6121( 0) - 07/18/95 20:11 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6121 Version: ********** Check-in Date: ********** 1.Proposal Title: UV Photometry of the Degenerate X-ray Binary in NGC6712 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Hot Stars GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Phil Charles Oxford University CoI: Lydie Koch-Miramond CEN SACLAY N CoI: Michel Auriere Observatoire de Pic-du-Midi N CoI: Tim Naylor University of Keele N CoI: Jan van Paradijs University of Amsterdam N CoI: Andy Martin University of Oxford N ------------------------------------------------------------------------------------ 6. Abstract Ground-based imaging has revealed the optical counterpart of the luminous X- ray binary in the globular cluster NGC6712. It is a faint UV star with an indication of up to 0.4 mag variability. However, at B=21.2 and crowded by two brighter stars within 1 arcsec, only HST WFPC photometry will enable a detailed light curve of the X-ray source to be obtained. Given the distance to the cluster the X-ray source has M_V=5.6 which makes it a prime candidate for an underluminous and hence degenerate secondary. The orbital period will thus lie below 80 mins and is likely to be in the range 10--60 mins. With evidence already for variability we propose here for time -resolved CCD photometry to measure the orbital period and light curve in the UV, and thus confirm its degenerate nature. This would be a remarkable result as 2 of the 3 identified (optical/UV) sources in globular clusters would be degenerate, with important implications for the formation and evolution of globular cluster X- ray binaries. ------------------------------------------------------------------------------------ 6121( 0) - 07/18/95 20:11 - [ 2] Observations Description ------------------------ Time-resolved WFPC2 exposures using PC1 and filter F336W. With 5 min exposures and 3 min overhead we can obtain 6 observations per HST orbit after the initial acquisition. The observations need to be scheduled over 9 contiguous orbits in order for maximum sensitivity to detecting the orbital modulation. A subsequent (single) set of UBVRI images (using F336W, F439W, F555W, F675W and F814W) can be performed at any time. Exposure times for comparable signal to noise are 300, 300, 60, 60, 60 respectively. This can be accomplished in a single orbit. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6121( 0) - 07/18/95 20:11 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC6712 STAR, LMXB, STELLAR RA=18H 50M 21.07S +/- 0.5", DEC= 1950 V=21.0+/-0.3 CLUSTER, GLOBULAR -08D 46' 05" +/- 0.5" B-V=0.0+/-0.5 CLUSTER 6121( 0) - 07/18/95 20:11 - [ 4] Visit: 01 Visit Requirements: PCS MODE Fine 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 NGC6712 WFPC2 IMAGE PC1 F300W 53 300S NO SPLIT EXPAND MAXimum DURation 7M MINimum DURation 3M ------------------------------------------------------------------------------------------------------------------------------------ 6121( 0) - 07/18/95 20:11 - [ 5] Visit: 02 Visit Requirements: PCS MODE Fine 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 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC6712 WFPC2 IMAGE PC1 F336W 1 160S ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC6712 WFPC2 IMAGE PC1 F439W 1 160S ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC6712 WFPC2 IMAGE PC1 F555W 1 60S ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC6712 WFPC2 IMAGE PC1 F675W 1 60S ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC6712 WFPC2 IMAGE PC1 F814W 1 120S ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC6712 WFPC2 IMAGE PC1 F160BW 1 420S EXPAND MAXimum DURation 20M MINimum DURation 4M ------------------------------------------------------------------------------------------------------------------------------------ 6121( 0) - 07/18/95 20:11 - [ 6] Summary Form for Proposal 6121 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Hot Stars ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PCS MODE Fine NO SPLIT EXPAND MAXimum DURation 7M MINimum DURation 3M EXPAND MAXimum DURation 20M MINimum DURation 4M ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F300W F336W F439W F555W F675W F814W F160BW ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC6712 ------------------------------------------------------------------------------------------------------------------------------------