6 research outputs found
Molecular excitation in the Eagle nebula's fingers
Context: The M16 nebula is a relatively nearby Hii region, powered by O stars
from the open cluster NGC 6611, which borders to a Giant Molecular Cloud.
Radiation from these hot stars has sculpted columns of dense obscuring material
on a few arcmin scales. The interface between these pillars and the hot ionised
medium provides a textbook example of a Photodissociation Region (PDR).
Aims: To constrain the physical conditions of the atomic and molecular
material with submillimeter spectroscopic observations.
Methods: We used the APEX submillimeter telescope to map a ~3'x3' region in
the CO J=3-2, 4-3 and 7-6 rotational lines, and a subregion in atomic carbon
lines. We also observed C18O(3-2) and CO(7-6) with longer integrations on five
peaks found in the CO(3-2) map. The large scale structure of the pillars is
derived from the molecular lines' emission distribution. We estimate the
magnitude of the velocity gradient at the tips of the pillars and use LVG
modelling to constrain their densities and temperatures. Excitation
temperatures and carbon column densities are derived from the atomic carbon
lines.
Results: The atomic carbon lines are optically thin and excitation
temperatures are of order 60 K to 100 K, well consistent with observations of
other Hii region-molecular cloud interfaces. We derive somewhat lower
temperatures from the CO line ratios, of order 40 K. The Ci/CO ratio is around
0.1 at the fingers tips.Comment: 4 pages, APEX A&A special issue, accepte
High mass star formation in the IRAS 17233-3606 region: a new nearby and bright hot core in the southern sky
We present molecular line observations of the massive star forming region
IRAS 17233-3606 aimed at studying the molecular core associated with the
source. The observations were made using the Atacama Pathfinder Experiment
telescope in the CO (3-2) and HCO^+ (4-3) transitions, and in the CH_3OH
(6_K-5_K), (7_K-6_K) and CH_3CN (16_K-15_K) bands. For the CO(3-2) and HCO^+
(4-3) transitions, we obtained maps with a size of 70''\times 70''. The typical
angular resolution of the data is ~18''. Our observations reveal an
exceptionally rich molecular spectrum, a signpost of hot core activity.
Comparisons with two other prominent southern hot cores were made through
observations in the same frequency setups. We also detected a bipolar outflow
in CO (3-2) and HCO^+ (4-3) lines. Modelling reveals a hot core of size ~3''
and a temperature of 150 K in the IRAS17233-3606 region. The parameters of the
molecular outflow are derived through the analysis of the CO (3-2) emission,
and are typical of outflows driven by high-mass young stellar objects.Comment: 9 pages, 10 figures (plus 8 figures as Online material), accepted by
A&
On the magnetic ground state of an experimental S = 1/2 kagome antiferromagnet
We have carried out neutron powder-diffraction measurements on zinc
paratacamite ZnCu(OH)Cl with , and studied the heat
capacity in fields of up to 9 T for . The phase has
recently been shown to be an outstanding realisation of the kagom\'{e}
antiferromagnet. A weak mixing of Cu/Zn between the Cu and the Zn
sites, corresponding to % of all Cu for , is observed using
neutron diffraction. This ``antisite disorder'' provides a consistent
explanation of the field dependence of the heat capacity for . From comparison of the derived Cu occupancy of the Zn sites for with the magnetic susceptibility, we argue that for
zinc paratacamite is a spin liquid without a spin gap. The presence of unpaired
but nevertheless strongly interacting spins gives rise to a macroscopically
degenerate ground state manifold, with increasingly glassy dynamics as is
lowered.Comment: Thorough revision of manuscript. Added 1 figure. Manuscript submitted
to Physics Review Letter