Analysis of stellar variability in the B-Supergiant HD14134. Insights from spectroscopy and photometry

Analysis of stellar variability in the B-Supergiant HD14134. Analysis of stellar variability in the B-Supergiant HD14134. Insights from spectroscopy and photometry Insights from spectroscopy and photometry Suryani Guha1,2, Michaela Kraus1, Julieta P. Sánchez Arias1, Péter Németh3 1 Astronomical Institute, Czech Academy of Science, Fričova 298, 251 65 Ondřejov, Czech Republic 2 Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic 3 Astroserver.org, Fő tér 1, 8533 Malomsok, Hungary Motivation Motivation B-type supergiants are well known for their pronounced spectroscopic and photometric variability, often linked to stellar pulsations and associated changes in their atmospheric and wind properties. We investigate the B3Ia supergiant HD 14134, which shows significant variability in both its light curve and spectral lines (most notably H ). To explore the origin of this variability, we combine TESS photometry with optical spectroscopy obtained over a five-month period. In addition to Fourier α analysis, we employ the Weighted Wavelet Z-transform (WWZ) to capture time-dependent changes in frequency and amplitude, providing deeper insight into the nature of the detected variability. Our study establishes HD 14134 as a valuable case for investigating the interplay between pulsation activity and wind variability in B-supergiants. TESS photometry Figure 1: Target Pixel files of sector 18 (left) and sector 58 (right). Shown are the positions of HD 14134 (red star) and the background stars from Gaia DR2 (cyan dots). Hatched boxes mark the target masking (black) and the background masking (white). Figure 2: Final extracted and normalized TESS light curves of HD14134 (left) and the amplitude spectrum of their first Fourier transform (right). Spectroscopy: 51 high-resolution spectra (R = 40000, 3900-8600 Å) were collected with the Poznan Spectroscopic Telescope at the Winer Observatory in Arizona for HD 14134 between October 2017 and March 2018. Given the observed variability in the profiles and radial velocities, we selected representative spectral lines and computed their moments : Figure 3: Scalograms of the TESS light curves for Sector 18 (left) and Sector 58 (right). Orange arrows mark the time-averaged frequencies in the current sector, red arrows those (for comparison) of the other sector. The orange dashed line indicates the threshold values. Figure 5: Scalograms of the radial velocity variation of Si III (upper left), He I (bottom left) lines and normalized integrated flux (upper right). The horizontal green dashed line indicates the threshold for the lowest confident frequency identification. Figure 4: First (radial velocity, top panels) and third moments (skewness of the lineprofile, bottom panels) of the He I 6678 (left) and the Si III 4568 (right) lines. v = radial velocity of the line, I(v) = line intensity ∫vn∗I(v)dv ∫I(v)dv <vn> = 8040 8060 8080 8100 8120 8140 8160 8180 -300 -200 -100 0 100 200 HJD - 2450000 (d) Heliocentric Radial Velocity (km s-1) 0.85 0.9 0.95 1 1.05 1.1 1.15 Normalized Flux Figure 6: Variability of Hɑ profile The prominent frequency F1 in sector 18 is not the most prominent one in sector 58 →The frequencies change their amplitudes. F4 in sector 58 is not detected in sector 18 and F3 in sector 18 is not detected in sector 58. →Frequencies are not persistent. This project was co-funded by the European Union (Project 101183150 - OCEANS) and the Czech Science Foundation (GACR grant number 25-17532S).  WWZ allows us to trace changes in amplitude and frequency over time.  The scalograms reveal 4 and 3 frequencies in sector 18 and 58, respectively, and show their variable amplitudes and frequencies. The frequencies at 0.1298 d ¹ in Sector 18 and 0.1060 d ¹ in Sector 58 are detected only ⁻ ⁻ from the WWZ analysis. The nonstationary behavior of the signals, especially the temporal variations in frequency and amplitude, suggests a departure from stable, coherent pulsation and instead indicates a more complex and dynamic pulsational regime. Figure 7 : Since the Si III line is the least affected by the stellar wind, its radial velocity variations more reliably trace pulsations. The frequencies from the integrated flux contain both pulsations and wind variability. Figure 7 illustrates that the frequencies detected in photometry likely arise from a combination of intrinsic pulsations and wind-induced variability. The moment analysis suggests pulsations as plausible cause for the radial velocity variations. The scalograms show complex, lump-like quasi-periodic features, suggesting modulation of the underlying pulsations by the highly variable wind (as seen in Figure 6). Wind Variability Night-to-night variabilty in H -ɑ profiles indicating strong and variable stellar winds (Fig 6). Given that the TESS bandpass (600– 1000 nm) includes wind-sensitive lines like H and He I, α and similar frequencies appear in our spectra, wind modulation likely influences the photometric signals. Graphical comparison of the frequencies obtained from the scalograms of the radial velocity variation of the photosperic Si III and He I lines, the normalized integrated flux of the spectra, and the TESS photometry (averaged over the two sectors). The grey box indicates the threshold. Frequency analysis of the TESS light curves reveals a dominant and recurrent periodic signal of approximately five days but it does not persists over time. Frequencies (0.0927d-1, 0.3129d-1, 0.1443d-1) detected from the TESS photometry are quasi-periodic and transient in nature (Fig 3). The scalograms reveal a ~20 day period persistent over at least 80 days which might be a strange mode. Otherwise, complex, lumplike quasi-periodic features are seen, suggesting modulation of the underlying pulsations by the highly variable wind (seen Figure 6). As shown in Figure 4, the first and third moments vary in phase and display a coherent trend over the entire observation period, providing strong evidence that the observed variability is primarily driven by pulsational activity. Figure 7 illustrates that the frequencies detected in photometry likely arise from a combination of intrinsic pulsations and windinduced variability. Our analysis highlights the importance of simultaneous photometric and spectroscopic monitoring for studying variability in B-type supergiants. Conclusions : TESS light curves have been extracted for HD 14134. Apertures were chosen such that contamination from nearby sources is minimized. 0 5 10 sector 18 F1F2 F3 0.0 0.2 0.4 0.6 0.8 1.0 0 5 10 sector 58 F1F4 Amplitude (mmag) Frequency (d 1)