14778( 2) - 28-Jun-2016 20:04:04 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 14778 Version: 2 Check-in Time: 28-Jun-2016 20:04:04 STScI Edit Number: 0 Title Hiding in Plain Sight: The Low Mass Helium Star Companion of EL CVn ------------------------------------------------------------------------------------ Type Cycle GO 24 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Douglas Russell Gies Georgia State University Research Y Foundation CoI: Ms. Rachel Matson Georgia State University Research N Foundation CoI: Mr. Zhao Guo Georgia State University Research N Foundation CoI: Ms. Luqian Wang Georgia State University Research N Foundation ------------------------------------------------------------------------------------ Abstract Binary stars with orbital periods of a decade or less are destined to interact during their evolution. The mass donor star among intermediate binaries may be stripped of its envelope by mass transfer to reveal its helium core. In cases that avoid merger, the low mass helium star will remain in a binary orbit but be lost in the glare of the mass gainer star. Thanks to photometric time series from Kepler and WASP, we now know of 27 such systems that are oriented to produce mutual eclipses. Although the helium star companions are too small and faint in the optical band for spectroscopic detection, they contribute a larger fraction of the total flux in the ultraviolet. HST/COS measurements of one long period system, KOI-81, successfully detected the helium star's spectrum in the far-ultraviolet, leading to estimates of its mass and temperature. Here we propose to obtain new HST/COS FUV spectra of the prototype of this class of evolved binaries, EL CVn, and to determine the mass and physical properties of a star that barely escaped a merger. ------------------------------------------------------------------------------------ Observations Description ------------------------ We propose to obtain COS spectra of the FUV spectrum of EL CVn using the G160M grating to cover most of the spectrum from 1386 to 1774 Angstroms with a resolving power of 22, 000. In order to meet our radial velocity measurement criteria, we need to obtain a S/N per resolution element of 25 or better. This S/N level can be achieved with multiple exposures. We created model spectra from the UVBLUE grid for both component stars using temperatures from Maxted et al. (2014). We scaled the flux of the hot component by (R2/R1)^2, and then formed the sum of the two spectra. The summed spectrum was reduced for interstellar extinction using E(B-V)=0.065 and then normalized to the observed GALEX FUV flux in the vicinity of 1528 Angstroms. 14778( 2) - 28-Jun-2016 20:04:04 - [ 2] We used the COS ETC with the summed model spectrum to estimate that a single S/N = 12.3 spectrum can be obtained with an exposure time of 153 s. Following the example in the Instrument Handbook, we would obtain one exposure at each of four FP-POS spectral offsets and two CENWAVE postions to increase the net S/N to 35. By making four visits at different orbital phases, the final S/N in the reconstructed spectra will be about 69. Note that we expect to observe radial velocity semiamplitudes of 29 and 267 km/s for the orbits of the primary and white dwarf, respectively (Maxted et al. 2014), which should be readily measured. All these exposures will be made in TIME-TAG mode. There are no bright limit problems associated with this target. We estimate that there are 55 minutes of visibility per orbit for the position of EL CVn. In one orbit, we require 8 minutes for acquisition and a COS ACQ/IMAGE centering on the aperture (ICRS astrometry is good enough for this direct acquisition). This leaves time for eight science exposures of 153 sec each (with preparation and readout times included). Thus, we