NUGENT, Richard L. The Nature of the Double Star M40. Journal of the Royal Astronomical Society of Canada. 2002, roč. 96, s. 63–65. Dostupné online [cit. 2026-07-29]. Bibcode2002JRASC..96...63N. (anglicky)
MERRIFIELD, Michael R.; GRAY, Meghan E.; HARAN, Brady. Gaia Shows That Messier 40 is Definitely Not a Binary Star. The Observatory. 2017, roč. 137, s. 23–24. Dostupné online [cit. 2026-07-29]. Bibcode2017Obs...137...23M. arXiv1612.00834. (anglicky)
MERRIFIELD, Michael R.; GRAY, Meghan E.; HARAN, Brady. Gaia Shows That Messier 40 is Definitely Not a Binary Star. The Observatory. 2017, roč. 137, s. 23–24. Dostupné online [cit. 2026-07-29]. Bibcode2017Obs...137...23M. arXiv1612.00834. (anglicky)
NUGENT, Richard. A New Analysis of the Double Star M40. Journal of Double Star Observations. 2023-01-01, roč. 19, čís. 1, s. 9–16. Dostupné online [cit. 2026-07-29]. (anglicky)
NUGENT, Richard L. The Nature of the Double Star M40. Journal of the Royal Astronomical Society of Canada. 2002, roč. 96, s. 63–65. Dostupné online [cit. 2026-07-29]. Bibcode2002JRASC..96...63N. (anglicky)