Massive heartbeat stars from TESS Kołaczek-Szymański, P. A.; Pigulski, A.; Michalska, G. ...
Astronomy and astrophysics (Berlin),
03/2021, Letnik:
647
Journal Article
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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.
This paper presents the study on the formation of surface layer in A359/20SiCP metal matrix composite (MMC) during laser assisted turning, with the consideration of SiC particles’ sedimentation in a ...liquid matrix. The developed model includes the effect of gravity, buoyancy, resistive force of liquid matrix and centrifugal force of the rotating work material. On the basis of the proposed approach the instantaneous sedimentation speed, as well as the depth of sedimented SiC particles are calculated. Consequently, the applied model enables the selection of the effective depth of cut and tool’s angular distance from the laser beam, which can improve the machined surface quality and composite’s exploitation properties. The experiments confirm that sedimentation phenomenon plays an important role during the surface layer formation in laser heating conditions. Furthermore, the laser assisted turning with the selection of the recommended cutting conditions affects the improvement of surface quality, and composite’s wear resistance.
Context.
Eccentric ellipsoidal variables (also known as heartbeat stars) is a class of eccentric binaries in which proximity effects, and tidal distortion due to time-dependent tidal potential in ...particular, lead to measurable photometric variability close to the periastron passage. Varying tidal potential may also give rise to tidally excited oscillations (TEOs), which are forced eigenmodes with frequencies close to the integer multiples of the orbital frequency. TEOs may play an important role in the dynamical evolution of massive eccentric systems.
Aims.
Our study is aimed at detecting TEOs and characterising the long-term behaviour of their amplitudes and frequencies in the extreme-amplitude heartbeat star MACHO 80.7443.1718, consisting of a blue supergiant and a late O-type massive dwarf.
Methods.
We used two seasons of Transiting Exoplanet Survey Satellite (TESS) observations of the target to obtain new 30-min cadence photometry by means of the difference image analysis of TESS full-frame images. In order to extend the analysis to longer timescales, we supplemented the TESS data with 30-year long ground-based photometry of the target. Both TESS and ground-based photometry are carefully analysed by means of Fourier techniques in order to detect TEOs, examine the long-term stability of their amplitudes and frequencies, and characterise other types of variability in the system.
Results.
We confirm the detection of the known
n
= 23, 25, and 41 TEOs and announce the detection of two new TEOs, with
n
= 24 and 230, in the photometry of MACHO 80.7443.1718. Amplitudes of all TEOs were found to vary on a timescale of years or months. For
n
= 25, the TEO amplitude and frequency changes are related, which may indicate that the main cause of the amplitude drop in this TEO in TESS observations is the change in its frequency and increase in its detuning parameter. The light curve of the
n
= 230 TEO is strongly non-sinusoidal. Its high frequency may indicate that the oscillation is a strange mode. Stochastic variability observed in the target fits the behaviour observed in massive stars well and independently confirms that the primary is an evolved star. We also find that the orbital period of the system decreases at a rate of about 11 s (yr)
−1
. This can be explained by several phenomena: a significant mass loss, mass transfer between components, tidal dissipation, and the presence of a tertiary in the system. All of these phenomena may contribute to the observed changes.
Conclusions.
The discovery of variable amplitudes and frequencies of TEOs prompts for similar studies in other eccentric elliptical variables with TEOs. Long-term photometric monitoring of these targets is also desirable. The results we obtained pose a challenge for theory. In particular, it needs to be explained why
n
= 230 TEO is excited. In a general context, studies on the long-term behaviour of TEOs may help to explain the role of TEOs in the dynamical evolution of massive eccentric systems.
