J/A+A/701/A103 XX Tri photometry (Kovari+, 2025)
Four decades of photometry of XX Trianguli, 'the most spotted star' in the sky.
Kovari Zs., Strassmeier K.G., Olah K., Seli B., Henry G.W., Vida K.
<Astron. Astrophys. 701, A103 (2025)>
=2025A&A...701A.103K 2025A&A...701A.103K (SIMBAD/NED BibCode)
ADC_Keywords: Stars, late-type ; Photometry, UBVRI
Keywords: stars: activity - stars: late-type - stars: individual: XX Tri -
starspots
Abstract:
Over the past 40 years the brightness variations of XX Tri, a single
line RS Canum Venaticorum (RS CVn)-type binary system with a
synchronized K-giant primary, has exceeded one magnit ude in the V
band. Although these changes are primarily caused by starspots, an
additional activity-related mechanism may also be behind the long-term
trend of overall brightness increase.
By compiling the most complete photometric data set so far, we attempt
to examin e how the nature of seasonal-to-decadal changes can be
linked to global magnetis m.
To find the long-term activity cycles and their properties a
time-frequency anal yser code is used. We divided the entire data set
into four consecutive interval s, for which we separately determined
the Fourier spectra around the orbital per iod. This is performed with
a Fourier-transformation based frequency analyser to ol.
The long-term brightening of XX Tri was accompanied by a gradual
increase in the effective temperature, which resulted in a blueing
shift in the Herzsprung-Russ ell diagram. In the long term, a constant
cycle of about 4 years is most strongl y present in the entire data.
Besides, we also found a modulation of about 11 ye ars, and a slowly
decreasing cycle of about 5.7-5.2 years.
From the seasonal datasets we found that the most dominant
rotation-related periods are scattered around the orbital period. From
this we infer a solar-type surface differential rotation, although the
surface shear is significantly smaller than that of the Sun.
The 4-year cycle indicates flip-flop-like behavior: during this time,
the 2-3 active longitudes usually present on the stellar surface are
rearranged. The magnitude-range changes in the long term cannot be
interpreted solely as changes in the number and size of spots; the
unspotted brightness of XX Tri has also increased over the decades.
This should alert users of photometric spot models to reconsider the
basic concept of constant unspotted brightness in similar cases.
Description:
We present long-term optical photometry of XX Tri that have not been
published in print or in machine-readable format. See Section 2. of
the paper for the details. Differential magnitudes are measured with
HD 12478 (V=7.78, B-V=1.45, V-Ic=1.38) as the comparison star in all
cases.
Objects:
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RA (2000) DE Designation(s)
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02 03 47.11 +35 35 28.6 XX Tri = HD 12545
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
skiff.dat 19 327 V photometry from Skiff & Nations, (1991)
private communication in Strassmeier et al.
(1997A&AS..125...11S 1997A&AS..125...11S)
noltheni.dat 38 93 BVRIc photometry from Nolthenius
(1991IBVS.3589....1N 1991IBVS.3589....1N)
konkoly.dat 42 29 UBV(RI)c photometry from Konkoly Observatory
hooten.dat 19 16 V photometry from Hooten & Hall
(1990ApJS...74..225H 1990ApJS...74..225H)
henry_v.dat 19 2244 APT V photometry from T3, Tennessee State Univ.
henry_b.dat 19 2266 APT B photometry from T3, Tennessee State Univ.
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Byte-by-byte Description of file: skiff.dat
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Bytes Format Units Label Explanations
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1- 12 F12.4 d HJD Heliocentric Julian Date
14- 19 F6.4 mag dVmag Differential V magnitude
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Byte-by-byte Description of file: noltheni.dat
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Bytes Format Units Label Explanations
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1- 13 F13.5 d HJD Heliocentric Julian Date
15- 20 F6.3 mag dBmag ? Differential B magnitude
22- 26 F5.3 mag dVmag Differential V magnitude
28- 32 F5.3 mag dRmag ? Differential R magnitude
34- 38 F5.3 mag dIcmag Differential Ic magnitude
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Byte-by-byte Description of file: konkoly.dat
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Bytes Format Units Label Explanations
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1- 11 F11.3 d HJD Heliocentric Julian Date
13- 18 F6.3 mag Umag U magnitude
20- 24 F5.3 mag Bmag B magnitude
26- 30 F5.3 mag Vmag V magnitude
32- 36 F5.3 mag Rcmag Rc magnitude
38- 42 F5.3 mag Icmag Ic magnitude
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Byte-by-byte Description of file: hooten.dat
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Bytes Format Units Label Explanations
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1- 12 F12.4 d HJD Heliocentric Julian Date
14- 19 F6.4 mag dVmag Differential V magnitude
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Byte-by-byte Description of file: henry_v.dat
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Bytes Format Units Label Explanations
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1- 12 F12.4 d HJD Heliocentric Julian Date
14- 19 F6.3 mag dVmag Differential V magnitude
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Byte-by-byte Description of file: henry_b.dat
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Bytes Format Units Label Explanations
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1- 12 F12.4 d HJD Heliocentric Julian Date
14- 19 F6.3 mag dBmag Differential B magnitude
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Acknowledgements:
Balint Seli, seli.balint(at)csfk.org
(End) Patricia Vannier [CDS] 03-Jul-2025