Making waves in massive star asteroseismology

Massive stars play a major role not only in stellar evolution but also galactic evolution theory. This is because of their dynamical interaction with binary companions, but also because their strong winds and explosive deaths as supernovae provide chemical, radiative and kinematic feedback to their environments. Yet this feedback strongly depends on the physics of the supernova progenitor star. It is only in recent decades that asteroseismology – the study of stellar pulsations – has developed the necessary tools to a high level of sophistication to become a prime method at the forefront of astronomical research for constraining the physical processes at work within stellar interiors. For example, precise and accurate asteroseismic constraints on interior rotation, magnetic field strength and geometry, mixing and angular momentum transport processes of massive stars are becoming increasingly available across a wide range of masses. Moreover, ongoing large-scale time-series photometric surveys with space telescopes have revealed a large diversity in the variability of massive stars, including widespread coherent pulsations across a large range in mass and age, and the discovery of ubiquitous stochastic low-frequency (SLF) variability in their light curves. In this invited review, I discuss the progress made in understanding the physical processes at work within massive star interiors thanks to modern asteroseismic techniques, and conclude with a future outlook

Discovery of β Cep pulsations in the eclipsing binary V453 Cygni

V453 Cyg is an eclipsing binary containing 14 and 11 $\, \rm M_ødot$ stars in an eccentric short-period orbit. We have discovered β Cep-type pulsations in this system using Transiting Exoplanet Survey Satellite data. We identify seven significant pulsation frequencies, between 2.37 and 10.51 d−1, in the primary star. These include six frequencies that are separated by yet significantly offset from harmonics of the orbital frequency, indicating they are tidally perturbed modes. We have determined the physical properties of the system to high precision: V453 Cyg A is the first β Cep pulsator with a precise mass measurement. The system is a vital tracer of the physical processes that govern the evolution of massive single and binary stars

The Structure and Evolution of Stars: Introductory Remarks

In this introductory chapter of the Special Issue entitled ‘The Structure and Evolution of Stars’, we highlight the recent major progress made in our understanding of the physics that governs stellar interiors. In so doing, we combine insight from observations, 1D evolutionary modelling and 2D + 3D rotating (magneto)hydrodynamical simulations. Therefore, a complete and compelling picture of the necessary ingredients in state-of-the-art stellar structure theory and areas in which improvementsstillneedtobemadearecontextualised. Additionally, the over-arching perspective linking all the themes of subsequent chapters is presented

High-mass pulsators in eclipsing binaries observed using TESS

Pulsations and binarity are both common features of massive stars. The study of pulsating massive stars in eclipsing binary systems holds great potential for constraining stellar structure and evolution theory. However, prior to the all-sky Transiting Exoplanet Survey Satellite (TESS) mission, few such systems had been discovered or studied in detail. We have inspected the TESS light curves of a large number of eclipsing binaries known to contain high-mass stars, and compiled a list of 18 objects which show intrinsic variability. The light curves were modelled both to determine the physical properties of the systems, and to remove the effects of binarity in order to leave residual light curves suitable for asteroseismic analysis. Precise mass and radius measurements were obtained for delta Cir, CC Cas, SZ Cam V436 Per and V539 Ara. We searched the residual light curves for pulsation signatures and, within our sample of 18 objects, we find six definite and eight possible cases of beta Cephei pulsation, seven cases of stochastic low-frequency (SLF) variability, and eight instances of possible slowly pulsating B (SPB) star pulsation. The large number of pulsating eclipsing systems we have identified makes asteroseismology of high-mass stars in eclipsing binaries a feasible avenue to constrain the interior physics of a large sample of massive stars for the first time

A β Cephei pulsator and a changing orbital inclination in the high-mass eclipsing binary system VV Orionis

We present an analysis of the high-mass eclipsing binary system VV Ori based on photometry from the TESS satellite. The primary star (B1 V, 9.5 M⊙⁠) shows β Cephei pulsations and the secondary (B7 V, 3.8 M⊙⁠) is possibly a slowly pulsating B star. We detect 51 significant oscillation frequencies, including two multiplets with separations equal to the orbital frequency, indicating that the pulsations are tidally perturbed. We analyse the TESS light curve and published radial velocities to determine the physical properties of the system. Both stars are only the second of their pulsation type with a precisely measured mass. The orbital inclination is also currently decreasing, likely due to gravitational interactions with a third body

Suppressed phase variations in a high amplitude rapidly oscillating Ap star pulsating in a distorted quadrupole mode

