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We measure rotation periods and sinusoidal amplitudes in Evryscope light curves for 122 two-minute K5–M4 TESS targets selected for strong flaring. The Evryscope array of telescopes has observed all bright nearby stars in the south, producing 2-minute cadence light curves since 2016. Long-term, high-cadence observations of rotating flare stars probe...
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... the simulated rotators cannot reproduce the difference in the activity of our actual rotators, we conclude the difference between our actual short-period and long-period rotators is unlikely to be due to sample bias. These results are shown in Table 2. We note running the same statistics excluding the 29 periods that do not correlate with TESS reduces the significance of the tests, although the activity-versus-period trends are still visible when only including periods confirmed in both surveys. ...Context 2
... find that the fraction of the trials in which the A-D statistic and p-value of our simulated rotators more strongly distinguishes between short and long-periods than do the A-D statistic and p-value of our actual rotators is essentially zero. Across Table 2 do display a difference. We note that we do not conclusively confirm the higher activity of intermediate rotators detected in MEarth light curves by Mondrik et al. (2019). ...Context 3
... each observable, we test whether the fast and intermediate rotators come from the same population, and we test whether the intermediate and slow rotators come from the same population. We observe a general decrease in activity with decreasing rotation, in agreement with Table 2 and earlier studies (e.g. Newton et al. (2017); Davenport et al. (2019); Ilin et al. (2019)). ...Context 4
... observe 122 rotators in our sample of 284 The starspot coverage fraction, largest observed flare energy from each star, and superflare rate versus rotation period. All three types of activity decrease at longer rotation periods, as described by Table 2 and Table 3. To guide the eye, a grey line is overlaid on the decrease in stellar activity with period. ...Context 5
... red dashed lines indicate the boundaries between the Rossby numbers of fast, intermediate, slow rotators. All three types of activity decrease at longer rotation periods, as described by Table 2 and Table 3. However, the superflare rates of intermediate rotators show an apparent increase in flaring, if extremely-active stars (up arrows) are excluded. ...Similar publications
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A microlensing event is mainly used to search for free-floating planets (FFPs). To estimate the FFP mass and distance via the microlensing effect, a microlensing parallax is one of the key parameters. A short duration of FFP microlensing makes it difficult to yield a parallax by the observer’s motion at a recognizable level, so the FFP microlensing...
In this paper, we report the detection and follow-ups of a super stellar flare GWAC\,181229A with an amplitude of $\Delta R\sim$9.5 mag on a M9 type star by $\text{SVOM/GWAC}$ and the dedicated follow-up telescopes. The estimated bolometric energy $E_{bol}$ is $(5.56-9.25)\times10^{34}$ ergs, which places the event to be one of the most powerful fl...
Citations
... II Peg (Kochukhov et al. 2013) and HR 1099 (Donati 1999;Petit et al. 2004), a complex magnetic field was observed with the strength of 500-1000 G. A threshold magnetic field strength of B = 500 G was noted by Howard et al. (2020) for K5-M4 spectral types. Shulyak et al. (2019) detect strong ∼ kG magnetic fields for 29 active M-type dwarfs for a short rotation period (P < 4d). ...
We report the detection of two superflares along with other eight relatively moderate flares in a close binary RS CVn-type system DV Psc using TESS data. The flare energies were found to be in the range of 0.24–23.97 × 10³⁴ erg with a duration of a few minutes to an hour. Most of the flares were not during primary and secondary minima phases. The two superflares occurred at a phase of 0.1 and 0.55 and the stellar spot with a magnetic field B = 500-2000 G can explain the energetics. Since the period of the binary is increasing, we estimated the energy due to mass transfer and noted that accretion energy may provide energy for the flares. Based on the sample of flaring late-type star data, we noted that flares in DV Psc possibly may arrive from either of the stellar components as the correlation between Log E vs Log R does agree well with theoretical relation (E∝ R³). Based on the values of the rotation period for both stellar components, we conclude that DV Psc displays low flaring frequency for a fast rotator. The loop lengths were estimated to be around 3.65–4.55 × 10¹⁰ cm for superflare events which were ∼ three times less than the separation (1.40 × 10¹¹ cm) between the stellar component but if both loops occur at a similar time, the loops may interact and can trigger the observed superflares. We conclude that a large stellar spot or interconnecting magnetic field of lines among binary companions may trigger the superflares.
