131 research outputs found
Vortex in Maxwell-Chern-Simons models coupled to external backgrounds
We consider Maxwell-Chern-Simons models involving different non-minimal
coupling terms to a non relativistic massive scalar and further coupled to an
external uniform background charge. We study how these models can be
constrained to support static radially symmetric vortex configurations
saturating the lower bound for the energy. Models involving Zeeman-type
coupling support such vortices provided the potential has a "symmetry breaking"
form and a relation between parameters holds. In models where minimal coupling
is supplemented by magnetic and electric field dependant coupling terms, non
trivial vortex configurations minimizing the energy occur only when a non
linear potential is introduced. The corresponding vortices are studied
numericallyComment: LaTeX file, 2 figure
Embedded Stellar Clusters in the W3/W4/W5 Molecular Cloud Complex
We analyze the embedded stellar content in the vicinity of the W3/W4/W5 HII
regions using the FCRAO Outer Galaxy 12CO(J=1-0) Survey, the IRAS Point Source
Catalog, published radio continuum surveys, and new near-infrared and molecular
line observations. Thirty-four IRAS Point Sources are identified that have
far-infrared colors characteristic of embedded star forming regions, and we
have obtained K' mosaics and 13CO(J=1-0) maps for 32 of them. Ten of the IRAS
sources are associated with an OB star and 19 with a stellar cluster, although
three OB stars are not identified with a cluster. Half of the embedded stellar
population identified in the K' images is found in just the 5 richest clusters,
and 61% is contained in IRAS sources associated with an embedded OB star. Thus
rich clusters around OB stars contribute substantially to the stellar
population currently forming in the W3/W4/W5 region. Approximately 39% of the
cluster population is embedded in small clouds with an average mass of ~130 Mo
that are located as far as 100 pc from the W3/W4/W5 cloud complex. We speculate
that these small clouds are fragments of a cloud complex dispersed by previous
episodes of massive star formation. Finally, we find that 4 of the 5 known
embedded massive star forming sites in the W3 molecular cloud are found along
the interface with the W4 HII region despite the fact that most of the
molecular mass is contained in the interior regions of the cloud. These
observations are consistent with the classical notion that the W4 HII region
has triggered massive star formation along the eastern edge of the W3 molecular
cloud.Comment: to appear in ApJS, see http://astro.caltech.edu/~jmc/papers/w
The Stellar Content of Obscured Galactic Giant H II Regions III.: W31
We present near infrared (J, H, and K) photometry and moderate resolution
(lambda/Deltalambda = 3000) K-band spectroscopy of the embedded stellar cluster
in the giant H II region W31. Four of the brightest five cluster members are
early O--type stars based on their spectra. We derive a spectro--photometric
distance for W31 of 3.4 +/- 0.3 kpc using these new spectral types and infrared
photometry. The brightest cluster source at K is a red object which lies in the
region of the J - H vs. H - K color--color plot inhabited by stars with excess
emission in the K-band. This point source has an H plus K-band spectrum which
shows no photospheric features, which we interpret as being the result of
veiling by local dust emission. Strong Brackett series emission and permitted
FeII emission are detected in this source; the latter feature is suggestive of
a dense inflow or outflow. The near infrared position of this red source is
consistent with the position of a 5 GHz thermal radio source seen in previous
high angular resolution VLA images. We also identify several other K-band
sources containing excess emission with compact radio sources. These objects
may represent stars in the W31 cluster still embedded in their birth cocoons.Comment: LaTeX2e/aastex, 29 pages including 9 figures, 3 table
Evidence for a Massive Protocluster in S255N
S255N is a luminous far-infrared source that contains many indications of
active star formation but lacks a prominent near-infrared stellar cluster. We
present mid-infrared through radio observations aimed at exploring the
evolutionary state of this region. Our observations include 1.3mm continuum and
spectral line data from the Submillimeter Array, VLA 3.6cm continuum and 1.3cm
water maser data, and multicolor IRAC images from the Spitzer Space Telescope.
The cometary morphology of the previously-known UCHII region G192.584-0.041 is
clearly revealed in our sensitive, multi-configuration 3.6cm images. The 1.3mm
continuum emission has been resolved into three compact cores, all of which are
dominated by dust emission and have radii < 7000AU. The mass estimates for
these cores range from 6 to 35 Msun. The centroid of the brightest dust core
(SMA1) is offset by 1.1'' (2800 AU) from the peak of the cometary UCHII region
and exhibits the strongest HC3N, CN, and DCN line emission in the region. SMA1
also exhibits compact CH3OH, SiO, and H2CO emission and likely contains a young
hot core. We find spatial and kinematic evidence that SMA1 may contain further
multiplicity, with one of the components coincident with a newly-detected H2O
maser. There are no mid-infrared point source counterparts to any of the dust
cores, further suggesting an early evolutionary phase for these objects. The
dominant mid-infrared emission is a diffuse, broadband component that traces
the surface of the cometary UCHII region but is obscured by foreground material
on its southern edge. An additional 4.5 micron linear feature emanating to the
northeast of SMA1 is aligned with a cluster of methanol masers and likely
traces a outflow from a protostar within SMA1. Our observations provide direct
evidence that S255N is forming a cluster of intermediate to high-mass stars.Comment: 34 pages, 11 figures, accepted for publication in The Astronomical
Journa
The W51 Giant Molecular Cloud
We present 45"-47" angular resolution maps at 50" sampling of the 12CO and
13CO J=1-0 emission toward a 1.39 deg x 1.33 deg region in the W51 HII region
complex. These data permit the spatial and kinematic separation of several
spectral features observed along the line of sight to W51, and establish the
presence of a massive (1.2 x 10^6 Mo), large (83 pc x 114 pc) giant molecular
cloud (GMC), defined as the W51 GMC, centered at (l,b,V) = (49.5 deg, -0.2 deg,
