Magnetic field structure in single late-type giants: the effectively single giant V390 Aurigae

Konstantinova-Antova, R.; Aurière, M.; Petit, P.; Charbonnel, C.; Tsvetkova, S.; Lèbre, A.; Bogdanovski, R.

doi:10.1051/0004-6361/201116690

Cited by 21 publications

(18 citation statements)

References 64 publications

(88 reference statements)

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“…Depending on the thickness of the convective envelope and rotational rate in some stars, we also can observe an azimuthal belt in the magnetic map (e.g., V390 Aur, Konstantinova-Antova et al 2012). There is also a dependence of the magnetic field strength on rotation Aurière et al 2015), which is clear evidence of an α-ω dynamo operation.…”

Section: Discussionmentioning

confidence: 87%

The different origins of magnetic fields and activity in the Hertzsprung gap stars, OU Andromedae and 31 Comae

Borisova

Aurière

Petit

et al. 2016

A&A

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Context. When crossing the Hertzsprung gap, intermediate-mass stars develop a convective envelope. Fast rotators on the main sequence, or Ap star descendants, are expected to become magnetic active subgiants during this evolutionary phase. Aims. We compare the surface magnetic fields and activity indicators of two active, fast rotating red giants with similar masses and spectral class but different rotation rates -OU And (P rot = 24.2 d) and 31 Com (P rot = 6.8 d) -to address the question of the origin of their magnetism and high activity. Methods. Observations were carried out with the Narval spectropolarimeter in 2008 and 2013. We used the least-squares deconvolution (LSD) technique to extract Stokes V and I profiles with high signal-to-noise ratio to detect Zeeman signatures of the magnetic field of the stars. We then provide Zeeman-Doppler imaging (ZDI), activity indicators monitoring, and a precise estimation of stellar parameters. We use state-of-the-art stellar evolutionary models, including rotation, to infer the evolutionary status of our giants, as well as their initial rotation velocity on the main sequence, and we interpret our observational results in the light of the theoretical Rossby numbers. Results. The detected magnetic field of OU Andromedae (OU And) is a strong one. Its longitudinal component B l reaches 40 G and presents an about sinusoidal variation with reversal of the polarity. The magnetic topology of OU And is dominated by largescale elements and is mainly poloidal with an important dipole component, as well as a significant toroidal component. The detected magnetic field of 31 Comae (31 Com) is weaker, with a magnetic map showing a more complex field geometry, and poloidal and toroidal components of equal contributions. The evolutionary models show that the progenitors of OU And and 31 Com must have been rotating at velocities that correspond to 30 and 53%, respectively, of their critical rotation velocity on the zero age main sequence. Both OU And and 31 Com have very similar masses (2.7 and 2.85 M , respectively), and they both lie in the Hertzsprung gap. Conclusions. OU And appears to be the probable descendant of a magnetic Ap star, and 31 Com the descendant of a relatively fast rotator on the main sequence. Because of the relatively fast rotation in the Hertzsprung gap and the onset of the development of a convective envelope, OU And also has a dynamo in operation.

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Section: Discussionmentioning

confidence: 87%

The different origins of magnetic fields and activity in the Hertzsprung gap stars, OU Andromedae and 31 Comae

Borisova

Aurière

Petit

et al. 2016

A&A

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“…This result also needs be compared with spectro-polarimetric observations of magnetic RGs (e.g., Aurière et al 2011Aurière et al , 2015Konstantinova-Antova et al 2012 and the subsequent theoretical work by Charbonnel et al (2017). Aurière et al (2015) describes spectropolarimetric observations of a sample of 48 magnetically active RGs, and report clear detection of magnetic fields in 29 stars.…”

Section: Rotation Rate Versus Activitymentioning

confidence: 99%

Active red giants: Close binaries versus single rapid rotators

Gaulme

Jackiewicz

Spada

et al. 2020

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Oscillating red-giant stars have provided a wealth of asteroseismic information regarding their interiors and evolutionary states, which enables detailed studies of the Milky Way. The objective of this work is to determine what fraction of red-giant stars shows photometric rotational modulation, and understand its origin. One of the underlying questions is the role of close binarity in this population, which relies on the fact that red giants in short-period binary systems (less than 150 days or so) have been observed to display strong rotational modulation. We selected a sample of about 4500 relatively bright red giants observed by Kepler, and show that about 370 of them (∼8%) display rotational modulation. Almost all have oscillation amplitudes below the median of the sample, while 30 of them are not oscillating at all. Of the 85 of these red giants with rotational modulation chosen for follow-up radial-velocity observation and analysis, 34 show clear evidence of spectroscopic binarity. Surprisingly, 26 of the 30 nonoscillators are in this group of binaries. On the contrary, about 85% of the active red giants with detectable oscillations are not part of close binaries. With the help of the stellar masses and evolutionary states computed from the oscillation properties, we shed light on the origin of their activity. It appears that low-mass red-giant branch stars tend to be magnetically inactive, while intermediate-mass ones tend to be highly active. The opposite trends are true for helium-core burning (red clump) stars, whereby the lower-mass clump stars are comparatively more active and the higher-mass ones are less active. In other words, we find that low-mass red-giant branch stars gain angular momentum as they evolve to clump stars, while higher-mass ones lose angular momentum. The trend observed with low-mass stars leads to possible scenarios of planet engulfment or other merging events during the shell-burning phase. Regarding intermediate-mass stars, the rotation periods that we measured are long with respect to theoretical expectations reported in the literature, which reinforces the existence of an unidentified sink of angular momentum after the main sequence. This article establishes strong links between rotational modulation, tidal interactions, (surface) magnetic fields, and oscillation suppression. There is a wealth of physics to be studied in these targets that is not available in the Sun.

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“…The surface magnetic topology, sometimes along with its temporal evolution, has been reconstructed for a small number of cool giants -EK Eri, which is a descendant of an Ap star (Aurière et al 2011), V390 Aur, a single giant (although it is a binary component, it can be considered single for our purpose because synchronization plays no role as far as its fast rotation and magnetic activity are concerned; cf. Konstantinova-Antova et al 2012), the early K-type primary giant of the RS CVn binary IM Peg (Berdyugina & Marsden 2006), and the FK Com star HD 199178 (Petit et al 2004).…”

Section: Introductionmentioning

confidence: 99%

Magnetic field structure in single late-type giants:βCeti in 2010–2012

Tsvetkova

Petit

Aurière

et al. 2013

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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 B l . 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 B l . 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 B l 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 B l 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.

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Magnetic field structure in single late-type giants: the effectively single giant V390 Aurigae

Cited by 21 publications

References 64 publications

The different origins of magnetic fields and activity in the Hertzsprung gap stars, OU Andromedae and 31 Comae

The different origins of magnetic fields and activity in the Hertzsprung gap stars, OU Andromedae and 31 Comae

Active red giants: Close binaries versus single rapid rotators

Magnetic field structure in single late-type giants:βCeti in 2010–2012

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