Blue large-amplitude pulsators (BLAPs) form a small group of hot objects pulsating in a fundamental radial mode with periods of the order of 30 min. Proposed evolutionary scenarios explain them as ...evolved low-mass stars: ∼0.3
M
⊙
shell-hydrogen-burning objects with a degenerated helium core, more massive (0.5–0.8)
M
⊙
core-helium-burning stars, or ∼0.7
M
⊙
surviving companions of type Ia supernovae. Therefore, their origin remains to be established. Using data from Transiting Exoplanet Survey Satellite, we discovered that HD 133729 is a binary consisting of a late B-type main-sequence star and a BLAP. The BLAP pulsates with a period of 32.37 min decreasing at a rate of ( − 7.11 ± 0.33) × 10
−11
. The light curve is typical for BLAPs, but it shows an unusual 40-s drop at the descending branch. Due to light dilution by a brighter companion, the observed amplitude of pulsation is much smaller than in other BLAPs. From available photometry, we derived times of maximum light, which revealed the binary nature of the star via an O−C diagram. The diagram shows variations with a period of 23.08433 d that we attribute to the light-travel-time effect in the system. The analysis of these variations allowed us to derive the spectroscopic parameters of the BLAP’s orbit around the binary’s centre of mass. The presence of a hot companion in the system was confirmed by the analysis of its spectral energy distribution, which was also used to place the components in the Hertzsprung-Russell diagram. The obtained position of the BLAP fully agrees with the location of the other members of the class. With the estimated
V
≈ 11 mag and the
Gaia
distance of less than 0.5 kpc, the BLAP is the brightest and the nearest of all known BLAPs. It may become a key object in the verification of the evolutionary scenarios for this class of variables. We argue that low-mass progenitors of the BLAP are excluded if the components are coeval and no mass transfer between the components took place.
Context.
Massive and intermediate-mass stars reside in binary systems at a much higher rate than low-mass stars. At the same time, binaries containing massive main-sequence (MS) component(s) are ...often characterised by eccentric orbits, and can therefore be observed as eccentric ellipsoidal variables (EEVs). The orbital phase-dependent tidal potential acting on the components of EEVs can induce tidally excited oscillations (TEOs), which can affect the evolution of the binary system.
Aims.
We investigate how the history of resonances between the eigenmode spectra of the EEV components and the tidal forcing frequencies depends on the initial parameters of the system, limiting our study to the MS. Each resonance is a potential source of TEO. We are particularly interested in the total number of resonances, their average rate of occurrence, and their distribution in time.
Methods.
We synthesised 20 000 evolutionary models of the EEVs across the MS using Modules for Experiments in Stellar Astrophysics (
MESA
) software for stellar structure and evolution. We considered a range of masses of the primary component from 5 to 30
M
⊙
. Later, using the
GYRE
stellar non-adiabatic oscillations code, we calculated the eigenfrequencies for each model recorded by
MESA
. We focused only on the
l
= 2,
m
= 0, +2 modes, which are suspected of being dominant TEOs. Knowing the temporal changes in the orbital parameters of simulated EEVs and the changes in the eigenfrequency spectra for both components, we were able to determine so-called resonance curves, which describe the overall chance of a resonance occurring and therefore of a TEO occurring. We analysed the resonance curves by constructing basic statistics for them and analysing their morphology using machine learning methods, including the Uniform Manifold Approximation and Projection (UMAP) tool.
Results.
The EEV resonance curves from our sample are characterised by a striking diversity, including the occurrence of exceptionally long resonances or the absence of resonances for long evolutionary times. We find that the total number of resonances encountered by components in the MS phase ranges from ∼10
2
to ∼10
3
, mostly depending on the initial eccentricity. We also noticed that the average rate of resonances is about an order of magnitude higher (∼10
2
Myr
−1
) for the most massive components in the assumed range than for EEVs with intermediate-mass stars (∼10
1
Myr
−1
). The distribution of resonances over time is strongly inhomogeneous, and its shape depends mainly on whether the system is able to circularise its orbit before the primary component reaches the terminal-age main sequence (TAMS). Both components may be subject to increased resonance rates as they approach the TAMS. Thanks to the low-dimensional UMAP embeddings performed for the resonance curves, we argue that their morphology changes smoothly across the resulting manifold for different initial EEV conditions. The structure of the embeddings allowed us to explore the whole space of resonance curves in terms of their morphology and to isolate some extreme cases.
