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Interstellar Reddening Effect on the Age Dating of Population II Stars

Dipartimento di Fisica e Astronomia, Universitá di Padova, 35122 Padova, Italy
INAF—Osservatorio Astronomico di Padova, 35122 Padova, Italy
INAF—Osservatorio Astronomico di Teramo, via M. Maggini, sn, 64100 Teramo, Italy
Astrophysics Research Institute, Liverpool John Moores University, Liverpool L3 5RF, UK
Author to whom correspondence should be addressed.
Academic Editors: Duncan A. Forbes and Ericson D. López
Galaxies 2017, 5(3), 28;
Received: 27 April 2017 / Revised: 15 June 2017 / Accepted: 18 June 2017 / Published: 22 June 2017
(This article belongs to the Special Issue On the Origin (and Evolution) of Baryonic Galaxy Halos)
PDF [731 KB, uploaded 22 June 2017]


The age measurement of the stellar halo component of the Galaxy is based mainly on the comparison of the main sequence turn-off luminosity of the globular cluster (GC) stars with theoretical isochrones. The standard procedure includes a vertical shift, in order to account for the distance and extinction to the cluster, and a horizontal one, to compensate the reddening. However, the photometry is typically performed with broad-band filters where the shape of the stellar spectra introduces a shift of the effective wavelength response of the system, dependent on the effective temperature (or color index) of the star. The result is an increasing distortion—actually a rotation and a progressive compression with the temperature—of the color-magnitude diagrams relatively to the standard unreddened isochrones, with increasing reddening. This effect is usually negligible for reddening E ( B - V ) on the order of or smaller than 0.15, but it can be quite relevant at larger extinction values. While the ratio of the absorption to the reddening is widely discussed in the literature, the importance of the latter effect is often overlooked. In this contribution, we present isochron simulations and discuss the expected effects on age dating of high-reddening globular clusters. View Full-Text
Keywords: interstellar matter; stellar evolution; galactic halo interstellar matter; stellar evolution; galactic halo

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Ortolani, S.; Cassisi, S.; Salaris, M. Interstellar Reddening Effect on the Age Dating of Population II Stars. Galaxies 2017, 5, 28.

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