Characteristics of the Galaxy according to Cepheids (& Young Massive Stars)

Daniel J. Majaess, David G. Turner, David J. Lane

Department of Astronomy and Physics, Saint Mary's University, Halifax, Nova Scotia, Canada;
The Abbey Ridge Observatory, Stillwater Lake, Nova Scotia, Canada;

Classical and Type II Cepheids are used to reinvestigate specific properties
of the Galaxy. A new Type II reddening-free Cepheid distance parameterization
is formulated from LMC Cepheids (OGLE), with uncertainties typically no larger
than 5-15%. A distance to the Galactic centre of R0=7.8+-0.6 kpc is derived
from the median distance to Type II Cepheids in the bulge (OGLE), R0=7.7+-0.7
kpc from a distance to the near side of the bulge combined with an estimated
bulge radius of 1.3+-0.3 kpc derived from planetary nebulae. The distance of
the Sun from the Galactic plane inferred from classical Cepheid variables is
Zsun=26+-3 pc, a result dependent on the sample's distance and direction
because of the complicating effects of Gould's Belt and warping in the Galactic
disk. Classical Cepheids and young open clusters delineate consistent and
obvious spiral features, although their characteristics do not match
conventional pictures of the Galaxy's spiral pattern. The Sagittarius-Carina
arm is confirmed as a major spiral arm that appears to originate from a
different Galactic region than suggested previously. Furthermore, a major
feature is observed to emanate from Cygnus-Vulpecula and may continue locally
near the Sun. Significant concerns related to the effects of metallicity on the
VI-based reddening-free Cepheid distance relations used here are allayed by
demonstrating that the computed distances to the Galactic centre, and to
several globular clusters (M54, NGC 6441, M15, and M5) and galaxies (NGC 5128
and NGC 3198) which likely host Type II Cepheids: agree with literature results
to within the uncertainties.

Reference: MNRAS
Status: Manuscript has been accepted


Comments: alt. contact: