1,257 research outputs found
BRIDGE: A Direct-tree Hybrid N-body Algorithm for Fully Self-consistent Simulations of Star Clusters and their Parent Galaxies
We developed a new direct-tree hybrid N-body algorithm for fully
self-consistent N-body simulations of star clusters in their parent galaxies.
In such simulations, star clusters need high accuracy, while galaxies need a
fast scheme because of the large number of the particles required to model it.
In our new algorithm, the internal motion of the star cluster is calculated
accurately using the direct Hermite scheme with individual timesteps and all
other motions are calculated using the tree code with second-order leapfrog
integrator. The direct and tree schemes are combined using an extension of the
mixed variable symplectic (MVS) scheme. Thus, the Hamiltonian corresponding to
everything other than the internal motion of the star cluster is integrated
with the leapfrog, which is symplectic. Using this algorithm, we performed
fully self-consistent N-body simulations of star clusters in their parent
galaxy. The internal and orbital evolutions of the star cluster agreed well
with those obtained using the direct scheme. We also performed fully
self-consistent N-body simulation for large-N models (). In
this case, the calculation speed was seven times faster than what would be if
the direct scheme was used.Comment: 12 pages, 13 figures, Accepted for PAS
Cohabitation and Family Formation in Japan
This paper documents the prevalence, duration, and marital outcomes of cohabiting unions in Japan. It then examines the correlates of cohabitation experiences and describes differences in the family formation trajectories of women who have and have not cohabited. Cohabitation has increased rapidly among recent cohorts of women and cohabiting unions in Japan tend to be relatively short and almost as likely to dissolve as to result in marriage. Life table analyses demonstrate that the cumulative probabilities of marriage and parenthood are roughly similar for women who did and did not cohabit. The most notable difference is in the pathways to family formation, with women who cohabited more likely to both marry subsequent to pregnancy and delay childbearing within marriage. Taken as a whole, these results suggest that cohabiting unions in Japan are best viewed as an emerging stage in the marriage process rather than as an alternative to marriage or singlehood. We conclude with speculation about the likelihood of further increases in cohabitation in Japan and the potential implications for marriage and fertility.
Marital Dissolution in Japan
Very little is known about recent trends in divorce in Japan. In this paper, we use Japanese vital statistics and census data to describe trends in the experience of marital dissolution across the life course, and to examine change over time in educational differentials in divorce. Cumulative probabilities of marital dissolution have increased rapidly across successive marriage cohorts over the past twenty years, and synthetic period estimates suggest that roughly one-third of Japanese marriages are now likely to end in divorce. Estimates of educational differentials also indicate a rapid increase in the extent to which divorce is concentrated at lower levels of education. While educational differentials were negligible in 1980, by 2000, women who had not gone beyond high school were far more likely to be divorced than those with more education.divorce, education, educational differentials, Japan, marital dissolution, marriage, marriage cohorts, synthetic cohort estimates
A search for changing-look AGN in the Grossan catalog
We observed with XMM-Newton 4 objects selected from the Grossan catalog, with
the aim to search for new 'changing-look' AGN. The sample includes all the
sources which showed in subsequent observations a flux much lower than the one
measured with HEAO A-1: NGC 7674, NGC 4968, IRAS 13218+0552 and NGC 1667. None
of the sources was caught in a high flux state during the XMM-Newton
observations, whose analysis reveal they are all likely Compton-thick objects.
We suggest that, for all the sources, potential problems with the HEAO A-1
source identification and flux measurement prevent us from being certain that
the HEAO A-1 data represent a putative 'high' state for these objects.
