0 Assigned ID: 3487 ----- Attempting Submission 1 (Fri Mar 25 20:04:24 GMT 2022) ----- 0 ----- Attempting Submission 1 (Fri Jul 01 14:04:21 GMT 2022) ----- Will the Recurrent Nova T Pyxidis Become a Type Ia Supernova? The recurrent nova T Pyx has erupted six times since 1890. The last outburst in 2011 offered a unique opportunity to catch T Pyx with HST as it transited into quiescence. The system has now passed its nebular phase and settled into a deep quiescence state where the UV and optical emissions are dominated by the accretion disk. Earlier HST COS observations have provided FUV spectroscopy showing the decline phase and indicating that T Pyx is accreting at a very high rate. As a result, the T Pyx WD might be growing in mass, and therefore may be on its way to explode as a Type Ia supernova (SN Ia). HST STIS optical spectra were obtained during the nebular phase to study the expanding nebular material, but no STIS optical spectra have yet been obtained during the quiescent phase to help derive an accurate mass accretion rate: to model the disk properly UV and optical spectra must be collected because the inner disk dominates in the FUV and the outer disk dominates in the optical. We request the first combined optical (STIS) and FUV (COS) spectroscopic observation of T Pyx during the deep quiescent phase to properly model the disk and derive an accurate mass accretion rate. In addition, we will measure the width and velocity of the hydrogen and helium lines to better model the inner disk (lines in emission) and outer disk (lines in absorption). These observations will assess whether the T Pyx WD mass is growing, and hence whether T Pyx is indeed a viable SN Ia progenitor. Even though SNe Ia are the tools used to demonstrate that the Universe is accelerating, the exact nature of SN Ia progenitors has not been confirmed. In order to obtain a broad spectral coverage of the target T Pyxidis (covering the UV and Optical), we request two sets of observations, each for 2 orbits, totalling 4 orbits. The first set (visit) is configured in the COS/FUV Spectroscopic mode for two orbits. The first orbit with the G140L spectral element centered at 1105 Angstrom. The second orbit, following immediately the first COS one above, with the G130M spectral element centered at 1055 Angstrom. Both with the PSA Aperture. The second set (visit) is configured in the (optical) STIS/CCD Spectroscopic mode for two orbits. The first orbit with the G750L grating centered at 7751 Angstrom. The second orbit, following immediately the first STIS one above, with the G430L grating centered at 4300 Angstrom. Both in ACCUM mode, with the 52x0.1E1 aperture. The E1 aperture was chosen for STIS as the ETC warns about a low electron per pixel causing poor CTE. Since we are using the G750L (7751) configuration we also added a flat field exposure (2 iteration) to allow for correction of the fringes appearing above 7000 Angstroms. The two visits should ideally be spaced as close as possible in time, we request a separation between them of 1 orbit to one month (about 500 orbits) - the target luminosity is not expected to undergo any detectable change over this period of time (though over a few months to a year it may show a slight decrease). Since T Pyx is a variable (a recurrent nova), we will request the AAVSO to monitor it to make sure it doesn't (unexpectedly) erupt (its last eruption was 11 years ago, and the time between eruptions is 20-40 years). Such eruptions have short timescales (days) and may require the safe target offset procedure (STOP) to which we will fully comply (the AAVSO can provide photometric monitoring for more than 7 consecutive days leading to the HST observations and within 24 hours of the target being observed by HST - for the two visits). PI Godon has a long expertise in the modeling of accretion disks in cataclysmic variables and in the last years has extended his ultraviolet spectroscopic analysis of disks into the optical. He has a long expertise in the use and application of the suite of code TLUSTY to generate stellar spectra and accretion disk spectra. Over the years he has provided many attempts to confront CV spectra with disk models and by doing so has advanced this important topic. He is the author or co-author on 44 HST publications and has expertise with HST STIS and COS spectra and their analysis. He has also expertise on accretion disk boundary layers, in hydrodynamics and computational fluid dynamics. Co-I Sion has leading expertise in the structure and evolution of accreting white dwarfs in interacting binaries as well as the physical processes and evolution of single white dwarfs. He has been the PI on numerous successful HST proposals beginning in Cycle 2 through Cycle 25 and is the lead author or co-author on 84 HST-refereed publications in major refereed journals. He has extensive experience in the modeling of UV spectra of cataclysmic variables with accretion disk and white dwarf photospheres, starting with the launch of HST. He also has extensive experience with quasi-static evolutionary simulations of accreting white dwarfs. Co-I Robert Williams has analyzed the spectra of novae using both ground and space-based telescopes. His research has focused on using relative line intensities to deduce physical conditions in the gas producing the spectrum. He is familiar with diagnostics that enable information to be obtained for mass-transfer binaries where the primary and secondary stars, the accretion disk, and the ejecta all contribute to the complex spectrum as it evolves over time. Co-I Darnley has been a named investigato on 9 HST programs (including one DD and on AR) since cycle 15. This also includes 4 programs as PI within the last 5 cycles. These programs have results in 11 refereed publicaions, 5 as lead author. He has extensive experience with high mass accretion rate recurrent novae and the STIS instrument. Stellar Physics and Stellar Types 6 false false true false false false false AVAILABLE STAR ACCRETION DISK RECURRENT NOVA NO This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 UNIDENTIFIED BLANK FIELD NO This target is a blank piece of sky which is the bright object safe pointing and is 9.494 arcseconds away at a PA 1.3 degrees from NOVA-PYX-1890 J2000 COS/FUV Spectroscopic No No G130M 1055 COS/FUV Spectroscopic No No G140L 1105 STIS/CCD Spectroscopic No No G750L 7751 STIS/CCD Spectroscopic No No G430L 4300 /private/var/folders/w_/lrgrpxmn21l5cct7f1x383qw0002kw/T/OPVisit7452303886340582689.xml Timing link suitability includes constraints ([02 After 01 by 0.1 to 33.1 days] [01 After 03 by at least 3.0 days]) The scheduling data was generated by CASM 30.3. CASM was run in Phase II mode. This should be scheduled in evening-local time. Flags need to be cleared during the work day. Weekends are to be avoided since the CS must clear the target within 24 hours of HST execution. 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