Context.
Gravity-mode asteroseismology has significantly improved our understanding of mixing in intermediate mass stars. However, theoretical pulsation periods of stellar models remain in tension ...with observations, and it is often unclear how the models of these stars should be further improved. Inversions provide a path forward by directly probing the internal structure of these stars from their pulsation periods, quantifying which parts of the model are in need of improvement. This method has been used with success in the case of solar-like pulsators, but has not yet been applied to main-sequence gravity-mode pulsators.
Aims.
Our aim is to determine whether structure inversions for gravity-mode pulsators are feasible. We focus on the case of slowly rotating slowly pulsating B-type (SPB) stars.
Methods.
We computed and analyzed dipole mode kernels for three variables pairs: (
ρ
,
c
), (
N
2
,
c
), and (
N
2
,
ρ
). We assessed the potential of these kernels by predicting the oscillation frequencies of a model after perturbing its structure. We then tested two inversion methods, regularized least squares (RLS) and subtractive optimally localized averages (SOLA), using a model grid computed with the MESA stellar evolution code and the GYRE pulsation code.
Results.
We find that changing the stellar structure affects the oscillation frequencies in a nonlinear way. The oscillation modes for which this nonlinear dependency is the strongest are in resonance with the near-core peak in the buoyancy frequency. The near-core region of the star can be probed with SOLA, while RLS requires fine tuning to obtain accurate results. Both RLS and SOLA are strongly affected by the nonlinear dependencies on the structure differences, as these methods are based on a first-order approximation. These inversion methods need to be modified for meaningful applications of inversions to SPB stars.
Conclusions.
Our results show that inversions of gravity-mode pulsators are possible in principle, but that the typical inversion methods developed for solar-like oscillators are not applicable. Future work should focus on developing nonlinear inversion methods.
Context. The search for twins of the Sun and Earth relies on accurate characterization of stellar and the exoplanetary parameters age, mass, and radius. In the modern era of asteroseismology, ...parameters of solar-like stars are derived by fitting theoretical models to observational data, which include measurements of their oscillation frequencies, metallicity Fe/H, and effective temperature Teff. Furthermore, combining this information with transit data yields the corresponding parameters for their associated exoplanets. Aims. While values of Fe/H and Teff are commonly stated to a precision of ∼0.1 dex and ∼100 K, the impact of systematic errors in their measurement has not been studied in practice within the context of the parameters derived from them. Here we seek to quantify this. Methods. We used the Stellar Parameters in an Instant (SPI) pipeline to estimate the parameters of nearly 100 stars observed by Kepler and Gaia, many of which are confirmed planet hosts. We adjusted the reported spectroscopic measurements of these stars by introducing faux systematic errors and, separately, artificially increasing the reported uncertainties of the measurements, and quantified the differences in the resulting parameters. Results. We find that a systematic error of 0.1 dex in Fe/H translates to differences of only 4%, 2%, and 1% on average in the resulting stellar ages, masses, and radii, which are well within their uncertainties (∼11%, 3.5%, 1.4%) as derived by SPI. We also find that increasing the uncertainty of Fe/H measurements by 0.1 dex increases the uncertainties of the ages, masses, and radii by only 0.01 Gyr, 0.02 M⊙, and 0.01 R⊙, which are again well below their reported uncertainties (∼0.5 Gyr, 0.04 M⊙, 0.02 R⊙). The results for Teff at 100 K are similar. Conclusions. Stellar parameters from SPI are unchanged within uncertainties by errors of up to 0.14 dex or 175 K. They are even more robust to errors in Teff than the seismic scaling relations. Consequently, the parameters for their exoplanets are also robust.
