Classical Cepheids in the Galactic outer ring R₁R ′₂

Abstract

The kinematics and distribution of classical Cepheids within ∼ 3 kpc from the Sun suggest the existence of the outer ring R1R ′ 2 in the Galaxy. The optimum value of the solar position angle with respect to the major axis of the bar, θ b , providing the best agreement between the distribution of Cepheids and model particles is θ b = 37 ± 13• . The kinematical features obtained for Cepheids with negative Galactocentric radial velocity VR are consistent with the solar location near the descending segment of the outer ring R2. The sharp rise of extinction toward of the Galactic center can be explained by the presence of the outer ring R1 near the Sun.

Evidence of the Galactic outer ring R 1 R 2 ′ $R_{1}R_{2}'$ from young open clusters and OB-associations

“…We found that extinction A V toward open clusters grows most rapidly in the direction of the Galactic center (l = 315-360 • and 0-45 • ) and in the sector 45-90 • , while it is minimal in the direction of the the Carina complex 270-315 • and the anticenter 225-270 • . Note that we found similar features in the variations of extinction for classical Cepheids (Mel'nik et al 2015). Possibly, the sharp growth of extinction can be attributed to the presence of the Galactic outer ring R 1 at the heliocentric distance 1-2 kpc in the direction to the Galactic center.…”

“…V . Note that we found similar features in variations of extinction for classical Cepheids (Mel'nik et al 2015). Both groups of young objects, open clusters and Cepheids, show a sharp growth of extinction in the direction toward the Galactic center (see also Neckel & Klare 1980;Marshall et al 2006).…”

“…The morphological and kinematical features discussed have also been found for the sample of classical Cepheids (Mel'nik et al 2015). Thus, all types of objects -young open clusters, OB-associations and classical Cepheids -suggest the presence of the outer ring R 1 R ′ 2 in the Galaxy.…”

“…2b). We have also found some kinematical features in the distribution of Cepheids, which suggest the location of the Sun near the descending segment of the ring R 2 (Mel'nik et al 2015).…”

“…Note that our study of the sample of classical Cepheids yields θ b = 37 ± 13 • for the position angle of the Sun with respect to the bar's major axis (Mel'nik et al 2015). And the cause of this coincidence is that a tuning-fork-like structure is also present in the Cepheid distribution.…”