848 research outputs found
Recent activity of the Be/X-ray binary system SAX J2103.5+4545
Aims. We present a multiwavelength study of the Be/X-ray binary system SAX
J2103.5+4545 with the goal of better characterizing the transient behaviour of
this source.
Methods. SAX J2103.5+4545 was observed by Swift-XRT four times in 2007 from
April 25 to May 5, and during quiescence in 2012 August 31. In addition, this
source has been monitored from the ground-based astronomical observatories of
El Teide (Tenerife, Spain), Roque de los Muchachos (La Palma, Spain) and Sierra
Nevada (Granada, Spain) since 2011 August, and from the TUBITAK National
Observatory (Antalya, Turkey) since 2009 June. We have performed spectral and
photometric temporal analyses in order to investigate the different states
exhibited by SAX J2103.5+4545.
Results. In X-rays, an absorbed power law model provided the best fit for all
the XRT spectra. An iron-line feature at ~6.42 keV was present in all the
observations except for that taken during quiescence in 2012. The photon
indexes are consistent with previous studies of SAX J2103.5+4545 in high/low
luminosity states. Pulsations were found in all the XRT data from 2007
(2.839(2) mHz; MJD 54222.02), but not during quiescence. Both optical outbursts
in 2010 and 2012 lasted for about 8/9 months (as the one in 2007 probably did
and the current one in 2014 might do) and were most probably caused by mass
ejection events from the Be star that eventually fed the circumstellar disc.
All of these outbursts started about 3 months before the triggering of the
X-ray activity, and about the same period before the maximum of the H_alpha
line equivalent width (in emission) was reached at only ~ -5 \AA. In this work
we found that the global correlation between the BV variability and the X-ray
intensity was also observed at longer wavelengths in the IR domain.Comment: 11 pages, 7 figures, and online material (2 tables). Submitted to A&A
in 2014 Januar
Photometry of Be Stars in the vicinity of COROT primary targets for asteroseismology
We present differential photometry of Be stars close to potential COROT
primary targets for asteroseismology. Several stars are found to be short
period variables. We propose them to be considered as secondary targets in the
COROT asteroseismology fields.Comment: 7 pages, 6 figures, submitted to Communications in Asteroseismolog
A 0535+26: an X-ray/Optical Tour
We compiled X-ray and Optical observations of the accreting X-ray binary
system A 0535+262 since its discovery in 1975, that will allow us to shed light
on the unpredictable behavior of this binary system. We present the data in
terms of the Be-disk interaction with the neutron star companion. In addition,
we show recent results from the continuous monitoring of this source by the
Gamma-ray Burst Monitor(GBM), on board the Fermi observatory, since its launch
in 2008 June 11.Comment: 4 pages, 5 figures, Conference proceeding of "Astrophysics of Neutron
Stars 2010 - a conference in honor of M. Ali Alpar", 2-6 August 2010, Cesme,
Izmir, Turke
A multiscale agent-based in silico model of liver fibrosis progression
Chronic hepatic inflammation involves a complex interplay of inflammatory and mechanical influences, ultimately manifesting in a characteristic histopathology of liver fibrosis. We created an agent-based model (ABM) of liver tissue in order to computationally examine the consequence of liver inflammation. Our liver fibrosis ABM (LFABM) is comprised of literature-derived rules describing molecular and histopathological aspects of inflammation and fibrosis in a section of chemically injured liver. Hepatocytes are modeled as agents within hexagonal lobules. Injury triggers an inflammatory reaction, which leads to activation of local Kupffer cells and recruitment of monocytes from circulation. Portal fibroblasts and hepatic stellate cells are activated locally by the products of inflammation. The various agents in the simulation are regulated by above-threshold concentrations of pro- and anti-inflammatory cytokines and damage-associated molecular pattern molecules. The simulation progresses from chronic inflammation to collagen deposition, exhibiting periportal fibrosis followed by bridging fibrosis, and culminating in disruption of the regular lobular structure. The ABM exhibited key histopathological features observed in liver sections from rats treated with carbon tetrachloride (CCl4). An in silico "tension test" for the hepatic lobules predicted an overall increase in tissue stiffness, in line with clinical elastography literature and published studies in CCl4-treated rats. Therapy simulations suggested differential anti-fibrotic effects of neutralizing tumor necrosis factor alpha vs. enhancing M2 Kupffer cells. We conclude that a computational model of liver inflammation on a structural skeleton of physical forces can recapitulate key histopathological and macroscopic properties of CCl4-injured liver. This multiscale approach linking molecular and chemomechanical stimuli enables a model that could be used to gain translationally relevant insights into liver fibrosis
A photometric study of Be stars located in the seismology fields of COROT
Context. In preparation for the COROT mission, an exhaustive photometric study of Be stars located in the seismology fields of the mission has been performed. The very precise and long-time-spanned photometric observations gathered by the COROT satellite will give important clues on the origin of the Be phenomenon. Aims. The aim of this work is to find short-period variable Be stars located in the seismology fields of COROT, and to study and characterise their pulsational properties.
