J/MNRAS/513/2615 Study of UCD's flares from SSO survey (Murray+, 2022)
A study of flares in the ultra-cool regime from SPECULOOS-South.
Murray C.A., Queloz D., Gillon M., Demory B.O., Triaud A.H.M.J., de Wit J.,
Burdanov A., Chinchilla P., Delrez L., Dransfield G., Ducrot E.,
Garcia L.J., Gomez Maqueo Chew Y., Gunther M.N., Jehin E., Mccormac J.,
Niraula P., Pedersen P.P., Pozuelos F.J., Rackham B.V., Schanche N.,
Sebastian D., Thompson S.J., Timmermans M., Wells R.
<Mon. Not. R. Astron. Soc. 513, 2615-2634 (2022)>
=2022MNRAS.513.2615M 2022MNRAS.513.2615M (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Stars, flare ; Stars, dwarfs ; Stars, M-type ;
Stars, L-type ; Photometry ; Optical ; Infrared ; Spectral types ;
Effective temperatures ; Stars, diameters ; Stars, masses
Keywords: planet-star interactions - stars: flare - stars: rotation
Abstract:
We present a study of photometric flares on 154 low-mass (≤0.2 M☉)
objects observed by the SPECULOOS-South Observatory from 2018 June 1
to 2020 March 23. In this sample, we identify 85 flaring objects,
ranging in spectral type from M4 to L0. We detect 234 flares in this
sample, with energies between 1029.2 and 1032.7 erg, using both
automated and manual methods. With this work, we present the largest
photometric sample of flares on late-M and ultra-cool dwarfs to date.
By extending previous M dwarf flare studies into the ultra-cool
regime, we find M5-M7 stars are more likely to flare than both
earlier, and later, M dwarfs. By performing artificial flare
injection-recovery tests, we demonstrate that we can detect a
significant proportion of flares down to an amplitude of 1 per cent,
and we are most sensitive to flares on the coolest stars. Our results
reveal an absence of high-energy flares on the reddest dwarfs. To
probe the relations between rotation and activity for fully convective
stars, we extract rotation periods for fast rotators and lower-bound
period estimates of slow rotators. These rotation periods span from
2.2 h to 65 d, and we find that the proportion of flaring stars
increases for the most fastest rotators. Finally, we discuss the
impact of our flare sample on planets orbiting ultra-cool stars. As
stars become cooler, they flare less frequently; therefore, it is
unlikely that planets around the most reddest dwarfs would enter the
'abiogenesis' zone or drive visible-light photosynthesis through
flares alone.
Description:
The Search for habitable Planets EClipsing ULtra-cOOl Stars
(SPECULOOS) project (Gillon 2018NatAs...2..344G 2018NatAs...2..344G; Burdanov et al.
2018haex.bookE.130B 2018haex.bookE.130B; Delrez et al. 2018SPIE10700E..1ID; Jehin et al.
2018Msngr.174....2J 2018Msngr.174....2J; Sebastian et al. 2021A&A...645A.100S 2021A&A...645A.100S, Cat.
J/A+A/645/A100) aims to search for transiting planets around the
nearest (within 40 pc) UCD stars. SPECULOOS's motivation is to
provide temperate, terrestrial planets for detailed atmospheric
characterization with the James Webb Space Telescope (Gardner et al.
2006SSRv..123..485G 2006SSRv..123..485G) and future extremely large telescopes. The
SPECULOOS target catalogue of ultra-cool objects is defined in
Sebastian et al. (2021A&A...645A.100S 2021A&A...645A.100S, Cat. J/A+A/645/A100). SPECULOOS
comprises a network of 1-m class telescopes spread across the Northern
and Southern Hemispheres. The largest facility, the SPECULOOS-Southern
Observatory (SSO) in Cerro Paranal, Chile, consists of four identical,
robotic telescopes, (i.e see section Introduction).
For this study, we defined a data set spanning from 2018 June 1 to
2020 March 23, using observations from all four telescopes in the SSO.
While this start date is before official scientific operations began,
it marks a point of stability in the commissioning phase. Over nights
in this sample, we have observed 176 unique photometric targets for at
least one night. These observations have typical exposure times of
20-60 s. The majority, though not all, of this data sample are in the
SPECULOOS target list (86 per cent), as defined in Sebastian et al.
(2021A&A...645A.100S 2021A&A...645A.100S, Cat. J/A+A/645/A100). We remove any objects that
are not part of SPECULOOS's usual 'survey mode'. If we choose only the
objects that have been observed more than 20 h with one telescope,
this provides us instead with 154 targets. These 154 objects define
the SPECULOOS-South data sample, (i.e see section 2 Speculoos-south
south data sample).
Thanks to flare detection process (i.e section 3 Generating the
speculoos-south flare sample for manually and automatic flare
detections on SSO light curves) and rotation classification (i.e
section 4 Identifying rotation periods), we are able to provide
results as presented in the tablesso.dat where 50 per cent of the 154
targets shows flares, these 78 stars represent the flare sample (i.e
see section 5.1 SPECULOOS-South flare sample).
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablesso.dat 67 154 *SPECULOOS-South data sample
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Note on tablesso.dat: Target and scientific programs are described in more
details in the section 2 Speculoos-south data sample and in Sebastian et al.
2021A&A...645A.100S 2021A&A...645A.100S, Cat. J/A+A/645/A100. Refer to the section 3 Generating the
speculoos-south flare sample for flare detection, modelling and flare energy
extractions.
