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International LOFAR stations, equipped with powerful backends, can be used as individual telescopes, and provide data sets complementary to those obtained with the LOFAR Core. Such “local mode” observations are particularly adapted to monitoring observations, where the advantage of having a high observing cadence (one observation per week) outweighs the reduced sensitivity of a single station when compared to the full array. With such observations, it is possible to monitor the temporal evolution of the pulsars’ behaviour via its dispersion, scattering, intensity, and profile shape. We present recent studies performed in the LOFAR low band (10-90 MHz).
The pulsar’s signal passes through the interstellar medium (ISM) which leads to both chromatic dispersive delays and multipath pulse broadening. These effects have a strong frequency dependence (f−2 and f−4 respectively). Pulse profiles of pulsars are also frequency-dependent leading to some degeneracy with the ISM imprint. Furthermore, many pulsars show a turnover of their spectrum around ~100 MHz. For all these reasons, the frequency band below 100 MHz contains a lot of information about both the pulsar emission and the ISM. Our study is based on a LOw Frequency ARray (LOFAR) monitoring campaign using the international station FR606. Firstly, we demonstrate the importance of a monitoring campaign. Secondly, we calculate median spectra and locate the turnover frequency for 3 pulsars (B0809+74, B1133+16, B1508+55).
Photometric observations of o And collected from 1994 to 1998 are presented. Neither multimodal pulsations nor rotational modulation seems able to explain completely the complex light curves, but a model based on the pulsations together with some type of magnetic activity could be applicable.
The star 53 Psc (HD 3379, B2.5IV) has been observed as variable by several authors (Sareyan et al., 1979) with frequencies around 10 c d–1 and has been classified as a β Cephei star. Conversely, other authors (e.g. Percy, 1971) found it to be constant.
New high resolution, high signal-to-noise ratio, Spectroscopic observations have been performed at the Observatoire de Haute-Provence in 1996 over 11 nights. The spectral domain covers around 200 Å and is centered on Hδ. Radial velocities were deduced from an auto-correlation technique with a scatter around 0.4kms−1.
No high frequency variations are observed. Three frequencies have been detected with a false alarm detection above the 1 % level. A fourth one may be present but its amplitude is below this 1 % level. Results are displayed in Table 1.
High spectral and time resolution observations show that the monoperiodic β Cephei star BW Vul presents differences in both line profiles and velocities from one cycle to another, which may be due to the consequence of the passage of two strong shock waves.
Recently Aerts et al. (1994, Paper I) discovered multi-periodicity in the variations of optical lines of β Cephei. They identified the frequency of the radial pulsation (f1 = 5.25cycles/day), and additionally found 2 frequencies (f2 = 5.38 c/d, f3 = 4.92 c/d) close to the main frequency. The amplitude of these variations was found to be much smaller than that of the radial pulsation. Aerts et al. (1994) attributed these small variations at the newly found frequencies to non-radial pulsation modes of the star, but labelled the mode-identifications as uncertain.
HD 147394 is a Slowly Pulsating B star for which we found three periods in the moments of the Si II 4128-4130 lines: f1 = 0.8008 c/d, f2 = 0.7813 c/d and f3 = 0.6710 c/d. A mode identification is perform ed by using the moment method.
We present a method for the analysis of latitude distribution associated with temperature and/or velocity perturbations of the stellar surface due to non-radial pulsation (NRP) modes in rapidly rotating B stars. The technique is applied together with Fourier Doppler Imaging (FDI) to high resolution and high signal-to-noise ratio spectroscopic observations of ϵ Per. The main advantage of this approach is that it decomposes complex multi-periodic line profile variations into single components, allowing the detailed analysis of each mode separately. We study the 10.6-d−1 frequency that is particularly important for modal analysis of non-radial pulsations in the star.
We review the current status of our long-term monitoring project on slowly pulsating B stars that we started in the course of 1996 and that was recently completed as far as the first part of our plan is concerned. In total, we have selected 17 southern and 8 northern stars. The idea is to fully exploit our current data in the near future and to select the most interesting targets for further very-long-term follow-up monitoring. A first conclusion is that half of the southern targets turn out to be spectroscopic binaries. Some of these have circular orbits and periods of the same order of magnitude as the intrinsic pulsation period(s) of the primary. The eccentric binaries have periods ranging from 12 to 460 d. For most stars the photometric behaviour is dominated by the same frequency as the intrinsic spectroscopic variability. Multiperiodicity in the expected frequency range is found for almost all stars. Two objects, however, turn out to have only one dominant pulsation mode.
During the past five years, we monitored the Hα line of β Cep. The strength of the Hα emission, first discovered in 1990, is linearly declining with time. Several options are explored, but a satisfactory explanation for the recurring phases of Hα emission is not yet found.
