9398( 7) - 11/20/02 17:46 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9398 Version: 7 Check-in Date: 20-Nov-2002 17:45:23 1.Proposal Title: Understanding Irradiation and Dipping Behaviour in Low Mass X-ray Binaries ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 11 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Robert Hynes University of Texas at Austin CoI: Dr. Carole Haswell The Open University N CoI: Prof. Keith Horne University of St Andrews N CoI: Prof. Phil Charles The University of Southampton N CoI: Prof. Andrew King The University of Leicester N CoI: Prof. Edward Robinson The University of Texas at Austin N CoI: Dr. Daniel Rolfe The University of Leicester N ------------------------------------------------------------------------------------ 5. Abstract It is now clear that X-ray irradiation is the driving force behind many of the observed properties of accretion discs on a huge range of scales from Galactic interacting binaries to AGN. However to study the detailed physics of this process requires the accessible timescales and geometrical constraints afforded by Galactic low mass X-ray binaries (LMXBs). The ideal object for this study is EXO 0748-676 (UY Vol) because of its high inclination and full spectrum of LMXB phenomenology: type I bursts, dips and total eclipses. It is also remarkable as it was designated a transient on its discovery in 1985, but remains X-ray active to this day, thereby providing a potential unifying link between persistent and transient systems. Its present high state is likely maintained by X-ray heating; hence we can learn about a disk strongly influenced by irradiation. STIS TIMETAG observations in the far-UV will eclipse map continuum and emission lines; examine obscuration by the likely thick disk rim; and search for the UV signatures of dips and bursts. This provides an unprecedented range of techniques with which to probe the structure of an irradiated accretion disk and further our understanding of the irradiation of accretion flows in general. ------------------------------------------------------------------------------------ 9398( 7) - 11/20/02 17:46 - [ 2] Observations Description ------------------------ Our primary goal is to obtain time-resolved G140L spectra to facilitate eclipse mapping and to search for UV signatures of dips and bursts. These must span at least two complete orbits of the binary system to discriminate random variability from systematic geometrical effects. TIMETAG mode will be used to obtain maximum time resolution for the orbital light curve, and is essential to record short duration phenomena such as bursts and dips. Our secondary goal is to extend coverage into the near-UV with the G230L grating and measure the depth of the 2175 Angstrom interstellar absorption. Together with simultaneous optical spectroscopy this will allow us to measure the 1150-6700 Angstrom spectral energy distribution. This G230L spectrum should also be obtained in TIMETAG mode in order to exploit bursts or dips that may occur during it. Our requirement is two visits of three Continuous Viewing Zone (CVZ) orbits each. The number of orbits we request is dictated by the need to cover at least two orbital periods of the binary. This is essential if we are to distinguish repeatable orbital variations from stochastic flickering. The binary period is 3.82-hr, so to obtain full phase coverage of a single binary orbit would require 230-min on target in addition to overheads. We estimate overheads of 20-min at the beginning of such a visit, for guide star acquisition, target acquisition, grating/aperture initialization and wavelength calibration. No peakup is necessary as we use a wide slit. Each visit will primarily comprise a continuous sequence of G140L exposures with a fixed configuration. Small gaps in coverage due to wavelength calibrations are acceptable. To cover a single binary orbit, we therefore require a minimum time of 250-min per visit, hence three 96-min CVZ orbits. This will allow us up to 38-min per visit to perform our G230L observations of the near-UV. Assuming 8-min overhead to change gratings, this allows up to 60-min total exposure in the near-UV (over the two visits) which will well define the average near-UV spectrum. In 2A 1822-371, UV eclipses last ~0.15 in phase. Assuming EXO 0748-676 is similar, then phase bins of 0.01 will give ~15 points through the eclipse. This corresponds to a 138-s bin. We have used the archival IUE/SWP spectra of EXO 0748-676 and the STIS Spectroscopic ETC to perform simulations of a 138-s exposure (corresponding to a 0.01 phase bin) and estimate that we will be able to achieve a signal-to- noise ratio of 10 for the CIV 1550 Angstrom emission line light curve and an average of ~35 for 50 Angstrom binned continuum light curves. The orbital modulation in EXO 0748-676 is 0.6 magnitudes in the B band (~40 percent flux) and X-ray eclipses are almost total (~100 percent modulation seen in 2A 1822- 371 is 70 percent of peak flux, so we anticipate that our observations will resolve continuum orbital structure very well, and will be sufficient to determine how each emission line is modulated and whether they are eclipsed or not. In order to resolve faster structure such as dips and bursts we will integrate over the entire bandpass of the G140L grating. Our simulations predict an integrated 