J/A+A/480/495 Patterns of color variations in close binaries (Messina, 2008)
Long-term magnetic activity in close binary systems.
I. Patterns of color variations.
Messina S.
<Astron. Astrophys. 480, 495 (2008)>
=2008A&A...480..495M 2008A&A...480..495M
ADC_Keywords: Stars, variable ; Stars, double and multiple ; Photometry, UBV
Keywords: stars: activity - stars: close binaries - stars: late-type -
stars: magnetic fields - stars: starspot -
techniques: photometric
Abstract:
This is the first of a series of papers in which we present the
results of a long-term photometric monitoring project carried out at
Catania Astrophysical Observatory aimed at studying magnetic activity
in late-type components of close binary systems, its dependence on
global stellar parameters, and its evolution on different time scales
from days to years. In this first paper, we present the complete
observation dataset and new results of an investigation into the
origin of brightness and color variations observed in the well-known
magnetically active close binary stars: AR Psc, VY Ari, UX Ari,
V711 Tau, EI Eri, V1149 Ori, DH Leo, HU Vir, RS CVn, V775 Her, AR Lac,
SZ Psc, II Peg and BY Dra .
About 38000 high-precision photoelectric nightly observations in the
U, B and V filters are analysed. Correlation and regression analyses
of the V magnitude vs. U-B and B-V color variations are carried
out and a comparison with model variations for a grid of active region
temperature and filling factor values is also performed.
We find the existence of two different patterns of color variation.
Eight stars in our sample: BY Dr, VY Ari, V775 Her, II Peg, V1149 Ori,
HU Vir, EI Eri and DH Leo become redder when they become fainter, as
is expected from the presence of active regions consisting of cool
spots. The other six stars show the opposite behaviour, i.e. they
become bluer when they become fainter. For V711 Tau this behaviour
could be explained by the increased relative U- and B- flux
contribution by the earlier-type component of the binary system when
the cooler component becomes fainter. On the other hand, for AR Psc,
UX Ari, RS CVn, SZ Psc and AR Lac the existence of hot photospheric
faculae must be invoked. We also found that in single-lined and
double-lined binary stars in which the fainter component is inactive
or much less active the V magnitude is correlated to B-V and U-B color
variations in more than 60% of observation seasons. The correlation
is found in less than 40% of observation seasons when the fainter
component has a non-negligible level of activity and/or hot faculae
are present but they are either spatially or temporally uncorrelated
to spots.
Description:
We present a summary of the UBV photometric observations collected at
OAC (Catania Astrophysical Observatory) for a sample of 14 close
binary systems. We present the results of our correlation and
regression analyses of V magnitude-color variations and color-color
variations on the short timescale (rotation) and long timescale
(activity cycle).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 110 14 Program stars
table4.dat 96 477 Summary of photometric observations
table5.dat 106 478 Summary of correlation and regression analyses
table6.dat 87 14 Short timescale (rotation): average slopes of linear
fits to B-V vs. V, U-B vs.V, and U-B vs. B-V
table7.dat 56 98 Long timescale: average slopes of linear fits
to B-V vs. V, U-B vs.V, and U-B vs. B-V
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Seq Sequential number
4- 12 A9 --- Target Target's name
14- 15 I2 h RAh Simbad right ascension (J2000)
17- 18 I2 min RAm Simbad right ascension (J2000)
20- 23 F4.1 s RAs Simbad right ascension (J2000)
25 A1 --- DE- Simbad declination sign (J2000)
26- 27 I2 deg DEd Simbad declination (J2000)
29- 30 I2 arcmin DEm Simbad declination (J2000)
32- 33 I2 arcsec DEs Simbad declination (J2000)
35- 40 I6 --- HD HD number
42- 56 A15 --- SpType MK spectral type
58- 68 F11.8 d Per Period
70- 74 F5.3 mag Vmag Brightest V magnitude
76- 80 F5.3 mag Vamp V-band light curve amplitude
82- 86 F5.3 mag <B-V> Mean B-V colour index
88- 92 F5.3 mag <U-B> Mean U-B colour index
94- 97 F4.1 --- Lc/LhV ? Total flux ratio in the V band of the cool
to the hot component
98 A1 --- n_Lc/LhV [a] a if total flux of the hot to the cool
component
100-103 F4.1 --- Lc/LhB ? Total flux ratio in the B band of the cool
to the hot component
