Confirmation of Solar-Like Oscillations in η Bootis

2002 ◽  
Vol 185 ◽  
pp. 470-471
Author(s):  
H. Kjeldsen ◽  
T.R. Bedding ◽  
I.K. Baldry ◽  
S. Frandsen ◽  
H. Bruntt ◽  
...  
Keyword(s):  
Theoretical Models ◽  
Frequency Separation ◽  
Balmer Line ◽  
Average Amplitude ◽  
Optical Telescope ◽  
Oscillation Modes ◽  
Excess Power ◽  
Large Frequency ◽  
Line Equivalent Width ◽  
Made In

Kjeldsen et al. (1995) detected excess power in the GO subgiant η Boo from measurements of Balmer-line equivalent widths. The excess was at the expected level, and these authors were able to extract frequency separations and individual frequencies which agreed well with theoretical models (Christensen-Dalsgaard et al., 1995; Guenther & Demarque, 1996). A more detailed discussion of theoretical models for η Bootis was given by Di Mauro & Christensen-Dalsgaard (2001).Kjeldsen et al. (1995) estimated the average amplitude of the strongest modes to be 7 times solar, corresponding to 1.6 m/s in velocity. 13 individual oscillation modes were identified consistent with a large frequency separation of 40.3 μHz. We note, however, that a search for velocity oscillations in this star by Brown et al. (1997) failed to detect a signal, setting limits at a level below that expected on the basis of the Kjeldsen et al. result.In this paper we report further observations made in 1998. We observed this star in Balmer-line equivalent width with the 2.5-m Nordic Optical Telescope and in velocity with the 24-inch Lick CAT.

scholarly journals Asteroseismic masses of four evolved planet-hosting stars using SONG and TESS: resolving the retired A-star mass controversy

2020 ◽  
Vol 496 (4) ◽  
pp. 5423-5435
Author(s):  
Sai Prathyusha Malla ◽  
Dennis Stello ◽  
Daniel Huber ◽  
Benjamin T Montet ◽  
Timothy R Bedding ◽  
...  
Keyword(s):  
Stellar Mass ◽  
Frequency Separation ◽  
The Past ◽  
Characteristic Oscillation ◽  
Red Giant ◽  
Stellar Masses ◽  
Mass Dependent ◽  
Large Frequency ◽  
Dual Site ◽  
Made In

ABSTRACT The study of planet occurrence as a function of stellar mass is important for a better understanding of planet formation. Estimating stellar mass, especially in the red giant regime, is difficult. In particular, stellar masses of a sample of evolved planet-hosting stars based on spectroscopy and grid-based modelling have been put to question over the past decade with claims they were overestimated. Although efforts have been made in the past to reconcile this dispute using asteroseismology, results were inconclusive. In an attempt to resolve this controversy, we study four more evolved planet-hosting stars in this paper using asteroseismology, and we revisit previous results to make an informed study of the whole ensemble in a self-consistent way. For the four new stars, we measure their masses by locating their characteristic oscillation frequency, νmax, from their radial velocity time series observed by SONG. For two stars, we are also able to measure the large frequency separation, Δν, helped by extended SONG single-site and dual-site observations and new Transiting Exoplanet Survey Satellite observations. We establish the robustness of the νmax-only-based results by determining the stellar mass from Δν, and from both Δν and νmax. We then compare the seismic masses of the full ensemble of 16 stars with the spectroscopic masses from three different literature sources. We find an offset between the seismic and spectroscopic mass scales that is mass dependent, suggesting that the previously claimed overestimation of spectroscopic masses only affects stars more massive than about 1.6 M⊙.

scholarly journals Asteroseismology of two Kepler detached eclipsing binaries

2020 ◽  
Vol 642 ◽  
pp. A91
Author(s):  
A. Liakos
Keyword(s):  
Theoretical Models ◽  
Eclipsing Binaries ◽  
Pulsation Period ◽  
Oscillation Modes ◽  
Modeling Techniques ◽  
Degree Of Certainty ◽  
Detached Binaries ◽  
Scuti Stars ◽  
Absolute Parameters ◽  
Oscillation Properties

The present work contains light curve, spectroscopic, and asteroseismic analyses for KIC 04851217 and KIC 10686876. These systems are detached eclipsing binaries hosting a pulsating component of δ Scuti type and have been observed with the unprecedented accuracy of the Kepler space telescope. Using ground-based spectroscopic observations, the spectral types of the primary components of the systems were estimated as A6V and A5V for KIC 04851217 and KIC 10686876, respectively, with an uncertainty of one subclass. The present spectral classification, together with literature radial velocity curves, were used to model the light curves of the systems and, therefore, to calculate the absolute parameters of their components with a higher degree of certainty. The photometric data were analysed using standard eclipsing binary modeling techniques, while their residuals were further analysed using Fourier transformation techniques to extract the pulsation frequencies of their host δ Scuti stars. The oscillation modes of the independent frequencies were identified using theoretical models of δ Scuti stars. The distances of the systems were calculated using the relation between the luminosity and the pulsation period for δ Scuti stars. Here, the physical and the oscillation properties of the pulsating components of these systems are discussed and compared with others of the same type. Moreover, using all the currently known cases of δ Scuti stars in detached binaries, updated correlations between orbital and dominant pulsation periods and between log g and pulsation periods are derived. It can concluded that the proximity of the companion plays significant role in the evolution of the pulsational frequencies.

