708 research outputs found
Two new pulsating low-mass pre-white dwarfs or SX Phenix stars?*
Context. The discovery of pulsations in low-mass stars opens an opportunity
for probing their interiors and to determine their evolution, by employing the
tools of asteroseismology. Aims. We aim to analyze high-speed photometry of
SDSSJ145847.02070754.46 and SDSSJ173001.94070600.25 and discover
brightness variabilities. In order to locate these stars in the diagram we fit optical spectra (SDSS) with synthetic non-magnetic
spectra derived from model atmospheres. Methods. To carry out this study, we
used the photometric data obtained by us for these stars with the 2.15m
telescope at CASLEO, Argentina. We analyzed their light curves and we apply the
Discrete Fourier Transform to determine the pulsation frequencies. Finally, we
compare both stars in the diagram, with known two
pre-white dwarfs, seven pulsating pre-ELM white dwarf stars, Scuti and
SX Phe stars. Results. We report the discovery of pulsations in
SDSSJ145847.02070754.46 and SDSSJ173001.94070600.25. We determine their
effective temperature and surface gravity to be = 7 972 200
K, = 4.25 0.5 and = 7 925 200 K, =
4.25 0.5, respectively. With these parameters these new pulsating
low-mass stars can be identified with either ELM white dwarfs (with ~ 0.17 Mo)
or more massive SX Phe stars. We identified pulsation periods of 3 278.7 and 1
633.9 s for SDSSJ145847.02070754.46 and a pulsation period of 3 367.1 s for
SDSSJ173001.94070600.25. These two new objects together with those of Maxted
et al. (2013, 2014) indicate the possible existence of a new instability domain
towards the late stages of evolution of low-mass white dwarf stars, although
their identification with SX Phe stars cannot be discarded.Comment: 5 pages, 5 figures, 1 table, accepted for publication in A&A
Effect of biofilm formation in a hostile oxidative stress environment on the survival of Campylobacter jejuni recovered from poultry in Iraqi markets
Background and Aim: Campylobacter jejuni is a major contributor to bacterial enteritis, a common health problem. The resistance of this microaerophilic bacterium to oxidative stress allows it to thrive under aerobic conditions. This study aimed to investigate whether the capacity of C. jejuni to form biofilms in the presence of oxidative stress contributes to the pathogen’s ability to thrive in agricultural settings as well as in chicken slaughter lines.
Materials and Methods: Twenty identified strains originating from chicken samples (eight from caeca contents and 12 from frozen chicken carcasses) were previously isolated and identified according to standard bacteriological protocols, followed by confirmation at the species level using multiplex polymerase chain reaction assay. Crystal violet staining was used to evaluate biofilm formation by these bacteria. Two exposure periods to gaseous ozone (1 and 2 min) were used to assess resistance to oxidative damage.
Results: Most of the strong biofilm-forming Campylobacter strains came from imported frozen chicken meat (25%), whereas only 10% came from caeca content. After exposure to gaseous ozone at 600 mg/h for 2 min, strong biofilm-producing strains exhibited a higher survival rate with a limited reduction of up to 3 logs, whereas negative biofilm-producing strains exhibited a limited survival rate with a reduction of 6 logs.
Conclusion: Based on our findings, we hypothesized that the presence of C. jejuni strains capable of forming biofilms in poultry farms and/or chicken production facilities triggers a public health alarm as this bacterium seems to be able to adapt more easily to live and thrive in hostile environmental conditions
The pulsating DA white dwarf star EC 14012-1446: results from four epochs of time-resolved photometry
The pulsating DA white dwarfs are the coolest degenerate stars that undergo
self-driven oscillations. Understanding their interior structure will help to
understand the previous evolution of the star. To this end, we report the
analysis of more than 200 h of time-resolved CCD photometry of the pulsating DA
white dwarf star EC 14012-1446 acquired during four observing epochs in three
different years, including a coordinated three-site campaign. A total of 19
independent frequencies in the star's light variations together with 148
combination signals up to fifth order could be detected. We are unable to
obtain the period spacing of the normal modes and therefore a mass estimate of
the star, but we infer a fairly short rotation period of 0.61 +/- 0.03 d,
assuming the rotationally split modes are l=1. The pulsation modes of the star
undergo amplitude and frequency variations, in the sense that modes with higher
radial overtone show more pronounced variability and that amplitude changes are
always accompanied by frequency variations. Most of the second-order
combination frequencies detected have amplitudes that are a function of their
parent mode amplitudes, but we found a few cases of possible resonantly excited
modes. We point out the complications in the analysis and interpretation of
data sets of pulsating white dwarfs that are affected by combination
frequencies of the form f_A+f_B-f_C intruding into the frequency range of the
independent modes.Comment: 14 pages, 6 figures, 6 tables. MNRAS, in pres
Towards a pure ZZ Ceti instability strip
We have observed again two stars inside the ZZ Ceti instability strip that
were previously classified as not-observed-to-vary (NOV) by Mukadam et al.
