217,854 research outputs found
The Source of Maser Emission W33C (G12.8-0.2)
Results of observations of the maser sources toward the W33C region
(G12.8-0.2) carried out on the 22-m radio telescope of the Pushchino Radio
Astronomy Observatory in the 1.35-cm H2O line and on the Large radio telescope
in Nancay (France) in the main (1665 and 1667 MHz) and satellite (1612 and 1720
MHz) OH lines are reported. Multiple, strongly variable short-lived H2O
emission features were detected in a broad interval of radial velocities, from
-7 to 55 km/s. OH maser emission in the 1667-MHz line was discovered in a
velocity range of 35-41 km/s. Stokes parameters of maser emission in the main
OH lines 1665 and 1667 MHz were measured. Zeeman splitting was detected in the
1665-MHz line at 33.4 and 39.4 km/s and in the 1667 MHz line only at 39.4 km/s.
The magnetic field intensity was estimated. A appreciable variability of Zeeman
splitting components was observed at 39 and 39.8 km/s in both main lines. The
extended spectrum and fast variability of the H2O maser emission together with
the variability of the Zeeman splitting components in the main OH lines can be
due to the composite clumpy structure of the molecular cloud and to the
presence in it of large-scale rotation and bipolar outflow as well as of
turbulent motions of material.Comment: 7 pages, 2 tables, 8 figures, accepted by Astronomicheskii Zhurnal
(Astronomy Reports
Warm thick target solar gamma-ray source revisited
The 1.63 MeV gamma-ray line of Ne-20 is sensitive to protons of lower energies than most other nuclear de-excitation lines. Its unexpected strength has been taken as evidence for a solar flare fast ion distribution that remains steep at low energies, and thus has a large total energy content. It has also been suggested that its strength might instead reflect the enhancement of ion lifetimes that occurs when ambient temperatures exceed 10(7) K. Here we revisit this idea ( a) recognising that ions may be effectively trapped in high temperature regions and (b) taking account of the contribution to the line of all ions above threshold. The strength of the 1.63 MeV line relative to other de-excitation lines has been used to estimate the steepness (e.g. energy power-law index) of the ion distribution. We show that these estimates must be significantly revised if primary ions are contained in a region with temperature in the few 10(7) K range, lower than found elsewhere. Such a region would almost certainly be coronal, so we also briefly review other arguments for and against coronal gamma-ray sources
OH spectral evolution of oxygen-rich late-type stars
We investigated the main-line spectral evolution with shell thickness of
oxygen rich AGB stars. The study is based on a sample of 30 sources distributed
along the IRAS colour-colour diagram. The sources were chosen to trace the
Miras with thick shells and the whole range of OH/IR stars. The Miras exhibit a
1665 MHz emission strength comparable to that at 1667 MHz. Even though the
Miras of the study have quite thick shells, their spectral characteristics in
both main lines attest to a strong heterogeneity in their OH shell with, in
particular, the presence of significant turbulence and acceleration. The
expansion velocity has been found to be about the same at 1665 and 1667 MHz,
taking into account a possible velocity turbulence of 1-2km/s at the location
of the main-line maser emission. An increase in the intensity ratio 1667/1665
with shell thickness has been found. A plausible explanation for such a
phenomenon is that competitive gain in favour of the 1667 MHz line increases
when the shell is getting thicker. There is an evolution in the spectral
profile shape with the appearance of a substantial inter-peak signal when the
shell is getting thicker. Also, inter-peak components are found and can be as
strong as the external standard peaks when the shell is very thick. This trend
for an increase of the signal in between the two main peaks is thought to be
the result of an increase of the saturation with shell thickness. All sources
but two - a Mira and an OH/IR star from the lower part of the colour-colour
diagram - are weakly polarized. The strong polarization observed for those two
particular objects is thought to be the result of perturbations in their
shells.Comment: 19 pages, 12 figures, accepted for publication in A&
The Governance of Genomic Information: Will It Come of Age?
