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 Mpc and determined the stellar metallicity of Cas 1, (or ). Such an eXtremely Metal-Poor (XMP) dwarf would be a nearby analogue of I Zw 18 and a valuable object fo...
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Veröffentlicht in: | Astrophysical bulletin 2024-09, Vol.79 (3), p.389-398 |
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Zusammenfassung: | 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
Mpc and determined the stellar metallicity of Cas 1,
(or
). 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
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 (
Mpc) and Maffei 1/Maffei 2 (
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
are
and
dex. The measured Balmer decrements result in the upper limit MW extinction in this direction of
. This is smaller by
than
, used in the previous estimates of the distance to Cas 1. This reduces the original EDD distance to
Mpc. We use the LV galaxies relationship between their
and blue absolute magnitude,
, published by Berg et al. in 2012, to restrict
for Cas 1. The related distance estimate to Cas 1 is 1.64 Mpc with the 1
uncertainty of a factor of 2.17. From obtained here
, we conclude that Cas 1 is not an XMP dwarf. Its newly derived distances are consistent with each other within 1
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. |
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ISSN: | 1990-3413 1990-3421 |
DOI: | 10.1134/S1990341324600686 |