521 research outputs found
C18O (3-2) observations of the Cometary Globule CG 12: a cold core and a C18O hot spot
The feasibility of observing the C18O (3-2) spectral line in cold clouds with
the APEX telescope has been tested. As the line at 329.330 GHz lies in the wing
of a strong atmospheric H2O absorption it can be observed only at high altitude
observatories. Using the three lowest rotational levels instead of only two
helps to narrow down the physical properties of dark clouds and globules. The
centres of two C18O maxima in the high latitude low mass star forming region CG
12 were mapped in C18O (3-2) and the data were analyzed together with spectral
line data from the SEST. The T_MB(3-2)/T_MB(2-1) ratio in the northern C18O
maximum, CG 12 N, is 0.8, and in the southern maximum, CG 12 S, ~2. CG 12 N is
modelled as a 120'' diameter (0.4pc) cold core with a mass of 27 Msun. A small
size maximum with a narrow, 0.8 kms-1, C18O (3-2) spectral line with a peak
temperature of T_MB ~11 K was detected in CG 12 S. This maximum is modelled as
a 60'' to 80'' diameter (~0.2pc) hot (80 K < Tex < 200 K) ~1.6 Msun clump. The
source lies on the axis of a highly collimated bipolar molecular outflow near
its driving source. This is the first detection of such a compact, warm object
in a low mass star forming region.Comment: APEX A&A special issue, accepte
A new proof for the decidability of D0L ultimate periodicity
We give a new proof for the decidability of the D0L ultimate periodicity
problem based on the decidability of p-periodicity of morphic words adapted to
the approach of Harju and Linna.Comment: In Proceedings WORDS 2011, arXiv:1108.341
Generalized tight-binding transport model for graphene nanoribbon-based systems
An extended tight-binding model that includes up to third-nearest-neighbor hopping and a Hubbard mean-field interaction term is tested against ab initio local spin-density approximation results of band structures for armchair- and zigzag-edged graphene nanoribbons. A single tight-binding parameter set is found to accurately reproduce the ab initio results for both the armchair and zigzag cases. Transport calculations based on the extended tight-binding model faithfully reproduce the results of ab initio transport calculations of graphene nanoribbon-based systems.Peer reviewe
Physical properties of dense cores in Orion B9
We aim to determine the physical and chemical properties of dense cores in
Orion B9. We observed the NH3(1,1) and (2,2), and the N2H+(3-2) lines towards
the submm peak positions. These data are used in conjunction with our LABOCA
870 micron dust continuum data. The gas kinetic temperature in the cores is
between ~9.4-13.9 K. The non-thermal velocity dispersion is subsonic in most of
the cores. The non-thermal linewidth in protostellar cores appears to increase
with increasing bolometric luminosity. The core masses are very likely drawn
from the same parent distribution as the core masses in Orion B North. Starless
cores in the region are likely to be gravitationally bound, and thus
prestellar. Some of the cores have a lower radial velocity than the systemic
velocity of the region, suggesting that they are members of the "low-velocity
part" of Orion B. The observed core-separation distances deviate from the
corresponding random-like model distributions. The distances between the
nearest-neighbours are comparable to the thermal Jeans length. The fractional
abundances of NH3 and N2H+ in the cores are ~1.5-9.8x10^{-8} and
~0.2-5.9x10^{-10}, respectively. The NH3 abundance appears to decrease with
increasing H2 column and number densities. The NH3/N2H+ column density ratio is
larger in starless cores than in cores with embedded protostars. The core
population in Orion B9 is comparable in physical properties to those in nearby
low-mass star-forming regions. It is unclear if the origin of cores could be
explained by turbulent fragmentation. On the other hand, many of the core
properties conform with the picture of dynamic core evolution. The Orion B9
region has probably been influenced by the feedback from the nearby Ori OB 1b
group, and the fragmentation of the parental cloud into cores could be caused
by gravitational instability.Comment: 17 pages, 11 figures, 7 tables. Accepted for publication in Astronomy
and Astrophysics. Version 2: minor language corrections adde
Broken Symmetry in Density-Functional Theory: Analysis and Cure
We present a detailed analysis of the broken-symmetry mean-field solutions
using a four-electron rectangular quantum dot as a model system. Comparisons of
the density-functional theory predictions with the exact ones show that the
symmetry breaking results from the single-configuration wave function used in
the mean-field approach. As a general cure we present a scheme that
systematically incorporates several configurations into the density-functional
theory and restores the symmetry. This cure is easily applicable to any
density-functional approach.Comment: 4 pages, 4 figures, submitted to PR
A Multi-Wavelength High Resolution Study of the S255 Star Forming Region. General structure and kinematics
We present observational data for two main components (S255IR and S255N) of
the S255 high mass star forming region in continuum and molecular lines
obtained at 1.3 mm and 1.1 mm with the SMA, at 1.3 cm with the VLA and at 23
and 50 cm with the GMRT. The angular resolution was from ~ 2" to ~ 5" for all
instruments. With the SMA we detected a total of about 50 spectral lines of 20
different molecules (including isotopologues). About half of the lines and half
of the species (in particular N2H+, SiO, C34S, DCN, DNC, DCO+, HC3N, H2CO,
H2CS, SO2) have not been previously reported in S255IR and partly in S255N at
high angular resolution. Our data reveal several new clumps in the S255IR and
S255N areas by their millimeter wave continuum emission. Masses of these clumps
are estimated at a few solar masses. The line widths greatly exceed expected
thermal widths. These clumps have practically no association with NIR or radio
continuum sources, implying a very early stage of evolution. At the same time,
our SiO data indicate the presence of high-velocity outflows related to some of
these clumps. In some cases, strong molecular emission at velocities of the
quiescent gas has no detectable counterpart in the continuum. We discuss the
main features of the distribution of NH3, N2H+, and deuterated molecules. We
estimate properties of decimeter wave radio continuum sources and their
relationship with the molecular material.Comment: 21 pages, 26 figures, accepted for publication in Astrophysical
Journa
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