J/AJ/169/27 M dwarfs flares timing & energy from TESS & Swift (Howard+, 2025)
Preparing for the Early eVolution Explorer: Characterizing the photochemical
inputs and transit detection efficiencies of young planets using multiwavelength
flare observations by TESS and Swift.
Howard W.S., MacGregor M.A., Feinstein A.D., Vega L.D., Cody A.M.,
Turner N.J., Scott V.J., Burt J.A., Venuti L.
<Astron. J., 169, 27 (2025)>
=2025AJ....169...27H 2025AJ....169...27H
ADC_Keywords: Stars, flare; Photometry, ultraviolet; Photometry, infrared;
Optical; Stars, dwarfs; Stars, M-type
Keywords: Exoplanet atmospheric evolution ; Young star clusters ;
Stellar flares ; Near ultraviolet astronomy
Abstract:
Ultraviolet flare emission can drive photochemistry in exoplanet
atmospheres and even serve as the primary source of uncertainty in
atmospheric retrievals. Additionally, flare energy budgets are not
well understood due to a paucity of simultaneous observations. We
present new near-UV (NUV) and optical observations of flares from
three M dwarfs obtained at 20s cadence with Swift and the Transiting
Exoplanet Survey Satellite (TESS), along with a reanalysis of flares
from two M dwarfs in order to explore the energy budget and timing of
flares at NUV-optical wavelengths. We find a 9000K blackbody
underestimates the NUV flux by ≥2x for 54±14% of flares and
14.8x for one flare. We report time lags between the bands of 0.5-6.6min
and develop a method to predict the qualitative flare shape
and time lag to 36%±30% accuracy. The scatter present in
optical-NUV relations is reduced by a factor of 2.0±0.6 when
comparing the total NUV energy with the TESS energy during the FWHM
duration due to the exclusion of the Teff ∼5000K tail. We show the NUV
light curve can be used to remove flares from the optical light curve
and consistently detect planets with 20% smaller transits than is
possible without flare detrending. Finally, we demonstrate a
10x increase in the literature number of multiwavelength flares with
the Early eVolution Explorer (EVE), an astrophysics Small Explorer
concept to observe young clusters with simultaneous NUV and optical
bands in order to detect young planets, assess their photochemical
radiation environments, and observe accretion.
Description:
Monitoring of each star was performed with the Swift Ultraviolet/Optical
Telescope (UVOT). The observations of the five stars in the sample
took place as follows: GJ 674 from 2023-06-17 to 2023-06-28, G 41-14
from 2023-01-26 to 2023-01-29, EV Lac from 2022-10-24 to 2022-10-27,
AP Col from 2020-12-06 to 2020-12-07, and YZ CMi from 2021-01-23 to
2021-01-23. G 41-14, GJ 674, AP Col, and YZ CMi were each observed in
the UVM2 filter (1990-2500Å), while EV Lac was observed in the UVW2
filter (1600-2260Å).
The Transiting Exoplanet Survey Satellite (TESS) observed GJ 674 (TIC
218263393), G 41-14 (TIC 283784587), EV Lac (TIC 154101678), AP Col
(TIC 160329609), and YZ CMi (TIC 266744225) at 20s cadence using four
10.5cm telescopes in a red optical (600-1000nm) bandpass. The
observations took place as follows: GJ 674 from 2023-06-02 to
2023-06-30, G 41-14 from 2023-01-18 to 2023-02-12, EV Lac from
2022-09-30 to 2022-10-29, AP Col from 2020-11-20 to 2020-12-16, and
YZ CMi from 2021-01-14 to 2021-02-08. The TESS observations completely
covered the UVOT observations for a total of 27.1hr of simultaneous
monitoring across all five stars. We note not all overlapping coverage
is usable due to times with low NUV count rates.
Objects:
----------------------------------------------------
RA (2000) DE Designation(s)
----------------------------------------------------
06 04 52.14 -34 33 35.7 AP Col = TIC 160329609
22 46 49.73 +44 20 02.3 EV Lac = TIC 154101678
08 58 56.32 +08 28 26.0 G 41-14 = TIC 283784587
17 28 39.94 -46 53 42.6 GJ 674 = TIC 218263393
07 44 40.17 +03 33 08.8 YZ CMi = TIC 266744225
----------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 102 13 Times and time lag properties of flares observed
with Swift and TESS
table3.dat 66 13 Flare energy budgets of flares observed with Swift
and TESS
table4.dat 54 114 Flare yields for candidate young cluster pointings
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See also:
I/347 : Distances to 1.33 billion stars in Gaia DR2 (Bailer-Jones+, 2018)
I/355 : Gaia DR3 (Gaia Collaboration, 2022)
J/A+A/474/293 : Radial velocities of GJ 674 (Bonfils+, 2007)
J/AJ/134/2340 : Membership of Praesepe & Coma Berenices clusters (Kraus+, 2007)
J/AJ/135/785 : SDSS-DR5 low-mass star spectroscopic sample (West+, 2008)
J/ApJS/207/15 : M dwarf flare spectra (Kowalski+, 2013)
J/ApJS/209/5 : Superflares of Kepler stars. I. (Shibayama+, 2013)
J/ApJ/812/3 : MEarth mid-to-late M dwarfs rotation & kinematics (West+, 2015)
