Messier 35 (NGC 2168) DANCe

I. Membership, proper motions, and multiwavelength photometry^⋆

¹ Centro de Astrobiología, depto de Astrofísica, INTA-CSIC, PO Box 78, ESAC Campus, Villanueva de la Cañada, 28691 Madrid, Spain
e-mail: hbouy@cab.inta-csic.es
² Institut d’Astrophysique de Paris, CNRS UMR 7095 and UPMC, 98bis Bd Arago, 75014 Paris, France
³ Dpt. de Inteligencia Artificial, UNED, Juan del Rosal 16, 28040 Madrid, Spain
⁴ University Grenoble Alpes, IPAG, 38000 Grenoble, France
⁵ CNRS, IPAG, 38000 Grenoble, France
⁶ Canada-France-Hawaii Telescope Corporation, 65-1238 Mamalahoa Highway, Kamuela, HI96743, USA
⁷ European Space Astronomy Centre (ESA), PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
⁸ ISDEFE – ESAC, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
⁹ Las Campanas Observatory, Carnegie Institution of Washington, Colina el Pino, 601 Casilla, La Serena, Chile

Received: 12 December 2014
Accepted: 18 January 2015

Abstract

Context. Messier 35 (NGC 2168) is an important young nearby cluster. Its age, richness and relative proximity make it an ideal target for stellar evolution studies. The Kepler K2 mission recently observed it and provided a high accuracy photometric time series of a large number of sources in this area of the sky. Identifying the cluster’s members is therefore of high importance to optimize the interpretation and analysis of the Kepler K2 data.

Aims. We aim to identify the cluster’s members by deriving membership probabilities for the sources within 1°  of the cluster’s center, which is farther away than equivalent previous studies.

Methods. We measure accurate proper motions and multiwavelength (optical and near-infrared) photometry using ground-based archival images of the cluster. We use these measurements to compute membership probabilities. The list of candidate members from the literature is used as a training set to identify the cluster’s locus in a multidimensional space made of proper motions, luminosities, and colors.

Results. The final catalog includes 338 892 sources with multiwavelength photometry. Approximately half (194 452) were detected at more than two epochs and we measured their proper motion and used it to derive membership probability. A total of 4349 candidate members with membership probabilities greater than 50% are found in this sample in the luminosity range between 10 mag and 22 mag. The slow proper motion of the cluster and the overlap of its sequence with the field and background sequences in almost all color–magnitude and color–color diagrams complicate the analysis and the contamination level is expected to be significant. Our study, nevertheless, provides a coherent and quantitative membership analysis of Messier 35 based on a large fraction of the best ground-based data sets obtained over the past 18 years. As such, it represents a valuable input for follow-up studies using, in particular, the Kepler K2 photometric time series.