J/A+A/703/A155 Additional periodicities in TESS 1O Cepheids (Plachy+, 2025)
Exploring low-amplitude variability in first-overtone Cepheids with TESS.
Plachy E., Netzel H., Bodi A.
<Astron. Astrophys. 703, A155 (2025)>
=2025A&A...703A.155P 2025A&A...703A.155P (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Stars, variable ; Photometry ; Optical
Keywords: techniques: photometric - stars: oscillations -
stars: variables: Cepheids
Abstract:
Classical Cepheid stars that pulsate in the first overtone radial mode
often exhibit additional periodicities at the millimagnitude level.
Extensive studies of the OGLE data of the Magellanic Clouds have
revealed distinct groups based on the ratio of the star's additional
period to the period of the first overtone mode. These groups are
similar to those found in overtone RR Lyrae stars. Theoretical
calculations suggest that some of the observed periodicities are
consistent with non-radial modes, while others remain unexplained.
Currently, we only know of a handful of examples from the Galactic
Cepheid sample that exhibit low-amplitude periodicities. The purpose
of this study is to undertake a systematic search for low-amplitude
variability in overtone Cepheids of the Milky Way in the photometric
data of the full-frame images of the Transiting Exoplanet Survey
Satellite (TESS), which were produced with the MIT Quick Look
Pipeline. We applied standard Fourier analysis and classified the
additional signals according to the ratio of their period to the
overtone pulsation period. We find 127 stars in total that exhibit
additional periodicities. In 17 of these stars, the periodicities can
be identified as a second radial overtone. A further 83 of the stars
were observed to display periodic signals with a Px/P1O ratio in the
range 0.60-0.65. In 15 stars, the P1O/Px is found to be ∼0.68; six of
these stars are also found to be in the previous group. Furthermore,
we observed the presence of low-amplitude signals in 22 stars outside
the aforementioned period ratio ranges. It is possible that some are
direct detections of non-radial modes, with no harmonic frequency peak
in the 0.60-0.65 period range. Most of the properties of the
additional signals detected in this study are consistent with previous
findings regarding Cepheids in the Magellanic Clouds. However, TESS
measurements reveal that the amplitudes and frequencies of these
signals often vary within a TESS sector, a phenomenon that challenges
theoretical models. We also find that reliable analysis of these
signals with TESS is possible for a moderate fraction of overtone
Cepheids. The primary constraints are the limited extent of the data
and the relatively poor photometric quality in some Galactic fields.
Further careful corrections to the light curves may improve
detectability.
Description:
We selected the targets for our analysis from the March 2025 version
of the Pietrukowicz et al. (2021AcA....71..205P 2021AcA....71..205P, see Cat.
J/AcA/69/305) catalog
(https://www.astrouw.edu.pl/ogle/ogle4/OCVS/allGalCep.listID), the
most complete and regularly updated list of verified classical
Cepheids in the Milky Way, collected from various sky surveys and the
literature.
Tables include the list and properties of stars that we found to
exhibit low-amplitude periodicities of different types.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 104 127 Name list of stars with additional periodicities
table3.dat 116 47 New 1O2O stars found in the analyzed sample
table4.dat 109 37 Stars with additional frequencies near the
P1O/P068∼0.68 ratio
table5.dat 152 230 Stars with additional frequencies near the
P0.61/P1O∼0.60-0.65 ratio
table6.dat 141 46 Stars with other additional frequencies
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See also:
IV/39 : TESS Input Catalog version 8.2 (TIC v8.2) (Paegert+, 2021)
J/MNRAS/478/1425 : Single-mode OGLE Cepheids additional modes (Suveges+, 2018)
J/AcA/69/305 : Northern Galactic disk classical Cepheids (Skowron+, 2019)
J/AcA/70/101 : OGLE IV Galactic Cepheids (Soszynski+, 2020)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 9 I9 --- TIC TESS identification of the star
11- 29 I19 --- GaiaDR3 Gaia identification of the star
31- 58 A28 --- Other Other identification of the star
60- 69 F10.6 deg RAdeg Right Ascension (J2000)
71- 80 F10.6 deg DEdeg Declination (J2000)
82- 88 F7.4 mag Tmag Brightness in TESS passband
90-104 A15 --- Group Group of the additional mode (1)
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Note (1): Group as:
1O2O = second radial overtone
