J/A+A/646/A34 Search for flares and CMEs in SDSS data (Koller+, 2021)
Search for flares and associated CMEs on late-type main-sequence stars in
optical SDSS spectra.
Koller F., Leitzinger M., Temmer M., Odert P., Beck P.G., Veronig A.
<Astron. Astrophys. 646, A34 (2021)>
=2021A&A...646A..34K 2021A&A...646A..34K (SIMBAD/NED BibCode)
ADC_Keywords: Stars, flare ; Stars, late-type ; Balmer lines
Keywords: stars: activity - stars: flares - stars: late-type
Abstract:
This work aims to detect and classify stellar flares and potential
stellar coronal mass ejection (CME) signatures in optical spectra
provided by the Sloan Digital Sky Survey (SDSS) data release 14. The
sample is constrained to all F, G, K, and M main-sequence type stars,
resulting in more than 630000 stars. This work makes use of the
individual spectral exposures provided by the SDSS.
An automatic flare search was performed by detecting significant
amplitude changes in the Hα and Hβ spectral lines after a
Gaussian profile was fit to the line core. CMEs were searched for by
identifying asymmetries in the Balmer lines caused by the Doppler
effect of plasma motions in the line of sight.
We identified 281 flares on late-type stars (spectral types K3-M9).
We identified six possible CME candidates showing excess flux in
Balmer line wings. Flare energies in Hα were calculated and
masses of the CME candidates were estimated. The derived Hα
flare energies range from 3x1028-2x1033erg. The Hα flare
energy increases with earlier types, while the fraction of flaring
times increases with later types. Mass estimates for the CME
candidates are in the range of 6x1016-6x1018g, and the highest
projected velocities are ∼300-700km/s. The low detection rate of
CMEs we obtained agrees with previous studies, suggesting that for
late-type main-sequence stars the CME occurrence rate that can be
detected with optical spectroscopy is low.
Description:
This file contains the complete list of flares found by this work and
their most important derived or collected parameters. The in-depth
description of the derivation of these parameters is given in the
article.
The optical spectra by SDSSS data release 14 (2018ApJS..235...42A 2018ApJS..235...42A)
that we used in this work consist of several single spectra, which are
combined to a final coadded spectrum for each observed object. We used
the single spectra to find temporal changes in Balmer lines,
indicating flaring events. With the latest GAIA data release
(2018A&A...616A...1G 2018A&A...616A...1G), we were able to derive energy and luminosity
values for the flares. We focused on the Halpha Balmer line due to the
better S/N. Our methods were based on line fitting algorithms to
detect changes from one observation to another.
Similar to the work by Hilton et al. (2010, Cat. J/AJ/140/1402) we
give stellar coordinates as RAdeg and DEdeg as the first parameters to
distinguish between the objects. In addition to that, the
Plate-MJD-Fiber number serves as a unique identifier for the flaring
SDSS spectrum. The stellar position is not enough because objects can
be observed multiple times at different surveys by SDSS, resulting in
different sets of single spectra. The method and the categorization of
the S/N bins are defined in the article.
The spectral type classified by SDSS and by other literature is given.
The distance and the source for the value is given when possible. The
defined quiet flag and the consideration flag give insight on the
reliability of the derived values. Whether a flare was also detected
in Hilton et al. (2010, Cat. J/AJ/140/1402) is given in a separate
column. The flare energy, the luminosity, and the associated errors
were derived using the SDSS spectra as is described in the article
(see Sect.4.2.2) and given here in units of W and W/s (J).
The peak spectrum and the spectrum used in the calculation as the
reference are given. Their number refer to the chronological order of
the single spectra. The number of available single spectra (in the
optical red domain containing Halpha) and the number of single spectra
in a flaring state are given. The overall time of these flaring
spectra is summed and given in units of minutes.
