For G160M observations, please consult Chapter 9 of the COS Instrument Handbook to estimate overheads and the number of exposures per orbit, and consequently the correct lifetime position. Use of LP4 with G160M requires justification in the "Special Requirements" section of the Phase I PDF. Use of the default LP6 with G160M requires no justification. Proposals can be submitted with the warning present. For G160M observations, please consult Chapter 9 of the COS Instrument Handbook to estimate overheads and the number of exposures per orbit, and consequently the correct lifetime position. Use of LP4 with G160M requires justification in the "Special Requirements" section of the Phase I PDF. Use of the default LP6 with G160M requires no justification. Proposals can be submitted with the warning present. For G160M observations, please consult Chapter 9 of the COS Instrument Handbook to estimate overheads and the number of exposures per orbit, and consequently the correct lifetime position. Use of LP4 with G160M requires justification in the "Special Requirements" section of the Phase I PDF. Use of the default LP6 with G160M requires no justification. Proposals can be submitted with the warning present. For G160M observations, please consult Chapter 9 of the COS Instrument Handbook to estimate overheads and the number of exposures per orbit, and consequently the correct lifetime position. Use of LP4 with G160M requires justification in the "Special Requirements" section of the Phase I PDF. Use of the default LP6 with G160M requires no justification. Proposals can be submitted with the warning present. For G160M observations, please consult Chapter 9 of the COS Instrument Handbook to estimate overheads and the number of exposures per orbit, and consequently the correct lifetime position. Use of LP4 with G160M requires justification in the "Special Requirements" section of the Phase I PDF. Use of the default LP6 with G160M requires no justification. Proposals can be submitted with the warning present. For G160M observations, please consult Chapter 9 of the COS Instrument Handbook to estimate overheads and the number of exposures per orbit, and consequently the correct lifetime position. Use of LP4 with G160M requires justification in the "Special Requirements" section of the Phase I PDF. Use of the default LP6 with G160M requires no justification. Proposals can be submitted with the warning present. 0 Assigned ID: 7544 ----- Attempting Submission 1 (Thu Apr 16 18:54:01 GMT 2026) ----- Use of LP6 as default lifetime position for COS G160M. See comments in target section about assumptions made about the emission line peak fluxes. 327285117 ----- Attempting Submission 1 (Sat Aug 15 21:32:51 GMT 2026) ----- Extreme Mass Transfer and Mass Loss in the Massive Interacting Binary W Serpentis W Ser is the proto-type of a rare type of interacting massive binary that is experiencing a stage of very high mass transfer rate. The donor will be stripped of its envelope, while the gainer will emerge as a massive rapid rotator. The evolutionary destiny is set by how much of the mass transfer is captured by the gainer or lost from the binary. W Ser is surrounded by a dense circumbinary disk that indicates that systemic mass loss is underway. The donor star is cool, so the flux in the ultraviolet spectrum originates in gas in the vicinity of the gainer star. HST/COS spectra obtained around the orbit will show where and how the high excitation emission lines are formed through accretion power. These observations will demonstrate the importance of systemic mass loss for massive binaries and their remnants. The binary consists of a cool mass donor and a hot mass gainer embedded in an accretion disk. The accretion disk flux will dominate in the FUV, and in this program we record the orbital phase variations in the FUV continuum and emission lines to map out the flux components from the accretion stream, occulting disk, and outflow into a circumbinary disk. The COS G160M grating is ideal for the required spectral resolution to measure Doppler shifts of several key emission lines including Si IV 1400, C IV 1550, and O III 1666. We plan to obtain FUV spectra using three central wavelengths (1533, 1577, and 1600 Angstroms) to cover the gaps between the A and B segments of COS. The spectra will made with all four FP-POS offset positions in each case to optimize the S/N ratio. Based upon ETC calculations, we expect to obtain a net S/N = 10 in the continuum and 35 at the peak of the strongest emission line per visit. There will be six visits to sample the full range of orbital phase with one of these centered on the eclipse of the disk by the mass donor star to determine the spatial extent of the eclipsed flux. The total counts at the brightest pixel summmed over six visits is about 60 counts, so the observations meet the safety requirements of COS. Dr. Douglas Gies is a Regents' Professor in the Department of Physics and Astronomy and the Director of the Center for High Angular Resolution Astronomy (CHARA) at Georgia State University. He has led a long career of studies of massive stars using space-based and ground-based telescopes including the GSU CHARA Array interferometer at Mount Wilson Observatory. Dr. Katherine Shepard is a lecturer at Vanderbilt University and an expert on spectroscopic and interferometric observations of W Ser binaries. Stellar Physics and Stellar Types 6 false true false false false false false SUPPORTED STAR ALGOL