| 其他摘要 | Based on the photometric and spectroscopic observations, the investigation on the
magnetic activities and their evolution for stars with different internal structures, ro-
tational velocities and located at different evolution stages, could provide the clues to
improve the solar and stellar dynamo theories. On the other hand, such studies can also
help to understand the role of magnetic field in the formation and evolution, habitability
and atmospheres of exoplanets. This thesis mainly includes three parts: 1. Use the ob-
servational data of the activity K2V single star USNO-B1.0 1388-0463685, which was
newly discovered in the Yunnan-Hong Kong wide-field photometric survey, to study the
short-term evolution and long-term regularity of its surface spots. We find that the star
rotates extremely fast and shows strong Li I absorption line, which indicates that it is in
a relatively young evolutionary stage and has not yet undergone the magnetic braking
process. We have reconstructed its surface spot images with the photometric data from
2016 to 2020 by means of light curve inversion method. In the short term, its surface
spots show rapid evolution on a time scale of 50 days. In the long term, the amplitudes
of light curves show a regular variation with a period of 2.4 years. The active regions
usually appear in the same hemisphere, suggesting that the magnetic process is driven
by an oscillating nonaxisymmetrical dynamo. The emissions of the chromospheric ac-
tivity indicators show the rotational modulation, and exhibit an obvious anti-correlation
with the simultaneous light curves. In addition, the emissions in He I D3 line indicate
the existence of extremely strong energy release on its surface, which may be attributed
to flare events. 2. Based on high-resolution spectral data obtained from 3 observato-
ries in 2005, 2006, 2008, and 2014, we have reconstructed the surface spot patterns
of the young K2V single star LQ Hya using Doppler imaging technique. The results
confirm the bimodal spot distribution along latitude. The chromospheric activity indi-
cators show obvious rotational modulation, which is anti-correlated with the simultane-
ous light curves. The magnetic activity indicators around phase 0.9 in 2014 show the
stronger emission, which can be attributed to the flare event. In addition, the same trend has been found in the H𝛼 emission intensity and the spot activity level between 2003 and
2014. This may indicate the existence of a chromospheric activity cycle, similar to the
spot cycle. 3. The high-resolution transit spectra from ESO archive are used to obtain
the excess absorption of resonance Na I D lines due to the atmosphere of HD 189733b,
and to study the impact of magnetic activity on the detection of such excess absorption.
The time-series of integral intensities of H𝛼 line show that a super-flare erupted during
the transit event, which started near the middle of the transit window and reached the
maximum near the egress, lasting for more than 2.5 hours. We have used two methods
(transit light curve and transmission spectrum) to detect the possible excess absorption
signal in Na I D lines. The excess absorption with a similar amount to previous studies
has been detected in the ingress of the transit light curve and in the line center of the
transmission spectrum. The second half of the light curve is obviously affected by the
flare event, showing an upward trend. |
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