6624( 19) - 08/28/96 16:26 - [ 0] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6624 Version: 19 Check-in Date: 28-Aug-1996 17:23:12 1.Proposal Title: Time-Resolved Spectrophotometry of the Smallest Mass Function Binary Star ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle BINARIES AND STAR FOR GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Dr. Bruce Margon University of Washington CoI: Stefanie Wachter University of Washington N CoI: Scott Anderson University of Washington Y ------------------------------------------------------------------------------------ 6. Abstract The 7 s X-ray pulsar X1626-67 is one of the rare cases in which an X-ray pulsar is a member of a low mass X-ray binary (LMXB) system. The optical counterpart (KZ TrA) exhibits optical pulsations with the same period as the X-ray pulsations. No Dopppler variations due to orbital motion in the X-ray pulse arrival times have been detected, but an additional lower frequency optical sideband pulsation indicates a probable orbital period of about 40 min. The system has the smallest known mass function of any binary system mbox(f(M)<=sssim 10^-6 M_\odot) and its evolutionary history is still a puzzle. We propose to use the HST/FOS to obtain time resolved spectra over the 40 min orbit. The optical spectrum of KZ TrA is almost featureless and provides few model constraints. In the UV, however, the spectra of LMXBs are usually characterized by numerous strong emission lines due to the ionizing flux of the incident X-rays. The line fluxes and ratios constrain the size, density, and degree of ionization in the emission region and are an invaluable tool in determining the physical conditions in the system. Monitoring of the line flux variations over the orbital cycle will constrain the location of the emission region in the system. We will also search for UV pulsations with the 7 s period in the continuum and the lines, which could be very strong. ------------------------------------------------------------------------------------ Observations Description ------------------------ KZ TrA is on the edge of the HST Continuous Viewing Zone. CVZ constraints for Cycle 6 FOS GO proposals are especially complex, and we do not assume or request here that this will be executed as a CVZ proposal, but merely point out that there is a substantial probability that CVZ observing will prove to be possible, significantly enhancing observing efficiency. We select the 0.3'' aperture to minimize geocoronal LyAlpha contamination for this relatively faint object, and thus maximize the possibility of the detection of stellar LyAlpha emission. Data will be taken with FOS/BL and G160L (1140-2508 Angstrom) resulting in a resolution of about 6.3 Angstrom . The wavelength coverage is ideal since it contains all the important UV emission features commonly seen in LMXBs (e.g. NV 1240 Angstrom , CIV 1550 Angstrom , HeII 1640 Angstrom , and CIII 2296 Angstrom). Since there is no UV flux published for X1626-67, we estimate the flux by comparison to Her X-1. The average of several published fluxes for Her X-1 at 1500 Angstrom , including our own HST measurement, is about 1.5 * 10^-13 erg cm^-2 s^-1 AA^-1 with a corresponding V-magnitude of V=13.1 mag. The reddening of X1626-67 has been determined by van Paradijs et al. (1986) to be E(B-V)=0.1. Scaling the UV flux by the optical magnitudes and taking into account the extinction for X1626-67 at 1500 Angstrom\\ (A_1500 ~eq 1.0 mag), we estimate a flux of about 5 * 10^-16 erg cm^-2 s^-1 AA^-1 at 1500 Angstrom . This estimate is conservative, as it uses the V~18.5 mag of van Paradijs (1995); magnitudes ~ 0.5 brighter are also found in the literature (Angelini et al. 1995). According to the FOS instrument handbook (version 6.0), this estimated UV flux should yield a countrate of 0.018 counts s^-1 diode^-1 at 1500 Angstrom . We wish to acquire spectra phase resolved over the 40 min orbital period. For