فهرست مطالب

Astronomy and Astrophysic - Volume:1 Issue: 1, Spring 2014

Iranian Journal of Astronomy and Astrophysic
Volume:1 Issue: 1, Spring 2014

  • تاریخ انتشار: 1394/02/25
  • تعداد عناوین: 7
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  • E.P.J. Van Den Heuvel Pages 1-15
    In 2012 it was forty years ago that the discovery of the first X-ray binary Centaurus X-3 became known. That same year it was discovered that apart from the High-Mass X-ray Binaries (HMXBs) there are also Low-Mass X-ray Binaries (LMXBs), and that Cygnus X-1 is most probably a black hole. By 1975 also the new class of Be/X-ray binaries was discovered. After this it took 28 years before ESAs INTEGRAL satellite team discovered two new classes of High-Mass X-ray Binaries: the highly obscured supergiant systems and the Supergiant Fast X-ray Transients (SFXT). In most HMXBs the neutron stars have very long spin periods. The causes of these long periods and of the outbursts of SFXTs are discussed. Furthermore, the formation rate, duration of the X-ray phase and the later evolution after the X-ray phase of the HMXBs are discussed. Many systems will later in life merge to form Thorne-Zytkow Objects. The fate of such objects is still unclear, but the relatively high formation rate of supergiant HMXBs in the Galaxy (of order 6×10-4yr-1) implies that their remnants must be all around us. Finally, the evidence for the existence of three groups of neutron star masses, derived from the study of X-ray binaries and binary radio pulsars, is briefly discussed, as well as the origins of these three types of neutron stars.
    Keywords: X-rays, X-ray Binaries, Neutron stars, black holes, stellar evolution, transients
  • Jamshid Ghanbari, Arezoo Tajmohammadi Pages 17-28
    In this work we solve the set of hydrodynamical equations for accretion disks in the spherical coordinates (r,θ,ϕ) to obtain the explicit structure along θ direction. We study a two-dimensional advective accretion disc in the presence of thermal conduction. We find self-similar solutions for an axisymmetric, rotating, steady, viscous-resistive disk. We show that the global structure of an advection-dominated accretion flow (ADAFs) is sensitive to viscosity, advection, wind and thermal conduction parameters. We discuss how the radial flows, meridional velocity, rotation velocity, sound speed and density of accretion flows may vary with the advection, thermal conduction and wind parameters. We will find that the radial velocity in nearby the equator, angular velocity and sound speed decrease by increasing the thermal conduction parameter and meridional velocity increases by increasing it.
    Keywords: accretion disk, wind, thermal conduction
  • Iraj Gholami Pages 29-42
    Given the sensitivity of current ground-based Gravitational Wave (GW) detectors, any continuous-wave signal we can realistically expect will be at a level or below the background noise. Hence, any data analysis of detector data will need to rely on statistical techniques to separate the signal from the noise. While with the current sensitivity of our detectors we do not expect to detect any true GW signals in our data, we can still set upper limits (UL) on their amplitude. These upper limits, in fact, tell us how weak a signal strength we would detect. In setting upper limit using two popular method, Bayesian and Frequentist, there is always the question of realistic results. In this paper, we try to give an estimate of how realistically we can set the upper limit using the above mentioned methods. And if any, which one is preferred for our future data analysis work.
    Keywords: Gravitational waves, frequency domain, Bayesian, data analysis, upper limits
  • Hosein Haghi, Hamed Ghasemi, Hongsheng Zhao Pages 43-56
    The rotation curves of a sample of 46 low- and high-surface brightness galaxies are considered in the context of Milgrom's modi_ed dynamics (MOND) to test a new interpolating function proposed by Zhao et al. (2010) [1] and compare with the results of simple interpolating function. The predicted rotation curves are calculated from the total baryonic matter based on the B-band surface photometry, and the observed distribution of neutral hydrogen, in which the one adjustable parameter is the stellar mass-to-light ratio. The predicted rotation curves generally agree with the observed curves for both interpolating functions. We show that the _tted M=L in the B-band correlates with B-V color in the sense expected from what we know about stellar population synthesis models. Moreover, the mass-to-light ratios of MOND with new interpolating function is in consistent with scaled Salpeter's initial mass function of the SPS scheme, while those of MOND with simple interpolating function favor Kroupa IMF.
    Keywords: ISM: molecules, ISM: structure, instabilities
  • Nasibe Alipour, Hossein Safari Pages 57-63
