We highlight the importance of eclipsing double-line binaries in our understanding on star format... more We highlight the importance of eclipsing double-line binaries in our understanding on star formation and evolution. We review the recent discoveries of low-mass and sub-stellar eclipsing binaries belonging to star-forming regions, open clusters, and globular clusters identified by ground-based surveys and space missions with highresolution spectroscopic follow-up. These discoveries provide benchmark systems with known distances, metallicities, and ages to calibrate masses and radii predicted by state-of-the-art evolutionary models to a few percent. We report their density and discuss current limitations on the accuracy of the physical parameters. We discuss future opportunities and highlight future guidelines to fill gaps in age and metallicity to improve further our knowledge of low-mass stars and brown dwarfs.
Context. Very precise satellite photometry has revealed a large number of variable stars whose va... more Context. Very precise satellite photometry has revealed a large number of variable stars whose variability is caused either by surface spots or by binarity. Detailed studies of such variables provide insights into the physics of these objects. Aims. We study the nature of the periodic light variability of the white dwarf EPIC 206197016 that was observed by the K2 mission. Methods. We obtain phase-resolved medium-resolution spectroscopy of EPIC 206197016 using X-shooter spectrograph at VLT to understand the nature of the white dwarf variability. We use non-local thermodynamical equilibrium model atmospheres to determine stellar parameters at individual phases. Results. EPIC 206197016 is a hot DA white dwarf with T eff = 78 kK. The analysis of the spectra reveals periodic radial velocity variations that can result from gravitational interaction with an invisible secondary whose mass corresponds to a red dwarf. The close proximity of the two stars where the semimajor axis is about 3 R results in the irradiation of the companion with temperatures more than twice as high on the illuminated side compared to the nonilluminated hemisphere. This effect can explain the observed light variations. The spectra of the white dwarf show a particular feature of the Balmer lines called the Balmer line problem, where the observed cores of the lower Balmer lines are deeper than predicted. This can be attributed to either weak pollution of hydrogen in the white dwarf atmosphere by heavy elements or to the presence of a circumstellar cloud or disk.
Context. The galactic magnetic chemically peculiar (mCP) stars of the upper main sequence are wel... more Context. The galactic magnetic chemically peculiar (mCP) stars of the upper main sequence are well known as periodic spectral and light variables. The observed variability is obviously caused by the uneven distribution of overabundant chemical elements on the surfaces of rigidly rotating stars. The mechanism causing the clustering of some chemical elements into disparate structures on mCP stars has not been fully understood up to now. The observations of light changes of mCP candidates recently revealed in the nearby Large Magellanic Cloud (LMC) should provide us with information about their rotational periods and about the distribution of optically active elements on mCP stars born in other galaxies. Aims. We queried for photometry at the Optical Gravitational Lensing Experiment (OGLE)-III survey of published mCP candidates selected because of the presence of the characteristic λ5200 Å flux depression. In total, the intersection of both sources resulted in twelve stars. For these objects and two control stars, we searched for a periodic variability. Methods. We performed our own and standard periodogram time series analyses of all available data. The final results are, amongst others, the frequency of the maximum peak and the bootstrap probability of its reality. Results. We detected that only two mCP candidates, 190.1 1581 and 190.1 15527, may show some weak rotationally modulated light variations with periods of 1.23 and 0.49 days; however, the 49% and 32% probabilities of their reality are not very satisfying. The variability of the other 10 mCP candidates is too low to be detectable by their V and I OGLE photometry. Conclusions. The relatively low amplitude variability of the studied LMC mCP candidates sample can be explained by the absence of photometric spots of overabundant optically active chemical elements. The unexpected LMC mCPs behaviour is probably caused by different conditions during the star formation in the LMC and the Galaxy.
