Stellar activity with LAMOST. III. Temporal variability pattern in Pleiades, Praesepe, and Hyades

Fang, X.-S.; Bidin, C. Moni; Zhao, Gang; Zhang, Li-yun; Kumar, Yerra Bharat

doi:10.1093/mnras/staa1392

“…It is known that large solar plages are spatially associated with sunspots (Mandal et al 2017). Some previous studies also showed that there was an anticorrelation in the rotational phase between the chromospheric activity proxies (e.g., Ca II H and K, H α ) and light curves: the line emission was stronger when the amplitude of the light curve was near minimum (Dorren & Guinan 1982;Berdyugina et al 1999;Fang et al 2010Fang et al , 2020. This indicates that the plages are located in the outer chromosphere overlying the starspots in the visible photosphere.…”

Section: ¢ a R H And Light Curvesmentioning

confidence: 95%

Stellar Chromospheric Activities Revealed from the LAMOST-K2 Time-domain Survey

Han

¹

,

Wang²,

Yu³

et al. 2022

ApJS

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By using the LAMOST time-domain survey data, we study stellar activities based on the H α lines for about 2000 stars in four K2 plates. Two indices, R H α ′ and R H α + , are computed from LAMOST spectra, the former of which is derived by excluding the photospheric contributions to the H α lines, while the latter is derived by further subtracting the non-dynamo-driven chromospheric emission. Meanwhile, the periodicity and variation amplitudes are computed from K2 light curves. Both the R H α ′ –Ro relation and R H α + –Ro relation show complicated profiles in the nonsaturated decay region. Hot stars show flatter slopes and a higher activity level than cool stars, and the behavior is more notable in the R H α + –R o relation. This is consistent with recent studies using other activity proxies, including L x/L bol, R HK ′ , and amplitudes of optical light curves. This may suggest different kinds of stars follow different power laws in the decay region. Most of our targets have multiple observations, and some of them exhibit significant variability of Hα emissions, which may cause the large scatters shown in the decay region. We find three targets exhibiting positive correlation in a rotational phase, possibly indicating that their optical light curves are dominated by hot faculae rather than cool starspots.

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“…It is known that large solar plages are spatially associated with sunspots (Mandal et al 2017). Some previous studies also showed that there was an anti-correlation in the rotational phase between the chromospheric activity proxies (e.g., Ca II H&K, H α ) and light curves: the line emission was stronger when the amplitude of light curve was near minimum (Dorren & Guinan 1982;Berdyugina et al 1999;Fang et al 2010Fang et al , 2020. This indicates that the plages are located in the outer chromosphere overlying the starspots in the visible photosphere.…”

Section: R Hα and Light Curvesmentioning

confidence: 95%

Stellar chromospheric activities revealed from the LAMOST-K2 time-domain survey

Han¹,

Wang²,

Yang³

et al. 2022

Preprint

0

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By using the LAMOST time-domain survey data, we study stellar activities based on the H α lines for about 2000 stars in four K2 plates. Two indices, R Hα and R + Hα , are computed from LAMOST spectra, the former of which is derived by excluding the photospheric contributions to the H α lines, while the latter is derived by further subtracting the non-dynamo driven chromospheric emission. Meanwhile, the periodicity and variation amplitudes are computed from K2 light curves. Both the R Hα -Ro relation and R + Hα -Ro relation show complicated profiles in the non-saturated decay region. Hot stars show flatter slopes and higher activity level than cool stars, and the behaviour is more notable in the R + Hα -R o relation. This is consistent with recent studies using other activity proxies, including L x /L bol , R HK and amplitudes of optical light curves. This may suggest different kinds of stars follow different power laws in the decay region. Most of our targets have multiple observations, and some of them exhibit significant variability of Hα emissions, which may cause the large scatters shown in the decay region. We find three targets exhibiting positive correlation in rotational phase, possibly indicating that their optical light curves are dominated by hot faculae rather than cool starspots.

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“…To determine the chromospheric activity, we used the relationship between the EW of Hα and T eff to evaluate the activity of stars. In the project of determining the activity standard, we used several groups of data, which include the activity judgment line formulated by Fang et al (2016Fang et al ( , 2020 based on LAMOST low-resolution spectra, the catalog of standard stars published by Du et al (2019) based on the LAMOST survey, and the standard stars obtained from the website 8 to jointly formulate a curve to evaluate the star activity of LAMOST medium-resolution spectrum. Zhao et al (2015) have developed a curve to judge stellar activity by using the relationship between S HK and T eff .…”

Section: Chromospheric Activity and Variationmentioning

confidence: 99%

“…Our standard line also referred to his method in the final determination. Finally, we got a standard line similar to Fang et al (2016Fang et al ( , 2020, and this line is also suitable for LAMOST medium-resolution observations, so we continue to use their results. We plotted the results in Figure 3, where the red line is the activity judgment line formulated by the standard stars, the stars above this line are active, and the stars below this line are inactive.…”

Section: Chromospheric Activity and Variationmentioning

confidence: 99%

Magnetic Activity and Physical Parameters of Exoplanet Host Stars Based on LAMOST DR7, TESS, Kepler, and K2 Surveys

Su¹,

Zhang²,

Schwarz³

et al. 2022

ApJS

Self Cite

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Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) low- and medium-resolution spectroscopic surveys are important for determination of the orbital parameters and chromospheric activity of extrasolar planet systems. We crossmatched the exoplanet catalog confirmed before 2021 March 11 with the LAMOST DR7 survey to study their properties. There are 1026 targets with exoplanets observed in the LAMOST DR7 low-resolution spectroscopic survey and 158 targets in the medium-resolution spectroscopic survey. We have calculated the equivalent width of the Hα line and determined their stellar activity. The Hα and flare intensities are almost constant for the Rossby number Ro ≤ 0.12 in the saturated regime and decrease with increasing Ro in the unsaturated regime. In addition, we searched the flare events of all stars with exoplanets in the Transiting Exoplanet Survey Satellite (TESS), Kepler, and K2 surveys. Among the 733 extrasolar planetary systems observed by TESS, we found 481 flares from 57 stars. For Kepler data, we obtained the light curve of 1699 stars and found 1886 flares from 417 stars. For K2 data, we obtained the light curves of 347 stars and found 467 flares from 89 stars. There were light curves of 361 objects with obvious eclipse observed from the TESS survey. We have fitted their light curves with a high signal-to-noise ratio using the JKTEBOP program, and we reobtained the orbital parameters, such as inclination, radius, and period. In the end, we made a judgment on the habitability of exoplanets of stars with flares.

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Stellar activity with LAMOST. III. Temporal variability pattern in Pleiades, Praesepe, and Hyades

Cited by 9 publications

References 85 publications

Stellar Chromospheric Activities Revealed from the LAMOST-K2 Time-domain Survey

Stellar Chromospheric Activities Revealed from the LAMOST-K2 Time-domain Survey

Stellar chromospheric activities revealed from the LAMOST-K2 time-domain survey

Magnetic Activity and Physical Parameters of Exoplanet Host Stars Based on LAMOST DR7, TESS, Kepler, and K2 Surveys

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