18439( 2) - 07-Aug-2026 14:34:03 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18439 Version: 2 Check-in Time: 07-Aug-2026 14:34:03 STScI Edit Number: 0 Title Wind velocity variations as a clue to late stage binary evolution processes ------------------------------------------------------------------------------------ Type Cycle GO 34 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Gloria Koenigsberger National Autonomous University of Mexico Y CoI: Dr. D. John Hillier University of Pittsburgh N CoI: Dr. Nidia Morrell Carnegie Institution of Washington N CoI: Dr. Roberto C. Gamen National University of La Plata N CoI: Dr. Werner Schmutz Physikalisch-Meteorologisches N Observatorium Davos (PMOD) CoI: Dr. Julian M. Pittard University of Leeds N ------------------------------------------------------------------------------------ Abstract Recent 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. ------------------------------------------------------------------------------------ Observations Description ------------------------ 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. 18439( 2) - 07-Aug-2026 14:34:03 - [ 2] 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. ------------------------------------------------------------------------------------ 18439( 2) - 07-Aug-2026 14:34:03 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD-5980 EXT-STAR, WOLF RAYET - RA=00H59M26.5839S, J2000 V = 11.31 +/- 0.1 WN DEC=-72D09'53.93" Reference Frame: ICRS Extended: NO 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.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. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 1.9655397541311307E-4 -0.0013379999700191547 6.08E-5 ------------------------------------------------------------------------------------------------------------------------------------ 18439( 2) - 07-Aug-2026 14:34:03 - [ 4] Visit: 01 Visit Requirements: Period 19.266032 D AND ZERO-PHASE HJD2450036.41 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 HD-5980 STIS/CCD ACQ F28X50LP MIRROR 1 0.5 S (0.5 PHASE 0.98 TO 0.02 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 HD-5980 STIS/FUV ACCUM 0.2X0.2 E140M 1425 1 2316 S -MAMA (2316 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 HD-5980 STIS/FUV ACCUM 0.2X0.2 E140M 1425 1 1642 S -MAMA (1642 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 HD-5980 STIS/CCD ACCUM 52X0.2 G230LB 2375 1 300 S (300 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 HD-5980 STIS/CCD ACCUM 52X0.2 G430L 4300 1 50 S see below (60 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 | ------------------------------------------------------------------------------------------------------------------------------------ HD-5980 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A HD-5980 2 STIS/FUV ACCUM 0.2X0.2 E140M 1425 none none none none 1 N/A -MAMA HD-5980 3 STIS/FUV ACCUM 0.2X0.2 E140M 1425 none none none none 2 N/A -MAMA HD-5980 4 STIS/CCD ACCUM 52X0.2 G230LB 2375 none none none 1 2 N/A HD-5980 4 STIS/CCD ACCUM 52X0.2 G230LB 2375 none none none 2 2 N/A HD-5980 5 STIS/CCD ACCUM 52X0.2 G430L 4300 none none none 1 2 60.0 S HD-5980 5 STIS/CCD ACCUM 52X0.2 G430L 4300 none none none 2 2 0 S 18439( 2) - 07-Aug-2026 14:34:03 - [ 5] Visit: 02 Visit Requirements: Period 19.266032 D AND ZERO-PHASE HJD2450036.441 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 HD-5980 STIS/CCD ACQ F28X50LP MIRROR 1 0.5 S (0.5 PHASE 0.34 TO 0.38 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 HD-5980 STIS/FUV ACCUM 0.2X0.2 E140M 1425 1 2316 S -MAMA (2316 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 HD-5980 STIS/FUV ACCUM 0.2X0.2 E140M 1425 1 1748 S PHASE 0.34 TO 0.38 -MAMA (1748 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 HD-5980 STIS/CCD ACCUM 52X0.2 G230LB 2375 1 300 S (300 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 HD-5980 STIS/CCD ACCUM 52X0.2 G430L 4300 1 60 S (60 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 | ------------------------------------------------------------------------------------------------------------------------------------ HD-5980 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A HD-5980 2 STIS/FUV ACCUM 0.2X0.2 E140M 1425 none none none none 1 N/A -MAMA HD-5980 3 STIS/FUV ACCUM 0.2X0.2 E140M 1425 none none none none 2 N/A -MAMA HD-5980 4 STIS/CCD ACCUM 52X0.2 G230LB 2375 none none none 1 2 N/A HD-5980 4 STIS/CCD ACCUM 52X0.2 G230LB 2375 none none none 2 2 N/A HD-5980 5 STIS/CCD ACCUM 52X0.2 G430L 4300 none none none 1 2 N/A HD-5980 5 STIS/CCD ACCUM 52X0.2 G430L 4300 none none none 2 2 N/A 18439( 2) - 07-Aug-2026 14:34:03 - [ 6] Visit: 03 Visit Requirements: Period 19.266032 D AND ZERO-PHASE HJD2450036.441 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 HD-5980 STIS/CCD ACQ F28X50LP MIRROR 1 0.5 S (0.5 PHASE 0.7 TO 0.8 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 HD-5980 STIS/FUV ACCUM 0.2X0.2 E140M 1425 1 2316 S -MAMA (2316 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 HD-5980 STIS/FUV ACCUM 0.2X0.2 E140M 1425 1 1642 S -MAMA (1642 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 HD-5980 STIS/CCD ACCUM 52X0.2 G230LB 2375 1 300 S (300 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 HD-5980 STIS/CCD ACCUM 52X0.2 G430L 4300 1 50 S see below (60 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 | ------------------------------------------------------------------------------------------------------------------------------------ HD-5980 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A HD-5980 2 STIS/FUV ACCUM 0.2X0.2 E140M 1425 none none none none 1 N/A -MAMA HD-5980 3 STIS/FUV ACCUM 0.2X0.2 E140M 1425 none none none none 2 N/A -MAMA HD-5980 4 STIS/CCD ACCUM 52X0.2 G230LB 2375 none none none 1 2 N/A HD-5980 4 STIS/CCD ACCUM 52X0.2 G230LB 2375 none none none 2 2 N/A HD-5980 5 STIS/CCD ACCUM 52X0.2 G430L 4300 none none none 1 2 60.0 S HD-5980 5 STIS/CCD ACCUM 52X0.2 G430L 4300 none none none 2 2 0 S 18439( 2) - 07-Aug-2026 14:34:03 - [ 7] Summary Form for Proposal 18439 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 0.2X0.2, 52X0.2, F28X50LP ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, ACQ ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PHASE 0.34 TO 0.38, PHASE 0.7 TO 0.8, PHASE 0.98 TO 0.02, Period 19.266032 D AND ZERO-PHASE HJD2450036.41, Period 19.266032 D AND ZERO-PHASE HJD2450036.441 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements E140M, G230LB, G430L, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD-5980 ------------------------------------------------------------------------------------------------------------------------------------