NGTS-EB-8: a double-lined eclipsing M+M binary discovered by citizen scientists

Sean M. O’Brien; Megan E. Schwamb; Christopher A. Watson; Louise D. Nielsen; Edward M. Bryant; Sarah L. Casewell; Matthew R. Burleigh; Lucy Fortson; Samuel Gill; Chris J. Lintott; Katlyn L. Hobbs; Ioannis Apergis; Daniel Bayliss; Jorge Fernández Fernández; Maximilian N. Günther; Faith Hawthorn; James S. Jenkins; Alicia Kendall; James McCormac; Ernst J. W. de Mooij; Toby Rodel; Suman Saha; Laura Trouille; Richard G. West; Peter J. Wheatley; Marius Constantin Agafitei; Deniz Rüzgar Apaydın; Elisabeth Baeten; Bruce Baller; Jeff Carabott; Sallyann Chesson; Sebastián Alejandro Freigeiro; Virgilio Gonano; Matthias Hanke; Pete Hermes; Avery Hildebrand; John S. Langley; See Min Lim; Leo Ryan McCarthy; Graham Mitchell; Ken O’Neill; Charles R. Pearson; Nolan Reket; Jeanne Riethmiller; Juergen Saeftel; Arttu Sainio; Charlie Steiner; Amanda Strickland; Christopher Tanner; Ivan A. Terentev; Ernest Jude P. Tiu; Sergey Y. Tumanov; Marciniak Urszula; Pia Vahlenkamp; Femke de Vroome; Paweł Wantuch; Timothy Woodruff

doi:10.3847/1538-3881/ae0e0d

NGTS-EB-8: a double-lined eclipsing M+M binary discovered by citizen scientists

Sean M. O’Brien^*, Megan E. Schwamb, Christopher A. Watson, Louise D. Nielsen, Edward M. Bryant, Sarah L. Casewell, Matthew R. Burleigh, Lucy Fortson, Samuel Gill, Chris J. Lintott, Katlyn L. Hobbs, Ioannis Apergis, Daniel Bayliss, Jorge Fernández Fernández, Maximilian N. Günther, Faith Hawthorn, James S. Jenkins, Alicia Kendall, James McCormac, Ernst J. W. de MooijToby Rodel, Suman Saha, Laura Trouille, Richard G. West, Peter J. Wheatley, Marius Constantin Agafitei, Deniz Rüzgar Apaydın, Elisabeth Baeten, Bruce Baller, Jeff Carabott, Sallyann Chesson, Sebastián Alejandro Freigeiro, Virgilio Gonano, Matthias Hanke, Pete Hermes, Avery Hildebrand, John S. Langley, See Min Lim, Leo Ryan McCarthy, Graham Mitchell, Ken O’Neill, Charles R. Pearson, Nolan Reket, Jeanne Riethmiller, Juergen Saeftel, Arttu Sainio, Charlie Steiner, Amanda Strickland, Christopher Tanner, Ivan A. Terentev, Ernest Jude P. Tiu, Sergey Y. Tumanov, Marciniak Urszula, Pia Vahlenkamp, Femke de Vroome, Paweł Wantuch, Timothy Woodruff

^*Corresponding author for this work

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Abstract

We report the identification and characterization of a new binary system composed of two near-equal mass M-dwarfs. The binary NGTS-EB-8 was identified as a planet candidate in data from the Next Generation Transit Survey (NGTS) by citizen scientists participating in the Planet Hunters NGTS project. High-resolution spectroscopic observations reveal the system to be a double-lined binary. By modeling the photometric and radial velocity observations, we determine an orbital period of 4.2 days and the masses and radii of both stars to be M_A=0.250^+0.005_−0.004 M⊙, M_B=0.208^+0.005_−0.004 M⊙, and R_A=0.255^+0.004_−0.005 R⊙, R_B=0.233^+0.006_−0.005 R⊙, respectively. We detect Balmer line emission from at least one of the stars but no significant flare activity. We note that both components lie in the fully convective regime of low-mass stars (≲0.35 M⊙); therefore, they can be a valuable test for stellar evolutionary models. We demonstrate that the photometric observations, speckle imaging, and initial radial velocity measurements were unable to identify the true nature of this system and highlight that high-resolution spectroscopic observations are crucial in determining whether systems such as this are in fact binaries.

