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Wittkowski M.,ESO | Boboltz D.A.,U.S. Naval Observatory | Ireland M.,Macquarie University | Karovicova I.,ESO | And 8 more authors.
Astronomy and Astrophysics | Year: 2011

Aims. We investigate the structure and shape of the photospheric and molecular layers of the atmospheres of four Mira variables. Methods. We obtained near-infrared K-band spectro-interferometric observations of the Mira variables R Cnc, X Hya, W Vel, and RW Vel with a spectral resolution of about 1500 using the AMBER instrument at the VLTI. We obtained concurrent JHKL photometry using the the Mk II instrument at the SAAO. Results. The Mira stars in our sample are found to have wavelength-dependent visibility values that are consistent with earlier low-resolution AMBER observations of S Ori and with the predictions of dynamic model atmosphere series based on self-excited pulsation models. The corresponding wavelength-dependent uniform disk (UD) diameters show a minimum near the near-continuum bandpass at 2.25  μm. They then increase by up to 30% toward the H2O band at 2.0  μm and by up to 70% at the CO bandheads between 2.29  μm and 2.48  μm. The dynamic model atmosphere series show a consistent wavelength-dependence, and their parameters such as the visual phase, effective temperature, and distances are consistent with independent estimates. The closure phases have significantly wavelength-dependent and non-zero values at all wavelengths indicating deviations from point symmetry. For example, the R Cnc closure phase is 110°â€‰ ±   4° in the 2.0  μm H 2O band, corresponding for instance to an additional unresolved spot contributing 3% of the total flux at a separation of ~4  mas. Conclusions. Our observations are consistent with the predictions of the latest dynamic model atmosphere series based on self-excited pulsation models. The wavelength-dependent radius variations are interpreted as the effect of molecular layers lying above the photosphere. The wavelength-dependent closure phase values are indicative of deviations from point symmetry at all wavelengths, thus a complex non-spherical stratification of the extended atmosphere. In particular, the significant deviation from point symmetry in the H2O band is interpreted as a signature on large scales (there being a few across the stellar disk) of inhomogeneities or clumps in the water vapor layer. The observed inhomogeneities might possibly be caused by pulsation-and shock-induced chaotic motion in the extended atmosphere. © 2011 ESO. Source


Miley G.,Leiden University | Carignan C.,University of Montreal | Carignan C.,Observatoire Dastrophysique Of Luniversite Of Ouagadougou Odauo | Carignan C.,University of Cape Town | Govender K.,South African Astronomical Observatory SAAO
Proceedings of the International Astronomical Union | Year: 2010

During the next decade the IAU intends to mobilize talented astronomers, engineers and teachers around the world, in the service of developing countries. I shall review the content of the IAU Strategic Plan 2010 - 2020 "Astronomy for the Developing World" and give you an update on its implementation. Astronomy is a unique tool for stimulating capacity building because it combines cutting-edge technology with fundamental science and has deep cultural roots. The plan envisages a substantial increase in IAU education and development activities during the next decade. These activities will be bottom-up, with a strong regional influence. An integrated approach tailored to the conditions and needs of each country will involve a mix of education at primary, secondary and tertiary levels and public outreach. As a crucial component of the strategy, the IAU together with the South African National Research Foundation will set up a small office to coordinate and plan the various global activities at the SAAO in Cape Town. © Copyright International Astronomical Union 2011. Source


Ramatsoku M.,University of Groningen | Ramatsoku M.,University of Cape Town | Ramatsoku M.,Netherlands Institute for Radio Astronomy | Verheijen M.A.W.,University of Groningen | And 11 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2016

We present results of a blind 21cm HI-line imaging survey of a galaxy overdensity located behind theMilkyWay at ℓ, b ≈ 160°, 0. ° 5. The overdensity corresponds to a zone-of-avoidance crossing of the Perseus-Pisces Supercluster filament. Although it is known that this filament contains an X-ray galaxy cluster (3C 129) hosting two strong radio galaxies, little is known about galaxies associated with this potentially rich cluster because of the high Galactic dust extinction. We mapped a sky area of~9.6 deg2 using theWesterbork Synthesis RadioTelescope in a hexagonal mosaic of 35 pointings observed for 12 h each, in the radial velocity range cz = 2400-16 600 km s-1. The survey has a sensitivity of 0.36 mJy beam-1 rms at a velocity resolution of 16.5 km s-1. We detected 211 galaxies, 62 per cent of which have a near-infrared counterpart in the UKIDSS Galactic Plane Survey. We present a catalogue of the HI properties and an HI atlas containing total intensity maps, position-velocity diagrams, global HI profiles and UKIDSS counterpart images. For the resolved galaxies we also present HI velocity fields and radial HI surface density profiles. A brief analysis of the structures outlined by these galaxies finds that 87 of them lie at the distance of the Perseus-Pisces Supercluster (cz ~ 4000-8000 km s-1) and seem to form part of the 3C 129 cluster. Further 72 detections trace an overdensity at a velocity of cz ≈ 10 000 km s-1 and seem to coincide with a structure predicted from mass density reconstructions in the first 2MASS Redshift Survey. © 2016 The Authors. Published by Oxford University Press on behalf of The Royal Astronomical Society. Source


Hernandez A.G.,University of Porto | Lignieres F.,CNRS Institute for research in astrophysics and planetology | Balona L.,South African Astronomical Observatory SAAO | Reese D.R.,University of Birmingham | And 3 more authors.
EPJ Web of Conferences | Year: 2015

High precision photometric observations from space has led to the detection of hundreds of frequencies in the light curves of δ Scuti pulsators. In this work, we analyzed a sample of Kepler δ Sct stars to search for frequency patterns in the p-mode regime. To avoid g-modes, we looked at the mode density histogram (MDH). We then used the Fourier transform technique (FT), histograms of frequency differences (HFD) and Echelle diagrams (ED) to find periodicities in the frequency content. We compared the results with those expected for SCF rotating models [4] with the aim of identifying large separations and rotational splittings. © Owned by the authors, published by EDP Sciences, 2015. Source


Hakala P.J.,University of Turku | Charles P.A.,South African Astronomical Observatory SAAO | Muhli P.,National Land Survey of Finland
Monthly Notices of the Royal Astronomical Society | Year: 2011

We present results from several years of fast optical photometry of 4U0614+091 (V1055 Orionis), a candidate ultracompact X-ray binary most likely consisting of a neutron star and a degenerate secondary. We find evidence for strong accretion-driven variability at all epochs, which manifests itself as red noise. This flickering produces transient peaks in the observed power spectrum in the 15-65min period range. Only in one of our 12 optical data sets can we see evidence for a period that cannot be reproduced using the red noise model. This period of 51min coincides with the strongest period detected by Shahbaz et al. and can thus be taken as the prime candidate for the orbital period of the system. Furthermore, we find some tentative evidence for the X-ray versus optical flux anticorrelation discovered by Machin et al. using our data together with the all-sky X-ray monitoring data from RXTE/All Sky Monitor. We propose that the complex time series behaviour of 4U0614+09 is a result of drastic changes in the accretion disc geometry/structure on time-scales from hours to days. Finally, we want to draw attention to the interpretation of moderately strong peaks in the power spectra of especially accreting sources. Many of such 'periods' can probably be attributed to the presence of red noise (i.e. correlated events) in the data. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS. Source

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