article published yes Emma T. Chickles author Joheen Chakraborty author Kevin B. Burdge author Vik S. Dhillon author Paul Draghis author Kareem El-Badry author Matthew J. Green author Aaron Householder author Sarah Hughes author Christopher Layden author Stuart P. Littlefair author James Munday author Ingrid Pelisoli author Maya S. Redden author John Tonry author Joannes C van Roestel author 4d122fc8-6083-11f0-87a5-97d68b860333 Francesco Elio Angile author Alex J. Brown author Noel Castro Segura author Jack Dinsmore author Martin Dyer author Gabor Furesz author Michelle Gabutti author James Garbutt author Juliana García-Mejía author Daniel Jarvis author Mark R. Kennedy author Paul Kerry author James Mccormac author Geoffrey Mo author Dave Osip author Steven Parsons author Eleanor Pike author John J. Piotrowski author Roger W. Romani author David Sahman author Rob Simcoe author IlCa department We report the discovery of ATLAS J101342.5−451656.8 (hereafter ATLAS J1013−4516), an 8.56 minute orbital-period mass-transferring AM Canum Venaticorum (AM CVn) binary with a mean Gaia magnitude of G = 19.51, identified via periodic variability in light curves from the Asteroid Terrestrial-impact Last Alert System (ATLAS) of Gaia white dwarf candidates. Follow-up with the Large Lenslet Array Magellan Spectrograph shows a helium-dominated accretion disk, and high-speed ULTRACAM photometry reveals pronounced primary and secondary eclipses. We construct a decade-long timing baseline leveraging light curves from the ATLAS and Gaia surveys, as well as the high-speed imagers ULTRACAM on the New Energy Telescope and proto-Lightspeed on the Magellan Clay telescope. From this timing baseline, we measure an orbital period derivative of P 1.60 0.07 10 = ± × 12 s s−1. Interpreted in the context of stable mass transfer, the magnitude and sign of P indicate that the orbital evolution is governed by the interplay between gravitationalwave-driven angular-momentum losses and mass transfer, directly probing the donor’s structural response to mass loss. We constrain the accretor and donor mass based on stable mass-transfer arguments assuming angularmomentum loss dominated by gravitational-wave emission, allowing us to infer the characteristic gravitational wave strain of the binary for future space-based GW observatories such as the Laser Interferometer Space Antenna (LISA). We predict a characteristic strain corresponding to a 4 yr LISA signal-to-noise ratio ≳10, establishing ATLAS J1013−4516 as a strong prospective LISA source that will probe long-term orbital evolution in the mass-transferring regime. https://research-explorer.ista.ac.at/download/21705/21782/2026_AstrophysicalJournal_Chickles.pdf application/pdfno https://creativecommons.org/licenses/by/4.0/ IOP Publishing2026 eng 0004-637X 1538-4357 2601.0792510.3847/1538-4357/ae4871 10002 Chickles, Emma T., et al. “An Eclipsing 8.56 Minutes Orbital Period Mass-Transferring Binary.” <i>The Astrophysical Journal</i>, vol. 1000, no. 2, 237, IOP Publishing, 2026, doi:<a href="https://doi.org/10.3847/1538-4357/ae4871">10.3847/1538-4357/ae4871</a>. Chickles, E. T., Chakraborty, J., Burdge, K. B., Dhillon, V. S., Draghis, P., El-Badry, K., … Simcoe, R. (2026). An eclipsing 8.56 minutes orbital period mass-transferring binary. <i>The Astrophysical Journal</i>. IOP Publishing. <a href="https://doi.org/10.3847/1538-4357/ae4871">https://doi.org/10.3847/1538-4357/ae4871</a> Chickles ET, Chakraborty J, Burdge KB, Dhillon VS, Draghis P, El-Badry K, Green MJ, Householder A, Hughes S, Layden C, Littlefair SP, Munday J, Pelisoli I, Redden MS, Tonry J, van Roestel JC, Angile FE, Brown AJ, Segura NC, Dinsmore J, Dyer M, Furesz G, Gabutti M, Garbutt J, García-Mejía J, Jarvis D, Kennedy MR, Kerry P, Mccormac J, Mo G, Osip D, Parsons S, Pike E, Piotrowski JJ, Romani RW, Sahman D, Simcoe R. 2026. An eclipsing 8.56 minutes orbital period mass-transferring binary. The Astrophysical Journal. 1000(2), 237. Chickles, Emma T., Joheen Chakraborty, Kevin B. Burdge, Vik S. Dhillon, Paul Draghis, Kareem El-Badry, Matthew J. Green, et al. “An Eclipsing 8.56 Minutes Orbital Period Mass-Transferring Binary.” <i>The Astrophysical Journal</i>. IOP Publishing, 2026. <a href="https://doi.org/10.3847/1538-4357/ae4871">https://doi.org/10.3847/1538-4357/ae4871</a>. E. T. Chickles <i>et al.</i>, “An eclipsing 8.56 minutes orbital period mass-transferring binary,” <i>The Astrophysical Journal</i>, vol. 1000, no. 2. IOP Publishing, 2026. E.T. Chickles, J. Chakraborty, K.B. Burdge, V.S. Dhillon, P. Draghis, K. El-Badry, M.J. Green, A. Householder, S. Hughes, C. Layden, S.P. Littlefair, J. Munday, I. Pelisoli, M.S. Redden, J. Tonry, J.C. van Roestel, F.E. Angile, A.J. Brown, N.C. Segura, J. Dinsmore, M. Dyer, G. Furesz, M. Gabutti, J. Garbutt, J. García-Mejía, D. Jarvis, M.R. Kennedy, P. Kerry, J. Mccormac, G. Mo, D. Osip, S. Parsons, E. Pike, J.J. Piotrowski, R.W. Romani, D. Sahman, R. Simcoe, The Astrophysical Journal 1000 (2026). Chickles ET, Chakraborty J, Burdge KB, et al. An eclipsing 8.56 minutes orbital period mass-transferring binary. <i>The Astrophysical Journal</i>. 2026;1000(2). doi:<a href="https://doi.org/10.3847/1538-4357/ae4871">10.3847/1538-4357/ae4871</a> 217052026-04-12T22:01:47Z2026-05-04T06:37:12Z