Conclusions.
Resonances between tidal forcing frequencies and stellar eigenfrequencies cannot be considered rare events for EEVs with massive and intermediate-mass MS stars. On average, we should observe TEOs more frequently in EEVs that contain massive components than those that contain intermediate-mass ones. The TEOs will be particularly well pronounced for EEVs whose component(s) are close to the TAMS, which calls for observational verification. Given the total number of resonances and their rates, TEOs may play an important role in the transport of angular momentum within massive and intermediate-mass stars (mainly near the TAMS).
Context. The evolution of massive stars is dominated by interactions within binary and multiple systems. In order to accurately model this evolution, it is necessary to investigate all possible forms ...of an interaction in binary systems that may affect the evolution of the components. One of the “laboratories” plausible for this kind of investigation is the massive eccentric binary system MACHO 80.7443.1718 (ExtEV), which exhibits an exceptionally large amplitude of light variability close to the periastron passage of its 32.8-day orbit. Aims. We examine whether the light variability of ExtEV can be explained by a wind-wind collision (WWC) binary system model. We also critically review other models proposed to explain the light curve of ExtEV. Methods. We conducted an analysis of (i) the broadband multicolor photometry of ExtEV spanning a wide range of wavelengths from the ultraviolet to near-infrared, (ii) the time-series space photometry from the Transiting Exoplanet Survey Satellite (TESS), (iii) ground-based Johnson UBV photometry, and (iv) time-series high-resolution spectroscopy. To derive the parameters of the primary component of the system, we fit the spectral energy distribution (SED) and calculated evolutionary models of massive stars that included mass loss. Using radial-velocity data, we determined the spectroscopic parameters of the system. We also fit an analytical model of light variations to the TESS light curve of ExtEV. Results. The ExtEV system exhibits an infrared excess, indicating an increased mass-loss rate. The system does not match the characteristics of Be stars, however. We rule out the possibility of the presence of a Keplerian disk around the primary component. We also argue that the scenario with periodic Roche-lobe overflow at periastron may not be consistent with the observations of ExtEV. Analysis of the SED suggests that the primary component has a radius of about 30 R ⊙ and a luminosity of ∼6.6 × 10 5 L ⊙ . With the analysis of the radial-velocity data, we refine the orbital parameters of ExtEV and find evidence for the presence of a tertiary component in the system. Using evolutionary models we demonstrate that the primary component’s mass is between 25 and 45 M ⊙ . We successfully reproduced the light curve of ExtEV with our analytical model, showing that the dominant processes shaping its light curve can be attributed to the atmospheric eclipse and light scattered in the WWC cone. We also estimate the primary’s mass loss rate due to stellar wind for 4.5 × 10 −5 M ⊙ yr −1 . Conclusions. ExtEV is most likely not an extreme eccentric ellipsoidal variable, but rather an exceptional WWC binary system. The mass loss rate we derived exceeds theoretical predictions by up to two orders of magnitude. This implies that the wind in the system is likely enhanced by tidal interactions, rotation, and possibly also tidally excited oscillations. Therefore, ExtEV represents a rare evolutionary phase of a binary system that may help to understand the role of companion-driven enhanced mass loss in the evolution of massive binary systems.
•Ultrasonic velocity can discriminate various kinds of Mechanically Separated Meat.•Ultrasonic velocity is highly correlated with protein, fat, and sodium content.•Calcium content is not a reliable ...parameter to discriminate various kinds of meat.•Density is a reliable parameter to discriminate various kinds of meat samples.
