49 research outputs found
ISO Spectroscopy of Young Stellar Objects
Observations of gas-phase and solid-state species toward
young stellar objects (YSOs) with the spectrometers
on board the Infrared Space Observatory
are reviewed. The excitation and abundances of
the atoms and molecules are sensitive to the changing
physical conditions during star-formation. In
the cold outer envelopes around YSOs, interstellar
ices contain a significant fraction of the heavy element
abundances, in particular oxygen. Different ice
phases can be distinguished, and evidence is found for
heating and segregation of the ices in more evolved
objects. The inner warm envelopes around YSOs are
probed through absorption and emission of gas-phase
molecules, including CO, CO_2, CH_4 and H_2O. An
overview of the wealth of observations on gas-phase
H_2O in star-forming regions is presented. Gas/solid
ratios are determined, which provide information on
the importance of gas-grain chemistry and high temperature
gas-phase reactions. The line ratios of molecules
such as H_2, CO and H_2O are powerful probes
to constrain the physical parameters of the gas. Together
with atomic and ionic lines such as [0 I]
63 µm, [S I] 25 µm and (Si II] 35 µm, they can also
be used to distinguish between photon- and shock-heated
gas. Finally, spectroscopic data on circumstellar
disks around young stars are mentioned. The
results are discussed in the context of the physical
and chemical evolution of YSOs
A multiwavelength study of the supernova remnant G296.8-0.3
We report XMM-Newton observations of the Galactic supernova remnant
G296.8-0.3, together with complementary radio and infrared data. The spatial
and spectral properties of the X-ray emission, detected towards G296.8-0.3, was
investigated in order to explore the possible evolutionary scenarios and the
physical connexion with its unusual morphology detected at radio frequencies.
G296.8-0.3 displays diffuse X-ray emission correlated with the peculiar radio
morphology detected in the interior of the remnant and with the shell-like
radio structure observed to the northwest side of the object. The X-ray
emission peaks in the soft/medium energy range (0.5-3.0 keV). The X-ray
spectral analysis confirms that the column density is high (NH \sim 0.64 x
10^{22} cm^{-2}) which supports a distant location (d>9 kpc) for the SNR. Its
X-ray spectrum can be well represented by a thermal (PSHOCK) model, with kT
\sim 0.86 keV, an ionization timescale of 6.1 x 10^{10} cm^{-3} s, and low
abundance (0.12 Z_sun). The 24 microns observations show shell-like emission
correlated with part of the northwest and southeast boundaries of the SNR. In
addition a point-like X-ray source is also detected close to the geometrical
center of the radio SNR. The object presents some characteristics of the
so-called compact central objects (CCO). Its X-ray spectrum is consistent with
those found at other CCOs and the value of NH is consistent with that of
G296.8-0.3, which suggests a physical connexion with the SNR.Comment: Accepted for publication in Astrophysics & Space Scienc