Chromospheric Activity of Periodic Variable Stars Based on the LAMOST Low- and Medium-resolution Spectral Survey

2021 ◽  
Vol 253 (2) ◽  
pp. 51
Author(s):  
Liu Long ◽  
Li-yun Zhang ◽  
Shao-Lan Bi ◽  
Jianrong Shi ◽  
Hong-Peng Lu ◽  
...  
New Astronomy ◽  
2018 ◽  
Vol 61 ◽  
pp. 36-58 ◽  
Author(s):  
Liyun Zhang ◽  
Hongpeng Lu ◽  
Xianming L. Han ◽  
Linyan Jiang ◽  
Zhongmu Li ◽  
...  

2021 ◽  
Vol 21 (4) ◽  
pp. 096
Author(s):  
Chao-Jian Wu ◽  
Hong Wu ◽  
Wei Zhang ◽  
Juan-Juan Ren ◽  
Jian-Jun Chen ◽  
...  

2021 ◽  
Vol 21 (10) ◽  
pp. 265
Author(s):  
Jian-Ping Xiong ◽  
Bo Zhang ◽  
Chao Liu ◽  
Jiao Li ◽  
Yong-Heng Zhao ◽  
...  

Abstract The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) started a median-resolution spectroscopic (MRS, R ∼7500) survey since October 2018. The main scientific goals of MRS, including binary stars, pulsators and other variable stars, were launched with a time-domain spectroscopic survey. However, the systematic errors, including the bias induced from wavelength calibration and the systematic difference between different spectrographs, have to be carefully considered during radial velocity measurement. In this work, we provide a technique to correct the systematics in the wavelength calibration based on the relative radial velocity measurements from LAMOST MRS spectra. We show that, for the stars with multi-epoch spectra, the systematic bias which is induced from the exposures on different nights can be corrected well for LAMOST MRS in each spectrograph. In addition, the precision of radial velocity zero-point of multi-epoch time-domain observations reaches below 0.5 km s−1. As a by-product, we also give the constant star candidates**, which can be the secondary radial-velocity standard star candidates of LAMOST MRS time-domain surveys.


2020 ◽  
Vol 495 (1) ◽  
pp. 1252-1270 ◽  
Author(s):  
Li-yun Zhang ◽  
Liu Long ◽  
Jianrong Shi ◽  
Hong-peng Lu ◽  
Qi Gao ◽  
...  

ABSTRACT Stellar magnetic activity is an interesting phenomenon in late-type stars. We use the medium-resolution spectroscopic observations of 406 069 late-type stars from LAMOST to explore their properties. We perform a statistical analysis on the magnetic activity of the stars and their associated physical parameters. Our samples are cross-matched with other data bases (LAMOST DR5, VSX, and SDSS DR12) to obtain additional observational properties. The equivalent widths (EWs) of Hα lines, an indicator of chromospheric activity, are calculated. According to the EWs of the Hα line, we detect 8816 spectra with apparent Hα emission for a total of 2115 stars among the 2 108 565 spectra analysed. Furthermore, 1521 of these stars show variability in their Hα lines. In addition, we detect 2132 flare events associated with 41 542 stars from the catalogue by cross-matching our LAMOST medium-resolution samples and the Kepler and K2 data bases. We also confirm a weak relationship of the flare amplitude with increasing Rossby number. There is a clear decease in the strength of chromospheric activity (LHα/Lbol) with increasing rotation period. Moreover, the ratio of the flare energy and stellar luminosity is found to decrease with the stellar mass.


New Astronomy ◽  
2016 ◽  
Vol 44 ◽  
pp. 66-77 ◽  
Author(s):  
Liyun Zhang ◽  
Qingfeng Pi ◽  
Xianming L. Han ◽  
Jianrong Shi ◽  
Daimei Wang ◽  
...  

