17182( 5) - 22-Nov-2023 17:50:58 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17182 Version: 5 Check-in Time: 22-Nov-2023 17:50:58 STScI Edit Number: 1 Title The hot remnant core of the mass donor in a unique Be star binary HD 92406 - two stellar eclipses and two disk occultations per orbit ------------------------------------------------------------------------------------ Type Cycle GO 30 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Jonathan M Labadie-Bartz University of Oklahoma Norman Campus Y CoI: Dr. Alex Carciofi Universidade de Sao Paulo N CoI: Mr. Tajan Henrique de Amorim Sr. Universidade de Sao Paulo N ------------------------------------------------------------------------------------ Abstract About 20% of the B-type stars are rotating very rapidly. Among these are the classical Be stars, which eject material and build up gaseous circumstellar 'decretion' disks. Rotation plays a significant role in the structure and evolution of massive stars, yet in many aspects is poorly understood. One viable evolutionary pathway to acquire near-critical rotation is through binary interaction - namely mass and angular momentum transfer. The remaining core of the mass donor is now a hot stripped star. Some models suggest the binary channel is dominant in creating rapid rotators. Yet, only about 15 rapidly rotating Be + stripped star binaries are known, virtually all of which were detected and characterized with UV spectroscopy. This proposal aims to characterize a new Be + stripped star binary, HD 92406, using HST UV spectroscopy. HD 92406 is exceptionally valuable as there are two stellar eclipses and two disk occulations per binary orbit - this is the only known eclipsing binary that hosts a Be star. HD 92406 is the first putative late-type Be + stripped star binary, occupying a unique niche in the rapidly rotating binary population. UV spectroscopy taken at two specific orbital phases (one when the sdO is hidden behind the Be star) offers the unique opportunity to measure directly the spectrum of an sdO star for the first time. With that, the parameters of the stripped star in HD 92406 can be determined with sufficient precision to reveal its evolutionary tracks via comparison with binary evolution models. A full analysis promises to make this a benchmark system, with properties determined with far higher precision than what is typically possible. ------------------------------------------------------------------------------------ Observations Description ------------------------ This is an EB, with the primary (brighter in the UV) being a small stripped star (about B0), and a main-sequence late-B type star (about B9). We are planning two visits - one during the primary (total) eclipse (so the observed flux will be that from the MS B9 star), and one near quadrature. Besides the eclipses, there is low-amplitude pulsation (at about the <1% level) in optical photometry. For both visits (each 1 orbit) we intend to use the same instrument configuration: STIS/FUV-MAMA, E140M, 0.2x0.2, central wavelength = 1425. 1 exposure of 1100 s. STIS/NUV-MAMA, E230M, 0.2x0.2, central wavelength = 2124. 1 exposure of 424 s, to immediately follow the above FUV exposure. 17182( 5) - 22-Nov-2023 17:50:58 - [ 2] Based on our analysis of optical data for the system, we have a two-stellar-component model spectrum that we are using to estimate the expected UV flux. This model, with the extinction that we have calculated [E(B-V) = 0.065] matches very well with archival IUE data that cover the FUV + NUV. We have used this spectral model in the ETC, where for the in-eclipse visit the input model spectrum is only from the MS B9 star, and in the at-quadrature visit the model spectrum includes both stars (and so is brighter). REDUCED GYRO MODE: This should not have a significant impact on our proposal. As far as we can tell, our target is still in a good place on the sky even in reduced-gyro mode, and the additional two minutes of overhead is not significant. If, however, reduced-gyro mode limits our ability to schedule the single in-eclipse visit, we can modify the observing strategy to be less constrained. ------------------------------------------------------------------------------------ 17182( 5) - 22-Nov-2023 17:50:58 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD92406 STAR, B6-B9.5 V-IV, BE, RA=10H38M47.2587S +/- J2000 V = 9.15 EMISSION LINE STAR, SDB 0.0002694", DEC=-58D43'32.36" +/- 0.0002807" Reference Frame: ICRS Extended: NO Comments: Coordinates and PM from Gaia DR3. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2016.0 -0.0010075706708548957 -0.001012 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 17182( 5) - 22-Nov-2023 17:50:58 - [ 4] Visit: 01 (in eclipse) Visit Requirements: Period 32.1854 D AND ZERO-PHASE HJD2459545.3533 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 HD92406 STIS/CCD ACQ F28X50OII MIRROR 1 2 S (2 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 HD92406 STIS/FUV ACCUM 0.2X0.2 E140M 1425 1 1100 S PHASE 0.20 TO 0.28 -MAMA see below (1070 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 HD92406 STIS/NUV ACCUM 0.2X0.2 E230M 2124 1 424 S PHASE 0.20 TO 0.28 -MAMA see below (394 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 | ------------------------------------------------------------------------------------------------------------------------------------ HD92406 1 STIS/CCD ACQ F28X50OI MIRROR none none none none 1 N/A I HD92406 2 STIS/FUV ACCUM 0.2X0.2 E140M 1425 none none none none 1 1070.0 S -MAMA HD92406 3 STIS/NUV ACCUM 0.2X0.2 E230M 2124 none none none none 1 394.0 S -MAMA 17182( 5) - 22-Nov-2023 17:50:58 - [ 5] Visit: 02 (at quadrature) Visit Requirements: Period 32.1854 D AND ZERO-PHASE HJD2459545.3533 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 HD92406 STIS/CCD ACQ F28X50OII MIRROR 1 2 S (2 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 HD92406 STIS/FUV ACCUM 0.2X0.2 E140M 1425 1 1100 S PHASE 0.76 TO 0.84 -MAMA (1100 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 HD92406 STIS/NUV ACCUM 0.2X0.2 E230M 2124 1 424 S (424 PHASE 0.76 TO 0.84 -MAMA 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 | ------------------------------------------------------------------------------------------------------------------------------------ HD92406 1 STIS/CCD ACQ F28X50OI MIRROR none none none none 1 N/A I HD92406 2 STIS/FUV ACCUM 0.2X0.2 E140M 1425 none none none none 1 N/A -MAMA HD92406 3 STIS/NUV ACCUM 0.2X0.2 E230M 2124 none none none none 1 N/A -MAMA 17182( 5) - 22-Nov-2023 17:50:58 - [ 6] Summary Form for Proposal 17182 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 0.2X0.2, F28X50OII ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/FUV-MAMA, STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, ACQ ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PHASE 0.20 TO 0.28, PHASE 0.76 TO 0.84, Period 32.1854 D AND ZERO-PHASE HJD2459545.3533 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements E140M, E230M, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD92406 ------------------------------------------------------------------------------------------------------------------------------------