We present the results of a multisite photometric observing campaign on the rapidly oscillating Ap (roAp) star 2MASS 16400299-0737293 (J1640; $V=12.7$). We analyse photometric $B$ data to show the star pulsates at a frequency of $151.93$ d$^{-1}$ ($1758.45 \mu$Hz; $P=9.5$ min) with a peak-to-peak amplitude of 20.68 mmag, making it one of the highest amplitude roAp stars. No further pulsation modes are detected. The stellar rotation period is measured at $3.6747\pm0.0005$ d, and we show that rotational modulation due to spots is in anti-phase between broadband and $B$ observations. Analysis and modelling of the pulsation reveals this star to be pulsating in a distorted quadrupole mode, but with a strong spherically symmetric component. The pulsational phase variation in this star is suppressed, leading to the conclusion that the contribution of $\ell>2$ components dictate the shape of phase variations in roAp stars that pulsate in quadrupole modes. This is only the fourth time such a strong pulsation phase suppression has been observed, leading us to question the mechanisms at work in these stars. We classify J1640 as an A7 Vp SrEu(Cr) star through analysis of classification resolution spectra

Impacts of Co-Solvent Flushing on Microbial Populations Capable of Degrading Trichloroethylene

With increased application of co-solvent flushing technologies for removal of nonaqueous phase liquids from groundwater aquifers, concern over the effects of the solvent on native microorganisms and their ability to degrade residual contaminant has also arisen. This study assessed the impact of ethanol flushing on the numbers and activity potentials of trichloroethylene (TCE)-degrading microbial populations present in aquifer soils taken immediately after and 2 years after ethanol flushing of a former dry cleaners site. Polymerase chain reaction analysis revealed soluble methane monooxygenase genes in methanotrophic enrichments, and 16S rRNA analysis identified Methylocystis parvus with 98% similarity, further indicating the presence of a type II methanotroph. Dissimilatory sulfite reductase genes in sulfate-reducing enrichments prepared were also observed. Ethanol flushing was simulated in columns packed with uncontaminated soils from the dry cleaners site that were dosed with TCE at concentrations observed in the field; after flushing, the columns were subjected to a continuous flow of 500 pore volumes of groundwater per week. Total acridine orange direct cell counts of the flushed and nonflushed soils decreased over the 15-week testing period, but after 5 weeks, the flushed soils maintained higher cell counts than the nonflushed soils. Inhibition of methanogenesis by sulfate reduction was observed in all column soils, as was increasing removal of total methane by soils incubated under methanotrophic conditions. These results showed that impacts of ethanol were not as severe as anticipated and imply that ethanol may mitigate the toxicity of TCE to the microorganisms

The mass discrepancy in intermediate- and high-mass eclipsing binaries: The need for higher convective core masses

Context. Eclipsing, spectroscopic double-lined binary star systems are excellent laboratories for calibrating theories of stellar interior structure and evolution. Their precise and accurate masses and radii measured from binary dynamics offer model-independent constraints and challenge current theories of stellar evolution. Aims. We aim to investigate the mass discrepancy in binary stars. This is the significant difference between stellar components’ masses measured from binary dynamics and those inferred from models of stellar evolution via positions of the components in the Teff − log g Kiel diagram. We study the effect of near-core mixing on the mass of the convective core of the stars and interpret the results in the context of the mass discrepancy. Methods. We fitted stellar isochrones computed from a grid of MESA stellar evolution models to a homogeneous sample of eleven high-mass binary systems. Two scenarios are considered where individual stellar components of a binary system are treated independent of each other and where they are forced to have the same age and initial chemical composition. We also study the effect of the microturbulent velocity and turbulent pressure on the atmosphere model structure and stellar spectral lines, and its link with the mass discrepancy. Results. We find that the mass discrepancy is present in our sample and that it is anti-correlated with the surface gravity of the star. No correlations are found with other fundamental and atmospheric parameters, including the stellar mass. The mass discrepancy can be partially accounted for by increasing the amount of near-core mixing in stellar evolution models. We also find that ignoring the microturbulent velocity and turbulent pressure in stellar atmosphere models of hot evolved stars results in the overestimation of their effective temperature by up to 8%. Together with enhanced near-core mixing, this can almost entirely account for the ∼30% mass discrepancy found for the evolved primary component of V380 Cyg. Conclusions. We find a strong link between the mass discrepancy and the convective core mass. The mass discrepancy can be solved by considering the combined effect of extra near-core boundary mixing and the consistent treatment in the spectrum analysis of hot evolved stars. Our binary modelling results in convective core masses between 17 and 35% of the stellar mass, which is in excellent agreement with the results from gravity-mode asteroseismology of single stars. This implies larger helium core masses near the end of the main sequence than have been anticipated so far

Hear it through the grapevine

Dominic M Bowman and the ECN Committee share their perspective of the RAS Early Career Network's first career event: postdoctoral career advice from the communit