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Abstract Five self-lensing binaries (SLBs) have been discovered with data from the Kepler mission. One of these systems is KIC 8145411, which was reported to host an extremely low mass (ELM; 0.2M⊙) white dwarf (WD) in a 456 days orbit with a solar-type companion. The system has been dubbed “impossible,” because evolutionary models predict that ∼0.2M⊙WDs should only be found in tight orbits (Porb≲ days). In this work, we show that KIC 8145411 is in fact a hierarchical triple system: it contains a WD orbiting a solar-type star, with another solar-type star ∼700 au away. The wide companion was unresolved in the Kepler light curves, was just barely resolved in Gaia DR3, and is resolved beyond any doubt by high-resolution imaging. We show that the presence of this tertiary confounded previous mass measurements of the WD for two reason: it dilutes the amplitude of the self-lensing pulses, and it reduces the apparent radial velocity (RV) variability amplitude of the WD’s companion due to line blending. By jointly fitting the system’s light curves, RVs, and multi-band photometry using a model with two luminous stars, we obtain a revised WD mass of (0.53 ± 0.01)M⊙. Both luminous stars are near the end of their main-sequence evolution. The WD is thus not an ELM WD, and the system does not suffer the previously proposed challenges to its formation history. Similar to the other SLBs and the population of astrometric WD binaries recently identified from Gaia data, KIC 8145411 has parameters in tension with standard expectations for formation through both stable and unstable mass transfer (MT). The system’s properties are likely best understood as a result of unstable MT from an AGB star donor.
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A Search for Self-lensing Binaries with TESS and Constraints on their Occurrence Rate
Abstract Five self-lensing binaries (SLBs) have been discovered with Kepler light curves. They contain white dwarfs (WDs) in AU-scale orbits that gravitationally lens solar-type companions. Forming SLBs likely requires common envelope evolution when the WD progenitor is an AGB star and has a weakly bound envelope. No SLBs have yet been discovered with data from the Transiting Exoplanet Survey Satellite (TESS), which observes far more stars than Kepler did. Identifying self-lensing in TESS data is made challenging by the fact that TESS only observes most stars for ∼25 days at a time, so only a single lensing event will be observed for typical SLBs. TESS’s smaller aperture also makes it sensitive only to SLBs a factor of ∼100 brighter than those to which Kepler is sensitive. We demonstrate that TESS has nevertheless likely already observed ∼4 times more detectable SLBs than Kepler. We describe a search for non-repeating self-lensing signals in TESS light curves and present preliminary candidates for which spectroscopic follow-up is ongoing. We calculate the sensitivity of our search with injection and recovery tests on TESS and Kepler light curves. Based on the 5 SLBs discovered with Kepler light curves, we estimate that (1.1 ± 0.6)% of solar-type stars are orbited by WDs with periods of 100–1000 days. This implies a space density of AU-scale WD + main sequence (MS) binaries a factor of 20–100 larger than that of astrometrically identified WD + MS binaries with orbits in Gaia DR3. We conclude that the Gaia sample is still quite incomplete, mainly because WD + MS binaries can only be unambiguously identified as such for high mass ratios.
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- Award ID(s):
- 2307232
- PAR ID:
- 10561449
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- Publications of the Astronomical Society of the Pacific
- Volume:
- 136
- Issue:
- 12
- ISSN:
- 0004-6280
- Format(s):
- Medium: X Size: Article No. 124202
- Size(s):
- Article No. 124202
- Sponsoring Org:
- National Science Foundation
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