Normalized to: J.
[1]
oai:arXiv.org:astro-ph/9910400 [pdf] - 108954
Properties of Dust Grains in Planetary Nebulae - I. The Ionized Region
of NGC 6445
Submitted: 1999-10-21
In this paper we study new infrared spectra of the evolved planetary nebula
NGC 6445 obtained with ISO. These data show that the thermal emission from the
grains is very cool and has a low flux compared to H beta. A model of the
ionized region is constructed, using the photo-ionization code CLOUDY 90.05.
Based on this model, we show from depletions in the gas phase elements that
little grain destruction can have occurred in the ionized region of NGC 6445.
We also argue that dust-gas separation in the nebula is not plausible. The most
likely conclusion is that grains are residing inside the ionized region of NGC
6445 and that the low temperature and flux of the grain emission are caused by
the low luminosity of the central star and the low optical depth of the grains.
This implies that the bulk of the silicon-bearing grains in this nebula were
able to survive exposure to hard UV photons for at least several thousands of
years, contradicting previously published results.
A comparison between optical and infrared diagnostic line ratios gives a
marginal indication for the presence of a t^2-effect in the nebula. However,
the evidence is not convincing and other explanations for the discrepancy are
also plausible.
The off-source spectrum taken with ISO-LWS clearly shows the presence of a
warm cirrus component with a temperature of 24 K as well as a very cold
component with a temperature of 7 K. Since our observation encompasses only a
small region of the sky, it is not clear how extended the 7 K component is and
whether it contributed significantly to the FIRAS spectrum taken by COBE.
Because our line of sight is in the galactic plane, the very cold component
could be a starless core.
[2]
oai:arXiv.org:astro-ph/9802234 [pdf] - 100405
New Limits to the IR Background: Bounds on Radiative Neutrino Decay and
on VMO Contributions to the Dark Matter Problem
Biller, S. D.;
Buckley, J.;
Burdett, A.;
Gordo, J. Bussons;
Carter-Lewis, D. A.;
Fegan, D. J.;
Findley, J.;
Gaidos, J. A.;
Hillas, A. M.;
Krennrich, F.;
Lamb, R. C.;
Lessard, R.;
McEnery, J. E.;
Mohanty, G.;
Quinn, J.;
Rodgers, A. J.;
Rose, H. J.;
Samuelson, F.;
Sembroski, G.;
Skelton, P.;
Weekes, T. C.;
J;
Zweerink
Submitted: 1998-02-18
From considering the effect of gamma-gamma interactions on recently observed
TeV gamma-ray spectra, improved limits are set to the density of extragalactic
infrared (IR) photons which are robust and essentially model-independent. The
resulting limits are up to two orders of magnitude more restrictive than direct
observations in the 0.025-0.3eV regime. These limits are used to improve
constraints on radiative neutrino decay in the mass range above 0.05eV and on
Very Massive Objects (VMOs) as providing the dark matter needed to explain
galaxy rotation curves.