SYSTEM CIRCUMSTELLAR MATTER EMISSION LINE STAR SHELL STAR NO 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. The ETC calculations were made using IUE low dispersion spectra as the source for flux. There are three bright emission lines in the range 1342 to 1774 Angstroms: Si IV 1400 C IV 1550 O III 1666 The peak intensities are reduced in the low dispersion IUE spectra, but there are two HST/GHRS spectra in the archive with comparable spectral resolution to COS. These record the Si IV doublet that is narrower but fully resolved and appears with a peak flux that is 4.36 times larger (peak to continuum) than that of the low resolution IUE spectrum. The other two lines are formed in similar environments in the binary system, so they should also be fully resolved at the COS spectral resolution. Consequently, we multiplied the IUE fluxes of these three emission lines by the same factor of 4.36 to estimate the peak emission line fluxes. This will lead to a small over-estimate of the total wavelength-integrated counts in the ETC, but the emission line peak counts should be consistent with the expectations from the archival HST/GHRS spectra of the target. J2000 J2000 F(1500) = 1.4E-13 erg/s/cm^2/Angstrom COS/FUV Spectroscopic No No G160M 1533 COS/FUV Spectroscopic No No G160M 1533 COS/FUV Spectroscopic No No G160M 1533 COS/FUV Spectroscopic No No G160M 1533 COS/FUV Spectroscopic No No G160M 1533 COS/FUV Spectroscopic No No G160M 1533 /Users/douglasgies/Proposals/HST_34/W_Ser/OP-cache/wser-v01.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. Visit 1 corresponds to an eclipse phase. Primary minimum occurs at HJD 2461775.8089 or phaseIngress)=0.046. Epoch used for APT is T(min)-0.65 days, so that this eclipse visit occurs between phase 0.0 and 0.092. (Tic-Visit :proposal-id 18356 :visit-id "01" :proposal-version -1 :trans-version "20260618" :date "15-Aug-2026 15:40:35.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 226560 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18356 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18356 :visit-id "01" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2592 :al-overhead-at-end 0 :internal-dur-at-end 357 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2976 :pcs-gap 0 ) true 1 0 /Users/douglasgies/Proposals/HST_34/W_Ser/OP-cache/wser-v02.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. Visit 2 for phase 0.095 to 0.270. (Tic-Visit :proposal-id 18356 :visit-id "02" :proposal-version -1 :trans-version "20260618" :date "15-Aug-2026 15:52:05.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 226560 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18356 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18356 :visit-id "02" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2592 :al-overhead-at-end 0 :internal-dur-at-end 357 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2976 :pcs-gap 0 ) true 1 0 /Users/douglasgies/Proposals/HST_34/W_Ser/OP-cache/wser-v03.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. Visit 3 for phase 0.276 to 0.452. (Tic-Visit :proposal-id 18356 :visit-id "03" :proposal-version -1 :trans-version "20260618" :date "15-Aug-2026 15:52:06.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 226560 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18356 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18356 :visit-id "03" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2592 :al-overhead-at-end 0 :internal-dur-at-end 357 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2976 :pcs-gap 0 ) true 1 0 /Users/douglasgies/Proposals/HST_34/W_Ser/OP-cache/wser-v04.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. Visit 4 for phase 0.458 to 0.634. (Tic-Visit :proposal-id 18356 :visit-id "04" :proposal-version -1 :trans-version "20260618" :date "15-Aug-2026 15:52:06.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 226560 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18356 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18356 :visit-id "04" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2592 :al-overhead-at-end 0 :internal-dur-at-end 357 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2976 :pcs-gap 0 ) true 1 0 /Users/douglasgies/Proposals/HST_34/W_Ser/OP-cache/wser-v05.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. Visit 5 for phase 0.640 to 0.815. (Tic-Visit :proposal-id 18356 :visit-id "05" :proposal-version -1 :trans-version "20260618" :date "15-Aug-2026 15:52:07.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 226560 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18356 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18356 :visit-id "05" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2592 :al-overhead-at-end 0 :internal-dur-at-end 357 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2976 :pcs-gap 0 ) true 1 0 /Users/douglasgies/Proposals/HST_34/W_Ser/OP-cache/wser-v06.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. Visit 6 for phase 0.821 to 0.997. (Tic-Visit :proposal-id 18356 :visit-id "06" :proposal-version -1 :trans-version "20260618" :date "15-Aug-2026 15:52:08.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 226560 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18356 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18356 :visit-id "06" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2592 :al-overhead-at-end 0 :internal-dur-at-end 357 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2976 :pcs-gap 0 ) true 1 0