Methods. Light curves obtained at the Observatorio de Sierra Nevada, together with data from Hipparcos and ASAS-3 for a total of 84 Be stars, were analysed in order to search for short-term variations. We applied standard Fourier techniques and non-linear least-square fitting to the time series. Results. We found 7 multiperiodic, 21 mono-periodic and 26 non-variable Be stars. Short-term variability was detected in 74% of early-type Be stars and in 31% of mid- to late-type Be stars. We show that non-radial pulsations are more frequent among Be stars than in slow-rotating B stars of the same spectral [email protected]; [email protected]
T35: a small automatic telescope for long-term observing campaigns
The T35 is a small telescope (14") equipped with a large format CCD camera
installed in the Sierra Nevada Observatory (SNO) in Southern Spain. This
telescope will be a useful tool for the detecting and studying pulsating stars,
particularly, in open clusters. In this paper, we describe the automation
process of the T35 and show also some images taken with the new
instrumentation.Comment: 13 pages, 9 figures. Accepted for publication in the special issue
"Robotic Astronomy" of Advances of Astronom
Detection of a large Be circumstellar disk during X-ray quiescence of XTE J1946+274
We present a multiwavelength study of the Be/X-ray binary system XTE
J1946+274 with the main goal of better characterizing its behavior during X-ray
quiescence. We aim to shed light on the mechanism which triggers the X-ray
activity for this source. XTE J1946+274 was observed by Chandra-ACIS during
quiescence in 2013 March 12. In addition, this source has been monitored from
the ground-based astronomical observatories of El Teide (Tenerife, Spain),
Roque de los Muchachos (La Palma, Spain) and Sierra Nevada (Granada, Spain)
since 2011 September, and from the TUBITAK National Observatory (Antalya,
Turkey) since 2005 April. We have performed spectral and photometric temporal
analyses in order to investigate the quiescent state and transient behavior of
this binary system. In 2006, a long mass ejection event took place from the Be
star, lasting for about seven years. We also found that a large Be
circumstellar disk was present during quiescence, although major X-ray activity
was not observed. We made an attempt to explain this scenario by assuming the
permanently presence of a tilted and warped Be circumstellar disk. The 0.3-10
keV X-ray spectrum during quiescence was well fitted with either an absorbed
blackbody or absorbed power-law models. The main parameters obtained for these
models were kT=1.43+/-0.17 and Gamma=0.9+/-0.4 (with N_H~2-7E+22 cm-2). The
0.3-10 keV flux of the source was ~0.8E-12 erg-1 cm-2 s-1. Pulsations were
found with P_pulse=15.757(1) s (MJD 56363.115) and an rms pulse fraction of
32.1(3)%. The observed X-ray luminosity during quiescent periods may be
explained by the neutron star being in supersonic propeller regimen.Comment: 9 pages, 7 figures, accepte
The Carotenogenesis Pathway via the Isoprenoid-β-carotene Interference Approach in a New Strain of Dunaliella salina Isolated from Baja California Mexico
D. salina is one of the recognized natural sources to produce β-carotene, and an useful model for studying the role of inhibitors and enhancers of carotenogenesis. However there is little information in D. salina regarding whether the isoprenoid substrate can be influenced by stress factors (carotenogenic) or selective inhibitors which in turn may further contribute to elucidate the early steps of carotenogenesis and biosynthesis of β-carotene. In this study, Dunaliella salina (BC02) isolated from La Salina BC Mexico, was subjected to the method of isoprenoids-β-carotene interference in order to promote the interruption or accumulation of the programmed biosynthesis of carotenoids. When Carotenogenic and non-carotenogenic cells of D. salina BC02 were grown under photoautotrophic growth conditions in the presence of 200 µM fosmidomycin, carotenogenesis and the synthesis of β-carotene were interrupted after two days in cultured D. salina cells. This result is an indirect consequence of the inhibition of the synthesis of isoprenoids and activity of the recombinant DXR enzyme thereby preventing the conversion of 1-deoxy-D-xylulose 5-phosphate (DXP) to 2-C-methyl-D-erythritol (MEP) and consequently interrupts the early steps of carotenogenesis in D. salina. The effect at the level of proteins and RNA was not evident. Mevinolin treated D. salina cells exhibited carotenogenesis and β-carotene levels very similar to those of control cell cultures indicating that mevinolin not pursued any indirect action in the biosynthesis of isoprenoids and had no effect at the level of the HMG-CoA reductase, the key enzyme of the Ac/MVA pathway
X-Ray and Optical Observations of A 0535+26
We present recent contemporaneous X-ray and optical observations of the
Be/X-ray binary system A\,0535+26 with the \textit{Fermi}/Gamma-ray Burst
Monitor (GBM) and several ground-based observatories. These new observations
are put into the context of the rich historical data (since 1978) and
discussed in terms of the neutron star Be-disk interaction. The Be
circumstellar disk was exceptionally large just before the 2009 December giant
outburst, which may explain the origin of the unusual recent X-ray activity of
this source. We found a peculiar evolution of the pulse profile during this
giant outburst, with the two main components evolving in opposite ways with
energy. A hard 30-70 mHz X-ray QPO was detected with GBM during this 2009
December giant outburst. It becomes stronger with increasing energy and
disappears at energies below 25\,keV. In the long-term a strong optical/X-ray
correlation was found for this system, however in the medium-term the
H EW and the V-band brightness showed an anti-correlation after
2002 Agust. Each giant X-ray outburst occurred during a decline phase of
the optical brightness, while the H showed a strong emission. In late
2010 and before the 2011 February outburst, rapid V/R variations are observed
in the strength of the two peaks of the H line. These had a period of
\,25 days and we suggest the presence of a global one-armed oscillation
to explain this scenario. A general pattern might be inferred, where the disk
becomes weaker and shows V/R variability beginning \,6 months following a
giant outburst.Comment: 18, 11 figures, 1 tabl
- …