J/A+A/698/A287 VELOCE modulation zoo. III. (Barbey+, 2025)
The VELOCE Modulation zoo. III. Detecting additional pulsation modes in optical
spectra of classical Cepheids using semi-partial distance correlation
periodograms.
Barbey K., Anderson R.I., Viviani G., Netzel H., Binnenfeld A., Zucker S.,
Shahaf S., Dumusque X.
<Astron. Astrophys. 698, A287 (2025)>
=2025A&A...698A.287B 2025A&A...698A.287B (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable ; Spectra, optical
Keywords: methods: statistical - techniques: spectroscopic -
stars: oscillations - stars: variables: Cepheids
Abstract:
Known for their large amplitude radial pulsations, classical Cepheids
are critical standard candles in astrophysics. However, they also
exhibit various pulsational irregularities and additional signals that
provide deeper insights into their structure and evolution. These
signals appear in spectroscopic observations as shape deformations of
the spectral lines. Using semi-partial distance correlation
periodograms, we analysed high-precision spectroscopic data from the
VELOCE project for four stars: δ Cephei (δ Cep), BG Crucis
(BG Cru), X Sagittarii (X Sgr), and Polaris. For δ Cephei, our
control star, only the main radial mode was detected, confirming its
stability and suitability as a benchmark for the method. In BG Crucis,
a strong additional signal at approximately 3.01 days was identified,
likely linked to line splitting. X Sagittarii exhibited dominant
additional signals, notably one at approximately 12.31 days, also
associated with significant line splitting. Polaris revealed multiple
low-frequency signals, with the most prominent candidate at
approximately 59.86 days, which might be linked to the rotation period
of the star. We explored the semi-partial distance correlation
periodograms by incorporating cross-correlation functions (CCFs) and
their variants, such as the median-subtracted CCFs, which improved
sensitivity to line shape variations. In particular, the latter
enabled the faithful detection of primary and additional signals
present in the 1D spectra of fainter stars and low-amplitude
pulsators. The semi-partial distance correlation periodograms
demonstrated their utility for isolating signals associated with line
shape variations although the analyses were complicated by the
presence of artefact subharmonics and a visible low-frequency power
increase for Polaris and BG Crucis. This study underscores the
potential of the method for finding new and unexpected signals as well
as detailed analyses of Cepheid pulsations and opens new pathways for
asteroseismic investigations.
Description:
Our analysis uses the SPARTA (Binnenfeld et al., 2022A&A...659A.189B 2022A&A...659A.189B)
package to construct shape and shift periodograms from s1d spectra. We
have adapted the method to support CCF and their derived
functions (gaussian fit, median-subtracted CCF and gaussian
fit-subtracted CCF). Our periodogram results are split into 8 files
for 4 stars (delCep, BGCru, Polaris, and XSgr), 2 per star. One file
per star contains the CCF and CCF-derived periodograms (GLS, Shape,
and Shift) and the other file contains the periodograms built using
spectra (GLS, Shape, and Shift too).
Objects:
----------------------------------------------
RA (2000) DE Designation(s)
----------------------------------------------
12 31 40.33 -59 25 26.1 BG Cru = 35 Cru
02 31 49.09 +89 15 50.7 Polaris = alf UMi
17 47 33.62 -27 49 50.8 X Sgr = 3 Sgr
22 29 10.26 +58 24 54.6 delta Cep = 27 Cep
----------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 78 4 Summary of the data set used
bgcruccf.dat 302 17777 BG Cru CCF and CCF-derived periodograms datasets
bgcrusp.dat 96 17777 BG Cru spectra periodograms
dcepccf.dat 302 16373 delta Cep CCF and CCF-derived periodograms datasets
dcepsp.dat 96 13989 delta Cep spectra periodograms
polarccf.dat 302 10645 Polaris CCF and CCF-derived periodograms datasets
polarsp.dat 96 9952 Polaris spectra periodograms
xsgrccf.dat 302 14837 X Sgr CCF and CCF-derived periodograms datasets
xsgrsp.dat 96 14837 X Sgr spectra periodograms
BGCru/* . 523 Individual fits spectra for BG Cru
delCep/* . 293 Individual fits spectra for delta Cep
Polaris/* . 263 Individual fits spectra for Polaris
XSgr/* . 185 Individual fits spectra for X Sgr
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See also:
J/A+A/686/A177 : VELOCE I. Cepheids high-precision RVs (Anderson+, 2024)
J/A+A/687/A118 : VELOCE modulation zoo. I. (Netzel+, 2024)
J/A+A/694/A273 : VELOCE modulation zoo. II. (Netzel+, 2025)
zenodo.org/records/10793507 : VELOCE DR1
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 A9 --- Star Star name
12- 13 I2 h RAh Right ascension (J2000)
15- 16 I2 min RAm Right ascension (J2000)
18- 22 F5.2 s RAs Right ascension (J2000)
24 A1 --- DE- Declination sign (J2000)
25- 26 I2 deg DEd Declination (J2000)
28- 29 I2 arcmin DEm Declination (J2000)
31- 34 F4.1 arcsec DEs Declination (J2000)
36- 38 F3.1 mag Gmag ?=- Intensity-averaged Gaia DR3 G-band magnitude
40- 47 F8.6 d Prot VELOCE period
49- 54 A6 --- Inst Instrument
56- 66 A11 --- Baseline BJD range (BJD-2400000)
68- 70 I3 --- Nobs Number of observations
72- 78 A7 --- Sp Name of the repertory with individual
fits spectra
--------------------------------------------------------------------------------
Byte-by-byte Description of file: *ccf.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 18 F18.16 --- Freq Frequency in 1 over day
20- 41 E22.17 --- Cgls C dataset GLS power
43- 65 E23.17 --- Cshape C dataset Shape power
67- 89 E23.17 --- Cshift C dataset Shift power
91-112 E22.17 --- ggls g dataset GLS power
114-136 E23.17 --- gshape g dataset Shape power
138-160 E23.17 --- gshift g dataset Shift power
162-183 E22.17 --- Ctildegls Ctilde dataset GLS power
185-207 E23.17 --- Ctildeshape Ctilde dataset Shape power
209-231 E23.17 --- Ctildeshift Ctilde dataset Shift power
233-254 E22.17 --- Cggls Cg dataset GLS power
256-278 E23.17 --- Cgshape Cg dataset Shape power
280-302 E23.17 --- Cgshift Cg dataset Shift power
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Byte-by-byte Description of file: *sp.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 21 F21.19 --- Freq Frequency in 1 over day
23- 44 E22.20 --- gls GLS power
46 I1 --- pdc [0] PDC power (null)
48 I1 --- usurper [0] Usurper power (null)
50- 72 E23.20 --- shape Shape power
74- 96 E23.20 --- shift Shift power
--------------------------------------------------------------------------------
Acknowledgements:
Kent Barbey, kentbarbey2598(at)gmail.com
References:
Netzel et al., Paper I 2024A&A...687A.118N 2024A&A...687A.118N, Cat. J/A+A/687/A118
Netzel et al., Paper II 2025A&A...694A.273N 2025A&A...694A.273N, Cat. J/A+A/694/A273
(End) Patricia Vannier [CDS] 22-Apr-2025