An Optical and Infrared Photometric Study of the Young Open Cluster IC 1805 in the Giant H ii Region W4* ^†

Abstract

We present deep wide-field optical CCD photometry and mid-infrared Spitzer/IRAC and MIPS 24µm data for about 100,000 stars in the young open cluster IC 1805. The members of IC 1805 were selected from their location in the various color-color and color-magnitude diagrams, and the presence of Hα emission, mid-infrared excess emission, and X-ray emission. The reddening law toward IC 1805 is nearly normal (R V = 3.05 ± 0.06). However, the distance modulus of the cluster is estimated to be 11.9 ± 0.2 mag (d = 2.4 ± 0.2 kpc) from the reddening-free color-magnitude diagrams, which is larger than the distance to the nearby massive star-forming region W3(OH) measured from the radio VLBA astrometry. We also determined the age of IC 1805 (τ M ST O = 3.5 Myr). In addition, we critically compared the age and mass scale from two pre-main-sequence evolution models. The initial mass function with a Salpeter-type slope of Γ = -1.3 ± 0.2 was obtained and the total mass of IC 1805 was estimated to be about 2700 ± 200 M . Finally, we found our distance determination to be statistically consistent with the Tycho-Gaia Astrometric Solution Data Release 1, within the errors. The proper motion of the B-type stars shows an elongated distribution along the Galactic plane, which could be explained by some of the B-type stars being formed in small clouds dispersed by previous episodes of star formation or supernova explosions.

The Villafranca catalog of Galactic OB groups

“…The previous distance measurements to IC 1805 span a large range of values from 1.45 kpc (Zucker et al 2020) to 3.79 kpc (Foster & MacWilliams 2006), to mention only results in the last two decades. Our value of 2075 +44 −42 pc is in between those two and also between the distances of two analyses from isochrone fitting of optical photometry from the last decade: 1.7 kpc of Kharchenko et al (2012) and 2.4 kpc of Sung et al (2017). It is also within two sigmas of the two precise maser distances to the nearby IC 1795 (Megeath et al 2008).…”

Gaia-DR2 distance to the W3 Complex in the Perseus Arm

“…In a large-scale context, the distance to W3 is also consistent with the distances to the massive clusters located in W4 (IC 1805) and W5 (IC 1848), at distances of 2.3-2.4 (Sung et al 2017) and 1.9-2.2 kpc (Chauhan et al 2011), respectively. These three complexes cover a considerable portion of the Perseus arm of about 3 degrees (from 134 • to 137 • ) in the Galactic anti-centre direction, allowing us to set a firm location of the Perseus spiral arm with high confidence.…”

“…Previous non-kinematic distances to these stellar clusters, especially IC 1805 (in W4), indicate values in the range of 2.3-2.4 kpc (Kwon & Lee 1983;Massey et al 1995;Sung et al 2017), while the distance to IC 1848 (W5) ranges from 1.9 to 2.2 kpc (Becker & Fenkart 1971;Georgelin & Georgelin 1976;Chauhan et al 2011). Also, the kinematic distance to W5, d ∼ 3 kpc, is about 1.5 times larger than its stellar distances (Ginsburg et al 2011).…”

The Sejong Open Cluster Survey (SOS). VII. A Photometric Study of the Young Open Cluster IC 1590

“…In the case of intracluster media, R V,cl can be high because some SFR are so young that large dust grains may still remain without having been destroyed by UV photons from massive stars. Abnormal high extinction laws have been reported in some young open clusters (e.g., Hur et al 2012;Lim et al 2015a;Fang et al 2021), while others have not (e.g., Sung et al 2017). The interstellar extinction due to the dust associated with IC 1590 was claimed to be larger from R V (Guetter & Turner 1997;Sharma et al 2012).…”