5873( 13) - 11/20/95 19:42 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 5873 Version: 13 Check-in Date: ********** 1.Proposal Title: UV/X-ray spectroscopy of Cyg X-2 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Hot Stars GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Saeqa Vrtilek University of Maryland CoI: John Raymond Smithsonian Astrophysical Observatory N CoI: Francis Primini Smithsonian Astrophysical Observatory N CoI: Timothy Kallman Goddard Space Flight Center N CoI: Richard McCray Joint Institute for Laboratory N Astrophysics CoI: Bram Boroson Joint Institute for Laboratory N Astrophysics CoI: Fumiaki Nagase ISAS N ------------------------------------------------------------------------------------ 6. Abstract We propose to observe simultaneously the UV and X-ray spectral variabilites of Cyg X -2 with HST and ASCA. Previous simultaneous UV/X-ray observations using GINGA and IUE showed a unique relationship between the X-ray spectral states and the UV flux. IUE, however, is not able to measure the short timescales and kinematic velocities of interest in this system. We will use the GHRS G160M with time resolution of 0.5s in the vicinity of the NV and HeII lines. From delays between X-ray and UV line variations, we can analyze the radial structure of velocity in the disk. This will provide an unprecedented probe into the structure and dynamics of the accretion flow, enable us to test models of the UV emission, and constrain properties of the secondary star. We will also use the G140L with a time resolution of 50ms to search for the quasi-periodic oscillations so far seen only in the X-rays. Finding QPOs in the UV would be very important; since the X- ray flux can be easily modulated by geometric effects and emission in the visible can be confused with that of the non- collapsed secondary, the UV observations are most likely to yield direct evidence of the phenomenon related to the accretion disk. ------------------------------------------------------------------------------------ 5873( 13) - 11/20/95 19:42 - [ 2] Observations Description ------------------------ We will utilize the GHRS G160M in RAPID mode (with readout every 0.5s) to study the NV and HeII lines which are expected to vary on a timescale of minutes. The average flux observed from IUE at the N V line is F_Lambda~eq 2 * 10^-14 erg cm^-2 s^-1 AA^-1, corresponding to a counting rate of .01 counts s^-1 diode^- 1. Since we measure the width of the N V emission line to be approximately 12 Angstrom, by summing the diodes over the line we expect a counting rate of approximately 1.6 counts s^-1 in the line. The resolution of G160M at 1240 Angstrom is ~0.08Angstrom corresponding to a velocity resolution of 19 km s^-1. In a 60 minute observation we will get 6.9* 10^3 counts in the line (which spans 167 diodes). This gives 41 counts/s per velocity resolution element. For He II with an average flux from IUE of 8 * 10^-15 erg cm ^-2 s^-1 AA^-1 a 120 minute observation would give 28 counts/s per velocity resolution element. We will utilize the GHRS G140L in RAPID mode with high data rate to allow readout every 50ms in order to search for UV signatures of the QPOs. The average continuum flux observed from IUE at 1300Angstrom is F_Lambda~eq 4 * 10^ -15 erg cm^-2 s^-1 AA^-1, corresponding to a counting rate of .07 counts s^ -1 diode^-1. If we integrate over the total 140L bandpass of roughly 286 Angstrom, centered at 1400 Angstrom we obtain 35 cts/s. 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. For a typical case of Cyg X-2 in the normal branch, the X-ray QPO's have Delta f = 5 Hz and r ~ 0.1. Thus we need an observing time of T ~ 1470 s for a 3Sigma and 5,880 s for a 5Sigma measurement. The 20-minute integration limit for high data readout mode will give us a 3 Sigma limit. We understand that it is possible to get a significantly longer high data rate exposure if the on-board tape recorder is bypassed and the data are sent down to the ground in real time. We realize that real time contacts are a limited resource; and only point out that finding UV QPOs simultaneously with X-ray detections could be very important. Cyg X-2 is the only source for which this is currently possible. We request a total time on source of 240 minutes (60-min integration with G160M centered on NV; 120-min integration with G160M centered on HeII; and a 60-min integration with G140L centered at 1400 Angstrom). Assuming a 53-minute viewing window for Cyg X-2, with one guide star acquisition (12 minutes), one target acquisition (11 minutes), 5 target re -acquisitions of 6 minutes each, and 3 instrument read-outs of 4 minutes each, the total number of satellite orbits we require is 6. Real Time Justification ----------------------- The HST observations will be coordinated with simultaneous observations by ASCA. Simultaneous X-ray observations with ASCA add a vital dimension to the proposed program allowing us to analyze the radial structure of velocity in the disk and providing an unprecedented probe into the structure and dynamics of the accretion flow. The HST observations by themselves