Monitoring of the magnetic field topology and activity of the core helium-burning giant beta Ceti in the period 2010-2013

Beta Ceti is a slowly rotating (v sin i = 3.5 kms−1) single giant. In our previous study (Tsvetkova et al. (2013)) we showed that it is in the core He-burning phase and we reconstructed two Zeeman Doppler imaging (ZDI) maps (using data from 2010 and 2011) revealing a simple large-scale magnetic field structure. We concluded that the magnetic field of beta Ceti could have a fossil field origin. In addition, the study of Aurière et al. (2015) about the properties and origin of the magnetism of late-type giants, where beta Ceti was a member of that sample, revealed that this star did not follow the general trends for dynamo-generated magnetic fields. Now, we present a new ZDI map of beta Ceti and compare the new results with our previous study. This monitoring for several years of the magnetic field topology and line activity indicators variability supports our previous conclusion about the fossil field origin of the magnetic field of beta Ceti

Magnetic field variability in RZ Ari - an evolved M giant

International audienceRZ Ari is a fast rotating apparently single M giant of 2.2 Msun. It is fairly evolved to tip RGB or early AGB stage. In addition, the star is known as semi-regular variable. We have studied its longitudinal magnetic field variability using spectropolarimetric data obtained with Narval at Telescope Bernard Lyot, Pic du Midi Observatory, France in the period 2008 - 2018. Two periods were identified using the Lomb - Scargle method: 1310 days and 498 days. The second one is very close to the Long Secondary Period of RZ Ari (480 days) and maybe we observe for first time an interplay of the magnetic field and pulsations for a M giant. Taking into account literature data we determined the radius of the star (117.2 Rsun) that is consistent with the AGB phase. Our work hypothesis is that RZ Ari with its fast rotation is an intermediate case of dynamo generated magnetic field and shock wave compression generated fields as we observe in Miras. These stars are the next evolutionary stage, after early-AGB stars. Further study is required to confirm or reject the hypothesis and to understand better the interplay of the magnetic field and pulsation in this fairly evolved giant

Magnetic field variability in RZ ARI – a fairly evolved M giant

https://www.astro.bas.bg/XIBSAC/Proceedings/Proceedings_11BSAC.pdfInternational audienceRZ Ari is a fast rotating apparently single M giant of 2.2 Msun. It is fairly evolved to tip RGB or early AGB stage. In addition, the star is known as semi-regular variable. We have studied its longitudinal magnetic field variability using spectropolarimetric data obtained with Narval at Telescope Bernard Lyot, Pic du Midi Observatory, France in the period 2008 - 2018. Two periods were identified using the Lomb - Scargle method: 1310 days and 498 days. The second one is very close to the Long Secondary Period of RZ Ari (480 days) and maybe we observe for first time an interplay of the magnetic field and pulsations for a M giant. Taking into account literature data we determined the radius of the star (117.2 Rsun) that is consistent with the AGB phase. Our work hypothesis is that RZ Ari with its fast rotation is an intermediate case of dynamo generated magnetic field and shock wave compression generated fields as we observe in Miras. These stars are the next evolutionary stage, after early-AGB stars. Further study is required to confirm or reject the hypothesis and to understand better the interplay of the magnetic field and pulsation in this fairly evolved giant

Magnetic field variability in RZ Ari - an evolved M giant

International audienceRZ Ari is a fast rotating apparently single M giant of 2.2 Msun. It is fairly evolved to tip RGB or early AGB stage. In addition, the star is known as semi-regular variable. We have studied its longitudinal magnetic field variability using spectropolarimetric data obtained with Narval at Telescope Bernard Lyot, Pic du Midi Observatory, France in the period 2008 - 2018. Two periods were identified using the Lomb - Scargle method: 1310 days and 498 days. The second one is very close to the Long Secondary Period of RZ Ari (480 days) and maybe we observe for first time an interplay of the magnetic field and pulsations for a M giant. Taking into account literature data we determined the radius of the star (117.2 Rsun) that is consistent with the AGB phase. Our work hypothesis is that RZ Ari with its fast rotation is an intermediate case of dynamo generated magnetic field and shock wave compression generated fields as we observe in Miras. These stars are the next evolutionary stage, after early-AGB stars. Further study is required to confirm or reject the hypothesis and to understand better the interplay of the magnetic field and pulsation in this fairly evolved giant

Magnetic field variability in RZ Ari - an evolved M giant

International audienceRZ Ari is a fast rotating apparently single M giant of 2.2 Msun. It is fairly evolved to tip RGB or early AGB stage. In addition, the star is known as semi-regular variable. We have studied its longitudinal magnetic field variability using spectropolarimetric data obtained with Narval at Telescope Bernard Lyot, Pic du Midi Observatory, France in the period 2008 - 2018. Two periods were identified using the Lomb - Scargle method: 1310 days and 498 days. The second one is very close to the Long Secondary Period of RZ Ari (480 days) and maybe we observe for first time an interplay of the magnetic field and pulsations for a M giant. Taking into account literature data we determined the radius of the star (117.2 Rsun) that is consistent with the AGB phase. Our work hypothesis is that RZ Ari with its fast rotation is an intermediate case of dynamo generated magnetic field and shock wave compression generated fields as we observe in Miras. These stars are the next evolutionary stage, after early-AGB stars. Further study is required to confirm or reject the hypothesis and to understand better the interplay of the magnetic field and pulsation in this fairly evolved giant

Monitoring of the magnetic field topology and activity of the core helium-burning giant β Ceti in the period 2007 - 2013

International audienceWe present a second spectropolarimetric study dedicated to the single giant β Ceti. Adding new data to our previously published data, we are able to trace the evolution of the magnetic activity of the giant for the period from 2007 to 2013. We apply the same data reduction procedures and methods as in our earlier study, so we could reliably compare the results. We reconstruct a third magnetic map, applying the Zeeman Doppler imaging (ZDI) method. From our new observations we recover a dipolar magnetic topology similar to that obtained previously, supporting the long-term stability of the large-scale magnetic field of β Ceti. To visualise the magnetic field lines that extend above the surface, we perform field extrapolations using a potential field method. In contrast to the large-scale field, the behaviour of the activity indicators Hα, Ca II H&K and Ca II IRT suggests an evolution of the small-scale magnetic structures in the chromosphere. This study presents for the first time a long-term monitoring of the magnetic activity of a probable Ap star descendant, which confirms the stability of its large-scale magnetic field