Additional comments made during the visual inspection of all flaring
spectra are added.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablec.dat 217 281 Flaring star and flare properties
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See also:
J/AJ/140/1402 : M dwarf flares from SDSS spectra (Hilton+, 2010)
Byte-by-byte Description of file: tablec.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg SDSS right ascension (J2000.0)
10- 19 F10.5 deg DEdeg SDSS declination (J2000.0)
21- 35 A15 --- P-MJD-F SDSS Plate-MJD-Fiber Identifier
37- 39 A3 --- Method Method used (1)
41- 46 A6 --- S/Nbin Signal to Noise ratio bin (2)
48- 54 A7 --- SpType Spectral type
56- 59 A4 --- r_SpType Spectral type source (3)
61- 62 A2 --- SpTypeSDSS Spectral type by SDSS
64- 69 F6.1 pc Dist ? Distance (4)
71- 74 A4 --- r_Dist Distance source (5)
76 I1 --- Quiet [0/2]? Quiet flag (6)
78- 91 A14 --- FlareEvol Flare evolution estimates (7)
93-100 A8 --- Consider Consideration flag (8)
102-104 A3 --- H2010 Flare present in Hilton et al., 2010,
Cat. J/AJ/140/1402(9)
106-113 A8 --- Platequal Plate quality by SDSS (10)
115-121 E7.1 J EHaFlare ? Flare energy in Halpha (in W/s unit)
123-129 E7.1 J e_EHaFlare ? Flare energy error in Halpha (in W/s unit)
131-137 E7.1 W LHaFlare ? Peak flare luminosity in Halpha
139-145 E7.1 W e_LHaFlare ? Peak flare luminosity error in Halpha
147-148 I2 --- Nexp Number of exposures (11)
150 I1 --- NflSpec Number of flaring spectra (12)
152-153 I2 --- NRefspec Number of reference spectrum (13)
155-156 I2 --- NPeakspec Number of flare peak spectrum (14)
158-160 I3 min Fltimeall Summed time of flaring spectra (15)
162-217 A56 --- Comments Comments (16)
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Note (1): Method used to identify flares as follows:.
HTM = high-threshold method (see Sect. 3.1.1)
LTM = low-threshold method (see Sect. 3.1.1)
ELM = Emission line method (see Sect. 3.1.2)
R = Reevaluated flares also found by Hilton et al. (2010, J/AJ/140/1402)
that were originally rejected after visual inspection.
Note (2): S/N Bin: Categorization of object into specific S/N bin
(see Sect. 2.3) Classifications are High, Medium, Low, and Lowest.
Note (3): Sources for the spectral type are denoted as follows:
S1 = West et al., 2011AJ....141...97W 2011AJ....141...97W; J/AJ/141/97
S2 = West et al., 2008AJ....135..785W 2008AJ....135..785W; J/AJ/135/785
S3 = Kleinman et al., 2013ApJS..204....5K 2013ApJS..204....5K; J/ApJS/204/5
S4 = Cook et al., 2016MNRAS.457.2192C 2016MNRAS.457.2192C; J/MNRAS/457/2192
S5 = McGehee, 2006AJ....131.2959M 2006AJ....131.2959M; J/AJ/131/2959
S6 = Guieu et al., 2006A&A...446..485G 2006A&A...446..485G; J/A+A/446/485
S7 = Newton et al., 2014AJ....147...20N 2014AJ....147...20N; J/AJ/147/20
S8 = Briceno et al., 2019AJ....157...85B 2019AJ....157...85B; J/AJ/157/85
S9 = Kraus & Hillenbrand, 2009ApJ...704..531K 2009ApJ...704..531K; J/ApJ/704/531
S10 = Luhman et al., 2017AJ....153...46L 2017AJ....153...46L; J/AJ/153/46
S11 = Zhang et al., 2010MNRAS.404.1817Z 2010MNRAS.404.1817Z; J/MNRAS/404/1817
S12 = Morgan et al., 2012AJ....144...93M 2012AJ....144...93M; J/AJ/144/93
S13 = Kowalski et al., 2009AJ....138..633K 2009AJ....138..633K;
S14 = Zhong et al., 2015RAA....15.1154Z 2015RAA....15.1154Z; J/other/RAA/15.1154
S15 = Skiff, 2014yCat....1.2023S 2014yCat....1.2023S; B/mk
SDSS = Spectral type from SDSS file if no literature data was available
Note (4): Stellar distance in parsec. For distances derived by using parallaxes,
the inversion of the parallax without further correction was used.
