10806( 5) - 09-Apr-2008 18:49:57 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 10806 Version: 5 Check-in Time: 09-Apr-2008 18:49:57 STScI Edit Number: 1 Title Accretion in the closest binary systems known ------------------------------------------------------------------------------------ Type Cycle Parallel Pointing Tolerance GO 15 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Danny Steeghs Smithsonian Institution Astrophysical Observatory CoI: Dr. Gijs Nelemans Radboud University Nijmegen N CoI: Dr. Thomas R. Marsh The University of Warwick N CoI: Dr. Paul Groot Radboud University Nijmegen N CoI: Dr. Boris T. Gaensicke The University of Warwick N CoI: Dr. Gijsbert Roelofs Smithsonian Institution Astrophysical N Observatory ------------------------------------------------------------------------------------ Abstract Recently, three variable stars have been identified as likely accreting binary systems with ultra-short orbital periods. Optical and X-ray observations have revealed periodicities of 5-10 minutes, making them the closest binaries known as well as strong sources of gravitational wave emission. Such short-period accreting binaries form the cornerstone to our understanding of binary formation and evolution, in particular of the large double white dwarf population in our galaxy, a candidate progenitor population for Type Ia supernovae. We propose to obtain the first UV spectroscopy of these objects using the ACS prisms in order to (i) determine the temperature of the primary and the composition of their donor stars, (ii) correlate the UV variability with other wavebands and determine if the periods are indeed orbital. These UV observations are essential in order to unequivocally determine whether these are indeed the most compact binaries known. ------------------------------------------------------------------------------------ Observations Description ------------------------ Our targets are ultra-compact binary systems containing an accreting white dwarf feeding off a low mass degenerate companion, which is likely another white dwarf. We propose to employ the prisms on ACS to obtain time resolved UV spectroscopy of our two targets which have binary periods of 5-10 minutes only. By using both the SBC PR110L prism as well as the HRC PR200L, we will cover a wide wavelength range from 1150-3600A. This is essential to ensure we can account for the effect of modest reddening and derive a well constrained temperature for the accreting white dwarf. A large number of strong emission lines are also expected across this wavelength range as well as Ly-alpha. We need to establish the UV variations as a function of the proposed orbital periods, so we will take a series of identical short exposures covering several binary periods. This will allow us to fold the UV time-series on the accurately known periods and study the wavelength dependence of the orbital modulations. These have amplitudes of 15-20% in the optical range but are expected to be higher in the UV. The exposure times have been optimised to ensure efficient orbit packing yet at the same time adequately sample the short orbital periods. 10806( 5) - 09-Apr-2008 18:49:57 - [ 2] For ES Cet, with a period of 10.3 minutes, the exposures are close to 90s, whereas for RXJ0806 we drop them to 60s to accomodate its 5 minute orbit. Each set of prism spectra is preceded by a short imaging observations to serve as a reference. We have used a manual image here to optimise the orbit usage and have set the AUTOIMAGE flag to no. The image is then followed by a series of identical prism exposures that fill the remainder of the orbit. The observations are split into two visits, one visit per object. Within each visit, we acquire both HRC and SBC spectroscopy to provide the required wavelength range. For ES Cet, the UV flux is well established thanks to IUE fluxes, providing a good S/N of 50-60 per exposure. One orbit each in HRB/SBC will suffice. For RXJ0806, we expect a S/N of 7-15 per exposure, and we thus spend two SBC orbits on RXJ0806, and one orbit on the HRC exposures. For our brighter target, ES Cet, SBC-MAMA count-rates are in a safe regime. Although the source is variable with expected amplitudes of 20-30%, the system has never shown any large amplitude brightness variations since its discovery. It is persistently accreting at high rates, and thus one does not expect it to exhibit accretion driven outburst events. We aim to obtain supporting observations near any scheduled HST visits to provide additional constraints on its flux. