1,503 research outputs found
X-Ray Emitting Ejecta of Supernova Remnant N132D
The brightest supernova remnant in the Magellanic Clouds, N132D, belongs to
the rare class of oxygen-rich remnants, about a dozen objects that show optical
emission from pure heavy-element ejecta. They originate in explosions of
massive stars that produce large amounts of O, although only a tiny fraction of
that O is found to emit at optical wavelengths. We report the detection of
substantial amounts of O at X-ray wavelengths in a recent 100 ks Chandra ACIS
observation of N132D. A comparison between subarcsecond-resolution Chandra and
Hubble images reveals a good match between clumpy X-ray and optically emitting
ejecta on large (but not small) scales. Ejecta spectra are dominated by strong
lines of He- and H-like O; they exhibit substantial spatial variations
partially caused by patchy absorption within the LMC. Because optical ejecta
are concentrated in a 5 pc radius elliptical expanding shell, the detected
ejecta X-ray emission also originates in this shell.Comment: 5 pages, 6 figures, ApJ Letters, in pres
A compact design for a magnetic synchrotron to store beams of hydrogen atoms
We present a design for an atomic synchrotron consisting of 40 hybrid
magnetic hexapole lenses arranged in a circle. We show that for realistic
parameters, hydrogen atoms with a velocity up to 600 m/s can be stored in a
1-meter diameter ring, which implies that the atoms can be injected in the ring
directly from a pulsed supersonic beam source. This ring can be used to study
collisions between stored hydrogen atoms and molecular beams of many different
atoms and molecules. The advantage of using a synchrotron is two-fold: (i) the
collision partners move in the same direction as the stored atoms, resulting in
a small relative velocity and thus a low collision energy, and (ii) by storing
atoms for many round-trips, the sensitivity to collisions is enhanced by a
factor of 100-1000. In the proposed ring, the cross-sections for collisions
between hydrogen, the most abundant atom in the universe, with any atom or
molecule that can be put in a beam, including He, H, CO, ammonia and OH can
be measured at energies below 100 K. We discuss the possibility to use optical
transitions to load hydrogen atoms into the ring without influencing the atoms
that are already stored. In this way it will be possible to reach high
densities of stored hydrogen atoms.Comment: 9 pages, 3 figure
Warble infestations in some Canadian caribou and their significance
Warble fly larvae (Oedemagena tarandi) occurred in 97-100% of barren-ground caribou (R.t. groen-landicus) sampled in March from the Beverly herd. In December, they occurred in 98% of males and 75% of females. Larvae numbers increased up to several-fold from December to March. Within age classes, males generally were more heavily infected than females. Annual differences were small. Larvae occurred in 14 and 26% of two populations of Peary caribou (Rangifer tarandus pearyi) on the Canadian Arctic Islands. In them, incidences of larvae were unrelated to sex or age. Greater than average numbers of larvae in barren-ground caribou sometimes were associated with females in relatively poor condition and therefore less fecund. These results are discussed in relation to current hypotheses of the factors that affect warble infections
Dense, Fe-rich Ejecta in Supernova Remnants DEM L238 and DEM L249: A New Class of Type Ia Supernova?
We present observations of two LMC supernova remnants (SNRs), DEM L238 and
DEM L249, with the Chandra and XMM-Newton X-ray satellites. Bright central
emission, surrounded by a faint shell, is present in both remnants. The central
emission has an entirely thermal spectrum dominated by strong Fe L-shell lines,
with the deduced Fe abundance in excess of solar and not consistent with the
LMC abundance. This Fe overabundance leads to the conclusion that DEM L238 and
DEM L249 are remnants of thermonuclear (Type Ia) explosions. The shell emission
originates in gas swept up and heated by the blast wave. A standard Sedov
analysis implies about 50 solar masses in both swept-up shells, SNR ages
between 10,000 and 15,000 yr, low (< 0.05 cm^-3) preshock densities, and
subluminous explosions with energies of 3x10^50 ergs. The central Fe-rich
supernova ejecta are close to collisional ionization equilibrium. Their
presence is unexpected, because standard Type Ia SNR models predict faint
ejecta emission with short ionization ages. Both SNRs belong to a previously
unrecognized class of Type Ia SNRs characterized by bright interior emission.
Denser than expected ejecta and/or a dense circumstellar medium around the
progenitors are required to explain the presence of Fe-rich ejecta in these
SNRs. Substantial amounts of circumstellar gas are more likely to be present in
explosions of more massive Type Ia progenitors. DEM L238, DEM L249, and similar
SNRs could be remnants of ``prompt'' Type Ia explosions with young (~100 Myr
old) progenitors.Comment: 24 pages, 8 figures, ApJ, in pres
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