X-ray stars observed in LAMOST spectral survey

Lu, Hongpeng; Zhang, Li-yun; Han, Xianming L.; Shi, Jianrong

doi:10.1007/s10509-018-3328-8

Cited by 3 publications

(2 citation statements)

References 123 publications

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“…We discuss this phenomenon in Section 4.2. As a comparison, we show the emission of stellar magnetic activity lines of a main-sequence star (LAMOST J053243.80−002715.2; Lu et al 2018) in Fig. 4.…”

Section: Stellar Magnetic Activity Analysismentioning

confidence: 99%

Magnetic activity and age estimation of red giants using neural networks

Karoff

Zhang

2021

Monthly Notices of the Royal Astronomical Society

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In this work, we analyzed the magnetic activity of 5349 LAMOST low-dispersion spectra of 3539 red giants by calculating equivalent width of magnetic activity lines (Hα, Hβ, Hγ, Hδ, $\rm {Ca~{\small II}\,\,H \& K}$ , $\rm {Ca~{\small II}\,\,IRT}$ ). Combining LAMOST spectral parameters, asteroseismic parameters, and equivalent widths of the magnetic activity lines, an attempt was made to estimate the age of red giants using neural networks. By using the neural networks to select the input parameters, we get the best age estimation of the red giants with the input parameters ‘Teff’, ‘[Fe/H]’, ‘log g’, ‘Vmax’ and ‘ΔV’, which is in line with expectations. The average value of the relative error between the estimated age and the isochronous age is 22.4%. The age estimation was not improved by adding the equivalent widths of more magnetic activity lines. This indicates that the equivalent widths of these spectral lines are not directly related to the age of the red giants. The reason for this might be that the dynamo operating in the outer layers of the red giants has shut off at the end of core-hydrogen-burning. The absence of emission in all the magnetic activity lines of the 5349 LAMOST spectra also confirms this conclusion. In addition, the results indicate that the equivalent widths of the magnetic activity lines are more related to the effective temperature, which is also in line with expectations.

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Section: Stellar Magnetic Activity Analysismentioning

confidence: 99%

Magnetic activity and age estimation of red giants using neural networks

Karoff

Zhang

2021

Monthly Notices of the Royal Astronomical Society

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“…In this study, we first noticed from the observed spectra of four low-mass M-type eclipsing binaries that the chromospheric activity indicators of H α , H β , H γ , H δ , and CaII H&K lines show emissions (see Figure 2). We used the same method as Lu et al (2018) to calculate the equivalent width of these chromospheric active lines. From Table 7, we can see that the equivalent widths of the H α lines of the four M-type eclipsing binaries are greater than 0.75 Å, and the equivalent widths of the H β , H γ , H δ , and CaII H&K lines are greater than 1.0 Å.…”

Section: Chromospheric Activitymentioning

confidence: 99%

Photometric and Spectroscopic Studies of Four New Low-mass M-type Eclipsing Binaries

Long

Zhang

Han

et al. 2018

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We performed multicolor photometric and spectroscopic observations of four new low-mass M-type eclipsing binaries (HAT 225-03429, CRTS J085623.0+282620, CRTS J110302.4+201611, 2MASS J16344899+3716423) in 2017. We obtained new VRI light curves and minimum times of these four systems. Based on our minimum times, we updated the orbital periods and the linear ephemerides using the least squares method. We analyzed these four systems using the Wilson-Devinney program, and obtained the orbital and starspot parameters. The results of our analysis of the light curves indicate that HAT 225-03429 and CRTS J085623.0+282620 are detached eclipsing binaries, CRTS J110302.4+201611 is a semi-detached eclipsing binary, and 2MASS J16344899+3716423 is a contact binary. We performed LAMOST spectroscopic studies of chromospheric activity indicators (H α , H β , H γ , H δ , and Ca II H&K lines) for these four systems for the first time. We first determined their spectral types and calculated the equivalent widths of their chromospheric active indicators. These indicators show that the four low-mass M-type eclipsing binaries are active. Furthermore, the radii of these stars are notably larger than model predictions for their masses, except for the secondary component of HAT 225-03429 and the primary component of CRTS J110302.4+201611.

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