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TOPIC: Carina Dwarf Spheroidal Galaxy

Blobrana

L

Posts: 131433

Date: Jul 31 17:13 2015

Carina Dwarf Galaxy	Permalink

Title: The Araucaria Project: The distance to the Carina Dwarf Galaxy from infrared photometry of RR Lyrae stars Author: P. Karczmarek, G. Pietrzynski, W. Gieren, K. Suchomska, P. Konorski, M. Górski, B. Pilecki, D. Graczyk, P. Wielgórski We obtained single-phase near-infrared (NIR) magnitudes in the J- and K-band for a sample of 33 RR Lyrae stars in the Carina dSph galaxy. Applying different theoretical and empirical calibrations of the NIR period-luminosity-metallicity relation for RR Lyrae stars, we find consistent results and obtain a true, reddening-corrected distance modulus of 20.118 ± 0.017 (statistical) ± 0.11 (systematic) mag. This value is in excellent agreement with the results obtained in the context of the Araucaria Project from NIR photometry of Red Clump stars (20.165 ± 0.015) and Tip of Red Giant Branch (20.09 ± 0.03 ± 0.12 mag in J-band, 20.14 ± 0.04 ± 0.14 mag in K-band), as well as with most independent distance determinations to this galaxy. The near-infrared RR Lyrae method proved to be a reliable tool for accurate distance determination at the 5 percent level or better, particularly for galaxies and globular clusters that lack young standard candles, like Cepheids. Read more (1052kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: Sep 13 08:59 2014

Carina Dwarf Spheroidal Galaxy	Permalink

Title: The episodic Star Formation History of the Carina Dwarf Spheroidal Galaxy Author: T. J. L. de Boer, E. Tolstoy, B. Lemasle, A. Saha, E. W. Olszewski, M. Mateo, M. J. Irwin, G. Battaglia We present deep photometry of the Carina dwarf Spheroidal galaxy in the B,V filters from CTIO/MOSAIC, out to and beyond the tidal radius. The accurately calibrated photometry is combined with spectroscopic metallicity distributions of Red Giant Branch stars to determine the detailed star formation and chemical evolution history. The star formation history confirms the episodic formation history of Carina and quantifies the duration and strength of each episode in great detail, as a function radius from the centre. Two main episodes of star formation occurred at old (>8 Gyr) and intermediate (2-8 Gyr) ages, both enriching stars starting from low metallicities ([Fe/H]<-2 dex). By dividing the SFH into two components, we determine that 60pm9 percent of the total number of stars formed within the intermediate age episode. Furthermore, within the tidal radius (0.48 degrees or 888 pc) a total mass in stars of 1.07±0.08 x10^6 solar masses was formed, giving Carina a stellar mass-to-light ratio of 1.8±0.8. Combining the detailed star formation history with spectroscopic observations of RGB stars, we are able to determine the detailed age-metallicity relation of each episode and the timescale of alpha-element evolution of Carina from individual stars. The oldest episode displays a tight age-metallicity relation over 6 Gyr with steadily declining alpha-element abundances and a possible alpha-element knee at [Fe/H]~ -2.5 dex. The intermediate age sequence displays a more complex age-metallicity relation starting from low metallicity and a sequence in alpha-element abundances with a slope much steeper than observed in the old episode, starting from [Fe/H]=-1.8 dex and [Mg/Fe]~0.4 dex and declining to Mg-poor values ([Mg/Fe]<-0.5 dex). This indicates clearly that both episodes of star formation formed from gas with different abundance patterns, inconsistent with simple evolution in an isolated system. Read more (1304kb, PDF) __________________

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