J/A+A/695/A114 LMC and SMC Cepheid candidates periods (Rathour+, 2025)
Non-evolutionary effects on period change in Magellanic Cepheids.
II. Empirical constraints on non-linear period changes.
Rathour R.S., Smolec R., Hajdu G., Ziolkowska O., Hocde V., Soszynski I.,
Udalski A., Karczmarek P.
<Astron. Astrophys. 695, A114 (2025)>
=2025A&A...695A.114R 2025A&A...695A.114R (SIMBAD/NED BibCode)
ADC_Keywords: Magellanic Clouds ; Stars, variable ; Optical
Keywords: stars: general - stars: oscillations - stars: variables: Cepheids
Abstract:
Classical Cepheids are not only excellent standard candles, but also
invaluable tools to test stellar evolution and pulsation theories.
Rates of their pulsation period change, quantified usually through O-C
diagrams, can be confronted with predictions of stellar evolution
theory. On the other hand, period changes on much shorter time scales
(∼102-104 days), attributed to non-evolutionary effects are often
detected and lack detailed explanation.
We aim to provide a systematic and quantitative description of
irregular or non-linear period changes in Cepheids. Such a study is
crucial for a complete understanding of period changes in Cepheids and
is key to decoupling the evolutionary aspects from the
non-evolutionary ones.
We analysed part of the OGLE data for classical Cepheids in the
Magellanic Clouds (MCs; from both Large Magellanic Cloud, LMC, and the
Small Magellanic Cloud, SMC) using the modified Hertzsprung O-C
technique. A sample of 3658 stars, with the best quality data and void
of additional low-amplitude periodicities (e.g. due to non-radial
pulsations), that could impact the results, was selected for analysis.
Based on O-C shapes, stars were classified into three categories: no
period change (class 1), linear period change (class 2), and irregular
change (class 3). The Eddington-Plakidis test, wavelet analysis,
Stetson index, and instantaneous period method were used to
characterise class 3 candidates. We also investigated the correlation
between the irregular period change in Cepheids and their metallicity
environment
In our investigation, 33.5±0.7% of analysed stars show irregular
period changes. Considering the pulsation mode, irregular period
changes were detected in 16.5±0.7% of the analysed fundamental mode
stars and in 68.1±1.2% of the first overtone stars. The amplitude of
variability in the O-C diagrams increases with the pulsation period,
and at a given pulsation period, it is larger for first overtone
stars. While the increase is linear for first overtone stars, for
fundamental mode stars it becomes steeper as the pulsation period
increases. Time scales of the observed variability range from a few
hundred to a few thousand days.
Irregular period changes are a ubiquitous property of classical
Cepheids and may impact the derivation of secular, evolutionary period
change rates; hence their quantitative characterisation is essential.
The nature of these changes is still unknown. Our research provides
observational constraints on their modelling. The markedly higher
frequency of irregular period variations in first overtone Cepheids is
a key observation that must be accounted for by the models.
Description:
We have analysed OGLE data for classical Cepheids in the Magellanic
Clouds with the goal of investigating pulsation period changes.
Analysed sample counts 4729 Cepheids, of which 1943 are in the LMC
(1313 F-mode and 630 1O mode) and 2786 in the SMC (1852 F-mode,
934 1O mode).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 32 2656 List of class 1 Cepheid candidates
table3.dat 49 484 List of class 2 Cepheid candidates
table4.dat 89 1316 List of class 3 Cepheid candidates
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See also:
J/AcA/65/297 : OGLE4 LMC and SMC Cepheids (Soszynski+, 2015)
J/A+A/686/A268 : New binary systems in Magellanic Clouds (Rathour+, 2024)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 A2 --- Mode [F 1O] Pulsation mode
4- 20 A17 --- Name OGLE name
(OGLE-LMC-CEP-NNNN or OGLE-SMC-CEP-NNNN)
23- 32 F10.7 d Ppul Pulsation period
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 A2 --- Mode [F 1O] Pulsation mode
4- 20 A17 --- Name OGLE name
(OGLE-LMC-CEP-NNNN or OGLE-SMC-CEP-NNNN)
22- 32 F11.8 d Ppul Pulsation period
35- 42 F8.3 d/Myr dP/dt Period change rate
44- 49 F6.3 d/Myr e_dP/dt Period change rate error
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 A2 --- Mode [F 1O] Pulsation mode
4- 20 A17 --- Name OGLE name
(OGLE-LMC-CEP-NNNN or OGLE-SMC-CEP-NNNN)
22- 31 F10.7 d Ppul Pulsation period
34- 40 F7.5 --- epsilon ?=- Period fluctuation parameter epsilon
from E-P test
42- 45 I4 d PerDom Dominant variability period from Wavelet method
47- 55 F9.4 --- AmpDom ?=- Dominant amplitude from Wavelet method
57- 64 F8.5 --- Lindex Stetson L index
66- 74 F9.7 --- sigma Standard deviation for instantaneous period
values calculated at O-C points,
from instantaneous period method
82- 89 F8.6 --- DeltaP Difference between the maximum and minimum
instantaneous period, DeltaP,
from instantaneous period method
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History:
copied at https://zenodo.org/records/14637988
References:
Rathour et al., Paper I 2024A&A...686A.268R 2024A&A...686A.268R, Cat. J/A+A/686/A268
(End) Patricia Vannier [CDS] 23-May-2025