scholarly journals Kepler eclipsing binaries with δ Scuti components and tidally induced heartbeat stars

2015 ◽  
Vol 11 (A29B) ◽  
pp. 648-652
Author(s):  
Zhao Guo ◽  
Douglas R. Gies ◽  
Rachel A. Matson
Keyword(s):  
Binary Stars ◽  
High Frequency ◽  
Eclipsing Binaries ◽  
Frequency Separation ◽  
High Frequency Oscillations ◽  
Orbital Frequency ◽  
Scuti Stars ◽  
Large Frequency ◽  
Δ Scuti Stars ◽  
Stellar Density

Abstractδ Scuti stars are generally fast rotators and their pulsations are not in the asymptotic regime, so the interpretation of their pulsation spectra is a very difficult task. Binary stars, especially eclipsing systems, offer us the opportunity to constrain the space of fundamental stellar parameters. Firstly, we show the results of KIC9851944 and KIC4851217 as two case studies. We found the signature of the large frequency separation in the pulsational spectrum of both stars. The observed mean stellar density and the large frequency separation obey the linear relation in the log-log space as found by Suarez et al. (2014) and García Hernández et al. (2015). Second, we apply the simple ‘one-layer model’ of Moreno & Koenigsberger (1999) to the prototype heartbeat star KOI-54. The model naturally reproduces the tidally induced high frequency oscillations and their frequencies are very close to the observed frequency at 90 and 91 times the orbital frequency.

Probing Convective Mixing in Stellar Interiors with α Centauri A and B

2017 ◽  
Vol 14 (S339) ◽  
pp. 308-308
Author(s):  
M. Joyce ◽  
B. Chaboyer
Keyword(s):  
Optical Observations ◽  
Frequency Separation ◽  
Composition Gradient ◽  
Small Frequency ◽  
Convective Mixing ◽  
Important Constraint ◽  
The Mean ◽  
Stellar Interiors ◽  
Large Frequency ◽  
Better Than

AbstractThe bright nearby binary α Centauri constitutes an excellent laboratory for testing stellar evolution models. The mass, radius, and luminosity of α Cen A and B are known to better than 1% accuracy thanks to recent interferometric and adaptive optical observations, and p-mode oscillations have been observed in both stars. We present new stellar models which fit simultaneously the classical and seismic observations, with particular emphasis on the convective mixing length parameter MLT – the adaptivity of which is necessary to fit the models to observations. The oscillation data provide an important constraint on the models, as the small frequency separation is sensitive to the composition gradient in the core of the stars, while the large frequency separation constrains the mean density of the stars, providing an independent check on the mass and radius.

scholarly journals Observation of Global 160-min Infrared (Differential) Intensity Variation of the Sun

1983 ◽  
Vol 66 ◽  
pp. 21-35
Author(s):  
V.A. Kotov ◽  
S. Koutchmy ◽  
O. Koutchmy
Keyword(s):  
Low Frequency ◽  
Intensity Variation ◽  
Solar Limb ◽  
The Sun ◽  
Average Amplitude ◽  
Instrument Analysis ◽  
Limb Intensity ◽  
Limb Darkening ◽  
Global Fluctuations ◽  
Made In

AbstractThe method developed and the instrument designed for detecting variations of the solar limb darkening at the atmospheric transparency window of the solar opacity minimum region of λ 1.65 µ are described. This differential technique proved to be successful in rejecting undesirable low frequency noises due to the atmosphere and to the instrument. Analysis of observations made in 1977, 1978, and 1981 indicates the persistance of global fluctuations of the IR differential, center-to-limb intensity at the wellknown 160 min period with an average amplitude of about ± 2 x 10-4 in units of the ‘average Sun’ intensity near 1.65 µm.

Band gap Green's functions and localized oscillations

2007 ◽  
Vol 463 (2086) ◽  
pp. 2709-2727 ◽  
Author(s):  
Alexander B Movchan ◽  
Leonid I Slepyan
Keyword(s):  
Band Gap ◽  
Green's Functions ◽  
Green’S Functions ◽  
Discrete Models ◽  
Square Lattice ◽  
Asymptotic Expressions ◽  
Oscillation Modes ◽  
Non Local ◽  
Localized Mode ◽  
Made In

We consider some typical continuous and discrete models of structures possessing band gaps, and analyse the localized oscillation modes. General considerations show that such modes can exist at any frequency within the band gap provided an admissible local mass variation is made. In particular, we show that the upper bound of the sinusoidal wave frequency exists in a non-local interaction homogeneous waveguide, and we construct a localized mode existing there at high frequencies. The localized modes are introduced via the Green's functions for the corresponding uniform systems. We construct such functions and, in particular, present asymptotic expressions of the band gap anisotropic Green's function for the two-dimensional square lattice. The emphasis is made on the notion of the depth of band gap and evaluation of the rate of localization of the vibration modes. Detailed analysis of the extremal localization is conducted. In particular, this concerns an algorithm of a ‘neutral’ perturbation where the total mass of a complex central cell is not changed

