505 research outputs found
The Near-Infrared Structure and Spectra of the Bipolar Nebulae M 2--9 and Afgl 2688: The Role of UV-Pumping and Shocks in Molecular Hydrogen Excitation
High-resolution near-infrared images and moderate resolution spectra were
obtained of the bipolar nebulae M~2--9 and AFGL 2688. The ability to spatially
and spectrally resolve the various components of the nebulae has proved to be
important in determining their physical structure and characteristics. In
M~2--9, the lobes are found to have a double-shell structure. Analysis of \h2\
line ratios indicates that the \h2\ emission is radiatively excited. A
well-resolved photodissociation region is observed in the lobes. The spectrum
of the central source is dominated by H recombination lines and a strong
continuum rising towards longer wavelengths consistent with a K
blackbody. In AFGL 2688, the emission from the bright lobes is mainly continuum
reflected from the central star. Several molecular features from C and CN
are present. In the extreme end of the N lobe and in the E equatorial region,
the emission is dominated by lines of \h2 in the 2--2.5 \microns region. The
observed \h2 line ratios indicate that the emission is collisionally excited,
with an excitation temperature K.Comment: 28 pages, 13 figures,uuencoded compressed postscript, printed version
available by request from [email protected], IfA-94/3
Mass return to the interstellar medium from highly-evolved carbon stars
Data produced by the Infrared Astronomy Satellite (IRAS) was surveyed at the mid- and far-infrared wavelengths. Visually-identified carbon stars in the 12/25/60 micron color-color diagram were plotted, along with the location of a number of mass-losing stars that lie near the location of the carbon stars, but are not carbon rich. The final sample consisted of 619 objects, which were estimated to be contaminated by 7 % noncarbon-rich objects. The mass return rate was estimated for all evolved circumstellar envelopes. The IRAS Point Source Catalog (PSC) was also searched for the entire class of stars with excess emission. Mass-loss rates, lifetimes, and birthrates for evolved stars were also estimated
Spherical single-roll dynamos at large magnetic Reynolds numbers
This paper concerns kinematic helical dynamos in a spherical fluid body
surrounded by an insulator. In particular, we examine their behaviour in the
regime of large magnetic Reynolds number \Rm, for which dynamo action is
usually concentrated upon a simple resonant stream-surface. The dynamo
eigensolutions are computed numerically for two representative single-roll
flows using a compact spherical harmonic decomposition and fourth-order
finite-differences in radius. These solutions are then compared with the growth
rates and eigenfunctions of the Gilbert and Ponty (2000) large \Rm asymptotic
theory. We find good agreement between the growth rates when \Rm>10^4, and
between the eigenfunctions when \Rm>10^5.Comment: 36 pages, 8 figures. V2: incorrect labels in Fig3 corrected. The
article appears in Physics of Fluids, 22, 066601, and may be found at
http://pof.aip.org/phfle6/v22/i6/p066601_s1 . (Copyright 2010 American
Institute of Physics. This article may be downloaded for personal use only.
Any other use requires prior permission of the author and the American
Institute of Physics
Is the Cepheus E Outflow driven by a Class 0 Protostar?
New early release observations of the Cepheus E outflow and its embedded
source, obtained with the Spitzer Space Telescope, are presented. We show the
driving source is detected in all 4 IRAC bands, which suggests that traditional
Class 0 classification, although essentially correct, needs to accommodate the
new high sensitivity infrared arrays and their ability to detected deeply
embedded sources. The IRAC, MIPS 24 and 70 microns new photometric points are
consistent with a spectral energy distribution dominated by a cold, dense
envelope surrounding the protostar. The Cep E outflow, unlike its more famous
cousin the HH 46/47 outflow, displays a very similar morphology in the near and
mid-infrared wavelengths, and is detected at 24 microns. The interface between
the dense molecular gas (where Cep E lies) and less dense interstellar medium,
is well traced by the emission at 8 and 24 microns, and is one of the most
exotic features of the new IRAC and MIPS images. IRS observations of the North
lobe of the flow confirm that most of the emission is due to the excitation of
pure H2 rotational transitions arising from a relatively cold (Tex~700 K) and
dense (N{H}~9.6E20 cm-2 molecular gas.Comment: 14 pages (pre-print format), including 6 figures. Published in ApJ
Special Spitzer Issue (2004
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