157 research outputs found
Unusual Carbonaceous Dust Distribution in PN G095.2+00.7
We investigate the polycyclic aromatic hydrocarbon features in the young
Galactic planetary nebula PN G095.2+00.7 based on mid-infrared observations.
The near- to mid-infrared spectra obtained with the AKARI/IRC and the
Spitzer/IRS show the PAH features as well as the broad emission feature at 12
{\mu}m usually seen in proto-planetary nebulae (pPNe). The spatially resolved
spectra obtained with Subaru/COMICS suggest that the broad emission around 12
{\mu}m is distributed in a shell-like structure, but the unidentified infrared
band at 11.3 {\mu}m is selectively enhanced at the southern part of the nebula.
The variation can be explained by a difference in the amount of the UV
radiation to excite PAHs, and does not necessarily require the chemical
processing of dust grains and PAHs. It suggests that the UV self-extinction is
important to understand the mid-infrared spectral features. We propose a
mechanism which accounts for the evolutionary sequence of the mid-infrared dust
features seen in a transition from pPNe to PNe.Comment: 6 pages, 4 figure
Performance of an electron gun for a high-brightness X-ray generator
The development of an electron gun for a high-brightness X-ray generator whose target brilliance is 60 kW mm−2 is reported
Search for the Infrared Emission Features from Deuterated Interstellar Polycyclic Aromatic Hydrocarbons
We report the results of a search for emission features from interstellar
deuterated polycyclic aromatic hydrocarbons (PAHs) in the 4um region with the
Infrared Camera (IRC) onboard AKARI. No significant excess emission is seen in
4.3-4.7um in the spectra toward the Orion Bar and M17 after the subtraction of
line emission from the ionized gas. A small excess of emission remains at
around 4.4 and 4.65um, but the ratio of their intensity to that of the band
emission from PAHs at 3.3-3.5um is estimated as 2-3%. This is an order of
magnitude smaller than the values previously reported and also those predicted
by the model of deuterium depletion onto PAHs. Since the subtraction of the
ionized gas emission introduces an uncertainty, the deuterated PAH features are
also searched for in the reflection nebula GN 18.14.0, which does not show
emission lines from ionized gas. We obtain a similar result that excess
emission in the 4um region, if present, is about 2% of the PAH band emission in
the 3um region. The present study does not find evidence for the presence of
the large amount of deuterated PAHs that the depletion model predicts. The
results are discussed in the context of deuterium depletion in the interstellar
medium.Comment: 24 pages, 6 figures, to appear in Ap
Akari/irc near-infrared spectral atlas of galactic planetary nebulae
Near-infrared (2.5–5.0 μm) low-resolution (λ/Δλ ~ 100) spectra of 72 Galactic planetary nebulae (PNe) were obtained with the Infrared Camera (IRC) in the post-helium phase. The IRC, equipped with a 1' × 1' window for spectroscopy of a point source, was capable of obtaining near-infrared spectra in a slit-less mode without any flux loss due to a slit. The spectra show emission features including hydrogen recombination lines and the 3.3–3.5 μm hydrocarbon features. The intensity and equivalent width of the emission features were measured by spectral fitting. We made a catalog providing unique information on the investigation of the near-infrared emission of PNe. In this paper, details of the observations and characteristics of the catalog are describe
Research and development of an electron beam focusing system for a high-brightness X-ray generator
In order to minimize the size of the X-ray source for a U-shaped rotating anticathode X-ray generator, the electron beam is focused over a short distance by a combined-function bending magnet. Simulation predicts that the beam brightness will reach almost 500 kW mm−2 for a 120 keV/75 mA beam
Involvement of S-adenosylmethionine-dependent halide/thiol methyltransferase (HTMT) in methyl halide emissions from agricultural plants: isolation and characterization of an HTMT-coding gene from Raphanus sativus (daikon radish)
<p>Abstract</p> <p>Background</p> <p>Biogenic emissions of methyl halides (CH<sub>3</sub>Cl, CH<sub>3</sub>Br and CH<sub>3</sub>I) are the major source of these compounds in the atmosphere; however, there are few reports about the halide profiles and strengths of these emissions. Halide ion methyltransferase (HMT) and halide/thiol methyltransferase (HTMT) enzymes concerning these emissions have been purified and characterized from several organisms including marine algae, fungi, and higher plants; however, the correlation between emission profiles of methyl halides and the enzymatic properties of HMT/HTMT, and their role in vivo remains unclear.</p> <p>Results</p> <p>Thirty-five higher plant species were screened, and high CH<sub>3</sub>I emissions and HMT/HTMT activities were found in higher plants belonging to the Poaceae family, including wheat (<it>Triticum aestivum </it>L.) and paddy rice (<it>Oryza sativa </it>L.), as well as the Brassicaceae family, including daikon radish (<it>Raphanus sativus</it>). The in vivo emission of CH<sub>3</sub>I clearly correlated with HMT/HTMT activity. The emission of CH<sub>3</sub>I from the sprouting leaves of <it>R. sativus</it>, <it>T. aestivum </it>and <it>O. sativa </it>grown hydroponically increased with increasing concentrations of supplied iodide. A gene encoding an <it>S</it>-adenosylmethionine halide/thiol methyltransferase (HTMT) was cloned from <it>R. sativus </it>and expressed in <it>Escherichia coli </it>as a soluble protein. The recombinant <it>R. sativus </it>HTMT (RsHTMT) was revealed to possess high specificity for iodide (I<sup>-</sup>), bisulfide ([SH]<sup>-</sup>), and thiocyanate ([SCN]<sup>-</sup>) ions.</p> <p>Conclusion</p> <p>The present findings suggest that HMT/HTMT activity is present in several families of higher plants including Poaceae and Brassicaceae, and is involved in the formation of methyl halides. Moreover, it was found that the emission of methyl iodide from plants was affected by the iodide concentration in the cultures. The recombinant RsHTMT demonstrated enzymatic properties similar to those of <it>Brassica oleracea </it>HTMT, especially in terms of its high specificity for iodide, bisulfide, and thiocyanate ions. A survey of biogenic emissions of methyl halides strongly suggests that the HTM/HTMT reaction is the key to understanding the biogenesis of methyl halides and methylated sulfur compounds in nature.</p
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