{"id":3862,"date":"2023-11-30T09:24:17","date_gmt":"2023-11-30T08:24:17","guid":{"rendered":"https:\/\/stel.asu.cas.cz\/en\/?page_id=3862"},"modified":"2024-05-21T16:58:56","modified_gmt":"2024-05-21T14:58:56","slug":"department-seminar-2018","status":"publish","type":"page","link":"https:\/\/stel.asu.cas.cz\/en\/seminars\/department-seminars\/department-seminar-2018\/","title":{"rendered":"Department Seminar 2018"},"content":{"rendered":"\n

17 December, 2018 at 1:00 PM<\/span><\/h4>\n\n\n\n

On the rotation period of the O giant \u03be Persei: a magnetic star?<\/span><\/h3>\n\n\n\n

Natallia Sudnik<\/strong><\/h3>\n\n\n\n

(The Maxim Tank Belarusian State Pedagogical University)<\/em><\/p>\n\n\n\n

Many spectral lines in OB stars show unexplained variability on a rotational timescale. This occurs for example in the so-called discrete absorption components (DACs) in UV wind-line profiles and in many wind-sensitive optical lines. This variability is generally considered to be cyclical (like sunspots), rather than periodic. The absence of strict periodicity is in accordance with the lack of evidence for a permanent magnetic field, with typical upper limits of \u223c 300 G. We aim to identify regions in spectra of the O7.5III(n)((f)) star \u03be Persei that are formed very close to the star and which suffer a minimum of contamination with disturbing features like doublet overlap or irregular surface phenomena which may prevent the detection of a periodic signal. We present strong evidence for a rotation period of 2.0406 d of the \u03be Per, derived from the N IV \u03bb1718 wind line in 12 yr of IUE data. Since this period can be ruled out as due to nonradial pulsations, we predict that \u03be Per has a (corotating) magnetic dipole field. We calculate the most favorable phase to attempt new magnetic measurements. In contrast to earlier work, we can exclude \u223c 4 d as the rotation period, since this is constrained by the stellar parameters. The sinusoidal behavior implies that only one magnetic pole is visible, which gives i \u223c 56, and hence \u03b2 should be near 90\u2212 i = 34. We propose that the azimuthal distribution of strong DACs corresponds to the location of a magnetic pole on the surface. The crucial observational test consists of detecting a magnetic field.<\/p>\n\n\n\n

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5 December, 2018 at 2:00 PM<\/span><\/h4>\n\n\n\n

Using hot subdwarf binaries to constrain RLOF models<\/span><\/h3>\n\n\n\n

Joris Vos<\/strong><\/h3>\n\n\n\n

(The Institute of Physic and Astronomy, University of Potsdam, Germany)<\/em><\/p>\n\n\n\n

Hot subdwarf B (sdB) stars are evolved core helium burning stars that have lost most of their hydrogen envelope due to binary interaction on the red giant branch. As sdB stars in wide binary systems can only be created by stable Roche lobe overflow, they are a great test sample to constrain the theoretical models for stable mass loss on the red giant branch. We have setup a long term monitoring program using high resolution spectrographs on different telescopes to create a sample of solved long period sdB binaries. An important advantage of using wide sdB binaries in these studies is that all of them are double lined binaries, and the GAIA data shows that it is a uniform population of canonical sdB stars. This way the sdB+MS binaries provide much stronger constraints on theoretical models than many other systems. The first results of our observing program are now available. We found two main features in the orbital parameters. The majority of the systems has eccentric orbits with systems on longer orbital period having a higher eccentricity. As these systems have undergone mass loss near the tip of the RGB, circularisation theory predicts them to be circularized. Our observations suggest that efficient eccentricity pumping mechanisms are active during the mass loss phase. A second finding is a strong correlation between the mass ratio and the orbital period. Using binary evolution models, this relation is used to derive an upper limit on the critical mass ratio for stable RLOF which depends on the orbital period of the system. Furthermore a split in the P-q relation seems to indicate two different groups with somewhat different formation histories.<\/p>\n\n\n\n

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28 November, 2018 at 1:30 PM<\/span><\/h4>\n\n\n\n

HDUST and SHELLSPEC codes – two tools for modelling the stellar observables<\/span><\/h3>\n\n\n\n

Mohammad Ghoreyshi<\/strong><\/h3>\n\n\n\n

(Tartu Observatory, Estonia)<\/em><\/p>\n\n\n\n

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31 October, 2018 at 11:00 AM<\/span><\/h4>\n\n\n\n

Binary stars as the key to understand planetary nebulae<\/span><\/h3>\n\n\n\n

Henri Boffin<\/strong><\/h3>\n\n\n\n

(ESO Garching, Germany)<\/em><\/p>\n\n\n\n

Binarity and mass transfer appear to play a key role in the shaping and, most likely, in the formation of planetary nebulae (PNe), thereby explaining the large fraction of axisymmetric morphologies. I present the binary hypothesis for PNe and its current status. Recent discoveries have led to a dramatic increase in the number of post-common envelope binary central stars of PNe, thereby allowing us to envisage statistical studies. Moreover, these binary systems let us study in detail the mass transfer episodes before and after the common envelope, and I present the evidences for mass transfer – and accretion – prior to the common envelope phase.<\/p>\n\n\n\n

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14 August, 2018 at 11:00 AM<\/span><\/h4>\n\n\n\n

Spectral research of young stars at Shamakhy Astrophycial Observatory<\/span><\/h3>\n\n\n\n

Gunel Bahaddinova<\/strong><\/h3>\n\n\n\n

(Shamakhy Astrophycial Observatory, Azerbaijan)<\/em><\/p>\n\n\n\n

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7 February, 2018 at 2:00 PM<\/span><\/h4>\n\n\n\n

OPERA tool for reduction of echelle spectra from OES<\/span><\/h3>\n\n\n\n

Romana Grossova<\/strong><\/h3>\n\n\n\n

(Masaryk University, Brno, Czech Republic)<\/em><\/p>\n\n\n\n

OPERA is an open-source software package developed by a CFHT scientific group in Hawaii for reducing echelle data from ESPaDOnS. Later on, it was adapted to several other instruments, including OES. In comparison with the reduction software IRAF, OPERA was able to solve a long-standing problem of tilted lines in the OES spectra. A user-friendly GUI framework was developed for the fast routine reduction of your scientific data.<\/p>\n\n\n\n

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<\/p>\n","protected":false},"excerpt":{"rendered":"

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