Classical Cepheids and the spiral structure of the Milky Way

TL;DR

This study maps the Milky Way's spiral structure using 565 classical Cepheids, determining the spiral pattern's pitch angle, phase angle, and pattern speed with high precision.

Contribution

It provides the most complete Cepheid-based mapping of the Galaxy's spiral arms, including precise measurements of the pattern's pitch angle and speed.

Findings

Pitch angle of 9.5 degrees with 0.1 degree accuracy

Solar phase angle in the spiral pattern is 121 degrees

Pattern speed of 25.2 km/s/kpc

Abstract

We use the currently most complete collection of reliable Cepheid positions (565 stars) out to ~5 kpc based mostly on our photometric data to outline the spiral pattern of our Galaxy. We find the pitch-angle to be equal to 9--10 degrees with the most accurate estimate (i=9.5 +/-0.1 degrees) obtained assuming that the spiral pattern has a four-armed structure, and the solar phase angle in the spiral pattern to be chi_0 = 121+/-3 degrees. The pattern speed is found to be Omega_P=25.2+/-0.5km/s/kpc based on a comparison of the positions of the spiral arms delineated by Cepheids and maser sources and the age difference between these objects.