Twenty-year monitoring of the surface magnetic fields of chemically peculiar stars

Giarrusso, M.; Cecconi, M.; Cosentino, R.; Munari, Matteo; Ghedina, A.; Ambrosino, Filippo; Boschin, W.; Leone, F.

doi:10.1093/mnras/stac1488

Cited by 12 publications

(15 citation statements)

References 63 publications

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“…5. No measurements of the mean longitudinal magnetic field after 2007 were presented by Giarrusso et al (2022). Our measurement of the mean longitudinal field strength using all lines, Bz = 1.54 ± 0.02 kG, does not confirm the slight increase, but the small differences in the field values can be caused by the choice of spectral lines used in the measurements.…”

Section: Hd 137949 = 33 Libcontrasting

confidence: 57%

“…On the other hand, Giarrusso et al (2022) recently reported that B and Bz -values have shown a slight increase over several years, indicating that the rotation period should be longer than 27 yr. Our measurement of the mean field modulus using the HARPSpol observations obtained in 2012 August, B = 4.76±0.02 kG, is of the same order as reported by Giarrusso et al (2022). As an illustration, we show the Zeeman subcomponents of the resolved magnetically split Fe ii line at 6149.258 Å in Fig.…”

Section: Hd 137949 = 33 Libmentioning

confidence: 96%

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Magnetic field measurements of sharp-lined Ap stars

Järvinen

Hubrig

Jayaraman

et al. 2022

Monthly Notices of the Royal Astronomical Society

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Previous observations suggested that Ap and Bp stars exhibit a bimodal distribution of surface magnetic field strengths and that actually only few or no stars exist with magnetic dipole field strengths below 300 G down to a few Gauss. As the number of Ap and Bp stars currently known to possess weak magnetic fields is not large, it is necessary to carry out additional spectropolarimetric studies of Ap and Bp stars to prove whether the assumption of the existence of a critical value for the stability of magnetic fields is realistic. In this study, we present high-resolution HARPSpol magnetic field measurements for a sample of Ap stars with sharp spectral lines with a view to characterize the strengths of their magnetic fields. Out of the studied seven sharp-lined stars, two stars, HD 174779 and HD 203932, exhibit a rather weak longitudinal magnetic field with <Bz > = − 45 ± 3 G and <Bz > =21 ± 4 G, respectively. Additionally, TESS observations were used to test previous conclusions on the differentiation of rotation periods of Ap and Bp stars. Apart from HD 189832 and HD 203932, all other studied sharp-lined stars have long rotation periods. Since an explanation for the slow rotation of Ap stars is currently missing, additional studies of slowly rotating Ap and Bp stars are necessary to improve our understanding of the formation and evolution of Ap and Bp stars.

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Section: Hd 137949 = 33 Libcontrasting

confidence: 57%

Section: Hd 137949 = 33 Libmentioning

confidence: 96%

Magnetic field measurements of sharp-lined Ap stars

Järvinen

Hubrig

Jayaraman

et al. 2022

Monthly Notices of the Royal Astronomical Society

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“…The period estimation has since been refined using magnetic field measurements covering a wider temporal baseline by Landstreet, Bagnulo & Fossati (2014) (P rot = 2800±250 d). Finally, collecting new high sensitivity magnetic field measurements (typical errors a few tens of gauss), Giarrusso et al (2022) both confirmed the above period and improved on its precision (P rot = 2830 ± 140 d).…”

Section: Summary On Kq Velsupporting

confidence: 56%

“…Collecting a large number of additional spectra, the orbital period, the mass function, and other orbital parameters have been constrained by Mathys (2017). These orbital parameters are well in good agreement with values estimated by Giarrusso et al (2022), the latter having slightly higher uncertainty.…”

Section: Summary On Kq Velsupporting

confidence: 53%

“…When observed at visible wavelengths high-resolution spectra of KQ Vel show only evidence of an early-type magnetic star (Bailey et al 2015). This long-period magnetic star (P rot = 2830 d; Giarrusso et al 2022) is a member of a high eccentricity multiple system as directly evidenced by the measured radial velocities (Mathys 2017), but no evidence of the companion is seen at visible wavelengths, hence its nature remains unclear. The only direct measurement of the companion's brightness was performed at the infrared domain with interferometric observations reported by Schöller et al (2020).…”

Section: Discussionmentioning

confidence: 95%

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Discovery and origin of the radio emission from the multiple stellar system KQVel