... The reason for the high superflare rate is still under debate at the current stage. There is some evidence supporting that superflares are more likely to occur on young stars with fast rotation (Howard et al. 2020). However, other studies found an enhanced superflare rate in stars with intermediate rotation periods (10-70 days; Mondrik et al. 2019). ...
Stellar white-light flares are believed to play an essential role in the physical and chemical properties of the atmosphere of the surrounding exoplanets. Here we report an optical monitoring campaign on the nearby flaring system EI Cnc carried out by the Ground-based Wide Angle Camera (GWAC) and its dedicated follow-up telescope. A superflare, coming from the brighter component EI CncA, was detected and observed, in which four components are required to properly model the complex decay light curve. The lower limit of flare energy in the R − band is estimated to be 3.3 × 10 ³² erg. A total of 27 flares are additionally detected from the GWAC archive data with a total duration of 290 hr. The inferred cumulative flare frequency distribution follows a quite shallow power-law function with a slope of β = − 0.50 ± 0.03 over the energy range between 10 ³⁰ and 10 ³³ erg, which reinforces the trend that stars cooler than M4 show enhanced superflare activity. The flares identified in EI Cnc enable us to extend the τ – E relationship previously established in the white-light superflares of solar-type stars down to an energy as low as ∼10 ³⁰ erg (i.e., by 3 orders): τ ∝ E 0.42±0.02 , which suggests a common flare mechanism for stars with a type from M to solar-like and implies an invariant of B 1/3 υ A in the white-light flares.
... Lastly, there are a number of efforts underway to classify photometric variables with much finer physical and observational categories than has been done in this work. Notable examples are the OGLE project (Udalski et al. 2008), the Gaia DR3 variability search (Gaia Collaboration et al. 2021;Rimoldini et al. 2023), specific types of variable stars observed with TESS (e.g., Antoci et al. 2019;Howard et al. 2020b;Hon et al. 2021;Avallone et al. 2022;Barac et al. 2022;Holcomb et al. 2022;Kurtz 2022;Prša et al. 2022a;Saunders et al. 2022), and many others. The TESS Asteroseismic Science Operations Center (TASOC) is engaged in much more detailed and individualized analysis of certain types of stellar variability (Audenaert et al. 2021). ...
During its 2 yr Prime Mission, TESS observed over 232,000 stars at a 2 minute cadence across ∼70% of the sky. These data provide a record of photometric variability across a range of astrophysically interesting timescales, probing stellar rotation, stellar binarity, and pulsations. We have analyzed the TESS 2 minute light curves to identify periodic variability on timescales of 0.01–13 days, and explored the results across various stellar properties. We have identified over 46,000 periodic variables with high confidence, and another 38,000 with moderate confidence. These light curves show differences in variability type across the Hertzsprung–Russell diagram, with distinct groupings of rotational, eclipsing, and pulsational variables. We also see interesting patterns across period–luminosity space, with clear correlations between period and luminosity for high-mass pulsators, evolved stars, and contact binary systems, a discontinuity corresponding to the Kraft break, and a lower occurrence of periodic variability in main-sequence stars on timescales of 1.5–2 days. The variable stars identified in this work are cross-identified with several other variability catalogs, from which we find good agreement between the measured periods of variability. There are ∼65,000 variable stars that are newly identified in this work, which includes the rotation rates of low-mass stars, high-frequency pulsation periods for high-mass stars, and a variety of giant star variability.
... It is out of the scope of this work to attempt a full-blown analysis of real observations, since that would require 1. careful and extensive sample selection, 2. flare finding and vetting, and 3. rotation period measurements on many stars, including corrections for completeness. However, for smaller samples of stars, analysis that includes several of these steps exists in the literature (Howard et al. 2020a;Tu et al. 2021;Ramsay et al. 2020). We have primarily focused on low-mass, and particularly M dwarfs, in this work (see Fig 2, and the flare model from Davenport et al. 2014). ...
