J/ApJ/905/34 2017-2020 photometry of Betelgeuse (Harper+, 2020)
The photospheric temperatures of Betelgeuse during the Great Dimming of
2019/2020: no new dust required.
Harper G.M., Guinan E.F., Wasatonic R., Ryde N.
<Astrophys. J., 905, 34 (2020)>
=2020ApJ...905...34H 2020ApJ...905...34H
ADC_Keywords: Stars, supergiant; Stars, M-type; Photometry, infrared; Optical;
Effective temperatures
Keywords: M supergiant stars ; Stellar atmospheres ; Circumstellar dust ;
Stellar photospheres ; Atmospheric variability
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
(Teff) significantly lower than that found by
Levesque & Massey (2020ApJ...891L..37L 2020ApJ...891L..37L). Synthetic photometry from
MARCS-model photospheres and spectra reveal that the V band, TiO
index, and C-band photometry, and previously reported 4000-6800Å
spectra can be quantitatively reproduced if there are multiple
photospheric components, as hinted at by Very Large Telescope
(VLT)-SPHERE images in Montarges+ (2020, ESO Press Release). If the
cooler component has ΔTeff≥250K cooler than 3650K, then no new
dust is required to explain the available empirical constraints. A
coincidence of the dominant short-(∼430days) and long-period (∼5.8yr)
V-band variations occurred near the time of deep minimum
(Guinan+ 2019ATel13365....1G 2019ATel13365....1G). This is in tandem with the strong
correlation of V mag and photospheric radial velocities, recently
reported by Dupree+ (2020ApJ...899...68D 2020ApJ...899...68D). 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.
Description:
Photometric observations of Betelgeuse have been conducted at
Wasatonic Observatory (Allentown, PA) since 1996 September. The
observations were carried out with a f/10 20cm (8inch) Celestron
Schmidt-Cassegrain Telescope (SCT) for the first five observing
seasons, followed by using a f/10 28cm (11inch) SCT for the remaining
19 seasons. An uncooled Optec SSP-3 photometer was employed. The SSP-3
has a red-near-IR sensitive PIN-photodiode detector with a broad
spectral range from 3000 to 11000Å.
V-band photometry was conducted using a wide-band V filter (5550Å)
that closely matches the V bandpass of the Johnson UBV system. In
addition, three intermediate band Wing red/near-IR filters were
employed. The Wing A filter is centered on the strong γ(0,0)
TiO7190Å band head, while the central wavelengths of the Wing B
(7500Å) and C (10240Å) filters are centered on near-IR continuum
regions; see Section 2.
Objects:
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RA (ICRS) DE Designation(s)
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05 55 10.31 +07 24 25.4 Betelgeuse = * alf Ori
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
fig1a.dat 41 118 Five years of photometry: Teff and C magnitudes,
averaged into 7 day bins
fig1b.dat 27 209 Five years of V-band photometry
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See also:
III/150 : Perkins Revised MK Types for the Cooler Stars (Keenan+ 1989)
II/177 : Near IR Photometry of a Sample of IRAS Point Sources (Fouque+ 1992)
J/A+A/281/817 : Model atmospheres for Vega (Castelli+ 1994)
J/A+A/545/A99 : 2 supergiants and 2 hypergiants radio spectra (Teyssier+, 2012)
J/ApJ/893/11 : Massive star variability in M31 from iPTF (Soraisam+, 2020)
J/ApJ/902/63 : SMEI photometry of Betelgeuse (Joyce+, 2020)
J/A+A/650/L17 : HERMES spectra of Betelgeuse (Kravchenko+, 2021)
J/other/Nat/594.365 : Betelgeuse during its Great Dimming (Montarges+, 2021)
Byte-by-byte Description of file: fig1a.dat
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Bytes Format Units Label Explanations
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1- 9 F9.1 d HJD Heliocentric Julian Date
13- 18 F6.1 K Teff [3491/3732] Calculated, 7-day binned effective
temperature derived from the TiO index
using Equation 2
22- 25 F4.1 K e_Teff [11/33] The 1σ uncertainty in Teff
29- 34 F6.3 mag Cmag [-2.8/-2.39] 7-day binned Wing C band (1.024um)
magnitude
37- 41 F5.3 mag e_Cmag [0.017/0.04] The 1σ uncertainty in Cmag
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Byte-by-byte Description of file: fig1b.dat
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Bytes Format Units Label Explanations
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1- 11 F11.3 d HJD Heliocentric Julian Date
16- 20 F5.3 mag Vmag [0.29/1.62] Unbinned V band (0.555um) magnitude
23- 27 F5.3 mag e_Vmag [0.026] Error similar to the symbol size
in Figure 1 (always "0.026")
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 02-May-2022