0 Assigned ID: 1001 ----- Attempting Submission 1 (Fri Apr 05 23:53:08 GMT 2019) ----- HST Phase I Proposal 1001 (7min.apt) successfully submitted. Receipt: # 1001-1 ----- Attempting Submission 2 (Fri Apr 05 23:53:57 GMT 2019) ----- INEFFICIENT ORDERING OF FP-POS POSITIONS INEFFICIENT ORDERING OF FP-POS POSITIONS INEFFICIENT ORDERING OF FP-POS POSITIONS Updated buffer times as suggested 1041222634 ----- Attempting Submission 1 (Wed Jul 24 18:04:53 GMT 2019) ----- ----- Attempting Submission 2 (Tue Dec 03 22:26:48 GMT 2019) ----- "We cycle through the FP-POS positions orbit-by-orbit, so the switching occurs occur during Earth occultation, and does not affect the efficiency of the program." ZTF J1539+5027: the Shortest Period Eclipsing White Dwarf Binary Here, we propose to obtain high resolution ultraviolet spectroscopy using COS on the shortest eclipsing binary system known, the double white dwarf binary ZTF J1539+5027 (submitted to Nature). This deeply eclipsing binary system has an orbital period of 6.91 minutes and exhibits a rapid orbital decay due to the emission of gravitational radiation. The binary emits gravitational waves near the peak of the Laser Interferometer Space Antenna's (LISA) sensitivity, making it one of the strongest LISA gravitational wave sources, with detection expected within the first week of operations. We are requesting Hubble's unique capability to obtain high resolution far-ultraviolet spectroscopy because the more compact white dwarf in this system is 50,000K despite its short cooling age, suggesting heating via accretion; however, no signs of accretion have been detected in the optical or X-ray. If we fail to detect metal lines visible uniquely in the UV, we will be able place an upper limit on the accretion rate to a level 8 orders of magnitude below what is currently possible in the X-ray or optical, ruling out the possibility that this white dwarf is currently heated by ongoing mass-transfer. If we detect metal lines, we will measure the accretion rate, obtain precise radial velocity semi-amplitudes of the components. Additionally, by using Lyman absorption lines as well as the ratio of metal lines (if present), we will be able to accurately measure the temperature of the primary, refining the distance estimate to the system. Finally, by obtaining a high SNR ultraviolet lightcurve, we will constrain the temperature ratio of the two components. This program will obtain time-resolved intermediate resolution spectroscopy of the ultra-short-period eclipsig double-white dwarf binary to (1) determine an accurate effective temperature of the hotter white dwarf from it's Ly alpha absorption profile (2) construct a far-ultraviolet eclipse light curve to model the stellar radii (3) probe for photospheric metal lines arising from accretion from the companion The target acqusition is done via near-UV imaging. However, as the primary, which totally dominates the ultraviolet flux, is eclipsed every 7min, we need to implement an ephemeris timing constraint to avoid that the target acquisition occurs during primary eclipse. We split this ten-orbit program into two five-orbit visits, using the 1291A and 1222A central wavelengths to maximise the total wavelength range covered: extending the blue Ly alpha wing, and covering the Si IV 1393/1403A resonance lines. We will achieve a combined signal-to-noise ratio of ~20 in the overlapping region. The time-tagged photon stream will be used to construct average spectra on the 7min orbital period of the system, and far-ultraviolet light curves in at least two wavelength bands . Burdge is a graduate student with experience in characterizing ultracompact white dwarf binaries, and will perform lightcurve modelling on the ultraviolet lightcurve, a careful timing analysis of the data, and integrate the overall ultraviolet analysis results with the existing optical and X-ray observations to characterize the system. Coughlin is an expert in gravitational waves and optical photometry. He will assist in reducing and analyzing the observations. Kaplan is an expert in studying compact binaries with accreting objects, and will help physically interpret the results of the analysis as a constraint on the accretion rate in this system. Prince has experience in compact object astrophysics including studies of detached and accreting white dwarfs, radio pulsar systems, including magnetars, and high-mass X-ray binaries. He was the US co-chair of the LISA International Science Team and NASA LISA Mission Scientist. He is co-PI on the Zwicky Transient Facility project. Kulkarni is the PI of the Zwicky Transient Facility project and has expertise in a broad range of astrophysics and has worked on supernovae, millisecond pulsars, fast radio bursts, old neutron stars, young neutron stars, brown dwarfs, soft gamma-ray repeaters, supernova remnants, gamma-ray bursts, and new types of optical transients. He has been active in development of instrumentation for time-domain astronomy at optical, radio, and, more recently, at ultraviolet wavelengths. Fuller is an expert in various theoretical aspects of white dwarf binaries, including tidal dissipation in such systems, and will lead the theoretical interpretation of the results. Gaensicke has been PI of 20 HST programs, carrying out far-ultraviolet spectroscopy of white dwarfs, including large, medium, small GO programs and several snapshot programs. He has in-depth experience in the analysis and interpretation of the observations of accreting white dwarfs, both in binary systems, and evolved planetary systems. He will implement the observations, and lead the analysis. Toloza is an expert in the analysis of COS time-tag observations. She will carry out the COS data reduction and the computation of white dwarf model atmospheres. Stellar Physics 6 false false true false false false false SUPPORTED STAR DA NO J2000 J2000 GALEX FUV=18.75 NUV=19.33 COS/FUV Spectroscopic No No G130M 1291 C:\Users\Kevin\AppData\Local\Temp\OPVisit3122985752305297999.xml The scheduling data was generated by CASM 27.2. CASM was run in Phase II mode. 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