Estimation of the Parameters of the Spiral Pattern in the Galaxy Based on a Sample of Classical Cepheids

TL;DR

This study refines the geometric parameters of two spiral arms in the Milky Way using classical Cepheids, estimating a consistent pitch angle of about -12 degrees for the galaxy's grand-design spiral pattern.

Contribution

It provides new, precise measurements of the pitch angles and positions of the Carina-Sagittarius and Outer spiral arms based on a large sample of Cepheids with accurate distances.

Findings

Estimated pitch angles of approximately -12 degrees for both arms.

Determined the positions of the spiral arms at about 7.3 kpc and 12.9 kpc.

Confirmed a consistent grand-design spiral pattern in the Galaxy.

Abstract

We consider a sample of Galactic classical Cepheids with highly accurate estimates of their distances taken from Skowron et al., where they were determined based on the period-luminosity relation. We have refined the geometric characteristics of two spiral arm segments-the Carina-Sagittarius and Outer ones. For this purpose, we have selected 269 Cepheids belonging to the Carina-Sagittarius arm with ages in the range 80-120 Myr. From them we have estimated the pitch angle of the spiral pattern $i=-11.9\pm0.2^\circ$ and the position of this arm $a_0=7.32\pm0.05$ kpc for the adopted $R_0=8.1\pm0.1$ kpc. In the Outer arm we have selected 343 Cepheids with ages in the range 120-300 Myr. From them we have found $i=-11.5\pm0.5^\circ$ and $a_0=12.89\pm0.06$ kpc. Adhering to the model of a grand-design spiral pattern in the Galaxy with one pitch angle for all arms, we can conclude that this angle is close to $-12^\circ$.