Long-Term Spot Photometry and Differential Rotation of The Spotted Flare Stars EV Lac and By Dra

1993 ◽  
pp. 157-159 ◽  
Author(s):  
K. P. Panov
Keyword(s):  
Differential Rotation ◽  
Flare Stars ◽  
Ev Lac

scholarly journals Long-Term Spot Photometry and Differential Rotation of the Spotted Flare Stars Ev Lac and by Dra

1993 ◽  
Vol 157 ◽  
pp. 157-159
Author(s):  
K.P. Panov
Keyword(s):  
Differential Rotation ◽  
Astronomical Observatory ◽  
Light Curves ◽  
Rotational Period ◽  
Rotational Modulation ◽  
Balmer Lines ◽  
Flare Stars ◽  
Ev Lac ◽  
Image Position

Ev Lac = Gliese 873 (dM4.5e) is a well-known flare star with hydrogen Balmer lines as well as with Ca II lines in emission. Rotational modulation by starspots has been discovered by Pettersen (1980) who determined the photometric (rotational) period P = 4.378 d. Spot photometry of EV Lac was obtained with the 60 cm telescope of the Bulgarian National Astronomical Observatory in the years 1983–87 and 1989–91. For these years (except for 1989 and 1990) light curves are available in the V and B bands. From the BNAO-data and the data published by Pettersen (1980) a new ephemerishas been derived which shows a slight revision of the period.

Long-Term Changes of the Flare Stars EV Lac and by Dra

1982 ◽  
pp. 253-276 ◽  
Author(s):  
L. N. Mavridis ◽  
G. Asteriadis ◽  
F. M. Mahmoud
Keyword(s):  
Long Term Changes ◽  
Flare Stars ◽  
Ev Lac

scholarly journals Photometric Research of Pre-flare and Extra-flare Activity of Flare Stars

1995 ◽  
Vol 151 ◽  
pp. 110-111
Author(s):  
G. Roizman ◽  
L. Pustil’nik ◽  
D. Pundak
Keyword(s):  
Spectral Lines ◽  
Flare Star ◽  
Flare Activity ◽  
Jordan Valley ◽  
Preliminary Results ◽  
Regional College ◽  
Flare Stars ◽  
Ev Lac ◽  
Low Amplitude

Preliminary results of a photometric search for non-flare activity of the flare star EV Lac during June-August 1994 are presented. These observations are part of the long-term project entitled “Investigation of pre-flare processes on flare stars” being carried out at the Observatory of the Jordan Valley Regional College since July 1994. The project was motivated by reports of the existence of slow, low-amplitude non-periodic variability of both spectral lines and continuum outside/between flares (Rodono et al. 1979, Roizman et al. 1984).

scholarly journals Learning about Stellar Dynamos from Long–term Photometry of Starspots

1991 ◽  
Vol 130 ◽  
pp. 353-369 ◽  
Author(s):  
Douglas S. Hall
Keyword(s):  
Differential Rotation ◽  
Rotation Period ◽  
Turnover Time ◽  
Rotating Stars ◽  
Photometric Variability ◽  
Solar Type ◽  
Magnetic Cycles ◽  
The Many ◽  
Rapidly Rotating Stars

AbstractSpottedness, as evidenced by photometric variability in 277 late-type binary and single stars, is found to occur when the Rossby number is less than about 2/3. This holds true when the convective turnover time versus B–V relation of Gilliland is used for dwarfs and also for subgiants and giants if their turnover times are twice and four times longer, respectively, than for dwarfs. Differential rotation is found correlated with rotation period (rapidly rotating stars approaching solid-body rotation) and also with lobe-filling factor (the differential rotation coefficient k is 2.5 times larger for F = 0 than F = 1). Also reviewed are latitude extent of spottedness, latitude drift during a solar-type cycle, sector structure and preferential longitudes, starspot lifetimes, and the many observational manifestations of magnetic cycles.

