The usefulness of 2MASS JHK_s photometry for open cluster studies

D. G. Turner

Department of Astronomy and Physics, Saint Mary's University, Halifax, Nova Scotia, B3H 3C3, Canada (turner@ap.smu.ca).

Received 2010 September 23
Accepted 2011 February 1

RESUMEN

Se utilizan datos en JHK_s para inferir el enrojecimiento y la distancia a cúmulos abiertos para los cuales son limitados los datos disponibles en el óptico. Se obtienen relaciones color–color y color–magnitud intrínsecos de la ZAMS con referencia a calibraciones existentes, estrellas estándar, tres cúmulos enrojecidos uniformemente: Stock 16, NGC 2362, y NGC 2281, y las enanas no–enrojecidas de las Hiadas. El método para inferir el enrojecimiento interestelar y la distancia a cúmulos abiertos escasamente poblados se aplica a Berkeley 44, Turner 1, y Collinder 419, cuyos resultados existentes están en conflicto con los inferidos a partir de los datos en JHK_s. Los últimos dos cúmulos son de especial interés: Turner 1 porque alberga a la Cefeida clásica con el período más largo de la Galaxia, y Collinder 419 porque yace en el complejo Cygnus X.

ABSTRACT

2MASS JHK_s data are used to infer the reddening and distance of open clusters for which limited optical data are available. Intrinsic ZAMS color–color and color–magnitude relations are derived with reference to existing calibrations, standard stars, three uniformly–reddened clusters: Stock 16, NGC 2362, and NGC 2281, and unreddened Hyades dwarfs. The method of inferring interstellar reddening and distance for sparsely–populated open clusters is applied to Berkeley 44, Turner 1, and Collinder 419, for which existing results conflict with those inferred from JHK_s data. The last two clusters are of special interest: Turner 1 because it hosts the Galaxy's longest–period classical Cepheid, and Collinder 419 because it lies in the Cygnus X complex.

Key Words: dust, extinction — Galaxy: open clusters and associations: general — Hertzsprung–Russell and C–M diagrams — methods: data analysis.

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