J/A+A/606/A58 Activity cycles in young solar-like stars (Distefano+, 2017)
Activity cycles in members of young loose stellar associations.
Distefano E., Lanzafame. A.C., Lanza A.F., Messina S., Spada F.
<Astron. Astrophys. 606, A58 (2017)>
=2017A&A...606A..58D 2017A&A...606A..58D (SIMBAD/NED BibCode)
ADC_Keywords: Associations, stellar ; Stars, G-type
Keywords: stars: solar-type - stars: starspots - stars: activity -
open clusters and associations: general - stars: rotation -
stars: magnetic fields
Abstract:
Magnetic cycles analogous to the solar cycle have been detected in
tens of solar-like stars by analyzing long-term time series of
different magnetic activity indexes. The relationship between the
cycle properties and global stellar parameters is not fully understood
yet. One reason for this is the lack of long-term time series for
stars covering a wide range of stellar parameters.
We searched for activity cycles in a sample of 90 young solar-like
stars with ages between 4 and 95 Myr with the aim to investigate the
properties of activity cycles in this age range.
We measured the length Pcyc of a given cycle by analyzing the
long-term time series of three different activity indexes: the period
of rotational modulation, the amplitude of the rotational modulation
and the median magnitude in the V band. For each star, we also
computed the global magnetic activity index that is proportional
to the amplitude of the rotational modulation and can be regarded as a
proxy of the mean level of the surface magnetic activity.
We detected activity cycles in 67 stars. Secondary cycles were also
detected in 32 stars of the sample. The lack of correlation between
Pcyc and Prot and the position of our targets in the
Pcyc/Prot-Ro-1 diagram suggest that these stars belong to the
so-called transitional branch and that the dynamo acting in these
stars is different from the solar dynamo and from that acting in the
older Mt. Wilson stars. This statement is also supported by the
analysis of the butterfly diagrams whose patterns are very different
from those seen in the solar case.
We computed the Spearman correlation coefficient rS between Pcyc,
and various stellar parameters. We found that Pcyc in our
sample is uncorrelated with all the investigated parameters. The
index is positively correlated with the convective turnover timescale,
the magnetic diffusivity timescale τdiff, and the dynamo number
DN, whereas it is anti-correlated with the effective temperature
Teff, the photometric shear ΔΩphot and the radius RC
at which the convective zone is located.
We investigated how Pcyc and evolve with the stellar age. We
found that Pcyc is about constant and that decreases with the
stellar age in the range 4-95Myr. Finally we investigated the
magnetic activity of the star AB Dor A by merging All Sky Automatic
Survey (ASAS) time series with previous long-term photometric data. We
estimated the length of the AB Dor A primary cycle as
Pcyc=16.78±2yr and we also found shorter secondary cycles with
lengths of 400d, 190d, and 90d, respectively.
Description:
In the file table2.dat, the main physical parameters are reported for
90 stars belonging to young loose stellar rotation.
The parameters and the procedure used to compute them are described in
detail in the Sec 2.2 of the paper.
In the file table3.dat, we reported the periods of the cycles detected
in 67 stars by analyzing the activity index time-series. For each
star, the three activity index time-series are supplied.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 86 90 List of the targets investigated in the present
work
table3.dat 42 135 List of the cycles detected in the present work
vmed/* . 90 Individual Vmed time-series
iqr/* . 90 Individual IQR time-series
prot/* . 90 Individual Prot time-series
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See also:
J/A+A/588/A38 : Light curves of spotted solar-type stars (Lehtinen+, 2016)
J/A+A/591/A43 : Differential rotation in solar-like stars (Distefano+, 2016)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 14 A14 --- ASAS ASAS ID (JHHMMSS+DDMM.m)
16- 22 A7 --- Assoc Association
24- 28 F5.2 d Prot Rotation period
30- 34 F5.3 rad/d DOp Photometric shear, ΔΩphot (1)
36- 39 F4.2 Msun M ?=- Mass
41- 47 F7.2 K Teff ?=- Effective temperature
49- 52 F4.2 Rsun RC ?=- Radius at the base of Convection Zone
54- 56 I3 d tauC ?=- Convective turnover timescale
58- 61 I4 d taudiff ?=- Magnetic diffusivity timescale
63- 68 I6 --- DN ?=- Dynamo number
70- 74 F5.3 --- Ro ?=- Rossby Number
76- 80 F5.3 --- RoBr ?=- Empirical Rossby Number
82- 86 F5.3 --- Average Interquartile range
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Note (1): Photometric shear as defined in Sec. 2.2 of the paper.
ΔΩphot=Ωmax-Ωmin=2π/Pmin-2π/Pmax,
where Pmin and Pmax are the minimum and maximum values of the Prot index and
are interpreted as the rotation periods of two Active Regions occurring at
two different latitudes. This parameter can be regarded as a lower limit for
the surface differential rotation.
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Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 14 A14 --- ASAS ASAS ID (JHHMMSS+DDMM.m)
16 A1 --- l_Pcyc Limit flag on Pcyc
17- 20 I4 d Pcyc Cycle Period
22- 24 I3 d e_Pcyc ?=- Error on Cycle Period
26 A1 --- l_FAP Limit flag on FAP
27- 30 F4.2 --- FAP ?=- False Alarm Probability
32- 34 A3 --- Method Detection algorithm (1)
36- 38 A3 --- ActInd Activity Index (2)
40- 42 A3 --- Mult Sequential number of detected cycle (3)
--------------------------------------------------------------------------------
Note (1): This flag indicates the period search algorithm used to measure
the cycle period as follows:
LS = Lomb-Scargle
PDM = Phase Dispersion Minimization
V = Visual inspection
Note (2): This flag indicates the activity index used to infer the cycle period
as follows:
A = Amplitude Variability
M = Median magnitude
P = rotation period
Note (3): The cycles detected in a given star were ranked from the longest
to the shortest.
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Byte-by-byte Description of file (#): vmed/*
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 14 F14.6 d JD Julian Date corresponding to the center
of the 100 d segments on which the ASAS
time series has been splitted
16- 24 F9.6 mag Vmed Median magnitude in the 100-d segment
--------------------------------------------------------------------------------
Byte-by-byte Description of file (#): iqr/*
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 14 F14.6 d JD Julian Day corresponding to the center
of the 100-d segments on which the ASAS
time series has been splitted
17- 24 F8.6 mag IQR Average Interquartile range in the 100-d segment
--------------------------------------------------------------------------------
Byte-by-byte Description of file (#): prot/*
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 14 F14.6 d JD Julian Day corresponding to the center
of the 100-d segments on which the ASAS
time series has been splitted
16- 24 F9.6 d Prot Rotation period detected in the 100-d segment
--------------------------------------------------------------------------------
Acknowledgements:
Elisa Distefano, eds(at)oact.inaf.it
(End) Patricia Vannier [CDS] 06-Jul-2017