Context.
Stellar components in binaries are subject to tidal forces which influence asteroseismic properties. Tidally pertubed pulsations have been reported for different objects but none of these ...are in their pre-main sequence phase of evolution. This makes RS Cha, consisting of two
δ
Scuti stars and with pulsational characteristics influenced by tidal effects, the first such object observed.
Aims.
We aim to investigate the pulsational properties of the eclipsing binary RS Cha in terms of the theory of tidally perturbed pulsations.
Methods.
Based on photometric time series obtained from the TESS satellite, we performed binary modelling using
PHOEBE
to interpret the binary light curve and to allow the investigation of the pulsations of both components in RS Cha. We modelled the detrended light curve with the superposition of linear modes. The frequencies were then interpreted as self excited modes perturbed by tidal forces.
Results.
We find evidence for tidally perturbed modes, which enables the identification of pulsation modes. RS Cha mainly exhibits dipole modes, while one prominent
l
= 2 or
l
= 3 mode is also inferred. The latter verifies previous results from spectroscopic time series.
Conclusion.
This work shows that RS Cha is an ideal candidate to test the theory of tidally perturbed pulsations within the framework of asteroseismic modelling. The identification of multiple pulsation modes using this theory is unprecedented and will be a keystone in the future of pre-main sequence asteroseismology. However, amplitude modulation caused by the changing light ratio during the orbital phase in an eclipsing binary also plays a significant role, which can complicate mode identification.
Context. In recent years, our understanding of solar-like oscillations from main sequence to red giant stars has improved dramatically thanks to pristine data collected from space telescopes. One of ...the remaining open questions focuses on the observational identification of solar-like oscillations in pre-main sequence stars. Aims. We aim to develop an improved method to search for solar-like oscillations in pre-main sequence stars and apply it to data collected by the Kepler K2 mission. Methods. Our software APOLLO includes a novel way to detect low signal-to-noise ratio solar-like oscillations in the presence of a high background level. Results. By calibrating our method using known solar-like oscillators from the main Kepler mission, we apply it to T Tauri stars observed by Kepler K2 and identify several candidate pre-main sequence solar-like oscillators. Conclusions. We find that our method is robust even when applied to time-series of observational lengths as short as those obtained with the TESS satellite in one sector. We identify EPIC 205375290 as a possible candidate for solar-like oscillations in a pre-main sequence star with νmax ≃ 242 μHz. We also derive its fundamental parameters to be Teff = 3670 ± 180 K, log g = 3.85 ± 0.3, v sin i = 8 ± 1 km s−1, and about solar metallicity from a high-resolution spectrum obtained from the Keck archive.
Context.
F-type stars are characterised by several physical processes such as different pulsation mechanisms, rotation, convection, diffusion, and magnetic fields. The rapidly rotating
δ
Scuti star
β
...Cas can be considered as a benchmark star to study the interaction of several of these effects.
Aims.
We investigate the pulsational and magnetic field properties of
β
Cas. We also determine the star’s apparent fundamental parameters and chemical abundances.
Methods.
Based on photometric time series obtained from three different space missions (BRITE-Constellation, SMEI, and TESS), we conduct a frequency analysis and investigate the stability of the pulsation amplitudes over four years of observations. We investigate the presence of a magnetic field and its properties using spectropolarimetric observations taken with the Narval instrument by applying the least-squares deconvolution and Zeeman-Doppler imaging techniques.
Results.
The star
β
Cas shows only three independent
p
-mode frequencies down to the few ppm-level; its highest amplitude frequency is suggested to be an
n
= 3,
ℓ
= 2,
m
= 0 mode. Its magnetic field structure is quite complex and almost certainly of a dynamo origin. The atmosphere of
β
Cas is slightly deficient in iron peak elements and slightly overabundant in C, O, and heavier elements.
Conclusions.
Atypically for
δ
Scuti stars, we can only detect three pulsation modes down to exceptionally low noise levels for
β
Cas. The star is also one of very few
δ
Scuti pulsators known to date to show a measurable magnetic field and the first
δ
Scuti star with a dynamo magnetic field. These characteristics make
β
Cas an interesting target for future studies of dynamo processes in the thin convective envelopes of F-type stars, the transition region between fossil and dynamo fields, and the interaction between pulsations and magnetic field.
Context.
The physics of early stellar evolution (e.g. accretion processes) is often not properly included in the calculations of pre-main-sequence models, leading to insufficient model grids and ...hence systematic errors in the results.
Aims.
We aim to investigate current and improved approaches for the asteroseismic modelling of pre-main-sequence
δ
Scuti stars.
Methods.
We calculated an extensive grid of pre-main-sequence models including the early accretion phase and used the resulting equilibrium models as input to calculate theoretical frequency spectra. These spectra were used to investigate different approaches in modelling echelle diagrams to find the most reliable methods. By applying Petersen diagrams, we present a simple algorithm to extract echelle diagrams from observed pulsation frequencies.
Results.
