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Mennickent R.E.,University of Concepcion | Djurasevic G.,Astronomical Observatory | Djurasevic G.,Isaac Newton Institute of Chile
Monthly Notices of the Royal Astronomical Society | Year: 2013

We modelled the V-band light curve of ß Lyrae (Lyr) with two stellar components plus an optically thick accretion disc around the gainer assuming a semidetached configuration. We present the results of this calculation, giving physical parameters for the stars and the disc, along with general system dimensions.We discuss the evolutionary stage of the system finding the best match with one of the evolutionary models of Van Rensbergen et al. According to this model, the system is found at age 2.30 x 107 yr, in the phase of rapid mass transfer, the second one in the life of this binary, in a Case-B mass-exchange stage with M= 1.58 x 10-5 M⊙ yr-1. This result, along with the reported rate of orbital period change and observational evidence of mass-loss, suggests that the mass transfer in ß Lyr is quasi-conservative. The best model indicates that ß Lyr finished a relatively large mass-loss episode 31 400 yr ago. The light-curve model that best fit the observations has inclination angle i = 81°, M1 = 13.2 M⊙, M2 = 3.0 M⊙, R1 = 6.0R⊙ and R2 = 15.2 R⊙. The disc contributes 22 per cent to the total V-band light curve at quadrature, has a radius of 28.3 R⊙ and the outer edge thickness is 11.2 R⊙. The light-curve model is significantly better with two bright regions in the disc rim with temperatures 10 and 20 per cent higher than the disc outer edge temperature.We compare our results with earlier studies of this interacting binary. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source


Pavlovic M.Z.,University of Belgrade | Urosevic D.,University of Belgrade | Urosevic D.,Isaac Newton Institute of Chile | Vukotic B.,Astronomical Observatory | And 2 more authors.
Astrophysical Journal, Supplement Series | Year: 2013

In this paper, we present new empirical radio surface-brightness-to- diameter (Σ-D) relations for supernova remnants (SNRs) in our Galaxy. We also present new theoretical derivations of the Σ-D relation based on equipartition or on a constant ratio between cosmic rays and magnetic field energy. A new calibration sample of 60 Galactic SNRs with independently determined distances is created. Instead of (standard) vertical regression, used in previous papers, different fitting procedures are applied to the calibration sample in the log Σ-log D plane. Non-standard regressions are used to satisfy the requirement that values of parameters obtained from the fitting of Σ-D and D-Σ relations should be invariant within estimated uncertainties. We impose symmetry between Σ-D and D-Σ due to the existence of large scatter in both D and Σ. Using four fitting methods that treat Σ and D symmetrically, different Σ-D slopes β are obtained for the calibration sample. Monte Carlo simulations verify that the slopes of the empirical Σ-D relation should be determined by using orthogonal regression because of its good performance in data sets with severe scatter. The slope derived here (β = 4.8) is significantly steeper than those derived in previous studies. This new slope is closer to the updated theoretically predicted surface-brightness-diameter slope in the radio range of the Sedov phase. We also analyze the empirical Σ-D relations for SNRs in a dense environment of molecular clouds and for SNRs evolving in the lower-density interstellar medium. Applying new empirical relations to estimate distances of Galactic SNRs results in a dramatically changed distance scale. © 2013. The American Astronomical Society. All rights reserved.. Source


Mennickent R.E.,University of Concepcion | Djurasevic G.,Astronomical Observatory | Djurasevic G.,Isaac Newton Institute of Chile | Kolaczkowski Z.,University of Concepcion | Michalska G.,University of Concepcion
Monthly Notices of the Royal Astronomical Society | Year: 2012

V393 Scorpii is a bright Galactic Double Periodic Variable showing a long photometric cycle of ≈253d. We present new VIJK photometric time series for V393 Scorpii along with the analysis of All Sky Automated Survey (ASAS) V-band photometry. We disentangled all light curves into the orbital and long-cycle components. The ASAS V-band orbital light curve was modelled with two stellar components plus a circumprimary optically thick disc assuming a semi-detached configuration. We present the results of this calculation, giving physical parameters for the stars and the disc, along with general system dimensions. Our results are in close agreement with those previously found by Mennickent et al. from infrared (IR) spectroscopy and the modelling of the spectral energy distribution. The stability of the orbital light curve suggests that the stellar plus disc configuration remains stable during the long cycle. Therefore, the long cycle should be produced by an additional variable and not-eclipsed emitting structure. We discuss the evolutionary stage of the system finding the best match with one of the evolutionary models of van Rensbergen et al. According to these models, the system is found to be after an episode of fast mass exchange that transferred 4 M ⊙ from the donor to the gainer in a period of 400000 years. We argue that a significant fraction of this mass has not been accreted by the gainer but remains in an optically thick massive (~2 M ⊙) disc-like surrounding pseudo-photosphere whose luminosity is not driven by viscosity but probably by reprocessed stellar radiation. Finally, we provide the result of our search for Galactic Double Periodic Variables and briefly discuss the outliers β Lyr and RX Cas. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS. Source


