Redetermination of the Parameters of the Galactic Spiral Pattern from Classical Cepheids

TL;DR

This study refines the parameters of the Milky Way's spiral arms using classical Cepheids, adjusting distances and analyzing their distribution to determine spiral pattern characteristics and the Sun's position relative to corotation.

Contribution

It provides new measurements of the spiral arms' pitch angles and positions, and estimates the spiral pattern's angular rotation speed based on an extensive Cepheid sample.

Findings

Refined the pitch angles of the Carina-Sagittarius and Outer arms.

Estimated the spiral pattern's angular rotation speed as 27±1 km/s/kpc.

Located the Sun near the corotation radius between the Sun and Perseus arm.

Abstract

We have studied a sample of Galactic classical Cepheids with their distance estimates taken from Skowron et al. (2019), where they were determined based on the period-luminosity relation. In this paper the Skowron et al. (2019) distances were increased by 10\%, according to the results of our kinematic analysis of these Cepheids obtained by us previously. We have refined the geometric characteristics of two spiral arms: the Carina-Sagittarius and Outer ones. The Galactocentric distance of the Sun was assumed to be $8.1\pm0.1$~kpc. Based on 257 Cepheids belonging to a Carina-Sagittarius arm segment with ages in the range 80--120 Myr, we have found the pitch angle of the spiral pattern $i=-12.7\pm0.4^\circ$ and the position of this arm $a_0=7.28\pm0.05$~kpc. Based on 352 Cepheids from the Outer arm with ages in the range 120--300 Myr, we have found $i=-12.0\pm0.5^\circ$ and $a_0=13.03\pm0.06$~kpc. Based on a sample of 1618 Cepheids with ages in the range 80--300 Myr, we have constructed a wavelet map in the ``position angle--logarithm of distance'' plane. The following estimates have been obtained from our analysis of this map: $i=-12.9\pm0.4^\circ$ and $a_0=7.43\pm0.05$~kpc for the Carina-Sagittarius arm and $i=-12.5\pm0 .5^\circ$ and $a_0=13.33\pm0.06$~kpc for the Outer arm. We have found that the Sun is very close to the corotation radius that is located between the Sun and the Perseus arm and estimates the angular rotation speed of the spiral pattern $\Omega_p = 27\pm1$ km s$^{-1}$ kpc$^{-1}$.