3,347 research outputs found
Exploring Potential Modifiers of the Association between Neurodevelopmental Disorders and Risk of Bullying Exposure
This survey study examines data from the National Survey of Childrenâs Health to determine which sociodemographic factors might modify the association between neurodevelopmental disorders and being bullied
A composite HII region luminosity function in H alpha of unprecedented statistical weight
Context. Statistical properties of HII region populations in disk galaxies
yield important clues to the physics of massive star formation.
Aims. We present a set of HII region catalogues and luminosity functions for
a sample of 56 spiral galaxies in order to derive the most general form of
their luminosity function.
Methods. HII region luminosity functions are derived for individual galaxies
which, after photometric calibration, are summed to form a total luminosity
function comprising 17,797 HII regions from 53 galaxies.
Results. The total luminosity function, above its lower limit of
completeness, is clearly best fitted by a double power law with a significantly
steeper slope for the high luminosity portion of the function. This change of
slope has been reported in the literature for individual galaxies, and occurs
at a luminosity of log L = 38.6\pm0.1 (L in erg/s) which has been termed the
Stromgren luminosity. A steep fall off in the luminosity function above log L =
40 is also noted, and is related to an upper limit to the luminosities of
underlying massive stellar clusters. Detailed data are presented for the
individual sample galaxies.
Conclusions. The luminosity functions of HII regions in spiral galaxies show
a two slope power law behaviour, with a significantly steeper slope for the
high luminosity branch. This can be modelled by assuming that the high
luminosity regions are density bounded, though the scenario is complicated by
the inhomogeneity of the ionized interstellar medium. The break, irrespective
of its origin, is of potential use as a distance indicator for disc galaxies.Comment: Accepted for publication as a Letter in Astronomy & Astrophysics.
Latex with postscript figures. Online-only tables and figures are included in
this preprint. The HII region catalogues for 56 galaxies will be published
electronically on the CDS but are available also on request from the author
A major star formation region in the receding tip of the stellar Galactic bar
We present an analysis of the optical spectroscopy of 58 stars in the
Galactic plane at \arcdeg, where a prominent excess in the flux
distribution and star counts have been observed in several spectral regions, in
particular in the Two Micron Galactic Survey (TMGS) catalog. The sources were
selected from the TMGS, to have a magnitude brighter than +5 mag and be
within 2 degrees of the Galactic plane. More than 60% of the spectra correspond
to stars of luminosity class I, and a significant proportion of the remainder
are very late giants which would also be fast evolving. This very high
concentration of young sources points to the existence of a major star
formation region in the Galactic plane, located just inside the assumed origin
of the Scutum spiral arm. Such regions can form due to the concentrations of
shocked gas where a galactic bar meets a spiral arm, as is observed at the ends
of the bars of face-on external galaxies. Thus, the presence of a massive star
formation region is very strong supporting evidence for the presence of a bar
in our Galaxy.Comment: 13 pages (latex) + 4 figures (eps), accepted in ApJ Let
The kinematics of the quadrupolar nebula M1-75 and the identification of its central star
The link between the shaping of bipolar planetary nebulae and their central
stars is still poorly understood. The kinematics and shaping of the multipolar
nebula M 1-75 are hereby investigated, and the location and nature of its
central star are briefly discussed. Fabry-Perot data from GHaFAS on the WHT
sampling the Doppler shift of the [N II] 658.3 nm line are used to study the
dynamics of the nebula, by means of a detailed 3-D spatio-kinematical model.
Multi-wavelength images and spectra from the WFC and IDS on the INT, and from
ACAM on the WHT, allowed us to constrain the parameters of the central star.
