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Miszalski B.,South African Astronomical Observatory | Mikolajewska J.,Nicolaus Copernicus Astronomical Center
Monthly Notices of the Royal Astronomical Society | Year: 2014

We introduce the first results from an ongoing, systematic survey for new symbiotic stars selected from the AAO/UKST SuperCOSMOS Ha Survey. The survey aims to identify and characterize the fainter population of symbiotic stars under-represented in extant catalogues. The accreting white dwarfs (WDs) in symbiotic stars, fuelled by their red giant donors with high mass-loss rate winds, make them promising candidates for Type Ia supernovae. Several candidates were observed spectroscopically with the Southern African Large Telescope. A total of 12 bona fide and 3 possible symbiotic stars were identified. The most remarkable example is a rare carbon-rich symbiotic star that displays coronal [Fe X] λ 6375 emission, suggesting it may be a supersoft X-ray source with a massive WD. Several other emission line objectswith near-infrared colours similar to symbiotic stars are listed in an appendix, including six B[e] stars, four planetary nebulae (PNe), two possible Be stars, one [WC9] Wolf-Rayet (WR) central star of a PN and one WC9WR star. These initial discoveries will help shape and refine the candidate selection criteria that we expect will uncover several more symbiotic stars as the survey progresses. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Bolejko K.,University of Oxford | Celerier M.-N.,University Paris Diderot | Krasinski A.,Nicolaus Copernicus Astronomical Center
Classical and Quantum Gravity | Year: 2011

Recently, inhomogeneous generalizations of the Friedmann-Lematre-Robertson- Walker (FLRW) cosmological models have gained interest in the astrophysical community and are more often employed to study cosmological phenomena. However, in many papers the inhomogeneous cosmological models are treated as an alternative to the FLRW models. In fact, they are not an alternative, but an exact perturbation of the latter, and are gradually becoming a necessity in modern cosmology. The assumption of homogeneity is just a first approximation introduced to simplify equations. So far this assumption is commonly believed to have worked well, but future and more precise observations will not be properly analysed unless inhomogeneities are taken into account. This paper reviews recent developments in the field and shows the importance of an inhomogeneous framework in the analysis of cosmological observations. © 2011 IOP Publishing Ltd. Source

Miszalski B.,South African Astronomical Observatory | MikoLajewska J.,Nicolaus Copernicus Astronomical Center | Udalski A.,University of Warsaw
Monthly Notices of the Royal Astronomical Society | Year: 2013

Symbiotic stars are interacting binaries with the longest orbital periods, and their multicomponent structure makes them rich astrophysical laboratories. The accretion of a high-mass-lossratered giant wind on to a white dwarf (WD) makes them promising Type Ia supernova (SN Ia) progenitor.Systematic surveys for new Galactic symbiotic stars are critical to identify new promising SN Iaprogenitors (e.g. RS Oph) and to better estimate the total population size to compare against SN Ia rates. Central to the latter objective is building a complete census of symbiotic stars towards the Galactic bulge. Here we report on the results of a systematic survey of Hα emission-line stars covering 35 deg2. It is distinguished by the combination of deep optical spectroscopy and long-termlight curves that improve the certainty of our classifications. A total of 20 bona fide symbiotic stars are found (13 S-types, 6 D-types and 1 D'-type), 35 per cent of which show the symbiotic specific Raman-scattered OVI emission bands, as well as 15 possible symbiotic stars that require further study (six S-types and nine D-types). Light curves show a diverse range of variability including stellar pulsations (semi-regular and Mira), orbital variations and slow changes due to dust. Orbital periods are determined for five S-types and Mira pulsation periods for three D-types. The most significant D-type found is H1-45 and its carbon Mira with a pulsation period of 408.6 d, corresponding to an estimated period-luminosity relation distance of ̃6.2 ± 1.4 kpc and MK = -8.06 ± 0.12 mag. If H1-45 belongs to the Galactic bulge, then it would be the first bona fide luminous carbon star to be identified in the Galactic bulge population. The lack of luminous carbon stars in the bulge is a longstanding unsolved problem. A possible explanation for H1-45 may be that the carbon enhancement was accreted from the progenitor of the WD companion. A wide variety of unusual emission-line stars were also identified. These include central stars of planetary nebulae (PNe) [one(WC10-11) Wolf-Rayet and five with high-density cores], two novae, two WN6 Wolf-Rayet stars, two possible Be stars, a B[e] star with a bipolar outflow, an ultracompact HII region and a dMe flare star. Dust obscuration events were found in two central stars of PNe, increasing the known cases tofive, as well as one WN6 star. There is considerable scope to uncover several more symbiotic starstowards the bulge, many of which are currently misclassified as PNe, provided that deep spectroscopy is combined with optical and near-infrared light curves. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Kazantzidis S.,Ohio State University | Lokas E.L.,Nicolaus Copernicus Astronomical Center | Mayer L.,University of Zurich
Astrophysical Journal Letters | Year: 2013

According to the tidal stirring model, late type, rotationally supported dwarfs resembling present day dwarf irregular (dIrr) galaxies can transform into dwarf spheroidals (dSphs) via interactions with Milky-Way-sized hosts. We perform collisionless N-body simulations to investigate for the first time how tidal stirring depends on the dark matter (DM) density distribution in the central stellar region of the progenitor disky dwarf. Specifically, we explore various asymptotic inner slopes γ of the dwarf DM density profiles (ρr -γ). For a given orbit inside the primary galaxy, rotationally supported dwarfs embedded in DM halos with core-like distributions (γ = 0.2) and mild density cusps (γ = 0.6) demonstrate a substantially enhanced likelihood and efficiency of transformation into dSphs compared to their counterparts with steeper DM density profiles (γ = 1). Such shallow DM distributions are akin to those of observed dIrrs highlighting tidal stirring as a plausible model for the Local Group (LG) morphology-density relation. When γ < 1, a single pericentric passage can induce dSph formation and disky dwarfs on low-eccentricity or large-pericenter orbits are able to transform; these new results allow tidal stirring to explain virtually all known dSphs across a wide range of distances from their hosts. A subset of disky dwarfs initially embedded in DM halos with shallow density profiles are eventually disrupted by the primary; those that survive as dSphs are generally on orbits with lower eccentricities and/or larger pericenters compared to those of typical cold dark matter satellites. The latter could explain the peculiar orbits of several LG dSphs such as Fornax, Leo I, Tucana, and Cetus. © 2013. The American Astronomical Society. All rights reserved.. Source

Hellwing W.A.,Nicolaus Copernicus Astronomical Center
Annalen der Physik (Leipzig) | Year: 2010

Based on a set of cosmological N-body simulations we analyze properties of the dark matter (DM) haloes in a galaxy mass range (1011-10 13h-1M⊙) in modified ?CDM cosmology with additional dynamically screened scalar interactions in DM sector. Our simulations show that scalar interactions support picture of the Island Universe. Rapid structure formation processes are shifted into higher redshifts resulting in a much smaller accretion and merging rates for galactic haloes at low redshifts. Finally, we present how this "fifth" force affects halo properties, like density profile, triaxiality, ellipticities and the spin parameter. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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