Monthly Notices of the Royal Astronomical Society, Aug 3, 2017
A longitudinal magnetic field with a strength of 5.2 kG was recently detected in CPD −62 • 2124, ... more A longitudinal magnetic field with a strength of 5.2 kG was recently detected in CPD −62 • 2124, which has a fractional main-sequence lifetime of about 60%. Strongly magnetic early-B type chemically peculiar stars in an advanced evolutionary state are of special interest to understand the evolution of the angular momentum and spin-down timescales in the presence of a global magnetic field. We exploited 17 FORS 2 low-resolution spectropolarimetric observations and 844 ASAS3 photometric measurements for the determination of the rotation period, pulsations, and the magnetic field geometry of the star. We calculated periodograms and applied phenomenological models of photometric, spectral and spectropolarimetric variability. We found that all quantities studied, specifically equivalent widths, the mean longitudinal magnetic field B z , and the flux in the V filter, vary with the same period P = 2.628 d, which was identified as the rotation period. The observed variations can be fully explained by a rigidly rotating main-sequence star with an uneven distribution of chemical elements, photometric spots, and a stable, nearly dipolar magnetic field with a polar field strength of about 21 kG, frozen into the body of the star. The magnetic field of CPD −62 • 2124 is tilted to the rotation axis by β = 28 • ± 7 • , while the inclination of the rotation axis towards the line of sight is only i = 20 • ± 5 •. In the acquired FORS 2 spectra, we detect short-term line profile variations indicating the presence of β Cephei type pulsations. As of today, no other pulsating star of this type is known to possess such a strong magnetic field.
Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray, Aug 31, 2022
We present a near-UV space telescope on a ∼70kg micro-satellite with a moderately fast repointing... more We present a near-UV space telescope on a ∼70kg micro-satellite with a moderately fast repointing capability and a near real-time alert communication system that has been proposed in response to a call for an ambitious Czech national mission. The mission, which has recently been approved for Phase 0, A, and B1 study shall measure the brightness evolution of kilonovae, resulting from mergers of neutron stars in the near-UV band and thus it shall distinguish between different explosion scenarios. Between the observations of transient sources, the satellite shall perform observations of other targets of interest, a large part of which will be chosen in open competition.
Contact binaries below the short-period limit of 0.22 days are very rare. Here we define them as ... more Contact binaries below the short-period limit of 0.22 days are very rare. Here we define them as the "extremely short-period contact binaries". Observations and investigations of extremely short-period contact binaries can provide important information on the origin and evolutionary processes of contact binaries. We have monitored some such binaries for several years using several small telescopes as well as 2 m-class telescopes. We detected some new extremely short-period contact binaries and derived photometric solutions and period changes for them. Possible reasons for the low occurrence of the extremely short-period contact binaries are discussed.
Short description of wide spread variable star research and monitoring in the Czech Republic with... more Short description of wide spread variable star research and monitoring in the Czech Republic with present outputs, mainly four project of VSES of CAS of AS CR - BRNO (eclipsing binary), MEDUSA (intrinsic variable stars), TRESCA (transiting exoplanets) and HERO (high energy objects), OEJV (Open European Journal on Variable Stars), ETD (Exoplanet transit Database).
Three decades of a precise photometric and spectroscopic monitoring of the young hot magnetic che... more Three decades of a precise photometric and spectroscopic monitoring of the young hot magnetic chemically peculiar star HD 37776 have revealed its continual rotational deceleration, increasing the period by a remarkable 18 s! The deceleration was interpreted as the rotational braking of the outer stellar layers due to the angular momentum loss in the stellar magnetosphere. Observational data have been recently supplemented by own new photometric data. We present here the results of the sophisticated analysis of all available observed data showing that the period reached its maximum of 1.538766 d in the year 2004, when the rotation period began to decrease. The nature of such unpredicted period changes and the paradox of the spin-down time are briefly discussed.
Nový eruptivni trpaslik 2MASS J11182030+1347392 = 1RXS J111819.9+134739 byl objeven nahodně při f... more Nový eruptivni trpaslik 2MASS J11182030+1347392 = 1RXS J111819.9+134739 byl objeven nahodně při fotometrickem pozorovani v noci 22/23. unora 2012.
Discovery of the record-breaking rotational braking of the helium-strong CP star HD 37776 and its... more Discovery of the record-breaking rotational braking of the helium-strong CP star HD 37776 and its interpretation.