    Solar mini-dimmings can be detect in the Extreme Ultra-Violet coronal eruptions. Here, sequences of 171_A images taken by Solar Dynamic Observatory/Atmospheric Imaging Assembaly on 13 June 2010 are used. In this special day, both of coronal mass ejection and prominence were observed. The average velocities and accelerations of 500 mini-dimmings which were detected using on feature based classifier (Alipour et al 2012) [1] are studied. The large number of mini-dimmings shows positive accelerations in the beginning times as similar as Coronal Mass Ejections. On the the start time of prominence eruptions, the number of mini-dimmings is increased to a maximum values. There is a positive correlation between the kinematics of mini-dimmings and both CME and prominences. This study can be extended to understand the exact relationship of CMEs and mini-dimmings.
    Keywords: Sun: CMEs, mini, dimming, prominence
  • Habib G. Khosroshahi, Louisa A. Nolan Pages 65-76
    It is inferred from the symmetrical and luminous X-ray emission of fossil groups that they are mature, relaxed galaxy systems. Cosmological simulations and observations focusing on their dark halo and inter-galactic medium properties confirm their early formation. Recent photometric observations suggest that, unlike the majority of non-fossil brightest group galaxies (BGGs), the central early-type galaxies in fossil groups do not have boxy isophotes, and are therefore likely to have formed in non-equal-mass, gas-rich galaxy-galaxy mergers.
    Although the isophotal shapes of early-types can be used to infer the nature of the parent galaxies of their most recent mergers, detailed star-formation histories of the galaxies are also needed, in order to uncover the epoch of these mergers and the differences in the physical processes which produce fossil groups rather than `normal' galaxy groups. In this study, we use a powerful long-baseline (UV-optical), multi-component, stellar population fitting technique to disentangle the star-formation history of the dominant central giant elliptical galaxy in a sample of five fossil groups, and compare this with a control sample of non-fossil BGGs, in an attempt to fully understand their merger histories. Our technique allows us to identify multiple epochs of star formation in a single galaxy, and constrain the metallicities of the constituent stellar populations.
    Resolving the populations in this way gives us a much clearer picture of galaxie's histories than simply using the mean age / metallicity of total stellar populations recovered by more conventional techniques using absorption line strengths.
    We find that i) the dominant stellar components in both galaxy samples are old (>10 Gyr), metal-rich (≥solar) and statistically indistinguishable in terms of their ages, metallicities and relative mass fractions; ii) the ages of the secondary, younger stellar components are also statistically indistinguishable between the two samples; iii) the central fossil galaxies have secondary stellar components which have significantly lower metallicities than the corresponding stellar populations in the BGG sample.
    In a gas-rich merger, dissipation dilutes the previously-enriched gas in the central regions of the parent galaxies with gas which has not been metal-enriched, lowering the metallicity of the stars produced. Hence, we conclude that the central fossil galaxies are the products of early and exceptionally gas-rich mergers, which leaves them with lower metallicities in their most recent merger-induced stellar populations than their BGG counterparts. In contrast, although the last starburst-inducing merger of the 'normal' BGGs occurred at the same epoch as that of the fossil BGGs, they have undergone a subsequent dissipation-less merger, leaving them in the present day with boxy isophotes and more disturbed x-ray emission, but no further significant star formation.
    Keywords: ISM: molecules, ISM: structure, instabilities
  • Mehdi Khakian Ghomi, Maedeh Fazlalizadeh, Mahmoud Bahmanabadi, Hadi Hedayati Kh Pages 77-85
    Geomagnetic field is a one of the candidates for creation of anisotropy in azimuth distribution of extensive air showers over the entered cosmic rays to the atmosphere. Here we present the question: Is there any azimuth anisotropy flux in the upper level of the atmosphere due to the geomagnetic field over the entered cosmic-rays? The obtained answer is: yes. This investigation showed an agreement with a similar functionality to the experimental results, but its amplitude is smaller. We calculated the effect over the primary protons and alpha particles with consideration of their abundances, and found that this effect by itself is not as large as the expected value of experimental results. Therefore we need to investigate the secondary particles for the next step. But for a real simulation of extensive air showers, it is necessary to be applied this anisotropy flux as a seed for the secondary particle in the next step.
    Keywords: Azimuth anisotropy, Cosmic Ray, Gamma Ray, Extensive Air Shower, Geomagnetic field