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87 results on '"Konstantinova-Antova, R."'

53. Fast UBVRI colorimetry of stellar flares on EV Lacertae

Author

Zhilyaev, B., Romanyuk, Ya., Svyatogorov, O., Verlyuk, I., Alekseev, I., Lovkaya, M., Avgoloupis, S., Contadakis, M., Seiradakis, J., Antov, A., and Konstantinova-Antova, R.

Subjects
Plenary Sessions
Published
2003

62. Exploring the magnetic topologies of cool stars

Author

Morin, J., primary, Donati, J.-F., additional, Petit, P., additional, Albert, L., additional, Auriére, M., additional, Cabanac, R., additional, Catala, C., additional, Delfosse, X., additional, Dintrans, B., additional, Fares, R., additional, Forveille, T., additional, Gastine, T., additional, Jardine, M., additional, Konstantinova-Antova, R., additional, Lanoux, J., additional, Lignires, F., additional, Morgenthaler, A., additional, Paletou, F., additional, Velez, J.C. Ramirez, additional, Solanki, S.K., additional, Thado, S., additional, and Van Grootel, V., additional

Published
2010
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66. Lithium and magnetic fields in giant stars

Author

Lèbre, A., primary, Palacios, A., additional, do Nascimento, J. D., additional, Konstantinova-Antova, R., additional, Kolev, D., additional, Aurière, M., additional, de Laverny, P., additional, and De Medeiros, J. R., additional

Published
2009
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67. Discovery of a weak magnetic field in the photosphere of the single giant Pollux

Author

Aurière, M., primary, Wade, G. A., additional, Konstantinova-Antova, R., additional, Charbonnel, C., additional, Catala, C., additional, Weiss, W. W., additional, Roudier, T., additional, Petit, P., additional, Donati, J.-F., additional, Alecian, E., additional, Cabanac, R., additional, Van Eck, S., additional, Folsom, C. P., additional, and Power, J., additional

Published
2009
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73. Fast colorimetry of the flare star EV Lacertae fromUBVRIobservations in 2004

Author

Zhilyaev, B. E., primary, Romanyuk, Ya. O., additional, Svyatogorov, O. A., additional, Verlyuk, I. A., additional, Kaminsky, B., additional, Andreev, M., additional, Sergeev, A. V., additional, Gershberg, R. E., additional, Lovkaya, M. N., additional, Avgoloupis, S. J., additional, Seiradakis, J. H., additional, Contadakis, M. E., additional, Antov, A. P., additional, Konstantinova-Antova, R. K., additional, and Bogdanovski, R., additional

Published
2007
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74. A BCool magnetic snapshot survey of solar-type stars.

Author

Marsden, S. C., Petit, P., Jeffers, S. V., Morin, J., Fares, R., Reiners, A., do Nascimento, J.-D., Aurière, M., Bouvier, J., Carter, B. D., Catala, C., Dintrans, B., Donati, J.-F., Gastine, T., Jardine, M., Konstantinova-Antova, R., Lanoux, J., Lignières, F., Morgenthaler, A., and Ramìrez-Vèlez, J. C.

Subjects
MAGNETIC fields, SOLAR system, HIGH resolution imaging, SPECTROPOLARIMETERS, ROTATIONAL motion, SOLAR chromosphere
Abstract

We present the results of a major high-resolution spectropolarimetric BCool project magnetic survey of 170 solar-type stars. Surface magnetic fields were detected on 67 stars, with 21 classified as mature solar-type stars, a result that increases by a factor of 4 the number of mature solar-type stars on which magnetic fields have been observed. In addition, a magnetic field was detected for 3 out of 18 of the subgiant stars surveyed. For the population of K-dwarfs, the mean value of |Bl| (|Bl|mean) was also found to be higher (5.7 G) than |Bl|mean measured for the G-dwarfs (3.2 G) and the F-dwarfs (3.3 G). For the sample as a whole, |Bl|mean increases with rotation rate and decreases with age, and the upper envelope for |Bl| correlates well with the observed chromospheric emission. Stars with a chromospheric S-index greater than about 0.2 show a high magnetic field detection rate and so offer optimal targets for future studies. This survey constitutes the most extensive spectropolarimetric survey of cool stars undertaken to date, and suggests that it is feasible to pursue magnetic mapping of a wide range of moderately active solar-type stars to improve our understanding of their surface fields and dynamos. [ABSTRACT FROM AUTHOR]

