12799( 3) - 12-Mar-2012 17:48:12 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 12799 Version: 3 Check-in Time: 12-Mar-2012 17:48:12 STScI Edit Number: 0 Title The Unique Recurrent Nova T Pyxidis: The Transition to Quiescence ------------------------------------------------------------------------------------ Type Cycle GO/DD 19 ------------------------------------------------------------------------------------ Investigators Contact? PI: Prof. Edward M. Sion Villanova University CoI: Dr. Patrick Godon Villanova University N CoI: Dr. Robert E. Williams Space Telescope Science Institute N CoI: Dr. Sumner G. Starrfield Arizona State University N CoI: Dr. Gregory James Schwarz American Astronomical Society N CoI: Dr. Steve Shore Universita di Pisa N CoI: Dr. Charles E. Woodward University of Minnesota - Twin Cities N CoI: Dr. Kim Page University of Leicester N CoI: Dr. Paul Kuin University College London (UCL) N ------------------------------------------------------------------------------------ Abstract The surprising April, 2011 explosion of the recurrent nova T Pyxidis offers a unique opportunity to catch T Pyx as it transitions into quiescence where we expect to see the FUV continuum fade, emission lines weaken and transition to the continuum in quiescence. Our three earlier STIS observations of T Pyx centered on the outburst maximum. By obtaining a complete cooling curve of the heated, bloated white dwarf in the FUV where the white dwarf and (possibly) the accretion disk dominate, we will discriminate between the cooling of a massive (near Chandrasekhat mass) post-nova white dwarf versus the cooling of a less massive white dwarf. We predict it will reach quiescence by the Fall of 2012 when a standard GO is planned. New post-recurrent nova cooling calculations are being done by Starrfield et al. (2012) in support of this proposal. Our modeling of this unique sequence should yield or constrain the white dwarf mass, detail the accretion environment, discover how much the WD was heated by the outburst, constrain the accretion rate, and possibly help explain why its latest nova outburst was delayed by 44 years. If, as we expect for its short recurrence time, the white dwarf is massive (1.35 solar mass) and near the Chandrasekhat limit. This is very likely the last time that an observation of a complete cooling curve, at least for the lifetime of COS, will be possible. Nothing is known about the cooling behavior of the white dwarf in recurrent novae so soon after outburst in the FUV with the necessary resolution. ------------------------------------------------------------------------------------ Observations Description ------------------------ As discussed with the STScI staff, we decide to use STIS with the E140M configuration (for safety reason) and COS with the G130 configuration (1055A). We discuss below safety issues and exposure time. T Pyx was observed last with STIS E140M several months ago (STIS spectrum n.3) and its flux was found to be 5 times larger than when observed in quiescence with IUE (see Figure 3 of proposal). To a good accuracy we estimate that the continuum flux level of T Pyx at the 12799( 3) - 12-Mar-2012 17:48:12 - [ 2] time of the observations will be at least twice that of the IUE continuum flux level (as shown in Figure 3 of our proposal) with the possible addition of emission lines. We first check a 100, 000K WD using our stellar atmosphere code TLUSTY and SYNSPEC (from I. Hubeny). At a distance of 3, 500pc, even with a bloated radius, the WD flux is found to be only a fraction of the existing STIS (n.3) or IUE spectra flux level. It is clear that from the WD itself there is no restriction nor safety concern as no emission lines are expected from the WD at all. For safety reasons we assume that at the time of the observations, the spectrum of T Pyx could have a flux as large as the one in its STIS spectrum n.3 and that the main dominating emission line will be from Nitrogen 5 (N V 1240 - a doublet), all the other lines will have decreased in strength as they already did (though it is very likely that even that NV will have much decreased). We put this STIS (n.3) spectrum into the ETC for STIS with E140M. Requesting a SNR of 10 at 1440A (where there is no emission lines only continuum) we obtained an exposure time of 4584s and no warning. For COS (G130 1055A) the existing STIS spectrum does not cover the shorter wavelengths and therefore it cannot be used in the ETC. We estimate the disk to dominate the spectrum, and its peak temperature will also reach about 100, 000K. We therefore assume a 100, 000K spectrum and we scale it to fit the flux level of the STIS spectrum around 1300-1400A (continuum). We then use this scaled spectrum in the ETC for COS. For a 2000s exposure time the ETC returns a SNR of about 4 at 1000A (2/3 of the buffer is less than 2000s). The count rate returned for segment A is 767 and 60 for segement B. We do not expect the flux to be that high, but put this maximum flux here are an upper limit for safety purpose. Since the possibility of using only segment B of COS was raised by the COS team, with a lower sensitivity, we will use the segmented COS spectrum only to assess the flux level of the continuum as a lower or upper limit and we do not require a high quality spectrum in that region (otherwise the exposure time would increase drastically). The guide star time, the target aqcuisition time and the instrument overhead time totals about 1, 600s for COS and 1200s for STIS for the first orbit and about half of that for the second orbit. The estimated visibiliy time is 55min or 3, 300s. First orbit for STIS has 2100s of observing time, and 2500s for the second orbit, totalling about 4600s - that's the estimate, the exact time appears after running the orbit planner. In the present configuration and with the present restriction and using COS to estimate the flux level as an upper or lower limit, we request 2 orbits for STIS and only one orbit for COS. On the overall the emission from the ejecta has decreased substantially and now the central object is the main source. So we can now more easily observed the decline of the system itself to quiescence and for the target acquisition we consider the source to be a point source. Its accuracy is known to less than 0.4arcsec. 