0 Assigned ID: 5473 ----- Attempting Submission 1 (Tue Mar 26 16:30:26 GMT 2024) ----- We have changed the first visit and exposure from TIME-TAG mode to ACCUM to reduce the data dumps. 1367110520 ----- Attempting Submission 1 (Fri Aug 16 12:31:21 GMT 2024) ----- HST Phase II Proposal 17799 successfully submitted. Receipt: # 17799-1 ----- Attempting Submission 2 (Sat Oct 12 19:57:18 GMT 2024) ----- We have a heavy data volume warning in our Time-Tag mode exposures. We adjusted the buffer time to the maximum possible value considering the count rate of the object, to limit the number of buffers. Consulting with our support scientist this warning does not affect the observations, only the schedulability of the visit. 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. One visit for SB744 with three HST orbits and three science exposures, each exposures followed by a wavecal: 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. Over the past decade our team has built expertise in high resolution spectroscopy and radial velocity followup of hot subdwarf binaries based on ESO/VLT/UVES data. Hot subdwarf observations are analysed with non-Local Thermal Equilibrium (non-LTE) (Tlusty) models with our custom methods available on the web (www.astroserver.org). For modeling observed composite spectra we combine Tlusty NLTE and Atlas9 LTE synthetic spectra and derive the surface parameters of the binary members, as well as the obital parameters. The sharp metal lines in the sdOB component of SB 744 were discovered and analysed with this method and all models were calculated from fundamental atomic data. Dr Peter Nemeth: Researcher at the Astronomical Institute of the Czech Academy of Sciences (AsU) and Astroserver.org. He has experience with high resolution UV and optical spectral modeling and abundance analyses based on the Tlusty and CMFGEN codes. Expert on hot subdwarfs, white dwarfs, atomic data management in the calculations and wavelength space spectral decomposition. Dr Stephane Vennes: Honorary Associate Professor at the Australian National University (ANU). Expert in modeling stellar atmospheres of compact objects. He developed a model atmosphere code for radiative and convective equilibrium that includes magnetic fields, and peculiar element distributions by solving the equations of diffusive equilibrium. Dr Adela Kawka: Expert in compact objects, binary populations, and modeling radiative transfer in white dwarf atmospheres and magnetic fields. Dr Lilia Ferrario: Professor and Director of the Mathematical Sciences Institute at the ANU. Expert in stellar evolution modeling and the theory of radiative transfer. Dr Joris Vos: Researcher at the AsU. Expert in precision radial velocity measurements, binary evolution, artificial intelligence-aided binary population synthesis, and developer of the MESA binary modules. Dr Alexey Bobrick: Postdoctoral researcher at Technion Institute. Expert in stellar interactions, including white dwarf mergers and mass transfer, as well as modelling with the MESA code. Dr Maja Vuckovic: Professor at the University of Valparaiso. Expert in binary evolution, compact stars, spectroscopic observational techniques, and photometric time series analysis. Eduardo Arancibia Rojas: PhD student at the University of Valparaiso. Expert on MESA modeling of hot subdwarfs. Stellar Physics and Stellar Types Stellar Populations and the Interstellar Medium 6 false false true false false false false false SUPPORTED STAR COMPOSITE SPECTRAL TYPE G V-IV HORIZONTAL BRANCH STAR SDB SDO 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. J2000 J2000 disentangled sdOB V-Magnitude: 12.8 STIS/FUV-MAMA Spectroscopic No No E140M 1425 1728762847010 /tmp/OPVisit9908134597234822475.xml The scheduling data was generated by CASM 32.1.1. CASM was run in Phase II mode. 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