Context. Heartbeat stars are eccentric binaries that exhibit a characteristic shape of brightness changes close to the periastron passage, primarily caused by a variable tidal distortion of the components. Variable tidal potential can drive tidally excited oscillations (TEOs), which are usually gravity modes. Studies of heartbeat stars and TEOs open up new possibilities for probing the interiors of massive stars. There are only a few massive (masses of components ≳2 M⊙) systems of this type that are known thus far. Aims. Using TESS data from the first 16 sectors, we searched for new massive heartbeat stars and TEOs using a sample of over 300 eccentric spectroscopic binaries. Methods. We analysed 2 min and 30 min cadence TESS data. Then we fitted Kumar’s analytical model to the light curves of stars showing heartbeats and performed a times-series analysis of the residuals searching for TEOs and periodic intrinsic variability. Results. We found 20 massive heartbeat systems, of which 7 exhibit TEOs. The TEOs occur at harmonics of orbital frequencies in the range between 3 and 36, with the median value equal to 9, which is lower than those in known Kepler systems with TEOs. The most massive system in this sample is the quadruple star HD 5980, a member of the Small Magellanic Cloud. With a total mass of ∼150 M⊙ it is the most massive system showing a heartbeat. Six stars in the sample of the new heartbeat stars are eclipsing. A comparison of the parameters derived from fitting Kumar’s model and from light-curve modelling shows that Kumar’s model does not provide reliable parameters. In other words, the orbital parameters can be reliably derived from fitting heartbeat light curves only if the model includes all proximity effects. Finally, intrinsic pulsations of β Cep, SPB, δ Sct, and γ Dor-type were found in nine heartbeat systems. This opens an interesting possibility for studies of pulsation-binarity interaction and the co-existence of forced and self-excited oscillations.
We report an analysis of the first known β Cep pulsator observed by the TESS mission, the runaway star PHL 346 = HN Aqr. The star, previously known as a singly-periodic pulsator, has at least 34 oscillation modes excited, 12 of those in the g-mode domain and 22 p modes. Analysis of archival data implies that the amplitude and frequency of the dominant mode and the stellar radial velocity were variable over time. A binary nature would be inconsistent with the inferred ejection velocity from the Galactic disc of 420 km s −1 , which is too large to be survivable by a runaway binary system. A kinematic analysis of the star results in an age constraint (23 ± 1 Myr) that can be imposed on asteroseismic modelling and that can be used to remove degeneracies in the modelling process. Our attempts to match the excitation of the observed frequency spectrum resulted in pulsation models that were too young. Hence, asteroseismic studies of runaway pulsators can become vital not only in tracing the evolutionary history of such objects, but to understand the interior structure of massive stars in general. TESS is now opening up these stars for detailed asteroseismic investigation.
Context. Precise continuum normalisation of merged échelle spectra is a demanding task that is necessary for various detailed spectroscopic analyses. Automatic methods have limited effectiveness due to the variety of features present in the spectra of stars. This complexity often leads to the necessity for manual normalisation which is highly time-consuming. Aims. The aim of this work is to develop a fully automated normalisation tool that works with order-merged spectra and offers flexible manual fine-tuning, if necessary. Methods. The core of the proposed method uses the novel, fully convolutional deep neural network (SUPP Network) that was trained to predict a pseudo-continuum. The post-processing step uses smoothing splines that give access to regressed knots, which are useful for optional manual corrections. The active learning technique was applied to deal with possible biases that may arise from training with synthetic spectra and to extend the applicability of the proposed method to features absent in this kind of spectra. Results. The developed normalisation method was tested with high-resolution spectra of stars with spectral types from O to G, and gives a root mean squared (RMS) error over the set of test stars equal to 0.0128 in the spectral range from 3900 Å to 7000 Å and 0.0081 in the range from 4200 Å to 7000 Å. Experiments with synthetic spectra give a RMS of the order of 0.0050. Conclusions. The proposed method leads to results that are comparable to careful manual normalisation. Additionally, this approach is general and can be used in other fields of astronomy where background modelling or trend removal is a part of data processing.
The magnetic chemically peculiar (Ap/CP2) star 21 Com has been extensively studied in the past, albeit with widely differing and sometimes contradictory results, in particular concerning the occurrence of short term variability between about 5 to 90 minutes. We have performed a new investigation of 21 Com using MOST satellite and high-cadence ground-based photometry, time series spectroscopy, and evolutionary and pulsational modeling. Our analysis confirms that 21 Com is a classical CP2 star showing increased abundances of, in particular, Cr and Sr. From spectroscopic analysis, we have derived T eff = 8 900 ± 200 K, log g = 3.9 ± 0.2, and υ sin i = 63 ± 2 km s −1 . Our modeling efforts suggest that 21 Com is a main sequence (MS) star seen equator-on with a mass of 2.29 ± 0.10 M ⊙ and a radius of R = 2.6 ± 0.2 R ⊙ . Our extensive photometric data confirm the existence of rotational light variability with a period of 2.05219(2) d. However, no significant frequencies with a semi-amplitude exceeding 0.2 mmag were found in the frequency range from 5 to 399 d −1 . Our RV data also do not indicate short-term variability. We calculated pulsational models assuming different metallicities and ages, which do not predict the occurrence of unstable modes. The star 18 Com, often employed as comparison star for 21 Com in the past, has been identified as a periodic variable (P = 1.41645 d). While it is impossible to assess whether 21 Com has exhibited short-term variability in the past, the new observational data and several issues/inconsistencies identified in previous studies strongly suggest that 21 Com is neither a δ Scuti nor a roAp pulsator but a "well-behaved" CP2 star exhibiting its trademark rotational variability.
Photometric and spectroscopic time-series of chemically peculiar mercury–manganese (HgMn) stars show variability, which in most cases is interpreted as the effect of binarity or surface spots. Until recently, pulsations have not been detected in these objects. However, the analysis of the Transiting Exoplanet Survey Satellite (TESS) photometric time-series of a large sample of HgMn stars resulted in a small sample of candidates for pulsating variables. In this paper, we present a thorough analysis of one of them, HD 29589. High-resolution spectroscopic data were used to determine the atmospheric parameters and a detailed chemical composition of the star. The obtained effective temperature, Teff = 14 400 ± 200 K, places this star among the high-temperature HgMn stars. The determined abundance pattern is typical for this class of objects. Interferometric data were used to discuss the properties of the secondary in the HD 29589 system. More than 20 independent frequencies were identified in the TESS time-series of this star, which we interpret as high-order g-modes. We found regular period spacing, which is due to the presence of consecutive prograde dipole modes. The exact matching of the six frequencies in the series and the position of the star in the Hertzsprung–Russell diagram allowed us to constrain the internal structure of HD 29589. We derived the overshooting parameter, fov = 0.028−0.03, mass M = 3.4 M⊙ and metallicity Z = 0.008. A detailed analysis of pulsating HgMn stars will allow us to understand the influence of the chemical peculiarity on the pulsation characteristics of these objects.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.