0 Assigned ID: 3622 ----- Attempting Submission 1 (Fri Mar 25 22:05:28 GMT 2022) ----- Resubmitting with an addition Visit 6. This is a repeat observation of Visit 2, which failed due to guide star acquisition issues and a repeat observation was approved with HOPR 92484. -1099668618 ----- Attempting Submission 1 (Thu Jul 14 14:33:24 GMT 2022) ----- ----- Attempting Submission 2 (Fri Jun 02 15:04:09 GMT 2023) ----- Testing the Limits of Mass Transfer Stability With A Post-Mass-Transfer Binary In M67 Many important systems result from mass transfer (MT) in low-mass binaries including double white dwarf (WD) binaries and Type Ia supernovae. A key uncertainty in modeling these systems is whether the MT will be unstable, resulting in a common envelope that dramatically shrinks the binary orbit. In particular, theory suggests that most MT from an RGB donor should be unstable, but observations reveal many systems that challenge this hypothesis. Here we target WOCS 14020, a main sequence-WD binary in open cluster M67. The orbital period of 359 days suggests the system evolved through stable MT from an RGB donor star. WOCS 14020 is uniquely poised to test the limits of MT stability; the primary main-sequence star is one of the lowest mass outcomes of MT in the cluster, and canonical MT models predict MT on to lower mass accretors to be increasingly unstable. We request 10 orbits of COS FUV spectroscopy to measure the WD mass and cooling age in this system, which together define the evolutionary state of the donor star during MT. Further, WOCS 14020's membership in M67 provides many important constraints that are not usually available in modeling post-MT binaries. Together, this will allow us to construct an unusually detailed evolutionary history for WOCS 14020, and explore whether non-conservative mass transfer models yield stable MT evolution and reproduce the observed system. The results will be an important test of whether non-conservative MT models can empirically match the extent of the post-MT population of a benchmark open cluster. The precise WD mass and age measurements required are only possible with FUV spectroscopy, a capability unique to HST. We propose 10 orbits of FUV COS spectroscopy of the Lyman-alpha region of WOCS 14020, a post-mass-transfer main sequence-white dwarf binary in the open cluster M67 with an orbital period of 359 days. Using this spectrum we will measure the effective temperature and surface gravity of the WD, breaking the degeneracy between temperature and surface gravity with the known distance to M67. We can then use these measurements to constrain the mass, radius, and cooling age for the WD component, allowing us to model the formation history of this system in exceptional detail. The main sequence component of WOCS 14020 is a G-type main-sequence star with a temperature of 5990 K. This temperature is cool enough that the Wien tail of the SED drops off rapidly in the UV, and thus FUV spectroscopy will be dominated by the flux from the white dwarf (WD) companion. We can be confident that the WD will be detectable with COS based on previous HST/ACS/SBC FUV photometry in the derived bandpasses of F140N and F150N along with F165LP (HST-GO 16244; PI Mathieu). The derived fluxes are 9.37e-17 erg s-1 cm-2 A-1 in F140N, 1.18e-16 erg s-1 cm-2 A-1 in F150N, and 1.12e-16 erg s-1 cm-2 A-1 in F165LP. The FUV photometry shows a clear photometric excess above the flux expected from the WOCS 14020 main sequence component alone, compelling evidence that a detectable, hot WD is present. Photometric fits are degenerate between temperature, mass, and radius, and therefore the photometry cannot well constrain the WD mass and core composition. However, the photometric detections allow us to calculate COS exposure times by scaling possible WD spectral models to the observed FUV fluxes. For the ETC calculations presented here, we adopt a spectral model that combines a 0.39 Msun, 12,250 K WD and a 5990 K main sequence star, reddened to match the M67 reddening of E(B-V)= 0.041, and normalized to the observed V-band and HST FUV photometry. We note that the true mass and temperature of the WD may differ somewhat from these chosen values, but because we can scale to the observed FUV photometry the exposure time calculated should yield sufficient S/N across the range of plausible white dwarf parameters. We propose to observe WOCS 14020 with COS using the G140L grating with a central wavelength setting of 1105 Angstroms, providing a spectral range of 1130-2000 A and a spectral resolution of ~0.6 A. This encompasses the Lyman-alpha absorption line at 1216 A, which is essential to determining the WD temperature and gravity. A 407-minute integration with COS will yield a S/N ~ 10 in the wing of Lyman-alpha at 1280 A, after binning to ~1.5 As. This is the signal level necessary to fit WD atmospheres to models in previous studies (e.g. Landsman et al. 1997, Gosnell et al. 2015). Although higher S/N is possible by binning G130M spectra, we require the widest wavelength coverage possible for our fitting purposes, which is provided by the G140L grating. The target position and proper motion are both very well known from Gaia, so target acquisition can be carried out with NUV imaging instead of a search pattern. Gaia coordinates have uncertainties less than 0.1 mas. M67 has a total of 52 minutes of visibility per orbit. Including guide star acquisition, target acquisition, and overheads we have requested a total allocation of 10 orbits. These orbits will be divided into five visits of 2 orbits each to protect the detector of COS and aid in scheduling. We will use all four FP-POS positions during each visit. There are no special timing considerations