Messier 35 orM35, also known asNGC 2168 or theShoe-Buckle Cluster, is a relatively closeopen cluster ofstars in the west ofGemini, at about the declination of the Sun when the latter is atJune solstice.[a] It was discovered byPhilippe Loys de Chéseaux around 1745 and independently discovered byJohn Bevis before 1750.[3] It is scattered over part of the sky almost the size of thefull moon and is 2,970light-years (912parsecs) away.[1] The compact open clusterNGC 2158 lies directly southwest of it.
Leonard & Merritt (1989) computed the mass of M35 using astatistical technique based onproper 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] Bouyet al. in 2015 found a mass of around1,600 M☉ within the central27.5' × 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 asparallax andproper motion) and spectral data published before 2015.[4] The cluster'smetallicity is [Fe/H] =−0.21±0.10, where −1 would be ten times less metallic than the sun.[4]
Of 418 probable members, Leineret al. in 2015 found 64 that have variableradial velocities thus arebinary star systems.[9] Four probable members arechemically peculiars, whileHD 41995, which in the (telescopic angular) cluster field, showsemission lines.[10] Huet al. in 2005 found 13variable 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.
