6694( 3) - 02/19/96 15:45 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6694 Version: 3 Check-in Date: 19-Feb-1996 11:06:34 1.Proposal Title: High resolution UV imaging of M33-X8, the nuclear X-ray source in M33 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle GALAXIES & CLUSTERS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Phil Charles Oxford University CoI: Pasi Hakala Oxford University N CoI: Knox Long Space Telescope Science Institute N ------------------------------------------------------------------------------------ 6. Abstract The nucleus of M33 is known to contain the most luminous steady X-ray source in the Local Group (Long et al.,1981). Our recent ROSAT observations, however, indicate that the X-ray emission shows peculiar variability at short, less than an hour, timescales. The identification and study of the X-ray source at optical wavelengths is impossible using ground based techniques, as the (almost) stellar nucleus (V ~ 14.9) dominates the flux. However, the nuclear X-ray source has L_X ~ 10^39 erg s^- 1, which means that, if it has a typical L_X/L_opt of ~ 500 (a conservative assumption), the expected V magnitude (at the distance of M33) would be ~ 22. However, most of the optical light comes from late type stars, in a slightly extended core, which means that high resolution far UV imaging with HST provides the only means for identifying M33-X8. This source could be the crucial link between luminous X-ray binaries and ``micro-''AGN, and is by far the closest of its type. ------------------------------------------------------------------------------------ 6694( 3) - 02/19/96 15:45 - [ 2] Observations Description ------------------------ We will use the WFPC2 with F170BW, F300W, F439W and F555W filters. The identification of the X-ray source will be based on its extreme UV colour and possible variability. We estimate that given the distance of 720kpc, X-ray luminosity of 10^39 erg sec^-1 and a typical L_X/L_opt of 500, we will achieve 1000 and 4600 counts in 1000 seconds for the F170W and F300W filters respectively. For F439W we will detect 1500 cts in 500 sec and for the F555W 1200 counts in 100 secs. The table below gives the estimated count rates in 1000 sec exposure for both M33-X8 and the rest of the nucleus. These estimates, however, give the total number of counts. Earlier ground based observations by Gallagher et al (1982) have shown that even at 1" seeing the nucleus is not a point source (approximate extent ~ 1"). This results in a reduction of counts per pixel by a factor of ~ 100, when compared to a point source like M33-X8. We propose to obtain three 800 sec FW170BW images during the first orbit and single images with the rest of the filters during the second orbit. begintabularlll & & , Filter & M33-X8 & M33 core, & & , F170W & 1032 cts & 1407 cts, F300W & 4625 & 3925, F439W & 3032 & 147607, F555W & 11900 & 1004101 endtabular Real Time Justification ----------------------- We have already received further ROSAT HRI time (50ksec) to continue our study of the X-ray variability of M33-X8. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: , ------------------------------------------------------------------------------------ 6694( 3) - 02/19/96 15:45 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 M33-X8 STAR,LMXB,GALAXY,SPIRAL RA=1H 33M 50.85S +/- J2000 SURF-BKG(B) = 14.5+/-0.2 0.5",DEC=30D 39' 36.8" +/- 0.5" V = 21.9+/-0.5 B-V = 0.0 6694( 3) - 02/19/96 15:45 - [ 4] Visit: 01 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 M33-X8 WFPC2 IMAGE PC1 F160BW 1 2500S ------------------------------------------------------------------------------------------------------------------------------------ 2 M33-X8 WFPC2 IMAGE PC1 F300W 1 1700S ------------------------------------------------------------------------------------------------------------------------------------ 3 M33-X8 WFPC2 IMAGE PC1 F439W 1 500S ------------------------------------------------------------------------------------------------------------------------------------ 4 M33-X8 WFPC2 IMAGE PC1 F555W 1 100S ------------------------------------------------------------------------------------------------------------------------------------ 6694( 3) - 02/19/96 15:45 - [ 5] Summary Form for Proposal 6694 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category GALAXIES & CLUSTERS ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F160BW F300W F439W F555W ------------------------------------------------------------------------------------------------------------------------------------ Target Names M33-X8 ------------------------------------------------------------------------------------------------------------------------------------