for these observations and no expected risks to the COS detectors. The target is a binary system, and the primary star in the binary is a G-type main sequence star with no large flares detected in Kepler/K2 observations. The binary system is too wide (Porb= 359 days) for there to be ongoing accretion or outbursts, and the HST UV photometry is also consistent with an older (~300 Myr), quiet WD system. The star's location within the central regions of a well-studied old open cluster ensures that nearby sources are well-characterized, and all are older inactive stars. No nearby bright or flaring sources will present a risk. The BOT tool returns one source as a Health/Safety issue (Object ID: N8X7000767) with a spectral type of **O5V**. This is actually our target which is a G type star (5990 K) with a white dwarf companion, and is not a threat to the detectors. We do not anticipate significant adverse impacts on this program if HST is reduced to 2-gyro mode. We do not have any timing or orientation restrictions and current schedulability is high, so we expect this program would continue to be schedulable under reduced gyro operations. This experimental design closely follows our team's previous successful observing proposal (HST Cycle 21- GO 13354; PI Mathieu) targeting blue straggler-white dwarf binaries for COS FUV spectroscopy. From our experience with these data, we have developed data reduction and analysis procedures for white dwarf spectral fitting. This previous proposal yielded mass and age constraints for two blue straggler-white dwarf binaries in NGC 188 (Gosnell et al. 2019). Given this experience, we are well poised to quickly produce high-quality scientific results from these observations. Gosnell wrote and maintains a software package for fitting white dwarf model atmospheres to UV spectra. This code has been successfully demonstrated for the NGC 188 blue stragglers in Gosnell et al. 2019. Using this code, Gosnell will oversee a very similar analysis of the COS spectra requested in this proposal. Leiner provides broad expertise in binary evolution and mass-transfer (Leiner et al. 2017, 2019, Gosnell et al. 2019), including both theoretical and observational knowledge of blue stragglers and blue lurker populations. Leiner will coordinate the team working on this proposal, and lead the binary evolution modeling we propose. Sills and Sun provide extensive expertise in theoretical stellar and binary evolution including both 1D stellar evolution codes and hydrodynamic simulations, particularly modeling blue straggler systems and main sequence-helium white dwarf binaries. Sun is an expert using MESA, our primary modeling tool for this project, and has used MESA previously to model detailed evolutionary histories of a blue straggler star (Sun et al. 2021). Geller and Mathieu are two of the foremost experts in observations of blue straggler stars, particularly in open clusters. They have done important work to establish the mass-transfer origin of blue straggler stars (Geller & Mathieu 2011), and were key advisors in developing the analysis pipelines for our previous COS work. Their input will continue to be valuable for our analysis and interpretation. Nine has led the analysis of previous HST/UV photometry of this target (Cycle 28--GO 16244) and will continue to assist in the analysis and interpretation of these results. Stellar Physics and Stellar Types 6 false false true false false false false false SUPPORTED STAR BLUE STRAGGLER G V-IV NO Coordinates and proper motions from Gaia DR3 J2000 NUV= 19.56, F150N= 1.18e-16 cgs, E(B-V)= 0.041 COS/FUV Spectroscopic No No G140L 1105 The scheduling data was generated by CASM 31.0. CASM was run in Phase II mode. 1684992244000 108.0147793621768 (Tic-Visit :proposal-id 17134 :visit-id "01" :proposal-version -1 :trans-version "20220630" :date "02-Jun-2023 10:02:39.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 87168 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17134 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17134 :visit-id "01" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2756 :al-overhead-at-end 0 :internal-dur-at-end 48 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3149 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17134 :visit-id "01" :orbit-number 2 :pcs-time 392 :si-vis-utilization 2757 :al-overhead-at-end 0 :internal-dur-at-end 360 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3149 :pcs-gap 0 ) true 2 0 The BOT tool returns one source as a Health/Safety issue (Object ID: N8X7000767) with a spectral type of **O5V**. This is actually our target which is a G type star (5990 K) with a white dwarf companion. The ETC run shows the global count rate is 1,449.751 cts/s, well below the global maximum. The scheduling data was generated by CASM 31.0. CASM was run in Phase II mode. 1679913251000 101.74364259482292 (Tic-Visit :proposal-id 17134 :visit-id "02" :proposal-version -1 :trans-version "20220630" :date "02-Jun-2023 10:02:40.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 87168 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17134 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17134 :visit-id "02" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2756 :al-overhead-at-end 0 :internal-dur-at-end 48 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3149 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17134 :visit-id "02" :orbit-number 2 :pcs-time 392 :si-vis-utilization 2757 :al-overhead-at-end 0 :internal-dur-at-end 360 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3149 :pcs-gap 0 ) true 2 0 The BOT tool returns one source as a Health/Safety issue (Object ID: N8X7000767) with a spectral type of **O5V**. This is actually our target which is a G type star (5990 K) with a white dwarf companion. The ETC run shows the global count rate is 1,449.751 cts/s, well below the global maximum. The scheduling data was generated by CASM 31.0. CASM was run in Phase II mode. Repeat of Visit 2 observation (HOPR 92484) (Tic-Visit :proposal-id 17134 :visit-id "06" :proposal-version -1 :trans-version "20220630" :date "02-Jun-2023 09:43:58.