3,015,411 research outputs found
Radio pulsar populations
The goal of this article is to summarize the current state of play in the
field of radio pulsar statistics. Simply put, from the observed sample of
objects from a variety of surveys with different telescopes, we wish to infer
the properties of the underlying sample and to connect these with other
astrophysical populations (for example supernova remnants or X-ray binaries).
The main problem we need to tackle is the fact that, like many areas of
science, the observed populations are often heavily biased by a variety of
selection effects. After a review of the main effects relevant to radio
pulsars, I discuss techniques to correct for them and summarize some of the
most recent results. Perhaps the main point I would like to make in this
article is that current models to describe the population are far from complete
and often suffer from strong covariances between input parameters. That said,
there are a number of very interesting conclusions that can be made concerning
the evolution of neutron stars based on current data. While the focus of this
review will be on the population of isolated Galactic pulsars, I will also
briefly comment on millisecond and binary pulsars as well as the pulsar content
of globular clusters and the Magellanic Clouds.Comment: 16 pages, 6 figures, to appear in Proceedings of ICREA Workshop on
The High-Energy Emission from Pulsars and their Systems, Sant Cugat, Spain,
2010 April 12-16 (Springer
Stellar Populations in Bulges
We present line strengths in the bulges and inner disks of 38 galaxies in the
local universe, including several galaxies whose bulges were previously
identified as being disk-like in their colors or kinematics, to see if their
spectral properties reveal evidence for secular evolution. We find that red
bulges of all Hubble types are similar to luminous ellipticals in their central
stellar populations. They have large luminosity-weighted ages, metallicities,
and alpha/Fe ratios. Blue bulges can be separated into a metal-poor class that
is restricted to late-types with small velocity dispersion and a young,
metal-rich class that includes all Hubble types and velocity dispersions.
Luminosity-weighted metallicities and alpha/Fe ratios are sensitive to central
velocity dispersion and maximum disk rotational velocity. Red bulges and
ellipticals follow the same scaling relations. We see differences in some
scaling relations between blue and red bulges and between bulges of barred and
unbarred galaxies. Most bulges have decreasing metallicity with increasing
radius; galaxies with larger central metallicities have steeper gradients.
Where positive age gradients (with the central regions being younger) are
present, they are invariably in barred galaxies. The metallicities of bulges
are correlated with those of their disks. While this and the differences
between barred and unbarred galaxies suggest that secular evolution cannot be
ignored, our results are generally consistent with the hypothesis that mergers
have been the dominant mechanism responsible for bulge formation.Comment: 30 pages, 21 figures; submitted to MNRA
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