Observations carried out for 5 years on o And show that 65 to 85% of its light variations can be described by a double wave: A sin (2πt/P1 + ϕ1) + B sin (2πt/P2 + ϕ2) + C with P1 ≈ 1.6 d = 2P2. When determined independently, P1 and P2 are always found in a 2:1 ratio (within 1%), while they can vary together by as much as 4%. The peak to peak amplitudes of this double-wave fit lay between 40 and 140 mmag (and can even be reduced to less than 10 mmag - our 1987 observations). The rest of the light variations do not show any permanent period or behavior, although a ∼ 2.3 d. (i.e. ≈ 3P1/2) period is frequently detected. Sometimes a marginal ∼ 6 d. period or time constant has been detected.
In spite of the quality of our photometric data, the precision on the periods and amplitudes obtained over a few nights is never increased by longer observations: our phase diagrams show significant irregular displacements around the average double-wave analytical solution if we include longer data strings (Fig. 1). This phenomenon was already apparent in our 1992 study (Sareyan et al., 1998): the star shows real irregular behaviour superimposed onto its double-wave “mean” light curve; these changes may show up as a progressive, or sometimes abrupt, modification of the shape of the double-wave light curve (Fig. 1).
We present the results of 1.5 years of Spectroscopic monitoring of 10 bright northern SPB candidates discovered from the Hipparcos mission. All stars have line-profile variations and are periodic, with periods corresponding to high-order g-modes. We therefore confirm them to be new SPBs.
20 Leo is a spectroscopic triple system composed of 3 very similar stars, one of which seems to be a δ Sct star. Observations at high spectral and high time resolution have been obtained at the Observatoire de Haute Provence with the ELODIE spectrograph on the 1.9-m telescope. The spectra were taken during 7 nights in 2003 January and cover the whole optical domain from 3900 to 6800 Å. We used a Fourier transform technique recently developed by P. Hadrava to disentangle the combined spectrum. Application of the method allows the derivation of radial velocities at all orbital phases (even at phases of complete blending), as well as individual spectra for each component. From these computations we deduced more accurate individual radial velocities and improved orbital parameters describing the motion of the inner binary. Model atmospheres were used to analyze each individual spectrum and determine stellar fundamental parameters of the three components such as effective temperature, surface gravity and projected rotation velocity.
The aim of our article was to review the current literature on the effects of metabolic (re) programming on childhood obesity. PubMed/MEDLINE was the data source used to track the studies. Descriptors applied: children obesity, epigenetic, metabolic programming, exercise and nutrition. The focus was to analyze and discuss the international findings on the theme. The gathering of the papers was performed between June and August 2014. The search of articles with the descriptors used found 33.054 studies. In all, 5.709 studies were selected by crossing chosen keywords. Among these, after careful reading of the titles, 712 papers were considered potential as references. After applying inclusion/exclusion criteria, 50 studies were selected from 132 eligible abstracts. Most studies linked the development and treatment of obesity from epigenetically stimulated metabolic programming during the early stages of pregnancy and life. This review provides theoretical basis to the understanding that the programmed development of childhood obesity may be linked to early exposure to environmental factors, such as (nutrition and regular practice of exercise) and stimulus can epigenetically alter the modulation of the obesogenic metabolic behavior during pregnancy and the developmental stages of children and/or postpone the pathophysiologic disease stage to adulthood.
Undernutrition exposure during the perinatal period reduces the growth kinetic of the offspring and sensitizes it to the development of chronic adult metabolic diseases both in animals and in humans. Previous studies have demonstrated that a 50% maternal food restriction performed during the last week of gestation and during lactation has both short- and long-term consequences in the male rat offspring. Pups from undernourished mothers present a decreased intrauterine (IUGR) and extrauterine growth restriction. This is associated with a drastic reduction in their leptin plasma levels during lactation, and exhibit programming of their stress neuroendocrine systems (corticotroph axis and sympatho-adrenal system) in adulthood. In this study, we report that perinatally undernourished 6-month-old adult animals demonstrated increased leptinemia (at PND200), blood pressure (at PND180), food intake (from PND28 to PND168), locomotor activity (PND187) and altered regulation of glycemia (PND193). Cross-fostering experiments indicate that these alterations were prevented in IUGR offspring nursed by control mothers during lactation. Interestingly, the nutritional status of mothers during lactation (ad libitum feeding v. undernutrition) dictates the leptin plasma levels in pups, consistent with decreased leptin concentration in the milk of mothers subjected to perinatal undernutrition. As it has been reported that postnatal leptin levels in rodent neonates may have long-term metabolic consequences, restoration of plasma leptin levels in pups during lactation may contribute to the beneficial effects of cross-fostering IUGR offspring to control mothers. Collectively, our data suggest that modification of milk components may offer new therapeutic perspectives to prevent the programming of adult diseases in offspring from perinatally undernourished mothers.