434 research outputs found
Magnetic Fields in Star-Forming Molecular Clouds I. The First Polarimetry of OMC-3 in Orion A
The first polarimetric images of the OMC-3 region of the Orion A filamentary
molecular cloud are presented. Using the JCMT, we have detected polarized
thermal emission at 850 microns from dust along a 6' length of the dense
filament. The polarization pattern is highly ordered and is aligned with the
filament throughout most of the region. The plane-of-sky magnetic field
direction is perpendicular to the measured polarization. The mean percentage
polarization is 4.2% with a 1 sigma dispersion of 1%. This region is part of
the integral-shaped filament, and active star formation is ongoing along its
length. The protostellar outflow directions do not appear to be consistently
correlated with the direction of the plane-of-sky field or the filament
structure itself. Depolarization toward the filament center, previously
detected in many other star-forming cores and protostars, is also evident in
our data. (abstract abridged)Comment: 9 pages plus 2 figures (1 colour); accepted for publication in the
March 10, 2000 issue (vol. 531 #2) of The Astrophysical Journa
Deep Near-Infrared Observations and Identifications of Chandra Sources in the Orion Molecular Cloud 2 and 3
We conducted deep NIR imaging observations of the Orion molecular cloud 2 and
3 using QUIRC on the 88-inch telescope of the University of Hawaii. Our
purposes are 1) to generate a comprehensive NIR source catalog of these star
forming clouds, and 2) to identify the NIR counterpart of the Chandra X-ray
sources that have no counterpart in the 2MASS catalog. Our J-, H-, and K-band
observations are about 2 mag deeper than those of 2MASS, and well match the
current Chandra observation. We detected 1448 NIR sources, for which we derived
the position, the J-, H-, and K-band magnitude, and the 2MASS counterpart.
Using this catalog, we identified the NIR counterpart for about 42% of the
2MASS-unIDed Chandra sources. The nature of these Chandra sources are discussed
using their NIR colors and spatial distributions, and a dozen protostar and
brown dwarf candidates are identified.Comment: 39 pages, 9 postscript figures, accepted for publication in A
Detection of doubly-deuterated methanol in the solar-type protostar IRAS16293-2422
We report the first detection of doubly-deuterated methanol (CHD2OH), as well
as firm detections of the two singly-deuterated isotopomers of methanol (CH2DOH
and CH3OD), towards the solar-type protostar IRAS16293-2422. From the present
multifrequency observations, we derive the following abundance ratios:
[CHD2OH]/[CH3OH] = 0.2 +/- 0.1, [CH2DOH]/[CH3OH] = 0.9 +/- 0.3, [CH3OD]/[CH3OH]
= 0.04 +/- 0.02. The total abundance of the deuterated forms of methanol is
greater than that of its normal hydrogenated counterpart in the circumstellar
material of IRAS16293-2422, a circumstance not previously encountered.
Formaldehyde, which is thought to be the chemical precursor of methanol,
possesses a much lower fraction of deuterated isotopomers (~ 20%) with respect
to the main isotopic form in IRAS16293-2422. The observed fractionation of
methanol and formaldehyde provides a severe challenge to both gas-phase and
grain-surface models of deuteration. Two examples of the latter model are
roughly in agreement with our observations of CHD2OH and CH2DOH if the
accreting gas has a large (0.2-0.3) atomic D/H ratio. However, no gas-phase
model predicts such a high atomic D/H ratio, and hence some key ingredient
seems to be missing.Comment: 5 pages, 3 figure
The puzzling detection of D_2CO in the molecular cloud L1689N
We present new observations of the D_2CO emission towards the small cloud L1689N in the Ï Ophiuchus complex. We surveyed five positions, three being a cut across a shock site and two probing the quiescent gas of the molecular cloud. We detected D_2CO emission in the first three positions. The measured [D_2CO] /[ H2CO] is about 3%, whereas it is â€2% in the quiescent gas. We discuss the implications of these new observations, which suggest that the bulk of the D_2CO molecules is stored in grain mantles, and removed from the cold storage by the shock at the interface between the outflowing and quiescent gas. We review the predictions of the published models proposed to explain the observed high deuteration of formaldehyde. They fall in two basic schemes: gas phase and grain surface chemistry. None of the reviewed models is able to account for the observed [D_2CO] /[H_2CO] abundance ratio. A common characteristics shared by the models is apparently that all underestimate the atomic [D]/[H] ratio in the accreting gas
Effect of randomness and anisotropy on Turing patterns in reaction-diffusion systems
We study the effect of randomness and anisotropy on Turing patterns in
reaction-diffusion systems. For this purpose, the Gierer-Meinhardt model of
pattern formation is considered. The cases we study are: (i)randomness in the
underlying lattice structure, (ii)the case in which there is a probablity p
that at a lattice site both reaction and diffusion occur, otherwise there is
only diffusion and lastly, the effect of (iii) anisotropic and (iv) random
diffusion coefficients on the formation of Turing patterns. The general
conclusion is that the Turing mechanism of pattern formation is fairly robust
in the presence of randomness and anisotropy.Comment: 11 pages LaTeX, 14 postscript figures, accepted in Phys. Rev.
