15833( 2) - 25-Jul-2019 10:44:25 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15833 Version: 2 Check-in Time: 25-Jul-2019 10:44:25 STScI Edit Number: 0 Title Recurrent Nova M31N 2008-12a: Neon and Jets - Determining the ultimate fate of a Chandrasekhar mass white dwarf ------------------------------------------------------------------------------------ Type Cycle GO 27 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Matthew James Darnley Liverpool John Moores University Y CoI: Dr. Eamonn Harvey Liverpool John Moores University N CoI: Mr. Michael Healy Liverpool John Moores University N CoI: Dr. Martin Henze San Diego State University N CoI: Dr. Rebekah Hounsell University of Pennsylvania Y CoI: Ms. Fiona Murphy-Glaysher Liverpool John Moores University N CoI: Dr. Valerio A. R. M. Ribeiro Universidade de Aveiro N CoI: Prof. Allen W. Shafter San Diego State University Y CoI: Dr. Michael Shara American Museum of Natural History N CoI: Dr. Steven Charles Williams Lancaster University N CoI: Mr. Conor Ransome Liverpool John Moores University N ------------------------------------------------------------------------------------ Abstract M31N 2008-12a is the single most important nova system now known. With its one-year recurrence period, high-mass white dwarf, high mass accretion rate, low peak optical luminosity, and low ejecta mass, this system is the leading pre-explosion Supernova Type Ia single-degenerate candidate. The rapid decline from optical peak and the distance of M31 necessitate a request for disruptive target of opportunity observations. We propose a series of early eruption FUV spectroscopic observations to study the evolution of the composition of the ejecta, including probing the underlying composition of the white dwarf, CO vs. ONe, which is key to the ultimate fate of this system (SN Ia vs. accretion-induced collapse). A single Cycle 23 FUV spectrum taken just 3 days post-eruption found no evidence for neon, but the lack of other similarly high ionization lines suggests Ne lines may develop later in the evolution. That spectrum also presented evidence of a highly collimated - jet-like - ejecta. This new FUV series will take place on day 4, 5, 6, and 7, post-eruption, and will definitively explore the presense of Ne in the ejecta, provide key ejecta abundance information, and they will also probe the nature of the proposed outflows. The regularity of eruptions of M31N 2008-12a are unprecedented and this is the only thermonuclear nova system where we can accurately predict eruptions. The unique FUV capabilities of HST therefore allow us to study the physics of this vitally important system even at the great distance of M31, providing invaluable information about the ultimate fate of this remarkable system. ------------------------------------------------------------------------------------ Observations Description ------------------------ STIS Spectroscopy: The spectroscopic observations proposed here are to obtain a series of four FUV eruption spectra of the recurrent nova M31N 2008-12a, with the science goals of confirming the ejecta abundances (absolutely ruling out Ne), computing ejecta abundances and their evolution with time, exploring continuum emission mechanisms, and exploring the ejecta morphology and its 15833( 2) - 25-Jul-2019 10:44:25 - [ 2] evolution. As such, the proposed observations require a good signal-to-noise ratio (SNR) in both the continuum and expected emission lines. By employing STIS FUV MAMA G140L (1150-1737 Angstrom) grating utilising the 52" x 0.2" slit, we obtain coverage of the majority of the FUV regime, which is required, for e.g., to maximise the available lines for abundance calculations and to determine the continuum level. The 0.2" slit width provides a good compromise between resolution and throughput, allowing accurate absorption line measurements in the continuum. Additionally, the low-resolution grating selected generally provides the best throughput across the entire wavelength range. MAMA safety: We can confirm that, based on the expected luminosity of 12a (even at peak luminosity as seen in the eleven previous eruptions), we do not approach the bright object limits for the STIS MAMA detectors. We have not identified any bright sources within the nearby field that are expected to cause problems with the observation (all UV sources within the field are fainter than the peak luminosity of the nova). The past FUV and NUV spectra (with identical setup), and NUV imaging, of this object also confirms this. STIS target acquisition: The area around 12a is relatively uncrowded in the U-band and NUV, and even at the quiescence luminosity of 12a, the nearest brighter source is 3.5" away. As such, we intend to employ the STIS acquisition and peakup (ACQ / PEAK) to acquire and centre the target on the slit. We envisage no issues in acquiring 