The distribution of small-scale magnetic fields in stellar photospheres is an important ingredient in our understanding of the magnetism of low mass stars. Their spatial distribution connects the field generated in the stellar interior with the outer corona and the large scale field, and thereby affects the space weather of planets. Unfortunately, we lack techniques that can locate them on most low-mass stars. One strategy is to localize field concentrations using the flares that occur in their vicinity. We explore a new method that adapts the spot simulation software fleck to study the modulation of flaring times as a function of active latitude. We use empirical relations to construct flare light curves similar to those available from Kepler and the Transiting Exoplanet Survey Satellite (TESS), search them for flares, and use the waiting times between flares to determine the location of active latitudes. We find that the mean and standard deviation of the waiting time distribution provide a unique diagnostic of flaring latitudes as a function of the number of active regions. Latitudes are best recovered when stars have three or less active regions that flare repeatedly, and active latitude widths below 20 deg; when either increases, the information about the active latitude location is gradually lost. We demonstrate our technique on a sample of flaring G dwarfs observed with the Kepler satellite, and furthermore suggest that combining ensemble methods for spots and flares could overcome the limitations of each individual technique for the localization of surface magnetic fields.
... As a result, many new flare stars with high photometric precision can be studied (e.g., Tu et al. 2021;Howard & MacGregor 2022). On the ground, the Next Generation Transit Survey (Wheatley et al. 2018), ASAS-SN (Shappee et al. 2014), Evryscope (Law et al. 2015), and so on, have achieved fruitful results on flare study (e.g., Howard et al. 2020a;Rodríguez Martínez et al. 2020;Jackman et al. 2021). ...
In the archive of the Ground Wide Angle Camera (GWAC), we found 43 white light flares from 43 stars, among which, three are sympathetic or homologous flares, and one of them also has a quasi-periodic pulsation with a period of $13.0\pm1.5$ minutes. Among these 43 flare stars, there are 19 new active stars and 41 stars that have available TESS and/or K2 light curves, from which we found 931 stellar flares. We also obtained rotational or orbital periods of 34 GWAC flare stars, of which 33 are less than 5.4 days, and ephemerides of three eclipsing binaries from these light curves. Combining with low resolution spectra from LAMOST and the Xinglong 2.16m telescope, we found that $L_{\rm H\alpha}/L_{\rm bol}$ are in the saturation region in the rotation-activity diagram. From the LAMOST medium-resolution spectrum, we found that Star \#3 (HAT 178-02667) has double H$\alpha$ emissions which imply it is a binary, and two components are both active stars. Thirteen stars have flare frequency distributions (FFDs) from TESS and/or K2 light curves. These FFDs show that the flares detected by GWAC can occur at a frequency of 0.5 to 9.5 yr$^{-1}$. The impact of flares on habitable planets was also studied based on these FFDs, and flares from some GWAC flare stars may produce enough energetic flares to destroy ozone layers, but none can trigger prebiotic chemistry on their habitable planets.
... The largest contributor to this collection is the Kepler sample, with temperatures and rotation periods from Santos et al. (2019). The rest are predominantly M dwarfs with rotation periods from: the PS1 Medium Deep Survey (Kado-Fong et al. 2016), MEarth (Newton et al. 2016(Newton et al. , 2018, CARMENES (Díez Alonso et al. 2019), Evryscope (Howard et al. 2020), and the K2SDSS sample (Popinchalk et al. 2021). Popinchalk et al. (2021) provided the Gaia DR2 identifiers for the targets from all of these surveys, which we used to obtain temperatures from v8 of the TESS Input Catalog (TIC) (Stassun et al. 2019). ...
... Field M dwarfs follow a bimodality in their rotation periods (Kado-Fong et al. 2016;Newton et al. 2016;Howard et al. 2020). Using kinematic ages, Newton et al. (2016) speculated that the transition between the fast and slow populations must be quick, and must occur between the ages of 2 and 5 Gyr. ...
