694 research outputs found
Line and Continuum Variability in Active Galaxies
We compared optical spectroscopic and photometric data for 18 AGN galaxies
over 2 to 3 epochs, with time intervals of typically 5 to 10 years. We used the
Multi-Object Double Spectrograph (MODS) at the Large Binocular Telescope (LBT)
and compared the spectra to data taken from the SDSS database and the
literature. We find variations in the forbidden oxygen lines as well as in the
hydrogen recombination lines of these sources. For 4 of the sources we find
that, within the calibration uncertainties, the variations in continuum and
line spectra of the sources are very small. We argue that it is mainly the
difference in black hole mass between the samples that is responsible for the
different degree of continuum variability. In addition we find that for an
otherwise constant accretion rate the total line variability (dominated by the
narrow line contributions) reverberates the continuum variability with a
dependency . Since
this dependency is prominently expressed in the narrow line emission it implies
that the luminosity dominating part of the narrow line region must be very
compact with a size of the order of at least 10 light years. A comparison to
literature data shows that these findings describe the variability
characteristics of a total of 61 broad and narrow line sources.Comment: 30 pages including the appendix, 18 figures including the appendix.
Accepted 2015 September 3. Received 2015 August 24; in original form 2015
July 3 in Monthly Notices of the Royal Astronomical Societ
Sequential star formation in IRAS 06084-0611 (GGD 12-15): From intermediate-mass to high-mass stars
Context. The formation and early evolution of high- and intermediate-mass
stars towards the main sequence involves the interplay of stars in a clustered
and highly complex environment. To obtain a full census of this interaction,
the Formation and Early evolution of Massive Stars (FEMS) collaboration studies
a well-selected sample of 10 high-mass star-forming regions. Aims. In this
study we examine the stellar content of the high-mass star-forming region
centered on IRAS 06084-0611 in the Monoceros R2 cloud. Methods. Using the
near-infrared H- and K-band spectra from the VLT/SINFONI instrument on the ESO
Very Large Telescope (VLT)and photometric near-infrared NTT/SOFI, 2MASS and
Spitzer/IRAC data, we were able to determine the spectral types for the most
luminous stars in the cluster. Results. Two very young and reddened massive
stars have been detected by SINFONI: a massive Young Stellar Object (YSO) con-
sistent with an early-B spectral type and a Herbig Be star. Furthermore, stars
of spectral type G and K are detected while still in the Pre-Main Sequence
(PMS) phase. We derive additional properties such as temperatures, extinctions,
radii and masses. We present a Hertzsprung-Russell diagram and find most
objects having intermediate masses between \sim1.5-2.5 M\odot. For these stars
we derive a median cluster age of \sim4 Myr. Conclusions. Using Spitzer/IRAC
data we confirm earlier studies that the younger class 0/I objects are
centrally located while the class II objects are spread out over a larger area,
with rough scale size radii of \sim0.5 pc and \sim1.25 pc respectively.
Moreover, the presence of a massive YSO, an ultracompact H ii region and highly
reddened objects in the center of the cluster suggest a much younger age of < 1
Myr. A possible scenario for this observation would be sequential star
formation along the line of sight; from a cluster of intermediate-mass to
high-mass stars.Comment: 14 pages, 10 figures, 2 tables. Astronomy and Astrophysic
SUBARU and e-Merlin observations of NGC3718. Diaries of an SMBH recoil?
NGC3718 is a LINER galaxy, lying at a distance of about
Mpc away from earth and its similarities with NGC5128 often award it the name
"northern Centaurus A". We use high angular resolution ( mas) e-Merlin
radio and SUBARU NIR ( mas) data, to take a detailed view of the
processes taking place in its central region. In order to preserve some
objectivity in our interpretation, we combine our results with literature
values and findings from previous studies. Our NIR maps suggest, on one hand,
that towards the stellar bulge there are no large scale absorption phenomena
caused by the apparent dust lane and, on the other, that there is a significant
(local) contribution from hot ( K) dust to the nuclear NIR emission.
