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Register a new userOn the evolution of the magnetic field of Ap star $alpha^2$ CVn
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New high-precision measurements of the longitudinal magnetic field of Ap stars suggest the existence of secular intrinsic variations of the global magnetic field in some stars. We argue that such changes are apparent in the Ap star $alpha^2$ CVn in the time scale of $sim$ 10 years, which results from the analysis of literature data. Therefore, such an observation implies, that the rate of magnetic field evolution of Ap stars is much higher than was previously thought.
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We investigate the radial velocity and the magnetic field of the CP star alpha^2 CVn. The observed variation of the magnetic field is compared with that of our model. We search for a relation between the magnetic field and the distribution of the chemical elements. The period in the radial velocities is constant over a time interval of about 100 years.
This paper presents a series of 95 new measurements of the longitudinal (effective) magnetic field $B_e$ of the Ap star $gamma$ Equ (HD 201601). Observations were obtained at the coude focus of the 1-m reflector at the Special Astrophysical Observatory (SAO RAS) in Russia over a time period of 4190 days (more than 11 years). We compiled a long record of $B_e$ points, adding our measurements to all published data. The time series of magnetic data consists of 395 $B_e$ points extending for 24488 days, or over 67 years. Various methods of period determination were examined for the case in which the length of the observed time series is rather short and amounts only to ~69 percent of the period. We argue that the fitting of a sine wave to the observed $B_e$ points by least squares yields the most reliable period in the case of $gamma$ Equ. Therefore, the best period for long-term magnetic variations of $gamma$ Equ, and hence the rotational period, is $P_{rm rot}=35462.5 pm 1149$ days $= 97.16 pm 3.15$ years.
Context. The Ap stars that rotate extremely slowly, with periods of decades to centuries, represent one of the keys to the understanding of the processes leading to the differentiation of stellar rotation. Aims. We characterise the variations of the magnetic field of the Ap star HD 50169 and derive constraints about its structure. Methods. We combine published measurements of the mean longitudinal field <Bz> of HD 50169 with new determinations of this field moment from circular spectropolarimetry obtained at the 6-m telescope BTA of the Special Astrophysical Observatory of the Russian Academy of Sciences. For the mean magnetic field modulus <B>, literature data are complemented by the analysis of ESO spectra, both newly acquired and from the archive. Radial velocities are also obtained from these spectra. Results. We present the first determination of the rotation period of HD 50169, Prot = (29.04+/-0.82) y. HD 50169 is currently the longest-period Ap star for which magnetic field measurements have been obtained over more than a full cycle. The variation curves of both <Bz> and <B> have a significant degree of anharmonicity, and there is a definite phase shift between their respective extrema. We confirm that HD 50169 is a wide spectroscopic binary, refine its orbital elements, and suggest that the secondary is probably a dwarf star of spectral type M. Conclusions. The shapes and mutual phase shifts of the derived magnetic variation curves unquestionably indicate that the magnetic field of HD 50169 is not symmetric about an axis passing through its centre. Overall, HD 50169 appears similar to the bulk of the long-period Ap stars.
This work is a continuation of the studies of the ultrafast variability of line profiles in the spectra of early-type stars. Line profile variations (LPVs) in the spectrum a chemically peculiar A0Vp star $alpha^2,$CVn are investigated using the January 6, 2020 observations carried out with the 6-meter BTA telescope at Special Astrophysical observatory (SAO) of the Russian Academy of Sciences (RAS) equipped with the MSS spectrograph. Regular short-term periodic variations of the H$_beta$, Fe,II, and Cr,II lines were detected with periods ranging from $sim!$4 to $sim!$140 minutes. The magnetic field of the star was determined for all observations. The average measured longitudinal magnetic field component over the entire duration of observations is about $approx$600,G, which is close to the value expected from the well-known magnetic field phase curve.
Surface magnetic fields have a strong impact on stellar mass loss and rotation and, as a consequence, on the evolution of massive stars. In this work we study the influence of an evolving dipolar surface fossil magnetic field with an initial field strength of 4 kG on the characteristics of 15 M$_{odot}$ solar metallicity models using the Geneva stellar evolution code. Non-rotating and rotating models considering two different scenarios for internal angular momentum transport are computed, including magnetic field evolution, mass-loss quenching, and magnetic braking. Magnetic field evolution results in weakening the initially strong magnetic field, however, in our models an observable magnetic field is still maintained as the star evolves towards the red supergiant phase. At the given initial mass of the models, mass-loss quenching is modest. Magnetic braking greatly enhances chemical element mixing if radial differential rotation is allowed for, on the other hand, the inclusion of surface magnetic fields yields a lower surface enrichment in the case of near solid-body rotation. Models including surface magnetic fields show notably different trends on the Hunter diagram (plotting nitrogen abundance vs $v sin i$) compared to those that do not. The magnetic models agree qualitatively with the anomalous `Group 2 stars, showing slow surface rotation and high surface nitrogen enhancement on the main sequence.
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