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

Abstract

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 $(T_{\mathrm{eff}}$) 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 $\Delta T_{\mathrm{eff}}\ge 250$ K cooler than 3650 K, then no new dust is required to explain the available empirical constraints. A coincidence of the dominant short- ($\sim 430$ day) and long-period ($\sim 5.8$ 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.

Accepted ApJ - 19 pages, 5 figures

References in corpus (11)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• Variability in red supergiant stars: pulsations, long secondary periods and convection noise
• The close circumstellar environment of Betelgeuse - V. Rotation velocity and molecular envelope properties from ALMA
• What causes the large extensions of red-supergiant atmospheres? Comparisons of interferometric observations with 1-D hydrostatic, 3-D convection, and 1-D pulsating model atmospheres
• Spatially Resolved Ultraviolet Spectroscopy of the Great Dimming of Betelgeuse
• The period-luminosity relation of red supergiants with Gaia DR2
• Tomography of cool giant and supergiant star atmospheres II. Signature of convection in the atmosphere of the red supergiant star $\mu$ Cep
• The Secret Lives of Cepheids: $\delta$ Cep -- the Prototype of a New Class of Pulsating X-ray Variable Stars
• The inhomogeneous sub-millimeter atmosphere of Betelgeuse
• Betelgeuse fainter in the sub-millimetre too: an analysis of JCMT and APEX monitoring during the recent optical minimum
• ALMA and VLA reveal the lukewarm chromospheres of the nearby red supergiants Antares and Betelgeuse

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