This volume contains the proceedings of a cross-disciplinary science conference that took place i... more This volume contains the proceedings of a cross-disciplinary science conference that took place in the historic city of Litomysl in the Eastern Czech Republic on 8-12 September 2014 to celebrate the 100th anniversary of the birth in this city of Zdeněk Kopal, one of the most famous Czech astronomers of the 20th century. The meeting attracted over 120 experts in the fields of binary stars and planets from more than 25 countries around the world. Binary stars and planets form and evolve through processes involving redistribution and evolution of the angular momentum of collapsing interstellar clouds, through several dissipation and re-organization mechanisms. Both types of objects are studied in similar ways, with methods and tools developed by the binary-star community over many years, but now extensively applied to study planets. The theory and observation of these processes are now rapidly advancing and leading to new and exciting results, which made this meeting a timely opportunity for discussion and vigorous exchange of ideas. This volume will be of interest to researchers wishing to learn about new observational projects related to many aspects of binary star physics, as well as the discovery and characterization of exoplanets, particularly planets in binary star systems. Included as well are many presentations describing ongoing research on close and interacting binary stars, which was a subject close to the scientific interests of Zdeněk Kopal, as embodied in his monumental monograph "Close Binary Systems" (1959).
Aims. About thirty new times of minimum light recorded with photoelectric or CCD photometers were... more Aims. About thirty new times of minimum light recorded with photoelectric or CCD photometers were obtained for four earlytype eccentric-orbit eclipsing binaries CW Cep (P = 2. d 73, e = 0.029), V478 Cyg (2. d 88, 0.016), AG Per (2. d 03, 0.071), and IQ Per (1. d 74, 0.076). Methods. Their O−C diagrams were analysed using all reliable timings found in the literature, and elements of apsidal motion were improved. Results. We confirm relatively short periods of apsidal motion of about 46, 27, 76, and 124 years for CW Cep, V478 Cyg, AG Per, and IQ Per, respectively. The corresponding internal structure constants, log k 2 , are then found to be-2.12,-2.25,-2.15, and-2.36, under the assumption that the component stars rotate pseudosynchronously. The relativistic effects are negligible, being up to 8% of the total apsidal motion rate in all systems. Using the light-time effect solution, we have predicted a faint third component orbiting with a period of about 39 years for CW Cep.
The magnetic chemically peculiar (mCP) stars of the upper main sequence exhibit periodic light, m... more The magnetic chemically peculiar (mCP) stars of the upper main sequence exhibit periodic light, magnetic, radio, and spectroscopic variations that can be adequately explained by a model of a rigidly rotating magnetized star with persistent surface structures. The majority of mCP stars rotate at strictly constant periods. However, there are a few mCP stars whose rotation periods vary on timescales of decades while the shape of their phase curves remains unchanged. In the case of CU Vir and V901 Ori, we have detected it cyclic period variations. We demonstrate that the period oscillations of CU Vir may be a consequence of the interaction of the internal magnetic field and differential rotation.
Discovery of flares in the M dwarf CzeV502 and our follow-up results are presented. We classify i... more Discovery of flares in the M dwarf CzeV502 and our follow-up results are presented. We classify it as a dMe eruptive variable of UV Ceti type due to the X-ray activity, measured B − V of 1.5 mag, Hα; emission, and flares. Our monitoring revealed only one reliable and one suspected superflare in 58 nights (210 hrs). The strongest flare with ΔR = 1.5 mag (ΔB ≈ 6-8 mag) could have a total energy of 3E+34 erg. The ASAS-SN data may contain 4 events up to ΔV of 0.43 mag and 12.55 d periodicity corresponding to the rotation or possible binarity. Other brightenings in sky survey (ASAS-3, CRTS, NSVS, and KWS) are doubtful. No event was unveiled on the 1 600 photographic plates. The upper rate limit of 1-2 superflares/1 640 hrs corresponds to activity several orders higher than for other M-dwarfs, especially, for the slow rotators. The low amplitude flares ( ΔB < 0.5 mag) may be common (1 flare/4 hrs).
CQ UMa = HD 119213 is a member of an exclusive SrCrEu star club showing significant variability i... more CQ UMa = HD 119213 is a member of an exclusive SrCrEu star club showing significant variability in the c1 index, expressing the Balmer jump's height. The cause of the light variability of those cool mCP stars is not yet known. The group includes, e.g., CS Vir, VV Scl, BR Cru, and BS Cir, which is known to change its period. We are preparing a comprehensive study of these stars, most of which have sufficiently high-quality TESS photometry.<br> 58954 individual photometric, spectroscopic, and magnetic observations of CQ UMa obtained during the last 50 years helped us reveal a marginal acceleration of its rotation period as $\dot{P}=10(3)\times10^{-10}$, which is by far the slightest proven period change in mCPs. The case of CQ UMa suggests that the rotation period variability affects all types and mass categories of mCP stars and may not be as rare as we thought so far.
