One-Million-Year-Old Nascent Eclipsing Binaries in the LMC
Abstract
The light curves of nascent eclipsing binaries (EBs) feature sinusoidal reflection effects as a hot B-type main-sequence (MS) primary irradiates the near side of a cool, low-mass, pre-MS companion. We obtained multi-epoch echelle spectra with the MIKE spectrograph on the 6.5m Magellan-Clay Telescope of three nascent EBs embedded in H II regions within the LMC. By fitting atmospheric models to the spectra, the primaries are found to be mid-B dwarfs (T_eff,1 = 18,600-22,800 K; M_1 = 6.8-8.5 Msun). The dynamical masses of the secondaries are only M_2 = 0.38-0.95 Msun, yielding extremely small mass ratios q = M_2/M_1 = 0.05-0.11. Unlike solar-type primaries, which exhibit a dearth of close companions with q < 0.1 known as the brown dwarf desert, massive stars can readily form with very close companions below q < 0.1. By fitting PHOEBE models to the OGLE-III light curves, we measure the secondary radii R_2 = 2.0-2.8 Rsun and temperatures T_eff,2 = 4,000 K. The pre-MS companions are located high on the Hayashi track where evolutionary models indicate ages of only 1 Myr. Their extreme youth suggests that nascent EBs formed via inward disk migration during the previous embedded protostellar phase.
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BibTeX
@misc{frank2026onemillionyearold,
title = {{One-Million-Year-Old Nascent Eclipsing Binaries in the LMC}},
author = {Megan G. Frank and Maxwell Moe},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.32931},
eprint = {2610.32931},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.32931},
}
RIS
TY - UNPB
TI - One-Million-Year-Old Nascent Eclipsing Binaries in the LMC
AU - Megan G. Frank
AU - Maxwell Moe
PY - 2026
DA - 2026/10/23
PB - arXiv
DO - 10.48550/arxiv.2610.32931
UR - https://arxiv.org/abs/2610.32931
AB - The light curves of nascent eclipsing binaries (EBs) feature sinusoidal reflection effects as a hot B-type main-sequence (MS) primary irradiates the near side of a cool, low-mass, pre-MS companion. We obtained multi-epoch echelle spectra with the MIKE spectrograph on the 6.5m Magellan-Clay Telescope of three nascent EBs embedded in H II regions within the LMC. By fitting atmospheric models to the spectra, the primaries are found to be mid-B dwarfs (T_eff,1 = 18,600-22,800 K; M_1 = 6.8-8.5 Msun). The dynamical masses of the secondaries are only M_2 = 0.38-0.95 Msun, yielding extremely small mass ratios q = M_2/M_1 = 0.05-0.11. Unlike solar-type primaries, which exhibit a dearth of close companions with q < 0.1 known as the brown dwarf desert, massive stars can readily form with very close companions below q < 0.1. By fitting PHOEBE models to the OGLE-III light curves, we measure the secondary radii R_2 = 2.0-2.8 Rsun and temperatures T_eff,2 = 4,000 K. The pre-MS companions are located high on the Hayashi track where evolutionary models indicate ages of only 1 Myr. Their extreme youth suggests that nascent EBs formed via inward disk migration during the previous embedded protostellar phase.
ER -