Cepheid Variables in the Flared Outer Disk of our Galaxy
  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.