Note (5): Sources for the stellar distance. Gaia was used when available.
The sources are denoted as follows:
GAIA = Parallaxes by Gaia Collaboration, 2018A&A...616A...1G 2018A&A...616A...1G, I/345
D1 = Jones & West, 2016ApJ...817....1J 2016ApJ...817....1J; J/ApJ/817/1
D2 = West et al., 2011AJ....141...97W 2011AJ....141...97W; J/AJ/141/97
D3 = Stas-sun et al., 2018AJ....156..102S 2018AJ....156..102S; J/AJ/156/102
D4 = Theissen et al., 2017AJ....153...92T 2017AJ....153...92T; J/AJ/153/92
Note (6): Quiet flag indicates whether the reference spectrum for calculating
the flare energy was quiet (see Sect. 4.2) as follows:
1 = Quiet reference
2 = Reference spectrum probably quiet
0 = Reference spectrum has problems (e.g. cosmic-ray), energy calculation
not reliable
Note (7): Flares evolution estimates visible in the spectra (see Sect. 4.2.3).
The following abbreviations are used:
"rise" = flaring rise
"p. rise" = probably rise
"decay" = flare decay
"p. decay" = probably decay
"unclear" = activity visible, but impossible to declare evolution
"diff. activity" = the flare occurs at a different time, no evolution visible
"full" = rise and decay as well as a peak are visible
Note (8): Consideration flag indicates how reliable the flare is.
"Yes": Distinct flare
"Probable": clear activity in at least Halpha and Hbeta, but more caution in
handling them is appropriate
Note (9): A "Yes" Indicates whether the flare was also found by
Hilton et al. 2010AJ....140.1402H 2010AJ....140.1402H; J/AJ/140/1402
Note (10): Platequality read out from the SDSS .fits file header.
Platequality can either be "good", "marginal" or "poor".
Note (11): This number of exposures refers to the amount of available single
spectra that include the Halpha line for this object at this time.
Note (12): Number of single spectra that are in flaring state in this SDSS
spectrum.
Note (13): Number denoting which spectrum was used as a reference for the
calculation. The number refers to the chronological order: 1 refers to the
first spectrum that was observed. 0 means that the coadded spectrum was
used as a reference.
Note (14): Number denoting which spectrum shows the peak of the flare.
The number refers to the chronological order: 1 refers to the first
spectrum that was observed,.
Note (15): Summed time of all flaring single spectra in this SDSS spectrum in
minutes.
Note (16): Subjective comments added after confirming the flares.
Frequently used abbreviations and notes:
(Subjective estimated) significance and size of the flare using the
designations "large", "medium", "small", and "mini".
cons.: Indicates whether the flare is in a consecutive series of spectra.
Notes on wing variability: For example, "ha hb hg hd bothwings" means
enhanced wings in Hα, Hβ, Hγ, and Hδ.
When a Balmer line wing is mentioned, it indicates the possibility of
an enhancement. Possible absorptions are mentioned separately.
"CME?" indicates that this event was analyzed in depth to conclude
whether a CME did occur.
"New emission line" or "new em. line" indicates whether the flare
produced a Balmer emission line where no emission line was previously
visible (good indicator for flaring activity).
Other notes include: visible shifts in the data, high noise values,
"cont. em?" as the possibility of enhanced continuum emission due to the
flare, and many available spectra (as "many datapoints").
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Acknowledgements:
Florian Koller, flko(at)gmx.at
(End) Florian Koller [IGAM, Austria], Patricia Vannier [CDS] 29-Nov-2020