will need only one orbit for each visit to obtain a combined spectrum with the requisite S/N. Note that the binary orbital period (19 hours) is much longer than the HST orbit, so any orbital related changes over the duration of the exposures is small. In order to determine the orbital elements for each star from the Doppler shifts, we will require four visits, with two each around the times of highest and lowest radial velocity excursions. Because the orbital period is so short, there are many opportunities during Cycle 24 to obtain the spectra during the orbital phases required. ------------------------------------------------------------------------------------ 14778( 2) - 28-Jun-2016 20:04:04 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 V-EL-CVN STAR, A0-A3 V-IV RA=13H23M57.0187S +/- 0.00074", J2000 V = 9.42 +/- 0.02 F(1528 Angstroms) = DEC=+43D35'55.44" +/- 0.00088" 1.9e-13 erg/s/cm^2/Angstrom (GALEX FUV) Reference Frame: ICRS Extended: NO Comments: 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. 0.0017803870309511932 -0.01847 0.00384 ------------------------------------------------------------------------------------------------------------------------------------ 14778( 2) - 28-Jun-2016 20:04:04 - [ 4] Visit: 01 Visit Requirements: Period 0.7956269 D AND ZERO-PHASE HJD2454230.5558 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 V-EL-CVN COS/NUV ACQ/IMA BOA MIRRORA 1 15 S (15 PHASE 0.11 TO 0.26 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 V-EL-CVN COS/FUV TIME-TA PSA G160M 1577 BUFFER-TIME=153, FP-POS=ALL 1 153 S (612 G S) ------------------------------------------------------------------------------------------------------------------------------------ 3 V-EL-CVN COS/FUV TIME-TA PSA G160M 1600 BUFFER-TIME=153, FP-POS=ALL 1 153 S (612 G 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 | ------------------------------------------------------------------------------------------------------------------------------------ V-EL-CVN 1 COS/NUV ACQ/IMA BOA MIRRORA none none none none 1 N/A GE V-EL-CVN 2 COS/FUV TIME-TA PSA G160M 1577 none none none 1 1 N/A G V-EL-CVN 2 COS/FUV TIME-TA PSA G160M 1577 none none none 2 1 N/A G V-EL-CVN 2 COS/FUV TIME-TA PSA G160M 1577 none none none 3 1 N/A G V-EL-CVN 2 COS/FUV TIME-TA PSA G160M 1577 none none none 4 1 N/A G V-EL-CVN 3 COS/FUV TIME-TA PSA G160M 1600 none none none 1 1 N/A G V-EL-CVN 3 COS/FUV TIME-TA PSA G160M 1600 none none none 2 1 N/A G V-EL-CVN 3 COS/FUV TIME-TA PSA G160M 1600 none none none 3 1 N/A G V-EL-CVN 3 COS/FUV TIME-TA PSA G160M 1600 none none none 4 1 N/A G 14778( 2) - 28-Jun-2016 20:04:04 - [ 5] Visit: 02 Visit Requirements: Period 0.7956269 D AND ZERO-PHASE HJD2454230.5558 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 V-EL-CVN COS/NUV ACQ/IMA BOA MIRRORA 1 15 S (15 PHASE 0.24 TO 0.39 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 V-EL-CVN COS/FUV TIME-TA PSA G160M 1577 BUFFER-TIME=153, FP-POS=ALL 1 153 S (612 G S) ------------------------------------------------------------------------------------------------------------------------------------ 3 V-EL-CVN COS/FUV TIME-TA PSA G160M 1600 BUFFER-TIME=153, FP-POS=ALL 1 153 S (612 G 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 | ------------------------------------------------------------------------------------------------------------------------------------ V-EL-CVN 1 COS/NUV ACQ/IMA BOA MIRRORA none none none none 1 N/A GE V-EL-CVN 2 COS/FUV TIME-TA PSA G160M 1577 none none none 1 1 N/A G V-EL-CVN 2 COS/FUV TIME-TA PSA G160M 1577 none none none 2 1 N/A G V-EL-CVN 2 COS/FUV TIME-TA PSA G160M 1577 none none none 3 1 N/A G V-EL-CVN 2 COS/FUV TIME-TA PSA G160M 1577 none none none 4 1 N/A G V-EL-CVN 3 COS/FUV TIME-TA PSA G160M 1600 none none none 1 1 N/A G V-EL-CVN 3 COS/FUV TIME-TA PSA