2,542 research outputs found
Constraints on Area Variables in Regge Calculus
We describe a general method of obtaining the constraints between area
variables in one approach to area Regge calculus, and illustrate it with a
simple example. The simplicial complex is the simplest tessellation of the
4-sphere. The number of independent constraints on the variations of the
triangle areas is shown to equal the difference between the numbers of
triangles and edges, and a general method of choosing independent constraints
is described. The constraints chosen by using our method are shown to imply the
Regge equations of motion in our example.Comment: Typographical errors correcte
Star formation, structure, and formation mechanism of cometary globules: NIR observations of CG 1 and CG 2
Cometary globule (CG) 1 and CG 2 are "classic" CGs in the Gum Nebula. They
have compact heads and long dusty tails that point away from the centre of the
Gum Nebula. We study the structure of CG 1 and CG 2 and the star formation in
them to find clues to the CG formation mechanism. The two possible mechanisms,
radiation-driven implosion (RDI) and a supernova (SN) blast wave, produce a
characteristic mass distribution where the major part of the mass is situated
in either the head (RDI) or the tail (SN). CG 1 and CG 2 were imaged in the
near infrared (NIR) JsHKs bands. NIR photometry was used to locate NIR excess
objects and to create extinction maps of the CGs. The A_V maps allow us to
analyse the large-scale structure of CG 1 and CG 2. Archival images from the
WISE and Spitzer satellites and HIRES-processed IRAS images were used to study
the small-scale structure. In addition to the previously known CG 1 IRS 1 we
discovered three new NIR-excess objects, two in CG 1 and one in CG 2. CG 2 IRS
1 is the first detection of star formation in CG 2. Spectral energy
distribution (SED) fitting suggests the NIR-excess objects are young low-mass
stars. CG 1 IRS 1 is probably a class I protostar in the head of CG 1. CG 1 IRS
1 drives a bipolar outflow, which is very weak in CO, but the cavity walls are
seen in reflected light in our NIR and in the Spitzer 3.6 and 4.5 mum images.
Strong emission from excited polycyclic aromatic hydrocarbon particles and very
small grains were detected in the CG 1 tail. The total mass of CG 1 in the
observed area is 41.9 Msun of which 16.8 Msun lies in the head. For CG 2 these
values are 31.0 Msun total and 19.1 Msun in the head. The observed mass
distribution does not offer a firm conclusion for the formation mechanism of
these CGs: CG 1 is in too evolved a state, and in CG 2 part of the globule tail
was outside the observed area. (abridged)Comment: Accepted for publication in A&A. 22 pages, 24 figures. JHKs
photometry will be available electronicall
Rosette Globulettes and Shells in the Infrared
Tiny, dense clumps of sub-solar mass called globulettes form in giant
galactic HII regions. The young central clusters compress the surrounding
molecular shells which break up into clumps, filaments, and elephant trunks
that interact with UV light from the central OB stars. We study the nature of
the infrared emission and extinction in the shell and globulettes in the
Rosette Nebula (RN) and search for associated newborn stars. We imaged the
northwestern quadrant of the RN in the near-infrared (NIR) through JHKs and
narrow-band H2 1-0 S(1), Pbeta and continuum filters. NIR images were used to
study the surface brightness of the globulettes and associated bright rims. NIR
photometry was used to create an extinction map and to search for NIR excess
objects. Archival images from Spitzer IRAC and MIPS 24 and Herschel PACS
observations were used to further study the region and its stellar population
and to examine the structure of the shell and trunks. The globulettes and
elephant trunks have bright rims in the Ks band on the sides facing the central
cluster. Analysis of 21 globulettes where surface brightness in the H2 1-0 S(1)
line is detected shows that about a third of the surface brightness observed in
Ks is due to this line: the observed average of the H2/Ks surface brightness is
0.26+-0.02 in the globulettes cores and 0.30+-0.01 in the rims. The estimated
H2 1-0 S(1) surface brightness of the rims is 3-8*10^{-8}
Wm^{-2}sr^{-1}um^{-1}. The H2/Ks surface brightness ratio supports fluorescence
as the H2 excitation mechanism. The globulettes have number densities of
n(H2)~10^{-4} cm^{-3} or higher. We confirm the results from previous optical
and CO surveys that the larger globulettes contain very dense cores and dense
envelopes, and that their masses are sub-solar. Two NIR protostellar objects
were found in an elephant trunk and one in the most massive globulette in our
study. (abridged)Comment: Accepted for publication in A&A. 24 pages, 27 figures. JHKs
photometry will be available electronicall
Rosette nebula globules: Seahorse giving birth to a star
The Rosette Nebula is an HII region ionized mainly by the stellar cluster NGC