0.61 = additional frequencies at P0.61/P1O∼0.60-0.65
0.68 = stars where a clear additional signal at P1O/P0.68∼0.68 is visible
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Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 I9 --- TIC TESS Identification of the star
11- 21 A11 --- Sectors Sectors in which the star was observed
23- 29 F7.5 c/d f1O Frequency of the first overtone
31- 37 F7.5 c/d e_f1O Frequency of the first overtone error
39- 44 F6.4 --- A1O Fourier amplitude of the first overtone,
in relative flux ubits
46- 51 F6.4 --- e_A1O Fourier amplitude of the first overtone error,
in relative flux ubits
53- 59 F7.5 c/d f2O Frequency of the second overtone
61- 67 F7.5 c/d e_f2O Frequency of the second overtone error
69- 75 F7.5 --- A2O Fourier amplitude of the second overtone,
in relative flux ubits
77- 83 F7.5 --- e_A2O Fourier amplitude of the second overtone error,
in relative flux ubits
85- 92 F8.6 --- f1O/f2O Frequency ratio
94-101 F8.6 --- e_f1O/f2O Frequency ratio error
103-108 F6.4 --- A2O/A1O Amplitude ratio
111-116 F6.4 --- e_A2O/A1O Amplitude ratio error
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 I9 --- TIC TESS Identification of the star
11- 21 A11 --- Sectors Sectors in which the star was observed
23- 30 F8.6 c/d f1O Frequency of the first overtone
32- 39 F8.6 c/d e_f1O Frequency of the first overtone error
41- 47 F7.5 --- A1O Fourier amplitude of the first overtone,
in relative flux units
49- 55 F7.5 --- e_A1O Fourier amplitude of the first overtone error,
in relative flux units
57- 63 F7.5 c/d f0.68 Frequency at P1O/P0.68∼0.68
65- 71 F7.5 c/d e_f0.68 Frequency at P1O/P0.68∼0.68 error
73- 78 F6.4 --- f0.68/f1O Frequency ratio
80- 85 F6.4 --- e_f0.68/f1O Frequency ratio error
87- 92 F6.4 --- A0.68/A1O Amplitude ratio
94- 99 F6.4 --- e_A0.68/A1O Amplitude ratio error
101-109 A9 --- Remarks Remarks (G1)
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 I9 --- TIC TESS Identification of the star
11- 21 A11 --- Sectors Sectors in which the star was observed
23- 30 F8.6 c/d f1O ? Frequency of the first overtone
34- 41 F8.6 c/d e_f1O ? Frequency of the first overtone error
44- 50 F7.5 ---- A1O ? Fourier amplitude of the first overtone,
in relative flux units
52- 58 F7.5 ---- e_A1O ? Fourier amplitude of the first overtone
error, in relative flux units
61- 67 F7.5 c/d f0.61 ?=- Frequency in P0.61/P1O∼0.60-0.65 range
71- 77 F7.5 c/d e_f0.61 ? Frequency in P0.61/P1O∼0.60-0.65 range
error
80- 86 F7.5 c/d fsh ?=- Subharmonic frequency at 0.5f0.61
88- 94 F7.5 c/d e_fsh ? Subharmonic frequency at 0.5f0.61 error
97-103 F7.5 --- f0.61/f1O ?=- Frequency ratio
105-111 F7.5 --- e_f0.61/f1O ? Frequency ratio error
114-119 F6.4 --- A0.61/A1O ?=- Amplitude ratio with the first overtone
121-126 F6.4 --- e_A0.61/A1O ? Amplitude ratio with the first overtone
129-133 F5.3 --- Ash/A0.61 ?=- Amplitude ratio with the subharmonic
135-139 F5.3 --- e_Ash/A0.61 ? Amplitude ratio with the subharmonic
142-152 A11 --- Remarks Remarks (G1)
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 I9 --- TIC TESS Identification of the star
11- 21 A11 --- Sectors Sectors in which the star was observed
23- 29 F7.5 c/d f1O ? Frequency of the first overtone
31- 37 F7.5 c/d e_f1O ? Frequency of the first overtone error
40- 46 F7.5 --- A1O ? Fourier amplitude of the first overtone,
in relative flux units
48- 54 F7.5 --- e_A1O ? Fourier amplitude of the first overtone
error, in relative flux units
57- 63 F7.5 c/d fx Additional frequency
65- 71 F7.5 c/d e_fx Additional frequency
74- 80 F7.5 --- Ax Fourier amplitude of the additional signal,
in relative flux units
82- 88 F7.5 --- e_Ax Fourier amplitude of the additional signal
error, in relative flux units
91- 96 F6.4 --- fx/f1O Frequency ratio
99-104 F6.4 --- e_fx/f1O Frequency ratio error
108-113 F6.4 --- Ax/A1O Amplitude ratio
116-121 F6.4 --- e_Ax/A1O Amplitude ratio error
124-141 A18 --- Remarks Remarks (G1)
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Glibal notes:
Note (G1): Remarks as follows:
c = combination frequency
af = additional frequency
f_0.61 = signal in the P0.61/P1O∼0.60-0.65 range
f_0.68 = signal in the P1O/P0.68∼0.68
sh = subharmonic frequency without f0.61
sh? = possible subharmonic frequency
hif = half-integer frequency at 1.5f0.61
p = power excess near 0.5f0.61
shc = combination frequency at fsh+f1O
mod? = possible amplitude modulation
b = blend
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Acknowledgements:
Emese Plachy, eplachy(at)konkoly.hu
(End) Patricia Vannier [CDS] 20-Oct-2025