IC 1590, a young cluster embedded in the nebulosity of NGC 281

Abstract

Photoelectric and CCD photometry (to a limit of V=17.0) is presented for 61 and 243 stars, respectively--a total of 279 individual stars--in and about IC 1590, a young galactic cluster embedded in the nebulosity of NGC 281, the H II region S184. New spectroscopic observations are also presented for 20 stars in or near the cluster. A small amount of differential reddening is observed across the face of IC 1590, and is described by a visual reddening relation of slope E[subscript U-B]/E[subscript B-V]=0.735. From near infrared photometry of bright cluster members in the I and K bands and a variable-extinction analysis of ZAMS members, the value of R = A[subscript V]/E[subscript B-V], the ratio of total to selective absorption, is found to be 3.44[plus or minus]0.07, slightly larger than what has been found for other nearby galactic fields. Most of the cluster reddening appears to originate in dust clouds which are ~0.66 kpc and 2.0-2.2 kpc distant, the latter cloud lying in the immediate foreground of the cluster, which has a derived distance of 2.94[plus or minus]0.15 kpc (V[subscript 0]-M[subscript V] = 12.34[plus or minus]0.11 s.d., [plus or minus]0.03 s.e.). IC 1590 is extremely young and has an estimated age for its 63 identified probable members of 3.5([plus or minus]0.2) × 10[superscript 6] years, with very little evidence for age spread. Its well-defined sequence of 22 gravitationally-contracting stars, the choice of which is supported by star counts and reddening information, provides evidence for the extreme youth of the cluster's central trapezium system, HD 5005. According to the luminosity distribution of likely cluster members, the initial mass function for IC 1590 has a slope of [Gamma] = -1.00[plus or minus]0.21, similar to what has been found for other very young clusters and associations. Given that the photometric study terminates at a magnitude limit marginally brighter than where embedded protostars and T Tauri variables belonging to the cluster are expected to be found, IC 1590 would make an excellent target for Hubble Space Telescope observations.