378 research outputs found
Detection of HC11N in the Cold Dust Cloud TMC-1
Two consecutive rotational transitions of the long cyanopolyyne HC11N,
J=39-38, and J=38-37, have been detected in the cold dust cloud TMC-1 at the
frequencies expected from recent laboratory measurements by Travers et al.
(1996), and at about the expected intensities. The astronomical lines have a
mean radial velocity of 5.8(1) km/s, in good agreement with the shorter
cyanopolyynes HC7N and HC9N observed in this very sharp-lined source [5.82(5)
and 5.83(5) km/s, respectively]. The column density of HC11N is calculated to
be 2.8x10^(11) cm^(-2). The abundance of the cyanopolyynes decreases smoothly
with length to HC11N, the decrement from one to the next being about 6 for the
longer carbon chains.Comment: plain tex 10 pages plus 3 ps fig file
Triggered Star Formation by Massive Stars
We present our diagnosis of the role that massive stars play in the formation
of low- and intermediate-mass stars in OB associations (the Lambda Ori region,
Ori OB1, and Lac OB1 associations). We find that the classical T Tauri stars
and Herbig Ae/Be stars tend to line up between luminous O stars and
bright-rimmed or comet-shaped clouds; the closer to a cloud the progressively
younger they are. Our positional and chronological study lends support to the
validity of the radiation-driven implosion mechanism, where the Lyman continuum
photons from a luminous O star create expanding ionization fronts to evaporate
and compress nearby clouds into bright-rimmed or comet-shaped clouds. Implosive
pressure then causes dense clumps to collapse, prompting the formation of
low-mass stars on the cloud surface (i.e., the bright rim) and
intermediate-mass stars somewhat deeper in the cloud. These stars are a
signpost of current star formation; no young stars are seen leading the
ionization fronts further into the cloud. Young stars in bright-rimmed or
comet-shaped clouds are likely to have been formed by triggering, which would
result in an age spread of several megayears between the member stars or star
groups formed in the sequence.Comment: 2007, ApJ, 657, 88
The Binarity of the Magellanic Clouds and the Formation of the Magellanic Stream
The HST proper motion (PM) measurements of the Clouds have severe
implications for their interaction history with the Milky Way (MW) and with
each other. The Clouds are likely on their first passage about the MW and the
SMC's orbit about the LMC is better described as quasi-periodic rather than
circular. Binary L/SMC orbits that satisfy observational constraints on their
mutual interaction history (e.g. the formation of the Magellanic Bridge during
a collision between the Clouds ~300 Myr ago) can be located within 1 sigma of
the mean PMs. However, these binary orbits are not co-located with the
Magellanic Stream (MS) when projected on the plane of the sky and the
line-of-sight velocity gradient along the LMC's orbit is significantly steeper
than that along the MS. These combined results ultimately rule out a purely
tidal origin for the MS: tides are ineffective without multiple pericentric
passages and can neither decrease the velocity gradient nor explain the offset
stream in a polar orbit configuration. Alternatively, ram pressure stripping of
an extended gaseous disk may naturally explain the deviation. The offset also
suggests that observations of the little-explored region between RA 21h and 23h
are crucial for characterizing the full extent of the MS.Comment: 6 pages, 5 figures, to be published in proceedings of IAU Symposium
No. 256: The Magellanic System: Stars, Gas, and Galaxies, Jacco Th. van Loon
& Joana M. Oliveira, eds. 2009 (Cambridge: Cambridge University Press
Gamma-ray Emission Properties from Mature Pulsars in the Galaxy and in the Gould Belt
We study the -ray emission properties of pulsars by using a new
self-consistent outer gap model. The outer gap can exist in pulsars with age
over million years old if the effect of magnetic inclination angle as well as
the average properties of the outer gap are considered. The mature -ray
pulsars, whose ages are between 0.3 to 3 million years old, are able to move up
to high galactic latitude. Moreover, their -ray luminosity are weaker
and their spectra are softer than those of younger -ray pulsars in the
galactic plane significantly. We use a Monte Carlo method to simulate the
statistical properties of -ray pulsars in the Galaxy as well as in the
Gould Belt. We find that -ray pulsars located at and located at have very different
properties. High galactic latitude -ray pulsars are dominated by mature
pulsars with longer periods, weaker fluxes and softer spectra. If the pulsar
birth rate in the Galaxy and the Gould Belt are and respectively, there are 42 and 35 radio-quiet
-ray pulsars for respectively. Radio-quiet -ray pulsars from the Gould Belt
are 2 and 13 for
respectively. We suggest that a good fraction of unidentified EGRET
-ray sources may be these radio-quiet -ray pulsars. Furthermore
-ray pulsars located at satisfies whereas for
-ray pulsars in the galactic plane, where and respectively.Comment: 24 pages, 21 figures, accepted to be published in Ap
Open Clusters IC 4665 and Cr 359 and a Probable Birthplace of the Pulsar PSR B1929+10
Based on the epicyclic approximation, we have simulated the motion of the
young open star clusters IC 4665 and Collinder 359. The separation between the
cluster centers is shown to have been minimal 7 Myr ago, 36 pc. We have
established a close evolutionary connection between IC 4665 and the
Scorpius-Centaurus association -- the separation between the centers of these
structures was pc 15 Myr ago. In addition, the center of IC 4665
at this time was near two well-known regions of coronal gas: the Local Bubble
and the North Polar Spur. The star HIP 86768 is shown to be one of the
candidates for a binary (in the past) with the pulsar PSR B1929+10. At the
model radial velocity of the pulsar km s, a close
encounter of this pair occurs in the vicinity of IC 4665 at a time of -1.1 Myr.
