13108( 3) - 30-Jan-2013 18:03:03 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 13108 Version: 3 Check-in Time: 30-Jan-2013 18:03:03 STScI Edit Number: 0 Title The X-ray and UV spectra of the quiescent neutron star X-ray binary EXO 0748-676 ------------------------------------------------------------------------------------ Type Cycle GO 20 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Nathalie Degenaar University of Michigan Y CoI: Dr. Jon Matthew Miller University of Michigan N CoI: Dr. Rudy Wijnands Universiteit van Amsterdam N ------------------------------------------------------------------------------------ Abstract We propose a 45-ks Chandra observation to continue our monitoring of the quiescent neutron star X-ray binary EXO 0748-676. A 25-year long accretion outburst severely heated the neutron star crust, which has been gradually cooling since the source returned to quiescence in 2008. Monitoring this thermal evolution provides the unique opportunity to study the heating processes and thermal transport properties of the neutron star crust. In addition we propose for 9 orbits of HST time to investigate the UV spectrum of EXO 0748-676 to disentangle its quiescent accretion stream. This is of vital importance for a correct interpretation of the quiescent thermal X-ray emission and hence of the observed crust cooling. ------------------------------------------------------------------------------------ Observations Description ------------------------ The cold quiescent accretion disk in LMXBs is expected to peak in the UV band, with most ionized emission lines occurring in the FUV between ~1200-1700 Angstrom. Investigation of the quiescent accretion stream in EXO 0748-676 thus benets most from spectroscopic observations with the HST/COS. Given the expected faintness of our target we propose to use the COS with the low-resolution G140L grating to obtain the best possible S/N. The resolving power of the low-resolution grating is sucient to resolve the expected ionized emission lines (which have typical widths of ~10 Angstrom), and to determine whether these lines are single or double peaked. We propose to use the 1105 A setting that provides continuous coverage between 1118-2251A in segment A, while segment B is switched off. To determine the time required for the science exposures, we used the online HST-COS exposure time calculators (v. 20.1.1). We model our point source as a blackbody with a temperature of ~10, 000 K (as has been found from modeling a number of quiescent X-ray binaries; Hynes & Robinson 2012), where we normalized the continuum flux to the value inferred from XMM-Newton/OM data of our target (~5E-16 erg/cm2/s at 2910 Angstrom; Diaz-Trigo et al. 2011). The reddening towards our target is E(B-V))=0.12. We propose to use different FP-POS positions to reduce fixed-pattern noise and to minimize long-term gain sag. The total observing time of 9 orbits is spread over two visits. 13108( 3) - 30-Jan-2013 18:03:03 - [ 2] Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 13108( 3) - 30-Jan-2013 18:03:03 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 V-UY-VOL STAR, ACCRETION DISK, RA=07H48M33.7300S +/- 0.6", J2000 V = 16.9 Expected continuum flux in the LMXB, NEUTRON STAR, DEC=-67D45'7.90" +/- 0.6" FUV: ~(0.5-5)E-16 erg/cm2/s X-RAY BURSTER, X-RAY TRANSIENT Reference Frame: ICRS Comments: The target only became bright in 1985 so it is not in the GSC1 catalog. ------------------------------------------------------------------------------------------------------------------------------------ 13108( 3) - 30-Jan-2013 18:03:03 - [ 4] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 V-UY-VOL COS/NUV ACQ/SEA PSA MIRRORA CENTER=FLUX-WT, SCAN-SIZE=2, 1 51 S RCH STEP-SIZE=1.767 ------------------------------------------------------------------------------------------------------------------------------------ 2 V-UY-VOL COS/NUV ACQ/IMA PSA MIRRORA 1 51 S GE ------------------------------------------------------------------------------------------------------------------------------------ 3 V-UY-VOL COS/FUV TIME-TA PSA G140L 1105 FP-POS=1, BUFFER-TIME=2423 1 2423 S G ------------------------------------------------------------------------------------------------------------------------------------ 4 V-UY-VOL COS/FUV TIME-TA PSA G140L 1105 FP-POS=1, BUFFER-TIME=1557 1 1557 S G ------------------------------------------------------------------------------------------------------------------------------------ 5 V-UY-VOL COS/FUV TIME-TA PSA G140L 1105 FP-POS=1, BUFFER-TIME=1561 1 1561 S G ------------------------------------------------------------------------------------------------------------------------------------ 6 V-UY-VOL COS/FUV TIME-TA PSA G140L 1105 FP-POS=2, BUFFER-TIME=1558 1 1558 S G ------------------------------------------------------------------------------------------------------------------------------------ 7 V-UY-VOL COS/FUV TIME-TA PSA G140L 1105 FP-POS=2, BUFFER-TIME=1560 1 1560 S G ------------------------------------------------------------------------------------------------------------------------------------ 