J/A+A/599/A23 : Accretion-rotation connection in NGC 2264 (Venuti+, 2017)
J/ApJ/849/36 : Flaring activity of M dwarfs in the Kepler field (Yang+, 2017)
J/AJ/155/196 : Analysis of K2 LCs for memb. of USco & ρ Oph (Rebull+, 2018)
J/ApJ/881/9 : EvryFlare. I. Cool stars flares in southern sky (Howard+, 2019)
J/AJ/158/122 : Local structure & star formation history of MW (Kounkel+, 2019)
J/A+A/640/A112 : TRAPPIST-1 transit timings (Ducrot+, 2020)
J/AJ/159/60 : 8695 flares from 1228 stars in TESS sect. 1 & 2 (Gunther+, 2020)
J/ApJ/902/115 : EvryFlare. III. Superflares: Evryscope & TESS (Howard+, 2020)
J/AJ/160/279 : Untangling the Gal. II. Structure within 3kpc (Kounkel+, 2020)
J/A+A/638/A20 : M dwarfs X-ray activity & rotation relations (Magaudda+, 2020)
J/ApJ/905/107 : Spectroscopic activity indicators of TIC stars (Medina+, 2020)
J/AJ/159/166 : Membership & propert. of moving groups with Gaia (Ujjwal+, 2020)
J/AJ/162/197 : Photometry, rotation & Li in open cluster NCG2516 (Bouma+, 2021)
J/A+A/645/A42 : Flares in 5 open clusters (Ilin+, 2021)
J/AJ/161/171 : THYME. V. Discov. a new stellar association (Tofflemire+, 2021)
J/AJ/164/110 : HST/COS far-UV spect.:AU Microscopii flares (Feinstein+, 2022)
J/ApJ/926/204 : TESS monitoring campaign: low-mass flare stars (Howard+, 2022)
J/AJ/163/24 : Stellar populations in the Sco-Cen complex (Luhman, 2022)
J/AJ/163/156 : THYME. VI. TOI-1227 radial velocity (Mann+, 2022)
J/ApJ/939/94 : New associations in Gaia DR3 solar neighborhood (Moranta+, 2022)
J/AJ/164/17 : GJ 1243 flares properties with Kepler and TESS (Mendoza+, 2022)
J/A+A/678/A71 : Cluster ages in Sco-Cen (Ratzenboeck+, 2023)
J/ApJ/951/33 : X-ray-Opt. flare monitoring obs. of AU MIC. I. (Tristan+, 2023)
J/A+A/669/A15 : TESS flare events and physical parameters (Yang+, 2023)
J/ApJS/272/30 : Habitable Worlds Observatory (HWO): 164 targets (Harada+, 2024)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- ID Star identifier
8- 9 A2 --- Flare Flare number, F#
11- 15 F5.1 --- sigNUV [11.6/412] NUV detection significance
17- 20 F4.1 --- sigTESS [3.6/41] TESS detection significance
22- 32 F11.5 d TstartNUV [59189/60118] NUV start time (1)
34- 44 F11.5 d TcntrdNUV [59189/60118] NUV centroid time (1)
46- 56 F11.5 d TstopNUV [59189/60118] NUV end time (1)
58- 68 F11.5 d TstartTESS [59189/60118] TESS start time (1)
70- 80 F11.5 d TcntrdTESS [59189/60118] TESS centroid time (1)
82- 92 F11.5 d TstopTESS [59189/60118] TESS end time (1)
94- 96 F3.1 min Tlag [0.5/6.6] Observed time lag, NUV and TESS
peaks
98- 102 F5.2 --- L-G2G1 [-0.12/2.16] Degree (log-likelihood ratio)
that a two-Gaussian fit to the NUV peak is
preferred
--------------------------------------------------------------------------------
Note (1): Times are given in modified Julian dates, JD-2,400,000.5
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Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- ID Star identifier
8- 9 A2 --- Flare Flare number, F#
11- 15 F5.2 10+23J Enuv [1.7/63.4] Total energy measured in the NUV,
1e30erg
17- 20 F4.2 10+23J e_Enuv [0.1/1.7] Uncertainty in Enuv
22- 26 F5.2 10+23J Efuv [0.8/30] Total energy estimated in the FUV,
1e30erg (1)
28- 31 F4.1 10+23J e_Efuv [0.5/14] Uncertainty in Efuv
33- 38 F6.2 10+23J Etot-T [0.7/120] Total energy measured in the TESS
band, 1e30erg
40- 43 F4.2 10+23J e_Etot-T [0.2/1.2] Uncertainty in Etot-T
45- 50 F6.2 10+23J Efwhm-T [3.4/218] Peak energy during FWHM of TESS
band light curve
52- 55 F4.2 10+23J e_Efwhm-T [0.5/2.2] Uncertainty in Efwhm-T
57- 61 I5 K Teff [9100/24300] Effective temperature of flare
63- 66 F4.1 --- ECF [1.1/14.8] Empirical correction factor (2)
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Note (1): Total energy estimated for the FUV using the
Berger+ (2024MNRAS.532.4436B 2024MNRAS.532.4436B) relations.
Note (2): The amount by which the NUV is underestimated by a 9000K blackbody.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- --- [Theia]
7- 9 I3 --- Pointing [13/822] Candidate pointing identifier from
Theia catalog group number (J/AJ/158/122)
11 I1 --- Field [1/3] Subfield designation within Group
13- 19 F7.3 deg RAdeg [33.8/358] Field center right ascension
(J2000)
21- 27 F7.3 deg DEdeg [-74.6/64.4] Field center declination (J2000)
29- 31 I3 Myr Age [7/400] Age
33- 36 I4 --- nKdwarf [3/1077] Number of K dwarfs
38- 41 I4 --- nMdwarf [7/3308] Number of M dwarfs
43- 48 F6.1 --- yieldTESS [6.5/1413] TESS-band flare yield per 30days
stare time
50- 54 F5.1 --- yieldNUV [0.4/105] NUV flare yield per 30days stare
time
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History:
From electronic version of the journal
(End) Prepared by [AAS], Robin Leichtnam [CDS] 06-Nov-2025