8138( 3) - 07/28/99 10:00 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8138 Version: 3 Check-in Date: 18-Feb-1999 09:48:24 1.Proposal Title: Ultraviolet Spectroscopy of the X-ray Transient CI Cam ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 8 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Edward Robinson University of Texas CoI: Dr. Paul Roche University of Sussex N CoI: Mr. Robert Hynes University of Sussex N CoI: Dr. William F. Welsh University of Texas at Austin N CoI: Dr. Beverly J. Wills University of Texas at Austin N CoI: Dr. Carole Haswell University of Sussex N CoI: Dr. Simon Clarke University of Sussex N ------------------------------------------------------------------------------------ 5. Abstract The transient X-ray source XTE J0421+560 erupted on 1998 March 31. Transient X-ray sources are all binary stars that contain an accreting neutron star or black hole, but the XTE J0421+560 binary system is unusual and possibly unique. It emitted strong, non-thermal radio flux during its eruption and possibly ejected a pair of relativistic jets. The eruption decayed in a few days, more rapidly than most X-ray transients. CI Cam, the optical counterpart of XTE J0421+560, is the brightest known X-ray transient, allowing high- resolution measurements of its spectrum. Its optical and near- infrared spectrum is dominated by strong emission lines, with remarkably strong Fe II emission. The spectrum shows that there is a complex circumstellar environment containing at least two or possibly three kinematically and thermally distinct shells. There is also a high velocity wind, which may have been produced during the outburst. We will obtain the first ultraviolet spectrum of CI Cam. Using the MAMA echelle gratings we will measure: the ultraviolet continuum, the reddening, the line profiles, and the Fe II emission line ratios. From these data will determine whether the system is a high-- or low--mass X-ray binary, the wind structure, the physical conditions in the shells and the accretion flow, and the cause of the anomalously strong Fe II emission. ------------------------------------------------------------------------------------ 8138( 3) - 07/28/99 10:00 - [ 2] Observations Description ------------------------ To achieve our scientific goals, we need high spectral resolution (better than 16 km s^-1) and large wavelength coverage (Ly Alpha to 2670 Angstrom). The spectral resolution is required to resolve the thicket of narrow emission lines, especially the forest of Fe II lines. The broad wavelength coverage is required for the accretion flow modelling of the spectral energy distribution, to accurately determine the reddening and to observe as many different lines from the same element as possible (e.g. C II, C III and C IV; Si II, Si III and Si IV). These requirements demand the use of the MAMA medium resolution echelle gratings: the E140M in the FUV (1150--1710 Angstrom) and the E230M in the NUV (1865--2673 Angstrom, using 2269 Angstrom central wavelength). The 0.2x0.2" slit will be used in all cases to maximize the throughput and photometric accuracy while minimizing problems of order overlap. We request a total of 4 HST orbits in one visit. Four orbits is the minimum needed to obtain a spectrum with an adequate S/N ratio (see below). Orbits 2, 3 & 4 will each contain two ACCUM exposures, to give us sensitivity to any variations in the spectrum (e.g. flickering, or radial velocity changes due to binary orbital motion). Orbit 1 will be devoted to target acquisition and an additional observation with the FUV E140M grating, since the E140M configuration yields the lowest countrates. Target ACQ will use the STIS/CCD and a peak--up into the 0.2x0.06" aperture to get the target well--centered in the 0.2" aperture (we will confer with STScI for help and advice with this). Although CI Cam is unusually bright in the optical (V=11.6), interstellar extinction greatly diminishes the UV flux. We estimate a value of E(B-V)=0.7-0.8 from the hydrogen column density based on fits to ASCA X-ray observations (Ueda, et al. 1998 ApJL 508, 167) and our own high resolution optical observations of several diffuse interstellar bands (Clark et al. 1998 MNRAS, submitted). The intrinsic spectrum of CI Cam in the UV is difficult to estimate. Since an accretion disk around a black hole or neutron star is expected to be rather hot, an O or B--star energy distribution should be a reasonable approximation. CI Cam has extremely strong emission lines in the optical. We