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See also:
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/MNRAS/497/3790 : TRAPPIST-South UCD Transit Survey (Lienhard+, 2020)
J/A+A/645/A100 : SPECULOOS. Ultracool dwarf transit survey (Sebastian+, 2021)
J/ApJ/812/3 : MEarth mid-to-late M dwarfs rotation & kinematics
(West+, 2015)
J/ApJ/858/55 : K2 ultracool dwarfs survey. III. M6-L0 flares (Paudel+,2018)
J/AJ/159/60 : 8695 flares from 1228 stars in TESS sectors 1 & 2
(Gunther+, 2020)
J/ApJ/905/107 : Spectroscopic activity indicators of TIC stars
(Medina+, 2020)
J/A+A/650/A138 : TRAPPIST-1 analogue stars TESS light curves (Seli+, 2021)
J/ApJ/788/48 : X-ray through NIR photometry of NGC 2617 (Shappee+, 2014)
J/ApJ/881/9 : EvryFlare. I. Cool stars's flares in southern sky
(Howard+, 2019)
J/ApJ/895/140 : EvryFlare. II. Parameters of 122 cool flare stars
(Howard+, 2020)
J/ApJ/902/115 : EvryFlare. III. Superflares from Evryscope & TESS
(Howard+, 2020)
J/ApJ/876/115 : Optical follow-up of ASAS-SN M dwarf flares (Schmidt+, 2019)
Byte-by-byte Description of file: tablesso.dat
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Bytes Format Units Label Explanations
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1- 19 I19 --- GaiaDR2 Unique source identifier from Gaia DR2 (TARGET)
21- 22 A2 --- SpType Spectral type from SPECULOOS UCDs transit
survey (SPT_CLASS) (1)
24- 27 I4 K Teff Star's effective temperature from SPECULOOS
UCDs transit survey (TEFF)
29- 32 F4.2 Rsun R* Star's radius from SPECULOOS UCDs transit
survey (RAD)
34- 37 F4.2 Msun M* Star's mass from SPECULOOS UCDs transit survey
(MASS)
39- 43 F5.2 mag Jmag 2MASS J magnitude (JMAG)
45- 63 F19.16 d Per ? Rotation period (CHECKED_PERIOD)
65 A1 --- Class Rotation classification (ROT_CLASS) (2)
67 A1 --- Flaring [Y N] Flag indicates if flares is detected or
not (FLARING) (3)
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Note (1): Spectral types are as follows:
L0 = Coolest and faintest stars or brown dwarfs that mark the
beginning of the L spectral class, 5 objects of our the sample
L1 = Early subtype within the L spectral class slightly cooler and
redder than L0 objects, 1 object of our the sample
L2 = L2 dwarfs are cooler and fainter objects than L1 but still hotter
than the later L subtypes (L3, L4, etc), 3 objects of our the
sample
M4 = M4 spectral types belong to the M-dwarf class, which consists
of the coolest and faintest main-sequence stars, 5 objects of our
the sample
M5 = M5 stars are cooler than M4 but warmer than M6, they low-mass
main-sequence stars that are very red and faint, 17 objects of
our the sample
M6 = Mark the coolest end of the M-dwarf sequence, cooler than M5,
approaching the hydrogen-burning limit, 66 objects of our the
sample
M7 = Very close to the hydrogen-burning limit of M-dwarf class,
cooler than M6, 31 objects of our the sample
M8 = Objects are brown dwarfs but a few low-mass stars exist near the
hydrogen-burning threshold, cooler than M7, 17 objects of our
the sample
M9 = M9 represents the coolest end of the M-dwarf sequence and marks
the transition to L dwarfs, 9 objects of our the sample
Note (2): Rotation classification are made as follows:
A = If a rotator passes all the criteria detailed in the section 4
Identifying rotation periods, 24 objects in our sample
B = If it fails any of the section 4 described Identifying rotation
periods criteria but the rotation still seems likely, 22 objects
in our sample
U = Any light curves for which we see some periodic structure, but
we cannot easily determine a period, 29 objects in our sample
N = If we do not detect any periodic signal or we cannot remove
correlations with systematics such as for very crowded fields,
56 objects in our sample
L = For the light curves where we see clear long-period rotation,
but the period is similar or longer than the time window observed
the best we can do is to estimate the lowest possible period we
measure, and acknowledge that there are large uncertainties on
these period values, 23 objects in our sample
As fully explained in the dedicated section 4, with the previously
identified flares and bad observations masked, we search for rotation
periods in the 154 low-mass objects with more than 20 h of
observation. We apply the Lomb-Scargle periodogram analysis (Lomb
1976Ap&SS..39..447L 1976Ap&SS..39..447L; Scargle 1982ApJ...263..835S 1982ApJ...263..835S) to our global light
curves, binned every 20 min. The SSO light curves are not uniformly
sampled, as we have gaps in our data, not only from the day/night
cycle, but also from bad weather, masked flares, and changes to our
observation strategy. We decided to apply a similar classification
system as Newton et al. (2016IAUS..314..124N 2016IAUS..314..124N) to our rotating objects.
Note (3): As the section 5.1 SPECULOOS-South flare sample reminds, we find that
of our 154 unique targets, 78 are considerated as flaring ones and 76
are not. These flaring stars span the spectral type range from M4
(Teff = 3160 K) to L0 (Teff = 2313 K).
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History:
From electronic version of the journal
(End) Luc Trabelsi [CDS] 17-Dec-2024