Leto¹,

Oskinova²,

Buemi³

et al. 2022

Preprint

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KQ Vel is a binary system composed of a slowly rotating magnetic Ap star with a companion of unknown nature. In this paper, we report the detection of its radio emission. We conducted a multi-frequency radio campaign using the ATCA interferometer (band-names: 16cm, 4cm, and 15mm). The target was detected in all bands. The most obvious explanation for the radio emission is that it originates in the magnetosphere of the Ap star, but this is shown unfeasible. The known stellar parameters of the Ap star enable us to exploit the scaling relationship for non-thermal gyro-synchrotron emission from early-type magnetic stars. This is a general relation demonstrating how radio emission from stars with centrifugal magnetospheres is supported by rotation. Using KQ Vel's parameters the predicted radio luminosity is more than five orders of magnitudes lower than the measured one. The extremely long rotation period rules out the Ap star as the source of the observed radio emission. Other possible explanations for the radio emission from KQ Vel, involving its unknown companion, have been explored. A scenario that matches the observed features (i.e. radio luminosity and spectrum, correlation to X-rays) is a hierarchical stellar system, where the possible companion of the magnetic star is a close binary (possibly of RS CVn type) with at least one magnetically active late-type star. To be compatible with the total mass of the system, the last scenario places strong constraints on the orbital inclination of the KQ Vel stellar system.

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Long-period Ap stars discovered with TESS data: Cycles 3 and 4

Mathys,

Holdsworth,

Kurtz

2024

A&A

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One of the most challenging aspects of the Ap stars is the extreme differentiation of their rotation periods, which span more than five orders of magnitude. The physical origin of this differentiation remains poorly understood. The consideration of the most slowly rotating Ap stars represents a promising approach to gain insight into the processes responsible for the rotational braking to which the Ap stars are subject. However, historically, the study of these stars focused primarily on the most strongly magnetic among them. This bias introduced an ambiguity in the conclusions that could be drawn, as it did not allow the distinction between the rotational and magnetic effects, nor the investigation of possible correlations between rotational and magnetic properties. We previously showed that the identification of super-slowly rotating Ap (ssrAp) star candidates (defined as Ap stars that have rotation periods $ through systematic exploitation of the available TESS photometric observations of Ap stars is an effective approach to build a sample devoid of magnetic bias. This approach rests on the presence of brightness spots on the surface of Ap stars that are not distributed symmetrically about their rotation axes and show long-term stability, hence are responsible for photometric variations with the stellar rotation period. In our previous analyses of TESS Cycle 1 and Cycle 2 data, we interpreted the Ap stars showing no such variability over the 27-d duration of a TESS sector as being ssrAp star candidates. Here, we applied the same approach to TESS Cycle 3 and Cycle 4 observations of Ap stars. We show, however, that two issues that had not been fully appreciated until now may lead to spurious identification of ssrAp star candidates. On the one hand, a considerable fraction of the Ap stars in the existing lists turn out to have erroneous or dubious spectral classifications. On the other hand, the TESS data processing may remove part of the variability signal, especially for stars with moderately long periods ($20\ d After critical evaluation of these effects, we report the identification of 25 new ssrAp star candidates and of eight stars with moderately long periods. Combining this list with the lists of ssrAp stars from Cycles 1 and 2 and with the list of ssrAp stars that were previously known but whose lack of variability was not detected in our study, we confirmed at a higher significance level the conclusions drawn in our earlier work. These include the lower rate of occurrence of super-slow rotation among weakly magnetic Ap stars than among strongly magnetic ones, the probable existence of a gap between sim 2 and sim 3\,kG in the distribution of the magnetic field strengths of the ssrAp stars, and the much higher rate of occurrence of rapid oscillations in ssrAp stars than in the whole population of Ap stars. The next step to gain further understanding of the ssrAp stars will be to obtain high-resolution spectra of those for which such observations have not been made yet, to constrain their rotation velocities and their magnetic fields.

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Twenty-year monitoring of the surface magnetic fields of chemically peculiar stars

Cited by 12 publications

References 63 publications

Magnetic field measurements of sharp-lined Ap stars

Magnetic field measurements of sharp-lined Ap stars

Discovery and origin of the radio emission from the multiple stellar system KQVel

Long-period Ap stars discovered with TESS data: Cycles 3 and 4

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