The two pairs of lobes, angularly separated by ~22 degrees, were ejected
simultaneously approx. ~3500-5000 years ago, at the adopted distance range from
3.5 to 5.0 kpc. The larger lobes show evidence of a slight degree of point
symmetry. The shaping of the nebula could be explained by wind interaction in a
system consisting of a post-AGB star surrounded by a disc warped by radiative
instabilities. This requires the system to be a close binary or a single star
which engulfed a planet as it died. On the other hand, we present broad- and
narrow-band images and a low S/N optical spectrum of the highly-reddened,
previously unnoticed star which is likely the nebular progenitor. Its estimated
V-I colour allows us to derive a rough estimate of the parameters and nature of
the central star.Comment: 8 pages, 6 figures, accepted for publication in Astronomy &
Astrophysic
A major star formation region in the receding tip of the stellar Galactic bar. II. Supplementary information and evidence that the bar is not the same structure as the triaxial bulge previouly reported
This paper is the second part of Garzon et al. (1997: ApJ 491, L31) in which
we presented an outline of the analysis of 60 spectra from a follow-up program
to the Two Micron Galactic Survey (TMGS) project in the l=27 deg., b=0 deg.
area. In this second part, we present a more detailed explanation of the
analysis as well a library of the spectra for more complete information for
each of the 60 stars, and further discussions on the implications for the
structure of the Galaxy.
This region contains a prominent excess in the flux distribution and star
counts previously observed in several spectral ranges, notably in the TMGS.
More than 50% of the spectra of the stars detected with m_K<5.0 mag, within a
very high confidence level, correspond to stars of luminosity class I, and a
significant proportion of the remainder are very late giants which must also be
rapidly evolving. We make the case, using all the available evidence, that we
are observing a region at the nearer end of the Galactic bar, where the Scutum
spiral arm breaks away, and that this is powerful evidence for the presence of
the bar. Alternative explanations do not give nearly such a satisfactory
account of the observations.
The space localization of one and, a fortiori, of both ends of the bar allows
us to infer a position angle for the bar of around 75 deg. with respect to the
Sun-Galactic centre line. The angle is different from that given by other
authors for the bar and this, we think, is because they refer to the triaxial
bulge and not to the bar as detected here.Comment: 21 pages, 1 table, 9 figures, accepted in A
Exponential Gain in Quantum Computing of Quantum Chaos and Localization
We present a quantum algorithm which simulates the quantum kicked rotator
model exponentially faster than classical algorithms. This shows that important
physical problems of quantum chaos, localization and Anderson transition can be
modelled efficiently on a quantum computer. We also show that a similar
algorithm simulates efficiently classical chaos in certain area-preserving
maps.Comment: final published versio
Simulating causal collapse models
We present simulations of causal dynamical collapse models of field theories
on a 1+1 null lattice. We use our simulations to compare and contrast two
possible interpretations of the models, one in which the field values are real
and the other in which the state vector is real. We suggest that a procedure of
coarse graining and renormalising the fundamental field can overcome its
noisiness and argue that this coarse grained renormalised field will show
interesting structure if the state vector does on the coarse grained scale.Comment: 18 pages, 8 fugures, LaTeX, Reference added, discussion of
probability distribution of labellings correcte
A composite H region luminosity function in Hα of unprecedented statistical weight
ABSTRACT Context. Statistical properties of H region populations in disk galaxies yield important clues to the physics of massive star formation. Aims. We present a set of H region catalogues and luminosity functions for a sample of 56 spiral galaxies in order to derive the most general form of their luminosity function. Methods. H region luminosity functions are derived for individual galaxies which, after photometric calibration, are summed to form a total luminosity function comprising 17,797 H regions from 53 galaxies. Results. The total luminosity function, above its lower limit of completeness, is clearly best fitted by a double power law with a significantly steeper slope for the high luminosity portion of the function. This change of slope has been reported in the literature for individual galaxies, and occurs at a luminosity of log L = 38.6 ± 0.1 (L in erg s â1 ) which has been termed the Strömgren luminosity. A steep fall off in the luminosity function above log L = 40 is also noted, and is related to an upper limit to the luminosities of underlying massive stellar clusters. Detailed data are presented for the individual sample galaxies. Conclusions. The luminosity functions of H regions in spiral galaxies show a two slope power law behaviour, with a significantly steeper slope for the high luminosity branch. This can be modelled by assuming that the high luminosity regions are density bounded, though the scenario is complicated by the inhomogeneity of the ionized interstellar medium. The break, irrespective of its origin, is of potential use as a distance indicator for disc galaxies
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