- ID:
- ivo://CDS.VizieR/J/A+A/645/A42
- Title:
- Flares in 5 open clusters
- Short Name:
- J/A+A/645/A42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Magnetic fields are a key component in the main sequence evolution of low mass stars. Flares, energetic eruptions on the surfaces of stars, are an unmistakable manifestation of magnetically driven emission. The occurrence rates and energy distributions of flares trace stellar characteristics such as mass and age. But before flares can be used to constrain stellar properties, the flaring-age-mass relation requires proper calibration. This work sets out to quantify flaring activity of independently age-dated main sequence stars for a broad range of spectral types using optical light curves obtained by the Kepler satellite. Drawing from the complete K2 archive, we searched 3435 80 day long light curves of 2111 open cluster members for flares using the open-source software packages K2SC to remove instrumental and astrophysical variability from K2 light curves, and AltaiPony to search and characterize the flare candidates. We confirmed a total of 3844 flares on high probability open cluster members with ages from zero age main sequence (Pleiades) to 3.6Gyr (M67). We extended the mass range probed in the first study of this series to span from Sun-like stars to mid-M dwarfs. We added the Hyades (690Myr) to the sample as a comparison cluster to Praesepe (750Myr), the 2.6Gyr old Ruprecht 147, and several hundred light curves from the late K2 Campaigns in the remaining clusters. We found that the flare energy distribution was similar in the entire parameter space, following a power law relation with an exponent between 1.84 and 2.39. We confirmed that flaring rates declined with age, and declined faster for higher mass stars. Our results are in good agreement with most previous statistical flare studies. We found evidence that a rapid decline in flaring activity occurred in M1-M2 dwarfs around Hyades/Praesepe age, when these stars spun down to rotation periods of about 10 d, while higher mass stars had already transitioned to lower flaring rates, and lower mass stars still resided in the saturated activity regime. We conclude that some discrepancies between our results and flare studies that used rotation periods for their age estimates could be explained by sample selection bias toward more active stars, but others may hint at limitations of using rotation as an age indicator without additional constraints from stellar activity.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/368/1392
- Title:
- Flares of the close binary FL Vir
- Short Name:
- J/MNRAS/368/1392
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of U-filter flare monitoring of the binary flare star FL Vir = Wolf 424 is presented. 57 flares with energies between 2x10^28^ and 2x10^31^erg were recorded in 20h of observation. The properties of flare occurrence and flare time-scales are analysed, and the flare activity level in 1980 April is determined to be L_f_(U)=8.0x10^26^erg/s. This is larger than previously published results and may indicate a variation in the flare activity level on a time-scale of years. An analysis of existing data indicates that the flare activity level correlates with the relative orbital positions of the stars.
- ID:
- ivo://CDS.VizieR/J/AJ/140/483
- Title:
- Flares of UV Cet type stars
- Short Name:
- J/AJ/140/483
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this study, a new method is presented to classify flares derived from the photoelectric photometry of UV Ceti type stars. This method is based on statistical analyses using an independent samples t-test. The data used in analyses were obtained from four flare stars observed between 2004 and 2007. The total number of flares obtained in the observations of AD Leo, EV Lac, EQ Peg, and V1054 Oph is 321 in the standard Johnson U band. As a result flares can be separated into two types, slow and fast, depending on the ratio of flare decay time to flare rise time. The ratio is below 3.5 for all slow flares, while it is above 3.5 for all fast flares. Also, according to the independent samples t-test, there is a difference of about 157 s between equivalent durations of slow and fast flares. In addition, there are significant differences between amplitudes and rise times of slow and fast flares.
- ID:
- ivo://CDS.VizieR/J/MNRAS/447/2714
- Title:
- Flare stars across the H-R diagram
- Short Name:
- J/MNRAS/447/2714
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- From Kepler data, we show that the incidence of flares on stars drops by only a factor of 4 from K-M dwarfs to A-F stars. Allowing for visibility effects, this implies that the true relative number of flare stars does not change very much from cool dwarfs to hot A stars. The idea that flares on A stars can be attributed to a cool companion has to be rejected because it leads to flare amplitudes two orders of magnitude smaller than actually observed. We confirm that spots on flare stars are generally larger than those on non-flare stars and that flare stars rotate significantly faster than non-flare stars. Analysis of 209 flare stars observed in Kepler short-cadence mode allows accurate measurements of flare shapes and duration. We find that about one-third of the flares have a bump or slope discontinuity on the decaying branch and that flares of long duration are to be found in stars with low surface gravities. Flare energies are strongly correlated with stellar luminosity and radius. The correlation with radius leads to a rough estimate of several tens of gauss for the typical magnetic field associated with a flare. The correlation with stellar luminosity can be understood if the typical flare loop length-scales approximately as the stellar radius. We examined the flare frequency as a function of orbital phase in three eclipsing binaries in which a large number of flares are visible. There appears to be no correlation of flaring with orbital phase, which weakens the hypothesis that flares in close binaries could be a result of reconnection of field lines connecting the two stars.