Abstract
We present the first analysis of Cepheid stars observed by the TESS space mission in Sectors 1–5. Our sample consists of 25 pulsators: ten fundamental mode, three overtone and two ...double-mode classical Cepheids, plus three type II and seven anomalous Cepheids. The targets were chosen from fields with different stellar densities, both from the Galactic field and from the Magellanic System. Three targets have 2 minutes cadence light curves available by the TESS Science Processing Operations Center: for the rest, we prepared custom light curves from the full-frame images with our own differential photometric FITSH pipeline. Our main goal was to explore the potential and the limitations of TESS concerning the various subtypes of Cepheids. We detected many low-amplitude features: weak modulation, period jitter, and timing variations due to light-time effect. We also report signs of nonradial modes and the first discovery of such a mode in an anomalous Cepheid, the overtone star XZ Cet, which we then confirmed with ground-based multicolor photometric measurements. We prepared a custom photometric solution to minimize saturation effects in the bright fundamental-mode classical Cepheid,
β
Dor with the
lightkurve
software, and we revealed strong evidence of cycle-to-cycle variations in the star. In several cases, however, fluctuations in the pulsation could not be distinguished from instrumental effects, such as contamination from nearby sources, which also varies between sectors. Finally, we discuss how precise light-curve shapes will be crucial not only for classification purposes but also to determine physical properties of these stars.
Abstract
Do white dwarfs have inner cores made of iron? Neutron-rich nuclei like
56
Fe experience a net gravitational force and sediment toward the core. Using new phase diagrams and molecular ...dynamics simulations, we show that
56
Fe should separate into mesoscopic Fe-rich crystallites due to its large charge relative to the background. At solar abundances, these crystallites rapidly precipitate and form an inner core of order 100 km and 10
−3
M
⊙
that may be detectable with asteroseismology. Associated cooling delays could be up to a Gyr for low-mass white dwarfs but are only ∼0.1 Gyr for massive white dwarfs, so while this mechanism may contribute to the Q-branch the heating is insufficient to fully explain it.
Context.
Transport of angular momentum in stellar interiors is currently not well understood. Asteroseismology can provide us with estimates of internal rotation of stars and thereby advances our ...understanding of angular momentum transport.
Aims.
We can measure core-rotation rates in red-giant stars and we can place upper bounds on surface-rotation rates using measurements of dipole (
l
= 1) modes. Here, we aim to determine the theoretical sensitivity of modes of different spherical degree towards the surface rotation. Additionally, we aim to identify modes that can potentially add sensitivity at intermediate radii.
Methods.
We used asteroseismic rotational inversions to probe the internal stellar rotation profiles in red-giant models from the base of the red-giant branch up to the luminosity bump. We used the inversion method of multiplicative optimally localised averages to assess how well internal and surface rotation rates can be recovered from different mode sets and different synthetic rotation profiles.
Results.
We confirm that dipole mixed modes are sufficient to set constraints on the average core-rotation rates in red giants. However, surface-rotation rates estimated with only dipole mixed modes are contaminated by the core rotation. We show that the sensitivity to surface rotation decreases from the base of the red-giant branch until it reaches a minimum at 60–80% of the bump luminosity due to a glitch in the buoyancy frequency. Thereafter, a narrow range of increased surface sensitivity just below the bump luminosity exists. Quadrupole and octopole modes have more sensitivity in the outer parts of the star. To obtain accurate estimates of rotation rates at intermediate radii (i.e. a fractional radius of ∼0.4), acoustic oscillation modes with a spherical degree of
l
≈ 10 are needed.
Conclusions.
We find a minimum and subsequent maximum in the sensitivity to the surface rotation rate in red giants below the luminosity bump. Furthermore, we show that, if observed, quadrupole and octopole modes enable us to distinguish between differential and solid body rotation in the convection zone. This will be important when investigating the transport of angular momentum between the core and the envelope.
OBJECTIVES—The aim of this study was to determine whether recurrent intravenous injections with Porphyromonas gingivalis (P gingivalis), mimicking periodontitis-associated bacteremia, promotes ...coronary artery and aortic atherosclerosis in pigs.
METHODS AND RESULTS—Pigs (n=36) fed low- or high-fat chow were divided into P gingivalis–sensitized and P gingivalis–challenged groups or P gingivalis–sensitized controls and saline-treated controls. Pigs were sensitized with 10 killed P gingivalis subcutaneously. Four weeks later all sensitized pigs in the group to be challenged started intravenous injections thrice weekly for 5 months with 10 to 10 colony forming units of P gingivalis while controls received saline. Anti–P gingivalis antibody, serum cholesterol, and complete blood counts were assayed monthly. Pigs were euthanized 2 weeks after the last injection, and coronary arteries and aortas were analyzed by histomorphometry and immunohistochemistry. Anti–P gingivalis antibody was increased by P gingivalis exposure. P gingivalis–challenged pigs developed a significantly greater amount of coronary and aortic atherosclerosis than controls in the normocholesterolemic group and nearly significant in the hypercholesterolemic group. P gingivalis was detected by polymerase chain reaction in arteries from most (94%, 16 of 17) P gingivalis–challenged pigs but not controls.
