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 R _ { 0 } = 7.8 \pm 0.6 kpc is derived from the median distance to Type II Cepheids in the bulge ( OGLE ) , R _ { 0 } = 7.7 \pm 0.7 kpc from a distance to the near side of the bulge combined with an estimated bulge radius of 1.3 \pm 0.3 kpc derived from planetary nebulae .
The distance of the Sun from the Galactic plane inferred from classical Cepheid variables is Z _ { \sun } = 26 \pm 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 .
An additional empirical test is proposed to constrain any putative metallicity dependence of Cepheid distance determinations through forced matches of distance estimates to a particular galaxy using both Type II and classical Cepheids .