Color–magnitude diagram constraints on the metallicities, ages, and star formation history of the stellar populations in the Carina dwarf spheroidal galaxy
- Department of Physics and Astronomy, University of Victoria, P.O. Box 1700, STN CSC, Victoria, BC, V8W 2Y2 (Canada)
- Herzberg Institute of Astrophysics, National Research Council of Canada, 5071 West Saanich Road, Victoria, BC, V9E 2E7 (Canada)
Victoria-Regina isochrones for −0.4 ⩽ [α/Fe] ⩽+0.4 and a wide range in [Fe/H], along with complementary zero-age horizontal branch (ZAHB) loci, have been applied to the color–magnitude diagram (CMD) of Carina. The color transformations that we have used have been “calibrated” so that isochrones provide excellent fits to the [(B−V){sub 0},M{sub V}] diagrams of M3 and M92 when well supported estimates of the globular cluster (GC) reddenings and metallicities are assumed. The adopted distance moduli, for both the GCs and Carina, are based on our ZAHB models, which are able to reproduce the old horizontal branch (HB) component (as well as the luminosity of the HB clump) of the dwarf spheroidal galaxy quite well—even if it spans a range in [Fe/H] of ∼1.5 dex, provided that [α/Fe] varies with [Fe/H] in approximately the way that has been derived spectroscopically. Ages derived here agree reasonably well with those found previously for the old and intermediate-age turnoff (TO) stars, as well as for the period of negligible star formation (SF) activity (∼6–10 Gyr ago). CMD simulations have been carried out for the faintest TO and subgiant stars. They indicate a clear preference for SF that lasted several Gyr instead of a short burst, with some indication that ages decrease with increasing [Fe/H]. In general, stellar models that assume spectroscopic metallicities provide satisfactory fits to the observations, including the thin giant branch of Carina, though higher oxygen abundances than those implied by the adopted values of [α/Fe] would have favorable consequences.
- OSTI ID:
- 22883158
- Journal Information:
- Astrophysical Journal, Vol. 805, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Since 2009, the country of publication for this journal is the UK.; ISSN 0004-637X
- Country of Publication:
- United Kingdom
- Language:
- English
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