Photometry of seven overlooked open clusters in the first and fourth Galactic quadrants

Abstract

CCD BVI photometry is presented for seven previously unstudied star clusters projected towards the inner side of the Galaxy: Trumpler 23, Lynga 3, Collinder 307, Ruprecht 134, ESO552SC16, AL 5 and Kronberger 3. Colour-magnitude diagrams of the cluster regions allow us to conclude that Lynga 3 and ESO552SC16 are not clusters, but groups of bright stars probably located in the Carina-Sagittarius spiral arm. AL 5 and Kronberger 3 are so embedded in a dense stellar field that we cannot confirm their nature. Trumpler 23 and Ruprecht 134 are two intermediate-age open clusters located well inside the solar ring which deserve further attention. Finally, Collinder 307 is an obscured younger cluster (250 Myr) located in the Carina-Sagittarius spiral arm. Our results emphasize the difficulty to search for open clusters in the inner regions of the Galaxy due to the richness of the field and the patchy nature of the interstellar absorption, but at the same time significantly contribute to a better understanding of this complicated regions of the Milky Way.