Water emission in NGC1333-IRAS4: The physical structure of the envelope
We report ISO-LWS far infrared observations of CO, water and oxygen lines
towards the protobinary system IRAS4 in the NGC1333 cloud. We detected several
water, OH, CO rotational lines, and two [OI] and [CII] fine structure lines.
Given the relatively poor spectral and spatial resolution of these
observations, assessing the origin of the observed emission is not
straightforward. In this paper, we focus on the water line emission and explore
the hypothesis that it originates in the envelopes that surround the two
protostars, IRAS4 A and B, thanks to an accurate model. The model reproduces
quite well the observed water line fluxes, predicting a density profile, mass
accretion rate, central mass, and water abundance profile in agreement with
previous works. We hence conclude that the emission from the envelopes is a
viable explanation for the observed water emission, although we cannot totally
rule out the alternative that the observed water emission originates in the
outflow
Recommended from our members
Far-infrared CO line emission of protostars in NGC 1333
Using the Long Wavelength Spectrometer aboard ISO, we have observed three very young sources (Class 0 or I) in the molecular cloud NGC1333. We discuss in this contribution the FIR CO line emission observed towards the sources themselves and conclude that both a rather warm (~ 1500 K) and dense (~ 105 cm-3) gas or a colder (~ 300 K) and much denser (â„ 108 cm-3) gas are consistent with the data. Based on this analysis only we cannot distinguish between the two cases and therefore assess whether the observed emission originates in a shock associated with the outflow or in the innermost, dense and warm regions of the envelopes that surround these sources
TIMASSS : The IRAS16293-2422 Millimeter And Submillimeter Spectral Survey: Tentative Detection of Deuterated Methyl Formate (DCOOCH3)
High deuterium fractionation is observed in various types of environment such
as prestellar cores, hot cores and hot corinos. It has proven to be an
efficient probe to study the physical and chemical conditions of these
environments. The study of the deuteration of different molecules helps us to
understand their formation. This is especially interesting for complex
molecules such as methanol and bigger molecules for which it may allow to
differentiate between gas-phase and solid-state formation pathways. Methanol
exhibits a high deuterium fractionation in hot corinos. Since CH3OH is thought
to be a precursor of methyl formate we expect that deuterated methyl formate is
produced in such environments. We have searched for the singly-deuterated
isotopologue of methyl formate, DCOOCH3, in IRAS 16293-2422, a hot corino
well-known for its high degree of methanol deuteration. We have used the
IRAM/JCMT unbiased spectral survey of IRAS 16293-2422 which allows us to search
for the DCOOCH3 rotational transitions within the survey spectral range (80-280
GHz, 328-366 GHz). The expected emission of deuterated methyl formate is
modelled at LTE and compared with the observations.} We have tentatively
detected DCOOCH3 in the protostar IRAS 16293-2422. We assign eight lines
detected in the IRAM survey to DCOOCH3. Three of these lines are affected by
blending problems and one line is affected by calibration uncertainties,
nevertheless the LTE emission model is compatible with the observations. A
simple LTE modelling of the two cores in IRAS 16293-2422, based on a previous
interferometric study of HCOOCH3, allows us to estimate the amount of DCOOCH3
in IRAS 16293-2422. Adopting an excitation temperature of 100 K and a source
size of 2\arcsec and 1\farcs5 for the A and B cores, respectively, we find that
N(A,DCOOCH3) = N(B,DCOOCH3) ~ 6.10^14 /cm2. The derived deuterium fractionation
is ~ 15%, consistent with values for other deuterated species in this source
and much greater than that expected from the deuterium cosmic abundance.
DCOOCH3, if its tentative detection is confirmed, should now be considered in
theoretical models that study complex molecule formation and their deuteration
mechanisms. Experimental work is also needed to investigate the different
chemical routes leading to the formation of deuterated methyl formate
- âŠ