12799( 3) - 12-Mar-2012 17:48:12 - [ 3] Real Time Justification ----------------------- We request that the STIS observation and COS observation be carried out one after the other, to ensure that the target has the same flux level and is exactly in the same state. Though it is unlikely that the target will change significantly even over a period of days, as it is cooling from its outburst (recurrent nova), we want to minimize the effect of any unpredictable (but small) change. Calibration Justification ------------------------- We are aware that the calibration for the present configuration of COS will not be available until Summer 2012 and we will first work on the STIS spectrum. Additional Comments ------------------- Additional emission lines are expected to be showing up in the COS spectrum, such as N iv (9201-925), S vi (933.5 and 944.5), C iii (977), N iii (991.6), O vi (1031.9, 1037.6). Additional lines would be on the segment A. All these lines are not expected to be as strong the N V (1240) line and should all be similar to the lines seen in the STIS spectrum n.3 or lower, therefore causing no safety problem to COS (these lines are usually broad but not too strong). Since that STIS spectrum was taken (3 months) the magnitude of the source has declined and we don't anticipate any strong lines to cause any problems to the instruments. As to the ejecta, from the shape and changes in the 3 STIS spectra obtaine last year (the lines have decreased in strength and the continuum has begun to appear), it is already in the otpically thin phase as the continuum from the central source is being revealed. We do not expect these ejecta lines to increase at this stage as the ejecta has dimmed a lot. The N V line is possibly from the central source all indicates it should also have decreased (as discussed at lengths in the email exchanges). ------------------------------------------------------------------------------------ 12799( 3) - 12-Mar-2012 17:48:12 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NOVA-PYX-189 STAR, ACCRETION DISK, RA=09H04M41.5000S +/- 0.1", J2000 V = 13.0 +/- 1.0 0 INTERACTING BINARY, DEC=-32D22'47.50" +/- 0.1" RECURRENT NOVA Reference Frame: ICRS Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. ------------------------------------------------------------------------------------------------------------------------------------ 12799( 3) - 12-Mar-2012 17:48:12 - [ 5] Visit: 01 Visit Requirements: SCHED 30%; BEFORE 01-APR-2012:00:00:00 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 NOVA-PYX-18 STIS/CCD ACQ F28X50LP MIRROR 1 1 S 90 ------------------------------------------------------------------------------------------------------------------------------------ 2 NOVA-PYX-18 STIS/FUV TIME-TA 0.2X0.2 E140M 1425 BUFFER-TIME=200 1 2300 S 90 -MAMA G see below ------------------------------------------------------------------------------------------------------------------------------------ 3 NOVA-PYX-18 STIS/FUV TIME-TA 0.2X0.2 E140M 1425 BUFFER-TIME=200 1 2300 S 90 -MAMA G see below ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ NOVA-PYX-1890 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A NOVA-PYX-1890 2 STIS/FUV TIME-TA 0.2X0.2 E140M 1425 none none none none 1 2457.0 S -MAMA G NOVA-PYX-1890 3 STIS/FUV TIME-TA 0.2X0.2 E140M 1425 none none none none 2 3023.0 S -MAMA G 12799( 3) - 12-Mar-2012 17:48:12 - [ 6] Visit: 02 Visit Requirements: SCHED 30%; AFTER 01 BY 1.9 Orbits TO 2.2 Orbits; BEFORE 01-APR-2012:00:00:00 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 NOVA-PYX-18 COS/NUV ACQ/IMA BOA MIRRORA 1 100 S 90 GE ------------------------------------------------------------------------------------------------------------------------------------ 2 NOVA-PYX-18 COS/FUV TIME-TA PSA G130M 1055 BUFFER-TIME=461, FP-POS=ALL 1 479 S 90 G see below ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ NOVA-PYX-1890 1 COS/NUV ACQ/IMA BOA MIRRORA none none none none 1 N/A GE NOVA-PYX-1890 2 COS/FUV TIME-TA PSA G130M 1055 none none none 1 1 461.0 S G NOVA-PYX-1890 2 COS/FUV TIME-TA PSA G130M 1055 none none none 2 1 461.0 S G NOVA-PYX-1890 2 COS/FUV TIME-TA PSA G130M 1055 none none none 3 1 461.0 S G NOVA-PYX-1890 2 COS/FUV TIME-TA PSA G130M 1055 none none none 4 1 461.0 S G 12799( 3) - 12-Mar-2012 17:48:12 - [ 7] Summary Form for Proposal 12799 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 0.2X0.2, BOA, F28X50LP, PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/FUV, COS/NUV, STIS/CCD, STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ, ACQ/IMAGE, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=200, BUFFER-TIME=461, FP-POS=ALL ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements AFTER 01 BY 1.9 Orbits TO 2.2 Orbits, BEFORE 01-APR-2012:00:00:00, SCHED 30% ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements E140M, G130M, MIRROR, MIRRORA ------------------------------------------------------------------------------------------------------------------------------------ Target Names NOVA-PYX-1890 ------------------------------------------------------------------------------------------------------------------------------------