Cepheid Variables in the Flared Outer Disk of our Galaxy

TL;DR

This study identifies young Cepheid variable stars in the outer regions of the Milky Way, providing evidence for a flared outer disk that extends beyond the Galactic plane, which was previously inferred mainly from gas observations.

Contribution

It reports the discovery of classical Cepheid stars in the flared outer disk of the Milky Way, confirming stellar presence in regions previously obscured and unconfirmed.

Findings

Five Cepheid stars found 1-2 kpc above/below Galactic plane

Stars located 13-22 kpc from Galactic center

Supports existence of a flared outer disk in the Milky Way

Abstract

Flaring and warping of the disk of the Milky Way have been inferred from observations of atomic hydrogen, but stars associated with flaring have not hitherto been reported. In the area beyond the Galactic centre the stars are largely hidden from view by dust, and the kinematic distances of the gas cannot be estimated. Thirty-two possible Cepheid stars (young pulsating variable stars) in the direction of the Galactic bulge were recently identified. With their well-calibrated period-luminosity relationships, Cepheid stars are useful distance indicators. When observations of these stars are made in two colours, so that their distance and reddening can be determined simultaneously, the problems of dust obscuration are minimized. Here we report that five of the candidates are classical Cepheid stars. These five stars are distributed from approximately one to two kiloparsecs above and below the plane of the Galaxy, at radial distances of about 13 to 22 kiloparsecs from the centre. The presence of these relatively young (less than 130 million years old) stars so far from the Galactic plane is puzzling, unless they are in the flared outer disk. If so, they may be associated with the outer molecular arm.