore the circumstellar environment and evolution. We will observe with the GHRS G140L at high data rate with time resolution of 50 ms in order to test for short timescale variability in the UV lines and continuum. A high frequency cutoff in the power spectrum of the variability in the UV lines will provide a measure of the size of the UV emitting region. We will also observe at medium and high spectral resolution in the vicinity of the strong lines LAlpha, C IV Lambda1550 and N V Lambda1240 in order to better measure the interstellar column density toward SCO-X1 and to test for evidence of X-ray ionization and winds. The UV spectral region is necessary for studying the effects of X-ray ionization; optical emission lines and continuum are much less sensitive to ionization effects. Neither the high time- resolution nor the high spectral resolution observations are feasible with IUE. ------------------------------------------------------------------------------------ 5867( 6) - 01/25/96 22:51 - [ 2] Observations Description ------------------------ We propose to observe SCO-X1 for a total of 6 satellite orbits. First will be with the GHRS 140L grating in the wavelength region 1300 -- 1580 Angstrom (i.e. including both the Si IV Lambda 1400 and C IV Lambda 1550 resonance lines) for one satellite orbit. The goal is to test for UV continuum and line strength variability at frequencies up to 10 Hz. We will utilize the RAPID mode with data readout every 50 ms. The flux observed from IUE at the C IV line is F_Lambda~eq 5 * 10^-13 erg cm^-2 s^-1 AA^-1, corresponding to a counting rate of 3.3 counts s^-1 diode^-1. Since we measure the width of the C IV emission line to be approximately 4 Angstrom, by summing the diodes over the line we expect a counting rate of approximately 23 counts s^-1. The time estimate for the G140L observation is based on the requirements for time-series analysis. In order to measure the power spectrum at a frequency f (in Hz) we require an observing time given by the formula T = (4n^2f)/(F^2r^4), where n is the number of ``sigmas'' of the detection, F is the count rate, and r is the fractional amplitude of the variability. In the space of the 20 minutes of data accumulation time available to a high time resolution observation per orbit, we can expect a ~eq5Sigma detection of variability at 10 Hz if r=0.2. At 1 Hz we will be sensitive to r=0.1 variability with comparable statistics. By binning up the entire bandpass of the G140L we expect a counting rate of 1660 s^-1, giving sensitivity to r=0.02 variations at ~eq5Sigma up to the limiting frequency of 20 Hz. Next, we will use the G160M grating in the vicinity of the L Alpha (1200-1233 Angstrom), N V (1220-1253 Angstrom) and C IV (1535 -1568 Angstrom) lines for one satellite orbit each to measure the damping wings of the interstellar LAlpha absorption and hence the interstellar column, and to measure the profiles of the N V and C IV emission lines. We expect counting rates of at least 0.05 counts s^-1 diode^-1 near these lines. This assumes the lowest line fluxes recorded by IUE ('horizontal branch'), which are a factor of ~2 lower than average. Thus, during one satellite orbit (43 minutes after subtracting reaquisitions and overhead) we can obtain at least 130 counts per diode from SCO-X1, and most probably several times more than this. This corresponds to a signal-to-noise ratio of approximately 11 for each diode. This compares favorably with the value obtained by IUE high resolution of approximately 4 when the source was in a high state. Finally, we will use the Echelle A grating in the vicinity of the N V Lambda1240 (order 45) and C IV Lambda1550 (order 36) lines for one satellite orbit each to search for narrow absorption components due to photoionized interstellar gas and a possible wind- blown bubble. We expect counting rates of at least .02 counts s^-1 diode^-1 near the N V and C IV lines, again using the most pessimistic estimates for the UV fluxes in these lines. With one satellite orbit each these observations will yield at least 53 counts diode^-1. We will therefore be sensitive to narrow (3 Km s^-1) absorption features superimposed on the broader intrinsic emission lines if they have optical depth Tau>= 0.7 at the 3Sigma level. If the source is in a brighter state, near its average flux, the sensitivity improves to Tau>= 0.3. Real Time Justification ----------------------- No special requirements. Calibration Justification ------------------------- Additional Comments ------------------- We request that this visit be scheduled after 1 Sep, 1995. This because we wish to schedule a simultaneous observation with XTE which will be launched on 1 Aug, 1995. XTE has a flexible scheduling policy, and so will schedule following the HST schedule as long as the date of the HST observation can be fixed one month in advance. ------------------------------------------------------------------------------------ 5867( 6) - 01/25/96 22:51 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 5867( 6) - 01/25/96 22:51 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 SCO-X1 STAR,LMXB RA = 16H 19M 55.07S +/- 0.08S, J2000 V = 12.4 DEC = -15D 38' 24.6" +/- 1.2", B-V = 0.2 PLATE-ID = 02C3 F-LINE(1500)=7+/-4e-12 A(V) = 1.2+/-0.2 F-CONT(1500)=5+/-1e-13 Comments: Coordinates are from GSC Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1983.500 -0.00044 -0.0201 0.0 5867( 6) - 01/25/96 22:51 - [ 5] Visit: 01 Visit Requirements: BETWEEN 17-JAN-1996 AND 10-MAR-1996 On Hold Comments: Additional Comments: We request that this visit be scheduled after 1 Sep, 1995. This because we wish to schedule a simultaneous observation with XTE which will be launched on 1 Aug, 1995. XTE has a flexible scheduling policy, and so will schedule following the HST schedule as long as the date of the HST observation can be fixed one month in advance. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 SCO-X1 HRS ACQ 2.0 MIRROR-N2 BRIGHT=RETURN 1 9S ONBOARD ACQuisition FOR 2-8 Comments: STEP-TIME=1S ------------------------------------------------------------------------------------------------------------------------------------ 2 SCO-X1 HRS ACCUM 2.0 G160M 1216. 1 2420.8S Comments: Exposure time is 40.3M ------------------------------------------------------------------------------------------------------------------------------------ 3 SCO-X1 HRS ACCUM 2.0 G160M 1550. 1 2420.8S ------------------------------------------------------------------------------------------------------------------------------------ 4 SCO-X1 HRS ACCUM 2.0 G160M 1240. 1 2420.8S ------------------------------------------------------------------------------------------------------------------------------------ 5 SCO-X1 HRS RAPID 2.0 G140L 1400. SAMPLE-TIME=0.1 1 14.5M ------------------------------------------------------------------------------------------------------------------------------------ 6 SCO-X1 HRS RAPID 2.0 G140L 1400. SAMPLE-TIME=0.1 1 14.5M ------------------------------------------------------------------------------------------------------------------------------------ 7 SCO-X1 HRS ACCUM 2.0 ECH-A 1240. 1 2638.4S Comments: Exposure time is 44M ------------------------------------------------------------------------------------------------------------------------------------ 8 SCO-X1 HRS ACCUM 2.0 ECH-A 1550. 1 2638.4S ------------------------------------------------------------------------------------------------------------------------------------ 5867( 6) - 01/25/96 22:51 - [ 6] Summary Form for Proposal 5867 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM RAPID ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BRIGHT=RETURN SAMPLE-TIME=0.1 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Hot Stars ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 17-JAN-1996 AND 10-MAR-1996 ONBOARD ACQuisition FOR 2-8 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR-N2 G160M G140L ECH-A ------------------------------------------------------------------------------------------------------------------------------------ Target Names SCO-X1 ------------------------------------------------------------------------------------------------------------------------------------