1,445 research outputs found
Aligator.jl - A Julia Package for Loop Invariant Generation
We describe the Aligator.jl software package for automatically generating all
polynomial invariants of the rich class of extended P-solvable loops with
nested conditionals. Aligator.jl is written in the programming language Julia
and is open-source. Aligator.jl transforms program loops into a system of
algebraic recurrences and implements techniques from symbolic computation to
solve recurrences, derive closed form solutions of loop variables and infer the
ideal of polynomial invariants by variable elimination based on Gr\"obner basis
computation
Dust emission from the lensed Lyman break galaxy cB58
We detect 1.2mm continuum emission from dust in the gravitationally lensed
Lyman break galaxy MS 1512+36-cB58. Our detected flux is surprisingly low:
relative to local starburst galaxies, cB58 appears to produce somewhat less
far-IR emission than its UV reddening predicts. After comparing several
different estimates of the source's dust content, we conclude that the apparent
discrepancy is most likely related to uncertainty in its UV spectral slope.
Alternate scenarios to account for a far-IR "deficit" which rely on a high dust
temperature or differential magnification are less satisfactory. Our result
underscores one of the risks inherent in characterizing the cosmic star
formation history from rest-UV data alone.Comment: 5 pages, 1 figure, accepted by A&A Letter
FUSE Observations of Outflowing OVI in the Dwarf Starburst Galaxy NGC1705
We report FUSE far-UV spectroscopy of the prototypical dwarf starburst galaxy
NGC 1705. These data allow us for the first time to probe the coronal-phase gas
(T = 10E5 to 10E6 K) that may dominate the radiative cooling of the
supernova-heated ISM and thereby determine the dynamical evolution of
starburst-driven outflows. We detect a broad (100 km/s) and blueshifted (by 80
km/s) OVI absorption-line arising in the previously-known galactic outflow. The
properties of the OVI absorption are inconsistent with the standard superbubble
model in which this gas arises in a conductive interface inside the outer
shell. We show that the superbubble in NGC 1705 is blowing out of the galaxy
ISM. During blow-out, coronal-phase gas can be created by hydrodynamical mixing
as hot gas rushes out through fissures in the fragmenting shell of cool gas. As
the coronal gas cools radiatively, it can naturally produce the observed OVI
column density and outflow speed. The OVI data show that the cooling rate in
the coronal-phase gas is less than about 10% of the supernova heating rate.
Since the X-ray luminosity from hotter gas is even smaller, we conclude that
radiative losses are insignificant. The outflow should be able to vent its
metals and kinetic energy out of the galaxy. This process has potentially
important implications for the evolution of dwarf galaxies and the IGM.Comment: ApJ (in press
Vergangenes verhandeln
This study in cultural history addresses the value of past relations in Gallo-Roman and Italian discourses on social status in late antiquity. The volume examines how senatorial figures referred back to ancestors and ancient times to better position themselves in relation to their peers. At a broader level, it describes the negotiative processes surrounding the establishment of rank
Taurus Tunable Filter -- seven years of observing
The Taurus Tunable Filter (TTF) has now been in regular use for seven years
on the Anglo-Australian Telescope. The instrument was also used for three years
(1996--1999) on the William Herschel Telescope. We present a brief review of
the different applications in order to illustrate the versatility of tunable
filters in optical/IR spectrophotometric imaging. Tunable filters are now
planned or are under development for 6-10m class telescopes which ensures their
use for years to come.Comment: PASA, accepted. 20 pages, 9 figure
On the Escape of Ionizing Radiation from Starbursts
Far-ultraviolet spectra obtained with show that the strong
1036 interstellar absorption-line is essentially black in five of
the UV-brightest local starburst galaxies. Since the opacity of the neutral ISM
below the Lyman-edge will be significantly larger than in the line, these
data provide strong constraints on the escape of ionizing radiation from these
starbursts. Interpreted as a a uniform absorbing slab, the implied optical
depth at the Lyman edge is huge (). Alternatively, the areal
covering factor of opaque material is typically 94%. Thus, the fraction
of ionizing stellar photons that escape the ISM of each galaxy is small: our
conservative estimates typically yield . Inclusion of
extinction due to dust will further decrease . An analogous analysis
of the rest-UV spectrum of the star-forming galaxy at =2.7
leads to similar constraints on . These new results agree with the
constraints provided by direct observations below the Lyman edge in a few other
local starbursts. However, they differ from the recently reported properties of
star-forming galaxies at 3. We assess the idea that the strong
galactic winds seen in many powerful starbursts clear channels through their
neutral ISM. We show empirically that such outflows may be a necessary - but
not sufficient - part of the process for creating a relatively porous ISM. We
note that observations will soon document the cosmic evolution in the
contribution of star-forming galaxies to the metagalactic ionizing background,
with important implications for the evolution of the IGM.Comment: 17 pages; ApJ, in pres
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