Nonetheless, based on the high flux state and Compton-thin spectrum of its
GINGA observation, NGC 7674 represents probably the sixth known case of a
'changing-look' Seyfert 2 galaxy. From the X-ray variability pattern, we can
estimate a likely lower limit of a few parsec to the distance of the inner
walls of the torus in this object. Remarkably, IRAS 13218+0552 was not detected
by XMM-Newton, despite being currently classified as a Seyfert 1 with a large
[OIII] flux. However, the original classification was likely to be affected by
an extreme velocity outflow component in the emission lines. The object likely
harbors an highly obscured AGN and should be re-classified as a Type 2 source.Comment: 11 pages, 12 figures, accepted for publication in A&
The X-ray spectra of Compton-thick Seyfert 2 galaxies as seen by BeppoSAX
Results from BeppoSAX observations of Compton--thick Seyfert 2 galaxies are
summarized and reviewed, and their general properties derived and discussed. In
five out of the seven observed sources, the nucleus is directly visible at high
X-ray energies, where the photons penetrate absorbers with column densities in
the range 1.1-4.3x10^{24} cm-2 (in the other two sources, NGC 1068 and NGC
7674, the nucleus is instead totally obscured at all energies, implying even
larger column densities). In most sources there is unambiguous evidence of a
reflection component from optically thick, cold matter, while in two (or maybe
four) cases there is also evidence of reflection from ionized matter. For the
sources with a measured X-ray luminosity, a comparison with the infrared
luminosity is made; while in two cases (the Circinus galaxy and NGC 4945) the
IR emission appears to be dominated by starburst activity, in the other three
sources (NGC 6240, Mrk 3 and TOL 0109-383) it is likely to be dominated by
reprocessing of the UV and X-ray photons emitted by an AGN.Comment: Accepted for publication in MNRA
Diffraction-limited Subaru imaging of M82: sharp mid-infrared view of the starburst core
We present new imaging at 12.81 and 11.7 microns of the central ~40"x30"
(~0.7x0.5 kpc) of the starburst galaxy M82. The observations were carried out
with the COMICS mid-infrared (mid-IR) imager on the 8.2m Subaru telescope, and
are diffraction-limited at an angular resolution of <0".4. The images show
extensive diffuse structures, including a 7"-long linear chimney-like feature
and another resembling the edges of a ruptured bubble. This is the clearest
view to date of the base of the kpc-scale dusty wind known in this galaxy.
These structures do not extrapolate to a single central point, implying
multiple ejection sites for the dust. In general, the distribution of dust
probed in the mid-IR anticorrelates with the locations of massive star clusters
that appear in the near-infrared. The 10-21 micron mid-IR emission,
spatially-integrated over the field of view, may be represented by hot dust
with temperature of ~160 K. Most discrete sources are found to have extended
morphologies. Several radio HII regions are identified for the first time in
the mid-IR. The only potential radio supernova remnant to have a mid-IR
counterpart is a source which has previously also been suggested to be a weak
active galactic nucleus. This source has an X-ray counterpart in Chandra data
which appears prominently above 3 keV and is best described as a hot (~2.6 keV)
absorbed thermal plasma with a 6.7 keV Fe K emission line, in addition to a
weaker and cooler thermal component. The mid-IR detection is consistent with
the presence of strong [NeII]12.81um line emission. The broad-band source
properties are complex, but the X-ray spectra do not support the active
galactic nucleus hypothesis. We discuss possible interpretations regarding the
nature of this source.Comment: Accepted for publication in PASJ Subaru special issue. High
resolution version available temporarily at
http://www.astro.isas.jaxa.jp/~pgandhi/pgandhi_m82.pd
Evolution of Star Clusters near the Galactic Center: Fully Self-consistent N-body Simulations
We have performed fully self-consistent -body simulations of star clusters
near the Galactic center (GC). Such simulations have not been performed because
it is difficult to perform fast and accurate simulations of such systems using
conventional methods. We used the Bridge code, which integrates the parent
galaxy using the tree algorithm and the star cluster using the fourth-order
Hermite scheme with individual timestep. The interaction between the parent
galaxy and the star cluster is calculate with the tree algorithm. Therefore,
the Bridge code can handle both the orbital and internal evolutions of star
clusters correctly at the same time. We investigated the evolution of star
clusters using the Bridge code and compared the results with previous studies.
We found that 1) the inspiral timescale of the star clusters is shorter than
that obtained with "traditional" simulations, in which the orbital evolution of
star clusters is calculated analytically using the dynamical friction formula
and 2) the core collapse of the star cluster increases the core density and
help the cluster survive. The initial conditions of star clusters is not so
severe as previously suggested.Comment: 19 pages, 19 figures, accepted for publication in Ap
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