scholarly journals Bolometric corrections of stellar oscillation amplitudes as observed by the Kepler, CoRoT, and TESS missions

2019 ◽  
Vol 489 (1) ◽  
pp. 1072-1081 ◽  
Author(s):  
Mikkel N Lund

ABSTRACT A better understanding of the amplitudes of stellar oscillation modes and surface granulation is essential for improving theories of mode physics and the properties of the outer convection zone of solar-like stars. A proper prediction of these amplitudes is also essential for appraising the detectability of solar-like oscillations for asteroseismic analysis. Comparisons with models, or between different photometric missions, are enabled by applying a bolometric correction, which converts mission-specific amplitudes to their corresponding bolometric (full light) values. We derive the bolometric correction factor for amplitudes of radial oscillation modes and surface granulation as observed by the Kepler, CoRoT, and TESS missions. The calculations are done assuming a stellar spectrum given by a black-body as well as by synthetic spectral flux densities from 1D model atmospheres. We derive a power-law and polynomial relations for the bolometric correction as a function of temperature from the black-body approximation and evaluate the deviations from adopting a more realistic spectrum. Across the full temperature range from 4000 to 7500 K, the amplitudes from TESS are in the black-body approximation predicted to be a factor ∼0.83–0.84 times those observed by Kepler. We find that using more realistic flux spectra over the black-body approximation can change the bolometric correction by as much as ${\sim }30{{\ \rm per\ cent}}$ at the lowest temperatures, but with a change typically within ${\sim }5\!-\!10 {{\ \rm per\ cent}}$ around a Teff of 5500–6000 K. We find that after Teff, the bolometric correction most strongly depends on $\rm [M/H]$, which could have an impact on reported metallicity dependences of amplitudes reported in the literature.

2007 ◽  
Vol 463 (3) ◽  
pp. 1211-1214 ◽  
Author(s):  
T. Appourchaux ◽  
J. Leibacher ◽  
P. Boumier

2010 ◽  
Vol 6 (S272) ◽  
pp. 416-417
Author(s):  
Finny Oktariani ◽  
Atsuo T. Okazaki

AbstractWe consider the effect of density distribution evolution on the global one-armed oscillation modes in disks around Be stars. Previous studies of global oscillations in Be disks assumed a power-law density distribution of the disk. However, observational results show that some Be stars exhibit evidence of formation and dissipation of the equatorial disk. This causes the disk density distribution can be far from a power-law form. Performing calculations for several times in the disk formation and dissipation stages, we find one-armed modes confined to the inner part of the disk in both stages. In the disk formation stage, the oscillation frequency stays approximately constant after the disk is fully developed. In the dissipation stage of the Be disk, the local precession frequency is, in general, higher than in the disk formation stage. Thus, we expect that V/R periods become shorter as the innermost part of the disk starts to accrete.


The theory of stellar evolution aims at predicting the luminosity L and radius R of a star as a function of its mass M , its initial composition, and its age. As the time scales are so long, comparison with observation must necessarily be indirect. A convenient method is to select clusters of stars, all born from similar material and at times close together compared with the evolutionary time scale, leaving just the mass as a parameter. However, the paucity of well-determined stellar masses forces us to eliminate the mass between the ( M, L ) and ( M, R ) relations. The ( L, R ) relation is studied indirectly by introducing the effective temperature T e , defined by L = (¼ acT 4 e ) (4 πR 2 ), where c is the velocity of light, and a the stefan-Boltzmann constant. Thus T e is the temperature of a black body having the same surface brightness as the star. The theorist’s ‘Hertzsprung-Russell diagram’ is a plot of log T e on a horizontal scale, increasing to the left, against log ( L/L ʘ ), where L ʘ is the solar luminosity. The observer’s diagram is a plot of V , the absolute magnitude in the visual waveband, against the colour index ( B ─ V ), where B is the blue magnitude. The transformation of one diagram into the other by means of the bolometric correction and the T e , ( B ─ V relation is still subject to considerable uncertainties at the extremes of high and low T e .


1991 ◽  
Vol 130 ◽  
pp. 504-506
Author(s):  
L.A. Pustil’nik

AbstractA theoretical interpretation is offered for the power-law dependence of the flare occurrence rate in red flare dwarfs. Flares on red dwarfs are regarded as being physically akin to solar flares, with the energy source being the magnetic field. A power law flare energy relation then emerges naturally. Model estimates of the corresponding spectral index β fit the observed values in most flare stars. Within the bounds of the interpretation offered the energy dependence of a flare event is determined by the character of the turbulence in the convection zone. The observed parameters of the dependence can be used to diagnose the character of the turbulence in the convection zones of flare stars.-


2004 ◽  
Vol 202 ◽  
pp. 356-358
Author(s):  
G. Meeus ◽  
J. Bouwman ◽  
L.B.F.M. Waters ◽  
C. Waelkens ◽  
M.E. van den Ancker

We present Infrared Space Observatory (ISO) spectra of 14 isolated Herbig Ae/Be stars. The IR spectra were combined with photometric data from the UV to the sub-mm region. We defined two key groups, based upon the spectral shape of the IR region. The results can be summarized as follows (see also Meeus et al. 2001): (1) the continuum of the IR to sub-mm region can be reconstructed by the sum of a power-law and a cool component, which can be represented by a black body. Possible locations for these components are an optically thick, geometrically thin disc (power-law component) and an optically thin flared region (black body); (2) remarkably, some sources lack the silicate bands; (3) PAH bands are present in at least 50% of our sample; with one exception, PAHs are not present in sources which only show a power-law continuum in the IR; (4) the dust in HAEBE stars shows strong evidence for coagulation; this dust processing is unrelated to any of the central star properties.


2021 ◽  
Vol 503 (1) ◽  
pp. 603-613
Author(s):  
Wenbin Lu ◽  
Jim Fuller ◽  
Yael Raveh ◽  
Hagai B Perets ◽  
Ting S Li ◽  
...  

ABSTRACT The hyper-velocity star S5-HVS1, ejected 5 Myr ago from the Galactic Centre at 1800 km s−1, was most likely produced by tidal break-up of a tight binary by the supermassive black hole SgrA*. Taking a Monte Carlo approach, we show that the former companion of S5-HVS1 was likely a main-sequence star between 1.2 and 6 M⊙ and was captured into a highly eccentric orbit with pericentre distance in the range of 1–10 au and semimajor axis about 103 au. We then explore the fate of the captured star. We find that the heat deposited by tidally excited stellar oscillation modes leads to runaway disruption if the pericentre distance is smaller than about $3\rm \, au$. Over the past 5 Myr, its angular momentum has been significantly modified by orbital relaxation, which may stochastically drive the pericentre inwards below $3\rm \, au$ and cause tidal disruption. We find an overall survival probability in the range 5 per cent to 50 per cent, depending on the local relaxation time in the close environment of the captured star, and the initial pericentre at capture. The pericentre distance of the surviving star has migrated to 10–100 au, making it potentially the most extreme member of the S-star cluster. From the ejection rate of S5-HVS1-like stars, we estimate that there may currently be a few stars in such highly eccentric orbits. They should be detectable (typically $K_{\rm s}\lesssim 18.5\,$ mag) by the GRAVITY instrument and by future Extremely Large Telescopes and hence provide an extraordinary probe of the spin of SgrA*.


1980 ◽  
Vol 5 ◽  
pp. 497-500
Author(s):  
Douglas Keeley

The structure of red giant stars allows non-radial oscillation modes which propagate as p-modes near the surface, to propagate below the convection zone as g-modes with very high radial wave number [Dziembowski (1971, 1977), Shibahashi and Osaki (1976)]. Under some conditions the oscillations in these two propagation regions can be treated as virtually independent normal modes [Shibahashi and Osaki (1976)]. This paper examines the situation in which this approximation is not good, and discusses possible observational consequences of the interaction of the two propagation regions.The linearized differential equations describing non-radial adiabatic oscillations in stars can be written in the form, 1a1b


Author(s):  
Paul D. Lasky

AbstractNeutron stars are excellent emitters of gravitational waves. Squeezing matter beyond nuclear densities invites exotic physical processes, many of which violently transfer large amounts of mass at relativistic velocities, disrupting spacetime and generating copious quantities of gravitational radiation. I review mechanisms for generating gravitational waves with neutron stars. This includes gravitational waves from radio and millisecond pulsars, magnetars, accreting systems, and newly born neutron stars, with mechanisms including magnetic and thermoelastic deformations, various stellar oscillation modes, and core superfluid turbulence. I also focus on what physics can be learnt from a gravitational wave detection, and where additional research is required to fully understand the dominant physical processes at play.


1988 ◽  
Vol 123 ◽  
pp. 155-160
Author(s):  
D.O. Gough ◽  
M.J. Thompson

Magnetic fields contribute to the splitting of the degeneracy of modes of like order and degree. The splitting is estimated for some simple hypothetical toroidal magnetic field configurations in the sun, and the results are compared with previous asymptotic estimates. Splitting by a field confined to a thin layer at the base of the convection zone is found not to agree with recent measurements.


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