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 10806( 5) - 09-Apr-2008 18:49:57 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 ES-CET STAR, INTERACTING RA=02H00M52.2100S +/- 0.25", J2000 V = 16.9 +/- 0.1 U-B=-1.1, BINARY DEC=-09D24'31.60" +/- 0.25" E(B-V)=0.025, F_lambda=5e-14 at 1200A (IUE) Reference Frame: ICRS Comments: UV flux is well characterised thanks to an IUE spectrum (flux levels of 2-5e-14 across IUE wavebands) as well as GALEX imaging (corresponding to flux levels of 2.8-3.6e-14). Object is variable at 20% level but intensive monitoring shows no large-amplitude variations or outbursts. ------------------------------------------------------------------------------------------------------------------------------------ 2 RX-J0806.3+1 STAR, INTERACTING RA=08H06M22.9500S +/- 0.4", J2000 V = 21.1 +/- 0.1 B-V=-0.2, E(B-V)=0.025 527 BINARY DEC=+15D27'31.10" +/- 0.4" Reference Frame: ICRS Comments: No UV observations exist for this target. However the SED has been characterised well both in the soft X-rays and the blue end of the optical range. Its faintness ensures that the SBC countrates will be far removed from the limits. The source is variable at a level of 10-20%, but repeated observations over many years show no large amplitude variations. ------------------------------------------------------------------------------------------------------------------------------------ 10806( 5) - 09-Apr-2008 18:49:57 - [ 4] Visit: 01 Visit Priority: Visit Requirements: PCS MODE FINE On Hold Comments: Additional Comments: WFPC2 and SBC prism observations are combined in 1 visit. The object is variable, and we need to obain both wave-bands at the same time so that the two spectral bands can be fitted jointly. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 ES-CET WFPC2 IMAGE PC1 F218W 6 40.0 S ------------------------------------------------------------------------------------------------------------------------------------ 2 ES-CET WFPC2 IMAGE PC1 F255W 6 40.0 S ------------------------------------------------------------------------------------------------------------------------------------ 3 ES-CET WFPC2 IMAGE PC1 F336W 6 40.0 S ------------------------------------------------------------------------------------------------------------------------------------ 4 ES-CET ACS/SBC ACCUM SBC F122M 1 26.0 S Comments: Manual zero-point instead of autoimage, use of narrow band Ly-alpha filter to keep countrates low ------------------------------------------------------------------------------------------------------------------------------------ 5 ES-CET ACS/SBC ACCUM SBC PR110L 20 91.0 S ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ ES-CET 1 WFPC2 IMAGE PC1 F218W none none 1 none 1 N/A ES-CET 1 WFPC2 IMAGE PC1 F218W none none 2 none 1 N/A ES-CET 1 WFPC2 IMAGE PC1 F218W none none 3 none 1 N/A ES-CET 1 WFPC2 IMAGE PC1 F218W none none 4 none 1 N/A ES-CET 1 WFPC2 IMAGE PC1 F218W none none 5 none 1 N/A ES-CET 1 WFPC2 IMAGE PC1 F218W none none 6 none 1 N/A ES-CET 2 WFPC2 IMAGE PC1 F255W none none 1 none 1 N/A ES-CET 2 WFPC2 IMAGE PC1 F255W none none 2 none 1 N/A ES-CET 2 WFPC2 IMAGE PC1 F255W none none 3 none 1 N/A ES-CET 2 WFPC2 IMAGE PC1 F255W none none 4 none 1 N/A ES-CET 2 WFPC2 IMAGE PC1 F255W none none 5 none 1 N/A ES-CET 2 WFPC2 IMAGE PC1 F255W none none 6 none 1 N/A ES-CET 3 WFPC2 IMAGE PC1 F336W none none 1 none 1 N/A ES-CET 3 WFPC2 IMAGE PC1 F336W none none 2 none 1 N/A ES-CET 3 WFPC2 IMAGE PC1 F336W none none 3 none 1 N/A ES-CET 3 WFPC2 IMAGE PC1 F336W none none 4 none 1 N/A ES-CET 3 WFPC2 IMAGE PC1 F336W none none 5 none 1 N/A ES-CET 3 WFPC2 IMAGE PC1 F336W none none 6 none 1 N/A ES-CET 4 ACS/SBC ACCUM SBC F122M none none none none 2 N/A ES-CET 5 ACS/SBC ACCUM SBC PR110L none none 1 none 2 N/A 10806( 5) - 09-Apr-2008 18:49:57 - [ 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 | ------------------------------------------------------------------------------------------------------------------------------------ ES-CET 5 ACS/SBC ACCUM