8 V-UY-VOL COS/FUV TIME-TA PSA G140L 1105 FP-POS=3, BUFFER-TIME=1558 1 1558 S G ------------------------------------------------------------------------------------------------------------------------------------ 9 V-UY-VOL COS/FUV TIME-TA PSA G140L 1105 FP-POS=3, BUFFER-TIME=1560 1 1560 S G ------------------------------------------------------------------------------------------------------------------------------------ 10 V-UY-VOL COS/FUV TIME-TA PSA G140L 1105 FP-POS=4, BUFFER-TIME=1558 1 1558 S G ------------------------------------------------------------------------------------------------------------------------------------ 11 V-UY-VOL COS/FUV TIME-TA PSA G140L 1105 FP-POS=4, BUFFER-TIME=1560 1 1560 S G ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ V-UY-VOL 1 COS/NUV ACQ/SEA PSA MIRRORA none none none none 1 N/A RCH 13108( 3) - 30-Jan-2013 18:03:03 - [ 5] Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ V-UY-VOL 2 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE V-UY-VOL 3 COS/FUV TIME-TA PSA G140L 1105 none none none none 1 N/A G V-UY-VOL 4 COS/FUV TIME-TA PSA G140L 1105 none none none none 2 N/A G V-UY-VOL 5 COS/FUV TIME-TA PSA G140L 1105 none none none none 2 N/A G V-UY-VOL 6 COS/FUV TIME-TA PSA G140L 1105 none none none none 3 N/A G V-UY-VOL 7 COS/FUV TIME-TA PSA G140L 1105 none none none none 3 N/A G V-UY-VOL 8 COS/FUV TIME-TA PSA G140L 1105 none none none none 4 N/A G V-UY-VOL 9 COS/FUV TIME-TA PSA G140L 1105 none none none none 4 N/A G V-UY-VOL 10 COS/FUV TIME-TA PSA G140L 1105 none none none none 5 N/A G V-UY-VOL 11 COS/FUV TIME-TA PSA G140L 1105 none none none none 5 N/A G 13108( 3) - 30-Jan-2013 18:03:03 - [ 6] Visit: 02 Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 V-UY-VOL COS/NUV ACQ/SEA PSA MIRRORA CENTER=FLUX-WT, SCAN-SIZE=2, 1 51 S RCH STEP-SIZE=1.767 ------------------------------------------------------------------------------------------------------------------------------------ 2 V-UY-VOL COS/NUV ACQ/IMA PSA MIRRORA 1 51 S GE ------------------------------------------------------------------------------------------------------------------------------------ 3 V-UY-VOL COS/FUV TIME-TA PSA G140L 1105 FP-POS=1, BUFFER-TIME=2423 1 2423 S G ------------------------------------------------------------------------------------------------------------------------------------ 4 V-UY-VOL COS/FUV TIME-TA PSA G140L 1105 FP-POS=1, BUFFER-TIME=1557 1 1557 S G ------------------------------------------------------------------------------------------------------------------------------------ 5 V-UY-VOL COS/FUV TIME-TA PSA G140L 1105 FP-POS=1, BUFFER-TIME=1561 1 1561 S G ------------------------------------------------------------------------------------------------------------------------------------ 6 V-UY-VOL COS/FUV TIME-TA PSA G140L 1105 FP-POS=2, BUFFER-TIME=1558 1 1558 S G ------------------------------------------------------------------------------------------------------------------------------------ 7 V-UY-VOL COS/FUV TIME-TA PSA G140L 1105 FP-POS=2, BUFFER-TIME=1560 1 1560 S G ------------------------------------------------------------------------------------------------------------------------------------ 8 V-UY-VOL COS/FUV TIME-TA PSA G140L 1105 FP-POS=3, BUFFER-TIME=1558 1 1558 S G ------------------------------------------------------------------------------------------------------------------------------------ 9 V-UY-VOL COS/FUV TIME-TA PSA G140L 1105 FP-POS=4, BUFFER-TIME=1557 1 1557 S G ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ V-UY-VOL 1 COS/NUV ACQ/SEA PSA MIRRORA none none none none 1 N/A RCH V-UY-VOL 2 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE V-UY-VOL 3 COS/FUV TIME-TA PSA G140L 1105 none none none none 1 N/A G V-UY-VOL 4 COS/FUV TIME-TA PSA G140L 1105 none none none none 2 N/A G 13108( 3) - 30-Jan-2013 18:03:03 - [ 7] Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ V-UY-VOL 5 COS/FUV TIME-TA PSA G140L 1105 none none none none 2 N/A G V-UY-VOL 6 COS/FUV TIME-TA PSA G140L 1105 none none none none 3 N/A G V-UY-VOL 7 COS/FUV TIME-TA PSA G140L 1105 none none none none 3 N/A G V-UY-VOL 8 COS/FUV TIME-TA PSA G140L 1105 none none none none 4 N/A G V-UY-VOL 9 COS/FUV TIME-TA PSA G140L 1105 none none none none 4 N/A G 13108( 3) - 30-Jan-2013 18:03:03 - [ 8] Summary Form for Proposal 13108 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/FUV, COS/NUV ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/IMAGE, ACQ/SEARCH, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=1557, BUFFER-TIME=1558, BUFFER-TIME=1560, BUFFER-TIME=1561, BUFFER-TIME=2423, CENTER=FLUX-WT, FP-POS=1, FP-POS=2, FP-POS=3, FP-POS=4, SCAN-SIZE=2, STEP-SIZE=1.767 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L, MIRRORA ------------------------------------------------------------------------------------------------------------------------------------ Target Names V-UY-VOL ------------------------------------------------------------------------------------------------------------------------------------