9038( 3) - 05/21/01 06:38 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 9038 Version: 3 Check-in Date: 21-May-2001 06:38:04 1.Proposal Title: The Evolution of Cataclysmic Variable Stars ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 10 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Thomas Marsh Southampton University CoI: Ms. Rachel North Department of Physics and Astronomy, N Southampton University ------------------------------------------------------------------------------------ 5. Abstract We have discovered that EM Cygni, one of the most well-known cataclysmic variable stars (CVs), is very likely in a triple system with a spatially-unresolved K dwarf. EM Cyg has well measured masses, and the white dwarf's mass of 1.1 Msun shows that it must have come from an AGB star. This, together with considerations of binary evolution, can be used to predict a lower limit to the present-day separation of EM Cyg and the K dwarf of > 18, AU. Ground-based imaging only puts an upper limit on the angular separation of 0.2'', equivalent to < 60, AU at the 300, pc distance of EM Cyg; this does not seriously test the evolutionary prediction. With HST and FGS1R on the other hand, we can resolve a separation 6 AU, providing a direct test of the evolutionary path that leads to CVs, as well as to the Super-Soft X-ray sources widely believed to be the progenitors of Type Ia supernovae. ------------------------------------------------------------------------------------ 9038( 3) - 05/21/01 06:38 - [ 2] Observations Description ------------------------ We propose to resolve EM Cyg from its companion using the FGS1R in its TRANS mode. North et al (2000) determined that the third star contributed about 16% of the light in R when EM Cyg was at V ~ 13.0. This is approximately the mean magnitude of EM Cyg, but as a dwarf nova it ranges from 14.3 to 12.0, and is of unpredictable magnitude within these limits at any particular epoch. Ground- based data indicates a separation below 0.2" but to be conservative in choosing scan lengths we assume < 0.4". From consultation with STScI we therefore adopt the following plan: (1) a POS mode measurement of the background near EM Cyg, followed by (2) as many TRANS mode scans of length 1.3" as can fit within the visibility window. Real Time Justification ----------------------- N/A N/A Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 9038( 3) - 05/21/01 06:38 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 EM-CYG STAR, DWARF NOVA, RA=19H 38M 40.14S +/- 0.3", J2000 V = -20 V = 13.4+/-1.0 INTERACTING BINARY DEC=30D 30' 28.2" +/- 0.3", B-V = 0.35+/-0.2 PLATE-ID=000J U-B = -0.7+/-0.1 E(B-V) = 0.05+/-0.03 Coordinate Source: GUIDE_STAR_CATALOG Comments: EM Cyg is a variable star. The range quoted on the V mag expresses this variability which is a combination of true variations and shallow eclipses. 2 DARK-SKY-REF CALIBRATION, SKY RA=19H 38M 35.0S +/- 1", DEC=30D J2000 V = 11+/-0.1 BACKGROUND 30' 27" +/- 1" Coordinate Source: OTHER_SOURCE Comments: This is a region that we have verified from ground- based images to be free of stars in order to obtain a sky background measurement. 9038( 3) - 05/21/01 06:38 - [ 4] Visit: 01 Visit Priority: Visit Requirements: 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 DARK-SKY-RE FGS POS PRIME F583W 1 30 S SEQ 1-2 NON-INT SAME POS F AS 2 Comments: I have used the SAME POS special requirement without, I admit, fully understanding the need for it. However there was a very similar example in the FGS manual and therefore I assume that I do need to specify it. ------------------------------------------------------------------------------------------------------------------------------------ 2 EM-CYG FGS TRANS PRIME F583W SCANS=51,STEP-SIZE=1.0 1 1670 S POS TARG 0, 0 Comments: POS TARG added by PC with permission from PI. Was recommended by Ed Nelan. ------------------------------------------------------------------------------------------------------------------------------------ 9038( 3) - 05/21/01 06:38 - [ 5] Summary Form for Proposal 9038 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PRIME ------------------------------------------------------------------------------------------------------------------------------------ Configurations FGS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes POS TRANS ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SCANS=51 STEP-SIZE=1.0 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements SEQ 1-2 NON-INT SAME POS AS 2 POS TARG 0, 0 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F583W ------------------------------------------------------------------------------------------------------------------------------------ Target Names DARK-SKY-REF EM-CYG ------------------------------------------------------------------------------------------------------------------------------------