0Assigned ID: 7435
----- Attempting Submission 1 (Thu Apr 16 15:56:46 GMT 2026) -----The optimum sequence of observations for the 3 visits is for orbital phases 0.00 and 0.36
(Visits 1 and 2) to occur within the same orbital period and orbital phase 0.75 (Visit 3) within
only a few orbital cycles of the first two. The Visit Planner indicates that the nearest windows
satisfying these conditions are:
Sept. 3 and 10 + Oct 26, 2026
Dec. 9 and 16, 2026 + Jan 30, 2027
It would be ideal for the observations to be performed during these windows because they coincide with
the possible observing windows from the ground for optical monitoring.-735730295----- Attempting Submission 1 (Fri Aug 07 14:24:20 GMT 2026) -----Wind velocity variations as a clue to late stage binary evolution processesRecent observations of very high-redshift star forming regions highlight the need to use nearby proxies to improve our understanding of massive star binary evolution, particularly with respect to processes responsible for enhancing heavy chemical element yields and producing more massive black hole end products. HD5980 is the ideal proxy for these studies. It is located in the Small Magellanic Cloud and its two nitrogen-rich Wolf-Rayet components are so massive and luminous, they can only be the product of highly efficient internal mixing processes, as needed to produce large heavy element yields. In addition, the primary component was observed to undergo a major eruption in 1994, reminiscent of such mass-shedding events observed in distant galaxies a few decades prior to a supernova. It is an eclipsing binary, thus allowing for precise determination of the orbit and stellar parameters. However, ultraviolet monitoring has provided the varying wind speeds only during the eruptive phase. This proposal aims to obtain the wind velocities and UV fluxes now that the system has returned to the pre-eruption state.
The requested HST/STIS spectroscopic observations will provide the valuable information needed to identify the eruption triggering mechanism, as well as yield insights into the role of binary interactions (prior to mass-transfer events) in low-metallicity, star-forming enviroments. They will also benefit wind-wind collision and interstellar medium studies. Only HST can provide observations of the UV resonance and low-excitation P Cygni lines needed to precisely measure the wind velocities of the different stars in the HD5980 system.HD5980 will be observed during 3 visits each lasting 2 orbits, in the 1170--1730 A spectral interval with STIS using the FUV MAMA detector, the E140M grating and the 0.2x0.2 slit. It will also be observed using the CCD detector and the G230LB and G430L gratings, which occupy only a small fraction of each visit and provide a uniformly flux-calibrated spectral energy distribution for comparison with the radiation transfer models.
Each visit corresponds to an orbital phase of the HD5980 eclipsing system. The orbital ephemeris has been updated recently by Schmutz et al. (2026, in preparation) based on the observed eclipse minima of Sterken & Breysacher (1997) and those extracted from the TESS archive: P=19.266032 days and T0=HJD 2450036.41. Primary eclipse is at phi=0 and secondary eclipse is at phi=0.36. We are requesting observations at orbital phases 0.00 +-0.02, 0.36 +- 0.02 and 0.75 +- 0.05.
For the FUV MAMA observations, the ETC indicates exposure times of 3800 sec in order to reach at least S/N=35 per resolution element at 1480 A, and adopting E(B-V)=0.06. These S/N will provide sufficient signal in the P Cyg absorptions for analysis.
The CCD G230LB observations will require an exposure time of at least 200 sec to provide S/N ~ 30 at the N IV 1718 A line. The sufficient exposure times for grating G430L is 50 sec. The total exposure time+overheads for the CCD spectra is approximately 20 min, asuming a 5 min overhead per CCD exposure. Adopting for the average visibility 53 minutes per orbit, each visit can be fit into 2 orbits. The first orbit will contain the target acquisition and part of the FUV-MAMA exposure. The second orbit will contain the second part of the FUV-MAMA exposure and the CCD spectra. The mixture of MAMA and CCD observations in the same orbit is justified by the short exposure time required for the CCD spectra.Dr. Koenigsberger is an expert in massive stars and in binary star interaction effects, and her investigations combine both the observational and the theoretical perspectives. She has led 4 past HST observing campaigns using STIS, the instrument being used in these proposed observations, the results of which are reported in 7 publications that have appeared over the past decades. Dr. John Hillier is an expert in radiative transfer and the study of massive stars and supernovae. He is the developer of CMFGEN which is routinely used to study O stars, W-R stars, LBVs, and the ejecta of supernovae. CMFGEN is available at www.pitt.edu/~hillier. He has also developed Monte Carlo codes that can be combined with the output of CMFGEN to model some of the effects occurring in binary systems. Dr. Julian Pittard is an expert in theoretical models and hydrodynamic simulations of wind-wind collisions in massive-star binaries. Dr. Nidia Morrell has expertise in massive star and supernova studies and in this project is responsible for acquiring and processing high resolution optical spectra, prior to and in coordination with the HST observations. Dr. Roberto Gamen will contribute with expertise in the analysis and interpretation of radial velocity curves and photometric variability. Dr. Werner Schmutz is an expert in radiation transfer for early type stars, particularly WR stars, and stellar winds, as well as in the Solar atmosphere, space weather, and solar irradiance. For this project he will also contribute know-how in binary orbits, wind-wind collisions, and stellar structure models.Stellar Physics and Stellar Types6falsetruefalsefalsefalsefalsefalseSUPPORTEDEXT-STARWOLF RAYET - WNNOThis 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.This object was generated by the targetselector and retrieved from the SIMBAD database.This object was generated by the targetselector and retrieved from the SIMBAD database.HD5980J2000J2000The scheduling data was generated by CASM 34.2.CASM was run in Phase I mode.STIS/FUV-MAMASpectroscopicNoNoE140M1425STIS/CCDSpectroscopicNoNoG230LB2375STIS/CCDSpectroscopicNoNoG430L4300The scheduling data was generated by CASM 34.2.CASM was run in Phase I mode.STIS/FUV-MAMASpectroscopicNoNoE140M1425STIS/CCDSpectroscopicNoNoG230LB2375STIS/CCDSpectroscopicNoNoG430L4300The scheduling data was generated by CASM 34.2.CASM was run in Phase I mode.STIS/FUV-MAMASpectroscopicNoNoE140M1425STIS/CCDSpectroscopicNoNoG230LB2375STIS/CCDSpectroscopicNoNoG430L4300/Users/gloria/HST/Cycle34/OP-cache/phaseI_18439_from_HST-v01.xmlThe scheduling data was generated by CASM 34.2.CASM was run in Phase II mode.(Tic-Visit
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