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

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 \(i={-}11.9^{\circ}\pm 0.2^{\circ}\) and the position of this arm \(a_{0}=7.32\pm 0.05\) kpc for the adopted \(R_{0}=8.1\pm 0.1\) kpc. In the Outer arm we have selected 343 Cepheids with ages in the range 120–300 Myr. From them we have found \(i={-}11.5^{\circ}\pm 0.5^{\circ}\) and \(a_{0}=12.89\pm 0.06\) 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 \({-}12^{\circ}\).