7363( 8) - 01/19/99 09:04 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7363 Version: 8 Check-in Date: 19-Jan-1999 09:04:06 1.Proposal Title: The Nature of Two New Optical Counterparts of Globular Cluster X-ray Sources ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 7 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Bruce Margon University of Washington CoI: Eric Deutsch University of Washington N CoI: Scott Anderson University of Washington Y CoI: Ronald Downes Space Telescope Science Institute N ------------------------------------------------------------------------------------ 5. Abstract The luminous bursting X-ray sources in globular clusters are exotic in nature ( e.g., one has the shortest known binary period of any star), can greatly influence the dynamical evolution of the cluster, and are the probable progenitors of cluster millisecond radio pulsars. Despite intensive efforts, only three thus far have reported optical counterparts, two due to HST observations. The handful of objects on hand have perplexing, different properties, and few obvious patterns have emerged. Here we discuss our recent discovery with HST of two further globular cluster X-ray source counterparts, in NGC 1851 and NGC 6441, and propose STIS observations to elucidate their nature. The object in NGC 1851 resembles in some ways the two ultrashort period (11 and 21 min) binaries in NGC 6624 and NGC 6712; we suggest observations to learn if 100\ luminosity cluster source counterparts fall into this odd category. Our NGC 6441 counterpart more closely resembles the known, higher-luminosity M 15 source, AC 211, thus finally providing more than one example of the class, and allowing an initial observational probe for the underlying explanation of the diversity of properties of these sources. ------------------------------------------------------------------------------------ 7363( 8) - 01/19/99 09:04 - [ 2] Observations Description ------------------------ STIS optical CCD spectra will be obtained for the NGC 6641 counterpart, with multiple readouts per HST orbit to permit sensitivity to expected spectral changes over the 5.7 hour X-ray period (and shorter timescale variability we have recently discovered in WFPC2 images). A narrow slit and preferred orientation are needed to limit contamination of the optical spectrum for many nearby objects in this crowded globular cluster core. A blind offset from a nearby bright cluster star is required for proper TA. In order that data may be adequately combined to look for variability, its is preferable that the data are obtained in a contiguous set of HST orbits. STIS MAMA imaging in TIME-TAG mode be obtained for the NGC 1851 counterpart, to search for a short (~10 min) orbital variation. The F25SRF2 filter was originally requested to avoid just geocoronal Lyman-alpha, but the object is very ultraviolet so this filter was preferred to the F25QTZ filter. In order to limit the frequency of data dumps and provide for an efficient TIME-TAG observation (i.e., long buffer time), we also originally requested a MAMA subarray, and hence as per earlier STScI "Update" instructions initially placed these observations ON HOLD pending availability of MAMA subarrays. However, we have since been advised that MAMA subarrays are still not well understood (May, 1998) and hence now opt for the full MAMA FOV with the F25QTZ filter instead; please contact GOs if a better understanding of subarrays develops that might allow us to go back to F25SRF2 filter. As this field is in a globular cluster overlight cautions are highly appropriate, and WFPC2 images are available (including in the UV) to confirm that MAMA imaging is safe. In order that data may be adequately combined to look for variability, it is preferable that the data are obtained in a contiguous set of HST orbits. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Paper Products: Media: ELECTRONIC Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 7363( 8) - 01/19/99 09:04 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6441- STAR, K III-I RA=17H 50M 11.732S+/-0.1S, DEC=- J2000 V = 13.3+/-1.0 OFFSET 37D 03' 10.88"+/-1.0", PLATE- ID=06AS Comments: OFFSET STAR 2 NGC6441-STAR UNIDENTIFIED, RA-OFF = 0.878S +/- 0.01S, DEC- J2000 V = 18.9+/-0.5 ULTRAVIOLET EMITTER, X- OFF = 4.38" +/- 0.1", FROM 1 RAY EMITTER 3 NGC1851-STAR UNIDENTIFIED, RA=5H 14M 6.887S +/- 0.010S, J2000 V = 20.5+/-1.0 ULTRAVIOLET EMITTER, X- DEC=-40D 2' 44.24" +/- 0.01", RAY EMITTER PLATE-ID=00AN 7363( 8) - 01/19/99 09:04 - [ 4] Visit: 01 Visit Priority: Visit Requirements: ORIENT 315D TO 360D On Hold Comments: Additional Comments: ORIENT 135D to 190D, or ORIENT 0D to 10D also fine. (ORIENT 90D to 135D, or ORIENT 270D to 315D may also be possible if requested orientation not scheduable, but the latter are not optimal). Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 101 NGC6441-OFF STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 0.4 S ONBOARD ACQ FOR 102 SET CD P Comments: ACQ on offset star ------------------------------------------------------------------------------------------------------------------------------------ 102 NGC6441-OFF STIS/C ACQ/PEA 52X0.1 MIRROR 1 0.3 S ONBOARD ACQ FOR 103-117 SET CD K Comments: Peak-up on offset star ------------------------------------------------------------------------------------------------------------------------------------ 103 NGC6441-STA STIS/C ACCUM 50CCD MIRROR GAIN=4 1 5 S MAX DUR 100% R CD Comments: Confirmation image after blind offset to target ------------------------------------------------------------------------------------------------------------------------------------ 104 NGC6441-STA STIS/C ACCUM 52X0.2 G430L 4300 CR-SPLIT=NO 4 470 S R CD ------------------------------------------------------------------------------------------------------------------------------------ 105 NGC6441-STA STIS/C ACCUM 52X0.2 G430L 4300 CR-SPLIT=NO 5 540 S R CD ------------------------------------------------------------------------------------------------------------------------------------ 109 NGC6441-STA STIS/C ACCUM 52X0.2 G430L 4300 CR-SPLIT=NO 5 540 S R CD ------------------------------------------------------------------------------------------------------------------------------------ 113 NGC6441-STA STIS/C ACCUM 52X0.2 G430L 4300 CR-SPLIT=NO 5 540 S R CD ------------------------------------------------------------------------------------------------------------------------------------ 117 NGC6441-STA STIS/C ACCUM 52X0.2 G430L 4300 CR-SPLIT=NO 5 540 S R CD ------------------------------------------------------------------------------------------------------------------------------------ 7363( 8) - 01/19/99 09:04 - [ 5] Visit: 02 Visit Priority: Visit Requirements: ORIENT 95D TO 120D On Hold Comments: Additional Comments: ORIENT 5D to 30D, 185D to 210D, or 275D to 300D also fine Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 201 NGC1851-STA STIS/F TIME-TA F25QTZ MIRROR BUFFER-TIME=2500 1 1300 S R UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 202 NGC1851-STA STIS/F TIME-TA F25QTZ MIRROR BUFFER-TIME=2500 1 1300 S R UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 203 NGC1851-STA STIS/F TIME-TA F25QTZ MIRROR BUFFER-TIME=2500 1 1400 S R UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 204 NGC1851-STA STIS/F TIME-TA F25QTZ MIRROR BUFFER-TIME=2500 1 1400 S R UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 205 NGC1851-STA STIS/F TIME-TA F25QTZ MIRROR BUFFER-TIME=2500 1 1400 S R UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 206 NGC1851-STA STIS/F TIME-TA F25QTZ MIRROR BUFFER-TIME=2500 1 1400 S R UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 207 NGC1851-STA STIS/F TIME-TA F25QTZ MIRROR BUFFER-TIME=2500 1 1400 S R UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 208 NGC1851-STA STIS/F TIME-TA F25QTZ MIRROR BUFFER-TIME=2500 1 1400 S R UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 7363( 8) - 01/19/99 09:04 - [ 6] Summary Form for Proposal 7363 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP 52X0.1 50CCD 52X0.2 F25QTZ ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACQ/PEAK ACCUM TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT GAIN=4 CR-SPLIT=NO BUFFER-TIME=2500 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 315D TO 360D ONBOARD ACQ FOR 102 ONBOARD ACQ FOR 103-117 MAX DUR 100% ORIENT 95D TO 120D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G430L ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC6441-OFFSET NGC6441-STAR NGC1851-STAR ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 4300 ------------------------------------------------------------------------------------------------------------------------------------