... Benchmarks include the Pleiades (120 Myr; Rebull et al. 2016), Praesepe (670 Myr; Douglas et al. 2017, 2019), NGC 6811 (1 Gyr; Curtis et al. 2019), NGC 752 (1.4 Gyr; Agüeros et al. 2018), NGC 6819/Ruprecht 147 (2.5 Gyr projected forward by Curtis et al./2.7 Gyr; Meibom et al. 2015; Curtis et al. 2020), M67 (4 Gyr;Barnes et al. 2016, and this work), and three field stars: α Cen B and 61 Cyg A and B(Table 3 ofCurtis et al. 2020, and references therein). Field stars are taken from a collection of literature sources: Kepler (Santos et al. 2019), the PS1 Medium Deep Survey (Kado-Fong et al. 2016), MEarth (Newton et al. 2016, 2018), CARMENES (Díez Alonso et al. 2019), Evryscope(Howard et al. 2020), and the K2SDSS sample(Popinchalk et al. 2021). ...
We present stellar rotation periods for late K- and early M-dwarf members of the 4 Gyr old open cluster M67 as calibrators for gyrochronology and tests of stellar spin-down models. Using Gaia EDR3 astrometry for cluster membership and Pan-STARRS (PS1) photometry for binary identification, we build this set of rotation periods from a campaign of monitoring M67 with the Canada-France-Hawaii Telescope's MegaPrime wide field imager. We identify 1807 members of M67, of which 294 are candidate single members with significant rotation period detections. Moreover, we fit a polynomial to the period versus color-derived effective temperature sequence observed in our data. We find that the rotation of very cool dwarfs can be explained by a simple solid-body spin-down between 2.7 and 4 Gyr. We compare this rotational sequence to the predictions of gyrochronological models and find that the best match is Skumanich-like spin-down, P_rot \propto t^0.62, applied to the sequence of Ruprecht 147. This suggests that, for spectral types K7-M0 with near-solar metallicity, once a star resumes spinning down, a simple Skumanich-like is sufficient to describe their rotation evolution, at least through the age of M67. Additionally, for stars in the range M1-M3, our data show that spin-down must have resumed prior to the age of M67, in conflict with predictions of the latest spin-down models.
... The largest contributor to this collection is the Kepler sample, with temperatures and rotation periods from Santos et al. (2019). The rest are predominantly M dwarfs with rotation periods from the PS1 Medium Deep Survey (Kado-Fong et al. 2016), MEarth (Newton et al. 2016(Newton et al. , 2018, CARMENES (Díez Alonso et al. 2019), Evryscope (Howard et al. 2020), and the K2SDSS sample (Popinchalk et al. 2021). Popinchalk et al. (2021) provided the Gaia DR2 identifiers for the targets from all of these surveys, which we used to obtain temperatures from v8 of the TESS Input Catalog (TIC; Stassun et al. 2019). ...
... Field M dwarfs follow a bimodality in their rotation periods (Kado-Fong et al. 2016;Newton et al. 2016;Howard et al. 2020). Using kinematic ages, Newton et al. (2016) speculated that the transition between the fast and slow populations must be quick and must occur between the ages of 2 and 5 Gyr. ...
We present stellar rotation periods for late K- and early M-dwarf members of the 4 Gyr old open cluster M67 as calibrators for gyrochronology and tests of stellar spin-down models. Using Gaia EDR3 astrometry for cluster membership and Pan-STARRS (PS1) photometry for binary identification, we build this set of rotation periods from a campaign of monitoring M67 with the Canada–France–Hawaii Telescope’s MegaPrime wide-field imager. We identify 1807 members of M67, of which 294 are candidate single members with significant rotation period detections. Moreover, we fit a polynomial to the period versus color-derived effective temperature sequence observed in our data. We find that the rotation of very cool dwarfs can be explained by simple solid-body spin-down between 2.7 and 4 Gyr. We compare this rotational sequence to the predictions of gyrochronological models and find that the best match is Skumanich-like spin-down, P rot ∝ t 0.62 , applied to the sequence of Ruprecht 147. This suggests that, for spectral types K7–M0 with near-solar metallicity, once a star resumes spinning down, a simple Skumanich-like relation is sufficient to describe their rotation evolution, at least through the age of M67. Additionally, for stars in the range M1–M3, our data show that spin-down must have resumed prior to the age of M67, in conflict with the predictions of the latest spin-down models.