Magnetic fields in the solar photosphere

2008 ◽  
Vol 366 (1884) ◽  
pp. 4465-4476 ◽  
Author(s):  
Paul J Bushby
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Active Regions ◽  
Theoretical Models ◽  
Solar Photosphere ◽  
Complex Field ◽  
Theoretical Understanding ◽  
Magnetic Features ◽  
Localized Magnetic Field ◽  
Made In

Recent high-resolution observations of the surface of the Sun have revealed the fine structure of a vast array of complex photospheric magnetic features. Observations of these magnetic field structures have already greatly enhanced our theoretical understanding of the interactions between magnetic fields and turbulent convection, and future photospheric observations will inevitably present new theoretical challenges. In this review, I discuss recent progress that has been made in the modelling of photospheric magnetic fields. In particular, I focus upon the complex field structures that are observed within the umbrae and the penumbrae of sunspots. On a much smaller scale, I also discuss models of the highly localized magnetic field structures that are observed in less magnetically active regions of the photosphere. As the spatial resolution of telescopes has improved over the last few years, it has now become possible to observe these features in detail, and theoretical models can now describe much of this behaviour. In the last section of this review, I discuss some of the remaining unanswered questions.

Intensity Profile of Electron Beam

1970 ◽  
Vol 28 ◽  
pp. 52-53
Author(s):  
S. M. Ohr ◽  
T. S. Noggle
Keyword(s):  
Electron Beam ◽  
Theoretical Models ◽  
Effective Area ◽  
Oak Ridge ◽  
Black And White ◽  
Viewing Screen ◽  
Shadow It ◽  
Electron Dosimetry ◽  
Made In

In situ studies of electron displacement damage in graphite are being made in Oak Ridge using a 200 kV Hitachi HU 200-E electron microscope. Examples of the damage structure that develops in the area upon which the illuminating beam is incident are shown in Fig. 1. The spot structures (both black and white) are identified as clusters of interstitial atoms. It is of particular interest in this study to have accurate electron dosimetry in order to relate the damage structures to theoretical models. In this paper we wish to report on the technique and some preliminary results obtained in measuring the intensity profiles of the electron beam.Measurements of the beam profiles have been made by replacing one of the side windows of the viewing chamber with a 1” brass plate in which is mounted a retractable arm which can insert a Faraday cup into a position on the axis and at a level approximately one-third the distance from the projector lens to the viewing screen. This arrangement allows one to take pictures with the cup in position, and from the shadow it casts determine its effective area in the magnified image of the beam.

scholarly journals Old and New from Multifrequency Astrophysics

2014 ◽  
Vol 1 (1) ◽  
pp. 1-12 ◽  
Author(s):  
Franco Giovannelli ◽  
Lola Sabau-Graziati
Keyword(s):  
Review Paper ◽  
Theoretical Models ◽  
Short Review ◽  
Experimental Results ◽  
Energy Bands ◽  
The Past ◽  
Limited Length ◽  
The Many ◽  
Made In

In this short review paper we comment on some the most important steps that have been made in the past decades for a better understanding of the physics governing our Universe. The results we discuss come from the many groundand-space-based experiments developed for measuring astrophysical sources in various energy bands. These experimental results are discussed within the framework of current theoretical models. Because of the limited length of this paper, we have selected only a few topics that, in our opinion, have been crucial for the progress of our understanding of the physics of cosmic sources.

scholarly journals Pulsations of rapidly rotating stars with compositional discontinuities

2013 ◽  
Vol 9 (S301) ◽  
pp. 169-172 ◽  
Author(s):  
Daniel R. Reese ◽  
Francisco Espinosa Lara ◽  
Michel Rieutord
Keyword(s):  
Frequency Separation ◽  
Rotating Stars ◽  
Physical Origin ◽  
Numerical Accuracy ◽  
Frequency Spectra ◽  
Acoustic Modes ◽  
Low Degree ◽  
Rapidly Rotating Stars ◽  
Theoretical Considerations ◽  
Large Frequency

AbstractRecent observations of rapidly rotating stars have revealed the presence of regular patterns in their pulsation spectra. This has raised the question as to their physical origin, and, in particular, whether they can be explained by an asymptotic frequency formula for low-degree acoustic modes, as recently discovered through numerical calculations and theoretical considerations. In this context, a key question is whether compositional/density gradients can adversely affect such patterns to the point of hindering their identification. To answer this question, we calculate frequency spectra using two-dimensional ESTER stellar models. These models use a multi-domain spectral approach, allowing us to easily insert a compositional discontinuity while retaining a high numerical accuracy. We analyse the effects of such discontinuities on both the frequencies and eigenfunctions of pulsation modes in the asymptotic regime. We find that although there is more scatter around the asymptotic frequency formula, the semi-large frequency separation can still be clearly identified in a spectrum of low-degree acoustic modes.

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