J/MNRAS/495/2949 Stellar activity with LAMOST. III. (Fang+, 2020)
Stellar activity with LAMOST. III.
Temporal variability pattern in Pleiades, Praesepe, and Hyades.
Fang X.-S., Moni Bidin C., Zhao G., Zhang L.-Y., Bharat Kumar Y.
<Mon. Not. R. Astron. Soc., 495, 2949-2965 (2020)>
=2020MNRAS.495.2949F 2020MNRAS.495.2949F (SIMBAD/NED BibCode)
ADC_Keywords: Stars, late-type ; Clusters, open ; Equivalent widths ;
Positional data ; Effective temperatures ; Spectra, optical
Keywords: stars: activity - stars: chromospheres - stars: late-type - starspots
Abstract:
We present the results from a systematic study of temporal variation
of stellar activity in young late-type stars. We used multi-epoch
LAMOST (Large sky Area Multi-Object fiber Spectroscopic Telescope)
low-resolution spectra of over 300 member candidates in three young
open clusters: Pleiades, Praesepe, and Hyades. The spectral
measurements of TiO band strength near 7050Å (TiO2) and equivalent
width of Hα line (EWHα) are used as the tracers of cool
spot coverage and chromospheric emission strength, respectively. The
analysis of time-variation patterns of these two tracers suggested
that there exist detectable variabilities in TiO2 and EWHα,
and their time-scales are in the wide range from days to years.
Results showed that more active stars, younger and fast rotators, tend
to have larger activity variations. There is a tendency of
anticorrelation between temporal variations in TiO2 and EWHα.
Also, appreciable anticorrelation in the rotational phase between
Hα emission and K2 brightness is detected in some M dwarfs,
indicating spatial co-location of the plages with cool star-spots;
however, cool stars do not always show such co-location features.
Furthermore, spot coverage and Hα emission were evident at all
rotational phases of several M dwarfs, indicating a basal level of
activity, perhaps due to many small and randomly located active
regions in the atmosphere.
Description:
The LAMOST (also called the Guo Shoujing Telescope), characterized by
both wide field of view of 20deg2 in the sky and large effective
aperture of ∼4m, is a reflecting Schmidt telescope located at the
Xinglong Observatory, China. By summer 2019, LAMOST obtained over 9
million stellar spectra with spectral resolving power of
R=λ/Δλ∼1800 (e.g. ∼3.6Å around 6500Å),
covering the wavelength range of 3700-9100Å (see Zhao et al.
2006ChJAA...6..265Z 2006ChJAA...6..265Z, 2012RAA....12..723Z 2012RAA....12..723Z; Luo et al.
2015RAA....15.1095L 2015RAA....15.1095L, Cat. V/146, for more details).
Our sample stars are from three nearby young open clusters having age
range from 100 to 700Myr. The clusters are Pleiades, Praesepe, and
Hyades. Following previous series (Fang et al. 2016MNRAS.463.2494F 2016MNRAS.463.2494F
(Paper I) and Fang et al. 2018MNRAS.476..908F 2018MNRAS.476..908F, Cat. J/MNRAS/476/908
(Papers II)), based on the member catalogues (for Pleiades, Stauffer
et al. 2007ApJS..172..663S 2007ApJS..172..663S, Cat. J/ApJS/172/663; Bouy et al.
2015A&A...577A.148B 2015A&A...577A.148B, Cat. J/A+A/577/A148; and for Praesepe and Hyades,
Douglas, Agueros & Covey 2014ApJ...795..161D 2014ApJ...795..161D, Cat. J/ApJ/795/161), we
retrieved the available multi-epoch (at least three epochs) LAMOST
low-resolution spectra collected until summer 2019 having SNR in r
band (SNRr) above 15.
We used available Gaia Data Release (DR2) parallaxes and proper
motions (Gaia Collaboration, 2018A&A...616A...1G 2018A&A...616A...1G, Cat. I/345) to
remove the contamination from field stars in our sample.
Our final sample consists of 312 late-type stars (113 Pleiades
members, 160 Praesepe members, and 39 Hyades members), and each star
has spectra of at least three epochs having SNRr>15.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 114 1184 Measurements from the multi-epoch LAMOST spectra
of representative sample
table3.dat 116 312 Basic information of sample stars and their
statistics of measurements
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
V/164 : LAMOST DR5 catalogs (Luo+, 2019)
J/ApJS/172/663 : Infrared observations of the Pleiades (Stauffer+, 2007)
J/A+A/577/A148 : The Seven Sisters DANCe. I. Pleiades (Bouy+, 2015)
J/ApJ/795/161 : Activity and rotation in Praesepe and the Hyades
(Douglas+, 2014)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- ID [1/312] Internal identifier
5- 13 I9 --- ObsID LAMOST spectrum identifier
15- 24 F10.5 d BJD Barycentric Julian Date BJD-2450000.0
26- 32 F7.4 0.1nm EWHa Equivalent width of the Hα line
34- 39 F6.4 0.1nm e_EWHa Error on EWHa
41- 50 F10.4 0.1nm EWHb ?=-9999 Equivalent width of the Hβ line
52- 61 F10.4 0.1nm e_EWHb ?=-9999 Error on EWHb
63- 72 F10.4 --- TiO2n ?=-9999 Strength of TiO2n (1)
74- 83 F10.4 --- e_TiO2n ?=-9999 Error on TiO2n
85- 94 F10.4 --- TiO5n ?=-9999 Strength of TiO5n (1)
96- 105 F10.4 --- e_TiO5n ?=-9999 Error on TiO5n
107- 114 A8 --- Cluster Cluster name
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Note (1): We used spectral index to estimate the strength of TiO molecular band
near 7050Å, namely the ratio of mean flux within TiO absorption
band to that in nearby continuum (Fabs/Fcont).
For TiO2n the absorption band considered is 7057-7064Å and for
TiO5n it is 7126-7135Å. The continuum band is 7042-7048Å for
both TiO2n and TiO5n.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- ID [1/312] Internal identifier
5- 23 I19 --- GaiaDR2 ? Gaia DR2 source identifier
25- 34 F10.6 deg RAdeg Right ascension (J2000)
36- 45 F10.6 deg DEdeg Declination (J2000)
47- 53 F7.2 K Teff Effective temperature
55- 64 F10.6 d Period ?=-99 Rotation period
66- 72 F7.4 0.1nm muEWHa Mean value of the Hα equivalent width
74- 79 F6.4 0.1nm AEWHa Amplitude of the Hα equivalent width
(maximum-minimum value)
81- 90 F10.4 --- muTiO2n ?=-9999 Mean value of the TiO2n strength
92- 101 F10.4 --- ATiO2n ?=-9999 Amplitude of the TiO2n strength
(maximum-minimum value)
103- 107 F5.2 --- Cxy ? Cross-correlation between TiO2n and
EWHα
109- 116 A8 --- Cluster Cluster name
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History:
From electronic version of the journal
References:
Fang et al., Paper I 2016MNRAS.463.2494F 2016MNRAS.463.2494F
Fang et al., Paper II 2018MNRAS.476..908F 2018MNRAS.476..908F, Cat. J/MNRAS/476/908
(End) Ana Fiallos [CDS] 19-Jun-2023