2021 ◽  
Vol 253 (1) ◽  
pp. 19
Author(s):  
Li-yun Zhang ◽  
Gang Meng ◽  
Liu Long ◽  
Jianrong Shi ◽  
Ming Zhong ◽  
...  

2013 ◽  
Vol 9 (S301) ◽  
pp. 439-440
Author(s):  
Anthony B. Kaye ◽  
Cristine Kristof ◽  
Richard O. Gray

AbstractThe definition of γ Dor stars as a new class of variable stars by Kaye et al. (1999) was based on a number of criteria, including the failure to detect any emission in the Ca II H & K lines in these stars (Kaye & Strassmeier 1998; KS98). Over the last 30 years, efforts continue to look for the blue edge of chromospheric activity. As a part of this effort, we put γ Dor stars to the test to see if magnetic fields play a non-trivial role in their variability.


2021 ◽  
Vol 21 (11) ◽  
pp. 280
Author(s):  
Wei Zhang ◽  
Hong Wu ◽  
Chao-Jian Wu ◽  
Juan-Juan Ren ◽  
Jian-Hun Chen ◽  
...  

Abstract We introduce a method of subtracting geocoronal Hα emissions from the spectra of LAMOST medium-resolution spectral survey of Galactic nebulae (LAMOST-MRS-N). The flux ratios of the Hα sky line to the adjacent OH λ6554 single line do not show a pattern or gradient distribution in a plate. More interestingly, the ratio is well correlated to solar altitude, which is the angle of the Sun relative to the Earthʼs horizon. It is found that the ratio decreases from 0.8 to 0.2 with the decreasing solar altitude from –17 to –73 degree. Based on this relation, which is described by a linear function, we can construct the Hα sky component and subtract it from the science spectrum. This method has been applied to the LAMOST-MRS-N data, and the contamination level of the Hα sky to nebula is reduced from 40% to less than 10%. The new generated spectra will significantly improve the accuracy of the classifications and the measurements of physical parameters of Galactic nebulae.


1967 ◽  
Vol 28 ◽  
pp. 207-244
Author(s):  
R. P. Kraft

(Ed. note:Encouraged by the success of the more informal approach in Christy's presentation, we tried an even more extreme experiment in this session, I-D. In essence, Kraft held the floor continuously all morning, and for the hour and a half afternoon session, serving as a combined Summary-Introductory speaker and a marathon-moderator of a running discussion on the line spectrum of cepheids. There was almost continuous interruption of his presentation; and most points raised from the floor were followed through in detail, no matter how digressive to the main presentation. This approach turned out to be much too extreme. It is wearing on the speaker, and the other members of the symposium feel more like an audience and less like participants in a dissective discussion. Because Kraft presented a compendious collection of empirical information, and, based on it, an exceedingly novel series of suggestions on the cepheid problem, these defects were probably aggravated by the first and alleviated by the second. I am much indebted to Kraft for working with me on a preliminary editing, to try to delete the side-excursions and to retain coherence about the main points. As usual, however, all responsibility for defects in final editing is wholly my own.)


1967 ◽  
Vol 28 ◽  
pp. 177-206
Author(s):  
J. B. Oke ◽  
C. A. Whitney

Pecker:The topic to be considered today is the continuous spectrum of certain stars, whose variability we attribute to a pulsation of some part of their structure. Obviously, this continuous spectrum provides a test of the pulsation theory to the extent that the continuum is completely and accurately observed and that we can analyse it to infer the structure of the star producing it. The continuum is one of the two possible spectral observations; the other is the line spectrum. It is obvious that from studies of the continuum alone, we obtain no direct information on the velocity fields in the star. We obtain information only on the thermodynamic structure of the photospheric layers of these stars–the photospheric layers being defined as those from which the observed continuum directly arises. So the problems arising in a study of the continuum are of two general kinds: completeness of observation, and adequacy of diagnostic interpretation. I will make a few comments on these, then turn the meeting over to Oke and Whitney.


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