ZTF J1539+5027: the Shortest Period Eclipsing White Dwarf Binary
Abstract
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.
- Publication:
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HST Proposal
- Pub Date:
- June 2019
- Bibcode:
- 2019hst..prop15897B