157 research outputs found
Exciting Maser Science with New Instruments - the Promise of the EVLA
In the near future, the Expanded Very Large Array (EVLA) will allow surveys
for maser sources with unprecedented sensitivity, spectral coverage and
spectroscopic capabilities. In particular, comprehensive surveys for many maser
species with simultaneous sensitive continuum imaging and absorption studies
will give a comprehensive radio picture of star formation in the Galactic plane
and elsewhere. Very efficient EVLA surveys for H2O megamasers in Active Galacic
Nuclei will be possible to practically arbitrary redshifts.
EVLA and Atacama Large Millimeter Array (ALMA) studies of H2O and SiO masers
will serve as high resolution probes of the innermost envelopes of oxygen-rich
evolved stars and HCN masers of carbon-rich stars.
Farther in the future, the Square Kilometer Array (SKA) promises the
detection of OH gigamasers at all conceivable redshifts and maser astrometry
with unprecedented accuracy.Comment: 10 pages, incl. 4 figures, iaus.cls, to appear the Procedings of IAU
Symp. 242 (Astrophysical masers and their environments) eds. J. Chapman & W.
Baan Replaced version with a few typos correcte
The Incidence of Highly-Obscured Star-Forming Regions in SINGS Galaxies
Using the new capabilities of the Spitzer Space Telescope and extensive
multiwavelength data from the Spitzer Infrared Nearby Galaxies Survey (SINGS),
it is now possible to study the infrared properties of star formation in nearby
galaxies down to scales equivalent to large HII regions. We are therefore able
to determine what fraction of large, infrared-selected star-forming regions in
normal galaxies are highly obscured and address how much of the star formation
we miss by relying solely on the optical portion of the spectrum. Employing a
new empirical method for deriving attenuations of infrared-selected
star-forming regions we investigate the statistics of obscured star formation
on 500pc scales in a sample of 38 nearby galaxies. We find that the median
attenuation is 1.4 magnitudes in H-alpha and that there is no evidence for a
substantial sub-population of uniformly highly-obscured star-forming regions.
The regions in the highly-obscured tail of the attenuation distribution
(A_H-alpha > 3) make up only ~4% of the sample of nearly 1800 regions, though
very embedded infrared sources on the much smaller scales and lower
luminosities of compact and ultracompact HII regions are almost certainly
present in greater numbers. The highly-obscured cases in our sample are
generally the bright, central regions of galaxies with high overall attenuation
but are not otherwise remarkable. We also find that a majority of the galaxies
show decreasing radial trends in H-alpha attenuation. The small fraction of
highly-obscured regions seen in this sample of normal, star-forming galaxies
suggests that on 500pc scales the timescale for significant dispersal or break
up of nearby, optically-thick dust clouds is short relative to the lifetime of
a typical star-forming region.Comment: Accepted for publication in ApJ; emulateapj style, 30 pages, 18
figures (compressed versions), 3 table
Millimeter multiplicity in DR21(OH): outflows, molecular cores and envelopes
We present sensitive high angular resolution ( 1) millimeter
continuum and line observations from the massive star forming region DR21(OH)
located in the Cygnus X molecular cloud. Within the well-known dusty MM1-2
molecular cores, we report the detection of a new cluster of about ten compact
continuum millimeter sources with masses between 5 and 24 M, and sizes
of a few thousands of astronomical units. These objects are likely to be large
dusty envelopes surrounding massive protostars, some of them most probably
driving several of the outflows that emanate from this region. Additionally, we
report the detection of strong millimeter emission of formaldehyde (HCO)
and methanol (CHOH) near 218 GHz as well as compact emission from the
typical outflow tracers carbon monoxide and silicon monoxide (CO and SiO)
toward this massive star-forming region. The HCO and CHOH emission is
luminous ( 10 L), well resolved, and found along the
collimated methanol maser outflow first identified at centimeter wavelengths
and in the sources SMA6 and SMA7. Our observations suggest that this maser
outflow might be energized by a millimeter source called SMA4 located in the
MM2 dusty core. The CO and SiO emission traces some other collimated outflows
that emanate from MM1-2 cores, and are not related with the low velocity maser
outflow.Comment: Accepted to Ap
Rednerinnen und Redner