1300-1700 Angstrom continuum signal- to-noise ratio of 8.4 for a 1-s bin. Optical (B band) bursts have rise times of 3-8-s and amplitudes (peak flux / persistent flux) of 2-4, so our observations will be able to resolve UV bursts; dip timescales are longer than those for bursts. Our quoted flux information is based on published optical photometry and an unpublished IUE SWP spectrum. The range spanned by optical photometry is V = 17.5+/-0.6, with colours of B-V = 0.14+/-0.07 (Wade et al., 1985, PASP, 97, 1092; Crampton et al., 1986, ApJ, 306, 599; Schmidtke & Cowley, 1987, AJ, 93, 374; van Paradijs et al., 1988, A&AS, 76, 185; Schoembs & Zoeschinger, 1990, A&A, 227, 105; Thomas et al., 1993, ApJ, 408, 651) We assume E(B-V)=0.42+/-0.03 (Schoembs and Zoeschinger, 1990, A&A, 227, 105), but the assumptions made by these authors may not be valid. Our G230L spectra will provide the definitive measurement. UV fluxes are taken from the archival IUE SWP spectrum. The CIV line may not be fully resolved, but is unlikely to be much narrower than this. 9398( 7) - 11/20/02 17:46 - [ 3] Real Time Justification ----------------------- To maximize the scientific gains of our program, we require CVZ time so that we can obtain unbroken phase coverage and observe the requisite two binary orbits most efficiently. The scientific yield of this project will be substantially enhanced if optical observations can be scheduled simultaneously. We have been awarded two nights of NOAO time to perform optical spectroscopy simultaneous with the two HST observations. Together with the far-UV lines observed by HST this will give comprehensive coverage of a range of species and excitations not possible in either the UV or optical alone. Kinematic resolution will be ~120 km/s, and so will be better than possible with the G140L grating in the UV. We realise that strict simultaneity may be incompatible with the CVZ requirements. Contemporaneous observations, within a few days, would still be useful, although simultaneous is preferable. In addition, the PI has access to fast optical photometry with the UCT frame transfer CCD camera at SAAO and Co-I Charles has experience in using this to observe LMXBs. We are seeking complementary observations here; the relevant proposal deadlines are either July or October 2002 depending on when HST observations will be scheduled. If SAAO time is awarded then ideally one HST visit should be simultaneous with each as they cannot observe the target simultaneously. A further benefit will be obtained if approved RXTE observations (2x30ks) can also be scheduled simultaneously. We anticipate that RXTE has the scheduling flexibility necessary to fit in with HST observations. We have successfully obtained simultaneous HST/RXTE observations for three black hole candidates through ToO observations (GRO J1655--40, XTE J1859+226 and XTE J1118+480). We are therefore confident that the scheduling would be possible. Visits 3 and 4 are alternatives to 1 and 2. They are specified to last the same time and use the same observing modes. The only difference between them is in the order and duration of exposures, so they should occupy exactly the same scheduling opportunities. When the starting date and time of the observations is known, we can decide whether to replace either or both visits with the alternative. This is necessary to ensure that we can always obtain uninterrupted coverage of an entire eclipse. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9398( 7) - 11/20/02 17:46 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 UY-VOL STAR, INTERACTING RA=07H 48M 33.85S +/- 0.14S, J2000 V = 17.5+/-0.6 BINARY, LMXB DEC=-67D 45' 07.36" +/- B-V = 0.14+/-0.07 0.80"PLATE-ID=01YR E(B-V) = 0.42+/-0.03 F-CONT(1600)=4e-15 F-LINE(1550)=9e-14 W-LINE(1550)=10 Coordinate Source: IMAGE_TIED_TO_GSC_FRAME Comments: Target only became bright in 1985 so is not visible in GSC plates. Coordinates based on recent NTT image. Mapping onto GSC frame used 11 unsaturated field stars measured from GSC plate and custom IDL transformation routine. RMS of fit was +/- 0.6" in RA and Dec. Checked against 5 other field stars also measured on both plates, with RA and Dec RMS +/- 0.8". 9398( 7) - 11/20/02 17:46 - [ 5] Visit: 01 Visit Priority: Visit Requirements: BETWEEN 17-FEB-2003 AND 20-FEB-2003 CVZ On Hold Comments: Additional Comments: Visit ideally to be coordinated with ground-based observations from CTIO awarded by the HST TAC. RXTE observations are also approved but it is anticipated that they will be more flexible than HST or CTIO. BETWEEN requirement dictated by the useful ground-based observing season for this target. Optimal time is Mid-December to Mid-February. NOTE: PI's new preference is for BETWEEN 17-FEB-2003 AND 20-FEB-2003. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 UY-VOL STIS/C ACQ F28X50L MIRROR 1 25 S CD P Comments: Should work for V=15.3-19.7, so variability is allowed for. ------------------------------------------------------------------------------------------------------------------------------------ 2 UY-VOL STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=1200 1 4000 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 3 UY-VOL STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=1200 1 4500 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 4 UY-VOL STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=1200 1 4970 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 5 UY-VOL STIS/N TIME-TA 52X0.5 G230L 2376 BUFFER-TIME=400 1 800 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 9398( 7) - 11/20/02 17:46 - [ 6] Visit: 02 Visit Priority: Visit Requirements: BETWEEN 17-FEB-2003 AND 20-FEB-2003 CVZ On Hold Comments: Additional Comments: Visit ideally to be coordinated with ground-based observations from CTIO awarded by the HST TAC. RXTE observations are also approved but it is anticipated that they will be more flexible than HST or CTIO. BETWEEN requirement dictated by the useful ground-based observing season for this target. Optimal time is Mid-December to Mid-February. NOTE: PI's new preference is for BETWEEN 17-FEB-2003 AND 20-FEB-2003. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 UY-VOL STIS/C ACQ F28X50L MIRROR 1 25 S CD P Comments: Should work for V=15.3-19.7, so variability is allowed for. ------------------------------------------------------------------------------------------------------------------------------------ 2 UY-VOL STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=1200 1 4000 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 3 UY-VOL STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=1200 1 4500 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 4 UY-VOL STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=1200 1 4970 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 5 UY-VOL STIS/N TIME-TA 52X0.5 G230L 2376 BUFFER-TIME=400 1 800 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 9398( 7) - 11/20/02 17:46 - [ 7] Visit: 03 Visit Priority: Visit Requirements: BETWEEN 17-FEB-2003 AND 20-FEB-2003 ON HOLD CVZ On Hold Comments: Alternative to visit 1. To be used if it gives better coverage of the eclipse when scheduling is known. Additional Comments: Visit ideally to be coordinated with ground-based observations from CTIO awarded by the HST TAC. RXTE observations are also approved but it is anticipated that they will be more flexible than HST or CTIO. BETWEEN requirement dictated by the useful ground-based observing season for this target. Optimal time is Mid-December to Mid-February. NOTE: PI's new preference is for BETWEEN 17-FEB-2003 AND 20-FEB-2003. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 UY-VOL STIS/C ACQ F28X50L MIRROR 1 25 S CD P Comments: Should work for V=15.3-19.7, so variability is allowed for ------------------------------------------------------------------------------------------------------------------------------------ 2 UY-VOL STIS/N TIME-TA 52X0.5 G230L 2376 BUFFER-TIME=400 1 800 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 3 UY-VOL STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=1200 1 5100 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 4 UY-VOL STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=1200 1 4800 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 5 UY-VOL STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=1200 1 3499 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 9398( 7) - 11/20/02 17:46 - [ 8] Visit: 04 Visit Priority: Visit Requirements: BETWEEN 17-FEB-2003 AND 20-FEB-2003 ON HOLD CVZ On Hold Comments: Alternative to visit 2. To be used if it gives better coverage of the eclipse when scheduling is known. Additional Comments: Visit ideally to be coordinated with ground-based observations from CTIO awarded by the HST TAC. RXTE observations are also approved but it is anticipated that they will be more flexible than HST or CTIO. BETWEEN requirement dictated by the useful ground-based observing season for this target. Optimal time is Mid-December to Mid-February. NOTE: PI's new preference is for BETWEEN 17-FEB-2003 AND 20-FEB-2003. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 UY-VOL STIS/C ACQ F28X50L MIRROR 1 25 S CD P Comments: Should work for V=15.3-19.7, so variability is allowed for ------------------------------------------------------------------------------------------------------------------------------------ 2 UY-VOL STIS/N TIME-TA 52X0.5 G230L 2376 BUFFER-TIME=400 1 800 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 3 UY-VOL STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=1200 1 5100 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 4 UY-VOL STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=1200 1 4800 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 5 UY-VOL STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=1200 1 3499 S UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 9398( 7) - 11/20/02 17:46 - [ 9] Summary Form for Proposal 9398 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP 52X0.5 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/FUV-MAMA STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=1200 BUFFER-TIME=400 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 17-FEB-2003 AND 20-FEB-2003 CVZ BETWEEN 17-FEB-2003 AND 20-FEB-2003 ON HOLD CVZ ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G140L G230L ------------------------------------------------------------------------------------------------------------------------------------ Target Names UY-VOL ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1425 2376 ------------------------------------------------------------------------------------------------------------------------------------