2003/10/31 by Barbara J. Anthony-Twarog, B. J. Anthony-Twarog, Bruce A. Twarog +1 · 2 citations
Physics and Astronomy · #Astrophysics and Star Formation Studies #Gamma-ray bursts and supernovae #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/381064
21 pages latex, 8 figures, 3 tables. Accepted by AJ for June 2004. Large files (fig.1.eps and table.2) may be downloaded at http://kubarb.phsx.ukans.edu/~anthony/ngc3680.html
arxiv created 2003/10/31 · openalex publication_date 2004/02/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/30
CCD photometry on the intermediate-band uvbyCa Hβ system is presented for the open cluster, NGC 3680. Restricting the data to probable cluster members using the color-magnitude diagram (CMD) and the photometric indices alone defines a sample of 34 stars at the cluster turnoff that imply E ( b - y ) = 0.042 ± 0.002 (s.e.m.) or E ( B - V ) = 0.058 ± 0.003 (s.e.m.), where the errors refer to internal errors alone. With this reddening, [Fe/H] is derived from both m 1 and hk using both b - y and Hβ as the temperature indices. The agreement among the four approaches is excellent, leading to final value of [Fe/H] = -0.14 ± 0.03 for the cluster and removing the apparent discrepancy between the past uvby analyses and extensive results from the red giants. The primary source of the photometric anomaly appears to be a zero-point offset in the original m 1 indices. Using the homogenized and combined V , b - y data from a variety of studies transformed to B - V , the cluster CMD is compared with NGC 752, IC 4651, and the core–convective-overshoot isochrones of Girardi et al. By interpolation to the proper metallicity, it is found that the E ( B - V ), m - M , and age for NGC 752, IC 4651, and NGC 3680 are (0.03, 8.30, 1.55 Gyr), (0.10, 10.20, 1.7 Gyr), and (0.06, 10.20, 1.85 Gyr), respectively. The revised age and metallicity sequence and the color distribution of the giants provide evidence for the suggestion that the giants defining the apparent clump in NGC 3680 are predominantly first-ascent giants, as indicated by their Li abundance, while the clump stars in NGC 752, 0.1 mag bluer in B - V , are He-core–burning stars. When combined with the color distribution in IC 4651, it is suggested that over this modest age range where He-core flash becomes important, the distribution of so-called clump stars switches from being dominated by He-core–burning stars to first-ascent giants in the bump phase.