Der vorliegende Band dokumentiert Reden, die zur Amtseinführung von Prof. Dr.-Ing. habil. Monika Auweter-Kurtz als Präsidentin der Universität Hamburg am 1. Februar 2007 gehalten wurden.This volume documents speeches given at the inauguration of Prof. Dr. -Ing. habil. Monika Auweter-Kurtz as President of the University of Hamburg on 1 February 200
Expanded Very Large Array Continuum Observations toward Hot Molecular Core Candidates
We have used the Expanded Very Large Array (EVLA) with two 1 GHz wide bands to obtain K-band (1.3 cm) continuum observations toward the following five hot molecular core candidates: IRAS 18151 – 1208, IRAS 18182 – 1433, IRAS 18345 – 0641, IRAS 18470 – 0044, and IRAS 19012 + 0536. The sources were selected from the 2002 list of Sridharan et al. and are characterized by high FIR luminosity, dense molecular and dust condensations, massive large-scale CO flows, and the absence of strong cm continuum emission. These properties are indicative of massive star-forming regions in an evolutionary phase prior to ultra- or hypercompact H II regions. We detect a total of 10 individual 1.3 cm continuum sources toward this sample, and derive in-band spectral indices between 19.3 and 25.5 GHz consistent with thermal free-free emission, for all sources except component A in IRAS 18182 – 1433, which has a negative spectral index indicative of synchrotron emission. We suggest that in most cases the 1.3 cm sources are due to shock-induced ionization, rather than direct photoionization by massive objects. The momentum rate present in these ionized flows is sufficient to drive the large-scale molecular flows. We discuss a number of morphological features supporting this hypothesis. The present observations demonstrate that the EVLA has sufficient sensitivity to study the regions near very young massive stars in the cm continuum
From North Africa to Latin America and back: comparative findings and theoretical reflections
Taking the different case studies of the book together, one general observation stands out: Key agents of socioeconomic contention, including movements by organized labor and the unemployed that were important in the run-up to the uprisings and that saw their political opportunities open up in the immediate aftermath of the revolutions, have since been effectively marginalized as political actors. The concluding chapter reflects on the causes of this weakness of socioeconomic contention by identifying comparative insights that emerge from the contributions to this volume and by situating them in the context of broader comparative and theoretical debates on the relationship between social movements and political change. More specifically, the chapter first discusses Egypt’s and Tunisia’s post-revolutionary trajectories from a comparative perspective. Second, it discusses these comparative findings in the light of experiences in Latin America. Third, drawing again on comparative scholarship on Latin America, the chapter offers a theoretical interpretation of some of the main dynamics observed in Egypt and Tunisia based on the notion of a popular-sector incorporation crisis. Fourth and finally, the chapter concludes with general implications and an outlook
Mitochondrial 2,4-dienoyl-CoA Reductase Deficiency in Mice Results in Severe Hypoglycemia with Stress Intolerance and Unimpaired Ketogenesis
The mitochondrial β-oxidation system is one of the central metabolic pathways of energy metabolism in mammals. Enzyme defects in this pathway cause fatty acid oxidation disorders. To elucidate the role of 2,4-dienoyl-CoA reductase (DECR) as an auxiliary enzyme in the mitochondrial β-oxidation of unsaturated fatty acids, we created a DECR–deficient mouse line. In Decr−/− mice, the mitochondrial β-oxidation of unsaturated fatty acids with double bonds is expected to halt at the level of trans-2, cis/trans-4-dienoyl-CoA intermediates. In line with this expectation, fasted Decr−/− mice displayed increased serum acylcarnitines, especially decadienoylcarnitine, a product of the incomplete oxidation of linoleic acid (C18:2), urinary excretion of unsaturated dicarboxylic acids, and hepatic steatosis, wherein unsaturated fatty acids accumulate in liver triacylglycerols. Metabolically challenged Decr−/− mice turned on ketogenesis, but unexpectedly developed hypoglycemia. Induced expression of peroxisomal β-oxidation and microsomal ω-oxidation enzymes reflect the increased lipid load, whereas reduced mRNA levels of PGC-1α and CREB, as well as enzymes in the gluconeogenetic pathway, can contribute to stress-induced hypoglycemia. Furthermore, the thermogenic response was perturbed, as demonstrated by intolerance to acute cold exposure. This study highlights the necessity of DECR and the breakdown of unsaturated fatty acids in the transition of intermediary metabolism from the fed to the fasted state
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