17799( 3) - 14-Oct-2024 13:11:50 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17799 Version: 3 Check-in Time: 14-Oct-2024 13:11:50 STScI Edit Number: 0 Title Ultraviolet properties of the heavy-metal hot subdwarf in the long period binary: SB 744 ------------------------------------------------------------------------------------ Type Cycle GO 32 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Peter Nemeth Astroserver.org Y CoI: Dr. Stephane Vennes Australian National University N CoI: Dr. Adela Kawka Curtin University N CoI: Prof. Lilia Ferrario Australian National University N CoI: Dr. Joris Vos Universitat Potsdam N CoI: Dr. Maja Vuckovic Universidad de Valparaiso N CoI: Mr. Eduardo Alfredo Universidad de Valparaiso N Arancibia-Rojas CoI: Alexey Bobrick Technion-Israel Institute of Technology N ------------------------------------------------------------------------------------ Abstract Hot subdwarfs are evolved low-mass stars found at the blue end of the Horizontal Branch, typically formed through binary evolution scenarios. These stars undergo significant mass loss, either through common envelope interactions or Roche lobe overflow (RLOF) evolution during the red giant branch phase. Alternatively, they may form via the merger of two helium core white dwarfs. One such star, SB 744, was chosen for radial velocity follow-up from a sample of long-period composite spectrum subdwarf binaries, to explore its RLOF evolution, orbital characteristics, masses and chemical compositions of the components. Our spectral analysis revealed prominent F and Pb lines in the optical spectrum and suggested a rich UV spectrum of the sdOB type primary. The presence of fluorine, a rare observation in stellar spectra, is linked to the nucleosynthesis processes in asymptotic giant branch stars and subsequent convective mixing in their atmospheres. Alternatively, the merger of two white dwarfs can induce flash nucleosynthesis, producing fluorine that is then mixed into the atmosphere. The binarity of SB 744 and the detection of fluorine and heavy metals in the spectrum of the sdOB star suggest a possible triple system progenitor where the inner binary experienced a merger. Although supported by binary evolution models, such a scenario has yet to be directly observed. A comprehensive UV spectral analysis of the sdOB star could confirm this hypothesis, with HST STIS observations offering precise measurements of metal abundances (including C, N, O, F, Si, and Fe) and the search for lines of heavy elements. ------------------------------------------------------------------------------------ Observations Description ------------------------ One visit for SB744 with three HST orbits and three science exposures, each exposures followed by a wavecal: 17799( 3) - 14-Oct-2024 13:11:50 - [ 2] A STIS/E140M (0.2x0.2) spectrum with S/N > 40 at 1350 AA is our goal. TIME-TAG mode is requested with a buffer time of 246 sec. ------------------------------------------------------------------------------------ 17799( 3) - 14-Oct-2024 13:11:50 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 SB-744 STAR, COMPOSITE RA=01H48M44.0375S, J2000 V = 12.31 disentangled sdOB SPECTRAL TYPE, G V-IV, DEC=-26D36'12.82" V-Magnitude: 12.8 HORIZONTAL BRANCH STAR, SDB, SDO Reference Frame: ICRS Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. SIMBAD listed proper motion for this target. When retrieving targets with PM from SIMBAD, APT requests the coordinates be calculated with an epoch of the year 2000. Do not modify this epoch. Always review coordinates using the Target Confirmation tool, which graphically displays the PM. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 0.006848174145995317 -0.046360999954231374 0.0021758000000000003 ------------------------------------------------------------------------------------------------------------------------------------ 17799( 3) - 14-Oct-2024 13:11:50 - [ 4] Visit: 01 (SB744) 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| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 SB-744 STIS/CCD ACQ F28X50LP MIRROR 1 1 S (1 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SB-744 STIS/FUV ACCUM 0.2X0.2 E140M 1425 1 2306 S -MAMA (2306 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 WAVE STIS/FUV ACCUM 0.2X0.2 E140M 1425 1 DEF (0 S) -MAMA ------------------------------------------------------------------------------------------------------------------------------------ 4 SB-744 STIS/FUV TIME-TA 0.2X0.2 E140M 1425 BUFFER-TIME=246, WAVECAL=NO 1 2622 S -MAMA G (2622 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 WAVE STIS/FUV ACCUM 0.2X0.2 E140M 1425 1 DEF (0 S) -MAMA ------------------------------------------------------------------------------------------------------------------------------------ 6 SB-744 STIS/FUV TIME-TA 0.2X0.2 E140M 1425 BUFFER-TIME=246, WAVECAL=NO 1 2622 S -MAMA G (2622 S) ------------------------------------------------------------------------------------------------------------------------------------ 7 WAVE STIS/FUV ACCUM 0.2X0.2 E140M 1425 1 DEF (0 S) -MAMA ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ SB-744 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A SB-744 2 STIS/FUV ACCUM 0.2X0.2 E140M 1425 none none none none 1 N/A -MAMA WAVE 3 STIS/FUV ACCUM 0.2X0.2 E140M 1425 none none none none 1 N/A -MAMA SB-744 4 STIS/FUV TIME-TA 0.2X0.2 E140M 1425 none none none none 2 N/A -MAMA G WAVE 5 STIS/FUV ACCUM 0.2X0.2 E140M 1425 none none none none 2 N/A -MAMA SB-744 6 STIS/FUV TIME-TA 0.2X0.2 E140M 1425 none none none none 3 N/A -MAMA G WAVE 7 STIS/FUV ACCUM 0.2X0.2 E140M 1425 none none none none 3 N/A -MAMA 17799( 3) - 14-Oct-2024 13:11:50 - [ 5] Summary Form for Proposal 17799 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 0.2X0.2, F28X50LP ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, ACQ, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=246, WAVECAL=NO ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements E140M, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names SB-744, WAVE ------------------------------------------------------------------------------------------------------------------------------------