five phase bins across the binary orbital period and a SNR of eight in each phase bin, we require a total integration time of 520 min. For this SNR calculation we assume 80\\% efficiency (see discussion of PERIOD mode below) and a darkcount rate of 0.007 counts s^-1 diode^-1. The target visibility duration for the declination of X1626-67 is 57 min. Accounting for guidestar reacquisition (6 min) and instrument overhead (6 min), that leaves 45 min available per HST orbit for science exposures; therefore 11.5 science orbits are needed in order to obtain the requisite 520 minutes total integration time. Note that during each HST orbit one full binary orbital cycle of X1626-67 will be observed spectroscopically. The observations have to be broken up into two visits to avoid the SAA. In order to limit the impact of long-term variability of the target, we would like the two visits as close in time as possible (<=sssim 3 weeks). This has the added advantage that we can then use the ``reuse target offset function'', i.e. we can avoid the necessity for a target acquistion during the second visit. During the first visit, target acquisition will be achieved via a four stage peak-up. The first three stages (7+14+20 min) plus the guide star acquisition (8 min) can be accomplished in the first orbit, and the last stage (20 min) in the 2nd orbit. The remainder of the 2nd orbit (25 min, after allowing for an additional 6 min for guide star reacquisition and instrument overhead each) and the following six HST orbits will be used for the science exposure. During the second visit the reuse target offset function will allow us to proceed directly with five orbits of science exposure, after the guide star acquisition (8 min). Hence we request a total of 13 orbits for the two visits. The total accumulated spectrum will have a SNR of 20, allowing a sensitive search for weaker features, and a good probe of the oddly enhanced abundances already suggested by the observed X-ray emission line. PERIOD mode wll be used throughout this observation to simultaneously observe ~10 phase bins across the 7 s pulse period. Even accounting for PERIOD mode deadtimes, such high time resolution can nonetheless be accomplished with an observing efficiency of at least 80\\% . For PERIOD mode, care has to be taken not to exceed the FOS on-board memory. However, as <200 diodes are required to fully sample the useful wavelength coverage of G160L/BL, 10 phase bins can be sampled while remaining safely below the 12,288 ``data size'' memory limit. This is true even for SUB-STEP=4 (and, of course, we could choose SUB-STEP=2 without any loss in spectral resolution). Note: PERIOD and RAPID mode observations with the FOS are always somewhat complex, but we have extensive past experience with both. Each mode has advantages and disadvantages for this particular observation, but at the relevant 7 s pulsar period, both are also capable of successfully executing this proposal. (Note, as per the scientific justification, that successful detection of rapid variability is only one part of the science goals; much of the analysis will be conducted with time-averaged data.) RAPID will have certain disadvantages regarding readout and telemetry overheads; PERIOD mode requires careful management of on-board FOS memory, as discussed above. We select PERIOD mode at this time, and the sensitivity calculations above are based on this assumption; however, we are confident that a change to RAPID, if required, will not substantially impact this observation. