On a new theoretical calibration of the Stroemgren hk metallicity index: NGC6522 as a first test case

Дата и время публикации : 2011-10-19T15:45:17Z

Авторы публикации и институты :
A. Calamida
G. Bono
C. Corsi
G. Iannicola
V. Ripepi
B. Anthony-Twarog
B. Twarog
M. Zoccali
R. Buonanno
S. Cassisi
I. Ferraro
F. Grundahl
A. Pietrinferni
L. Pulone

Ссылка на журнал-издание: Ссылка на журнал-издание не найдена
Коментарии к cтатье: Accepted for publication on The Astrophysical Journal Letters
Первичная категория: astro-ph.SR

Все категории : astro-ph.SR

Краткий обзор статьи: We present a new theoretical calibration of the Stroemgren metallicity index hk by using alpha-enhanced evolutionary models transformed into the observational plane by using atmosphere models with the same chemical mixture. We apply the new Metallicity–Index–Color (MIC) relations to a sample of 85 field red giants (RGs) and find that the difference between photometric estimates and spectroscopic measurements is on average smaller than 0.1 dex with a dispersion of sigma = 0.19 dex. The outcome is the same if we apply the MIC relations to a sample of eight RGs in the bulge globular cluster NGC6522, but the standard deviation ranges from 0.26 (hk, v-y) to 0.49 (hk, u-y). The difference is mainly caused by a difference in photometric accuracy. The new MIC relations based on the (Ca-y) color provide metallicities systematically more metal-rich than the spectroscopic ones. We found that the Ca-band is affected by Ca abundance and possibly by chromospheric activity.

Category: Physics