The results of the first synoptic survey of novae in the barred spiral and starburst galaxy, M83 ... more The results of the first synoptic survey of novae in the barred spiral and starburst galaxy, M83 (NGC 5236), are presented. A total of 19 novae and one background supernova were discovered during the course of a nearly 7 year survey comprised of over 200 individual nights of observation between 2012 December 12 and 2019 March 14. After correcting for the limiting magnitude and the spatial and temporal coverage of the survey, the nova rate in M83 was found to be R = 19+5 −3 yr−1. This rate, when normalized to the K-band luminosity of the galaxy, yields a luminosity-specific nova rate, ν K = 3.0+0.9 −0.6 × 10−10 yr −1 L ⊙,K −1. The spatial distribution of the novae is found to be more extended than the overall galaxy light suggesting that the observed novae are likely dominated by a disk population. This result is consistent with the observed novae light curves, which reveals that the M83 novae are on average more luminous at maximum light and fade faster when compared with novae obse...
arXiv: Instrumentation and Methods for Astrophysics, 2016
We present a simple phenomenological method for detrending of raw Kepler and MOST photometry, whi... more We present a simple phenomenological method for detrending of raw Kepler and MOST photometry, which is illustrated by means of photometric data processing of two periodically variable chemically peculiar stars, KIC 6950556 and HD 37633. In principle, this method may be applied to any type of periodically variable objects and satellite or ground based photometries. As a by product, we have identified KIC 6950556 as a magnetic chemically peculiar star with an ACV type variability.
We present the revealing of rotational instability of two well-known magnetic chemically peculiar... more We present the revealing of rotational instability of two well-known magnetic chemically peculiar star CU Virginis and V901 Orionis.
We highlight the importance of eclipsing double-line binaries in our understanding on star format... more We highlight the importance of eclipsing double-line binaries in our understanding on star formation and evolution. We review the recent discoveries of low-mass and sub-stellar eclipsing binaries belonging to star-forming regions, open clusters, and globular clusters identified by ground-based surveys and space missions with highresolution spectroscopic follow-up. These discoveries provide benchmark systems with known distances, metallicities, and ages to calibrate masses and radii predicted by state-of-the-art evolutionary models to a few percent. We report their density and discuss current limitations on the accuracy of the physical parameters. We discuss future opportunities and highlight future guidelines to fill gaps in age and metallicity to improve further our knowledge of low-mass stars and brown dwarfs.
Context. Very precise satellite photometry has revealed a large number of variable stars whose va... more Context. Very precise satellite photometry has revealed a large number of variable stars whose variability is caused either by surface spots or by binarity. Detailed studies of such variables provide insights into the physics of these objects. Aims. We study the nature of the periodic light variability of the white dwarf EPIC 206197016 that was observed by the K2 mission. Methods. We obtain phase-resolved medium-resolution spectroscopy of EPIC 206197016 using X-shooter spectrograph at VLT to understand the nature of the white dwarf variability. We use non-local thermodynamical equilibrium model atmospheres to determine stellar parameters at individual phases. Results. EPIC 206197016 is a hot DA white dwarf with T eff = 78 kK. The analysis of the spectra reveals periodic radial velocity variations that can result from gravitational interaction with an invisible secondary whose mass corresponds to a red dwarf. The close proximity of the two stars where the semimajor axis is about 3 R results in the irradiation of the companion with temperatures more than twice as high on the illuminated side compared to the nonilluminated hemisphere. This effect can explain the observed light variations. The spectra of the white dwarf show a particular feature of the Balmer lines called the Balmer line problem, where the observed cores of the lower Balmer lines are deeper than predicted. This can be attributed to either weak pollution of hydrogen in the white dwarf atmosphere by heavy elements or to the presence of a circumstellar cloud or disk.
