# An Optical and Infrared Photometric Study of the Young Open Cluster IC 1805 in the Giant H II Region W4

## TL;DR

This study provides a comprehensive optical and infrared analysis of the young open cluster IC 1805, determining its distance, age, initial mass function, and kinematic properties using multi-wavelength data and comparing models.

## Contribution

It offers the first detailed photometric and kinematic characterization of IC 1805, including distance, age, mass function, and proper motion analysis, with comparison to stellar evolution models.

## Key findings

- Distance to IC 1805 is about 2.4 kpc.
- Age of the cluster is approximately 3.5 million years.
- Initial mass function slope is Gamma = -1.3.

## Abstract

We present deep wide-field optical CCD photometry and mid-infrared Spitzer/IRAC and MIPS 24micron 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 Halpha 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 (tau_MSTO = 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 Gamma = -1.3+/-0.2 was obtained and the total mass of IC 1805 was estimated to be about 2700+/-200 M_sun. 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.