The position where this takes place appears to be closer to the offset compact
radio emission from our e-Merlin cm map, lying offset by pc from
the center of the underlying stellar bulge. The shape of the radio map suggests
the presence of one (or possibly two, forming an X-shape) bipolar structure(s)
() arcsec across, which combined with the balance between the
gas and the stellar velocity dispersions and the presence of hard X-ray
emission, point towards effects expected by AGN feedback. We also argue that
NGC3718 has a "core" in its surface brightness profile, despite the fact that
it is a gas-rich galaxy and we discuss its mixed photometric and spectroscopic
characteristics. The latter combined with the observed spatial and radio
offsets, the relative redshift between the broad and the narrow
line, the limited star formation activity and AGN
feedback, strongly imply the existence of an SMBH recoil. Finally, we discuss a
possible interpretation, that could naturally incorporate all these findings
into one physically consistent picture.Comment: 18 pages, 18 figures, 3 tables, accepted for publications in A&
Plasma Cholesterol Ester Fatty Acids: A New Biochemical Abnormality in Obstructive Jaundice
Changes in fatty acid patterns may explain many of the observed abnormalities found in
obstructive jaundice. This study looked at fatty acids in plasma cholesterol esters, in a group of
patients with obstructive jaundice and a matched group of controls. Significant abnormalities
were demonstrated, most importantly a fall in essential fatty acids, in the jaundiced group.
Overall the saturation of this fraction, as assessed by double bond index, rose. The essential fatty
acids are important as factors in membrane function and as precursors of eicosanoids. The
abnormalities found in this study provide further evidence of the significance of EFA in patients
with obstructive jaundice
Peer-review in a world with rational scientists: Toward selection of the average
One of the virtues of peer review is that it provides a self-regulating
selection mechanism for scientific work, papers and projects. Peer review as a
selection mechanism is hard to evaluate in terms of its efficiency. Serious
efforts to understand its strengths and weaknesses have not yet lead to clear
answers. In theory peer review works if the involved parties (editors and
referees) conform to a set of requirements, such as love for high quality
science, objectiveness, and absence of biases, nepotism, friend and clique
networks, selfishness, etc. If these requirements are violated, what is the
effect on the selection of high quality work? We study this question with a
simple agent based model. In particular we are interested in the effects of
rational referees, who might not have any incentive to see high quality work
other than their own published or promoted. We find that a small fraction of
incorrect (selfish or rational) referees can drastically reduce the quality of
the published (accepted) scientific standard. We quantify the fraction for
which peer review will no longer select better than pure chance. Decline of
quality of accepted scientific work is shown as a function of the fraction of
rational and unqualified referees. We show how a simple quality-increasing
policy of e.g. a journal can lead to a loss in overall scientific quality, and
how mutual support-networks of authors and referees deteriorate the system.Comment: 5 pages 4 figure
Nuclear Activity and the Conditions of Star-formation at the Galactic Center
The Galactic Center is the closest galactic nucleus that can be studied with
unprecedented angular resolution and sensitivity. We summarize recent basic
observational results on Sagittarius A* and the conditions for star formation
in the central stellar cluster. We cover results from the radio, infrared, and
X-ray domain and include results from simulation as well. From (sub-)mm and
near-infrared variability and near-infrared polarization data we find that the
SgrA* system (supermassive black hole spin, a potential temporary accretion
disk and/or outflow) is well ordered in its geometrical orientation and in its
emission process that we assume to reflect the accretion process onto the
supermassive black hole (SMBH).Comment: 11 pages, 4 figures, 1 table; published in PoS-SISSA Proceedings of
the: Frontier Research in Astrophysics - II, 23-28 May 2016, Mondello
(Palermo), Ital
Inhibition of hepatocyte growth factor-induced motility and in vitro invasion of human colon cancer cells by gamma-linolenic acid.
In this study we have determined the effects of the n-6 essential fatty acid gamma-linolenic acid (GLA) on the motility and invasive/metastatic nature of the human colon cancer cell lines HT115, HT29 and HRT18. Cell motility was induced by hepatocyte growth factor/scatter factor (HGF/SF) and measured by both colony scattering and dissociation from carrier beads. Invasiveness was measured in vitro by cellular invasion into extracellular matrix. At concentrations up to 100 microM (which had no effect on cell growth over the duration of the experiments) both cell motility and invasion induced by HGF/SF were markedly reduced by GLA and its lithium salt. The attachment of these cells to the extracellular matrix components (Matrigel and fibronectin) was also inhibited. There were also changes in the cell-surface E-cadherin, but not fibronectin receptor at similar concentrations. It is concluded that n-6 essential fatty acids have the ability to inhibit both motility and invasiveness of human colon cancer cells, perhaps by modifying cell-surface adhesion molecules
Treatment of premenstrual tension with lithium carbonate – A PILOT STUDY
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66408/1/j.1600-0447.1980.tb00569.x.pd
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