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- The relevant pulse period is changing with time. Please advise GOs as early as possible with potential scheduling dates, so that CYCLE-TIME, etc. for PERIOD mode observations may be appropriately updated. freq=0.13048862 - 7.1795E-13(t- t0) + 0.5 X 9.41E-22(t-t0)(t-t0), t0=MJD 49000 (Chakrabarty thesis) ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6624( 19) - 08/28/96 16:26 - [ 1] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 KZ-TRA STAR,LMXB RA=16H 32M 16.67S +/- 0.04S, 2000 V = 18.5+/-0.8 DEC=-67D 27' 39.4" +/- 1", PLATE -ID=00JI Comments: TA exposure time estimates based on V=19.3 and B- V=+0.1 6624( 19) - 08/28/96 16:26 - [ 2] Visit: 01 Visit Requirements: ORIENT 135D TO 135D SEQ 1-2 WITHIN 21D On Hold Comments: Additional Comments: 2nd visit requires reuse target offset function. Target is sometimes in CVZ, so efficiency can be markedly improved if schedulable in CVZ (although this is not required). Please contact GO if CVZ scheduling deemed feasible. The relevant pulse period is changing with time; please advise GOs as early as possible of likely scheduling dates, so that CYCLE-TIME, etc may be updated. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 101 KZ-TRA FOS/BL ACQ/PEA 4.3 MIRROR SEARCH-SIZE-X=1,SEARCH-SIZE-Y=3, 1 34.0 S ONBOARD ACQ FOR 102 K SCAN-STEP-Y=1.23 ------------------------------------------------------------------------------------------------------------------------------------ 102 KZ-TRA FOS/BL ACQ/PEA 1.0-PAI MIRROR SEARCH-SIZE-X=6,SCAN-STEP-X=0.61, 1 35.0 S ONBOARD ACQ FOR 103 K R-A SEARCH-SIZE-Y=2,SCAN-STEP-Y=0.61 Comments: Please confirm with FOS instrument scientist that TA/science into paired aperature still preferred with G160L ------------------------------------------------------------------------------------------------------------------------------------ 103 KZ-TRA FOS/BL ACQ/PEA 0.5-PAI MIRROR SEARCH-SIZE-X=3,SCAN-STEP-X=0.29, 1 39.0 S ONBOARD ACQ FOR 104 K R-A SEARCH-SIZE-Y=3,SCAN-STEP-Y=0.29 ------------------------------------------------------------------------------------------------------------------------------------ 104 KZ-TRA FOS/BL ACQ/PEA 0.25-PA MIRROR SEARCH-SIZE-X=4,SCAN-STEP-X=0.11, 1 47.0 S ONBOARD ACQ FOR 105-110 K IR-A SEARCH-SIZE-Y=4,SCAN-STEP-Y=0.11 SAVE OFFSET 1 ------------------------------------------------------------------------------------------------------------------------------------ 105 KZ-TRA FOS/BL PERIOD 0.5-PAI G160L 1050-25 BINS=8,CYCLE-TIME=7.668546875, 2 391.096 SEQ 105 NON-INT R-A 07 STEP-PATT=SINGLE ------------------------------------------------------------------------------------------------------------------------------------ 106 KZ-TRA FOS/BL PERIOD 0.5-PAI G160L 1050-25 BINS=8,CYCLE-TIME=7.668546875, 5 391.096 SEQ 106 NON-INT R-A 07 STEP-PATT=SINGLE ------------------------------------------------------------------------------------------------------------------------------------ 107 KZ-TRA FOS/BL PERIOD 0.5-PAI G160L 1050-25 BINS=8,CYCLE-TIME=7.668546875, 5 391.096 SEQ 107 NON-INT R-A 07 STEP-PATT=SINGLE ------------------------------------------------------------------------------------------------------------------------------------ 108 KZ-TRA FOS/BL PERIOD 0.5-PAI G160L 1050-25 BINS=8,CYCLE-TIME=7.668546875, 5 391.096 SEQ 108 NON-INT R-A 07 STEP-PATT=SINGLE ------------------------------------------------------------------------------------------------------------------------------------ 109 KZ-TRA FOS/BL PERIOD 0.5-PAI G160L 1050-25 BINS=8,CYCLE-TIME=7.668546875, 5 391.096 SEQ 109 NON-INT R-A 07 STEP-PATT=SINGLE ------------------------------------------------------------------------------------------------------------------------------------ 110 KZ-TRA FOS/BL PERIOD 0.5-PAI G160L 1050-25 BINS=8,CYCLE-TIME=7.668546875, 5 391.096 SEQ 110 NON-INT R-A 07 STEP-PATT=SINGLE ------------------------------------------------------------------------------------------------------------------------------------ 6624( 19) - 08/28/96 16:26 - [ 3] Visit: 02 Visit Requirements: ORIENT 135D TO 135D SEQ 1-2 WITHIN 21D On Hold Comments: Additional Comments: 2nd visit requires reuse target offset function. Target is sometimes in CVZ, so efficiency can be markedly improved if schedulable in CVZ (although this is not required). Please contact GO if CVZ scheduling deemed feasible. The relevant pulse period is changing with time; please advise GOs as early as possible of likely scheduling dates, so that CYCLE-TIME, etc may be updated. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 204 KZ-TRA FOS/BL ACQ/PEA 0.25-PA MIRROR SEARCH-SIZE-X=4,SCAN-STEP-X=0.11, 1 36 S USE OFFSET 1 ONBOARD ACQ K IR-A SEARCH-SIZE-Y=4,SCAN-STEP-Y=0.11 FOR 205-210 Comments: use target offset from visit 1, then perform final PU ------------------------------------------------------------------------------------------------------------------------------------ 205 KZ-TRA FOS/BL PERIOD 0.5-PAI G160L 1050-25 BINS=8,CYCLE-TIME=7.668546875, 2 391.096 SEQ 205 NON-INT R-A 07 STEP-PATT=SINGLE ------------------------------------------------------------------------------------------------------------------------------------ 206 KZ-TRA FOS/BL PERIOD 0.5-PAI G160L 1050-25 BINS=8,CYCLE-TIME=7.668546875, 5 391.096 SEQ 206 NON-INT R-A 07 STEP-PATT=SINGLE ------------------------------------------------------------------------------------------------------------------------------------ 207 KZ-TRA FOS/BL PERIOD 0.5-PAI G160L 1050-25 BINS=8,CYCLE-TIME=7.668546875, 5 391.096 SEQ 207 NON-INT R-A 07 STEP-PATT=SINGLE ------------------------------------------------------------------------------------------------------------------------------------ 208 KZ-TRA FOS/BL PERIOD 0.5-PAI G160L 1050-25 BINS=8,CYCLE-TIME=7.668546875, 5 391.096 SEQ 208 NON-INT R-A 07 STEP-PATT=SINGLE ------------------------------------------------------------------------------------------------------------------------------------ 209 KZ-TRA FOS/BL PERIOD 0.5-PAI G160L 1050-25 BINS=8,CYCLE-TIME=7.668546875, 5 391.096 SEQ 209 NON-INT R-A 07 STEP-PATT=SINGLE ------------------------------------------------------------------------------------------------------------------------------------ 210 KZ-TRA FOS/BL PERIOD 0.5-PAI G160L 1050-25 BINS=8,CYCLE-TIME=7.668546875, 5 391.096 SEQ 210 NON-INT R-A 07 STEP-PATT=SINGLE ------------------------------------------------------------------------------------------------------------------------------------ 6624( 19) - 08/28/96 16:26 - [ 4] Visit: 10 Visit Requirements: On Hold Comments: Additional Comments: This visit will execute a brief on-orbit test of the FOS PERIOD in a snapshot mode. It is not intended expected to yield scientific results. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 105 INTFLAT FOS/BL PERIOD 4.3 G130H BINS=5,CYCLE-TIME=7.668546875, 1 391.096 STEP-PATT=SINGLE ------------------------------------------------------------------------------------------------------------------------------------ 6624( 19) - 08/28/96 16:26 - [ 5] Summary Form for Proposal 6624 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/BL ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/PEAK PERIOD ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SEARCH-SIZE-X=1 SEARCH-SIZE-Y=3 SCAN-STEP-Y=1.23 SCAN-STEP-Y=0.61 SCAN-STEP-Y=0.29 SCAN-STEP-Y=0.11 STEP-PATT=SINGLE CYCLE-TIME=7.668546875 BINS=8 SEARCH-SIZE-Y=4 BINS=5 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category BINARIES AND STAR FORMATION ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 135D TO 135D SEQ 1-2 WITHIN 21D ONBOARD ACQ FOR 102 ONBOARD ACQ FOR 103 ONBOARD ACQ FOR 104 ONBOARD ACQ FOR 105-110 SAVE OFFSET 1 SEQ 105 NON-INT SEQ 106 NON-INT SEQ 107 NON-INT SEQ 108 NON-INT SEQ 109 NON-INT SEQ 110 NON-INT USE OFFSET 1 ONBOARD ACQ FOR 205-210 SEQ 205 NON-INT SEQ 206 NON-INT SEQ 207 NON-INT SEQ 208 NON-INT SEQ 209 NON-INT SEQ 210 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G160L G130H ------------------------------------------------------------------------------------------------------------------------------------ Target Names KZ-TRA INTFLAT ------------------------------------------------------------------------------------------------------------------------------------