scholarly journals Rapid spike flares on AD Leo and EV Lac

1990 ◽  
Vol 137 ◽  
pp. 27-30
Author(s):  
K. P. Panov ◽  
M. S. Ivanova ◽  
A. Antov
Keyword(s):  
Astronomical Observatory ◽  
Monitoring Time ◽  
Flare Stars ◽  
Ev Lac

Photoelectric U - band observations of the flare stars A Leo and EV Lac during the last 9 years obtained at the Bulgarian National Astronomical Observatory revealed 8 rapid spike flares on AD Leo and 9 rapid spike flares on EV Lac which duration is less than 6 seconds. The corresponding total monitoring time is 173.6 hours for AD Leo and 173.3 hours for EV Lac.

scholarly journals Flare-Like Events on the T-Tauri Star RU LUP1

1989 ◽  
Vol 104 (2) ◽  
pp. 139-142 ◽  
Author(s):  
F. Giovannelli ◽  
D. Castaldo ◽  
E. Covino ◽  
A.A. Vittone ◽  
C. Rossi
Keyword(s):  
Tauri Star ◽  
Quiescent State ◽  
Complete Coverage ◽  
Patchy Distribution ◽  
Active Star ◽  
X Ray ◽  
T Tauri ◽  
Observed Behaviour ◽  
Flare Stars

AbstractA long term multifrequency campaign on the T Tauri star RU Lupi has been carried out in the X-Ray, UV optical and IR spectral regions with ASTRON and IUE satellites and ESO 1.5 m+IDS, 1.4 m CAT, 0.5 m UBVRI and 1 m IR telescopes, respectively.We present two flare-like events occurred on April 17, 1984 and June 30, 1986. The first one was detected only in the UV, clue to lack the of simultaneous observations in other spectral regions. The second one was observed in UV, optical and IR regions showing a maximum roughly in the U band A comparison of the whole energy distribution of this event with that of a quiescent state observed on June 27 shows a flux enhancement of (89 ± 2)%. A detailed analysis of UV continuum and lines, namely N V, C I, CII, CIV, Si II and Si IV, shows that ihe surfaces fluxes of RU Lupi are always larger than those observed on typical flare stars and on the Sun by a factor of roughly 2 and 3 orders of magnitude, respectively. This fact allows us to conclude that RU Lupi activity cannot be explained even invoking a complete coverage by solar-like plages. On the contrary a patchy distribution of the emitting regions could explain the observed behaviour of this active star.

scholarly journals Long-Term Variations of Solar Differential Rotation and Sunspot Activity: Revisited

Solar Physics ◽  
2013 ◽  
Vol 289 (3) ◽  
pp. 759-768 ◽  
Author(s):  
K. J. Li ◽  
W. Feng ◽  
X. J. Shi ◽  
J. L. Xie ◽  
P. X. Gao ◽  
...  
Keyword(s):  
Differential Rotation ◽  
Sunspot Activity ◽  
Solar Differential Rotation ◽  
Long Term Variations

scholarly journals Flare Stars Database

1994 ◽  
Vol 161 ◽  
pp. 380-382
Author(s):  
M. Tsvetkov ◽  
M. Chukova ◽  
K. Tsvetkova
Keyword(s):  
Wide Field ◽  
Flare Activity ◽  
The Galaxy ◽  
Statistical Regularities ◽  
Ceti Type ◽  
Formation And Evolution ◽  
Flare Stars ◽  
Machine Readable

The important role of flare stars (UV Ceti type variables) in astrophysics is due to the fact that the flare activity is not only typical for red stars with small masses but is a necessary stage during their evolution. The flare star search in stellar aggregates has led to the accumulation of rich observational material allowing us to look for statistical regularities in star formation and evolution. At present, there are more than 1500 known flare stars in the Galaxy; these were discovered mainly during the last 30 years. Most results of the long term monitoring with wide-field telescopes are listed in existing catalogues of flare stars in stellar aggregates and in the solar neighbourhood. These catalogues and their machine-readable versions were the basis for the present database of flare stars in the Galaxy.

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