Accurate Mass Determination of the Nearby Single White Dwarf L145-141 (LAWD 37) through Astrometric Microlensing
Abstract
White dwarf (WD) is the final stage for a vast majority of stars, and WDs are important in a variety of astrophysical and galactic contexts. However, there are surprisingly few WDs with direct mass measurements, all of them in binaries.
It has been reported recently that the fifth-nearest WD, L145-141 (LAWD 37), will pass closely in front of a background star in late 2019, with an impact parameter of only 380 milliarcsec. As it passes in front, the WD will relativistically deflect the light from the background star, providing a unique opportunity for direct measurement of the WD's mass. The gravitational deflection angle depends only on the distances and relative positions of the stars, and on the mass of the WD. Since the distances and positions can be determined precisely before the event, the astrometric measurement offers a direct method to measure the mass of the WD to high accuracy ( 2.5%). Precision HST astrometry was recently used to measure the astrometric deflection caused by the nearby white dwarf Stein 2051B, and thus measure its mass-the first application of this technique outside the solar system. We now propose to repeat this experiment for a second WD. Relativistic astrometric microlensing is the only available model-independent technique for determining the mass of a single WD. Our target is of special interest because it is the second-nearest single WD (after van Maanen's Star). Our measurement will be the first model-independent mass measurement of a single WD, and will add to the surprisingly small number of accurate model-independent mass determinations for WDs-a key element in testing the theoretical mass-radius relation.- Publication:
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HST Proposal
- Pub Date:
- June 2019
- Bibcode:
- 2019hst..prop15961S