7392( 2) - 05/12/97 10:54 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7392 Version: 2 Check-in Date: 12-May-1997 10:49:22 1.Proposal Title: Raman scattering and X-ray ionization in LMC X-4 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle BINARY STARS GO 7 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: LEX KAPER EUROPEAN SOUTHERN OBSERVATORY CoI: Jacco Van Loon Astronomical Institute University of N Amsterdam CoI: Godelieve Hammerschlag-Hensberge Astronomical Institute University of N Amsterdam ------------------------------------------------------------------------------------ 6. Abstract We propose STIS observations of the High-Mass X-ray Binary (HMXB) LMC X-4: an X-ray pulsar with O star companion. Our aim is to detect Raman scattered emission lines in high-resolution FUV spectra and to study their orbital modulation. In IUE spectra of 4U1700-37 we found numerous Raman lines in a region centered at the He II line at 1640 Angstrom (Kaper et al. 1990). These lines are formed by Raman scattering of EUV emission lines produced by the X-ray source, through He II ions in the stellar wind. This allows a reconstruction of the X-ray source's EUV spectrum between 250 and 260 Angstrom in great detail. Radial velocity variations of the Raman lines could in principle reveal information about the orbital motion of the X-ray source. The probably less complicated EUV input spectrum in case of LMC X-4 (due to the lower metallicity) should make line identification possible. The FUV spectra and the included resonance lines further allow a detailed study of the stellar wind structure, the process of X-ray ionization, and the underlying O star. A quantitative explanation for the LMC sources' X-ray luminosities is still lacking. The proposed research provides an important new tool for the investigation of the inner regions around X-ray sources, and will provide new constraints on the system parameters. ------------------------------------------------------------------------------------ 7392( 2) - 05/12/97 10:54 - [ 2] Observations Description ------------------------ We propose observations of LMC X-4 in the medium-resolution echelle mode of STIS (FUV-MAMA, grating E140M, 0.2"x0.2" aperture). The wavelength range of 1125-1710 Angstrom covers both the region around He II 1640 where we expect the Raman lines and the important resonance lines of N V, Si IV, and C IV used to study the stellar wind structure. To determine the orbital modulation of both the UV P Cygni profiles and the predicted Raman lines, we need to observe the binary systems at different orbital phases. To obtain sufficient coverage of the radial velocity curve, at least five measurements are needed per system. Based on our experience with the IUE results, a signal-to-noise ratio > 10 is needed in order to detect the broad (2-3 Angstrom) and relatively weak Raman lines. We derived the FUV flux of LMC X-4 from low-resolution IUE spectra (Bonnet-Bidaud et al. 1981, A&A 101, 184). The STIS ETC calculates an exposure time of 27m for S/N=10. The source does not exceed the bright object count limits of the FUV MAMA. To be able to study the response of the stellar wind to the 13.5s X-ray pulsar we use the TIME-TAG mode of the STIS FUV MAMA detector. We propose to profit from the possibility to observe LMC X-4 during a continuous viewing zone, which makes our program much more efficient. Since our observations are time critical, the targets have to be observed in different (i.e. not contiguous) HST orbits. For this reason, target acquisition and peakup in the echelle aperture has to be carried out before each observation. Filling up the orbits with the condition that the obtained S/N exceeds 10 results in an exposure time of 58m for 1 CVZ orbit per spectrum of LMC X-4. For five phase points this amounts to a total of 5 CVZ orbits. The standard calibration procedure should be sufficient. Real Time Justification ----------------------- As we described above, we want to cover the orbital period of our targets at five different phase points: phi_orb=0.1, 0.3, 0.5, 0.7, and 0.9; this makes our