0This is a resubmission because during one orbit of Visit 01 (LS IV -14 116), HST failed to acquire the guide stars.
Following HOPR 92568 for this HST program (17072), a single repeat orbit was approved by the TTRB.
This orbit is implemented here as Visit 04.-880999639----- Attempting Submission 1 (Tue Jul 12 17:10:16 GMT 2022) -----
HST Phase II Proposal 17072 successfully submitted.
Receipt: # 17072-1
----- Attempting Submission 2 (Mon Jul 10 15:29:51 GMT 2023) -----From atomic physics to stellar evolution: decoding the heavy-metal subdwarfs with HSTHot subdwarf stars are helium-burning stars that are believed to form either via stripping of red giants' envelopes in binaries or by helium white dwarf mergers. They display a large variety of chemical peculiarities. Helium poor sdBs are found at Teff<35kK while extremely helium rich sdOs dominate at Teff>40kK. Particularly interesting are the rare mixed H/He composition iHe-sdOBs which bridge the gap. They may either be in a process of transition from red giant core to He-poor sdB, simply have insufficient hydrogen to quench the helium, or be the product of some other history. Several iHe-sdOBs show peculiar surface compositions with extraordinarily large enrichments of heavy elements (e.g. Zr, Pb by 4-6 dex). With two exceptions, these stars are completely unexplored in the space ultraviolet. We selected three "extreme chemistry" iHe-sdOBs that from a sequence of increasing Teff and helium abundance. This includes the recently discovered EC22536-5304, which resides in a binary with a very metal poor sdF-type companion, and likely formed via stripping by mass transfer to the sdF. UV spectra will allow us to determine
1) the abundances of a dozen or more species not observable in the optical, including the iron group,
2) the degree of stratification in the atmosphere (how thick is the enhanced layer?),
3) lead isotope ratios in the bright, lead-rich star HD127493.
The results will allow us to explore the processes that may lead to heavily stratified envelopes and to study the transformation of red giant cores or white dwarf mergers with a helium-enriched surface into helium-poor sdBs. In addition, they will test alternative scenarios, such as pollution by SN ejecta.First visit (LS IV -14 116):
The goal is a high S/N spectrum with the medium-resolution echelle E140M grism (using the standard 0.2x0.2 aperture). TIME-TAG is used when possible - for two out of three orbits, to limit the number of dumps. The ACCUM mode is used for the remaining orbit.
Second visit (EC22536-5304):
A STIS/E140M (0.2x0.2) spectrum with about S/N = 40 at 1350 AA is the goal. TIME-TAG is used when possible - for two out of three orbits, to limit the number of dumps. The ACCUM mode is used for the remaining orbit.
Third visit (HD127493):
A high-S/N (~100) observation with E140H/1271 using the 0.2x0.09 slit is the goal. The star is bright (V=10.08mag, Teff~41000K), and the ACCUM mode will be used.Matti Dorsch is a PhD student with Prof. Dr. Ulrich Heber and has extensively worked with FUV spectra of He-sdB stars and non-LTE model atmospheres. Both Prof. Dr. Ulrich Heber and Prof. Dr. C. S. Jeffery are leading experts in the hot subdwarf community and have extensive experience with the analysis of such stars, including FUV spectra. Laura Scott is a PhD student with Prof. Dr. C. S. Jeffery and is working on helium-rich stars. We have published several papers on the spectral analysis of iHe-sdBs, which include the most detailed abundance analyses performed for these stars. In our analyses we have made use of HST spectra, including STIS.Stellar Physics and Stellar Types6falsefalsetruefalsefalsefalsefalsefalseSUPPORTEDSTARSDONOJ2000J2000STARSDONOJ2000J2000STARSDONOJ2000J2000STIS/FUV-MAMASpectroscopicNoNoE140M1425STIS/FUV-MAMASpectroscopicNoNoE140M1425STIS/FUV-MAMASpectroscopicNoNoE140H1271The scheduling data was generated by CASM 31.0.CASM was run in Phase II mode.1687841972000250.45468000476973(Tic-Visit
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)true30The scheduling data was generated by CASM 31.0.CASM was run in Phase II mode.(Tic-Visit
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)true20The scheduling data was generated by CASM 31.0.CASM was run in Phase II mode.This is a new visit to repeat one orbit of Visit 01 of LS IV -14 116. During the original orbit HST failed to acquire the guide stars.
Following HOPR 92568 for this HST program (17072), this single repeat orbit was approved by the TTRB.(Tic-Visit
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