Original language	English
Article number	316
Number of pages	25
Journal	The Astronomical Journal
Volume	170
Issue number	6
Early online date	11 Nov 2025
DOIs	https://doi.org/10.3847/1538-3881/ae0e0d
Publication status	Published - 01 Dec 2025

Keywords

transit photometry
eclipsing binary stars
M dwarf stars

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NGTS-EB-8: a double-lined eclipsing M+M binary discovered by citizen scientists
Copyright 2025 the authors. This is an open access article published under a Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited.
Final published version, 4.21 MBLicence: CC BY

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O’Brien, S. M., Schwamb, M. E., Watson, C. A., Nielsen, L. D., Bryant, E. M., Casewell, S. L., Burleigh, M. R., Fortson, L., Gill, S., Lintott, C. J., Hobbs, K. L., Apergis, I., Bayliss, D., Fernández Fernández, J., Günther, M. N., Hawthorn, F., Jenkins, J. S., Kendall, A., McCormac, J., ... Woodruff, T. (2025). NGTS-EB-8: a double-lined eclipsing M+M binary discovered by citizen scientists. The Astronomical Journal, 170(6), Article 316. https://doi.org/10.3847/1538-3881/ae0e0d

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title = "NGTS-EB-8: a double-lined eclipsing M+M binary discovered by citizen scientists",

abstract = "We report the identification and characterization of a new binary system composed of two near-equal mass M-dwarfs. The binary NGTS-EB-8 was identified as a planet candidate in data from the Next Generation Transit Survey (NGTS) by citizen scientists participating in the Planet Hunters NGTS project. High-resolution spectroscopic observations reveal the system to be a double-lined binary. By modeling the photometric and radial velocity observations, we determine an orbital period of 4.2 days and the masses and radii of both stars to be MA=0.250+0.005−0.004 M⊙, MB=0.208+0.005−0.004 M⊙, and RA=0.255+0.004−0.005 R⊙, RB=0.233+0.006−0.005 R⊙, respectively. We detect Balmer line emission from at least one of the stars but no significant flare activity. We note that both components lie in the fully convective regime of low-mass stars (≲0.35 M⊙); therefore, they can be a valuable test for stellar evolutionary models. We demonstrate that the photometric observations, speckle imaging, and initial radial velocity measurements were unable to identify the true nature of this system and highlight that high-resolution spectroscopic observations are crucial in determining whether systems such as this are in fact binaries. ",

keywords = "transit photometry, eclipsing binary stars, M dwarf stars",

author = "O{\textquoteright}Brien, \{Sean M.\} and Schwamb, \{Megan E.\} and Watson, \{Christopher A.\} and Nielsen, \{Louise D.\} and Bryant, \{Edward M.\} and Casewell, \{Sarah L.\} and Burleigh, \{Matthew R.\} and Lucy Fortson and Samuel Gill and Lintott, \{Chris J.\} and Hobbs, \{Katlyn L.\} and Ioannis Apergis and Daniel Bayliss and \{Fern{\'a}ndez Fern{\'a}ndez\}, Jorge and G{\"u}nther, \{Maximilian N.\} and Faith Hawthorn and Jenkins, \{James S.\} and Alicia Kendall and James McCormac and \{de Mooij\}, \{Ernst J. W.\} and Toby Rodel and Suman Saha and Laura Trouille and West, \{Richard G.\} and Wheatley, \{Peter J.\} and Agafitei, \{Marius Constantin\} and Apaydın, \{Deniz R{\"u}zgar\} and Elisabeth Baeten and Bruce Baller and Jeff Carabott and Sallyann Chesson and Freigeiro, \{Sebasti{\'a}n Alejandro\} and Virgilio Gonano and Matthias Hanke and Pete Hermes and Avery Hildebrand and Langley, \{John S.\} and Lim, \{See Min\} and McCarthy, \{Leo Ryan\} and Graham Mitchell and Ken O{\textquoteright}Neill and Pearson, \{Charles R.\} and Nolan Reket and Jeanne Riethmiller and Juergen Saeftel and Arttu Sainio and Charlie Steiner and Amanda Strickland and Christopher Tanner and Terentev, \{Ivan A.\} and Tiu, \{Ernest Jude P.\} and Tumanov, \{Sergey Y.\} and Marciniak Urszula and Pia Vahlenkamp and \{de Vroome\}, Femke and Pawe{\l} Wantuch and Timothy Woodruff",

year = "2025",

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doi = "10.3847/1538-3881/ae0e0d",

language = "English",

volume = "170",

journal = "The Astronomical Journal",

issn = "0004-6256",

publisher = "The American Astronomical Society",

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O’Brien, SM , Schwamb, ME , Watson, CA, Nielsen, LD, Bryant, EM, Casewell, SL, Burleigh, MR, Fortson, L, Gill, S, Lintott, CJ, Hobbs, KL, Apergis, I, Bayliss, D, Fernández Fernández, J, Günther, MN, Hawthorn, F, Jenkins, JS, Kendall, A, McCormac, J, de Mooij, EJW, Rodel, T, Saha, S, Trouille, L, West, RG, Wheatley, PJ, Agafitei, MC, Apaydın, DR, Baeten, E, Baller, B, Carabott, J, Chesson, S, Freigeiro, SA, Gonano, V, Hanke, M, Hermes, P, Hildebrand, A, Langley, JS, Lim, SM, McCarthy, LR, Mitchell, G, O’Neill, K, Pearson, CR, Reket, N, Riethmiller, J, Saeftel, J, Sainio, A, Steiner, C, Strickland, A, Tanner, C, Terentev, IA, Tiu, EJP, Tumanov, SY, Urszula, M, Vahlenkamp, P, de Vroome, F, Wantuch, P & Woodruff, T 2025, 'NGTS-EB-8: a double-lined eclipsing M+M binary discovered by citizen scientists', The Astronomical Journal, vol. 170, no. 6, 316. https://doi.org/10.3847/1538-3881/ae0e0d

TY - JOUR

T1 - NGTS-EB-8: a double-lined eclipsing M+M binary discovered by citizen scientists

AU - O’Brien, Sean M.

