THE INTERMEDIATE AGE OPEN CLUSTER NGC-7044

Citation
A. Aparicio et al., THE INTERMEDIATE AGE OPEN CLUSTER NGC-7044, The Astronomical journal, 106(4), 1993, pp. 1547-1560
Citations number
40
Categorie Soggetti
Astronomy & Astrophysics
Journal title
ISSN journal
00046256
Volume
106
Issue
4
Year of publication
1993
Pages
1547 - 1560
Database
ISI
SICI code
0004-6256(1993)106:4<1547:TIAOCN>2.0.ZU;2-Q
Abstract
We present the photometric analysis for the open cluster NGC 7044, bas ed on Johnson-Cousins UBVR CCD observations of 896 stars in a region o f 4'20''x2'40'' in the cluster field. Reddening and metallicity are es timated by means of the location of selected samples of members in the (U-B) vs (B- V) diagram, with respect to the lines of the Hyades ZAMS and giants. This selection is performed by considering the location o f the representative points in both the V vs (B-V) and V vs (U-B) diag rams simultaneously. The final estimates are found to be very dependen t on whether, and to what extent, reddening slopes and absorption coef ficients are considered to vary with spectral type. Global considerati ons, based on the photometric information together with the results of the comparison with theoretical model isochrones, lead to the followi ng set of values: E(B-V)=0.57, [Fe/H]=0.0, (m-M)0=12.4, and log age(y) =9.4. We discuss to some extent the influence that varying absorption coefficients, published in the literature, would have on these estimat es. Our color-magnitude (CM) diagram is compared with selected sets of isochrones, based on evolutionary models computed with and without co nsidering convective overshooting from the stellar core during the pha ses of H and He core burning. Better general agreement is found when u sing the overshooting models, between predicted and observed features of the CM diagram, particularly in what concerns the properties of the so-called Red Giant Clump (RGC). With the adopted solution, NGC 7044 turns out to be one of the oldest intermediate-age clusters, very clos e to, or even beyond the limiting age separating the regimes of He fla sh and quiet onset of He burning in the red giant phase. The location of the RGC in absolute magnitude, together with the resulting (B-V)0 a t the turnoff, leads us to suggest that the efficiency of convective c ore overshooting in stars of masses around and below 1.5 M. should be slightly higher than that of the models used. An analysis of the spati al distribution of the stars suggest that a mass segregation mechanism is acting in the cluster, in the sense that the most massive members are concentrated in the center. Luminosity and mass functions have bee n computed; a classical power law fitted to the latter results in a sl ope of x=-1. 66 +/- 0.06.