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Detection of G2.

Avatar for Yuhan Yao Yuhan Yao
April 12, 2016

Detection of G2.

This slides is made for my first paper talk given on the star cluster's group meeting at KIAA-PKU.

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Yuhan Yao

April 12, 2016
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  1. Detection of galactic center source G2 at 3.8 microns during

    periapse passage Periapse: The point of a body's elliptical orbit about the system's centre of mass where the distance between the body and the centre of mass is at its minimum.
  2. • G2 : dusty red object associated with gas that

    shows tidal interactions as it nears the BH • Observation : test whether G2 is a gas cloud • Keck II LGSAO • NIRC2 : K’[2.1μm] & L’[3.8μm] broadband filters Object & Facility should be tidally disrupted during periapse passage
  3. Results • G2 has survived its closest approach to the

    black hole as a compact, unresolved source at L’ • G2’s L’ brightness measurements are consistent with those over the last decade • G2’s motion continues to be consistent with a Keplerian model.
  4. Conclusion & Inference • G2 has a central star of

    ∼30 L⊙, and is surrounded by a large optically thick dust shell(~2.6AU). • L’ and Br-γ emission arises primarily from internal and external heating, respectively. • G2 is a binary star merger product and will ultimately appear similar to the B-stars.
  5. Introduction • First detected in 2012: 3 M⊕ gas cloud

    ? Detection: an object(G2) approaching the SMBH Br-γ emission: dusty, 3 earth mass gas cloud If true, it will be disrupted and accreted Interest: can be followed through the predicted accretion
  6. Introduction • First detected in 2012: 3 M⊕ gas cloud

    ? • Alternative models: central stellar source • NIR: detectable at L’-M[3-5μm], faint at K’[2μm] • In Br-γ: slightly elongated core, tital tails • New L’ imaging observations of G2 during the closest approach and the following few months
  7. Result 1 G2 has survived its closest approach to the

    black hole as a compact, unresolved source at L’
  8. Conclusion G2 has an central star of ∼30 L⊙ ,

    and is surrounded by a thick dust shell
  9. Br-γ VS L’ emission Trace hot gas externally heated by

    ionizing photons Tidal interaction with the BH Only SOME gas associated with G2 has a size that exceeds its tidal radius Specially unresolved Continues to follow a well- defined Keplerian orbit Constant in brightness Come from a dust shell surrounding an underlying star
  10. Line 1: G2 has central stellar source •The L’ flux

    has been invariant at ∼ 2.1 mJy •In 2004, G2 had an L’ - M’ color of ∼ 0.3, which corresponds to a blackbody temperature of ∼ 560 K. • •No K’ detection has been made in any epoch. •The L’ emission is much more compact than the emission in Br-γ, and thus originates in a different region. 

  11. Line 2: G2 is a merger product • Tidal radius

    arguments • Tidal radius of the source has not become smaller than the source size for most of the time • For MBH = 4.3E6M⊙, the tidal radius is :
  12. Time development of the tidal radius Derived L’ size of

    G2(2.6AU): consistent with observation
  13. Br-γ VS L’ emission The Br-γ emission is a by-product

    of the tidal interaction, whereas the L’ emission traces the properties of the merger product.
  14. Future research… • Merger product • Eccentric orbit • S-star

    cluster • Is it possible that an important fraction of the S- stars has resulted from such mergers?