18101( 4) - 05-Nov-2025 19:58:49 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18101 Version: 4 Check-in Time: 05-Nov-2025 19:58:49 STScI Edit Number: 0 Title A New Approach to Determine the Ionizing Fluxes of Rapidly Rotating Oe Stars at Low Metallicity ------------------------------------------------------------------------------------ Type Cycle GO 33 ------------------------------------------------------------------------------------ Investigators Contact? PI: Prof. Aida Wofford National Autonomous University of Mexico Y CoI: Prof. Paul A. Crowther University of Sheffield N CoI: Prof. Sally Oey University of Michigan N CoI: Dr. Grace Telford University of Utah N CoI: Dr. Jorick Vink Armagh Observatory and Planetarium N CoI: Gautham Sabhahit Armagh Observatory and Planetarium N CoI: Oskar Francisco Arangure-Chong National Autonomous University of Mexico N CoI: Dr. Cristophe Morisset National Autonomous University of Mexico N CoI: Dr. Daniel Pauli Institute of Astronomy, KU Leuven N ------------------------------------------------------------------------------------ Abstract Oe rapidly-rotating main-sequence emission-line stars can dominate the ionization of H II regions, particularly at low metallicity, where they are relatively common and reach earlier (hotter) types. When line emission fills-in their key optical absorption lines, it is extremely challenging to infer their spectral type, effective temperature/Teff, and ionizing spectrum using conventional optical analysis. FUV spectra offer the only route for constraining these fundamental stellar properties. However, few FUV spectra of Oe stars are available, and most of them are of stars in complex regions that prevent us from using their associated nebulae to validate their ionizing fluxes. We have used data from the integral field spectroscopic survey, SDSS-V Local Volume Mapper, to identify two SMC-field Oe stars with relatively isolated H II regions. The stars have high-quality optical spectra from 6-8 m class telescopes and are likely to sample different temperature regimes (one early- and one late-type). We request HST/COS G130M+G160M observations of these stars in order to cover the crucial 1160-1190 and 1550 Ang spectral regions. The FUV spectra will enable us to assess the impact of rapid rotation on their ionizing fluxes and to infer stellar wind properties. Due to their isolation, the Oe star H II regions can be used to validate the stellar ionizing fluxes predicted from models fit to the HST/COS spectra. Our study will be the first that combines stellar and nebular spectra to constrain the highly uncertain contribution of Oe stars, known to be more common at low metallicity, to the ionizing fluxes/feedback of their host galaxies. ------------------------------------------------------------------------------------ Observations Description ------------------------ We will observe two rapidly-rotating O-type main sequence stars in the SMC, AzV 255 or LHA-115-S-31 (~O7V) and N80A or OGLE-SMC725.11.009683 (~O3V). We will use COS G130M (cenwave=1291) + G160M (cenwave=1611) for the first target (AzV 255), which has fluxes of 4.2e-13 erg/s/cm2 at 1300 A and 3.0e-13 at 1500 A, Gaia G=13.54 mag, and E(B-V)~0.04 mag. 18101( 4) - 05-Nov-2025 19:58:49 - [ 2] We will use COS G140L and cenwave = 800 for the second star, which is fainter (1.1e-14 erg/s/cm2 at 1300 Ang, Gaia G=17.84 mag) and more reddened (E(B-V)~0.3 mag). To avoid going over the brightness limits during the TA of N80A, which is located near a bright star, we will acquire instead an offset star (Gaia DR3 4687529716356335360, renamed N80A-OFFSET), which is a B1V star that has a V-band magnitude of 15.56 and E(B-V)~0.04 mag. For all exposure time calculations we will use Castelli and Kurucz Models models of the stars and the Milky Way extinction law to redden the models prior to their renormalization to the above observed reddened fluxes or magnitudes. For the TA of AzV 255, we use the BOA, MIRROB, the ACQ/IMAGE mode, and the recommended SNR=30 when using the BOA. For the TA of N80A-OFFSET, we use the PSA, MIRRORB, the ACQ/IMAGE mode, and the recommended SNR=20 (5s) when using the PSA. Guided by O-star observations from ULLYSES, we need spectroscopic observations to have a minimum SNR=20/six-pixel resel (G130M/1291 at 1150 Ang and G160M/1611 at 1590 Ang). For N80A we require a similar SNR=20 with G140L/800 at 1169 Ang. For this, the G130M and G160M science exposure times for AzV 255 need to be 276 s and 434 s, respectively; and for N80A, 1, 369 s. For AzV 255, the overhead times (in s) for the guide star acquisition and TA, G130M, and G160M exposures are 420, 206 and 1706, and 1706+117 s, respectively. Thus, overall, we will use 2 (2) orbits for observing N80A (AzV 255) with COS. ------------------------------------------------------------------------------------ 18101( 4) - 05-Nov-2025 19:58:49 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 LHA-115-S-31 EXT-STAR, MAIN SEQUENCE RA=01H00M42.0781S +/- 0.1", J2000 V = 12.74 O, OE DEC=-71D31'12.27" +/- 0.1" 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. