3 research outputs found
The PL calibration for Milky Way Cepheids and its implications for the distance scale
The rationale behind recent calibrations of the Cepheid PL relation using the
Wesenheit formulation is reviewed and reanalyzed, and it is shown that recent
conclusions regarding a possible change in slope of the PL relation for
short-period and long-period Cepheids are tied to a pathological distribution
of HST calibrators within the instability strip. A recalibration of the
period-luminosity relation is obtained using Galactic Cepheids in open clusters
and groups, the resulting relationship, described by log L/L_sun =
2.415(+-0.035) + 1.148(+-0.044)log P, exhibiting only the moderate scatter
expected from color spread within the instability strip. The relationship is
confirmed by Cepheids with HST parallaxes, although without the need for
Lutz-Kelker corrections, and in general by Cepheids with revised Hipparcos
parallaxes, albeit with concerns about the cited precisions of the latter. A
Wesenheit formulation of Wv = -2.259(+-0.083) - 4.185(+-0.103)log P for
Galactic Cepheids is tested successfully using Cepheids in the inner regions of
the galaxy NGC 4258, confirming the independent geometrical distance
established for the galaxy from OH masers. Differences between the extinction
properties of interstellar and extragalactic dust may yet play an important
role in the further calibration of the Cepheid PL relation and its application
to the extragalactic distance scale.Comment: Accepted for Publication (Astrophysics & Space Science
Polaris: History of Pulsation Activity since Discovery
The pulsation activity of small-amplitude Cepheid Alpha UMi (Polaris) during the period of its radial velocity observations has been analyzed. In the 20th century, Polaris was known to demonstrate a decrease in radial velocity amplitude to the minimum, in the 1980s. Thereafter, the amplitude has increased. The observations of September-December 2015 (21 spectra) obtained by 81cm telescope TCO with spectrograph have showed that radial velocity amplitude comes to 4.16 km/s and is approximately twice higher than the estimates made in 2007, with pulsation period adding 8.6 min
The distribution of the elements in the thin disc from classical Cepheids
Classical Cepheids are the most popular primary distance indicator. They allow us to determine the Galactic abundances gradients and to constrain the chemical enrichment of the thin disc. We present here results based on high resolution spectra of 63 Cepheids. They indicate local abundances inhomogeneities in the outer disc (Rg >10 kpc)