- 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.
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Search Results
- 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.
4765. Flat Galaxy Catalogue
- ID:
- ivo://CDS.VizieR/VII/162
- Title:
- Flat Galaxy Catalogue
- Short Name:
- VII/162
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A systematic search for disklike edge-on galaxies with a diameter larger than a=40 arcsec and major-to-minor axis ratio a/b>7 has been carried out by means of Palomar Observatory Sky Survey and ESO/SERC survey. As a result, we present new catalog of a flat galaxies (FGC) containing 4455 objects and covering about 56% of the whole sky for the first time. The catalog is assigned to study large-scale cosmic streamings and another problems of observational cosmology. Due to a better quality of the photographic emulsions used for the southern sky survey, the galaxies measured on ESO/SERC films extend to a surface magnitude slightly fainter than the same galaxies measured on POSS prints. So we present the catalog data separately for northern sky (DEC from -17.5 to +90 degrees) - FLAT GALAXY CATALOG , FGC, N = 2573 and for southern sky (DEC from -90 to -17.5 degrees) - SOUTHERN EXTENSION OF FLAT GALAXY CATALOG, FGCE, N = 1882. There are about 200 galaxies in a common region which were found and measured independently on POSS prints and ESO/SERC films. They were included in FGC, not in FGCE. The mean ratio <a(ESO)/a(POSS)> for them is equal to 1.26+/-0.4. This value is near to the result obtained by Lauberts (1982). Making some statistics it is easy to exclude FGCE galaxies with a <50arcsec to have the same depth of the sample. The Appendix to Flat Galaxy Catalog - Addendum - contains the data of 291 galaxies. They were selected in preliminary survey but rejected after more precise diameter measurements because of violation the a/b >= 7 criterion. In every case, these galaxies can be used in different observational programs.
- ID:
- ivo://CDS.VizieR/J/AJ/108/1
- Title:
- Flatness of clusters of galaxies
- Short Name:
- J/AJ/108/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We examine relations between shape, richness, and velocity dispersion for a sample of 350 clusters of galaxies of all morphologies, including those with visible substructure. For our sample the apparent shape of clusters is correlated with velocity dispersion and Abell (1958ApJS....3..211A) richness in the sense that poor, low dispersion clusters are flatter in the mean than their richer, higher dispersion counterparts. These characteristics are also exhibited by the X-ray emitting gas. There are virtually no highly flattened clusters having high richness or high velocity dispersions in the sample. We find that the variation of richness and velocity dispersion with apparent shape is too steep to be assigned to projection effects, and conclude rich, high dispersion clusters are intrinsically more nearly spherical than poorer clusters and that two-body relaxation is probably not an effective anisotropy damping mechanism in Abell clusters.
- ID:
- ivo://CDS.VizieR/J/AZh/77/407
- Title:
- Flat-spectrum radio sources at 0.97-21.7GHz
- Short Name:
- J/AZh/77/407
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of observations of a complete sample of flat-spectrum radio sources with spectral indices {alpha}>-0.5 are presented. The sample was selected from the Zelenchuk Survey at 3.9GHz (See Cat. <VIII/49>) and contains all sources with declinations 4-6 degrees, galactic latitudes |b|>10 degrees, and 3.9-GHz fluxes >200mJy. Spectra at 0.97-21.7 GHz were obtained for all 69 sample sources. The spectra were classified and a correlation between variability amplitude and spectrum shape was found.
- ID:
- ivo://CDS.VizieR/J/AZh/89/388
- Title:
- Flat-spectrum radio sources long-term variability
- Short Name:
- J/AZh/89/388
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The paper reports the results of ten-year centimeter-wavelength observations with the RATAN-600 radio telescope of a complete sample of 83 flat-spectrum sources from the GB6 catalog of the MGB Survey (Cat. VIII/40), with S_4.85_>200mJy at declinations 10{deg}-12{deg}30'. Starting in 2000, the observations were conducted simultaneously at six frequencies in the range 0.97-21.7GHz. Seventy-six sources (including 54 quasars) have been identified with optical objects, which have redshifts in the range z=0.331-3.601.
- ID:
- ivo://CDS.VizieR/J/MNRAS/368/1411
- Title:
- Flat-spectrum symmetric radio sources
- Short Name:
- J/MNRAS/368/1411
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The radio sources listed below were selected from the Jodrell-VLA Astrometric Survey and the Cosmic-Lens All-Sky Survey (part 1) and constitute a (non-complete) parent sample for the selection of flat-spectrum symmetric object candidates (the ones which show structure, when their VLA-A 8.4GHz data are analysed). The parent sample contains northern hemisphere objects with 8.4GHz flux densities greater than 100mJy, galactic latitudes greater than 10 degrees and 1.40-to-4.85GHz spectral indices (when known; if not, the source is kept in the sample) smaller than 0.50 (flat). The most relevant properties of the parent sample are listed in the Table.
- ID:
- ivo://CDS.VizieR/J/A+A/631/A59
- Title:
- Fluctuations of UV background from GALEX
- Short Name:
- J/A+A/631/A59
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The all sky survey run by the Galaxy Evolution Explorer (GALEX AIS) mapped about 85 % of the Galaxy at ultraviolet (UV) wavelengths and detected the diffuse UV background produced by the scattering of the radiation from OBA stars by interstellar dust grains. Against this background, diffuse weak structures are detected as well as the UV counterparts to nebulae and molecular clouds. To make full profit of the survey, unsupervised and semi-supervised procedures need to be implemented. The main objective of this work is to implement and analyze the results of the method developed by us for the blind detection of ISM features in the GALEX AIS. Most ISM features are detected at very low signal levels (dark filaments, globules) against the already faint UV background. We have defined an index the UV background fluctuations index (or UBF index) to identify areas of the sky where these fluctuations are detected. The algorithm is applied to the images obtained in the FUV (1344-1786{AA}) band since this is less polluted by stellar sources, facilitating the automated detection. The UBF index is shown to be sensitive to the main star forming regions within the Gould's Belt, as well as to some prominent loops like Loop I or the Eridanus and Monogem areas. The catalogue with the UBF index values is made available on-line to the community.