17 December, 2018 at 1:00 PM
On the rotation period of the O giant ξ Persei: a magnetic star?
Natallia Sudnik
(The Maxim Tank Belarusian State Pedagogical University)
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 ∼ 300 G. We aim to identify regions in spectra of the O7.5III(n)((f)) star ξ 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 ξ Per, derived from the N IV λ1718 wind line in 12 yr of IUE data. Since this period can be ruled out as due to nonradial pulsations, we predict that ξ 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 ∼ 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 ∼ 56, and hence β should be near 90− 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.
5 December 2018at 2:00 PM
Using hot subdwarf binaries to constrain RLOF models
Joris Vos
(The Institute of Physic and Astronomy, University of Potsdam, Germany)
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.
28 November, 2018 at 1:30 PM
HDUST and SHELLSPEC codes – two tools for modelling the stellar observables
Mohammad Ghoreyshi
(Tartu Observatory, Estonia)
31 October, 2018 at 11:00 AM
Binary stars as the key to understand planetary nebulae
Henri Boffin
(ESO Garching, Germany)
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.
14 August, 2018 at 11:00 AM
Spectral research of young stars at Shamakhy Astrophycial Observatory
Gunel Bahaddinova
(Shamakhy Astrophycial Observatory, Azerbaijan)
7 February, 2018 at 2:00 PM
OPERA tool for reduction of echelle spectra from OES
Roaman Grossova
(Masaryk University, Brno, Czech Republic)
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.
27 September 2017, at 1:00 PM
Binary stars with RR Lyrae component – why so rare?
Marek Skarka
(Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Science)
Large portion of stars of all spectral types is bound in binary systems. However, there is one spectacular exception. Among 100 000 catalogized stars of RR Lyrae type only several tens of binary candidates are known and none of them has been unambiguously confirmed yet. Could this lack of binaries be real? Why it is so difficult to discover RR Lyrae star in binary system? Are there any observational limitations? What methods are suitable for the search for such binaries? I will discuss all these questions, give an overview about the progress in last three years, and will show why many of the candidates could actually be false positives.
23 August, 2017 at 10:30 AM
Instrumentation at Astronomical Institute in the High Tatras-Slovakia
Martin Vanko
(Astronomical Institute of Slovak Academy of Sciences)
Astronomical Institute of the Slovak Academy of Sciences (AI SAS) runes several observatories located at different places in the High Tatras. Our telescopes are equipped with new high-end post-focus instruments producing valuable data in the field of the stellar and exoplanetary astronomy. First results will be presented in my talk. Finally, I will present existing and future projects between our Institutes.
18 May, 2017 at 11:00 AM
Blue atmosphere or stellar activity – is the blue atmosphere of the exoplanet GJ 3470 b real?
Silvia Kunz
(Thueringer Landessternwarte Tautenburg, Germany)
One of the big challenges in the field of exoplanet atmospheres is to distinguish the influence of stellar activity on transit measurements from real effects that can be seen in photometric measurements in different bands. Oshagh et al. (2014) assumed that an increase of planetary radii in the blue part of the spectrum can be explained with the presence of a hot plage region on the stellar surface. In particular they stated that the measured blue atmosphere of the sub-Uranus-mass low-density planet GJ 3470b could be mimicked by a plage region that covers only 2.56% of the star’s surface. We have developed a method to exclude the influence of plage regions on transit measurements. The Ca II H,K lines are tracers of stellar activity – especially of plage regions. If plage regions were occulted those lines should vary during transit. We therefore have observed one transit of GJ 3470 b with the high-resolution UVES spectrograph at the 8.2 m Very Large Telescope. We have found that the difference of the Ca II H,K lines in- and out-of-transit is only 0.67 ± 0.22% and have determined a magnetic filling factor of about 10–15%. In order to confirm the Rayleigh scattering slope we have analyzed the planet‘s lightcurve by observing three transits with the low-resolution OSIRIS spectrograph at the 10.4 m Gran Telescopio Canarias. With those almost simultaneous measurements of GJ3470b‘s transit we were able to confirm its Rayleigh scattering slope towards the blue.”