Context. The galactic magnetic chemically peculiar (mCP) stars of the upper main sequence are wel... more Context. The galactic magnetic chemically peculiar (mCP) stars of the upper main sequence are well known as periodic spectral and light variables. The observed variability is obviously caused by the uneven distribution of overabundant chemical elements on the surfaces of rigidly rotating stars. The mechanism causing the clustering of some chemical elements into disparate structures on mCP stars has not been fully understood up to now. The observations of light changes of mCP candidates recently revealed in the nearby Large Magellanic Cloud (LMC) should provide us with information about their rotational periods and about the distribution of optically active elements on mCP stars born in other galaxies. Aims. We queried for photometry at the Optical Gravitational Lensing Experiment (OGLE)-III survey of published mCP candidates selected because of the presence of the characteristic λ5200 Å flux depression. In total, the intersection of both sources resulted in twelve stars. For these objects and two control stars, we searched for a periodic variability. Methods. We performed our own and standard periodogram time series analyses of all available data. The final results are, amongst others, the frequency of the maximum peak and the bootstrap probability of its reality. Results. We detected that only two mCP candidates, 190.1 1581 and 190.1 15527, may show some weak rotationally modulated light variations with periods of 1.23 and 0.49 days; however, the 49% and 32% probabilities of their reality are not very satisfying. The variability of the other 10 mCP candidates is too low to be detectable by their V and I OGLE photometry. Conclusions. The relatively low amplitude variability of the studied LMC mCP candidates sample can be explained by the absence of photometric spots of overabundant optically active chemical elements. The unexpected LMC mCPs behaviour is probably caused by different conditions during the star formation in the LMC and the Galaxy.
Monthly Notices of the Royal Astronomical Society, Aug 3, 2017
A longitudinal magnetic field with a strength of 5.2 kG was recently detected in CPD −62 • 2124, ... more A longitudinal magnetic field with a strength of 5.2 kG was recently detected in CPD −62 • 2124, which has a fractional main-sequence lifetime of about 60%. Strongly magnetic early-B type chemically peculiar stars in an advanced evolutionary state are of special interest to understand the evolution of the angular momentum and spin-down timescales in the presence of a global magnetic field. We exploited 17 FORS 2 low-resolution spectropolarimetric observations and 844 ASAS3 photometric measurements for the determination of the rotation period, pulsations, and the magnetic field geometry of the star. We calculated periodograms and applied phenomenological models of photometric, spectral and spectropolarimetric variability. We found that all quantities studied, specifically equivalent widths, the mean longitudinal magnetic field B z , and the flux in the V filter, vary with the same period P = 2.628 d, which was identified as the rotation period. The observed variations can be fully explained by a rigidly rotating main-sequence star with an uneven distribution of chemical elements, photometric spots, and a stable, nearly dipolar magnetic field with a polar field strength of about 21 kG, frozen into the body of the star. The magnetic field of CPD −62 • 2124 is tilted to the rotation axis by β = 28 • ± 7 • , while the inclination of the rotation axis towards the line of sight is only i = 20 • ± 5 •. In the acquired FORS 2 spectra, we detect short-term line profile variations indicating the presence of β Cephei type pulsations. As of today, no other pulsating star of this type is known to possess such a strong magnetic field.
Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray, Aug 31, 2022
We present a near-UV space telescope on a ∼70kg micro-satellite with a moderately fast repointing... more We present a near-UV space telescope on a ∼70kg micro-satellite with a moderately fast repointing capability and a near real-time alert communication system that has been proposed in response to a call for an ambitious Czech national mission. The mission, which has recently been approved for Phase 0, A, and B1 study shall measure the brightness evolution of kilonovae, resulting from mergers of neutron stars in the near-UV band and thus it shall distinguish between different explosion scenarios. Between the observations of transient sources, the satellite shall perform observations of other targets of interest, a large part of which will be chosen in open competition.
Contact binaries below the short-period limit of 0.22 days are very rare. Here we define them as ... more Contact binaries below the short-period limit of 0.22 days are very rare. Here we define them as the "extremely short-period contact binaries". Observations and investigations of extremely short-period contact binaries can provide important information on the origin and evolutionary processes of contact binaries. We have monitored some such binaries for several years using several small telescopes as well as 2 m-class telescopes. We detected some new extremely short-period contact binaries and derived photometric solutions and period changes for them. Possible reasons for the low occurrence of the extremely short-period contact binaries are discussed.