CONCLUSIONS—Recurrent P gingivalis bacteremia induces aortic and coronary lesions consistent with atherosclerosis in normocholesterolemic pigs and increases aortic and coronary atherosclerosis in hypercholesterolemic pigs.
Context. The Transiting Exoplanet Survey Satellite (TESS) is observing bright known planet-host stars across almost the entire sky. These stars have been subject to extensive ground-based ...observations, providing a large number of radial velocity measurements. Aims. The objective of this work is to use the new TESS photometric observations to characterize the star λ2 Fornacis, and following this to update the parameters of the orbiting planet λ2 For b. Methods. We measured the frequencies of the p-mode oscillations in λ2 For, and in combination with non-seismic parameters estimated the stellar fundamental properties using stellar models. Using the revised stellar properties and a time series of archival radial velocities from the UCLES, HIRES and HARPS instruments spanning almost 20 years, we refit the orbit of λ2 For b and searched the residual radial velocities for remaining variability. Results. We find that λ2 For has a mass of 1.16 ± 0.03 M⊙ and a radius of 1.63 ± 0.04 R⊙, with an age of 6.3 ± 0.9 Gyr. This and the updated radial velocity measurements suggest a mass of λ2 For b of 16.8−1.3+1.2 M⊕, which is ∼5M⊕ less than literature estimates. We also detect an additional periodicity at 33 days in the radial velocity measurements, which is likely due to the rotation of the host star. Conclusions. While previous literature estimates of the properties of λ2 For are ambiguous, the asteroseismic measurements place the star firmly at the early stage of its subgiant evolutionary phase. Typically only short time series of photometric data are available from TESS, but by using asteroseismology it is still possible to provide tight constraints on the properties of bright stars that until now have only been observed from the ground. This prompts a reexamination of archival radial velocity data that have been accumulated in the past few decades in order to update the characteristics of the planet hosting systems observed by TESS for which asteroseismology is possible.
Abstract Background and aims Diabetes is a major risk factor for the development of atherosclerosis. Hyperglycemia stimulates vascular smooth muscle cells ( VS. MC) to secrete ligands that bind to ...the αVβ3 integrin, a receptor that regulates VS. MC proliferation and migration. This study determined whether an antibody that had previously been shown to block αVβ3 activation and to inhibit VS. MC proliferation and migration in vitro, inhibited the development of atherosclerosis in diabetic pigs. Methods Twenty diabetic pigs were maintained on a high fat diet for 22 weeks. Ten received injections of anti-β3 F(ab)2 and ten received control F(ab)2 for 18 weeks. Results The active antibody group showed reduction of atherosclerosis of 91 ± 9% in the left main, 71 ± 11%, in left anterior descending, 80 ± 10.2% in circumflex, and 76 ± 25% in right coronary artery, ( p < 0.01 compared to lesions areas from corresponding control treated arteries). There were significant reductions in both cell number and extracellular matrix. Histologic analysis showed neointimal hyperplasia with macrophage infiltration, calcifications and cholesterol clefts. Antibody treatment significantly reduced number of macrophages contained within lesions suggesting that this change contributed to the decrease in lesion cellularity. Analysis of the biochemical changes within the femoral arteries that received the active antibody showed a 46 ± 12% ( p < 0.05) reduction in the tyrosine phosphorylation of the β3 subunit of αVβ3 and a 40 ± 14% ( p < 0.05) reduction in MAP kinase activation. Conclusions Blocking ligand binding to the αVβ3 integrin inhibits its activation and attenuates increased VS. MC proliferation that is induced by chronic hyperglycemia. These changes result in significant decreases in atherosclerotic lesion size in the coronary arteries. The results suggest that this approach may have efficacy in treating the proliferative phase of atherosclerosis in patients with diabetes.
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