• Title/Summary/Keyword: Accretion disk

Search Result 133, Processing Time 0.027 seconds

New Instabilities in Accretion Flows onto Black Holes

  • MOLTENI D.;FAUCI F.;GERARDI G.;BISIKALO D.;KUZNETSOV O.;ACHARYA K.;CHAKRABARTI S.
    • Journal of The Korean Astronomical Society
    • /
    • v.34 no.4
    • /
    • pp.247-249
    • /
    • 2001

  • The accretion disks are usually supposed symmetric to reflection on the Z=0 plane. Asymmetries in the flow are be ver-y small in the vicinity of the compact accretor. However their existence can have a important role in the case of subkeplerian accretion flows onto black holes. These flows lead to strong heating and even to the formation of shocks close to the centrifugal barrier. Large asymmetries are due to the development of the KH instability triggered by the small turbulences at the layer separating the incoming flow from the out coming shocked flow. The consequence of this phenomenon is the production of asymmetric outflows of matter and quasi periodic oscillations of the inner disk regions up and down the Z=0 plane.

  • PDF

The Interaction Between Accretion from the Interstellar Medium and Accretion from the Evolved Binary Component in Barium Stars

  • Jeong, Yeuncheol;Yushchenko, Alexander V.;Doikov, Dmytry N.
    • Journal of Astronomy and Space Sciences
    • /
    • v.35 no.1
    • /
    • pp.1-6
    • /
    • 2018

  • The reanalysis of the previously published abundance pattern of mild barium star HD202109 (${\zeta}$ Cyg) and the chemical compositions of 129 thin disk barium stars facilitated the search for possible correlations of different stellar parameters with second ionization potentials of chemical elements. Results show that three valuable correlations exist in the atmospheres of barium stars. The first is the relationship between relative abundances and second ionization potentials. The second is the age dependence of mean correlation coefficients of relative abundances vs. second ionization potentials, and the third one is the changes in correlation coefficients of relative abundances vs. second ionization potentials as a function of stellar spatial velocities and overabundances of s-process elements. These findings demonstrate the possibility of hydrogen and helium accretion from the interstellar medium on the atmospheres of barium stars.

  • https://doi.org/10.5140/JASS.2018.35.1.1 인용 PDF KSCI HTML

High-resolution ALMA Study of the Proto-Brown-Dwarf Candidate L328-IRS

  • Lee, Chang Won;Kim, Gwanjeong;Myers, Philip C.;Saito, Masao;Kim, Shinyoung;Kwon, Woojin;Lyo, A-Ran;Soam, Archana;Kim, Mi-Ryang
    • The Bulletin of The Korean Astronomical Society
    • /
    • v.43 no.2
    • /
    • pp.39.1-39.1
    • /
    • 2018

  • We present our observational attempts to precisely measure the central mass of a proto-brown dwarf candidate, L328-IRS, in order to investigate whether L328-IRS is in the substellar mass regime. Observations were made for the central region of L328-IRS with the dust continuum and CO isotopologue line emission at ALMA band 6, discovering the detailed outflow activities and a deconvolved disk structure of a size of ${\sim}87AU{\times}{\sim}37AU$. We investigated the rotational velocities as a function of the disk radius, finding that its motions between 130 AU and 60 AU are partially fitted with a Keplerian orbit by a stellar object of ${\sim}0.30M_{\odot}$, while the motions within 60 AU do not follow any Keplerian orbit at all. This makes it difficult to lead a reliable estimation of the mass of L328-IRS. Nonetheless, our ALMA observations were useful enough to well constrain the inclination angle of the outflow cavity of L328-IRS as ${\sim}66^{\circ}$ degree, enabling us to better determine the mass accretion rate of ${\sim}8.9{\times}10^{-7}M_{\odot}yr-1$.From assumptions that the internal luminosity of L328-IRS is mostly due to this mass accretion process in the disk, or that L328-IRS has mostly accumulated the mass through this constant accretion rate during its outflow activity, its mass was estimated to be ${\sim}0.012-0.023M_{\odot}$, suggesting L328-IRS to be a substellar object. However, we leave our identification of L328-IRS as a proto-brown dwarf to be tentative because of various uncertainties especially regarding the mass accretion rate.

  • PDF

Radiation Driven Warping of Circumbinary Disks around Supermassive Black Hole Binaries in Active Galactic Nuclei

  • Hayasaki, Kimitake;Sohn, Bong Won;Okazaki, Atsuo T.;Jung, Taehyun;Zhao, Guangyao;Naito, Tsuguya
    • The Bulletin of The Korean Astronomical Society
    • /
    • v.39 no.2
    • /
    • pp.74.1-74.1
    • /
    • 2014

  • We study a wraping instability of a geometrically thin, non-self-gravitating disk surrounding binary supermassive black holes on a circular orbit. Such a circumbinay disk is subject to not only tidal torques due Line 8 to the binary gravitational potential but also radiative rorques due to radiation emitted from each accretion disk. We find tat a circumbinary disk initially aligned with the binary orbital plane is unstable to radiation-driven warping beyond the marginally stable warping radius, which is sensitive to both the ratio of vertical to horizontal shear viscosities and the mass-to-energy conversion efficiency. As expected, the tidal torques give no contribution to the growth of warping modes but tend to align the circumbinary disk with the orbital plane. Since the tidal torques can suppress the warping modes in the inner part of circumbinary disk, the circumbinaary disk starts to be warped at the radii larger than the marginally stable warping radius. If the warping radius is of the order of 0.1 pc, a resultant semi-major axis is estimated to be of the order of 10-2 pc to 10-4 pc for 107 Msun black hole. We also discuss the posibility that the central objects of observed warped maser disks in active galactic nuclei are binary supermassive black holes with a triple disk: two accretion disks around the individual black holes and one circumbinary disk surrounding them.

  • PDF