We show that model grids with insufficient input physics and imperfect modelling approaches lead to underestimated uncertainties and systematic errors in the extracted stellar parameters. Our re-discussion of HD 139614 leads to different stellar parameters than the ones derived by Murphy et al. (2021, MNRAS, 502, 1633). We performed a model comparison between this previous investigation and our results by applying the Akaike and Bayesian information criteria. While the results with regard to our ten-dimensional model are inconclusive, they show (very) strong evidence of a six-dimensional model with fixed accretion parameters (leading to almost identical stellar parameters to those of the ten-dimensional model) to be preferred over the model applied by Murphy et al. (2021, MNRAS, 502, 1633). In general, our modelling approach can provide narrow constraints on the stellar parameters (i.e. Δ
R
∼ 0.05
R
⊙
, Δlog
g
≲ 0.01, and Δ
M
⋆
∼ 0.1
M
⊙
).
Conclusions.
The extensively tested modelling approaches and automatic extraction of echelle diagrams should allow us to study many more pre-main-sequence
δ
Scuti stars in the future and lead to reliable stellar parameters.
Context.
The picture of pre-main-sequence evolution is often simplified by the application of classical initial models. Such models have large initial radii and sufficient uniform contraction to make ...them fully convective, however, real stars are born as small protostellar seeds in collapsing molecular clouds and obtain their final mass by means of accretion.
Aims.
We aim to constrain the input physics of accretion on protostellar seeds with the observed spectroscopic parameters and stellar pulsations of young stellar objects and pre-main-sequence stars.
Methods.
We conducted a literature search for spectroscopic samples of young stellar objects and pre-main-sequence stars, including all previously known pulsators. The sample size of pulsating pre-main-sequence stars was increased by analysing TESS observations and presenting additional discoveries in the CoRoT data. We employed Modules for Experiments in Stellar Astrophysics and
GYRE
to calculate evolutionary tracks of accreting protostellar seeds in a constant accretion scenario, the subsequent pre-main-sequence evolution, and their pulsation properties. We then compared the results with the observations to constrain the input physics.
Results.
We discuss 16 formerly unknown pulsating pre-main-sequence stars and candidates that are of any of the following type: slowly pulsating B-stars,
δ
Scuti,
γ
Doradus, or a
δ
Scuti -
γ
Doradus hybrid type. We find that evolutionary tracks with a mass accretion rate of 5 × 10
−6
M
⊙
yr
−1
and a fraction of injected accretion energy of
β
= 0.1 provide the best results for enveloping the spectroscopic parameters of pre-main-sequence stars in the constant accretion scenario. The calculated instability regions constrain the atmospheric boundary conditions to Eddington Gray atmospheres. Here, we discuss the future potential for additional constraints by instability regions that are dependent on radial order. Finally, we present a possible candidate star for pulsations in M-type young stellar objects.
Conclusions.
We show that evolutionary calculations of accreting protostellar seeds match the observed spectroscopic parameters of pre-main-sequence stars. Future observations that will allow for the identification of radial orders in particular will present opportunities for additional constraints.
Context.
Determining the effects of an accretion disk is crucial to understanding the evolution of young stars. During the combined evolution, stellar and disk parameters influence one another, which ...motivated us to develop a combined stellar and disk model. This makes a combined numerical model, with the disk evolving alongside the star, the next logical step in the progress of studying early stellar evolution.
Aims.
We aim to understand the effects of metallicity on the accretion disk and the stellar spin evolution during the T Tauri phase.
Methods.
We combined the numerical treatment of a hydrodynamic disk with stellar evolution, including a stellar spin model and allowing a self-consistent calculation of the back-reactions between the individual components.
Results.
We present the self-consistent theoretical evolution of T Tauri stars coupled to a stellar disk. We find that disks in low-metallicity environments are heated differently and have shorter lifetimes compared to their solar-metallicity counterparts. Differences in stellar radii, the contraction rate of the stellar radius, and the shorter disk lifetimes result in low-metallicity stars rotating more rapidly.
Conclusions.
We present an additional explanation for the observed short disk lifetimes in low-metallicity clusters. A combination of our model with those of previous studies (e.g., a metallicity-based photo-evaporation) could help us understand disk evolution and dispersal at different metallicities. Furthermore, our stellar spin evolution model includes several important effects that had previously been ignored (e.g., the stellar magnetic field strength and a realistic calculation of the disk lifetime). We encourage others to include our results as initial or input parameters in further spin evolution models that cover the stellar evolution toward and during the main sequence.
The development and application of a sophisticated virtual screening and selection protocol to identify potential, novel inhibitors of the human rhinovirus coat protein employing various ...computer-assisted strategies are described. A large commercially available database of compounds was screened using a highly selective, structure-based pharmacophore model generated with the program Catalyst. A docking study and a principal component analysis were carried out within the software package Cerius2 and served to validate and further refine the obtained results. These combined efforts led to the selection of six candidate structures, for which in vitro antirhinoviral activity could be shown in a biological assay.
