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The Astronomical Journal
Article . 1999 . Peer-reviewed
Data sources: Crossref
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https://dx.doi.org/10.48550/ar...
Article . 1999
License: arXiv Non-Exclusive Distribution
Data sources: Datacite
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Zeroing the Stellar Isochrone Scale: The Red Giant Clump Luminosity at Intermediate Metallicity

Authors: Twarog, B. A.; Anthony-Twarog, B. J.; Bricker, A. R.;

Zeroing the Stellar Isochrone Scale: The Red Giant Clump Luminosity at Intermediate Metallicity

Abstract

The color-magnitude diagrams of the open clusters NGC 2420 and NGC 2506 have been investigated as intermediate links between the solar neighborhood and the Magellanic Clouds. Two sets of theoretical isochrones which include convective overshoot are zeroed to the sun at solar abundance and to the unevolved main sequence dwarfs of the Hipparcos catalog at [Fe/H] = -0.4, requiring a differential of 0.4 mag between the unevolved main sequences at a given color. Adopting E(B-V) = 0.04 and [Fe/H] = -0.39 for NGC 2506 and 0.04 and -0.29 for NGC 2420,the respective apparent moduli are 12.70 and 12.15, while the ages of both clusters are approximately 1.9 +/- 0.2 or 2.2 +/- 0.2 Gyr, depending on the choice of isochrones. From the composite giant branch of the two clusters, the mean clump magnitudes in V and I are found to be 0.47 and -0.48 (-0.17,+0.14). Applying a metallicity correction to the M_I values, the cluster sample of Udalski (1998) leads to (m-M)_0 = 18.42 (+0.17,--0.15) and 18.91 (+0.18,--0.16) for the LMC and SMC, respectively. A caveat to this discussion and to the claim that clusters of the same abundance and age are identical is the observation that the (V-I) colors of the red giants in NGC 2506 are significantly redder at a given (B-V) than the giants in clusters of comparable age and/or metallicity. If the CCD photometry for NGC 2506 is tied to the standard system rather than using a general cluster relation between (B-V) and (V-I), the M_I for the clump will decrease by 0.1 mag.

1 table, 12 figures. Replaced 20-jan-99 by version with all figures. Accepted for April 1999 Astronomical Journal

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Keywords

Astrophysics (astro-ph), FOS: Physical sciences, Astrophysics

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selected citations
These citations are derived from selected sources.
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
42
Average
Top 10%
Top 10%
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