Short description of wide spread variable star research and monitoring in the Czech Republic with... more Short description of wide spread variable star research and monitoring in the Czech Republic with present outputs, mainly four project of VSES of CAS of AS CR - BRNO (eclipsing binary), MEDUSA (intrinsic variable stars), TRESCA (transiting exoplanets) and HERO (high energy objects), OEJV (Open European Journal on Variable Stars), ETD (Exoplanet transit Database).
Three decades of a precise photometric and spectroscopic monitoring of the young hot magnetic che... more Three decades of a precise photometric and spectroscopic monitoring of the young hot magnetic chemically peculiar star HD 37776 have revealed its continual rotational deceleration, increasing the period by a remarkable 18 s! The deceleration was interpreted as the rotational braking of the outer stellar layers due to the angular momentum loss in the stellar magnetosphere. Observational data have been recently supplemented by own new photometric data. We present here the results of the sophisticated analysis of all available observed data showing that the period reached its maximum of 1.538766 d in the year 2004, when the rotation period began to decrease. The nature of such unpredicted period changes and the paradox of the spin-down time are briefly discussed.
Nový eruptivni trpaslik 2MASS J11182030+1347392 = 1RXS J111819.9+134739 byl objeven nahodně při f... more Nový eruptivni trpaslik 2MASS J11182030+1347392 = 1RXS J111819.9+134739 byl objeven nahodně při fotometrickem pozorovani v noci 22/23. unora 2012.
Discovery of the record-breaking rotational braking of the helium-strong CP star HD 37776 and its... more Discovery of the record-breaking rotational braking of the helium-strong CP star HD 37776 and its interpretation.
This volume contains the proceedings of a cross-disciplinary science conference that took place i... more This volume contains the proceedings of a cross-disciplinary science conference that took place in the historic city of Litomysl in the Eastern Czech Republic on 8-12 September 2014 to celebrate the 100th anniversary of the birth in this city of Zdeněk Kopal, one of the most famous Czech astronomers of the 20th century. The meeting attracted over 120 experts in the fields of binary stars and planets from more than 25 countries around the world. Binary stars and planets form and evolve through processes involving redistribution and evolution of the angular momentum of collapsing interstellar clouds, through several dissipation and re-organization mechanisms. Both types of objects are studied in similar ways, with methods and tools developed by the binary-star community over many years, but now extensively applied to study planets. The theory and observation of these processes are now rapidly advancing and leading to new and exciting results, which made this meeting a timely opportunity for discussion and vigorous exchange of ideas. This volume will be of interest to researchers wishing to learn about new observational projects related to many aspects of binary star physics, as well as the discovery and characterization of exoplanets, particularly planets in binary star systems. Included as well are many presentations describing ongoing research on close and interacting binary stars, which was a subject close to the scientific interests of Zdeněk Kopal, as embodied in his monumental monograph "Close Binary Systems" (1959).
Aims. About thirty new times of minimum light recorded with photoelectric or CCD photometers were... more Aims. About thirty new times of minimum light recorded with photoelectric or CCD photometers were obtained for four earlytype eccentric-orbit eclipsing binaries CW Cep (P = 2. d 73, e = 0.029), V478 Cyg (2. d 88, 0.016), AG Per (2. d 03, 0.071), and IQ Per (1. d 74, 0.076). Methods. Their O−C diagrams were analysed using all reliable timings found in the literature, and elements of apsidal motion were improved. Results. We confirm relatively short periods of apsidal motion of about 46, 27, 76, and 124 years for CW Cep, V478 Cyg, AG Per, and IQ Per, respectively. The corresponding internal structure constants, log k 2 , are then found to be-2.12,-2.25,-2.15, and-2.36, under the assumption that the component stars rotate pseudosynchronously. The relativistic effects are negligible, being up to 8% of the total apsidal motion rate in all systems. Using the light-time effect solution, we have predicted a faint third component orbiting with a period of about 39 years for CW Cep.