Context. The picture of pre-main-sequence evolution is often simplified by the application of classical initial models. Such models have large initial radii and sufficient uniform contraction to make ...them fully convective, however, real stars are born as small protostellar seeds in collapsing molecular clouds and obtain their final mass by means of accretion. Aims. We aim to constrain the input physics of accretion on protostellar seeds with the observed spectroscopic parameters and stellar pulsations of young stellar objects and pre-main-sequence stars. Methods. We conducted a literature search for spectroscopic samples of young stellar objects and pre-main-sequence stars, including all previously known pulsators. The sample size of pulsating pre-main-sequence stars was increased by analysing TESS observations and presenting additional discoveries in the CoRoT data. We employed Modules for Experiments in Stellar Astrophysics and GYRE to calculate evolutionary tracks of accreting protostellar seeds in a constant accretion scenario, the subsequent pre-main-sequence evolution, and their pulsation properties. We then compared the results with the observations to constrain the input physics. Results. We discuss 16 formerly unknown pulsating pre-main-sequence stars and candidates that are of any of the following type: slowly pulsating B-stars, δ Scuti, γ Doradus, or a δ Scuti - γ Doradus hybrid type. We find that evolutionary tracks with a mass accretion rate of 5 × 10−6 M⊙ yr−1 and a fraction of injected accretion energy of β = 0.1 provide the best results for enveloping the spectroscopic parameters of pre-main-sequence stars in the constant accretion scenario. The calculated instability regions constrain the atmospheric boundary conditions to Eddington Gray atmospheres. Here, we discuss the future potential for additional constraints by instability regions that are dependent on radial order. Finally, we present a possible candidate star for pulsations in M-type young stellar objects. Conclusions. We show that evolutionary calculations of accreting protostellar seeds match the observed spectroscopic parameters of pre-main-sequence stars. Future observations that will allow for the identification of radial orders in particular will present opportunities for additional constraints.
Context.
In recent years, our understanding of solar-like oscillations from main sequence to red giant stars has improved dramatically thanks to pristine data collected from space telescopes. One of ...the remaining open questions focuses on the observational identification of solar-like oscillations in pre-main sequence stars.
Aims.
We aim to develop an improved method to search for solar-like oscillations in pre-main sequence stars and apply it to data collected by the
Kepler
K2 mission.
Methods.
Our software
APOLLO
includes a novel way to detect low signal-to-noise ratio solar-like oscillations in the presence of a high background level.
Results.
By calibrating our method using known solar-like oscillators from the main
Kepler
mission, we apply it to T Tauri stars observed by
Kepler
K2 and identify several candidate pre-main sequence solar-like oscillators.
Conclusions.
We find that our method is robust even when applied to time-series of observational lengths as short as those obtained with the TESS satellite in one sector. We identify EPIC 205375290 as a possible candidate for solar-like oscillations in a pre-main sequence star with
ν
max
≃ 242
μ
Hz. We also derive its fundamental parameters to be
T
eff
= 3670 ± 180 K, log
g
= 3.85 ± 0.3,
v
sin
i
= 8 ± 1 km s
−1
, and about solar metallicity from a high-resolution spectrum obtained from the Keck archive.
beta Cas Zwintz, K.; Neiner, C.; Kochukhov, Oleg ...
Astronomy and astrophysics (Berlin),
11/2020, Volume:
643
Journal Article
Peer reviewed
Context. F-type stars are characterised by several physical processes such as different pulsation mechanisms, rotation, convection, diffusion, and magnetic fields. The rapidly rotating delta Scuti ...star beta Cas can be considered as a benchmark star to study the interaction of several of these effects.Aims. We investigate the pulsational and magnetic field properties of beta Cas. We also determine the star's apparent fundamental parameters and chemical abundances.Methods. Based on photometric time series obtained from three different space missions (BRITE-Constellation, SMEI, and TESS), we conduct a frequency analysis and investigate the stability of the pulsation amplitudes over four years of observations. We investigate the presence of a magnetic field and its properties using spectropolarimetric observations taken with the Narval instrument by applying the least-squares deconvolution and Zeeman-Doppler imaging techniques.Results. The star beta Cas shows only three independent p-mode frequencies down to the few ppm-level; its highest amplitude frequency is suggested to be an n=3, l=2, m=0 mode. Its magnetic field structure is quite complex and almost certainly of a dynamo origin. The atmosphere of beta Cas is slightly deficient in iron peak elements and slightly overabundant in C, O, and heavier elements.Conclusions. Atypically for delta Scuti stars, we can only detect three pulsation modes down to exceptionally low noise levels for beta Cas. The star is also one of very few delta Scuti pulsators known to date to show a measurable magnetic field and the first delta Scuti star with a dynamo magnetic field. These characteristics make beta Cas an interesting target for future studies of dynamo processes in the thin convective envelopes of F-type stars, the transition region between fossil and dynamo fields, and the interaction between pulsations and magnetic field.
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