therefore use as an estimate for the intrinsic CI Cam spectrum a combination of an O--star and H II region spectrum; this was conveniently available in the STIS exposure time simulator (ETC) as the ``Orion Nebula II''model spectral distribution. In the FUV we anticipate a continuum S/N ratio of ~3 near Ly Alpha, ~9 at 1350 Angstrom, and ~5 at 1600 Angstrom. In the NUV, the S/N varies from ~7 at 1870 Angstrom to ~23 at 2670 Angstrom. These are per resolution element per orbit. Since the spectra have resolution > ~60, 000 we have ample freedom to combine bins to boost the S/N, at least by a factor of 4 in the FUV range, should we need to. In the NUV, our ability to bin the spectrum is limited by the need to resolve the narrow Fe II lines, but an additional factor of sqrt 2 is available, should we need it. Note that the emission lines are extremely strong and will stand out far above the continuum, but in no case will they approach MAMA bright--object limits. In summary, we expect adequate S/N for our science goals. Real Time Justification ----------------------- Although CI Cam is in the CVZ, the window is very small. Furthermore, we are only requesting 4 orbits and our program will not make optimal use of the CVZ. Therefore we do not request a CVZ observation. However, The visibility of CI Cam varies greatly over the year. Since we expect rather low S/N, please try to schedule the visit so that the on-target time is maximized within reasonable scheduling constraints. We will continue our program of high--resolution spectroscopy of CI Cam at McDonald Observatory. We will also continue to obtain optical and IR photometry at the Crimean Astrophysical Observatory and at McDonald. These place no constraint on HST scheduling. We will obtain contemporaneous ground--based observations to support our HST observations. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 8138( 3) - 07/28/99 10:00 - [ 3] Data Distribution Paper Products: YES Media: ELECTRONIC Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 8138( 3) - 07/28/99 10:00 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 CI-CAM STAR, X-RAY NOVAE, X- RA=04H 19M 42.16S +/- 0.3", J2000 V = 11.6+/-0.15 RAY TRANSIENT, DEC=+55D 59' 58.1" +/- 0.3", E(B-V) = 0.8+/-0.2 INTERACTING BINARY, MXB PLATE-ID=01YF B-V = -0.9 R = 10.6 U = 12 Comments: CI Cam is mildy variable; 0.15 mag fluctuation possible. A reddened early B or late O star should approximate the spectrum. 8138( 3) - 07/28/99 10:00 - [ 5] Visit: 01 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 CI-CAM STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 0.1 S ONBOARD ACQ FOR 2-6 CD P ------------------------------------------------------------------------------------------------------------------------------------ 2 CI-CAM STIS/C ACQ/PEA 0.2X0.0 MIRROR 1 0.1 S ONBOARD ACQ FOR 3-6 CD K 6 ------------------------------------------------------------------------------------------------------------------------------------ 3 CI-CAM STIS/F ACCUM 0.2X0.2 E140M 1425 1 2160 S EXPAND UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 4 CI-CAM STIS/F ACCUM 0.2X0.2 E140M 1425 2 1350 S SEQ 4 NON-INT; EXPAND UV-MAM A Comments: prefer auto wavecal during occultation if possible ------------------------------------------------------------------------------------------------------------------------------------ 5 CI-CAM STIS/F ACCUM 0.2X0.2 E140M 1425 2 1350 S SEQ 5 NON-INT; EXPAND UV-MAM A Comments: prefer auto wavecal during occultation if possible ------------------------------------------------------------------------------------------------------------------------------------ 6 CI-CAM STIS/N ACCUM 0.2X0.2 E230M 2269 2 1350 S SEQ 6 NON-INT; EXPAND UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8138( 3) - 07/28/99 10:00 - [ 6] Summary Form for Proposal 8138 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP 0.2X0.06 0.2X0.2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/FUV-MAMA STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 2-6 ONBOARD ACQ FOR 3-6 EXPAND SEQ 4 NON-INT; EXPAND SEQ 5 NON-INT; EXPAND SEQ 6 NON-INT; EXPAND ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR E140M E230M ------------------------------------------------------------------------------------------------------------------------------------ Target Names CI-CAM ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1425 2269 ------------------------------------------------------------------------------------------------------------------------------------