Published
2014

77. Detection of high‐frequency optical oscillation during the flare phase of EV Lac in 1999

Author

Contadakis, M. E., primary, Avgoloupis, S., additional, Seiradakis, J., additional, Zhilyaev, B. E., additional, Romanyuk, Ya. O., additional, Verlyuk, I. A., additional, Svyatogorov, O. A., additional, Khalack, V. R., additional, Sergeev, A. V., additional, Konstantinova‐Antova, R. K., additional, Antov, A. P., additional, Bachev, R. S., additional, Alekseev, I. Y., additional, Chalenko, V. E., additional, and Shakhovskoy, D. N., additional

Published
2004
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79. Fast colorimetry of the flare star EV Lacertae from UBVRIobservations in 2004

Author

Zhilyaev, B. E., Romanyuk, Ya. O., Svyatogorov, O. A., Verlyuk, I. A., Kaminsky, B., Andreev, M., Sergeev, A. V., Gershberg, R. E., Lovkaya, M. N., Avgoloupis, S. J., Seiradakis, J. H., Contadakis, M. E., Antov, A. P., Konstantinova-Antova, R. K., Bogdanovski, R., Zhilyaev, B. E., Romanyuk, Ya. O., Svyatogorov, O. A., Verlyuk, I. A., Kaminsky, B., Andreev, M., Sergeev, A. V., Gershberg, R. E., Lovkaya, M. N., Avgoloupis, S. J., Seiradakis, J. H., Contadakis, M. E., Antov, A. P., Konstantinova-Antova, R. K., and Bogdanovski, R.

Abstract

Aims.We report results of a quantitative colorimetric UBVRIanalysis of two flare events on the red dwarf EV Lac. The photometric data were obtained in September 2004, during the multi-site synchronous monitoring from the four observatories in Ukraine, Russia, Greece, and Bulgaria. These observations confirmed the presence of small-scale high-frequency oscillations (HFO) initially detected by Rodonó (1974, A&A, 32, 337) and recently reconfirmed by the authors. Here we discuss the color characteristics of flares and HFO.

Published
2007
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82. Magnetic field structure in single late-type giants: β Ceti in 2010-2012.

Author

Tsvetkova, S., Petit, P., Aurière, M., Konstantinova-Antova, R., Wade, G. A., Charbonnel, C., Decressin, T., and Bogdanovski, R.

Subjects
MAGNETIC fields, ASTROPHYSICAL spectropolarimetry, SIGNAL-to-noise ratio
Abstract

Aims. We study the behavior of the magnetic field and the line activity indicators of the single late-type giant β Ceti. Using spectropolarimetric data, we aim to reconstruct the magnetic field structure on the star's surface and to present the first magnetic maps for β Ceti. Methods. The data were obtained using two spectropolarimeters – Narval at the Bernard Lyot Télescope, Pic du Midi, France, and ESPaDOnS at CFHT, Hawaii. Thirty-eight circularly-polarized spectra have been collected in the period June 2010–January 2012. The least square deconvolution method was applied for extracting high signal-to-noise ratio line profiles, from which we measured the surface-averaged longitudinal magnetic field Bl. Chromospheric activity indicators CaII K, Hα, CaII IR (854.2 nm), and radial velocity were simultaneously measured, and their variability was analyzed along with the behavior of Bl. The Zeeman Doppler imaging (ZDI) inversion technique was employed for reconstructing the large-scale magnetic field and two magnetic maps of β Ceti are presented for two periods (June 2010–December 2010 and June 2011–January 2012). Results. The Bl stays with a same positive polarity for the whole observational period and shows significant variations in the interval 0.1–8.2 G. The behavior of the line activity indicators is in good agreement with the Bl variations. Searching for periodic signals in the Stokes V time series, we found a possible rotation period of 215 days. The two ZDI maps show a mainly axisymmetric and poloidal magnetic topology and a simple surface magnetic field configuration dominated by a dipole. Little evolution is observed between the two maps, in spite of a 1 yr interval between both subsets. We also use state-of-the-art stellar evolution models to constrain the evolutionary status of β Ceti. We derive a mass of 3.5 M⊚ and propose that this star is already in the central helium-burning phase. Conclusions. Considering all our results and the evolutionary status of the star, we suggest that dynamo action alone may not be efficient enough to account for the high magnetic activity of β Ceti. As an alternate option, we propose that it is a descendant of an Ap star presently undergoing central helium-burning and still exhibiting a remnant of the Ap star magnetic field. [ABSTRACT FROM AUTHOR]