SBC PR110L none none 2 none 2 N/A ES-CET 5 ACS/SBC ACCUM SBC PR110L none none 3 none 2 N/A ES-CET 5 ACS/SBC ACCUM SBC PR110L none none 4 none 2 N/A ES-CET 5 ACS/SBC ACCUM SBC PR110L none none 5 none 2 N/A ES-CET 5 ACS/SBC ACCUM SBC PR110L none none 6 none 2 N/A ES-CET 5 ACS/SBC ACCUM SBC PR110L none none 7 none 2 N/A ES-CET 5 ACS/SBC ACCUM SBC PR110L none none 8 none 2 N/A ES-CET 5 ACS/SBC ACCUM SBC PR110L none none 9 none 2 N/A ES-CET 5 ACS/SBC ACCUM SBC PR110L none none 10 none 2 N/A ES-CET 5 ACS/SBC ACCUM SBC PR110L none none 11 none 2 N/A ES-CET 5 ACS/SBC ACCUM SBC PR110L none none 12 none 2 N/A ES-CET 5 ACS/SBC ACCUM SBC PR110L none none 13 none 2 N/A ES-CET 5 ACS/SBC ACCUM SBC PR110L none none 14 none 2 N/A ES-CET 5 ACS/SBC ACCUM SBC PR110L none none 15 none 2 N/A ES-CET 5 ACS/SBC ACCUM SBC PR110L none none 16 none 2 N/A ES-CET 5 ACS/SBC ACCUM SBC PR110L none none 17 none 2 N/A ES-CET 5 ACS/SBC ACCUM SBC PR110L none none 18 none 2 N/A ES-CET 5 ACS/SBC ACCUM SBC PR110L none none 19 none 2 N/A ES-CET 5 ACS/SBC ACCUM SBC PR110L none none 20 none 2 N/A 10806( 5) - 09-Apr-2008 18:49:57 - [ 6] Visit: 02 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: HRC and SBC prism observations are combined in 1 visit. The object is variable, and we need to obain both wave-bands at the same time so that the two spectral bands can be fitted jointly. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 RX-J0806.3+ ACS/HRC ACCUM HRC F250W 1 66.0 S 1527 Comments: Zeropoint image instead of AUTOIMAGE ------------------------------------------------------------------------------------------------------------------------------------ 2 RX-J0806.3+ ACS/HRC ACCUM HRC PR200L CR-SPLIT=NO, AUTOIMAGE=NO 22 60.0 S 1527 ------------------------------------------------------------------------------------------------------------------------------------ 3 RX-J0806.3+ ACS/SBC ACCUM SBC F115LP 1 82.0 S 1527 Comments: Zeropoint image instead of AUTOIMAGE ------------------------------------------------------------------------------------------------------------------------------------ 4 RX-J0806.3+ ACS/SBC ACCUM SBC PR110L 52 62.0 S 1527 Comments: We want to phase-fold all exposures and thus want to keep the exposure times fixed. This is the reason the auto-adjust feature has not been used to fill out the last orbit (whihc has 35s left). ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ RX-J0806.3+1527 1 ACS/HRC ACCUM HRC F250W none none none 1 1 N/A RX-J0806.3+1527 1 ACS/HRC ACCUM HRC F250W none none none 2 1 N/A RX-J0806.3+1527 2 ACS/HRC ACCUM HRC PR200L none none 1 none 1 N/A RX-J0806.3+1527 2 ACS/HRC ACCUM HRC PR200L none none 2 none 1 N/A RX-J0806.3+1527 2 ACS/HRC ACCUM HRC PR200L none none 3 none 1 N/A RX-J0806.3+1527 2 ACS/HRC ACCUM HRC PR200L none none 4 none 1 N/A RX-J0806.3+1527 2 ACS/HRC ACCUM HRC PR200L none none 5 none 1 N/A RX-J0806.3+1527 2 ACS/HRC ACCUM HRC PR200L none none 6 none 1 N/A RX-J0806.3+1527 2 ACS/HRC ACCUM HRC PR200L none none 7 none 1 N/A RX-J0806.3+1527 2 ACS/HRC ACCUM HRC PR200L none none 8 none 1 N/A RX-J0806.3+1527 2 ACS/HRC ACCUM HRC PR200L none none 9 none 1 N/A RX-J0806.3+1527 2 ACS/HRC ACCUM HRC PR200L none none 10 none 1 N/A RX-J0806.3+1527 2 ACS/HRC ACCUM HRC PR200L none none 11 none 1 N/A RX-J0806.3+1527 2 ACS/HRC ACCUM HRC PR200L none none 12 none 1 N/A 10806( 5) - 09-Apr-2008 18:49:57 - [ 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 | ------------------------------------------------------------------------------------------------------------------------------------ RX-J0806.3+1527 2 ACS/HRC ACCUM HRC PR200L none none 13 none 1 N/A RX-J0806.3+1527 2 ACS/HRC ACCUM HRC PR200L none none 14 none 1 N/A RX-J0806.3+1527 2 ACS/HRC ACCUM HRC PR200L none none 15 none 1 N/A RX-J0806.3+1527 2 ACS/HRC ACCUM HRC PR200L none none 16 none 1 N/A RX-J0806.3+1527 2 ACS/HRC ACCUM HRC PR200L none none 17 none 1 N/A RX-J0806.3+1527 2 ACS/HRC ACCUM HRC PR200L none none 18 none 1 N/A RX-J0806.3+1527 2 ACS/HRC ACCUM HRC PR200L none none 19 none 1 N/A RX-J0806.3+1527 2 ACS/HRC ACCUM HRC PR200L none none 20 none 1 N/A RX-J0806.3+1527 2 ACS/HRC ACCUM HRC PR200L none none 21 none 1 N/A RX-J0806.3+1527 2 ACS/HRC ACCUM HRC PR200L none none 22 none 1 N/A RX-J0806.3+1527 3 ACS/SBC ACCUM SBC F115LP none none none none 2 