The magnetic chemically peculiar (mCP) stars of the upper main sequence exhibit periodic light, m... more The magnetic chemically peculiar (mCP) stars of the upper main sequence exhibit periodic light, magnetic, radio, and spectroscopic variations that can be adequately explained by a model of a rigidly rotating magnetized star with persistent surface structures. The majority of mCP stars rotate at strictly constant periods. However, there are a few mCP stars whose rotation periods vary on timescales of decades while the shape of their phase curves remains unchanged. In the case of CU Vir and V901 Ori, we have detected it cyclic period variations. We demonstrate that the period oscillations of CU Vir may be a consequence of the interaction of the internal magnetic field and differential rotation.
Discovery of flares in the M dwarf CzeV502 and our follow-up results are presented. We classify i... more Discovery of flares in the M dwarf CzeV502 and our follow-up results are presented. We classify it as a dMe eruptive variable of UV Ceti type due to the X-ray activity, measured B − V of 1.5 mag, Hα; emission, and flares. Our monitoring revealed only one reliable and one suspected superflare in 58 nights (210 hrs). The strongest flare with ΔR = 1.5 mag (ΔB ≈ 6-8 mag) could have a total energy of 3E+34 erg. The ASAS-SN data may contain 4 events up to ΔV of 0.43 mag and 12.55 d periodicity corresponding to the rotation or possible binarity. Other brightenings in sky survey (ASAS-3, CRTS, NSVS, and KWS) are doubtful. No event was unveiled on the 1 600 photographic plates. The upper rate limit of 1-2 superflares/1 640 hrs corresponds to activity several orders higher than for other M-dwarfs, especially, for the slow rotators. The low amplitude flares ( ΔB < 0.5 mag) may be common (1 flare/4 hrs).
CQ UMa = HD 119213 is a member of an exclusive SrCrEu star club showing significant variability i... more CQ UMa = HD 119213 is a member of an exclusive SrCrEu star club showing significant variability in the c1 index, expressing the Balmer jump's height. The cause of the light variability of those cool mCP stars is not yet known. The group includes, e.g., CS Vir, VV Scl, BR Cru, and BS Cir, which is known to change its period. We are preparing a comprehensive study of these stars, most of which have sufficiently high-quality TESS photometry.<br> 58954 individual photometric, spectroscopic, and magnetic observations of CQ UMa obtained during the last 50 years helped us reveal a marginal acceleration of its rotation period as $\dot{P}=10(3)\times10^{-10}$, which is by far the slightest proven period change in mCPs. The case of CQ UMa suggests that the rotation period variability affects all types and mass categories of mCP stars and may not be as rare as we thought so far.
The results of the first synoptic survey of novae in the barred spiral and starburst galaxy, M83 ... more The results of the first synoptic survey of novae in the barred spiral and starburst galaxy, M83 (NGC 5236), are presented. A total of 19 novae and one background supernova were discovered during the course of a nearly 7 year survey comprised of over 200 individual nights of observation between 2012 December 12 and 2019 March 14. After correcting for the limiting magnitude and the spatial and temporal coverage of the survey, the nova rate in M83 was found to be R = 19+5 −3 yr−1. This rate, when normalized to the K-band luminosity of the galaxy, yields a luminosity-specific nova rate, ν K = 3.0+0.9 −0.6 × 10−10 yr −1 L ⊙,K −1. The spatial distribution of the novae is found to be more extended than the overall galaxy light suggesting that the observed novae are likely dominated by a disk population. This result is consistent with the observed novae light curves, which reveals that the M83 novae are on average more luminous at maximum light and fade faster when compared with novae obse...
arXiv: Instrumentation and Methods for Astrophysics, 2016
We present a simple phenomenological method for detrending of raw Kepler and MOST photometry, whi... more We present a simple phenomenological method for detrending of raw Kepler and MOST photometry, which is illustrated by means of photometric data processing of two periodically variable chemically peculiar stars, KIC 6950556 and HD 37633. In principle, this method may be applied to any type of periodically variable objects and satellite or ground based photometries. As a by product, we have identified KIC 6950556 as a magnetic chemically peculiar star with an ACV type variability.
We present the revealing of rotational instability of two well-known magnetic chemically peculiar... more We present the revealing of rotational instability of two well-known magnetic chemically peculiar star CU Virginis and V901 Orionis.
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Papers by Miloslav Zejda