An innovative analytical ultrasonic method for identification and investigation of Mechanically Separated Meat (MSM) samples is presented. To this end, the ultrasonic wave velocity (f=5MHz) in the investigated meat samples was measured. The measured ultrasonic velocity ranged from 1553.4 to 1589.9 m/s. The investigations were performed for: 1) minced hand deboned chicken fillets, 2) low pressure MSM from chicken carcasses, 3) low pressure MSM from chicken collarbones, 4) high pressure MSM from chicken carcasses and 5) high pressure MSM from chicken collarbones. Statistically significant (p<0.001) differences in the ultrasonic velocity were observed for each of investigated kinds of meat. High significant correlations were found between the ultrasonic velocity and the content of protein, fat, sodium and density of the investigated meat. The applicability of the developed ultrasonic method for identifying various kinds of meat and to determine the content of protein, fat, sodium and density was demonstrated.
Background. There is limited information on acute heart failure (AHF) and its treatment in sub-Saharan Africa. Objective. To describe the clinical characteristics and causes of heart failure (HF), ...adherence to HF treatment guidelines, and mortality of patients with AHF presenting to Groote Schuur Hospital (GSH), Cape Town, South Africa. Methods. This sub-study of The Sub-Saharan Africa Survey of Heart Failure (THESUS-HF) was a prospective and observational survey that focused on the enrolment and follow-up of additional patients with AHF presenting to GSH and entered into the existing registry after publication of the primary THESUS-HF article in 2012. The patients were classified into prevalent (existing) or incident (new) cases of HF. Results. Of the 119 patients included, 69 (58.0%) were female and the mean (standard deviation) age was 49.9 (16.3) years. The majority of prevalent cases were patients of mixed ancestry (63.3%), and prevalent cases had more hypertension (70.0%), diabetes mellitus (36.7%), hyperlipidaemia (33.3%) and ischaemic heart disease (IHD) (36.7%) than incident cases. The top five causes of HF were cardiomyopathy (20.2%), IHD (19.3%), rheumatic valvular heart disease (RHD) (18.5%), cor pulmonale (11.8%) and hypertension (10.1%), with the remaining 20.1% consisting of miscellaneous causes including pericarditis, toxins and congenital heart disease. Most patients received renin-angiotensin system blockers and loop diuretics on discharge. There was a low rate of beta-blocker, aldosterone antagonist and digoxin use. Rehospitalisation within 180 days occurred in 25.2% of cases. In-hospital mortality was 8.4% and the case fatality rate at 6 months was 26.1%. Conclusion. In Cape Town, the main causes of AHF are cardiomyopathy, IHD and RHD. AHF affects a young population and is associated with a high rate of rehospitalisation and mortality. There is serious under-use of beta-blockers, aldosterone antagonists and digoxin. Emphasis on the rigorous application of treatment guidelines is needed to reduce readmission and mortality.
The European Association of Cardiovascular Imaging (EACVI) Scientific Initiatives Committee performed a global survey on radiation exposure in interventional echocardiography. The survey aimed to ...collect data on local practices for radioprotection in interventional echocardiography and to assess the awareness of echocardiography operators about radiation-related risks.
A total of 258 interventional echocardiographers from 52 different countries (48% European) responded to the survey. One hundred twenty-two (47%) participants were women. Two-thirds (76%) of interventional echocardiographers worked in tertiary care/university hospitals. Interventional echocardiography was the main clinical activity for 34% of the survey participants. The median time spent in the cath-lab for the echocardiographic monitoring of structural heart procedures was 10 (5-20) hours/month. Despite this, only 28% of interventional echocardiographers received periodic training and certification in radioprotection and 72% of them did not know their annual radiation dose. The main adopted personal protection devices were lead aprons and thyroid collars (95% and 92% of use, respectively). Dedicated architectural protective shielding was not available for 33% of interventional echocardiographers. Nearly two-thirds of responders thought that the radiation exposure of interventional echocardiographers was higher than that of interventional cardiologists and 72% claimed for an improvement in the radioprotection measures.
Radioprotection measures for interventional echocardiographers are widely variable across centres. Radioprotection devices are often underused by interventional echocardiographers, portending an increased radiation-related risk. International scientific societies working in the field should collaborate to endorse radioprotection training, promote reliable radiation dose assessment, and support the adoption of radioprotection shielding dedicated to interventional echocardiographers.
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