The nature of the light variability of the silicon star HR 7224

Krtička, Jiřı́; Mikulášek, Zdeněk; Henry, Gregory W.; Zverko, J.; Ziznovsky, J.; Skalický, Jan; Zvěřina, Pavel

doi:10.1051/0004-6361/200811123

Cited by 62 publications

(75 citation statements)

References 50 publications

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“…Mikulášek et al 2007Mikulášek et al , 2008a. Bright photometric spots seem to be closely connected with overabundance regions of Si or Fe, and the mechanism of the origin of their contrast in the optical spectrum region is well described in Krtička et al (2009).…”

Section: Introductionmentioning

confidence: 90%

Surface structure of the CoRoT CP2 target star HD 50773

Lüftinger¹,

Fröhlich

Weiß³

et al. 2010

A&A

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Aims. We compare surface maps of the chemically peculiar star HD 50773 produced with a Bayesian technique and based on high quality CoRoT photometry with those derived from rotation phase resolved spectropolarimetry. The goal is to investigate the correlation of surface brightness with surface chemical abundance distribution and the stellar magnetic surface field. Methods. The rotational period of the star was determined from a nearly 60 days long continuous light curve obtained during the initial run of CoRoT. Using a Bayesian approach to star-spot modelling, which in this work is applied for the first time for the photometric mapping of a CP star, we derived longitudes, latitudes and radii of four different spot areas. Additional parameters like stellar inclination and the spot's intensities were also determined. The CoRoT observations triggered an extensive ground-based spectroscopic and spectropolarimetric observing campaign and enabled us to obtain 19 different high resolution spectra in Stokes parameters I and V with NARVAL, ESPaDOnS, and SemelPol spectropolarimeters. Doppler and Magnetic Doppler imaging techniques allowed us to derive the magnetic field geometry of the star and the surface abundance distributions of Mg, Si, Ca, Ti, Cr, Fe, Ni, Y, and Cu. Results. We find a dominant dipolar structure of the surface magnetic field. The CoRoT light curve variations and abundances of most elements mapped are correlated with the aforementioned geometry: Cr, Fe, and Si are enhanced around the magnetic poles and coincide with the bright regions on the surface of HD 50773 as predicted by our light curve synthesis and confirmed by photometric imaging.

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Section: Introductionmentioning

confidence: 90%

Surface structure of the CoRoT CP2 target star HD 50773

Lüftinger¹,

Fröhlich

Weiß³

et al. 2010

A&A

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“…Krticka et al (2007) have also demonstrated that the light curve of the heliumstrong star HD 37776, an object quite comparable to a Cen in fundamental properties and in having quite pronounced line profile variations, can be almost completely accounted for by the inhomogeneous surface distribution of silicon and helium over the star's surface and the bound-free transitions of these elements and not surface temperature variations. More recent work on a cooler Ap star, HR 7224, also suggests that surface temperature variations do not exist in Ap stars (Krticka et al 2009). …”

Section: Doppler Imagingmentioning

confidence: 98%

Doppler imaging of the helium-variable star a Centauri

Bohlender¹,

Rice²,

Hechler³

2010

A&A

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Aims. The helium-peculiar star a Cen exhibits interesting line profile variations of elements such as iron, nitrogen and oxygen in addition to its well-known extreme helium variability. The objective of this paper is to use new high signal-to-noise, high-resolution spectra to perform a quantitative measurement of the helium, iron, nitrogen and oxygen abundances of the star and determine the relation of the concentrations of the heavier elements on the surface of the star to the helium concentration and perhaps to the magnetic field orientation. Methods. Doppler images have been created for the elements helium, iron, nitrogen and oxygen using the programs described in earlier papers by Rice and others. An alternative surface abundance mapping code has been used to model the helium line variations after our Doppler imaging of certain individual helium lines produced mediocre results. Results. Doppler imaging of the helium abundance of a Cen confirms the long-known existence of helium-rich and helium-poor hemispheres on the star and we measure a difference of more than two orders of magnitude in helium abundance from one side of the star to the other. Helium is overabundant by a factor of about 5 over much of the helium-rich hemisphere. Of particular note is our discovery that the helium-poor hemisphere has a very high abundance of 3 He, approximately equal to the 4 He abundance. a Cen is therefore a new member of the small group of helium-3 stars and the first well-established magnetic member of the class. For the three metals investigated here, there are two strong concentrations of abundance near the equator at longitude roughly 135 • consistent with the positive magnetic maximum and two somewhat weaker concentrations of abundance near longitude 315 • on the equator near where the helium concentration is centered and roughly where the negative peak of the magnetic field would be found. Another strong concentration is found near the equator at about longitude 45 • and this is not explainable in terms of any simple symmetry with the helium abundance or the apparent magnetic field main polar locations.

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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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The nature of the light variability of the silicon star HR 7224

Cited by 62 publications

References 50 publications

Surface structure of the CoRoT CP2 target star HD 50773

Surface structure of the CoRoT CP2 target star HD 50773

Doppler imaging of the helium-variable star a Centauri

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

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