2013A&A...554A...3S

The results of CCD photometry in the Vilnius seven-color system down to V=18mag are presented for 242 stars in the direction of the young open cluster IC1805 that is located in the active star-forming region W4 in the Cas OB6 association. Photometric data were used to classify stars into spectral and luminosity classes, and to determine their interstellar reddenings, extinctions and distances. We confirm the CH₃OH and H₂O maser VLBA parallax results that the cluster is located close to the front side of the Perseus arm, at a distance about 2.0 kpc. In the color-magnitude diagram, zero-age main sequence (ZAMS) stars of the cluster extend to spectral class A0. The extinction values for the majority of the cluster stars are between 2.2 and 2.7mag, with a mean value of 2.46mag. This extinction originates mainly between the Sun and the outer edge of the Local arm, in accordance with the distribution of CO clouds. In the Perseus arm and beyond, the extinction was investigated using the classification and reddening determination for A0-F0 stars measured in the r, i, Hα system of the IPHAS survey to r=19mag. The extinction A_V within the Perseus arm ranges from 2.5-4.5mag at the front edge to 3.0-5.0mag at the far edge. Possibly, we have found about 20 early A-type stars located in the Outer arm. The 2MASS JHK_s photometry for red giants gives much higher extinction values (up to about 6mag), which would correspond to the stars located behind dense clouds of both arms. In the area, using the WISE, 2MASS, and IPHAS photometry data, 18 possible young stellar objects (YSOs) of low masses are identified. Six high-mass YSOs (five Ae/Be stars and a F6e star) are known from previous investigations.