The completion of the Human Genome Project has opened up unprecedented possibilities in healthcare, but also ethical and social dilemmas in terms of how these can be achieved. Genomic information can be seen as a 'global public good' (GPG), in that it is represented by knowledge in the public domain and across national boundaries. Lack of investment, infrastructure and expertise in developing countries means that they are unable to take advantage of these GPG characteristics to address their health needs, fuelling fears of a growing 'genomics divide'. Some have suggested an international knowledge sharing and capacity building network, a Global Genomics Initiative, as a means to harness the potential of genomics to reduce inequalities in health between North and South. Three UNESCO declarations also call for cooperation between developed and developing countries in genomics research and science and technology in general. Using international relations theories around global governance and networks as a conceptual framework, this paper examines whether these initiatives are likely to succeed in providing effective governance of genomics
Insight into the OH polarimetric structure of OH 26.5+0.6
We present the first view of the magnetic field structure in the OH shell of
the extreme OH/IR star OH 26.5+0.6. MERLIN interferometric observations of this
object were obtained in December 1993 in full polarisation, at 1612, 1665 and
1667 MHz. The maser spots show a spheroidal distribution both at 1612 and 1667
MHz, while at 1665 MHz emission from the blue-shifted maser peak is
concentrated on the stellar position, and the red-shifted peak emission
exhibits a filamentary structure oriented on a SE-NW axis. The linear
polarisation in both main lines is rather faint, ranging from 9 to 20% at 1665
MHz and from 0 to 30% at 1667 MHz. At 1612 MHz most maser spots exhibit a
similar range of linear polarisation although those in the outermost parts of
the envelope reach values as high as 66%. This is particularly apparent in the
southern part of the shell. The detailed distribution of the polarisation
vectors could only be obtained at 1612 MHz. The polarisation vectors show a
highly structured distribution indicative of a poloidal magnetic field inclined
by 40-60 to the line of sight. The velocity distribution of the maser
spots with respect to the radial distance is well explained by an isotropic
outflow at constant velocity in the case of a prolate shaped spheroid envelope,
also tilted about 45-65 to the line of sight.Comment: 20 pages, 16 figures, accepted for publication in MNRA
OH main line masers in the M82 starburst
A study of the distribution of OH gas in the central region of the nearby
active starburst galaxy M82 has confirmed two previously known bright masers
and revealed several new main line masers. Three of these are seen only at 1665
MHz, one is detected only at 1667 MHz, while the rest are detected in both
lines. Observations covering both the 1665 and 1667 MHz lines, conducted with
both the Very Large Array (VLA) and the Multi-Element Radio Linked
Interferometer Network (MERLIN), have been used to accurately measure the
positions and velocities of these features. This has allowed a comparison with
catalogued continuum features in the starburst such as HII regions and
supernova remnants, as well as known water and satellite line OH masers. Most
of the main line masers appear to be associated with known HII regions although
the two detected only at 1665 MHz are seen along the same line of sight as
known supernova remnants.Comment: MNRAS accepted. 16 pages, 13 figure
Hydroxyl as a Tracer of H2 in the Envelope of MBM40
We observed 51 positions in the OH 1667 MHz main line transitions in the
translucent, high latitude cloud MBM40. We detected OH emission in 8 out of 8
positions in the molecular core of the cloud and 24 out of 43 in the
surrounding, lower extinction envelope and periphery of the cloud. Using a
linear relationship between the integrated OH line intensity and E(B-V), we
estimate the mass in the core, the envelope, and the periphery of the cloud to
be 4, 8, and 5 solar masses. As much as a third of the total cloud mass may be
found in the in the periphery (E(B-V) 0.12 mag) and about a half in the
envelope (0.12 E(B-V) 0.17 mag). If these results are applicable to
other translucent clouds the OH 1667 MHz line is an excellent tracer of gas in
very low extinction regions and high-sensitivity mapping of the envelopes of
molecular clouds may reveal the presence of significant quantities of molecular
mass.Comment: 26 pages, 3 figures, and 5 table
Long-term periodicity in LSI+61303 as beat frequency between orbital and precessional rate
Context: In the binary system LSI+61303 the peak flux density of the radio
outburst, which is related to the orbital period of 26.4960 +/- 0.0028d,
exibits a modulation of 1667 +/- 8 d. The radio emission at high spatial
resolution appears structured in a precessing jet with a precessional period of
27-28 d. Aims: How close is the precessional period of the radio jet to the
orbital period? Any periodicity in the radio emission should be revealed by
timing analysis. The aim of this work is to establish the accurate value of the
precessional period. Methods: We analyzed 6.7 years of the Green Bank
Interferometer database at 2.2 GHz and 8.3 GHz with the Lomb-Scargle and phase
dispersion minimization (PDM) methods and performed simulations. Results: The
periodograms show two periodicities, P1 = 26.49 +/- 0.07 d (\nu1=0.03775
d^{-1}) and P2 = 26.92 +/- 0.07 d (\nu2 = 0.03715 d^{-1}). Whereas radio
outbursts have been known to have nearly orbital occurrence P1 with timing
residuals exhibiting a puzzling sawtooth pattern, we probe in this paper that
they are actually periodical outbursts and that their period is Paverage=
(2/(\nu1 + \nu2)= 26.70 +/- 0.05 d. The period Paverage as well as the
long-term modulation Pbeat=1/(\nu1 - \nu2)=1667 +/- 393 d result from the beat
of the two close periods, the orbital P1 and the precessional P2 periods.
Conclusions: The precessional period, indicated by the astrometry to be of
27--28 d, is P2=26.92 d. The system \lsi seems to be one more case in astronomy
of beat, i.e., a phenomenon occurring when two physical processes create stable
variations of nearly equal frequencies. The very small difference in frequency
creates a long-term variation of period 1/(\nu1-\nu2). The long-term modulation
of 1667 d results from the beat of the two close orbital and precessional
rates.Comment: 8 pages, 4 figures, accepted for publication in A&
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