5,089 research outputs found
A database of circumstellar OH masers
We present a new database of circumstellar OH masers at 1612, 1665, and 1667
MHz in the Milky Way galaxy. The database (version 2.4) contains 13655
observations and 2341 different stars detected in at least one transition.
Detections at 1612\,MHz are considered to be complete until the end of 2014 as
long as they were published in refereed papers. Detections of the main lines
(1665 and 1667 MHz) and non-detections in all transitions are included only if
published after 1983. The database contains flux densities and velocities of
the two strongest maser peaks, the expansion velocity of the shell, and the
radial velocity of the star. Links are provided for about 100 stars (5\% of
all stars with OH masers) to interferometric observations and monitoring
programs of the maser emission published since their beginnings in the 1970s.
Access to the database is possible over the Web
(www.hs.uni-hamburg.de/maserdb), allowing cone searches for individual sources
and lists of sources. A general search is possible in selected regions of the
sky and by defining ranges of flux densities and/or velocities. Alternative
ways to access the data are via the German Virtual Observatory and the VizieR
library of astronomical catalogs.Comment: 9 pages, 7 figures, accepted for publication in Astronomy &
Astrophysics. Replaced because of faulty compilation of the pdf fil
Detection of the first X-ray selected large AGN group
We have examined the spatial distribution of 856 AGN detected by the ROSAT
All-Sky Survey (RASS) using a direct search for structures with the minimal
spanning tree. The AGNs were compiled from an area of 7000 deg^2, in which
optical identifications of RASS sources were made with the help of the
digitized objective prism plates of the Hamburg Quasar Survey (HQS). Redshifts
were taken from the literature or from own follow-up observations. The sample
probes the spatial distribution at low redshifts, since the redshift
distribution peaks at z=0.1. The application of the minimal spanning tree led
to a 1.8 sigma discovery of an AGN group with 7 members in a volume V=140*75*75
h^-3Mpc^3 in the Pisces constellation. With a mean redshift z=0.27 this group
is only the third discovered group at redshifts z<0.5. The RASS offers
excellent possibilities to study large scale structure with AGNs at low
redshifts, once these redshifts are determined.Comment: 6 pages, 4 figures, accepted for publication in MNRA
Study of extremely reddened AGB stars in the Galactic bulge
Context. Extremely reddened AGB stars lose mass at high rates of >10^-5
Msun/yr. This is the very last stage of AGB evolution, in which stars in the
mass range 2.0--4.0 Msun (for solar metallicity) should have been converted to
C stars already. The extremely reddened AGB stars in the Galactic bulge are
however predominantly O-rich, implying that they might be either low-mass stars
or stars at the upper end of the AGB mass range. Aims. To determine the mass
range of the most reddened AGB stars in the Galactic bulge. Methods. Using
Virtual Observatory tools, we constructed spectral energy distributions of a
sample of 37 evolved stars in the Galactic bulge with extremely red IRAS
colours. We fitted DUSTY models to the observational data to infer the
bolometric fluxes. Applying individual corrections for interstellar extinction
and adopting a common distance, we determined luminosities and mass-loss rates,
and inferred the progenitor mass range from comparisons with AGB evolutionary
models. Results. The observed spectral energy distributions are consistent with
a classification as reddened AGB stars, except for two stars, which are
proto-planetary nebula candidates. For the AGB stars, we found luminosities in
the range 3000--30,000 Lsun and mass-loss rates 10^-5--3x10^-4 Msun/yr. The
corresponding mass range is 1.1--6.0 Msun assuming solar metallicity.
Conclusions. Contrary to the predictions of the evolutionary models, the
luminosity distribution is continuous, with many O-rich AGB stars in the mass
range in which they should have been converted into C stars already. We suspect
that bulge AGB stars have higher than solar metallicity and therefore may avoid
the conversion to C-rich. The presence of low-mass stars in the sample shows
that their termination of the AGB evolution also occurs during a final phase of
very high mass-loss rate, leading to optically thick circumstellar shells
Non-perturbative determination of anisotropy coefficients in lattice gauge theories
We propose a new non-perturbative method to compute derivatives of gauge
coupling constants with respect to anisotropic lattice spacings (anisotropy
coefficients), which are required in an evaluation of thermodynamic quantities
from numerical simulations on the lattice. Our method is based on a precise
measurement of the finite temperature deconfining transition curve in the
lattice coupling parameter space extended to anisotropic lattices by applying
the spectral density method. We test the method for the cases of SU(2) and
SU(3) gauge theories at the deconfining transition point on lattices with the
lattice size in the time direction -- 6. In both cases, there is a
clear discrepancy between our results and perturbative values. A longstanding
problem, when one uses the perturbative anisotropy coefficients, is a
non-vanishing pressure gap at the deconfining transition point in the SU(3)
gauge theory. Using our non-perturbative anisotropy coefficients, we find that
this problem is completely resolved: we obtain and
on and 6 lattices, respectively.Comment: 24pages,7figures,5table
An Analysis
In lieu of an abstract, below is the essay\u27s first paragraph.
Molière, complying with the demands of Louis XIV of France, presented in 1670 a remarkable parody on Turkish customs and language. Le Bourgeois Gentilhomme has brought the plaudits of critics and audiences alike since that time. The play or piece is composed of three acts of character comedy in the folly on Monsieur Jourdain, and two of exaggeration and parody in the events leading up to and the Turkish ceremony. The action develops through a series of episodes rather than a well knit, unified intrigue. Superimposed on the satire on society is a whole-hearted humor prompted by the ignorance and credulity of the central figure, Jourdain, a tradesman who wishes to become a gentleman. He is not an arbitrary figure or character type, but a real human being with exaggerated idiosyncrasies. Molière had associated with this type character in his father\u27s shop. Some critics say that the author would have liked to write of this subject with a more exalted humor, but hurriedly debased it to farce in an effort to suit the wishes of the king
Critical behaviour and scaling functions of the three-dimensional O(6) model
We numerically investigate the three-dimensional O(6) model on 12^3 to 120^3
lattices within the critical region at zero magnetic field, as well as at
finite magnetic field on the critical isotherm and for several fixed couplings
in the broken and the symmetric phase. We obtain from the Binder cumulant at
vanishing magnetic field the critical coupling J_c=1.42865(3). The universal
value of the Binder cumulant at this point is g_r(J_c)=-1.94456(10). At the
critical coupling, the critical exponents \gamma=1.604(6), \beta=0.425(2) and
\nu=0.818(5) are determined from a finite-size-scaling analysis. Furthermore,
we verify predicted effects induced by massless Goldstone modes in the broken
phase. The results are well described by the perturbative form of the model's
equation of state. Our O(6)-result is compared to the corresponding Ising, O(2)
and O(4) scaling functions. Finally, we study the finite-size-scaling behaviour
of the magnetisation on the pseudocritical line.Comment: 13 pages, 20 figures, REVTEX, fixed an error in the determination of
R_\chi and changed the corresponding line in figure 13
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