Photometric study of open star clusters in II quadrant: Teutsch 1 and Riddle 4

• The physical parameters of the clusters under study are derived.
• The CCD photometric data for Teutsch 1 and Riddle 4 have been collected for the first time.
• Mass function and mass segregation have been studied for Teutsch 1 and Riddle 4.
• These star clusters alongwith other star clusters in longitude range 130–18° have been used to study the Galactic structure in the above longitude range.

We present the broad band UBVI   CCD photometry in the region of two open star clusters Teutsch 1 and Riddle 4 located in the second Galactic quadrant. The optical CCD data for these clusters are obtained for the first time. Radii of the clusters are estimated as 3′.5 for both the clusters. Using two color (U−B)(U−B) versus (B−V)(B−V) diagram we determined the reddening as E(B−V)=0.40± 0.05 mag for Teutsch 1 and 1.10 ± 0.05 mag for Riddle 4. Using 2MASS JHK   and optical data, we estimated E(J−K)=0.24± 0.05 mag and E(V−K)=1.40± 0.05 mag for Teutsch 1 and E(J−K)=0.47± 0.06 mag and E(V−K)=2.80± 0.06 mag for Riddle 4. Color-excess ratio indicates normal interstellar extinction law in the direction of both the clusters. We estimated distance as 4.3 ± 0.5 Kpc for Teutsch 1 and 2.8 ± 0.2 Kpc for Riddle 4 by comparing the color-magnitude diagram of the clusters with theoretical isochrones. The age of the clusters has been estimated as 200 ± 20 Myr for Teutsch 1 and 40 ± 10 Myr for Riddle 4 using the stellar isochrones of metallicity Z=0.02Z=0.02. The Mass function slope has been derived 1.89 ± 0.43 and 1.41 ± 0.70 for Teutsch 1 and Riddle 4 respectively. Our analysis indicates that both the clusters are dynamically relaxed. A slight bend of Galactic disc towards the southern latitude is found in the longitude range l=l= 130–180°.