Accretion process, magnetic fields, and apsidal motion in the pre-main sequence binary DQ Tau

Classical T Tauri stars (CTTSs) are young stellar objects that accrete materials from their accretion disc influenced by their strong magnetic field. The magnetic pressure truncates the disc at a few stellar radii and forces the material to leave the disc plane and fall onto the stellar surface by following the magnetic field lines. However, this global scheme may be disturbed by the presence of a companion interacting gravitationally with the accreting component. This work is aiming to study the accretion and the magnetic field of the tight eccentric binary DQ Tau, composed of two equal-mass ($\sim$ 0.6 \msun ) CTTSs interacting at different orbital phases. We investigated the variability of the system using a high-resolution spectroscopic and spectropolarimetric monitoring performed with ESPaDOnS at the CFHT. We provide the first ever magnetic field analysis of this system, the Zeeman-Doppler imaging revealed a stronger magnetic field for the secondary than the primary (1.2 kG and 0.5 kG, respectively), but the small-scale fields analysed through Zeeman intensification yielded similar strengths (about 2.5 kG). The magnetic field topology and strengths are compatible with the accretion processes on CTTSs. Both components of this system are accreting, with a change of the main accretor during the orbital motion. In addition, the system displays a strong enhancement of the mass accretion rate at periastron and apastron. We also discovered, for the first time in this system, the apsidal motion of the orbital ellipse.Comment: 18 pages, 20 figures. Accepted for publication in MNRA

Coupled waves as a model to describe chaotic turbulence pumped by radio waves in the ionosphere

Experimental results concerning plasma turbulence pumped in theionosphere by powerful radio waves suggest that the turbulence is due todeterministic chaos. To investigate the possibility of deterministic chaosin the ionosphere coupled wave systems have been studied to see chaoticdynamics. If coupled waves can exhibit chaos it is a possible way tomodel ionospheric chaos. The result showed that chaos was present inboth wave systems studied which means that they could possibly explainthe chaos, to verify this more studies needs to be done on theparameters relevant to the coupled wave systems in the ionosphere andfind if they are in a regime where chaos developsStudier av plasmaturbulens i jonosfären som pumpas av kraftfulla radiovågor antyder att turbulensen är kopplat till deterministiskt kaos. För att undersöka möjligheten för deterministiskt kaos i jonosfären studeras kopplade vågsystem om de kan innehålla kaotiska regimer. Om dessa system visar kaotiskt beteende skulle de kunna användas för att beskriva kaos i jonosfären. Resultatet visade att kaos var närvarande i de kopplade vågsystem som studerats, för att verifiera om de kan användas för att beskriva kaos i jonosfären måste närmare studier av de parametrar som modellen använder sig av göras för att se om de faller inom ett intervall där kaos uppstår

Coupled waves as a model to describe chaotic turbulence pumped by radio waves in the ionosphere

Experimental results concerning plasma turbulence pumped in theionosphere by powerful radio waves suggest that the turbulence is due todeterministic chaos. To investigate the possibility of deterministic chaosin the ionosphere coupled wave systems have been studied to see chaoticdynamics. If coupled waves can exhibit chaos it is a possible way tomodel ionospheric chaos. The result showed that chaos was present inboth wave systems studied which means that they could possibly explainthe chaos, to verify this more studies needs to be done on theparameters relevant to the coupled wave systems in the ionosphere andfind if they are in a regime where chaos developsStudier av plasmaturbulens i jonosfären som pumpas av kraftfulla radiovågor antyder att turbulensen är kopplat till deterministiskt kaos. För att undersöka möjligheten för deterministiskt kaos i jonosfären studeras kopplade vågsystem om de kan innehålla kaotiska regimer. Om dessa system visar kaotiskt beteende skulle de kunna användas för att beskriva kaos i jonosfären. Resultatet visade att kaos var närvarande i de kopplade vågsystem som studerats, för att verifiera om de kan användas för att beskriva kaos i jonosfären måste närmare studier av de parametrar som modellen använder sig av göras för att se om de faller inom ett intervall där kaos uppstår