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 1 none 2 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 2 none 2 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 3 none 2 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 4 none 2 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 5 none 2 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 6 none 2 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 7 none 2 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 8 none 2 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 9 none 2 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 10 none 2 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 11 none 2 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 12 none 2 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 13 none 2 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 14 none 2 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 15 none 2 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 16 none 2 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 17 none 2 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 18 none 2 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 19 none 2 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 20 none 2 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 21 none 2 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 22 none 2 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 23 none 2 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 24 none 2 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 25 none 2 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 26 none 3 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 27 none 3 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 28 none 3 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 29 none 3 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 30 none 3 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 31 none 3 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 32 none 3 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 33 none 3 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 34 none 3 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 35 none 3 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 36 none 3 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 37 none 3 N/A 10806( 5) - 09-Apr-2008 18:49:57 - [ 8] 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 | ------------------------------------------------------------------------------------------------------------------------------------ RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 38 none 3 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 39 none 3 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 40 none 3 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 41 none 3 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 42 none 3 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 43 none 3 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 44 none 3 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 45 none 3 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 46 none 3 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 47 none 3 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 48 none 3 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 49 none 3 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 50 none 3 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 51 none 3 N/A RX-J0806.3+1527 4 ACS/SBC ACCUM SBC PR110L none none 52 none 3 N/A 10806( 5) - 09-Apr-2008 18:49:57 - [ 9] Summary Form for Proposal 10806 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures HRC, PC1, SBC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/HRC, ACS/SBC, WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters AUTOIMAGE=NO, CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PCS MODE FINE ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F115LP, F122M, F218W, F250W, F255W, F336W, PR110L, PR200L ------------------------------------------------------------------------------------------------------------------------------------ Target Names ES-CET, RX-J0806.3+1527 ------------------------------------------------------------------------------------------------------------------------------------