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 87168 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17134 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17134 :visit-id "06" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2756 :al-overhead-at-end 0 :internal-dur-at-end 48 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3149 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17134 :visit-id "06" :orbit-number 2 :pcs-time 392 :si-vis-utilization 2757 :al-overhead-at-end 0 :internal-dur-at-end 360 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3149 :pcs-gap 0 ) true 2 0 The BOT tool returns one source as a Health/Safety issue (Object ID: N8X7000767) with a spectral type of **O5V**. This is actually our target which is a G type star (5990 K) with a white dwarf companion. The ETC run shows the global count rate is 1,449.751 cts/s, well below the global maximum. The scheduling data was generated by CASM 31.0. CASM was run in Phase II mode. 1676893158000 89.9778162652392 (Tic-Visit :proposal-id 17134 :visit-id "03" :proposal-version -1 :trans-version "20220630" :date "02-Jun-2023 10:02:41.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 87168 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17134 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17134 :visit-id "03" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2756 :al-overhead-at-end 0 :internal-dur-at-end 48 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3149 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17134 :visit-id "03" :orbit-number 2 :pcs-time 392 :si-vis-utilization 2757 :al-overhead-at-end 0 :internal-dur-at-end 360 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3149 :pcs-gap 0 ) true 2 0 The BOT tool returns one source as a Health/Safety issue (Object ID: N8X7000767) with a spectral type of **O5V**. This is actually our target which is a G type star (5990 K) with a white dwarf companion. The ETC run shows the global count rate is 1,449.751 cts/s, well below the global maximum. The scheduling data was generated by CASM 31.0. CASM was run in Phase II mode. 1685340314000 107.0 (Tic-Visit :proposal-id 17134 :visit-id "04" :proposal-version -1 :trans-version "20220630" :date "02-Jun-2023 10:02:41.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 87168 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17134 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17134 :visit-id "04" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2756 :al-overhead-at-end 0 :internal-dur-at-end 48 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3149 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17134 :visit-id "04" :orbit-number 2 :pcs-time 392 :si-vis-utilization 2757 :al-overhead-at-end 0 :internal-dur-at-end 360 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3149 :pcs-gap 0 ) true 2 0 The BOT tool returns one source as a Health/Safety issue (Object ID: N8X7000767) with a spectral type of **O5V**. This is actually our target which is a G type star (5990 K) with a white dwarf companion. The ETC run shows the global count rate is 1,449.751 cts/s, well below the global maximum. The scheduling data was generated by CASM 31.0. CASM was run in Phase II mode. 1685494371000 107.0 (Tic-Visit :proposal-id 17134 :visit-id "05" :proposal-version -1 :trans-version "20220630" :date "02-Jun-2023 10:02:42.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 87168 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17134 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17134 :visit-id "05" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2756 :al-overhead-at-end 0 :internal-dur-at-end 48 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3149 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17134 :visit-id "05" :orbit-number 2 :pcs-time 392 :si-vis-utilization 2757 :al-overhead-at-end 0 :internal-dur-at-end 360 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3149 :pcs-gap 0 ) true 2 0 The BOT tool returns one source as a Health/Safety issue (Object ID: N8X7000767) with a spectral type of **O5V**. This is actually our target which is a G type star (5990 K) with a white dwarf companion. The ETC run shows the global count rate is 1,449.751 cts/s, well below the global maximum. (Tic-Visit :proposal-id 17134 :visit-id "05" :proposal-version -1 :trans-version "20220630" :date "02-Jun-2023 10:02:42.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 87168 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17134 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17134 :visit-id "05" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2756 :al-overhead-at-end 0 :internal-dur-at-end 48 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3149 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17134 :visit-id "05" :orbit-number 2 :pcs-time 392 :si-vis-utilization 2757 :al-overhead-at-end 0 :internal-dur-at-end 360 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3149 :pcs-gap 0 ) false 2 0 The BOT tool returns one source as a Health/Safety issue (Object ID: N8X7000767) with a spectral type of **O5V**. This is actually our target which is a G type star (5990 K) with a white dwarf companion. The ETC run shows the global count rate is 1,449.751 cts/s, well below the global maximum.