AU - Schwamb, Megan E.

AU - Watson, Christopher A.

AU - Nielsen, Louise D.

AU - Bryant, Edward M.

AU - Casewell, Sarah L.

AU - Burleigh, Matthew R.

AU - Fortson, Lucy

AU - Gill, Samuel

AU - Lintott, Chris J.

AU - Hobbs, Katlyn L.

AU - Apergis, Ioannis

AU - Bayliss, Daniel

AU - Fernández Fernández, Jorge

AU - Günther, Maximilian N.

AU - Hawthorn, Faith

AU - Jenkins, James S.

AU - Kendall, Alicia

AU - McCormac, James

AU - de Mooij, Ernst J. W.

AU - Rodel, Toby

AU - Saha, Suman

AU - Trouille, Laura

AU - West, Richard G.

AU - Wheatley, Peter J.

AU - Agafitei, Marius Constantin

AU - Apaydın, Deniz Rüzgar

AU - Baeten, Elisabeth

AU - Baller, Bruce

AU - Carabott, Jeff

AU - Chesson, Sallyann

AU - Freigeiro, Sebastián Alejandro

AU - Gonano, Virgilio

AU - Hanke, Matthias

AU - Hermes, Pete

AU - Hildebrand, Avery

AU - Langley, John S.

AU - Lim, See Min

AU - McCarthy, Leo Ryan

AU - Mitchell, Graham

AU - O’Neill, Ken

AU - Pearson, Charles R.

AU - Reket, Nolan

AU - Riethmiller, Jeanne

AU - Saeftel, Juergen

AU - Sainio, Arttu

AU - Steiner, Charlie

AU - Strickland, Amanda

AU - Tanner, Christopher

AU - Terentev, Ivan A.

AU - Tiu, Ernest Jude P.

AU - Tumanov, Sergey Y.

AU - Urszula, Marciniak

AU - Vahlenkamp, Pia

AU - de Vroome, Femke

AU - Wantuch, Paweł

AU - Woodruff, Timothy

PY - 2025/12/1

Y1 - 2025/12/1

N2 - We report the identification and characterization of a new binary system composed of two near-equal mass M-dwarfs. The binary NGTS-EB-8 was identified as a planet candidate in data from the Next Generation Transit Survey (NGTS) by citizen scientists participating in the Planet Hunters NGTS project. High-resolution spectroscopic observations reveal the system to be a double-lined binary. By modeling the photometric and radial velocity observations, we determine an orbital period of 4.2 days and the masses and radii of both stars to be MA=0.250+0.005−0.004 M⊙, MB=0.208+0.005−0.004 M⊙, and RA=0.255+0.004−0.005 R⊙, RB=0.233+0.006−0.005 R⊙, respectively. We detect Balmer line emission from at least one of the stars but no significant flare activity. We note that both components lie in the fully convective regime of low-mass stars (≲0.35 M⊙); therefore, they can be a valuable test for stellar evolutionary models. We demonstrate that the photometric observations, speckle imaging, and initial radial velocity measurements were unable to identify the true nature of this system and highlight that high-resolution spectroscopic observations are crucial in determining whether systems such as this are in fact binaries.

AB - We report the identification and characterization of a new binary system composed of two near-equal mass M-dwarfs. The binary NGTS-EB-8 was identified as a planet candidate in data from the Next Generation Transit Survey (NGTS) by citizen scientists participating in the Planet Hunters NGTS project. High-resolution spectroscopic observations reveal the system to be a double-lined binary. By modeling the photometric and radial velocity observations, we determine an orbital period of 4.2 days and the masses and radii of both stars to be MA=0.250+0.005−0.004 M⊙, MB=0.208+0.005−0.004 M⊙, and RA=0.255+0.004−0.005 R⊙, RB=0.233+0.006−0.005 R⊙, respectively. We detect Balmer line emission from at least one of the stars but no significant flare activity. We note that both components lie in the fully convective regime of low-mass stars (≲0.35 M⊙); therefore, they can be a valuable test for stellar evolutionary models. We demonstrate that the photometric observations, speckle imaging, and initial radial velocity measurements were unable to identify the true nature of this system and highlight that high-resolution spectroscopic observations are crucial in determining whether systems such as this are in fact binaries.

KW - transit photometry

KW - eclipsing binary stars

KW - M dwarf stars

U2 - 10.3847/1538-3881/ae0e0d

DO - 10.3847/1538-3881/ae0e0d

M3 - Article

SN - 0004-6256

VL - 170

JO - The Astronomical Journal

JF - The Astronomical Journal

IS - 6

M1 - 316

ER -

NGTS-EB-8: a double-lined eclipsing M+M binary discovered by citizen scientists

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