(2004) and found them to be low-amplitude variables. Some evidence points to a
pure ZZ Ceti instability strip; other evidence contests it. The two stars
previously classified as NOV have Sloan Digital Sky Survey (SDSS) spectroscopic
effective temperatures that place them inside the ZZ Ceti instability strip,
and they were "contaminating" the strip as constant stars, which could indicate
that the instability strip was no longer a simple evolutionary stage. A pure
instability strip indicates that pulsation is a normal phase which all DAs must
go through. We used effective temperatures derived from SDSS optical spectra by
comparing them with model atmospheres to look for pulsators through
time-resolved photometry and stars previously classified as NOV. Our new
results indicate, but do not prove, a pure instability strip, because there are
still other NOV stars that need to be observed again. Additionally, we have
discovered five other ZZ Ceti stars based on their effective temperatures.Comment: 12 pages, 3 figur
First spectro-interferometric survey of Be stars I. Observations and constraints on the disks geometry and kinematics
Context. Classical Be stars are hot non-supergiant stars surrounded by a
gaseous circumstellar disk that is responsible for the observed infrared-excess
and emission lines. The phenomena involved in the disk formation still remain
highly debated. Aims. To progress in the understanding of the physical process
or processes responsible for the mass ejections and test the hypothesis that
they depend on the stellar parameters, we initiated a survey on the
circumstellar environment of the brightest Be stars. Methods. To achieve this
goal, we used spectro-interferometry, the only technique that combines high
spectral (R=12000) and high spatial (=4\,mas) resolutions.
Observations were carried out at the Paranal observatory with the VLTI/AMBER
instrument. We concentrated our observations on the Br emission line to
be able to study the kinematics within the circumstellar disk. Our sample is
composed of eight bright classical Be stars : Col, CMa,
Car, p Car, Cen, Cen, Ara, and \textit{o} Aqr.
Results. We managed to determine the disk extension in the line and the nearby
continuum for most targets. We also constrained the disk kinematics, showing
that it is dominated by rotation with a rotation law close to the Keplerian
one. Our survey also suggests that these stars are rotating at a mean velocity
of V/V\,=\,0.82\,\,0.08. This corresponds to a rotational rate
of \,=\,0.95\,\,0.02 Conclusions. We did not detect
any correlation between the stellar parameters and the structure of the
circumstellar environment. Moreover, it seems that a simple model of a
geometrically thin Keplerian disk can explain most of our spectrally resolved
K-band data. Nevertheless, some small departures from this model have been
detected for at least two objects (i.e, CMa and Col).
Finally, our Be stars sample suggests that rotation is the main physical
process driving the mass-ejection. Nevertheless, smaller effects from other
mechanisms have to be taken into account to fully explain how the residual
gravity is compensated.Comment: Astronomy and Astrophysics (2011) Accepte
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Functional Gait Disorders: Clinical presentations, Phenotypes and Implications for treatment.
BACKGROUND: Functional Gait Disorders (FGD) are a common presentation of motor-Functional Neurological Disorders (motor-FND) that affect walking ability. AIM: To provide a narrative review of the current literature on FGD. METHODS: A narrative overview of published literature was undertaken, based on a systematic search of relevant databases, authoritative texts and citation tracking. RESULTS: FGD is multidimensional and disabling, with numerous phenotypes described in the literature, including 'knee buckling,' 'astasia-abasia' and 'excessive slowness.' Motor symptoms such as weakness or tremor, and non-motor symptoms, such as pain and fatigue may contribute to the disability and distress in FGD. Phenotypic features and clinical signs are seen in FGD that demonstrate inconsistency and incongruity with structural disease. A limited number of treatment studies have specifically focussed on FGD, however, reporting of outcomes from motor-FND cohorts has demonstrated short and long-term improvements in walking ability through multidisciplinary rehabilitation. CONCLUSIONS: The relative contribution of motor and non-motor symptoms in FGD remains unknown, but it is likely that non-motor symptoms increase the illness burden and should be considered during assessment and treatment. Recommended treatment for FGD involves multidisciplinary rehabilitation, but optimum treatment elements are yet to be determined
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