Zeeman Doppler Imaging of the eclipsing binary UV Piscium

Magnetic fields are important for multiple physical processes in and around stars, for these reasons improving the understanding of how they are generated and maintained is of great value. In this work the magnetic field structure of the eclipsing binary UV Piscium is investigated. This is done by utilising the Zeeman-Doppler Imaging technique that reconstructs stellar magnetic maps by combining the information of how the magnetic field affects spectral lines with the rotational modulation of spectral lines. In order to improve the signal-to-noise ratio the least squares deconvolution technique was used to combine multiple spectral lines into an average line profile. The high resolution circular polarisation observations analysed in this work were taken by the ESPaDOnS spectograph at the Canada-France-Hawaii Telescope during August and September of 2016. We reconstructed detailed magnetic field maps and obtained the average magnetic field strengths of 137G for the primary and 88G for the secondary, which is not unusual values for stars of this type. The methods used are however likely to underestimate the magnetic field strengths. This is because the lack of linear polarisation profiles likely results in systematic underestimation of magnetic field strengths, especially meridional components. Another issue that became apparent in this work is that in eclipsing binaries, without linear polarisation observations, there is a degeneracy between the different hemispheres, resulting in further uncertainties in the determination of surface magnetic field geometry. We also found that there is indication of surface evolution on the time scale of months as some observations taken around fifty days earlier were could not be phased with the main data set

Zeeman Doppler Imaging of the eclipsing binary UV Piscium

Magnetic fields are important for multiple physical processes in and around stars, for these reasons improving the understanding of how they are generated and maintained is of great value. In this work the magnetic field structure of the eclipsing binary UV Piscium is investigated. This is done by utilising the Zeeman-Doppler Imaging technique that reconstructs stellar magnetic maps by combining the information of how the magnetic field affects spectral lines with the rotational modulation of spectral lines. In order to improve the signal-to-noise ratio the least squares deconvolution technique was used to combine multiple spectral lines into an average line profile. The high resolution circular polarisation observations analysed in this work were taken by the ESPaDOnS spectograph at the Canada-France-Hawaii Telescope during August and September of 2016. We reconstructed detailed magnetic field maps and obtained the average magnetic field strengths of 137G for the primary and 88G for the secondary, which is not unusual values for stars of this type. The methods used are however likely to underestimate the magnetic field strengths. This is because the lack of linear polarisation profiles likely results in systematic underestimation of magnetic field strengths, especially meridional components. Another issue that became apparent in this work is that in eclipsing binaries, without linear polarisation observations, there is a degeneracy between the different hemispheres, resulting in further uncertainties in the determination of surface magnetic field geometry. We also found that there is indication of surface evolution on the time scale of months as some observations taken around fifty days earlier were could not be phased with the main data set

Accretion and magnetism on young eccentric binaries : DQ Tau and AK Sco

The accretion and ejection of mass in pre-main-sequence (PMS) stars are key processes in stellar evolution as they shape the stellar angular momentum transport necessary for the stars' stability. Magnetospheric accretion on to classical T Tauri stars and low-mass PMS stars has been widely studied in the single-star case. This process cannot be directly transferred to PMS binary systems, as tidal and gravitation effects, and/or accretion from a circumbinary disc (with variable separation of the components in the case of eccentric orbits) are in place. This work examines the accretion process of two PMS eccentric binaries, DQ Tau and AK Sco, using high-resolution spectropolarimetric time series. We investigate how magnetospheric accretion can be applied to these systems by studying the accretion-related emission lines and the magnetic field of each system. We discover that both systems are showing signs of magnetospheric accretion, despite their slightly different configurations, and the weak magnetic field of AK Sco. Furthermore, the magnetic topology of DQ Tau A shows a change relative to the previous orbital cycle studied: previously dominated by the poloidal component, it is now dominated by the toroidal component. We also report an increase of the component's accretion and the absence of an accretion burst at the apastron, suggesting that the component's magnetic variation might be the cause of the inter-cycle variations of the system's accretion. We conclude on the presence of magnetospheric accretion for both systems, together with gravitational effects, especially for AK Sco, composed of more massive components

Accretion and magnetism on young eccentric binaries: DQ Tau and AK Sco

International audienceThe accretion and ejection of mass in pre-main-sequence (PMS) stars are key processes in stellar evolution as they shape the stellar angular momentum transport necessary for the stars’ stability. Magnetospheric accretion on to classical T Tauri stars and low-mass PMS stars has been widely studied in the single-star case. This process cannot be directly transferred to PMS binary systems, as tidal and gravitation effects, and/or accretion from a circumbinary disc (with variable separation of the components in the case of eccentric orbits) are in place. This work examines the accretion process of two PMS eccentric binaries, DQ Tau and AK Sco, using high-resolution spectropolarimetric time series. We investigate how magnetospheric accretion can be applied to these systems by studying the accretion-related emission lines and the magnetic field of each system. We discover that both systems are showing signs of magnetospheric accretion, despite their slightly different configurations, and the weak magnetic field of AK Sco. Furthermore, the magnetic topology of DQ Tau A shows a change relative to the previous orbital cycle studied: previously dominated by the poloidal component, it is now dominated by the toroidal component. We also report an increase of the component’s accretion and the absence of an accretion burst at the apastron, suggesting that the component’s magnetic variation might be the cause of the inter-cycle variations of the system’s accretion. We conclude on the presence of magnetospheric accretion for both systems, together with gravitational effects, especially for AK Sco, composed of more massive components