61 km/s). A second massive (1.9 x 10^5 Mo), elongated (136 pc x 22 pc)
molecular cloud is found at velocities of about 68 km/s along the southern edge
of the W51 GMC. Of the five radio continuum sources that classically define the
W51 region, the brightest source at lambda 6cm (G49.5-0.4) is spatially and
kinematically coincident with the W51 GMC and three (G48.9-0.3, G49.1-0.4, and
G49.2-0.4) are associated with the 68 km/s cloud. Published absorption line
spectra indicate that the fifth prominent continuum source (G49.4-0.3) is
located behind the W51 molecular cloud. The W51 GMC is among the upper 1% of
clouds in the Galactic disk by size and the upper 5-10% by mass. While the W51
GMC is larger and more massive than any nearby molecular cloud, the average H2
column density is not unusual given its size and the mean H2 volume density is
comparable to that in nearby clouds. The W51 GMC is also similar to other
clouds in that most of the molecular mass is contained in a diffuse envelope
that is not currently forming massive stars. We speculate that much of the
massive star formation activity in this region has resulted from a collision
between the 68 km/s cloud and the W51 GMC.Comment: Accepted for publication by the Astronomical Journal. 21 pages, plus
7 figures and 1 tabl
An Analysis of the Shapes of Interstellar Extinction Curves. V. The IR-Through-UV Curve Morphology
We study the IR-through-UV interstellar extinction curves towards 328
Galactic B and late-O stars. We use a new technique which employs stellar
atmosphere models in lieu of unreddened "standard" stars. This technique is
capable of virtually eliminating spectral mismatch errors in the curves. It
also allows a quantitative assessment of the errors and enables a rigorous
testing of the significance of relationships between various curve parameters,
regardless of whether their uncertainties are correlated. Analysis of the
curves gives the following results: (1) In accord with our previous findings,
the central position of the 2175 A extinction bump is mildly variable, its
width is highly variable, and the two variations are unrelated. (2) Strong
correlations are found among some extinction properties within the UV region,
and within the IR region. (3) With the exception of a few curves with extreme
(i.e., large) values of R(V), the UV and IR portions of Galactic extinction
curves are not correlated with each other. (4) The large sightline-to-sightline
variation seen in our sample implies that any average Galactic extinction curve
will always reflect the biases of its parent sample. (5) The use of an average
curve to deredden a spectral energy distribution (SED) will result in
significant errors, and a realistic error budget for the dereddened SED must
include the observed variance of Galactic curves. While the observed large
sightline-to-sightline variations, and the lack of correlation among the
various features of the curves, make it difficult to meaningfully characterize
average extinction properties, they demonstrate that extinction curves respond
sensitively to local conditions. Thus, each curve contains potentially unique
information about the grains along its sightline.Comment: To appear in the Astrophysical Journal, Part 1, July 1, 2007. Figures
and Tables which will appear only in the electronic version of the Journal
can be obtained via anonymous ftp from ftp://ftp.astronomy.villanova.edu .
After logging in, change directories to "fitz/FMV_EXTINCTION". A README file
describes the various files present in the director
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
Effects of the background radiation on radio pulsar and supernova remnant searches and the birth rates of these objects
In different directions of the Galaxy the Galactic background radio radiation
and radiation of complex star formation regions which include large number of
OB associations have different influences on radio pulsar (PSR) and supernova
remnant (SNR) searches. In this work we analyse the effects of these background
radiations on the observations of PSRs at 1400 MHz and SNRs at 1000 MHz. In the
interval l=0 the PSRs with flux F0.2 mJy and the SNRs
with surface brightness WmHzsr are
observable for all values of l and b. All the SNRs with
WmHzsr can be observed in the
interval 60l. We have examined samples of PSRs and SNRs to
estimate the birth rates of these objects in the region up to 3.2 kpc from the
Sun and also in the Galaxy. The birth rate of PSRs is about one in 200 years
and the birth rate of SNRs is about one in 65 years in our galaxy.Comment: revised versio
Dirac-like Monopoles in Three Dimensions and Their Possible Influences on the Dynamics of Particles
Dirac-like monopoles are studied in three-dimensional Abelian Maxwell and
Maxwell-Chern-Simons models. Their scalar nature is highlighted and discussed
through a dimensional reduction of four-dimensional electrodynamics with
electric and magnetic sources. Some general properties and similarities of them
when are considered in Minkowski or Euclidian space are mentioned. However, by
virtue of the structure of the space-time in which they are considered a number
of differences among them take place. Furthermore, we pay attention to some
consequences of these objects when acting upon usual particles. Among other
subjects, special attention is given to the study of a Lorentz-violating
non-minimal coupling between neutral fermions and the field generated by a
monopole alone. In addition, an analogue of the Aharonov-Casher effect is
discussed in this framework.Comment: 20 pages. Latex format. No figures. Accepted for publication in Phys.
Rev.
Modular Groups, Visibility Diagram and Quantum Hall Effect
We consider the action of the modular group on the set of
positive rational fractions. From this, we derive a model for a classification
of fractional (as well as integer) Hall states which can be visualized on two
``visibility" diagrams, the first one being associated with even denominator
fractions whereas the second one is linked to odd denominator fractions. We use
this model to predict, among some interesting physical quantities, the relative
ratios of the width of the different transversal resistivity plateaus. A
numerical simulation of the tranversal resistivity plot based on this last
prediction fits well with the present experimental data.Comment: 17 pages, plain TeX, 4 eps figures included (macro epsf.tex), 1
figure available from reques
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