2244. Elephant trunks, globules, and globulettes are seen at the interface
where the HII region and the surrounding molecular shell meet. We have observed
a field in the northwestern part of the Rosette Nebula where we study the small
globules protruding from the shell. Our aim is to measure their properties and
study their star formation history in continuation of our earlier study of the
features of the region. We imaged the region in broadband near-infrared (NIR)
JsHKs filters and narrowband H2 1-0 S(1), P, and continuum filters using
the SOFI camera at the ESO/NTT. The imaging was used to study the stellar
population and surface brightness, create visual extinction maps, and locate
star formation. Mid-infrared (MIR) Spitzer IRAC and WISE and optical NOT images
were used to further study the star formation and the structure of the
globules. The NIR and MIR observations indicate an outflow, which is confirmed
with CO observations made with APEX. The globules have mean number densities of
~. P is seen in absorption in the cores of
the globules where we measure visual extinctions of 11-16 mag. The shell and
the globules have bright rims in the observed bands. In the Ks band 20 to 40%
of the emission is due to fluorescent emission in the 2.12 m H2 line
similar to the tiny dense globulettes we studied earlier in a nearby region. We
identify several stellar NIR excess candidates and four of them are also
detected in the Spitzer IRAC 8.0 m image and studied further. We find an
outflow with a cavity wall bright in the 2.124 m H2 line and at 8.0 m
in one of the globules. The outflow originates from a Class I young stellar
object (YSO) embedded deep inside the globule. An H image suggests the
YSO drives a possible parsec-scale outflow. (abridged)Comment: 20 pages, 19 figures, accepted for publication in Astronomy and
Astrophysics, figures reduced for astro-p
Mass and motion of globulettes in the Rosette Nebula
We have investigated tiny molecular clumps in the Rosette Nebula. Radio
observations were made of molecular line emission from 16 globulettes
identified in a previous optical survey. In addtion, we collected images in the
NIR broad-band JHKs and narrow-band Paschen beta and H2. Ten objects, for which
we collected information from several transitions in 12CO and 13CO were
modelled using a spherically symmetric model. The best fit to observed line
ratios and intensities was obtained by assuming a model composed of a cool and
dense centre and warm and dense surface layer. The average masses derived range
from about 50 to 500 Jupiter masses, which is similar to earlier estimates
based on extinction measures. The globulettes selected are dense, with very
thin layers of fluorescent H2 emission. The NIR data shows that several
globulettes are very opaque and contain dense cores. Because of the high
density encountered already at the surface, the rims become thin, as evidenced
by our P beta images.
We conclude that the entire complex of shells, elephant trunks, and
globulettes in the northern part of the nebula is expanding with nearly the
same velocity of ~22 km/s, and with a very small spread in velocity among the
globulettes. Some globulettes are in the process of detaching from elephant
trunks and shells, while other more isolated objects must have detached long
ago and are lagging behind in the general expansion of the molecular shell. The
suggestion that some globulettes might collapse to form planetary-mass objects
or brown dwarfs is strengthened by our finding of dense cores in several
objects.Comment: 15 pages, 15 figures Astronomy and Astrophysics 201
Decay of an isolated monopole into a Dirac monopole configuration
We study numerically the detailed structure and decay dynamics of isolated
monopoles in conditions similar to those of their recent experimental
discovery. We find that the core of a monopole in the polar phase of a spin-1
Bose-Einstein condensate contains a small half-quantum vortex ring. Well after
the creation of the monopole, we observe a dynamical quantum phase transition
that destroys the polar phase. Strikingly, the resulting ferromagnetic order
parameter exhibits a Dirac monopole in its synthetic magnetic field.Comment: 6 pages, 5 figure
Microscopic Black Hole Pairs in Highly-Excited States
We consider the quantum mechanics of a system consisting of two identical,
Planck-size Schwarzschild black holes revolving around their common center of
mass. We find that even in a very highly-excited state such a system has very
sharp, discrete energy eigenstates, and the system performs very rapid
transitions from a one stationary state to another. For instance, when the
system is in the 100th excited state, the life times of the energy eigenstates
are of the order of s, and the energies of gravitons released in
transitions between nearby states are of the order of eV.Comment: 22 pages, 3 figures, uses RevTe
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