Local Volume Dwarf Cas 1: Gas Metallicity, Extinction, and Distance

Cas 1 is a Local Volume (LV) dIr. In 2019 Tikhonov, using HST images and the Tip of Red Giant Branch (TRGB) method, derived its distance \(D=1.61\pm 0.1\) Mpc and determined the stellar metallicity of Cas 1, \(z=0.0004\) (or \(Z_{\textrm{stars}}=Z_{\odot}/50\)). Such an eXtremely Metal-Poor (XMP) dwarf would be a nearby analogue of I Zw 18 and a valuable object for the follow-up detailed studies. Meanwhile, the distance to Cas 1 remains debatable. Its TRGB distance of \(4.5\pm 0.2\) Mpc, based on the deeper HST images, was presented in the Extragalactic Distance Database (EDD). It places Cas 1 in the field between groups of IC 342 (\(D=3.3\) Mpc) and Maffei 1/Maffei 2 (\(D=5.7\) Mpc). To test the suggested XMP nature of Cas 1, we conduct the 6-m telescope (BTA, SAO RAS) spectroscopy to estimate O/H in its two H II regions. We also use these spectra to derive, via the observed Balmer decrements, the upper limit of the MW extinction in Cas 1. The derived values of \(12+\log(\textrm{O/H})\) are \(7.83\pm 0.1\) and \(7.58\pm 0.1\) dex. The measured Balmer decrements result in the upper limit MW extinction in this direction of \(A_{B}=3\overset{\textrm{m}}{.}06\pm 0\overset{\textrm{m}}{.}14\). This is smaller by \(0\overset{\textrm{m}}{.}63\) than \(A_{B}\), used in the previous estimates of the distance to Cas 1. This reduces the original EDD distance to \(4.1\pm 0.36\) Mpc. We use the LV galaxies relationship between their \(12+\log(\textrm{O/H})\) and blue absolute magnitude, \(M_{B}\), published by Berg et al. in 2012, to restrict \(M_{B}\) for Cas 1. The related distance estimate to Cas 1 is 1.64 Mpc with the 1 \(\sigma\) uncertainty of a factor of 2.17. From obtained here \(Z({\textrm{gas}})\sim Z_{\odot}/10\), we conclude that Cas 1 is not an XMP dwarf. Its newly derived distances are consistent with each other within 1 \(\sigma\) errors, with the likely distance of about 3.73 Mpc. This distance favors Cas 1 to reside in the environs of IC 342, but not in the field.