0 Assigned ID: 37 ----- Attempting Submission 1 (Wed Feb 26 18:17:14 GMT 2020) ----- A single STIS/CCD acquisition exposure on a point source, and then filled up the time with G140L STIS/FUV-MAMA spectroscopy. 1789997853 ----- Attempting Submission 1 (Mon Jun 08 14:33:42 GMT 2020) ----- We propose to obtain low resolution ultraviolet spectroscopy of the newly identified 1201 s orbital period detached binary J2322+0509. This is the third shortest-period detached binary known, and it contains two He-core white dwarfs at a ~27 degree inclination. The low-inclination results in no visible photometric effects (e.g., eclipses, ellipsoidal variations), but makes this one of the strongest sources of gravitational waves in the mHz frequency range. Located 760 pc from the Sun, this binary has an estimated LISA 4-yr signal-to-noise ratio of 40. J2322+0509 is the first He+He white dwarf LISA verification binary, a source class that is predicted to account for one-third of all LISA ultra-compact binary detections. Here we request HST STIS observations in the far-ultraviolet to constrain the physical parameters of this binary precisely. The optical data on this system reveals about 15% contribution from the cooler secondary white dwarf, limiting the precision of our model atmosphere analysis on the primary white dwarf. The primary star is hot, and it dominates in the far-ultraviolet. Our STIS data will enable us to constrain the temperature and mass of the primary precisely, which in turn will constrain the radius and mass of the secondary star, and the inclination of the system. Well-measured white dwarf binaries will be among the best electromagnetic + gravitational wave laboratories for understanding the formation of compact objects, dynamical interactions and tides in binaries. J2322+0509 is one of the best such systems. Our goal is to obtain low-resolution STIS spectroscopy of J2322+0509 in the TIME-TAG mode. Since our target has GALEX FUV=18.52 mag, we will obtain low resolution observations with the G140L grating. A S/N =20 STIS spectrum will enable us to constrain the mass of the primary white dwarf in this system precisely. Given the relatively low-amplitude of the radial velocity variations and the broad Lyman alpha line, orbital smearing will have no effect on our analysis of the STIS data. Drs. Brown and Kilic lead the Extremely Low-Mass (ELM) Survey that has so far discovered about 100 short period double white dwarf systems, including the subject of this proposal, J2322+0509, along with several other LISA verification binaries. Dr. Brown is an expert on stellar spectroscopy and he also leads the Hypervelocity Star Survey, which discovered the majority of the hypervelocity stars currently known. He has extensive experience with observations of white dwarfs for radial velocity variability, and constraining their physical and binary orbital parameters. He is also a member of the NASA LISA Science Study team. Dr. Kilic is an expert on white dwarfs, short period binary systems, cool white dwarfs, and white dwarf cosmochronology. He has prior experience in HST data reduction for WFPC2, ACS, and COS (including the TIME-TAG mode), and he has experience working on both single-lined and double-lined binary white dwarf systems. Stellar Physics and Stellar Types 6 false false true false false false false SUPPORTED STAR DA NO J2000 J2000 GALEX FUV = 18.52 STIS/FUV-MAMA Spectroscopic No No G140L 1425 /Users/bursa/prop/HST2020/OP-cache/phase2-v01.xml 1591626094316 The scheduling data was generated by CASM 28.2. CASM was run in Phase II mode. 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