G160M 1600 none none none 2 1 N/A G V-EL-CVN 3 COS/FUV TIME-TA PSA G160M 1600 none none none 3 1 N/A G V-EL-CVN 3 COS/FUV TIME-TA PSA G160M 1600 none none none 4 1 N/A G 14778( 2) - 28-Jun-2016 20:04:04 - [ 6] Visit: 03 Visit Requirements: Period 0.7956269 D AND ZERO-PHASE HJD2454230.5558 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 V-EL-CVN COS/NUV ACQ/IMA BOA MIRRORA 1 15 S (15 PHASE 0.61 TO 0.76 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 V-EL-CVN COS/FUV TIME-TA PSA G160M 1577 BUFFER-TIME=153, FP-POS=ALL 1 153 S (612 G S) ------------------------------------------------------------------------------------------------------------------------------------ 3 V-EL-CVN COS/FUV TIME-TA PSA G160M 1600 BUFFER-TIME=153, FP-POS=ALL 1 153 S (612 G 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 | ------------------------------------------------------------------------------------------------------------------------------------ V-EL-CVN 1 COS/NUV ACQ/IMA BOA MIRRORA none none none none 1 N/A GE V-EL-CVN 2 COS/FUV TIME-TA PSA G160M 1577 none none none 1 1 N/A G V-EL-CVN 2 COS/FUV TIME-TA PSA G160M 1577 none none none 2 1 N/A G V-EL-CVN 2 COS/FUV TIME-TA PSA G160M 1577 none none none 3 1 N/A G V-EL-CVN 2 COS/FUV TIME-TA PSA G160M 1577 none none none 4 1 N/A G V-EL-CVN 3 COS/FUV TIME-TA PSA G160M 1600 none none none 1 1 N/A G V-EL-CVN 3 COS/FUV TIME-TA PSA G160M 1600 none none none 2 1 N/A G V-EL-CVN 3 COS/FUV TIME-TA PSA G160M 1600 none none none 3 1 N/A G V-EL-CVN 3 COS/FUV TIME-TA PSA G160M 1600 none none none 4 1 N/A G 14778( 2) - 28-Jun-2016 20:04:04 - [ 7] Visit: 04 Visit Requirements: Period 0.7956269 D AND ZERO-PHASE HJD2454230.5558 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 V-EL-CVN COS/NUV ACQ/IMA BOA MIRRORA 1 15 S (15 PHASE 0.74 TO 0.89 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 V-EL-CVN COS/FUV TIME-TA PSA G160M 1577 BUFFER-TIME=153, FP-POS=ALL 1 153 S (612 G S) ------------------------------------------------------------------------------------------------------------------------------------ 3 V-EL-CVN COS/FUV TIME-TA PSA G160M 1600 BUFFER-TIME=153, FP-POS=ALL 1 153 S (612 G 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 | ------------------------------------------------------------------------------------------------------------------------------------ V-EL-CVN 1 COS/NUV ACQ/IMA BOA MIRRORA none none none none 1 N/A GE V-EL-CVN 2 COS/FUV TIME-TA PSA G160M 1577 none none none 1 1 N/A G V-EL-CVN 2 COS/FUV TIME-TA PSA G160M 1577 none none none 2 1 N/A G V-EL-CVN 2 COS/FUV TIME-TA PSA G160M 1577 none none none 3 1 N/A G V-EL-CVN 2 COS/FUV TIME-TA PSA G160M 1577 none none none 4 1 N/A G V-EL-CVN 3 COS/FUV TIME-TA PSA G160M 1600 none none none 1 1 N/A G V-EL-CVN 3 COS/FUV TIME-TA PSA G160M 1600 none none none 2 1 N/A G V-EL-CVN 3 COS/FUV TIME-TA PSA G160M 1600 none none none 3 1 N/A G V-EL-CVN 3 COS/FUV TIME-TA PSA G160M 1600 none none none 4 1 N/A G 14778( 2) - 28-Jun-2016 20:04:04 - [ 8] Summary Form for Proposal 14778 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures BOA, PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/FUV, COS/NUV ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/IMAGE, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=153, FP-POS=ALL ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PHASE 0.11 TO 0.26, PHASE 0.24 TO 0.39, PHASE 0.61 TO 0.76, PHASE 0.74 TO 0.89, Period 0.7956269 D AND ZERO-PHASE HJD2454230.5558 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G160M, MIRRORA ------------------------------------------------------------------------------------------------------------------------------------ Target Names V-EL-CVN ------------------------------------------------------------------------------------------------------------------------------------