8341( 4) - 07/19/99 07:49 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8341 Version: 4 Check-in Date: 19-Jul-1999 07:49:20 1.Proposal Title: UV Spectroscopy of M33-X8: mini-AGN or black-hole binary? ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 8 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Phil Charles University of Oxford CoI: Dr. Guillaume Dubus University of Amsterdam N CoI: Dr. Knox Long Space Telescope Science Institute Y ------------------------------------------------------------------------------------ 5. Abstract The nucleus of M33 contains X-8, the most luminous steady X- ray source in the Local Group (Long et al, 1996). Our ROSAT long-term studies (Dubus et al, 1997) have shown that it exhibits a remarkable 106d periodicity which is similar to the ``super- orbital'' modulations seen in some galactic low-mass X-ray binaries. This indicates that X-8 is a single object, and our recent WFPC2 UV images reveal a ~16th magnitude UV source in the centre of the (almost) stellar M33 nucleus. However, the nature of this object cannot be gleaned from optical studies as the nucleus is dominated by a compact stellar core of ~F integrated spectral type. And with an L_X/L_UV ratio much too low to be typical of an X-ray binary (unless it is an accretion disc corona source), X-8 is likely to be the nearest example of a ``mini-AGN''. We are therefore applying for STIS far-UV to optical spectroscopy to study this potentially crucial link between X-ray binary behaviour (the periodicity) and that of A GN. ------------------------------------------------------------------------------------ 8341( 4) - 07/19/99 07:49 - [ 2] Observations Description ------------------------ Our aim is to use STIS with both the MAMA and CCD detectors in order to obtain wide wavelength coverage (1150- 5700Angstrom) far-UV, near-UV and optical spectroscopy of the nuclear source in M33. As described in the next section, we wish to orientate the slit so as to observe the very close blue star as well (see fig 2). Our WFPC2 UV images imply that X-8 is associated with a ~16th magnitude UV object at the very centre of M33. While optical spectra of the nucleus imply an F supergiant spectral type, this represents a sum of the central 1 arcsec, and it has been known for some time that there is a significant colour gradient into the core. The central 0.1 arcsec has U--V colours more typical of an A star. Given that our WFPC2 images show roughly comparable fluxes from the point source and diffuse light in the near and far UV (implying U=16) we have elected to use the 52x0.1 slit so as to improve the separation and S/N of the point source spectrum. This will be particularl y important for the optical spectr um where the normal stellar core is likely to be completely dominant. Using the STIS ETC we have therefore assumed an A0 star spectrum in order to estimate exposure times to reach a S/N of 20. i.e. bluer than the integrated optical spectrum, but comparable to existing colours of the nucleus. Because of its better spatial profile in the UV we have chosen the MAMA for the near- and far-UV spectra, and the CCD for the optical spectrum. The times required are:, begintabularlcr Grating & Lambda & t (secs) , , G140L & 1600 & 9700 , G230L & 2000 & 3100 , G430L & 4000 & 100 , endtabular Hence our request for a total of 6 orbits. Real Time Justification ----------------------- We wish to orientate the slit (to a rotation angle of 30.3949 degrees, west of north) so as to observe both the nucleus and the nearby (~1 arcsec) star which is visible in our WFPC2 images (see figure 2). There is still an (outside) chance that this star could be associated with the X-ray emission (as the X-ray location is only accurate to a few arcsecs), and this possibility can be eliminated with UV/optical spectroscopy taken simultaneously with the nucleus itself. The star is somewhat fainter than the nucleus so this arrangement has no implications for count rate limitations. We continue to obtain ROSAT HRI time to monitor the long-term X-ray variability of M33-X8 and other X-ray sources in M33. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 8341( 4) - 07/19/99 07:49 - [ 3] Data Distribution Paper Products: YES Media: ELECTRONIC Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 8341( 4) - 07/19/99 07:49 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 M33-NUCLEUS STELLAR CLUSTER, RA=1H 33M 50.875S +/- 1", J2000 V = 15.0 NUCLEUS, STAR, MXB DEC=30D 39' 36.77" +/- 1", PLATE -ID=00DV 8341( 4) - 07/19/99 07:49 - [ 5] Visit: 01 Visit Priority: Visit Requirements: ORIENT 14.894D TO 14.894D ORIENT 194.894D TO 194.894D On Hold Comments: Additional Comments: Tight orient requirement is to include B=19.45 F star about 1 arcsec from nucleus Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 M33-NUCLEUS STIS/C ACQ F28X50L MIRROR 1 1 S ONBOARD ACQ FOR 20, 30, CD P 40 ------------------------------------------------------------------------------------------------------------------------------------ 20 M33-NUCLEUS STIS/C ACQ/PEA 52X0.1 MIRROR 1 1 S ONBOARD ACQ FOR 30, 40 CD K ------------------------------------------------------------------------------------------------------------------------------------ 30 M33-NUCLEUS STIS/C ACCUM 52X0.1 G430L 4300 CR-SPLIT=3 1 2100 S CD ------------------------------------------------------------------------------------------------------------------------------------ 40 M33-NUCLEUS STIS/N ACCUM 52X0.1 G230L 2376 2 1200 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8341( 4) - 07/19/99 07:49 - [ 6] Visit: 02 Visit Priority: Visit Requirements: ORIENT 14.894D TO 14.894D ORIENT 194.894D TO 194.894D On Hold Comments: Additional Comments: Tight orient requirement is to include B=19.45 F star about 1 arcsec from nucleus Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 M33-NUCLEUS STIS/C ACQ F28X50L MIRROR 1 1 S ONBOARD ACQ FOR 20, 30 CD P ------------------------------------------------------------------------------------------------------------------------------------ 20 M33-NUCLEUS STIS/C ACQ/PEA 52X0.1 MIRROR 1 1 S ONBOARD ACQ FOR 30 CD K ------------------------------------------------------------------------------------------------------------------------------------ 30 M33-NUCLEUS STIS/F ACCUM 52X0.1 G140L 1425 2 900 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 40 M33-NUCLEUS STIS/F ACCUM 52X0.1 G140L 1425 6 1200 S UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8341( 4) - 07/19/99 07:49 - [ 7] Summary Form for Proposal 8341 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP 52X0.1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/NUV-MAMA STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=3 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 14.894D TO 14.894D ORIENT 194.894D TO 194.894D ONBOARD ACQ FOR 20, 30, 40 ONBOARD ACQ FOR 30, 40 ONBOARD ACQ FOR 20, 30 ONBOARD ACQ FOR 30 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G430L G230L G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names M33-NUCLEUS ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 4300 2376 1425 ------------------------------------------------------------------------------------------------------------------------------------