104 A1 --- n_Lc/LhB [a] a if total flux of the hot to the cool
component
106-109 F4.1 --- Lc/LhU ? Total flux ratio in the U band of the cool
to the hot component
110 A1 --- n_Lc/LhU [a] a if total flux of the hot to the cool
component
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 A9 --- Target Target's name
11- 17 F7.2 yr Epoch Mean Epoch of light curve
19- 28 F10.2 d HJDmean Mean Heliocentric Julian Day
30- 39 F10.2 d HJDini Initial Heliocentric Julian Day
41- 50 F10.2 d HJDend Final Heliocentric Julian Day
52- 54 I3 --- o_Vmag ? Number of average data points
56- 60 F5.3 mag Vmag Brightest V-band light curve magnitude
62- 66 F5.3 mag Vamp V-band light curve amplitude
68- 72 F5.3 mag B-V Mean B-V colour index
74- 78 F5.3 mag U-B ?=- Mean U-B colour index
80- 84 F5.3 mag e_Vmag V-band light curve standard deviation
86- 90 F5.3 mag eVmag(ck1-c) ?=- V-band standard deviation of check
minus comparison star
92- 96 A5 --- Tel Telescope used (1)
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Note (1): Telescopes as follows:
A = Phoenix-25
B = APt80/1xi
C = ESO 50cm
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Target Target's name
11- 22 F12.4 d HJDmean Mean Heliocentric Julian Date
24- 26 I3 --- o_bBV Number of data points for regression analysis
between B-V and V
28- 33 F6.3 --- bBV ?=- Slope of linear regression between
B-V and V
35- 40 F6.3 --- rBV ?=- Correlation coefficient between B-V and V
42 A1 --- l_alphaBV Limit flag on alphaBV
43- 46 F4.2 --- alphaBV ?=- Significance level of rBV
47 A1 --- --- [-]
48- 50 F3.1 --- alphaBVl ?=- Lower level od significance level of
rBV if interval
52- 54 I3 --- o_bUB ?=- Number of data points for regression
analysis between U-B and V
56- 61 F6.3 --- bUB ?=- Slope of linear regression between
U-B and V
63- 68 F6.3 --- rUB ?=- Correlation coefficient between U-B and V
70 A1 --- l_alphaUB Limit flag on alphaUB
71- 74 F4.2 --- alphaUB ?=- Significance level of rUB
75 A1 --- --- [-]
76- 78 F3.1 --- alphaUBl ?=- Lower value of significance level of
rUB if interval
80- 82 I3 --- o_bUBV ?=- Number of data points for regression
analysis between U-B and B-V
84- 89 F6.3 --- bUBV ?=- Slope of linear regression between
U-B and B-V
91- 96 F6.3 --- rUBV ?=- Correlation coefficient between
U-B and B-V
98 A1 --- l_alphaUBV Limit flag on alphaUBV
99-102 F4.2 --- alphaUBV ?=- Significance level of rUBV
103 A1 --- --- [-]
104-106 F3.1 --- alphaUBVl ?=- Lower value of significance level of
rUBV if interval
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Target Target's name
11- 12 I2 --- o_slopeBV Number of light curves used in regression
analysis B-V vs. V
14- 18 F5.2 --- slopeBV Average slope of the regression to B-V vs. V
20- 23 F4.2 --- e_slopeBV Uncertainty of the average slope (B-V vs. V)
25- 29 F5.2 --- slopeBVmin Minimum value of average slope (B-V vs. V)
31- 35 F5.2 --- slopeBVmax Maximum value of average slope (B-V vs. V)
37- 38 I2 --- o_slopeUB Number of light curves used in regression
analysis U-B vs. V
40- 44 F5.2 --- slopeUB Average slope of the regression to U-B vs. V
46- 49 F4.2 --- e_slopeUB Uncertainty of the average slope (U-B vs. V)
51- 55 F5.2 --- slopeUBmin Minimum value of average slope (U-B vs. V)
57- 61 F5.2 --- slopeUBmax Maximum value of average slope (U-B vs. V)
63- 64 I2 --- o_slopeUBV Number of light curves used in regression
analysis U-B vs. B-V
66- 70 F5.2 --- slopeUBV Average slope of the regression to U-B vs. B-V
72- 75 F4.2 --- e_slopeUBV ?=- Uncertainty of the average slope
(U-B vs. B-V)
77- 81 F5.2 --- slopeUBVmin ?=- Minimum value of average slope
(U-B vs. B-V)
83- 87 F5.2 --- slopeUBVmax ?=- Maximum value of average slope
(U-B vs. B-V)
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Byte-by-byte Description of file: table7.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Target Target's name
11- 22 A12 --- Param Parameters analysed for regression and
correlation analyses
26- 29 I4 --- o_slope Number of fitted data
31- 35 F5.2 --- slope Slope of linear regression
37- 40 F4.2 --- e_slope Slope uncertainty
42- 46 F5.2 --- r Correlation coefficient
48 A1 --- l_alpha limit flag on alpha
49- 52 F4.2 --- alpha Significance level
53 A1 --- --- [-]
54- 56 F3.1 --- alphal ? Lower value of significance level if interval
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Acknowledgements:
Sergio Messina, sergio.messina(at)oact.inaf.it
(End) Patricia Vannier [CDS] 14-Mar-2008