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 1.6720700389253357E-4 -0.0012019999076073873 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 2 OGLE-SMC725. EXT-STAR, MAIN SEQUENCE RA=01H08M27.8895S +/- 0.1", J2000 V = 17.688 11.009683 O, OE DEC=-72D00'10.29" +/- 0.1" Reference Frame: ICRS Extended: NO Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. The equatorial coordinates match those of Gaia DR3 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 1.1694787893998327E-4 -0.001294 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 3 N80A-OFFSET STAR, B0-B2 V-IV RA=01H08M26.2127S +/- J2000 V = 15.56 G = 15.50 0.0000307", DEC=-71D59'54.36" +/- 0.0000282" Reference Frame: ICRS Extended: NO Comments: The equatorial coordinates are from Gaia DR3 Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 1.7494868597642195E-4 -0.00122 0.0000066 ------------------------------------------------------------------------------------------------------------------------------------ 18101( 4) - 05-Nov-2025 19:58:49 - [ 4] Visit: 01 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 LHA-115-S-3 COS/NUV ACQ/IMA BOA MIRRORB 1 138 S (138 1 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 LHA-115-S-3 COS/FUV TIME-TA PSA G130M 1291 SEGMENT=BOTH, BUFFER-TIME=211, 1 276 S 1 G FP-POS=3 see below (252 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 LHA-115-S-3 COS/FUV TIME-TA PSA G130M 1291 SEGMENT=BOTH, BUFFER-TIME=211, 1 276 S 1 G FP-POS=4 see below (252 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 LHA-115-S-3 COS/FUV TIME-TA PSA G160M 1611 SEGMENT=BOTH, BUFFER-TIME=583, 1 434 S 1 G FP-POS=ALL see below (2981 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 | ------------------------------------------------------------------------------------------------------------------------------------ LHA-115-S-31 1 COS/NUV ACQ/IMA BOA MIRRORB none none none none 1 N/A GE LHA-115-S-31 2 COS/FUV TIME-TA PSA G130M 1291 none none none none 1 252 S G LHA-115-S-31 3 COS/FUV TIME-TA PSA G130M 1291 none none none none 1 252 S G LHA-115-S-31 4 COS/FUV TIME-TA PSA G160M 1611 none none none 1 1 572.0 S G LHA-115-S-31 4 COS/FUV TIME-TA PSA G160M 1611 none none none 2 2 788.0 S G LHA-115-S-31 4 COS/FUV TIME-TA PSA G160M 1611 none none none 3 2 788.0 S G LHA-115-S-31 4 COS/FUV TIME-TA PSA G160M 1611 none none none 4 2 833.0 S G 18101( 4) - 05-Nov-2025 19:58:49 - [ 5] Visit: 02 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 N80A-OFFSET COS/NUV ACQ/IMA PSA MIRRORB 1 5 S (5 S) GE ------------------------------------------------------------------------------------------------------------------------------------ 2 OGLE-SMC725 COS/FUV TIME-TA PSA G140L 800 BUFFER-TIME=4139, FP-POS=1 1 1135 S .11.009683 G see below (1129 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 OGLE-SMC725 COS/FUV TIME-TA PSA G140L 800 BUFFER-TIME=4139, FP-POS=2 1 1135 S .11.009683 G see below (1129 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 OGLE-SMC725 COS/FUV TIME-TA PSA G140L 800 BUFFER-TIME=4139, FP-POS=3 1 1135 S .11.009683 G see below (1276 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 OGLE-SMC725 COS/FUV TIME-TA PSA G140L 800 BUFFER-TIME=4139, FP-POS=4 1 1135 S .11.009683 G see below (1276 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 | ------------------------------------------------------------------------------------------------------------------------------------ N80A-OFFSET 1 COS/NUV ACQ/IMA PSA MIRRORB none none none none 1 N/A GE OGLE-SMC725.11.0096 2 COS/FUV TIME-TA PSA G140L 800 none none none none 1 1129.0 S 83 G OGLE-SMC725.11.0096 3 COS/FUV TIME-TA PSA G140L 800 none none none none 1 1129.0 S 83 G OGLE-SMC725.11.0096 4 COS/FUV TIME-TA PSA G140L 800 none none none none 2 1276.0 S 83 G OGLE-SMC725.11.0096 5 COS/FUV TIME-TA PSA G140L 800 none none none none 2 1276.0 S 83 G 18101( 4) - 05-Nov-2025 19:58:49 - [ 6] Summary Form for Proposal 18101 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures BOA, PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/FUV, COS/NUV ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/IMAGE, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=211, BUFFER-TIME=4139, BUFFER-TIME=583, FP-POS=1, FP-POS=2, FP-POS=3, FP-POS=4, FP-POS=ALL, SEGMENT=BOTH ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G130M, G140L, G160M, MIRRORB ------------------------------------------------------------------------------------------------------------------------------------ Target Names LHA-115-S-31, N80A-OFFSET, OGLE-SMC725.11.009683 ------------------------------------------------------------------------------------------------------------------------------------