9170( 4) - 05/17/01 17:14 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9170 Version: 4 Check-in Date: 17-May-2001 17:14:06 1.Proposal Title: The Post-CE Status of the Massive WD Binary LB11146 ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 10 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Edmund Nelan Space Telescope Science Institute CoI: Dr. Rex Saffer Villanova University N ------------------------------------------------------------------------------------ 5. Abstract By analysis of its spectrum, LB11146 was discovered to be a binary system composed of magnetic/nonmagnetic white dwarfs each having a mass estimated to be ~0.9 M_solar, making it the only known double degenerate system with a combined mass exceeding the Chandrasekhar limit. HST/FOC imaging failed to resolve the system down to ~0.030". This places a 50 percent probability that the stars are separated by less than ~1 A.U. and suggests that they shared a common envelope (CE) one or more times in the past as their massive progenitors evolved through the asymtotic giant branch. However, null results from radial velocity observations constrain the orbit to be larger than 0.1 A.U., which suggests that if this is a post-CE system, the orbital shrinkage was not extreme. We propose to observe this object at high angular resolution with FGS1r. With an angular resolution of ~7 mas, FGS1r can measure or place tighter constraints (down to 0.3 A.U.) on the WD separation to unambiguously determine if this is a post-CE system. If the system is resolved, followup studies can determine dynamical masses. If the system is found to to be post-CE, it will offer a rare opportunity for observationally estimating the elusive CE efficiency parameter alpha_CE. This is of great interest for evaluating the prospects of merging post-CE massive WDs as the mechanism for SN Ia. ------------------------------------------------------------------------------------ 9170( 4) - 05/17/01 17:14 - [ 2] Observations Description ------------------------ We request 2 HST orbits to observe this system on 2 epochs separated by about 4 months. If the system is resolved in both visits with an angular separation greater than ~0".010, the change in the position angle can be measured to determine if the orbit is close or wide with a small projection. If the object is not resolved in either visit, the case for a very close system becomes compelling. We will observe the target with FGS1r in Transfer Mode. The object will be scanned approximately 50 times to achieve the necessary S/N. Given that the binary components are of nearly equal temperature and mass (size), the magnitude difference will be small (~0.4), an ideal situation for resolving the system with the FGS. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9170( 4) - 05/17/01 17:14 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 LB11146 STAR, DA RA=09H 48M 46.74S +/- 2", J2000 V = 14.3+/-0.2 DEC=24D 21' 27.540" +/- 2", PLATE-ID=01X3 Coordinate Source: GUIDE_STAR_CATALOG 2 LB11146-SKY1 CALIBRATION, SKY RA=09H 48M 46.7S +/- 2", DEC=24D J2000 V = 9.0+/-0.0 BACKGROUND, PHOTOMETRIC 21' 00" +/- 2", PLATE-ID=01X3 Coordinate Source: GUIDE_STAR_CATALOG 3 LB11146-SKY2 CALIBRATION, RA=09H 48M 46.7S +/- 2", DEC=24D J2000 V = 9.0+/-0.0 ASTROMETRIC, 22' 0" +/- 2", PLATE-ID=01X3 PHOTOMETRIC Coordinate Source: GUIDE_STAR_CATALOG 9170( 4) - 05/17/01 17:14 - [ 4] Visit: 01 Visit Priority: Visit Requirements: SCHED 30% 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 LB11146-SKY FGS POS 1 F583W 1 10 S SAME POS AS 20 SEQ 10-30 1 NON-INT Comments: sky background measurement 1 ------------------------------------------------------------------------------------------------------------------------------------ 20 LB11146 FGS TRANS 1 F583W SCANS=37,STEP-SIZE=0.6, 1 1200 S POS TARG 0, 0 ACQ-DIST=20 Comments: scan length = 0.9" ------------------------------------------------------------------------------------------------------------------------------------ 30 LB11146 FGS TRANS 1 F583W SCANS=10,STEP-SIZE=1,ACQ-DIST=20 1 400 S SAME POS AS 20 Comments: scan length = 1.6" ------------------------------------------------------------------------------------------------------------------------------------ 9170( 4) - 05/17/01 17:14 - [ 5] Visit: 02 Visit Priority: Visit Requirements: SCHED 30% AFTER 01 BY 100 D TO 140 D 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 LB11146-SKY FGS POS 1 F583W 1 10 S SAME POS AS 20 SEQ 10-30 1 NON-INT Comments: sky background measurement 1 ------------------------------------------------------------------------------------------------------------------------------------ 20 LB11146 FGS TRANS 1 F583W SCANS=37,STEP-SIZE=0.6, 1 1200 S POS TARG 0, 0 ACQ-DIST=20 Comments: scan length = 0.9" ------------------------------------------------------------------------------------------------------------------------------------ 30 LB11146 FGS TRANS 1 F583W SCANS=10,STEP-SIZE=1,ACQ-DIST=20 1 400 S SAME POS AS 20 Comments: scan length = 1.6" ------------------------------------------------------------------------------------------------------------------------------------ 9170( 4) - 05/17/01 17:14 - [ 6] Summary Form for Proposal 9170 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations FGS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes POS TRANS ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SCANS=37 STEP-SIZE=0.6 ACQ-DIST=20 STEP-SIZE=1 SCANS=10 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements SCHED 30% SAME POS AS 20 SEQ 10-30 NON-INT POS TARG 0, 0 SAME POS AS 20 SCHED 30% AFTER 01 BY 100 D TO 140 D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F583W ------------------------------------------------------------------------------------------------------------------------------------ Target Names LB11146-SKY1 LB11146 ------------------------------------------------------------------------------------------------------------------------------------