Accretion process, magnetic fields, and apsidal motion in the pre-main sequence binary DQ Tau

International audienceClassical T Tauri stars (CTTSs) are young stellar objects that accrete materials from their accretion disc influenced by their strong magnetic field. The magnetic pressure truncates the disc at a few stellar radii and forces the material to leave the disc plane and fall onto the stellar surface by following the magnetic field lines. However, this global scheme may be disturbed by the presence of a companion interacting gravitationally with the accreting component. This work is aiming to study the accretion and the magnetic field of the tight eccentric binary DQ Tau, composed of two equal-mass ($\sim$ 0.6 \msun ) CTTSs interacting at different orbital phases. We investigated the variability of the system using a high-resolution spectroscopic and spectropolarimetric monitoring performed with ESPaDOnS at the CFHT. We provide the first ever magnetic field analysis of this system, the Zeeman-Doppler imaging revealed a stronger magnetic field for the secondary than the primary (1.2 kG and 0.5 kG, respectively), but the small-scale fields analysed through Zeeman intensification yielded similar strengths (about 2.5 kG). The magnetic field topology and strengths are compatible with the accretion processes on CTTSs. Both components of this system are accreting, with a change of the main accretor during the orbital motion. In addition, the system displays a strong enhancement of the mass accretion rate at periastron and apastron. We also discovered, for the first time in this system, the apsidal motion of the orbital ellipse

Accretion process, magnetic fields, and apsidal motion in the pre-main sequence binary DQ Tau

International audienceClassical T Tauri stars (CTTSs) are young stellar objects that accrete materials from their accretion disc influenced by their strong magnetic field. The magnetic pressure truncates the disc at a few stellar radii and forces the material to leave the disc plane and fall onto the stellar surface by following the magnetic field lines. However, this global scheme may be disturbed by the presence of a companion interacting gravitationally with the accreting component. This work is aiming to study the accretion and the magnetic field of the tight eccentric binary DQ Tau, composed of two equal-mass ($\sim$ 0.6 \msun ) CTTSs interacting at different orbital phases. We investigated the variability of the system using a high-resolution spectroscopic and spectropolarimetric monitoring performed with ESPaDOnS at the CFHT. We provide the first ever magnetic field analysis of this system, the Zeeman-Doppler imaging revealed a stronger magnetic field for the secondary than the primary (1.2 kG and 0.5 kG, respectively), but the small-scale fields analysed through Zeeman intensification yielded similar strengths (about 2.5 kG). The magnetic field topology and strengths are compatible with the accretion processes on CTTSs. Both components of this system are accreting, with a change of the main accretor during the orbital motion. In addition, the system displays a strong enhancement of the mass accretion rate at periastron and apastron. We also discovered, for the first time in this system, the apsidal motion of the orbital ellipse

Accretion process, magnetic fields, and apsidal motion in the pre-main sequence binary DQ Tau

International audienceClassical T Tauri stars (CTTSs) are young stellar objects that accrete materials from their accretion disc influenced by their strong magnetic field. The magnetic pressure truncates the disc at a few stellar radii and forces the material to leave the disc plane and fall onto the stellar surface by following the magnetic field lines. However, this global scheme may be disturbed by the presence of a companion interacting gravitationally with the accreting component. This work is aiming to study the accretion and the magnetic field of the tight eccentric binary DQ Tau, composed of two equal-mass ($\sim$ 0.6 \msun ) CTTSs interacting at different orbital phases. We investigated the variability of the system using a high-resolution spectroscopic and spectropolarimetric monitoring performed with ESPaDOnS at the CFHT. We provide the first ever magnetic field analysis of this system, the Zeeman-Doppler imaging revealed a stronger magnetic field for the secondary than the primary (1.2 kG and 0.5 kG, respectively), but the small-scale fields analysed through Zeeman intensification yielded similar strengths (about 2.5 kG). The magnetic field topology and strengths are compatible with the accretion processes on CTTSs. Both components of this system are accreting, with a change of the main accretor during the orbital motion. In addition, the system displays a strong enhancement of the mass accretion rate at periastron and apastron. We also discovered, for the first time in this system, the apsidal motion of the orbital ellipse