5 research outputs found
Cepheid Parallaxes and the Hubble Constant
Revised Hipparcos parallaxes for classical Cepheids are analysed together
with 10 HST-based parallaxes (Benedict et al.). In a reddening-free V,I
relation we find that the coefficient of logP is the same within the
uncertainties in our Galaxy as in the LMC, contrary to some previous
suggestions. Cepheids in the inner region of NGC4258 with near solar
metallicities (Macri et al.) confirm this result. We obtain a zero-point for
the reddening-free relation and apply it to Cepheids in galaxies used by
Sandage et al. to calibrate the absolute magnitudes of SNIa and to derive the
Hubble constant. We revise their result from 62 to 70+/-5 km/s/Mpc. The
Freedman et al. 2001 value is revised from 72 to 76+/-8 km/s/Mpc. These results
are insensitive to Cepheid metallicity corrections. The Cepheids in the inner
region of NGC4258 yield a modulus of 29.22+/-0.03(int) compared with a
maser-based modulus of 29.29+/-0.15. Distance moduli for the LMC, uncorrected
for any metallicity effects, are; 18.52+/-0.03 from a reddening-free relation
in V,I; 18.47+/-0.03 from a period-luminosity relation at K; 18.45+/-0.04 from
a period-luminosity-colour relation in J,K. Adopting a metallicity correction
in V,I from Marci et al. leads to a true LMC modulus of 18.39+/-0.05.Comment: 9 pages, 1 figure, on-line material from [email protected].
Accepted for MNRA
The Lick AGN Monitoring Project 2011: Dynamical Modeling of the Broad-Line Region
We present models of the H-emitting broad-line region (BLR) in seven
Seyfert 1 galaxies from the Lick AGN (Active Galactic Nucleus) Monitoring
Project 2011 sample, drawing inferences on the BLR structure and dynamics as
well as the mass of the central supermassive black hole. We find that the BLR
is generally a thick disk, viewed close to face-on, with preferential emission
back toward the ionizing source. The dynamics in our sample range from
near-circular elliptical orbits to inflowing or outflowing trajectories. We
measure black hole masses of for PG 1310108, for Mrk 50,
for Mrk 141, for Mrk 279,
for Mrk 1511, for NGC 4593, and
for Zw 229015. We use these black hole mass
measurements along with cross-correlation time lags and line widths to recover
the scale factor used in traditional reverberation mapping measurements.
Combining our results with other studies that use this modeling technique,
bringing our sample size to 16, we calculate a scale factor that can be used
for measuring black hole masses in other reverberation mapping campaigns. When
using the root-mean-square (rms) spectrum and using the line dispersion to
measure the line width, we find . Finally, we search for correlations between and other AGN
and BLR parameters and find marginal evidence that is correlated with
and the BLR inclination angle, but no significant evidence of a
correlation with the AGN luminosity or Eddington ratio.Comment: 26 pages, 14 figures. Accepted for publication in Ap
The Luminosities and Distance Scales of Type II Cepheid and RR Lyrae variables
Infrared and optical absolute magnitudes are derived for the type II Cepheids
kappa Pav and VY Pyx from revised Hipparcos parallaxes and for kappa Pav, V553
Cen and SW Tau from pulsation parallaxes. Phase-corrected JHK mags are given
for 142 RR Lyrae variables based on 2MASS data. RR Lyrae itself is overluminous
compared with LMC RR Lyraes at the classical Cepheid modulus (18.39) consistent
with a prediction of Catalan and Cortes. V553 Cen and SW Tau deviate by only
0.02 mag in the mean from the Matsunaga PL(K) relation for globular cluster
type II Cepheids with a zero-point based on the same LMC modulus. Comparing
directly these two stars with type II Cepheids in the LMC and in the Galactic
Bulge leads to an LMC modulus of 18.37\pm0.09 and a distance to the Galactic
Centre of 7.64\pm 0.21kpc. Kappa Pav may be a binary. V553 Cen and SW Tau show
that at optical wavelengths PL relations are wider for field stars than for
those in globular clusters (abridged).Comment: 29 pages, 13 figures, accepted for MNRA