At the same time, using currently available data for the pulsar B1929+10 at its
model radial velocity km s, we show that the hypothesis
of Hoogerwerf et al. (2001) about the breakup of the Oph--B1929+10
binary in the vicinity of Upper Scorpius (US) about 0.9 Myr ago is more
plausible.Comment: 19 pages, 8 figure
Some cultural consequences in Spain of the Spanish Invasion of Morocco 1859-60
This article argues is a contribution to the study of interrelationships between colonialism, art, and literature in the nineteenth century. The article argues that the Spanish invasion of Morocco in 1859 led to contradictions and tensions within liberal nationalism, not least because of concerns about the tensions between the need for military reassertion of Spain and the respect for the independence of nations. This led to some reconfiguration of Spanish intellectuals' already complex relationship with North Africa and Islam. A major, perhaps surprising consequence of this reconfiguration, was some equation of Moroccan identity with a monotonous surface that was resistant to the gaze. In consequence, the Catalan painter Fortuny's crucial experience of Morocco led him to value near blank surfaces, and thus to make a major contribution to the origins of modern art
Rapid Formation of Molecular Clouds and Stars in the Solar Neighborhood
Observations of both star-forming regions and young, gas-free stellar
associations indicate that most nearby molecular clouds form stars only over a
short time span before dispersal; large-scale flows in the diffuse interstellar
medium have the potential for forming clouds sufficiently rapidly, and for
producing stellar populations with ages much less than the lateral crossing
times of their host molecular clouds. We identify four important factors for
understanding rapid star formation and short cloud lifetimes. First, much of
the accumulation and dispersal of clouds near the solar circle might occur in
the atomic phase; only the high-density portion of a cloud's lifecycle is spent
in the molecular phase, thus helping to limit molecular cloud ``lifetimes''.
Second, once a cloud achieves a high enough column density to form \h2 and
CO, gravitational forces become larger than typical interstellar pressure
forces; thus star formation can follow rapidly upon molecular gas formation and
turbulent dissipation in limited areas of each cloud complex. Third, typical
magnetic fields are not strong enough to prevent rapid cloud formation and
gravitational collapse. Fourth, rapid dispersal of gas by newly-formed stars,
and reduction of shielding by a small expansion of the cloud after the first
events of star formation, might limit the length of the star formation epoch
and the lifetime of a cloud in its molecular state. This picture emphasizes the
importance of large-scale boundary conditions for understanding molecular cloud
formation, and implies that star formation is a highly dynamic, rather than
quasi-static, process.Comment: 41 pages, 10 figures, accepted by Ap
GASKAP -- The Galactic ASKAP Survey
A survey of the Milky Way disk and the Magellanic System at the wavelengths
of the 21-cm atomic hydrogen (HI) line and three 18-cm lines of the OH molecule
will be carried out with the Australian Square Kilometre Array Pathfinder
telescope. The survey will study the distribution of HI emission and absorption
with unprecedented angular and velocity resolution, as well as molecular line
thermal emission, absorption, and maser lines. The area to be covered includes
the Galactic plane (|b|< 10deg) at all declinations south of delta = +40deg,
spanning longitudes 167deg through 360deg to 79deg at b=0deg, plus the entire
area of the Magellanic Stream and Clouds, a total of 13,020 square degrees. The
brightness temperature sensitivity will be very good, typically sigma_T ~ 1 K
at resolution 30arcsec and 1 km/s. The survey has a wide spectrum of scientific
goals, from studies of galaxy evolution to star formation, with particular
contributions to understanding stellar wind kinematics, the thermal phases of
the interstellar medium, the interaction between gas in the disk and halo, and
the dynamical and thermal states of gas at various positions along the
Magellanic Stream.Comment: 45 pages, 8 figures, Pub. Astron. Soc. Australia (in press
Definitions, Criteria and Global Classification of Mast Cell Disorders with Special Reference to Mast Cell Activation Syndromes: A Consensus Proposal
Activation of tissue mast cells (MCs) and their abnormal growth and accumulation in various organs are typically found in primary MC disorders also referred to as mastocytosis. However, increasing numbers of patients are now being informed that their clinical findings are due to MC activation (MCA) that is neither associated with mastocytosis nor with a defined allergic or inflammatory reaction. In other patients with MCA, MCs appear to be clonal cells, but criteria for diagnosing mastocytosis are not met. A working conference was organized in 2010 with the aim to define criteria for diagnosing MCA and related disorders, and to propose a global unifying classification of all MC disorders and pathologic MC reactions. This classification includes three types of `MCA syndromes' (MCASs), namely primary MCAS, secondary MCAS and idiopathic MCAS. MCA is now defined by robust and generally applicable criteria, including (1) typical clinical symptoms, (2) a substantial transient increase in serum total tryptase level or an increase in other MC-derived mediators, such as histamine or prostaglandin D 2, or their urinary metabolites, and (3) a response of clinical symptoms to agents that attenuate the production or activities of MC mediators. These criteria should assist in the identification and diagnosis of patients with MCAS, and in avoiding misdiagnoses or overinterpretation of clinical symptoms in daily practice. Moreover, the MCAS concept should stimulate research in order to identify and exploit new molecular mechanisms and therapeutic targets. Copyright (C) 2011 S. Karger AG, Base
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