WIYN Open Cluster Study. LXXII. A uvbyCa Hbeta CCD Analysis of the Metal-Deficient Open Cluster, NGC 2506

TL;DR

This study provides detailed uvbyCa Hbeta photometry of the old, metal-deficient open cluster NGC 2506, deriving its fundamental parameters and identifying variable stars and probable cluster members.

Contribution

It offers the first comprehensive uvbyCa Hbeta photometric analysis of NGC 2506, including precise measurements of metallicity, reddening, and age, along with variable star identification.

Findings

Metallicity [Fe/H] ≈ -0.316 derived from multiple indices.

Reddening E(B-V) ≈ 0.058 with minimal variation across the cluster.

Age estimated at approximately 1.85 Gyr.

Abstract

Precision uvbyCa Hbeta photometry of the metal-deficient, old open cluster, NGC 2506, is presented. The survey covers an area 20 by 20 arcminutes, and extends to V~18 for b-y and Hbeta and to V~17.0 for c_1 and hk. For V < 16.0, photometric scatter among the indices leads to the recovery of 6 known variables within the cluster core and 5 new variables in the outer 5 arcmin of the survey field. Proper motions, radial velocities, and precise multicolor indices are used to isolate a highly probable sample of cluster members from the very rich color-magnitude diagram (CMD). From 257 highly probable members at the cluster turnoff, we derive a reddening estimate of E(b-y) = 0.042 +/- 0.001 (E(B-V) = 0.058 +/- 0.001), where the errors refer to the internal standard errors of the mean. [Fe/H] is derived from the A/F dwarf members using both m_1 and hk, leading to [Fe/H] = -0.296 +/- 0.011 (sem) and -0.317 +/- 0.004 (sem), respectively. The weighted average, heavily dominated by hk, is [Fe/H] = -0.316 +/- 0.033. Based upon red giant members, we place an upper limit of +/- 0.010 on the variation in the reddening across the face of the cluster. We also identify two dozen potential red giant cluster members outside the cluster core. Victoria-Regina isochrones on the Stromgren system produce an excellent match to the cluster for an apparent modulus of (m-M) = 12.75 +/- 0.1 and an age of 1.85 +/- 0.05 Gyr.