6,722 research outputs found
Near-arcsecond resolution observations of the hot corino of the solar type protostar IRAS 16293-2422
Complex organic molecules have previously been discovered in solar type
protostars, raising the questions of where and how they form in the envelope.
Possible formation mechanisms include grain mantle evaporation, interaction of
the outflow with its surroundings or the impact of UV/X-rays inside the
cavities. In this Letter we present the first interferometric observations of
two complex molecules, CH3CN and HCOOCH3, towards the solar type protostar
IRAS16293-2422. The images show that the emission originates from two compact
regions centered on the two components of the binary system. We discuss how
these results favor the grain mantle evaporation scenario and we investigate
the implications of these observations for the chemical composition and
physical and dynamical state of the two components.Comment: 5 pages (apjemulate), 2 figures; accepted by ApJ
HD line emission in Proto-Planetary Disks
%Context: {Previous studies have indicated that the 372.4 GHz ground
transition of ortho-HD might be a powerful probe of Proto-Planetary
Disks. The line could be especially suited for study of the disk mid-plane,
where the bulk of the mass resides and where planet formation takes place.}
%Aims: {Provide detailed theoretical predictions for the line intensity,
profile and maps expected for representative disk models.} %Methods: {We
determine the physical and chemical structure of the disks from the model
developed by Ceccarelli & Dominik (2005). The line emission is computed with
the new radiative transfer method developed recently by Elitzur & Asensio Ramos
(2006).} %Results: {We present intensity maps convolved with the expected ALMA
resolution, which delineate the origin of the HD 372.4 GHz line. In the
disk inner regions, the line probes the conditions in the mid-plane out to
radial distances of a few tens of AU, where Solar-like planetary systems might
form. In the disk outermost regions, the line originates from slightly above
the mid-plane. When the disk is spatially resolved, the variation of line
profile across the image provides important information about the velocity
field. Spectral profiles of the entire disk flux show a double peak shape at
most inclination angles.} %Conclusions: {Our study confirms that the 372.4 GHz
HD line provides powerful diagnostics of the mid-plane of
Proto-Planetary Disks. Current submillimeter telescopes are capable of
observing this line, though with some difficulties. The future ALMA
interferometer will have the sensitivity to observe and even spatially resolve
the HD line emission.}Comment: To appear in A&
Italian Historical Developments of Teaching and Museum Valorization of Mechanism Models
This paper presents an historical analysis of developments for the creation and usage of models of mechanisms in academic teaching fields, with the aim of re-evaluating the interest and usefulness of models in teaching and research, and of promoting their merits as a cultural heritage worthy of being preserved. The historical analysis is focused on developments in Italy, with specific attention given to physical models created and used for training young engineers in Italian engineering schools, using commercial products, but also original Italian creations. Examples are reported from the main Italian academic sites, where examples of such models of mechanisms have been preserved or have survived, also, as first attempts at museum valorization in terms of historical memorabilia of educational developments on mechanism design issues
First detection of triply-deuterated methanol
We report the first detection of triply-deuterated methanol, with 12 observed
transitions, towards the low-mass protostar IRAS 16293-2422, as well as
multifrequency observations of 13CH3OH, used to derive the column density of
the main isotopomer CH3OH. The derived fractionation ratio [CD3OH]/[CH3OH]
averaged on a 10'' beam is 1.4%. Together with previous CH2DOH and CHD2OH
observations, the present CD3OH observations are consistent with a formation of
methanol on grain surfaces, if the atomic D/H ratio is 0.1 to 0.3 in the
accreting gas. Such a high atomic ratio can be reached in the frame of
gas-phase chemical models including all deuterated isotopomers of H3+.Comment: Accepted by A&
Interplay between temperature and trap effects in one-dimensional lattice systems of bosonic particles
We investigate the interplay of temperature and trap effects in cold particle
systems at their quantum critical regime, such as cold bosonic atoms in optical
lattices at the transitions between Mott-insulator and superfluid phases. The
theoretical framework is provided by the one-dimensional Bose-Hubbard model in
the presence of an external trapping potential, and the trap-size scaling
theory describing the large trap-size behavior at a quantum critical point. We
present numerical results for the low-temperature behavior of the particle
density and the density-density correlation function at the Mott transitions,
and within the gapless superfluid phase.Comment: 9 page
Galaxy Peculiar Velocities and Infall onto Groups
We perform statistical analyses to study the infall of galaxies onto groups
and clusters in the nearby Universe. The study is based on the UZC and SSRS2
group catalogs and peculiar velocity samples. We find a clear signature of
infall of galaxies onto groups over a wide range of scales 5 h^{-1} Mpc<r<30
h^{-1} Mpc, with an infall amplitude on the order of a few hundred kilometers
per second. We obtain a significant increase in the infall amplitude with group
virial mass (M_{V}) and luminosity of group member galaxies (L_{g}). Groups
with M_{V}<10^{13} M_{\odot} show infall velocities V_{infall} \simeq 150 km
s^{-1} whereas for M_{V}>10^{13} M_{\odot} a larger infall is observed,
V_{infall} \simeq 200 km s^{-1}. Similarly, we find that galaxies surrounding
groups with L_{g}<10^{15} L_{\odot} have V_{infall} \simeq 100 km s^{-1},
whereas for L_{g}>10^{15} L_{\odot} groups, the amplitude of the galaxy infall
can be as large as V_{infall} \simeq 250 km s^{-1}. The observational results
are compared with the results obtained from mock group and galaxy samples
constructed from numerical simulations, which include galaxy formation through
semianalytical models. We obtain a general agreement between the results from
the mock catalogs and the observations. The infall of galaxies onto groups is
suitably reproduced in the simulations and, as in the observations, larger
virial mass and luminosity groups exhibit the largest galaxy infall amplitudes.
We derive estimates of the integrated mass overdensities associated with groups
by applying linear theory to the infall velocities after correcting for the
effects of distance uncertainties obtained using the mock catalogs. The
resulting overdensities are consistent with a power law with \delta \sim 1 at r
\sim 10 h^{-1}Mpc.Comment: 25 pages, 10 figure
Water emission in NGC1333-IRAS4: The physical structure of the envelope
We report ISO-LWS far infrared observations of CO, water and oxygen lines
towards the protobinary system IRAS4 in the NGC1333 cloud. We detected several
water, OH, CO rotational lines, and two [OI] and [CII] fine structure lines.
Given the relatively poor spectral and spatial resolution of these
observations, assessing the origin of the observed emission is not
straightforward. In this paper, we focus on the water line emission and explore
the hypothesis that it originates in the envelopes that surround the two
protostars, IRAS4 A and B, thanks to an accurate model. The model reproduces
quite well the observed water line fluxes, predicting a density profile, mass
accretion rate, central mass, and water abundance profile in agreement with
previous works. We hence conclude that the emission from the envelopes is a
viable explanation for the observed water emission, although we cannot totally
rule out the alternative that the observed water emission originates in the
outflow
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