100 research outputs found
The night-sky at the Calar Alto Observatory II: The sky at the near infrared
We present here the characterization of the night sky-brightness at the
near-infrared, the telescope seeing, and the fraction of useful time at the
Calar Alto observatory. For this study we have collected a large dataset
comprising 7311 near-infrared images taken regularly along the last four years
for the ALHAMBRA survey (J, H and Ks-bands), together with a more reduced
dataset of additional near-infrared images taken for the current study. In
addition we collected the information derived by the meteorological station at
the observatory during the last 10 years, together with the results from the
cloud sensor for the last ~2 years. We analyze the dependency of the
near-infrared night sky-brightness with the airmass and the seasons, studying
its origins and proposing a zenithal correction. A strong correlation is found
between the night sky-brightness in the Ks-band and the air temperature, with a
gradient of ~ -0.08 mag per 1 C degree. The typical (darkest) night
sky-brightness in the J, H and Ks-band are 15.95 mag (16.95 mag), 13.99 mag
(14.98 mag) and 12.39 mag (13.55 mag), respectively. These values show that
Calar Alto is as dark in the near-infrared as most of the other astronomical
astronomical sites in the world that we could compare with. Only Mauna Kea is
clearly darker in the Ks-band. The typical telescope seeing at the 3.5m is
~1.0" when converted to the V-band, being only slightly larger than the
atmospheric seeing measured at the same time by the seeing monitor, ~0.9".
Finally we estimate the fraction of useful time based on the relative humidity,
gust wind speed and presence of clouds. This fraction, ~72%, is very similar to
the one derived in Paper I, based on the fraction of time when the extinction
monitor is working.Comment: 15 pages, 6 figures, accepted to be published in PAS
Analysis of the Interaction Effects in the Southern Galaxy Pair Tol1238-364 and ESO381-G009
In the context of the connection among galaxy-galaxy interaction, starbursts
and nuclear activity, we present and discuss a quantitative morphological
analysis based on BVR images and a detailed spectroscopic investigation of two
interacting galaxies, the Seyfert 2 Tol1238-364 (IC 3639) and its companion
ESO381-G009, forming a triple system with ESO381-G006. Broad-band optical
photometry is complemented by Halpha imaging, which provides information about
the distribution of star forming regions across the galaxies. Long-slit
spectroscopic data obtained at different position angles of the slit are
employed to determine the physical conditions of circumnuclear and extranuclear
regions. A mixture of thermal and non-thermal ionizing radiation is found in
the surroundings of the nucleus of Tol1238-364 and the energy budget supports
the presence of a circumnuclear starburst.Several regions in both the galaxies
show anomalous line ratios: additional ionization by shock-heating and low
ionization of some extranuclear HII regions are suggested as possible
explanations. An analysis of the emission-line profiles reveals the presence of
a broad Halpha component in the nuclear region of Tol1238-364. Independent
estimates of the star formation rates (SFR) were obtained through
flux-calibrated Halpha-images and FIR emission in the four IRAS bands. Overall
SFR densities have been compared with the SFR densities derived from Halpha
emission in the individual regions of the galaxies sampled by long-slit
spectra. In both galaxies an enhancement of the star formation activity with
respect to isolated galaxies is revealed. The prevalence of starburst or
nuclear activity has been examined through FIR color indices. The interaction
scenario is discussed on the basis of the observed galaxy properties.Comment: Tentatively scheduled for publication in ApJS, v184 n2 October 2003
issue. A version with full resolution figures is available as unedited
preprint at http://www.journals.uchicago.edu/ApJ/future.htm
Evolutionary analysis implicates RNA polymerase II pausing and chromatin structure in nematode piRNA biogenesis
