J/A+A/660/A141 Light curve of the active star LQ Hya (Lehtinen+, 2022)
Topological changes in the magnetic field of LQ Hya during an activity minimum.
Lehtinen J.J., Kaepylae M.J., Hackman T., Kochukhov O., Willamo T.,
Marsden S.C., Jeffers S.V., Henry G.W., Jetsu L.
<Astron. Astrophys. 660, A141 (2022)>
=2022A&A...660A.141L 2022A&A...660A.141L (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable ; Photometry
Keywords: polarization - stars: activity - stars: imaging - starspots
Abstract:
Previous studies have related surface temperature maps, obtained with
the Doppler imaging (DI) technique, of LQ Hya with long-term
photometry. Here, we compare surface magnetic field maps, obtained
with the Zeeman Doppler imaging (ZDI) technique, with contemporaneous
photometry, with the aim of quantifying the star's magnetic cycle
characteristics.
We inverted Stokes IV spectropolarimetry, obtained with the HARPSpol
and ESPaDOnS instruments, into magnetic field and surface brightness
maps using a tomographic inversion code that models high
signal-to-noise ratio mean line profiles produced by the least squares
deconvolution (LSD) technique. The maps were compared against
long-term ground-based photometry acquired with the T3 0.40m
Automatic Photoelectric Telescope (APT) at Fairborn Observatory, which
offers a proxy for the spot cycle of the star, as well as with
chromospheric CaII H&K activity derived from the observed spectra.
The magnetic field and surface brightness maps reveal similar patterns
relative to previous DI and ZDI studies: non-axisymmetric polar
magnetic field structure, void of fields at mid-latitudes, and a
complex structure in the equatorial regions. There is a weak but clear
tendency of the polar structures to be linked with a strong radial
field and the equatorial ones with the azimuthal field. We find a
polarity reversal in the radial field between 2016 and 2017 that is
coincident with a spot minimum seen in the long-term photometry,
although the precise relation of chromospheric activity to the spot
activity remains complex and unclear. The inverted field strengths
cannot be easily related with the observed spottedness, but we find
that they are partially connected to the retrieved field complexity.
This field topology and the dominance of the poloidal field component,
when compared to global magnetoconvection models for rapidly rotating
young suns, could be explained by a turbulent dynamo, where
differential rotation does not play a major role (so-called 2 or 2
dynamos) and axi- and non-axisymmetric modes are excited
simultaneously. The complex equatorial magnetic field structure could
arise from the twisted (helical) wreaths often seen in these
simulations, while the polar feature would be connected to the mostly
poloidal non-axisymmetric component that has a smooth spatial
structure.
Description:
Detailed time series analysis of B- and V-band photometry of the young
active solar-type star LQ Hya. These data characterise the starspot
evolution of the star and supplement an analysis of simultaneous
magnetic surface maps produced using the Zeeman Doppler imaging
method.
The B- and V-band light curves are provided in the files lqhya_b.dat
and lqhya_v.dat as differential photometry against the comparison star
HD 82477. The light curves span from November 1987 to February 2019.
The numerical results of the light curve analysis are given in the
file res.dat. They have been derived using the continuous period
search (CPS) method, described in detail in Lehtinen et al.
(2011A&A...527A.136L 2011A&A...527A.136L, Cat. J/A+A/527/A136).
Objects:
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RA (2000) DE Designation(s)
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09 32 25.6 -11 11 04.7 V* LQ Hya = HD 82558
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
lqhya_b.dat 19 3356 B-band differential photometry
lqhya_v.dat 19 3296 V-band differential photometry
res.dat 104 122 Light curve fits for LQ Hya
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Byte-by-byte Description of file: lqhya_b.dat
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Bytes Format Units Label Explanations
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1- 12 F12.4 d HJD Heliodentric Julian Date
14- 19 F6.3 mag DBmag Differential B-band photometry
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Byte-by-byte Description of file: lqhya_v.dat
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Bytes Format Units Label Explanations
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1- 12 F12.4 d HJD Heliodentric Julian Date
14- 19 F6.3 mag DVmag Differential V-band photometry
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Byte-by-byte Description of files: res.dat
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Bytes Format Units Label Explanations
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1- 12 F12.4 d HJD Heliocentric Julian Date of light curve fit
14- 20 F7.4 mag M Light curve mean
22- 28 F7.4 mag e_M Error of M
30- 36 F7.4 mag Amp Light curve amplitude
38- 44 F7.4 mag e_Amp Error of Amp
46- 52 F7.4 d Per Period of light curve
54- 60 F7.4 d e_Per Error of Per
62- 74 F13.4 d tm1 Epoch of the primary minimum
76- 82 F7.4 d e_tm1 Error of tm1
84- 96 F13.4 d tm2 ? Epoch of the secondary minimum
98-104 F7.4 d e_tm2 ? Error of tm2
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Acknowledgements:
Jyri Lehtinen, jyri.j.lehtinen(at)helsinki.fi
(End) Patricia Vannier [CDS] 15-Mar-2022