3,781 research outputs found
Using deuterated H3+ and other molecular species to understand the formation of stars and planets
The H3+ ion plays a key role in the chemistry of dense interstellar gas
clouds where stars and planets are forming. The low temperatures and high
extinctions of such clouds make direct observations of H3+ impossible, but lead
to large abundances of H2D+ and D2H+ which are very useful probes of the early
stages of star and planet formation. Maps of H2D+ and D2H+ pure rotational line
emission toward star-forming regions show that the strong deuteration of H3+ is
the result of near-complete molecular depletion of CNO-bearing molecules onto
grain surfaces, which quickly disappears as cores warm up after stars have
formed.
In the warmer parts of interstellar gas clouds, H3+ transfers its proton to
other neutrals such as CO and N2, leading to a rich ionic chemistry. The
abundances of such species are useful tracers of physical conditions such as
the radiation field and the electron fraction. Recent observations of HF line
emission toward the Orion Bar imply a high electron fraction, and we suggest
that observations of OH+ and H2O+ emission may be used to probe the electron
density in the nuclei of external galaxies.Comment: Proceedings of the H3+ centennial symposium, to be published in RSPTA
(editor: T. Oka
A DC-coupled RF Amplifier in CMOS with DC-feedback
A CMOS multistage RF amplifier with DC coupling is presented. A complete optimisation of the various stages is done to maximize the RF gain for a given power budget. To decrease the effects of offsets and tolerances in high gain multistage amplifiers usually (lossy) AC coupling is used. The presented circuit employs DC coupling and DC control circuitry to avoid coupling-induced\ud
losses. Compared to existing competing AC-coupled designs the presented one has much more gain at the same power consumption with a lower die area. For the 3-stage design vehicle, with Rsrc = 500Ω and Cout = 400fF, the maximal signal power gain at 4mA supply current is 33dB at 1.9GHz
Probing the Interstellar Medium using HI absorption and emission towards the W3 HII region
HI spectra towards the W3 HII complex are presented and used to probe the
Galactic structure and interstellar medium conditions between us and this
region. The overall shape of the spectra is consistent with the predictions of
the Two-Arm Spiral Shock model wherein the gas found in the -40 km/s to -50
km/s range has been accelerated by some 20 km/s from its rotation curve
velocity. Spin temperatures of ~100 K are derived for the Local Arm gas, lower
than found in a previous, similar study towards DR 7. For the interarm region,
values on the order of 300 K are found, implying a negligible filling factor
for the Cold Neutral Medium (<< 1%). Some of the absorbing gas at velocities
near -40 km/s is confirmed to be associated with the HII regions.Comment: 23 pages, 6 figures, accepted for publication in the Astronomical
Journa
Identification of Pre-1950 Synthetic Organic Pigments in Artists’ Paints. A Non-Invasive Approach Using Handheld Raman Spectroscopy
There is little information on the actual use of early synthetic organic pigments (SOPs) in art objects, especially those from before 1950. Their presence can, however, pose a challenge to conservation because their chemical composition, as well as their lightfastness and sensitivity to solvents, are often unknown. Here, a study on the non-invasive identification of SOPs in historic pre-1950 varnished paint-outs from artists’ materials manufacturer Royal Talens is presented. The paints were analysed using a handheld Raman device. Spectra were evaluated by recording the spectra of the same samples with a benchtop instrument. This study demonstrated that the identification of SOPs in varnished oil paints with a non-invasive approach is possible and rather straightforward. The handheld Raman device allowed us to identify fourteen SOPs from eight pigment classes. Besides the occurrence of expected and the known SOPs of this time period, there were also some surprising results, like the detection of the triarylcarbonium pigments PG2 and PB8, and the monoazo Mordant Yellow 1
Discovery of distant high luminosity infrared galaxies
We have developed a method for selecting the most luminous galaxies detected
by IRAS based on their extreme values of R, the ratio of 60 micron and B-band
luminosity. These objects have optical counterparts that are close to or below
the limits of Schmidt surveys. We have tested our method on a 1079 deg^2 region
of sky, where we have selected a sample of IRAS sources with 60 micron flux
densities greater than 0.2 Jy, corresponding to a redshift limit z~1 for
objects with far-IR luminosities of 10^{13} L_sun. Optical identifications for
these were obtained from the UK Schmidt Telescope plates, using the likelihood
ratio method. Optical spectroscopy has been carried out to reliably identify
and measure the redshifts of six objects with very faint optical counterparts,
which are the only objects with R>100 in the sample. One object is a
hyperluminous infrared galaxy (HyLIG) at z=0.834. Of the remaining, fainter
objects, five are ultraluminous infrared galaxies (ULIGs) with a mean redshift
of 0.45, higher than the highest known redshift of any non-hyperluminous ULIG
prior to this study. High excitation lines reveal the presence of an active
nucleus in the HyLIG, just as in the other known infrared-selected HyLIGs. In
contrast, no high excitation lines are found in the non-hyperluminous ULIGs. We
discuss the implications of our results for the number density of HyLIGs at z<1
and for the evolution of the infrared galaxy population out to this redshift,
and show that substantial evolution is indicated. Our selection method is
robust against the presence of gravitational lensing if the optical and
infrared magnification factors are similar, and we suggest a way of using it to
select candidate gravitationally lensed infrared galaxies.Comment: 6 pages, accepted for publication in A&
Magnetic fields at the periphery of UCHII regions from carbon recombination line observations
Several indirect evidences indicate a magnetic origin for the non-thermal
width of spectral lines observed toward molecular clouds. In this letter, I
suggest that the origin of the non-thermal width of carbon recombination lines
(CRLs) observed from photo-dissociation regions (PDRs) near ultra-compact \HII\
regions is magnetic and that the magnitude of the line width is an estimate of
the \alfven speed. The magnetic field strengths estimated based on this
suggestion compare well with those measured toward molecular clouds with
densities similar to PDR densities. I conclude that multi-frequency CRL
observations have the potential to form a new tool to determine the field
strength near star forming regions.Comment: To appear in ApJ Letter
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