would allow both the search for QPO's in the UV and tests of the models for UV line emission; however knowing the frequencies of the QPO's from the X-ray observations will substantially lower the threshold for statistically significant detection of QPO's in the UV spectrum; knowing the size of the reprocessing region from cross-correlation of simultaneous X-ray and UV flux measurements will benefit the study of line emission. Cyg X-2 is visible to ASCA for 6 1/2 months of the year starting July 1, 1995 so coordination with HST should not be difficult. We need to utilize real-time contact in order to obtain a high data readout beyond the 20-minute integration limit. Calibration Justification ------------------------- Additional Comments ------------------- SIMULTANEOUS OBSERVATIONS WILL BE TAKEN BY THE ASCA X-RAY TELESCOPE. The time intervals when Cyg X-2 is visible to ASCA are: 19-APR-95 to 27-JUL-95; 22-OCT- 95 to 24-JAN-95; and 19-APR-96 to 27-JUL-96. We will need at least a one-month lead time on the week in which the observations takes place and a two weeks lead time on the exact time. We need to utilize real-time contact in order to obtain uninterrupted high data readout beyond the 20-minute limit: data gaps would have an adverse affect on our desired scientific goal. ------------------------------------------------------------------------------------ 5873( 13) - 11/20/95 19:42 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 5873( 13) - 11/20/95 19:42 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 4U2142+380 STAR, F0-F2, LMXB, RA = 21H 44M 41.10S +/- 0.04S, J2000 V = 14.6 +/- 0.1 DEC = 38D 19' 16.4" +/- 0.5", E(B-V) = 0.45 +/- 0.05 PLATE-ID = 004Z TYPE = F2 F-CONT(1300) = 4 +/- 1.0 E-15 F-LINE(1240) = 2.0 +/- 1.0 E-14 W-LINE(1240) = 12.0 +/- 3.0 F-LINE(1640) = 8.0 +/- 1.0 E-15 W-LINE(1640) = 10.0 +/- 3.0 Comments: Coordinates are from a parabolic centroid GASP measurement by Karla 5873( 13) - 11/20/95 19:42 - [ 5] Visit: 01 Visit Requirements: PCS MODE F PERIOD 236.23H AND ZERO-PHASE JD2449746.682 On Hold Comments: Additional Comments: SIMULTANEOUS OBSERVATIONS WILL BE TAKEN BY THE ASCA X-RAY TELESCOPE. The time intervals when Cyg X-2 is visible to ASCA are: 19-APR-95 to 27-JUL-95; 22-OCT-95 to 24-JAN-95; and 19-APR-96 to 27-JUL-96. We will need at least a one-month lead time on the week in which the observations takes place and a two weeks lead time on the exact time. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 4U2142+380 HRS ACQ 2.0 Mirror-N2 1 114.75S PHASE 0.4 TO 0.7 ONBOARD ACQ FOR 10-80 Comments: Need maximum step-time of 12.75s ------------------------------------------------------------------------------------------------------------------------------------ 10 4U2142+380 HRS RAPID 2.0 G160M 1225- SAMPLE-TIME = 1 865S 1255 0.5 ------------------------------------------------------------------------------------------------------------------------------------ 20 4U2142+380 HRS RAPID 2.0 G160M 1225- SAMPLE-TIME = 1 2986S 1255 0.5 ------------------------------------------------------------------------------------------------------------------------------------ 30 4U2142+380 HRS RAPID 2.0 G160M 1625- SAMPLE-TIME = 1 2986S 1655 0.5 ------------------------------------------------------------------------------------------------------------------------------------ 40 4U2142+380 HRS RAPID 2.0 G160M 1625- SAMPLE-TIME = 1 2986S 1655 0.5 ------------------------------------------------------------------------------------------------------------------------------------ 50 4U2142+380 HRS RAPID 2.0 G140L 1257- SAMPLE-TIME = 1 870S 1543 0.05 ------------------------------------------------------------------------------------------------------------------------------------ 60 4U2142+380 HRS RAPID 2.0 G140L 1257- SAMPLE-TIME = 1 870S 1543 0.05 ------------------------------------------------------------------------------------------------------------------------------------ 70 4U2142+380 HRS RAPID 2.0 G140L 1257- SAMPLE-TIME = 1 870S 1543 0.05 ------------------------------------------------------------------------------------------------------------------------------------ 80 4U2142+380 HRS RAPID 2.0 G140L 1257- SAMPLE-TIME = 1 870S 1543 0.05 ------------------------------------------------------------------------------------------------------------------------------------ 5873( 13) - 11/20/95 19:42 - [ 6] Summary Form for Proposal 5873 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations HRS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ RAPID ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SAMPLE-TIME = 0.5 SAMPLE-TIME = 0.05 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Hot Stars ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PCS MODE F PERIOD 236.23H AND ZERO-PHASE JD2449746.682 PHASE 0.4 TO 0.7 ONBOARD ACQ FOR 10-80 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements Mirror-N2 G160M G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names 4U2142+380 ------------------------------------------------------------------------------------------------------------------------------------