Published
2013
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83. Rotational velocities of the giants in symbiotic stars – I. D′-type symbiotics.

Author

Zamanov, R. K., Bode, M. F., Melo, C. H. F., Porter, J., Gomboc, A., and Konstantinova-Antova, R.

Subjects
STELLAR rotation, SYMBIOTIC stars, CATACLYSMIC variable stars, BINARY stars, VARIABLE stars, MASS loss (Astrophysics), ASTRONOMY, PHYSICAL sciences
Abstract

We have measured the rotational velocities of the mass donors in a number of D′-type symbiotic stars (SSs), using the cross-correlation function method. Four out of five D′ SSs with known appeared to be very fast rotators compared with the catalogues of for the corresponding spectral types. At least three of these stars rotate at a substantial fraction (≳0.5) of the critical velocity. This means that at least in D′-type SSs the cool components rotate faster than isolated giants. If these binary stars are synchronized, their orbital periods should be relatively short (4–60 d). We also briefly discuss the possible origin of the rapid rotation and its connection with mass loss and dust formation. [ABSTRACT FROM AUTHOR]

Published
2006
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84. EK Eridani: the tip of the iceberg of giants which have evolved from magnetic Ap stars

Author

Auri?re, M., Konstantinova-Antova, R., Petit, P., Charbonnel, C., Dintrans, B., Ligni?res, F., Roudier, T., Alecian, E., Donati, J., Landstreet, J., and Wade, G.

Abstract

Aims. We observe the slowly-rotating, active, single giant, EK?Eri, to study and infer the nature of its magnetic field directly.Methods. We used the spectropolarimeter NARVAL at the Telescope Bernard Lyot, Pic du Midi Observatory, and the Least Square Deconvolution method to create high signal-to-noise ratio Stokes?V profiles. We fitted the Stokes?V profiles with a model of the large-scale magnetic field. We studied the classical activity indicators, the Ca?ii?H and K?lines, the Ca?ii?infrared triplet, and H??line.Results. We detected the Stokes V signal of EK Eri securely and measured the longitudinal magnetic field?Blfor seven individual dates spanning 60% of the rotational period. The measured longitudinal magnetic field of EK?Eri reached about 100?G and was as strong as fields observed in RSCVn or FK?Com?type stars: this was found to be extraordinary when compared with the weak fields observed at the surfaces of slowly-rotating MS?stars or any single red giant previously observed with NARVAL. From our modeling, we infer that the mean surface magnetic field is about 270?G, and that the large scale magnetic field is dominated by a poloidal component. This is compatible with expectations for the descendant of a strongly magnetic Ap?star.

Published
2008

86. VizieR Online Data Catalog: BCool survey of solar-type stars (Marsden+ 2014)

Author

Marsden, S. C., Petit, P., Jeffers, S. V., Morin, J., Rim Fares, Reiners, A., Do Nascimento, J. -D, Auriere, M., Bouvier, J., Carter, B. D., Catala, C., Dintrans, B., Donati, J. -F, Gastine, T., Jardine, M., Konstantinova-Antova, R., Lanoux, J., Lignieres, F., Morgenthaler, A., Ramirez-Velez, J. C., Theado, S., Grootel, V., and BCool Collaboration

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