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Thread: Betelgeuse Fainting

  1. #181
    Join Date
    Aug 2003
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    2,031
    Betelgeuse seems closer in magnitude to Aldebaran, .8 mag., than it did last week. May be a lot of dust swirling in the area.

  2. #182
    Join Date
    Sep 2004
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    4,978
    Two different views on what caused the Great Dimming of Betelgeuse, 2019-2020.

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    https://arxiv.org/abs/2011.05982

    The Photospheric Temperatures of Betelgeuse during the Great Dimming of 2019/2020: No New Dust Required

    Graham M Harper (1), Edward F Guinan (2)Richard Wasatonic (2), Nils Ryde (3) ((1) University of Colorado Boulder, (2) Villanova University, (3) Lund University)

    The processes that shape the extended atmospheres of red supergiants (RSGs), heat their chromospheres, create molecular reservoirs, drive mass loss, and create dust remain poorly understood. Betelgeuse's V-band "Great Dimming" event of 2019 September /2020 February and its subsequent rapid brightening provides a rare opportunity to study these phenomena. Two different explanations have emerged to explain the dimming; new dust appeared in our line of sight attenuating the photospheric light, or a large portion of the photosphere had cooled. Here we present five years of Wing three-filter (A, B, and C band) TiO and near-IR photometry obtained at the Wasatonic Observatory. These reveal that parts of the photosphere had a mean effective temperature (Teff) significantly lower than that found by (Levesque & Massey 2020). Synthetic photometry from MARCS -model photospheres and spectra reveal that the V band, TiO index, and C-band photometry, and previously reported 4000-6800 Angstrom spectra can be quantitatively reproduced if there are multiple photospheric components, as hinted at by VLT-SPHERE images (Montarges et al. 2020). If the cooler component has ΔTeff ≥ 250K cooler than 3650 K, then no new dust is required to explain the available empirical constraints. A coincidence of the dominant short- (∼430 day) and long-period (∼5.8 yr) V-band variations occurred near the time of deep minimum (Guinan et al. 2019). This is in tandem with the strong correlation of V mag and photospheric radial velocities, recently reported by Dupree et al. (2020b). These suggest that the cooling of a large fraction of the visible star has a dynamic origin related to the photospheric motions, perhaps arising from pulsation or large-scale convective motions.

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    https://arxiv.org/abs/2010.04243

    Betelgeuse scope: Single-mode-fibers-assisted optical interferometer design for dedicated stellar activity monitoring

    Narsireddy Anugu, Katie M. Morzinski, Josh Eisner, Ewan Douglas, Dan Marrone, Steve Ertel, Sebastiaan Haffert, Oscar Montoya, Jordan Stone, Stefan Kraus, John Monnier, Jean-Baptiste Lebouquin, Jean-Philippe Berger, Julien Woillez, Miguel Montargès

    Betelgeuse has gone through a sudden shift in its brightness and dimmed mysteriously. This is likely caused by a hot blob of plasma ejected from Betelgeuse and then cooled to obscuring dust. If true, it is a remarkable opportunity to directly witness the formation of dust around a red supergiant star. Today's optical telescope facilities are not optimized for time-evolution monitoring of the Betelgeuse surface, so in this work, we propose a low-cost optical interferometer. The facility will consist of 12 × 4 inch optical telescopes mounted on the surface of a large radio dish for interferometric imaging; polarization-maintaining single-mode fibers will carry the coherent beams from the individual optical telescopes to an all-in-one beam combiner. A fast steering mirror assisted fiber injection system guides the flux into fibers. A metrology system senses vibration-induced piston errors in optical fibers, and these errors are corrected using fast-steering delay lines. We will present the design.
    Do good work. —Virgil Ivan "Gus" Grissom

  3. #183
    Join Date
    Aug 2003
    Posts
    2,031
    Tonight, Betelgeuse looks as if it is 0.1 magnitude fainter than Aldebaran.

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