Carina distance

Relevant publication:

The Araucaria Project: The Distance to the Carina Dwarf Galaxy from Infrared Photometry of RR Lyrae Stars

P. Karczmarek, G. Pietrzyński, W. Gieren, K. Suchomska, P. Konorski, M. Górski, B. Pilecki, D. Graczyk, P. Wielgórski

2015, AJ, 150:90 (← click to see the publication at ADS/arXiv)

We present distance modulus to the Carina dwarf spheroidal galaxy obtained from single-phase near-infrared magnitudes in the J- and K-band for a sample of 33 RR Lyrae (RRL) stars. The sample was carefully chosen from data published by Dall’Ora et al. (2003, AJ, 126, 197), who provided also RRL pulsational periods.

Near-infrared (NIR) photometry of RRLs, while minimizing the influence of both interstellar extinction and metallicity on the RRL luminosity, reveals a linear relationship between the luminosity and the metallicity and the logarithm of pulsational period, i.e. the PLZ relation.

We used five semi-theoretical and empirical, J- and K-band PLZ relations from the literature (Bono et al. 2003, MNRAS, 344, 1097; Catelan et al. 2004, ApJS, 154, 633; Sollima et al. 2008, MNRAS, 384, 1583; Dékány et al. 2013, ApJL, 776, L19) in order to perform the linear least squares fitting with a slope value fixed. This way, only one parameter – zero point of the calibration – was free, and therefore the uncertainty of the entire fit could be substantially reduced.

The zero point of the calibration, corrected for the effect of metallicity and interstellar extinction (both from literature), yielded the true distance modulus of 20.118 ± 0.017_(stat) ± 0.110_(sys) mag.

Our results are consistent with other distance determinations obtained within the Araucaria Project from NIR photometry of red clump stars (20.165 ± 0.015 mag) and the tip of red giant branch (20.09 ± 0.03 ± 0.12 mag in the J-band, 20.14 ± 0.04 ± 0.14 mag in the K-band), as well as with most independent distance determinations to the Carina galaxy. The NIR RRL method once more proves to be a reliable tool for accurate distance determination at the 5% level or better, particularly for galaxies and globular clusters that lack young standard candles, like Cepheids.