The VELOCE modulation zoo III. Detecting additional pulsation modes in optical spectra of classical Cepheids using semi-partial distance correlation periodograms

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 analyse high-precision spectroscopic data from the VELOCE project for four stars: $\delta$ Cep, BG Cru, X Sgr, and Polaris. For $\delta$ Cep, our control star, only the main radial mode is detected, confirming its stability and suitability as a benchmark for the method. In BG Cru, a strong additional signal at $\sim 3.01$ d is identified, likely linked to line splitting. X Sgr exhibits dominant additional signals, notably one at $\sim 12.31$ d, also associated with significant line splitting. Polaris reveals multiple low-frequency signals, with the most prominent candidate at $\sim 59.86$ d, which might be linked to the star's rotation period. We explore the semi-partial distance correlation periodograms by incorporating CCFs and their variants, such as the median-subtracted CCFs, which improves the sensitivity to variations in line shape. In particular, the latter enables 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 demonstrate their utility for isolating signals associated with line shape variations; although, the analyses are complicated by the presence of artefact subharmonics and a visible low-frequency power increase for Polaris and BG Cru. This study underscores the method's potential for finding new and unexpected signals as well as detailed analyses of Cepheid pulsations and opens new pathways for asteroseismic investigations.

16 pages, 7 figures, 6 tables

References in corpus (48)

• The Gaia mission
• Gaia Data Release 3: Summary of the content and survey properties
• Understanding the Lomb-Scargle Periodogram
• A box-fitting algorithm in the search for periodic transits
• No planet for HD 166435
• The CORALIE survey for southern extra-solar planets VII. Two short-period Saturnian companions to HD108147 and HD168746
• HERMES: a high-resolution fibre-fed spectrograph for the Mercator telescope
• Revealing δ Cephei's Secret Companion and Intriguing Past
• On the Effect of Rotation on Populations of Classical Cepheids II. Pulsation Analysis for Metallicities 0.014, 0.006, and 0.002
• Correcting for Telluric Absorption: Methods, Case Studies, and Release of the TelFit Code
• Gaia Data Release 3. Summary of the variability processing and analysis
• Rate of Period Change as a Diagnostic of Cepheid Properties
• Gaia DR3: Specific processing and validation of all-sky RR Lyrae and Cepheid stars -- The Cepheid sample
• Frequency analysis of Cepheids in the Large Magellanic Cloud. New types of classical Cepheid pulsators
• Tuning in on Cepheids: Radial velocity amplitude modulations. A source of systematic uncertainty for Baade-Wesselink distances
• Observations of Cepheids with the MOST satellite: Contrast between Pulsation Modes
• Investigating Cepheid $\ell$ Carinae's Cycle-to-cycle Variations via Contemporaneous Velocimetry and Interferometry
• Discovery of Cycle-to-cycle Modulated Spectral Line Variability and Velocity Gradients in Long-period Cepheids
• TESS observations of Cepheid stars: first light results
• The Kepler Cepheid V1154 Cyg revisited: light curve modulation and detection of granulation
• Observational calibration of the projection factor of Cepheids - III. The long-period Galactic Cepheid RS Puppis
• Polaris the Cepheid returns: 4.5 years of monitoring from ground and space
• Double-mode radial-non-radial RR Lyrae stars in the OGLE photometry of the Galactic bulge
• Non-linear modelling of beat Cepheids: Resonant and non-resonant models
• Discovery of a new group of double-periodic RR Lyrae stars in the OGLE-IV photometry
• Study of changes in the pulsation period of 148 Galactic Cepheid variables
• The census of non-radial pulsation in first-overtone RR Lyrae stars of the OGLE Galactic bulge collection
• Line profile variations in classical Cepheids. Evidence for non-radial pulsations?
• Precise Radial Velocities of Polaris: Detection of Amplitude Growth
• VELOcities of CEpheids (VELOCE) I. High-precision radial velocities of Cepheids
• Investigating light curve modulation via kernel smoothing. II. New additional modes in single-mode OGLE classical Cepheids
• Homing in on Polaris: A 7 M${}_{\odot }$ first-overtone Cepheid entering the instability strip for the first time
• Probing Polaris' Puzzling Radial Velocity Signals - Pulsational (In-)Stability, Orbital Motion, and Bisector Variations
• Frequency analysis of OGLE-IV photometry for classical Cepheids in Galactic fields: non-radial modes and modulations
• Investigating Light Curve Modulation via Kernel Smoothing. I. Application to 53 fundamental mode and first-overtone Cepheids in the LMC
• USuRPER: Unit-Sphere Representation PERiodogram for full spectra
• Frequency analysis of the first-overtone RR Lyrae stars based on the Extended Aperture Photometry from the K2 data
• Time series analysis of bright TESS RRc stars: Additional modes, phase variations and more
• New Periodograms Separating Orbital Radial Velocities and Spectral Shape Variation
• VELOcities of CEpheids (VELOCE) II. Systematic Search for Spectroscopic Binary Cepheids
• First Overtone Cepheids of the OGLE Magellanic Cloud Collection -- beyond radial modes
• Finding magnetic north: an extraordinary magnetic field detection in Polaris and first results of a magnetic survey of classical Cepheids
• The CoRoT discovery of a unique triple-mode cepheid in the galaxy
• Analysis of the possible Blazhko-effect Cepheid V473 Lyrae
• Non-radial modes in classical Cepheids. What to look for in spectroscopy?
• The VELOCE Modulation Zoo I. Spectroscopic detection of non-radial modes in the first-overtone Cepheids BG Crucis, QZ Normae, V0391 Normae, and V0411 Lacertae
• Blazhko Effect in Double Mode Cepheids
• The VELOCE modulation zoo II. Humps and splitting patterns in spectral lines of classical Cepheids