Dubravka Kotnik-Karuza

Magnetic field of a cylindrical coil

We calculate the magnetic fields of cylindrical coils due to a surface current and a volume current and compare our theoretical results to measured magnetic fields of two coil types: single-layer solenoid and cylindrical thick coil by a simple experimental apparatus. Good agreement is found with the theoretical results.

The effect of dust obscuration in RR Telescopii on optical and IR long-term photometry and Fe II emission lines

Aims. Infrared and optical photometric and spectroscopic observations of the symbiotic nova RR Tel are used to study the effects and properties of dust in symbiotic binaries containing a cool Mira component, as well as showing “obscuration events” of increased absorption, which are typical for such Miras. Methods. A set of photometric observations of the symbiotic nova RR Tel in different wavelength bands – visual from 1949 to 2002 and near-infrared (JHKL) from 1975 to 2002 – are presented. The variability due to the normal Mira pulsation was removed from the JHKL data, which were then compared with the American Association of Variable Star Observers’ (AAVSO) visual light curve. The changes of the Fe II emission line fluxes during the 1996-2000 obscuration episode were studied in the optical spectra taken with the Anglo-Australian telescope. Results. We discuss the three periods during which the Mira component was heavily obscured by dust as observed in the different wavelength bands. A change in the correlations of J with other infrared magnitudes was observed with the colour becoming redder after JD 2 446 600. Generally, J−K was comparable, while K −L was larger than typical values for single Miras. A distance estimate of 2.5 kpc, based on the IR data, is given. A larger flux decrease for the permitted than for the forbidden Fe II lines, during the obscuration episode studied, has been found. There is no evidence for other correlations with line properties, in particular with wavelength, which suggests obscuration due to separate optically thick clouds in the outer layers. Conclusions.

The region of Fe II emission line formation of the symbiotic nova RR Telescopii

In our investigation of the region of formation of the Fe II emission lines in RR Tel, we have applied the SAC method to the optical Fe II emission line fluxes measured by Crawford et al. (1999). It is possible to determine physical parameters of the line emitting region, because of the presence both of lines with large and much smaller optical thicknesses. The values we obtained, given in Tables 3 and 4, are limits in most cases. The upper limit to the excitation temperature of the metastable levels in the permitted line region of 6600 K, is close to the value of this temperature in the forbidden line region. Other excitation temperature limits corresponding to level population ratios were also found. The permitted lines are formed in a region with a radius between 1:8 10 12 cm and 1:6 10 14 cm, while the forbidden lines are formed in a region with a minimum radius of 5:3 10 12 cm. The populations of the lower levels of the permitted lines indicate a minimum column density of Fe+ of 3:0 10 18 atoms cm 2 and, by assuming cosmic abundances, to a minimum column density of 7:5 10 22 atoms cm 2 for H. If we assume a minimum radius of 1:0 10 14 cm, which is supposed to be that of dust condensation of the cool Mira component of this symbiotic binary, a minimum mass loss rate of 3:510 6 Mo yr 1 is found. Our results support a model according to which both the permitted and the forbidden lines are formed in the wind of the cool Mira component above the regions where absorption by dust is important. The forbidden and the permitted lines are not formed in quite the same region, the former being most probably formed further out in the part of an accelerated wind which is ionized by the hot component.

Modelling of dust around the symbiotic Mira RR Telescopii during obscuration epochs

Context. Symbiotic Miras represent a class of peculiar binaries whose nature is still not well understood. Physical properties of the circumstellar dust and associated physical mechanisms play an important role in understanding the evolution of symbiotic binaries and the interaction between their components. We present a model of inner dust regions around the cool Mira component of the symbiotic nova RR Tel based on the near-IR terrestrial photometry and infrared ISO spectra. Aims. Our goal is to find a comprehensive and consistent model of the circumstellar inner dust regions around the Mira component that can explain the observed photometric and spectroscopic features in the near- and mid-infrared. Methods. Available JHKL photometric observations from South African Astronomical Observatory were collected and corrected for Mira pulsations as well as for interstellar reddening to follow temporal changes of the near-infrared colours. Spectral energy distributions (SEDs) from 1 to 13 μm during obscuration epoch were reconstructed with the simultaneously available ISO/SWS spectra and JHKL magnitudes. The dust properties were determined by modelling both the reconstructed SEDs and the near-IR colours using the DUSTY numerical code. This 1D code solves radiative transfer through the circumstellar dust by calculating the dust temperature profile assuming spherical symmetry. Results. The Mira pulsation period of 387 days was found and confirmed with two independent fitting methods. A long-term variation of ∼7000 days, which cannot be attributed to orbital motion, was obtained from the analysis of the near-IR magnitudes. Reconstructed infrared SEDs were modelled successfully by a single dust shell with dust distribution enhanced by radiatively driven stellar winds. Mira temperature, dust sublimation temperature, grain diameter, density distribution, and optical depth have been obtained. Our model shows a maximum dust grain diameter of 4 μm, which is larger than expected and can be explained by grain growth in conditions of increased mass loss during obscuration epochs. Obscurations in the near-IR can be understood as a result of change of the dust optical depth and of the mass loss rate of Mira component. Change of the dust temperature on the inner boundary of the dust shell with pulsation phase have been identified by SED modelling. Assuming a gas-to-dust ratio of 200, we found a variable mass loss rate between 2.3 and 9.0 ×10 −6 M� /yr and estimated the distance to RR Tel to be 2.7 kpc. Our results suggest a relatively low influence of