12a for STIS spectroscopy, and again note past successful acquisition of 12a by STIS. Exposure time calculations: The SEDs from the 2013 - 2015 eruptions and the existing NUV spectrum indicates an optically thick free-free emission spectrum; we have based our continuum exposure time calculations upon such a spectrum, normalised to the Swift UVOT/UVW1 photometry at day 4, 5, 6, and 7 (m = 19; +1 mag/day) post-eruption. We also note that this is a conservative approach, as the light curves (UV included) enter a plateau-like phase at around day 4 post-eruption. We have also included a number of expected FUV emission lines in our exposure time calculations, N V, Si IV, and C IV. The lines fluxes and widths used are taken directly from the 2015 FUV spectrum of 12a, and the expected fluxes are reduced in line with the continuum as the eruption proceeds. Throughout our exposure time simulations, we have assumed a line-of-sight reddening towards 12a of E(B-V) = 0.1. Based on the estimated orbital visibility (49 mins to maximise flexibility) and the above simulations, we require three, four, five, and five HST orbits for the first, second, third, and fourth visits, respectively (to account for the waning flux). The equates to exposure times of 7, 087s, 9686s, 12, 285s, and 12, 285s for the four visits to allow us to achieve suitable SNRs for the continuum and selected emission lines. STIS Dithering: In order to remove detector defect and hot pixels a 3, 4, and 5 point STIS-ALONG-SLIT dither pattern has been applied to the 1st, 2nd, and last two epochs of FUV observations respectively. The dither patterns have been created using a 7 pixel point spacing in epoch 1, 5.24 in epoch 2, and 4.2 in the last two epochs to allow for an improved spatial resolution. 15833( 2) - 25-Jul-2019 10:44:25 - [ 3] STIS TIME-TAG MODE: Using the ETC and expected values for the peak luminosity of the nova we have determined a total global count rate significantly below 20, 000 c/s. We therefore wish to observe in the Time-tag mode for archival purposes and preservation of data. Buffer time for this mode has been calculated as 1/2 the exposure time for each observation. Scheduling: We request scheduability of 100%. As we do not exactly know when this object will go off we require as large a visit window as possible. It is thought that the nova may erupt in as early as November 2019. We have adjusted our exposure times accordingly to take account of the shortest orbital visibility needed to obtain 100% scheduability (approximately a five minute reduction per orbit from the numbers stated in the Phase I case). Due to the distance to M31N2008-12a, its intrinsic low peak luminosity, and rapid decline, the target is only accessible (feasible) for STIS spectroscopy for up to a week post-discovery. As such a Disruptive Target of Opportunity (dToO) status is required to achieve these science goals. With the lead-in time for a dToO typically 4 to 5 days, and the expected discovery at least one day pre-maximum, we have a 4 to 6 day window to obtain the four STIS FUV spectra (planned for days 4, 5, 6, and 7 post-eruption). As such a ToO of 3 days has been requested. ------------------------------------------------------------------------------------ 15833( 2) - 25-Jul-2019 10:44:25 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 M31N-2008-12 STAR, INTERACTING RA=00H45M28.8200S, J2000 V = 20.8 +/- 0.1 Maximum magnitudes A BINARY, RECURRENT NOVA DEC=+41D54'10.10" obtained by this system within observing window (day 3 onwards): Sloan i'=20.8+/-0.1, Sloan r'=20.4+/-0.1, B=21.0+/-0.1, U=19.2+/-0.5 Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 2 AQUSTAR CALIBRATION, APERTURE RA=00H45M28.5265S +/- 0.34043", J2000 V = 18.349 +/- 0.45 LOCATION DEC=+41D54'51.86" +/- 0.325062" Reference Frame: ICRS Extended: NO Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1986.91 0.0 0.0 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 15833( 2) - 25-Jul-2019 10:44:25 - [ 5] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type STIS-ALONG-SLIT Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.131 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 90.0 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type STIS-ALONG-SLIT Pattern_Purpose DITHER Number_Of_Points 3 Point_Spacing 0.175 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 90.0 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 3 Primary_Pattern Secondary_Pattern Pattern_Type STIS-ALONG-SLIT Pattern_Purpose DITHER Number_Of_Points 5 Point_Spacing 0.105 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 90.0 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 15833( 2) - 25-Jul-2019 10:44:25 - [ 6] Visit: 01 (UV Spec T0 G140L) Visit Requirements: SCHED 100%; ORIENT 232D TO 28 D; ORIENT 47D TO 204 D; ON HOLD ; TOO RESPONSE TIME 3.0D On Hold Comments: The dToO lead-in time is aproximatly 5 days, but we will detect the 2019 eruption at least 1 day before peak, so we will first observe 12a when the FUV light curve has decayed to 19 to 20 mag (AB system). The dToO lead-in time and the nova decay rate opens a small, 4 to 6 day, window (3 to7days post-eruption) during which FUV spectroscopy of this unique system is feasible. We therfore request a 3 day ToO. Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 AQUSTAR STIS/CCD ACQ F28X50LP MIRROR 1 30 S (30 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 M31N-2008-1 STIS/FUV TIME-TA 52X0.2D1 G140L 1425 BUFFER-TIME=1812 1 2000 S PATTERN 2 2 2A -MAMA G see below (7087 S) ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ AQUSTAR 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A M31N-2008-12A 2 STIS/FUV TIME-TA 52X0.2D1 G140L 1425 1 none none none 1 1889.0 S -MAMA G M31N-2008-12A 2 STIS/FUV TIME-TA 52X0.2D1 G140L 1425 2 none none none 2 2599.0 S -MAMA G M31N-2008-12A 2 STIS/FUV TIME-TA 52X0.2D1 G140L 1425 3 none none none 3 2599.0 S -MAMA G 15833( 2) - 25-Jul-2019 10:44:25 - [ 7] Visit: 02 (UV Spec T0 G140L) Visit Requirements: SCHED 100%; ORIENT 232D TO 28 D; ORIENT 47D TO 204 D; AFTER 01 BY 0.75 D TO 1.25 D 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| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 AQUSTAR STIS/CCD ACQ F28X50LP MIRROR 1 30 S (30 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 M31N-2008-1 STIS/FUV TIME-TA 52X0.2D1 G140L 1425 BUFFER-TIME=1211 1 2000 S PATTERN 1 2 2A -MAMA G see below (9686 S) ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ AQUSTAR 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A M31N-2008-12A 2 STIS/FUV TIME-TA 52X0.2D1 G140L 1425 1 none none none 1 1889.0 S -MAMA G M31N-2008-12A 2 STIS/FUV TIME-TA 52X0.2D1 G140L 1425 2 none none none 2 2599.0 S -MAMA G M31N-2008-12A 2 STIS/FUV TIME-TA 52X0.2D1 G140L 1425 3 none none none 3 2599.0 S -MAMA G M31N-2008-12A 2 STIS/FUV TIME-TA 52X0.2D1 G140L 1425 4 none none none 4 2599.0 S -MAMA G 15833( 2) - 25-Jul-2019 10:44:25 - [ 8] Visit: 03 (UV Spec T0 G140L) Visit Requirements: SCHED 100%; ORIENT 232D TO 28 D; ORIENT 47D TO 204 D; AFTER 01 BY 1.75 D TO 2.25 D 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| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 AQUSTAR STIS/CCD ACQ F28X50LP MIRROR 1 30 S (30 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 M31N-2008-1 STIS/FUV TIME-TA 52X0.2D1 G140L 1425 BUFFER-TIME=1229 1 2000 S PATTERN 3 2 2A -MAMA G see below (12285 S) ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ AQUSTAR 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A M31N-2008-12A 2 STIS/FUV TIME-TA 52X0.2D1 G140L 1425 1 none none none 1 1889.0 S -MAMA G M31N-2008-12A 2 STIS/FUV TIME-TA 52X0.2D1 G140L 1425 2 none none none 2 2599.0 S -MAMA G M31N-2008-12A 2 STIS/FUV TIME-TA 52X0.2D1 G140L 1425 3 none none none 3 2599.0 S -MAMA G M31N-2008-12A 2 STIS/FUV TIME-TA 52X0.2D1 G140L 1425 4 none none none 4 2599.0 S -MAMA G M31N-2008-12A 2 STIS/FUV TIME-TA 52X0.2D1 G140L 1425 5 none none none 5 2599.0 S -MAMA G 15833( 2) - 25-Jul-2019 10:44:25 - [ 9] Visit: 04 (UV Spec T0 G140L) Visit Requirements: SCHED 100%; ORIENT 232D TO 28 D; ORIENT 47D TO 204 D; AFTER 01 BY 2.75 D TO 3.25 D 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| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 AQUSTAR STIS/CCD ACQ F28X50LP MIRROR 1 30 S (30 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 M31N-2008-1 STIS/FUV TIME-TA 52X0.2D1 G140L 1425 BUFFER-TIME=1229 1 2000 S PATTERN 3 2 2A -MAMA G see below (12285 S) ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ AQUSTAR 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A M31N-2008-12A 2 STIS/FUV TIME-TA 52X0.2D1 G140L 1425 1 none none none 1 1889.0 S -MAMA G M31N-2008-12A 2 STIS/FUV TIME-TA 52X0.2D1 G140L 1425 2 none none none 2 2599.0 S -MAMA G M31N-2008-12A 2 STIS/FUV TIME-TA 52X0.2D1 G140L 1425 3 none none none 3 2599.0 S -MAMA G M31N-2008-12A 2 STIS/FUV TIME-TA 52X0.2D1 G140L 1425 4 none none none 4 2599.0 S -MAMA G M31N-2008-12A 2 STIS/FUV TIME-TA 52X0.2D1 G140L 1425 5 none none none 5 2599.0 S -MAMA G 15833( 2) - 25-Jul-2019 10:44:25 - [ 10] Summary Form for Proposal 15833 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 52X0.2D1, F28X50LP ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=1211, BUFFER-TIME=1229, BUFFER-TIME=1812 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements AFTER 01 BY 0.75 D TO 1.25 D, AFTER 01 BY 1.75 D TO 2.25 D, AFTER 01 BY 2.75 D TO 3.25 D, ON HOLD , ORIENT 232D TO 28 D, ORIENT 47D TO 204 D, PATTERN 1 2, PATTERN 2 2, PATTERN 3 2, SCHED 100%, TOO RESPONSE TIME 3.0D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names AQUSTAR, M31N-2008-12A ------------------------------------------------------------------------------------------------------------------------------------