Piwi-interacting RNAs (piRNAs) control transposable elements widely across metazoans but have rapidly evolving biogenesis pathways. In Caenorhabditis elegans, almost all piRNA loci are found within two 3Mb clusters on Chromosome IV. Each piRNA locus possesses an upstream motif that recruits RNA polymerase II to produce a ~28 nt precursor transcript. Here, we use comparative epigenomics across nematodes to gain insight into piRNA biogenesis. We show that the piRNA upstream motif is derived from core promoter elements controlling snRNA biogenesis. We describe two alternative modes of piRNA organisation in nematodes: in C. elegans and closely related nematodes, piRNAs are clustered within repressive H3K27me3 chromatin, whilst in other species, typified by Pristionchus pacificus, piRNAs are distributed genome-wide within introns of actively transcribed genes. In both groups, piRNA production depends on downstream sequence signals associated with RNA polymerase II pausing, which synergise with the chromatin environment to control piRNA precursor transcription
M31N 2007-11d: A Slowly-Rising, Luminous Nova in M31
We report a series of extensive photometric and spectroscopic observations of
the luminous M31 nova M31N 2007-11d. Our photometric observations coupled with
previous measurements show that the nova took at least four days to reach peak
brightness at R~14.9 on 20 Nov 2007 UT. After reaching maximum, the time for
the nova to decline 2 and 3 magnitudes from maximum light (t_2 and t_3) was
~9.5 and ~13 days, respectively, establishing that M31N 2007-11d was a
moderately fast declining nova. During the nova's evolution a total of three
spectra were obtained. The first spectrum was obtained one day after maximum
light (5 days post-discovery), followed by two additional spectra taken on the
decline at two and three weeks post-maximum. The initial spectrum reveals
narrow Balmer and Fe II emission with P Cygni profiles superimposed on a blue
continuum. These data along with the spectra obtained on the subsequent decline
clearly establish that M31N 2007-11d belongs to the Fe II spectroscopic class.
The properties of M31N 2007-11d are discussed within the context of other
luminous novae in M31, the Galaxy, and the LMC. Overall, M31N 2007-11d appears
to be remarkably similar to Nova LMC 1991, which was another bright,
slowly-rising, Fe II nova. A comparison of the available data for luminous
extragalactic novae suggest that the >~4 day rise to maximum light seen in M31N
2007-11d may not be unusual, and that the rise times of luminous Galactic
novae, usually assumed to be <~2 days, may have been underestimated.Comment: Accepted for publication in The Astrophysical Journal (28 pages, 6
figures
Endogenous Signaling by Omega-3 Docosahexaenoic Acid-derived Mediators Sustains Homeostatic Synaptic and Circuitry Integrity
The harmony and function of the complex brain circuits and synapses are sustained mainly by excitatory and inhibitory neurotransmission, neurotrophins, gene regulation, and factors, many of which are incompletely understood. A common feature of brain circuit components, such as dendrites, synaptic membranes, and other membranes of the nervous system, is that they are richly endowed in docosahexaenoic acid (DHA), the main member of the omega-3 essential fatty acid family. DHA is avidly retained and concentrated in the nervous system and known to play a role in neuroprotection, memory, and vision. Only recently has it become apparent why the surprisingly rapid increases in free (unesterified) DHA pool size take place at the onset of seizures or brain injury. This phenomenon began to be clarified by the discovery of neuroprotectin D1 (NPD1), the first-uncovered bioactive docosanoid formed from free DHA through 15-lipoxygenase-1 (15-LOX-1). NPD1 synthesis includes, as agonists, oxidative stress and neurotrophins. The evolving concept is that DHA-derived docosanoids set in motion endogenous signaling to sustain homeostatic synaptic and circuit integrity. NPD1 is anti-inflammatory, displays inflammatory resolving activities, and induces cell survival, which is in contrast to the pro-inflammatory actions of the many of omega-6 fatty acid family members. We highlight here studies relevant to the ability of DHA to sustain neuronal function and protect synapses and circuits in the context of DHA signalolipidomics. DHA signalolipidomics comprises the integration of the cellular/tissue mechanism of DHA uptake, its distribution among cellular compartments, the organization and function of membrane domains containing DHA phospholipids, and the precise cellular and molecular events revealed by the uncovering of signaling pathways regulated by docosanoids endowed with prohomeostatic and cell survival bioactivity. Therefore, this approach offers emerging targets for prevention, pharmaceutical intervention, and clinical translation involving DHA-mediated signaling
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