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Short-term variations of surface magnetism and
prominences of the young sun-like star V530 Per

Tianqi Cang, Pascal Petit, Jean-François Donati, Colin P. Folsom

► To cite this version:

Tianqi Cang, Pascal Petit, Jean-François Donati, Colin P. Folsom. Short-term variations of surface magnetism and prominences of the young sun-like star V530 Per. 21st Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, Jul 2022, Toulouse, France. 2022, 10.5281/zenodo.7350690. [https://doi.org/10.5281/zenodo.7350690](https://doi.org/10.5281/zenodo.7350690).

HAL Id: hal-04255175

https://hal.science/hal-04255175v1

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Distributed under a Creative Commons Attribution 4.0 International License
SHORT-TERM VARIATIONS OF SURFACE MAGNETISM AND
PROMINENCES OF THE YOUNG SUN-LIKE STAR V530 PER

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Tianqi Cang¹, Pascal Petit¹, Jean-François Donati¹, Colin Folsom¹,²

1. Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, CNRS, CNES, 31400 Toulouse, France
2. Tartu Observatory, University of Tartu, Observatooriumi 1, Tõravere, 61602 Tartumaa, Estonia

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## Abstract

V530 Per is a solar-like member of the young open cluster α Persei, with an ultra-short rotation period (P ~ 0.32d). We report on two spectropolarimetric campaigns using ESPaDOnS, aimed at characterizing the short-term variability of its magnetic activity and large-scale magnetic field. We used time-resolved spectropolarimetric observations obtained in 2006 and 2018 and reconstructed the brightness distribution and large-scale magnetic field geometry of V530 Per through Zeeman-Doppler imaging. Using the same data sets, we also mapped the spatial distribution of prominences through tomography of Hα emission. We reconstruct, at both epochs, a large, dark spot occupying the polar region of V530 Per while smaller (dark and bright) spots were reconstructed at lower latitudes. The maximal field strength reached ~1 kG. The surface differential rotation was consistent with a smooth Sun-like shear $dΩ = 0.053 ± 0.004 \text{ rad.d}^{-1}$, close to the solar shear level. The prominence pattern displayed a stable component that was confined close to the corotation radius. In 2018, we also observed rapidly evolving Hα emitting structures, over timescales ranging from minutes to days. The fast Hα evolution was not linked to any detected photospheric changes in the spot or magnetic coverage.

## Spectropolarimetric observations

We obtained 6 nights of time-series of spectropolarimetric observations of V530 Per in late 2006 and 2018. The data were collected by the ESPaDOnS spectropolarimeter (Donati et al. 2006a), mounted at the Canada-France-Hawaii Telescope (CFHT). Normalized, reduced 192 Stokes I and 48 Stokes V spectra are extracted. The LSD method (Donati et al. 1997) is used to combine a list of selected spectral lines to produce a pseudo line profile with improved S/N.

## Fundamental parameters

By combining literature measurements and ZDI results, we derived fundamental parameters of V530 Per. Details are shown below.

<table><thead><tr><th>Distance (pc)</th><th>Age (Myr)</th><th>Teff (K)</th><th>log g</th><th>Radius (Rsun)</th><th>Mass (Msun)</th><th>Rossby number</th><th>Period (d)</th><th>v sin (km/s)</th><th>INCL (deg)</th><th>dΩ (rad d<sup>-1</sup>)</th></tr></thead><tbody><tr><td>167 ±15</td><td>33 ±10</td><td>5281 ±96</td><td>4.39 ±0.11</td><td>1.04 ±0.11</td><td>1.03 ±0.13</td><td>0.0128 ±0.19</td><td>0.3205 ±0.0002</td><td>105.6 ±0.15</td><td>40 ±4</td><td>0.053 ±0.004</td></tr></tbody></table>

## Magnetic field

We applied the Zeeman Doppler Imaging technique (ZDI, Semel 1989; Donati et al. 2006b; Folsom et al. 2018) to model the two epochs of Stokes V data, in order to reconstruct the 2D magnetic field distribution of V530 Per (see Fig.3). According to the maps, the average surface magnetic field is 177G in 2006 and 222G in 2018, with local peaks slightly above 1kG. About 2/3 of the magnetic energy belongs to the toroidal field component. Moreover, the complexity of the magnetic field is very high, with less than 7% of the magnetic energy stored in the dipolar component.

<figure><img src="image_5.png" /><figcaption>**Fig 2.** Magnetic Map of V530 Per in 2006 (left) and 2018 (right). The three panels show different field components in a spherical projection. The color scale illustrates the field strength in Gauss. For the radial and meridional components, the strongest magnetic spots are found close to the pole. For the azimuthal component, a large region of negative field is reconstructed above a latitude of 45°.</figcaption></figure>

## Brightness imaging

By applying the Doppler Imaging method (DI, Vogt et al. 1987) using the code of Folsom et al. (2018), we recovered the surface brightness distribution of V530 Per in Fig 1. The reconstruction includes a solar-like differential rotation law, with a roughly solar shear level optimizing our model.

<figure><img src="image_6.png" /><figcaption>**Fig 1.** Logarithmic normalized brightness map of V530 Per. A large, dark spot is identified close to the pole, as well as a complex spot distribution at lower latitudes for both 2006 and 2018 epoch. Since the inclination is small, most of the southern hemisphere could not be observed and modeled.</figcaption></figure>

## Prominence system

For active stars, prominences are constituted of cool, dense gas trapped in closed magnetic loops. The prominence structure produces strong, rotationally-modulated, Hα emission. We reconstructed prominence maps of V530 Per for the two observational nights, unveiling a stable component that was confined close to the corotation radius and clues of short-term variations. The total mass stored as prominences is ≈4.6 × 10¹⁷ kg (≈2.3 × 10⁻¹³M☉). Our observation also suggests that as much as 3.5 × 10¹⁶ kg of material has been removed from the system within one day.

<figure><img src="image_7.png" /><figcaption>**Fig 3.** Prominence maps of V530 Per reconstructed from the data of 4 observational nights in 2 epochs. The inner, filled blue circle represents the stellar surface. Radial ticks inside this circle give the rotational phases of Hα observations. The outer dashed circle is the corotation radius. The color scale depicts the local Hα equivalent width, in units of picometers per 8 km s⁻¹ square pixel.</figcaption></figure>

## References

Donati, J. F., Semel, M., Carter, B. D., Rees, D. E., & Collier Cameron, A. 1997, MNRAS, 291, 658
Donati, J. F., Catala, C., Landstreet, J. D., & Petit, P. 2006a, in Astronomical Society of the Pacific Conference Series, Vol. 358, Solar Polarization 4, ed. R. Casini & B. W. Lites, 362
Donati, J. F., Howarth, I. D., Jardine, M. M., et al. 2006b, MNRAS, 370, 629
Folsom, C. P., Bouvier, J., Petit, P., et al. 2018, MNRAS, 474, 4956
Semel, M. 1989, A&A, 225, 456
Vogt, S. S., Penrod, G. D., & Hatzes, A. P. 1987, ApJ, 321, 496

E-mail: cangtq@mail.bnu.edu.cn

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