{"ID":23523539,"CreatedAt":"2026-09-18T02:58:45.531918055Z","UpdatedAt":"2026-09-18T02:58:45.531918055Z","DeletedAt":null,"paper_url":"https://arxiv.org/abs/2609.19268","arxiv_id":"2609.19268","title":"A census of massive eclipsing binaries in the Whirlpool Galaxy","abstract":"We present a census of massive eclipsing binary (EB) candidates in the Whirlpool Galaxy (M51), a face-on spiral galaxy at 7.5 Mpc with $Z\\sim Z_\\odot$. Using 34 epochs of red-optical Hubble Space Telescope (HST) photometry and a single epoch of broadband UV-optical photometry, we identify 173 massive EB candidates ($\u003e5~{\\rm M_\\odot}$) with orbital periods $P_{\\rm orb}$=1-30 days. The sample traces young stellar populations across the spiral arms of M51. Joint light-curve and spectral energy distribution fits for 136 systems yield binaries spanning $T_{\\rm eff}=10{,}000$-$50{,}000$ K, $R=7$-$66~{\\rm R_\\odot}$, and masses of $5$-$120~{\\rm M_\\odot}$. We use detailed injection-recovery simulations to quantify the survey's completeness and infer intrinsic properties of the massive binary population. At the population level, we infer a close-binary fraction of $f_{\\rm close}=27.4\\pm7.1\\%$ for $2\\leq P_{\\rm orb}/{\\rm d}\u003c20$ and $0.1\\leq q\\leq1$. Over the same period range, the intrinsic period distribution is consistent with being log-uniform, ${\\rm d}N/{\\rm d}\\log P_{\\rm orb}\\propto P_{\\rm orb}^π$ with $π=0.29\\pm0.32$. These demographics broadly match those of massive-star populations in the Milky Way, LMC, and SMC, with tentative evidence for a lower close-binary fraction at lower metallicity. Across the $\\sim0.2$-$1.1~Z_\\odot$ range spanned by these galaxies, the overall similarities suggest that the formation of close massive binaries depends only weakly on metallicity. Our survey establishes EBs as a powerful tool for measuring massive-binary demographics beyond the Local Group and provides a rich panchromatic census of $\\sim$100,000 luminous stars and variables in M51.","short_abstract":"We present a census of massive eclipsing binary (EB) candidates in the Whirlpool Galaxy (M51), a face-on spiral galaxy at 7.5 Mpc with $Z\\sim Z_\\odot$. Using 34 epochs of red-optical Hubble Space Telescope (HST) photometry and a single epoch of broadband UV-optical photometry, we identify 173 massive EB candidates ($\u003e5...","url_abs":"https://arxiv.org/abs/2609.19268","url_pdf":"https://arxiv.org/pdf/2609.19268v1","authors":"[\"Cheyanne Shariat\",\"Kareem El-Badry\",\"Maude Gull\",\"Daniel R. Weisz\",\"Charlie Conroy\",\"Alessandro Savino\"]","published":"2026-09-16T18:00:04Z","proceeding":"astro-ph.SR","tasks":"[\"astro-ph.SR\",\"astro-ph.GA\",\"astro-ph.HE\"]","methods":"[]","has_code":false}