... While multiwavelength observational campaigns of flares have been ongoing for decades (Hawley et al. 2003;Osten et al. 2005), the more recent development of exoplanet atmospheric science has led to a resurgence of these campaigns for exoplanet host stars (MacGregor et al. 2021). While photometric surveys like Kepler (Borucki et al. 2010) and all-sky surveys like the Transiting Exoplanet Survey Satellite (TESS; Ricker et al. 2014) provided crucial insight into the frequency of flares as a function of spectral type (Notsu et al. 2013;Davenport et al. 2014;Maehara et al. 2015;Loyd et al. 2018a;Howard et al. 2019;Günther et al. 2020;Feinstein et al. 2022), age (Ilin et al. 2019;Feinstein et al. 2020;Ilin et al. 2021), and rotation period (Doyle et al. 2018(Doyle et al. , 2019(Doyle et al. , 2020Howard et al. 2020;Seligman et al. 2022b), detailed spectroscopic studies of stellar flares connect broadband observations to those observed from the Sun. ...
High-energy X-ray and ultraviolet (UV) radiation from young stars impacts planetary atmospheric chemistry and mass loss. The active ∼22 Myr M dwarf AU Mic hosts two exoplanets orbiting interior to its debris disk. Therefore, this system provides a unique opportunity to quantify the effects of stellar X-ray and UV irradiation on planetary atmospheres as a function of both age and orbital separation. In this paper, we present over 5 hr of far-UV (FUV) observations of AU Mic taken with the Cosmic Origins Spectrograph (COS; 1070-1360 Å) on the Hubble Space Telescope (HST). We provide an itemization of 120 emission features in the HST/COS FUV spectrum and quantify the flux contributions from formation temperatures ranging from 10 ⁴ to 10 ⁷ K. We detect 13 flares in the FUV white-light curve with energies ranging from 10 ²⁹ to 10 ³¹ erg s. The majority of the energy in each of these flares is released from the transition region between the chromosphere and the corona. There is a 100× increase in flux at continuum wavelengths λ < 1100 Å in each flare, which may be caused by thermal Bremsstrahlung emission. We calculate that the baseline atmospheric mass-loss rate for AU Mic b is ∼10 ⁸ g s ⁻¹ , although this rate can be as high as ∼10 ¹⁴ g s ⁻¹ during flares with L flare ≃ 10 33 erg s ⁻¹ . Finally, we model the transmission spectra for AU Mic b and c with a new panchromatic spectrum of AU Mic and motivate future JWST observations of these planets.
... For example, by monitoring large numbers of active stars at high cadence, the Evryscopes have made new discoveries and placed constraints on flare and superflare activity that could impact potentially-habitable exoplanets. Observations from Evryscope-South have been used to discover the first superflare from Proxima Centauri, 3 characterize hundreds of other flares and superflares by placing constraints on flare frequencies, energies, and blackbody temperatures, [4][5][6] and place constraints on TRAPPIST-1 superflare occurrence and planetary habitability. 7 In recent years, affordable low-noise CMOS sensors and medium-aperture telescopes have made the next generation of the Evryscope, called the Argus Optical Array, reasonable to build at the mid-scale funding level. ...
... The Evryscopes have detected rapid transient events ranging from flares and superflares (e.g. Ref. [6][7][8][9][10] to optical reflections of space debris (e.g. Ref. 11). ...
Recent advancements in low-cost astronomical equipment, including high-quality medium-aperture telescopes and low-noise CMOS detectors, have made the deployment of large optical telescope arrays both financially feasible and scientifically interesting. The Argus Optical Array is one such system, composed of 900 eight-inch telescopes, which is planned to cover the entire night sky in each exposure and is capable of being the deepest and fastest Northern Hemisphere sky survey. With this new class of telescope comes new challenges: determining optimal individual telescope pointings to achieve required sky coverage and overlaps for large numbers of telescopes, and realizing those pointings using either individual mounts, larger mounting structures containing telescope subarrays, or the full array on a single mount. In this paper, we describe a method for creating a pointing pattern, and an algorithm for rapidly evaluating sky coverage and overlaps given that pattern, and apply it to the Argus Array. Using this pattern, telescopes are placed into a hemispherical arrangement, which can be mounted as a single monolithic array or split into several smaller subarrays. These methods can be applied to other large arrays where sky packing is challenging and evenly spaced array subdivisions are necessary for mounting.