[O/C] abundance ratio for cool giants from the receding tip of the stellar Galactic bar

Abstract We identified the TiO bands and measured their intensity jumps in the near-infrared spectra of 10 M giants located in the Galactic plane. The correlation between the measured intensity jumps and spectral subtypes for particular TiO bands was compared to the same type of correlation which includes intensity jumps calculated from model atmospheres for different [O/C] abundance ratios.

Atmospheric Thermal Structure of a Sample of M Type Giants

We present a study of atmospheric thermal structure of nine MIII giants located in the zone of a star formation region in the stellar Galactic bar. Vibrational temperatures of the layers of formation of δ, π and ε TiO molecular band systems have been determined spectroscopically. These temperatures have been associated to optical depths by use of an appropriate model atmospheres and in view of several Teff calibration scales. Significant temperature gradient in the upper atmospheric layers has been established.

Atlas of M7III Spectral Features in the Optical

The difficulties encountered in attempts to study the spectra of very late stars inspired us to prepare this spectral atlas containing essentially spectral features of M7III stars in the optical spectral region. As representative star we took the cool component of the binary symbiotic CH Cygni during one of its quiescent phases. Total number of 920 atomic lines and molecular bands have been identified with different degrees of reliability.

Ch Cygni: A symbiotic star in its transition phase to quiescence

Abstract In order to establish features of the transition period of the symbiotic star CH Cygni from activity to the quiescent phase, a behaviour of its cool component over the two years period (1987–1989) after its longest outburst has been investigated in the optical spectral region. Absorption and emission spectral lines have been measured and analysed. Physical parameters such as an excitation temperature and microturbulent velocity have been determined by the use of absorption lines and compared to the corresponding parameters belonging to normal stars of the same spectral type. The behaviour of the excitation temperature with time for some neutral metals suggests that quiescence has been reached gradually and that CH Cygni was very close to the condition of optical quiescency at the end of the investigated period. There was no evidence of a dependence of the microturbulent velocity on the temperature and of stratification with respect to the excitation potential. The emission line profiles, especial...

Dust around the Cool Component of D-Type Symbiotic Binaries

D type symbiotic binaries are an excellent astrophysical laboratory for investigation of the dust properties and dust formation under the influence of theMira stellar wind and nova activity and of the mass loss and mass transfer between components in such a widely separated system. We present a study of the properties of circumstellar dust in symbiotic Miras by use of long-term near-IR photometry and colour indices. The published JHKL magnitudes of o Ceti, RX Pup, KM Vel, V366 Car, V835 Cen, RR Tel, HM Sge and R Aqr have been collected, analyzed and corrected for short-term variations caused by Mira pulsations. Assuming spherical temperature distribution of the dust in the close neighbourhood of the Mira, the DUSTY code was used to solve the radiative transfer in order to determine the dust temperature and its properties in each particular case. Common dust properties of the symbiotic Miras have been found, suggesting similar conditions in the condensation region of the studied symbiotic Miras. Silicate dust with the inner dust shell radius determined by the dust condensation and with the dust temperature of 900−1200 K can fully explain the observed colour indices. R Aqr is an exception and showed lower dust temperature of 650 K. Obscuration events visible in light curves can be explained by variable dust optical depth with minimal variations of other dust properties. More active symbioticMiras that underwent recent nova outbursts showed higher dust optical depths and larger maximum grain sizes of the order of μm, which means that the post-nova activity could stimulate the dust formation and the grain growth. Optically thicker dust shells and higher dust condensation temperatures have been found in symbiotic Miras compared to their single counterparts, suggesting different conditions for dust production.

RR Tel: Determination of Dust Properties During Minimum Obscuration

Abstract the ISO infrared spectra and the SAAO long-term JHKL photometry of RR Tel in the epochs during minimum obscuration are studied in order to construct a circumstellar dust model. the spectral energy distribution in the near- and the mid-IR spectral range (1–15 μm) was obtained for an epoch without the pronounced dust obscuration. the DUSTY code was used to solve the radiative transfer through the dust and to determine the circumstellar dust properties of the inner dust regions around the Mira component. Dust temperature, maximum grain size, dust density distribution, mass-loss rate, terminal wind velocity and optical depth are determined. the spectral energy distribution and the long-term JHKL photometry during an epoch of minimum obscuration show almost unattenuated stellar source and strong dust emission which cannot be explained by a single dust shell model. We propose a two-component model consisting of an optically thin circmustellar dust shell and optically thick dust outside the line of sight in some kind of a flattened geometry, which is responsible for most of the observed dust thermal emission.