! Proposal 6624, submission 1 ! PI: Dr. Bruce Margon ! Received Fri Feb 2 13:08:38 EST 1996 ! From: anderson@titan.astro.washington.edu ! Hubble Space Telescope Cycle 6 (1996) Phase II Proposal Template ! $Id: 6624,v 19.1 1996/08/28 20:23:08 pepsa Exp $ ! Hubble Space Telescope Cycle 6 (1996) Phase II Proposal Template ! $Id: 6624,v 19.1 1996/08/28 20:23:08 pepsa Exp $ ! ! Refer to the HST Phase II Proposal Instructions to fill this out ! ! Anything after a "!" is ignored, and may be deleted ! ! All keywords with multiple entries are comma delimited except the ! Visit_Requirements and Special_Requirements keywords which can be ! delimited with carriage returns or semi-colons, but not commas ! ! For help call your Program Coordinator: Workman ! Phone: 410-338-4495 , E-mail: workman@stsci.edu ! ! This partially completed template was generated from a Phase I proposal. ! Name of Phase I Propossal: archive-0601.margon.prop ! Date generated: Fri Dec 22 18:44:57 EST 1995 ! Proposal_Information ! Section 4 Title: Time-Resolved Spectrophotometry of the Smallest Mass Function Binary Star Proposal_Category: GO Scientific_Category: BINARIES AND STAR FORMATION Cycle: 6 Investigators PI_name: Dr. Bruce Margon PI_Institution: University of Washington CoI_Name: Stefanie Wachter CoI_Institution: University of Washington Contact: ! Y or N (designate at most one contact) CoI_Name: Scott Anderson CoI_Institution: University of Washington Contact: Y ! Y or N (designate at most one contact) Abstract: ! Free format text (please update) 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. Questions ! Free format text (please update) Observing_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: ! Move appropriate text from Real_Time_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) Fixed_Targets ! Section 5.1 Target_Number: 1 Target_Name: KZ-TRA Alternate_Names: X1626-67 Description: STAR,LMXB Position: RA=16H 32M 16.67S +/- 0.04S, ! Most common specification format is DEC=-67D 27' 39.4" +/- 1", PLATE-ID=00JI Equinox: 2000 RV_or_Z: RA_PM: ! Units are seconds of time per year Dec_PM: ! Units are seconds of arc per year Epoch: Annual_Parallax: Flux: V=18.5+/-0.8 ! Include at least V and B-V Comments: TA exposure time estimates based on V=19.3 and B-V=+0.1 ! This is a template for a single visit containing a single exposure ! Repeat exposure and visit blocks as needed Visits ! Section 6 Visit_Number: 1 Visit_Requirements: ! Section 7.1 ! Uncomment or copy visit level special requirements needed ! Most of these requirements (including ORIENT) will limit scheduling ! PCS MODE [Fine | Gyro] ! GUIDing TOLerance ! DROP TO GYRO IF NECESSARY [NO REACQuisition] ORIENT 135D TO 135D ! ORIENTation TO FROM ! ORIENTation TO FROM NOMINAL ! SAME ORIENTation AS ! CVZ ! PARallel ! SCHEDulability ! AFTER [BY [TO ]] ! AFTER ! BEFORE ! BETWEEN AND ! GROUP WITHIN