Modelling the light variability of the Ap star<i>ε</i> Ursae Majoris

Shulyak, D.; Krtička, Jiřı́; Mikulášek, Zdeněk; Kochukhov, O.; Lüftinger, T.

doi:10.1051/0004-6361/201015094

Cited by 51 publications

(62 citation statements)

References 42 publications

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“…The theoretical light curves can be predicted using model atmospheres calculated with actual abundances from abundance maps of individual stars. A comparison of such theoretical light curves with observed ones supports the current picture of the light variability of CP stars (Krtička et al 2009(Krtička et al , 2012Shulyak et al 2010). This approach cannot be used for rotationally variable normal A stars because the expected abundance and line profile variations are prohibitively small for abundance mapping.…”

Section: Introductionsupporting

confidence: 79%

Visual and ultraviolet flux variability of the bright CP starθAurigae

Krtička

Mikulášek

Lüftinger

et al. 2015

A&A

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Context. Chemically peculiar stars of the upper part of the main sequence show periodical variability in line intensities and continua, modulated by the stellar rotation, which is attributed to the existence of chemical spots on the surface of these stars. The flux variability is caused by the changing redistribution rate of the radiative flux predominantly from the short-wavelength part of the spectra to the long-wavelength part, which is a result of abundance anomalies. Many details of this process are still unknown. Aims. We study the nature of the multi-spectral variability of one of the brightest chemically peculiar stars, θ Aur. Methods. We predict the flux variability of θ Aur from the emerging intensities calculated for individual surface elements of the star taking into account horizontal variation of chemical composition. The surface chemical composition was derived from Doppler abundance maps. Results. The simulated optical variability in the Strömgren photometric system and the ultraviolet flux variability agree well with observations. The IUE flux distribution is reproduced in great detail by our models in the near ultraviolet region. A minor disagreement remains between the observed and predicted fluxes in the far ultraviolet region. The resonance lines of magnesium and possibly also some lines of silicon are relatively weak in the ultraviolet domain, which indicates non-negligible vertical abundance gradients in the atmosphere. We also derive a new period of the star, P = 3.618 664(10) d, from all available photometric and magnetic measurements and show that the observed rotational period is constant over decades. Conclusions. The ultraviolet and visual variability of θ Aur is mostly caused by silicon bound-free absorption and chromium and iron line absorption. Manganese also contributes to the variability, but to a lesser extent. These elements redistribute the flux mainly from the far-ultraviolet region to the near-ultraviolet and optical regions in the surface abundance spots. The light variability is modulated by the stellar rotation. The ultraviolet domain is key for understanding the properties of chemically peculiar stars. It provides a detailed test for surface abundance models and comprises many lines that originate from states with a low excitation potential, which enable detecting vertical abundance gradients.

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Section: Introductionsupporting

confidence: 79%

Visual and ultraviolet flux variability of the bright CP starθAurigae

Krtička

Mikulášek

Lüftinger

et al. 2015

A&A

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“…However, as can be seen from e.g. Shulyak et al (2010a) and Krtička et al (2012), the amplitude of this variability is rather small to influence the derived effective temperatures much. For instance, using Adelman's spectrophotometric catalog, we find that the relative characteristic correction to the effective temperatures due to flux variability is only a few ten K's for all three target stars.…”

Section: Observationsmentioning

confidence: 94%

Fundamental parameters of bright Ap stars from wide-range energy distributions and advanced atmospheric models

Shulyak

Ryabchikova

Kochukhov

2013

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Aims. As a well-established procedure for the vast majority of normal main-sequence stars, determination of atmospheric and stellar parameters turns to be a challenging process in case of magnetic chemically peculiar stars. Inhomogeneous distribution of chemical elements and strong magnetic fields make most of the standard photometric and spectroscopic calibrations inapplicable for this class of stars. In this work we make use of available observed energy distributions calibrated to absolute units, stellar parallaxes, highresolution spectroscopic observations, and advanced stellar atmosphere models to derive parameters of three bright Ap stars: 33 Lib, γ Equ, and β CrB. Methods. Model atmospheres and fluxes were computed with the LLmodels code. Synth3 and Synthmag codes were used to compute profiles of individual spectral lines involved in abundance analysis. Results. For each of the stars, we construct a self-consistent atmospheric models assuming normal and depleted helium compositions and derive empirically stratification profiles of certain elements. The effective temperatures and surface gravities are found from the simultaneous fit to spectroscopic, photometric, and spectrophotometric observations calibrated to absolute units. We show that using advanced model atmospheres and accurate stellar parallaxes allows one to derive stellar radii with high accuracy, and these are consistent with those obtained from independent but more complicated interferometric observations.

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“…CPs are stars in the upper part of the main-sequence with B or A spectral types, which present an inhomogeneous surface distribution of chemical elements and yield near-sinusoidal light curves as a result of stellar rotation. Variability is often attributed to strong and stable magnetic fields (e.g., Lüftinger et al 2010;Krtička et al 2012), although cases with weak magnetic fields have been reported as well (e.g., Krtička et al 2009;Shulyak et al 2010). The amplitude of the light variations decreases with increasing wavelength (Catalano et al 1991).…”

Section: Candidate Rotating Variables/overcontact Binariesmentioning

confidence: 99%

Variability of massive stars with known spectral types in the Small Magellanic Cloud using 8 years of OGLE-III data

Kourniotis

Bonanos

Soszyński

et al. 2014

A&A

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We present a variability study of 4646 massive stars in the Small Magellanic Cloud (SMC) with known spectral types from the catalog of Bonanos et al. (2010) using the light curves from the OGLE-III database. The goal is to exploit the time domain information available through OGLE-III to gain insight into the processes that govern the evolution of massive stars. This variability survey of massive stars with known spectral types is larger than any previous survey by a factor of 7. We find that 60% of our sample (2766 stars) show no significant variability and 40% (1880 stars) exhibit variability distributed as follows: 807 stars display low-amplitude stochastic variability with fluctuations in the I-band of up to 0.05 mag, 443 stars present irregular variability of higher amplitude (76% of these are reported as variables for the first time), 205 are eclipsing binaries (including 101 newly discovered systems), 50 are candidate rotating variables, 126 are classical Cepheids, 188 stars exhibit short-term sinusoidal periodicity (P < 3 days) making them candidate "slowly pulsating B stars" and non-radial Be pulsators, and 61 periodic stars exhibit longer periods. We demonstrate the wealth of information provided in the time domain, by doubling the number of known massive eclipsing binary systems and identifying 189 new candidate early-type Be and 20 Oe stars in the SMC. In addition, we find that ∼80% of Be stars are photometrically variable in the OGLE-III time domain and provide evidence that short-term pulsating stars with additional photometric variability are rotating close to their break-up velocity.

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Modelling the light variability of the Ap starε Ursae Majoris

Cited by 51 publications

References 42 publications

Visual and ultraviolet flux variability of the bright CP starθAurigae

Visual and ultraviolet flux variability of the bright CP starθAurigae

Fundamental parameters of bright Ap stars from wide-range energy distributions and advanced atmospheric models

Variability of massive stars with known spectral types in the Small Magellanic Cloud using 8 years of OGLE-III data

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