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

Harper, Graham M.; Guinan, Edward F.; Wasatonic, Richard; Ryde, Nils (2020). The Photospheric Temperatures of Betelgeuse during the Great Dimming of 2019/2020 : No New Dust Required. Astrophysical Journal, 905, (1)
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| Published | English
Authors:
Harper, Graham M. ; Guinan, Edward F. ; Wasatonic, Richard ; Ryde, Nils
Department:
Lund Observatory - Has been reorganised
Abstract:

The processes that shape the extended atmospheres of red supergiants, 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 eff) significantly lower than that found by Levesque & Massey. Synthetic photometry from MARCS-model photospheres and spectra reveal that the V band, TiO index, and C-band photometry, and previously reported 4000-6800 Å spectra can be quantitatively reproduced if there are multiple photospheric components, as hinted at by Very Large Telescope (VLT)-SPHERE images in Montargès et al. If the cooler component has ΔT eff ≥ 250 K cooler than 3650 K, then no new dust is required to explain the available empirical constraints. A coincidence of the dominant short-(∼430 days) and long-period (∼5.8 yr) V-band variations occurred near the time of deep minimum (Guinan et al. 2019a). 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.

ISSN:
0004-637X
LUP-ID:
ad79e406-523e-4f14-b670-1f47247a8968 | Link: https://lup.lub.lu.se/record/ad79e406-523e-4f14-b670-1f47247a8968 | Statistics

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