- ID:
- ivo://CDS.VizieR/J/other/CoSka/51.78
- Title:
- Flare stars in nearby Galactic open clusters
- Short Name:
- J/other/CoSka/51
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The study is devoted to search for flare stars among confirmed members of Galactic open clusters using high-cadence photometry from TESS mission. We analyzed 957 high-cadence light curves of members from 136 open clusters. As a result, 56 flare stars were found, among them 8 hot B-A type objects. Of all flares, 63 % were detected in sample of cool stars (Teff<5000K), and 2 % - in stars of spectral type G, while 23% in K-type stars and approximately 34% of all detected flares are in M-type stars. Using the FLATW'RM (FLAre deTection With Ransac Method) flare finding algorithm, we estimated parameters of flares and rotation period of detected flare stars. The flare with the largest amplitude appears on the M3 type EQ Cha star. Statistical analysis did not reveal any direct correlation between ages, rotation periods and flaring activity.
- ID:
- ivo://CDS.VizieR/J/other/PZ/23.141
- Title:
- Flare stars in the Pleiades
- Short Name:
- J/other/PZ/23.14
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A brief account is given of the problems in identifying newly discovered variable stars with already known ones. These problems are most acute in dense stellar fields, for instance, in the Pleiades. To arrive to a homogeneous coordinates system for variable stars in the Pleiades, the author has measured the coordinates for nearly 550 stars in the region centered on Alcyone. This has made it possible to obtain for the first time accurate coordinates for 165 flare stars; then, for 46 stars we have round significant errors in the published coordinates. A cross-identification table between the GCVS (Cat. <II/139>) and the catalogue of Haro et al. (1982, Cat. <II/131>) has been compiled.
- ID:
- ivo://CDS.VizieR/J/ApJ/849/36
- Title:
- Flaring activity of M dwarfs in the Kepler field
- Short Name:
- J/ApJ/849/36
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Flare events are mainly due to magnetic reconnection and thus are indicative of stellar activity. The Kepler Space Observatory records numerous stellar activities with unprecedented high photometric precision in flux measurements. It is perfectly suitable for carrying out a statistical study of flares. Here we present 540 M dwarfs with flare events discovered using Kepler long-cadence data. The normalized flare energy, as defined by the ratio to bolometric stellar luminosity, L_flare_/L_bol_, is used to indicate the flare activity. We find that, similar to the X-ray luminosity relation, the L_flare_/L_bol_ versus P_rot_ relation can also be described with three phases, supersaturation, saturation, and exponential decay, corresponding to an ultra- short period, a short period, and a long period. The flare activity and the number fraction of flaring stars in M dwarfs rise steeply near M4, which is consistent with the prediction of a turbulent dynamo. The size of starspots are positively correlated with flare activity. The L_flare_/L_bol_ ratio has a power-law dependence on L_H{alpha}_/L_bol_, a parameter indicative of stellar chromosphere activity. According to this relation, a small enhancement in chromosphere activity may cause a huge rise in flare energy, which suggests that superflares or hyperflares may not need an extra excitation mechanism. Through a comparison study, we suggest that flare activity is a more suitable indicator for stellar activity, especially in the boundary region. However, contrary to what is expected, some M dwarfs with strong flares do not show any light variation caused by starspots. Follow-up observations are needed to investigate this problem.
- ID:
- ivo://CDS.VizieR/J/ApJ/846/34
- Title:
- Flaring gamma-ray sources; LAT 7.4yr (2FAV)
- Short Name:
- J/ApJ/846/34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the second catalog of flaring gamma-ray sources (2FAV) detected with the Fermi All-sky Variability Analysis (FAVA), a tool that blindly searches for transients over the entire sky observed by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. With respect to the first FAVA catalog, this catalog benefits from a larger data set, the latest LAT data release (Pass 8), as well as from an improved analysis that includes likelihood techniques for a more precise localization of the transients. Applying this analysis to the first 7.4 years of Fermi observations, and in two separate energy bands 0.1-0.8GeV and 0.8-300GeV, a total of 4547 flares were detected with significance greater than 6{sigma} (before trials), on the timescale of one week. Through spatial clustering of these flares, 518 variable gamma-ray sources were identified. Based on positional coincidence, likely counterparts have been found for 441 sources, mostly among the blazar class of active galactic nuclei. For 77 2FAV sources, no likely gamma-ray counterpart has been found. For each source in the catalog, we provide the time, location, and spectrum of each flaring episode. Studying the spectra of the flares, we observe a harder-when-brighter behavior for flares associated with blazars, with the exception of BL Lac flares detected in the low-energy band. The photon indexes of the flares are never significantly smaller than 1.5. For a leptonic model, and under the assumption of isotropy, this limit suggests that the spectrum of freshly accelerated electrons is never harder than p~2.
- ID:
- ivo://org.gavo.dc/flashheros/q/echssa
- Title:
- Flash/Heros Split-Order SSAP Service
- Short Name:
- F/H Orders SSAP
- Date:
- 15 Aug 2024 15:17:04
- Publisher:
- The GAVO DC team
- Description:
- Spectra from the Flash and Heros Echelle spectrographs developed at Landessternwarte Heidelberg and mounted at La Silla and various other observatories. The data mostly contains spectra of OB stars. Heros was the name of the instrument after Flash got a second channel in 1995.
6370. Flash/Heros SSAP
- ID:
- ivo://org.gavo.dc/flashheros/q/ssa
- Title:
- Flash/Heros SSAP
- Short Name:
- Flash/Heros SSAP
- Date:
- 15 Aug 2024 15:17:04
- Publisher:
- The GAVO DC team
- Description:
- Spectra from the Flash and Heros Echelle spectrographs developed at Landessternwarte Heidelberg and mounted at La Silla and various other observatories. The data mostly contains spectra of OB stars. Heros was the name of the instrument after Flash got a second channel in 1995.