proposal time-critical. Although we would prefer it, these five different phase points do not have to belong to one orbit of the system, which could facilitate scheduling. The ephemeris of the binary period is well-known: Target: LMC X-4 P_orb (days): 1.4084025 (6) phi_orb=0: JD 2448559.3598 (13) Reference: Woo et al. 1996, ApJ 467, 811 We selected CVZ observations, so that the number of requested orbits is minimal. An LMC X-4 observation, including overhead, now fits in (only) one orbit. Given the nature of the proposed targets, coordinated X-ray observations would provide a detailed knowledge of the X-ray state of the accreting source, which is known to vary with time. The scientific goals of this proposal can, however, be reached without the support of observations in other wavelength regions, using the observed time-averaged properties of the systems as input. The applicants are actively involved in various programs with other facilities (ESO, SAX, Rossi XTE, ISO) with observing time allocated for the proposed and other HMXBs, so that coordinated observations in principle could be arranged. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 7392( 2) - 05/12/97 10:54 - [ 3] Data Distribution Media: ELECTRONIC Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 7392( 2) - 05/12/97 10:54 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 LMCX-4 EXT- RA=05H 32M 49.56S +/- 0.3",DEC=- J2000 V = 14.0+/-0.2 STAR,WIND,MXB,INTERACTI 66D 22' 13.3" +/- 0.3",PLATE- E(B-V) = 0.1+/-0.05 NG BINARY,GIANT ID=06B0 F-CONT(1450)=3+/-1e-13 O,BINARY PULSAR TYPE=O7III-V B-V = -0.1+/-0.2 Comments: LMC X-4 is a 13.5s X-ray pulsar in a 1.4d orbit around the O giant Sk-Ph. The flux parameters are given for Sk-Ph (the X-ray pulsar is "invisible" in the ultraviolet and optical wavelength domains). 7392( 2) - 05/12/97 10:54 - [ 5] Visit: 01 Visit Requirements: PERIOD 1.4084025 D AND ZERO-PHASE JD2448559.359800 CVZ On Hold Comments: Additional Comments: The orbital ephemeris is obtained from J.W. Woo et al. 1996, ApJ 467, 811. Although we would prefer it, the 5 requested observations of LMC X-4 (which have to be obtained at different orbital phases of the system: phase 0.1, 0.3, 0.5, 0.7, and 0.9) do not need to be taken during one orbit (1.4d) of the system to facilitate scheduling. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 LMCX-4 STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 0.3 S ONBOARD ACQ FOR 20 CD P ------------------------------------------------------------------------------------------------------------------------------------ 20 LMCX-4 STIS/C ACQ/PEA 0.2X0.2 MIRROR 1 0.3 S ONBOARD ACQ FOR 30 CD K ------------------------------------------------------------------------------------------------------------------------------------ 30 LMCX-4 STIS/F TIME-TA 0.2X0.2 E140M 1425 BUFFER-TIME=1000 1 61 M PHASE 0.05 TO 0.15 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 7392( 2) - 05/12/97 10:54 - [ 6] Visit: 02 Visit Requirements: PERIOD 1.4084025 D AND ZERO-PHASE JD2448559.359800 CVZ On Hold Comments: Additional Comments: The orbital ephemeris is obtained from J.W. Woo et al. 1996, ApJ 467, 811. Although we would prefer it, the 5 requested observations of LMC X-4 (which have to be obtained at different orbital phases of the system: phase 0.1, 0.3, 0.5, 0.7, and 0.9) do not need to be taken during one orbit (1.4d) of the system to facilitate scheduling. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 LMCX-4 STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 0.3 S ONBOARD ACQ FOR 20 CD P ------------------------------------------------------------------------------------------------------------------------------------ 20 LMCX-4 STIS/C ACQ/PEA 0.2X0.2 MIRROR 1 0.3 S ONBOARD ACQ FOR 30 CD K ------------------------------------------------------------------------------------------------------------------------------------ 30 LMCX-4 STIS/F TIME-TA 0.2X0.2 E140M 1425 BUFFER-TIME=1000 1 61 M PHASE 0.25 TO 0.35 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 7392( 2) - 05/12/97 10:54 - [ 7] Visit: 03 Visit Requirements: PERIOD 1.4084025 D AND ZERO-PHASE JD2448559.359800 CVZ On Hold Comments: Additional Comments: The orbital ephemeris is obtained from J.W. Woo et al. 1996, ApJ 467, 811. Although we would prefer it, the 5 requested observations of LMC X-4 (which have to be obtained at different orbital phases of the system: phase 0.1, 0.3, 0.5, 0.7, and 0.9) do not need to be taken during one orbit (1.4d) of the system to facilitate scheduling. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 LMCX-4 STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 0.3 S ONBOARD ACQ FOR 20 CD P ------------------------------------------------------------------------------------------------------------------------------------ 20 LMCX-4 STIS/C ACQ/PEA 0.2X0.2 MIRROR 1 0.3 S ONBOARD ACQ FOR 30 CD K ------------------------------------------------------------------------------------------------------------------------------------ 30 LMCX-4 STIS/F TIME-TA 0.2X0.2 E140M 1425 BUFFER-TIME=1000 1 61 M PHASE 0.45 TO 0.55 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 7392( 2) - 05/12/97 10:54 - [ 8] Visit: 04 Visit Requirements: PERIOD 1.4084025 D AND ZERO-PHASE JD2448559.359800 CVZ On Hold Comments: Additional Comments: The orbital ephemeris is obtained from J.W. Woo et al. 1996, ApJ 467, 811. Although we would prefer it, the 5 requested observations of LMC X-4 (which have to be obtained at different orbital phases of the system: phase 0.1, 0.3, 0.5, 0.7, and 0.9) do not need to be taken during one orbit (1.4d) of the system to facilitate scheduling. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 LMCX-4 STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 0.3 S ONBOARD ACQ FOR 20 CD P ------------------------------------------------------------------------------------------------------------------------------------ 20 LMCX-4 STIS/C ACQ/PEA 0.2X0.2 MIRROR 1 0.3 S ONBOARD ACQ FOR 30 CD K ------------------------------------------------------------------------------------------------------------------------------------ 30 LMCX-4 STIS/F TIME-TA 0.2X0.2 E140M 1425 BUFFER-TIME=1000 1 61 M PHASE 0.65 TO 0.75 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 7392( 2) - 05/12/97 10:54 - [ 9] Visit: 05 Visit Requirements: PERIOD 1.4084025 D AND ZERO-PHASE JD2448559.359800 CVZ On Hold Comments: Additional Comments: The orbital ephemeris is obtained from J.W. Woo et al. 1996, ApJ 467, 811. Although we would prefer it, the 5 requested observations of LMC X-4 (which have to be obtained at different orbital phases of the system: phase 0.1, 0.3, 0.5, 0.7, and 0.9) do not need to be taken during one orbit (1.4d) of the system to facilitate scheduling. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 LMCX-4 STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 0.3 S ONBOARD ACQ FOR 20 CD P ------------------------------------------------------------------------------------------------------------------------------------ 20 LMCX-4 STIS/C ACQ/PEA 0.2X0.2 MIRROR 1 0.3 S ONBOARD ACQ FOR 30 CD K ------------------------------------------------------------------------------------------------------------------------------------ 30 LMCX-4 STIS/F TIME-TA 0.2X0.2 E140M 1425 BUFFER-TIME=1000 1 61 M PHASE 0.85 TO 0.95 UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 7392( 2) - 05/12/97 10:54 - [ 10] Summary Form for Proposal 7392 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAK TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT BUFFER-TIME=1000 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category BINARY STARS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PERIOD 1.4084025 D AND ZERO-PHASE JD2448559.359800 CVZ ONBOARD ACQ FOR 20 ONBOARD ACQ FOR 30 PHASE 0.05 TO 0.15 PHASE 0.25 TO 0.35 PHASE 0.45 TO 0.55 PHASE 0.65 TO 0.75 PHASE 0.85 TO 0.95 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR E140M ------------------------------------------------------------------------------------------------------------------------------------ Target Names LMCX-4 ------------------------------------------------------------------------------------------------------------------------------------