10999( 3) - 02/27/07 15:48 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 10999 Version: 3 Check-in Time: 27-Feb-2007 20:47:14 STScI Edit Number: 0 Title Testing the first direct measurement of cataclysmic variable evolution: the search for a circumbinary disk or a low?mass companion around NN Serpentis ------------------------------------------------------------------------------------ Type Cycle Parallel Pointing Tolerance GO 15 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Carolyn S. Brinkworth Spitzer Science Center CoI: Dr. Donald W. Hoard California Institute of Technology N CoI: Dr. Thomas R. Marsh The University of Warwick N CoI: Dr. Stefanie Wachter California Institute of Technology N ------------------------------------------------------------------------------------ Abstract We obtained high time-resolution photometry using the high speed CCD camera ULTRACAM between 2002 and 2004, which revealed a gradual reduction in the orbital period of the pre- cataclysmic variable NN Serpentis. There are three possible explanations for this period change: firstly, we may have been successful in obtaining the first and only direct measurement of the braking rate of a close binary system, in which case our measured values are approximately 2 orders of magnitude greater than predicted, and pose serious problems for the theory of close binary evolution. Secondly, the unusually high braking rate may be caused by the presence of a circumbinary disk, which would help to answer two of the outstanding problems with current CV theory - namely the high mass-transfer rates seen in some CVs, and the fact that the minimum observed value in the CV period distribution is approximately 15% longer than expected. Finally, our observations could be explained by a light travel-time effect caused by a third body in orbit around the binary, which would raise major questions about the evolutionary history of the system, in particular how a third body has managed to remain in a stable orbit throughout periods of intense mass-loss in the central binary. We intend to use IRAC observations to search for a mid-infrared excess in the spectral energy distribution of NN Ser, which would confirm the presence of either a disk or a third body. We then propose to use HST imaging to attempt to resolve a third body, allowing us to discriminate between the two possibilities. If both methods fail to reveal any extra system components, we will have ruled out our only remaining alternatives to a genuinely high angular momentum loss rate in this system, with profound implications for CV evolution. ------------------------------------------------------------------------------------ 10999( 3) - 02/27/07 15:48 - [ 2] Observations Description ------------------------ We will use the WFPC2 with both the F555W and F814W filters to obtain deep images of NN Ser. The goal is to detect a tertiary red dwarf companion, therefore we require the colour information to differentiate between the known central binary components and any third body. In order to remove cosmic rays, hot pixels and detector blemishes, minimise flat-fielding errors, and, most importantly, oversample the PSF, we will utilise an 4-point box dither pattern. To be certain that we image deeply enough, we have estimated the likely V- and I-band brightness of the central system and the tertiary companion. We used the WFPC2 ETC to obtain total- and sub-exposure times required to obtain a S/N of 30 for V=22 and I=20 respectively, while ensuring that the brighter central binary system is never over-exposed. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 10999( 3) - 02/27/07 15:48 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NN-SER STAR, CIRCUMSTELLAR RA=15H52M56.2000S +/- 0.1", J2000 V = 17.0+/-0.5 MATTER, DA, M V-IV, LOW DEC=+12D54'47.20" +/- 0.1" I=17+/10.5 MASS COMPANION Reference Frame: ICRS 10999( 3) - 02/27/07 15:48 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFPC2-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.559017 Line_Spacing 0.559017 Coordinate_Frame POS-TARG Pattern_Orient 26.56505 Angle_Between_Sides 143.130102 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 10999( 3) - 02/27/07 15:48 - [ 5] Visit: 01 Visit Priority: 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 NN-SER WFPC2 IMAGE WF2 F814W 1 60 S SAME OBSET 1; PATTERN 1 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 NN-SER WFPC2 IMAGE WF2 F555W 1 100 S SAME OBSET 2; PATTERN 1 2 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ NN-SER 1 WFPC2 IMAGE WF2 F814W 1 none none none 1 N/A NN-SER 1 WFPC2 IMAGE WF2 F814W 2 none none none 1 N/A NN-SER 1 WFPC2 IMAGE WF2 F814W 3 none none none 1 N/A NN-SER 1 WFPC2 IMAGE WF2 F814W 4 none none none 1 N/A NN-SER 2 WFPC2 IMAGE WF2 F555W 1 none none none 1 N/A NN-SER 2 WFPC2 IMAGE WF2 F555W 2 none none none 1 N/A NN-SER 2 WFPC2 IMAGE WF2 F555W 3 none none none 1 N/A NN-SER 2 WFPC2 IMAGE WF2 F555W 4 none none none 1 N/A 10999( 3) - 02/27/07 15:48 - [ 6] Summary Form for Proposal 10999 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WF2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements SAME OBSET 1; PATTERN 1 1; SAME OBSET 2; PATTERN 1 2; ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F814W F555W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NN-SER ------------------------------------------------------------------------------------------------------------------------------------