Messier 35 or M35, also known as NGC 2168 or the Shoe-Buckle Cluster, is a relatively close open cluster of stars in the west of Gemini, at about the declination of the Sun when the latter is at June solstice.[a] It was discovered by Philippe Loys de Chéseaux around 1745 and independently discovered by John Bevis before 1750.[3] It is scattered over part of the sky almost the size of the full moon and is 2,970 light-years (912 parsecs) away.[1] The compact open cluster NGC 2158 lies directly southwest of it.
Leonard & Merritt (1989) computed the mass of M35 using a statistical technique based on proper motion velocities of its stars. The mass within the central 3.75 parsecs (12.2 ly) was found to be between 1600 and 3200 solar masses,[b] consistent with the mass of a realistic stellar population within the same radius.[8] Bouy et al. in 2015 found a mass of around 1,600 M☉ within the central 27.5' × 27.5′. There are 305 stars that can be intrinsically shown to be extremely likely to be members,[c] and up to 4,349 averaging the 50% membership probability, from the kinematic (such as parallax and proper motion) and spectral data published before 2015.[4] The cluster's metallicity is [Fe/H] = −0.21±0.10, where −1 would be ten times less metallic than the sun.[4]
Of 418 probable members, Leiner et al. in 2015 found 64 that have variable radial velocities thus are binary star systems.[9] Four probable members are chemically peculiars, while HD 41995, which in the (telescopic angular) cluster field, shows emission lines.[10] Hu et al. in 2005 found 13 variable stars in the field; at least three are suspect as cluster members. To be a member means to have a gravitational tie or, if recently freed, having been created by the same event.[11]
^Leiner, E. M.; Mathieu, R. D.; Gosnell, N. M.; Geller, A. M. (July 2015). "WIYN Open Cluster Study. LXVI. Spectroscopic Binary Orbits in the Young Open Cluster M35 (NGC 2168)". The Astronomical Journal. 150 (1): 18. Bibcode:2015AJ....150...10L. doi:10.1088/0004-6256/150/1/10. S2CID123818978. 10.
^Hu, Juei-Hwa; et al. (August 2005). "Discovery of 13 New Variable Stars in the Field of the Open Cluster NGC 2168 (M35)". Chinese Journal of Astronomy and Astrophysics. 5 (4): 356–362. Bibcode:2005ChJAA...5..356H. doi:10.1088/1009-9271/5/4/003.