Makarov D.,University Claude Bernard Lyon 1 | Makarov D.,Isaac Newton Institute of Chile | Karachentsev I.,University Claude Bernard Lyon 1
Monthly Notices of the Royal Astronomical Society | Year: 2011

We present an all-sky catalogue of 395 nearby galaxy groups revealed in the Local Supercluster and its surroundings. The groups and their associations are identified among 10914 galaxies at |b| > 15° with radial velocities VLG < 3500kms-1. Our group-finding algorithm requires the group members to be located inside their zero-velocity surface. Hereby, we assume that individual galaxy masses are proportional to their total K-band luminosities, M/LK= 6M⊙/L⊙. The sample of our groups, where each group has n≥ 4 members, is characterized by the following medians: mean projected radius 〈R〉= 268kpc, radial velocity dispersion σV= 74kms-1, K-band luminosity LK= 1.2 × 1011L⊙, virial and projected masses Mvir= 2.4 × 1012 and Mp= 3.3 × 1012M⊙, respectively. Accounting for measurement error reduces the median masses by 30per cent. For 97per cent of identified groups the crossing time does not exceed the cosmic time, 13.7 Gyr, with the median at 3.8 Gyr. We examine different properties of the groups, in particular of the known nearby groups and clusters in Virgo and Fornax. About a quarter of our groups can be classified as fossil groups where the dominant galaxy is at least 10 times brighter than the other group members. In total, our algorithm identifies 54per cent of galaxies to be members of groups. Together with triple systems and pairs they gather 82per cent of the K-band light in the local Universe. We have obtained the local value of matter density to be Ωm= 0.08 ± 0.02 within a distance of ∼40Mpc assuming H0= 73kms-1Mpc-1. It is significantly smaller than the cosmic value, 0.28, in the standard ΛCDM model. The discrepancy between the global and local quantities of Ωm may be caused by the existence of a dark matter component unrelated to the virial masses of the galaxy systems. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS. Source


Acharova I.A.,Southern Federal University | Mishurov Y.N.,Russian Academy of Sciences | Kovtyukh V.V.,Odessa I I Mechnikov National University | Kovtyukh V.V.,Isaac Newton Institute of Chile
Monthly Notices of the Royal Astronomical Society | Year: 2012

We propose a statistical method for decomposition of contributions to iron production from various sources: Type II supernovae and the subpopulations of Type Ia supernovae, prompt (their progenitors are short-lived stars with ages lower than ~100Myr) and tardy (their progenitors are long-lived stars with ages >100Myr). To do that, we develop a theory of oxygen and iron synthesis that takes into account the influence of the spiral arms on the amount of the above elements synthesized by both Type II supernovae and prompt Type Ia supernovae. In the framework of the theory, we processed statistically the new, more precise, observational data on Cepheid abundances, which, as is well known, demonstrate non-trivial radial distributions of oxygen and iron in the Galactic disc with bends in the gradients. In our opinion, such fine structure in the distribution of elements along the Galactic disc enables one to decompose the amount of iron unambiguously into three components produced by the above three sources. In addition, by means of our statistical methods we solve this task without any preliminary suppositions about the ratios between the proportions of iron synthesized by the above sources. The total mass supplied to the Galactic disc during its life by all types of supernovae is ~(4.0 ± 0.4) × 10 7M ⊙, while the mass of iron occurring in the present interstellar medium (ISM) is ~(1.20 ± 0.05) × 10 7M ⊙, i.e. about two thirds of iron is contained in stars and stellar remnants. The relative proportion of iron synthesized by tardy type Ia supernovae for the lifetime of the Galaxy is ~35 per cent (in the present ISM this portion is ~50 per cent). Correspondingly, the total proportion of iron supplied to the disc by Type II supernovae and prompt Type Ia supernovae is ~65 per cent (in the present ISM this proportion is ~50 per cent). The above result depends slightly on the adopted mass of oxygen and iron synthesized during one supernova explosion and the shape (bimodal or smooth) of the so-called delay-time distribution function. The proportions of iron mass distributed between short-lived supernovae are usually as follows: depending on the ejected masses of oxygen or iron during one Type II supernova event, the relative proportion of iron supplied to the Galactic disc for its age varies in the range 12-32 per cent (in the present ISM 9-25 per cent); the proportion supplied by prompt Type Ia supernovae to the Galactic disc is 33-53 per cent (in the ISM 26-42 per cent). Our method also confirms that the bend in the observed slope of the oxygen radial distribution and the minimum in [O/Fe] at ~7kpc form in the vicinity of the location of the corotation resonance. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS. Source

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