Dimitris Nikolaidis

A Statistical Study of Physical Parameters of the C IV Density Regions in 20 Oe Stars

We detected the presence of Satellite Absorption Components (SACs) which accompany the C IV resonance lines in the spectra of 20 Oe stars of different spectral subtypes, taken with IUE. The values of the apparent rotational and radial velocities, the random velocities of the thermal motions of the ions, as well as the column density and the Full Width at Half Maximum (FWHM) of the independent regions of matter which produce the main and the satellites components of the studied spectral lines were calculated. The variations of these physical parameters are presented as a function of the spectral subtype.

Investigation of the Post‐Coronal Density Regions of Oe Stars, with the N V UV Resonance Lines

The presence of Satellite Absorption Components (SACs) in the N V resonance lines of 20 Oe stars of different spectral subtypes is considered. We calculated the values of the apparent rotational and radial velocities, the random ion velocities, as well as, the Full Width at Half Maximum (FWHM) and the column density of the independent regions of matter which produce the main and the satellites components of the studied spectral lines. We examine also the variations of these physical parameters as a function of the spectral subtype.

The Complex Structure of the Mg II

Here we consider the presence of absorption components shifted to the violet or red side of the main spectral line (satellite or discrete absorption components, i.e., SACs or DACs) in the regions of the Mg II resonance lines in Be stars a sw ell as their kinematical characteristics. Namely, our objective is to check whether there exists a common physical structure for the atmospheric regions creating SACs or DACs of the Mg II resonance lines. In order to do this, a statistical study of the Mg II �� 2795.523, 2802.698 u A lines in the spectra of 64 Be stars of all spectral subtypes and luminosity classes was performed. We found that the atmospherical absorption regions where the Mg II resonance lines originated may be formed of several independent density layers of matter that rotate with different velocities. It was also attempted to separate SACs and DACs according to low or high radial velocity. The emission lines were detected only in the earliest and latest spectral subtypes.

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The presence of Satellite Absorption Components (SACs) in the N IV spectral lines of 20 Oe stars of different spectral subtypes were analyzed and the physical parameters which characterize the corresponding N IV density regions were studied. We found that the N IV spectral lines consist of one or two Satellite Absorption Components. We calculate the values of the apparent rotational and radial velocities, the random ion velocities, as well as the Full Width at Half Maximum (FWHM), the absorbed energy and the column density of the independent regions of matter which produce the main and the satellite components of the studied spectral lines. Finally, we present the variations of these physical parameters as a function of the spectral subtype.

2795.523, 2802.698

The presence of Discrete Absorption Components (DACs) or Satellite Absorption Components (SACs) is a very common phenomenon in the atmospheres of hot emission stars (Danezis et al. 2003, Lyratzi & Danezis 2004) and result to the complex line profiles of these stars. The shapes of these lines are interpreted by the existence of two or more independent layers of matter nearby a star. These structures are responsible for the formation of a series of satellite components for each spectral line. Here we will present a model reproducing the complex profile of the spectral lines of Oe and Be stars with DACs and SACs (Danezis et al. 2003, Lyratzi & Danezis 2004). In general, this model has a line function for the complex structure of the spectral lines with DACs or SACs and include a function L that considers the kinematic (geometry) of an independent region. In the calculation of the function L we have considered the rotational velocities of the independent regions, as well as the random velocities within them. ...

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The spectra of Hot Emission Stars and AGNs present peculiar profiles that result from dynamical processes such as accretion and/or ejection of matter from these objects. In this paper we explain the idea of DACs and SACs phenomena, as a reason of spectral lines peculiarity in Hot Emission Stars and AGNs. We present the line function of a kinematical model enabling to study the physical parameters of the density regions in the plasma surrounding the considered objects, where DACs and SACs of a spectral line are created, producing the observed peculiar profiles. We also present some first general conclusions, deriving from the proposed model, including the relations among the physical parameters of the density regions of the plasma surrounding the Oe stars, where DACs and SACs are created, producing the observed peculiar profiles.

Regions of 64 Be Stars

In the spectra of Oe and Be stars, many spectral lines present peculiar and complex profiles due to the fact that the observed absorption features are composed of two or more absorption components (Discrete or Satellite Absorption Components—DACs/SACs). Here we detected the presence the SACs phenomenon in the C IV, N IV and N V spectral lines in 11 spectra of the Oe star HD 149757 (zeta Oph), taken with IUE during a period of 13 years.

The N IV Density Regions in the Spectra of 20 Oe Stars

In order to analyse the stellar spectra we use the Gauss‐Rotation method and we conclude that the SACs/DACs phenomena are able to explain, in a unique way, the complex and peculiar observed profiles. These results arise from the study of the Mg II (λλ 2795.523, 2802.698 A), SiIV (λλ 1393.755, 1402.77 A), and Hα (λ 6562,817 A) region of a great number of Be stars of all spectral subtypes and luminosity classes (64 in the case of Mg II resonance lines and 70 in the case of Si IV resonance limes). For the study of the regions which create the complex Hα line profiles we analyzed the OHP (Observatory of Haute Provence) spectrographs of 120 Be stars of all spectral subtypes and luminosity classes. We present the evolution of some kinematical parameters from the photosphere to the extreme cool envelope.

A New Modeling Approach For DACs And SACs Regions In The Atmospheres Of Hot Emissions Stars

We examine the timescale changes of C IV, N IV and N V spectral lines of the Oe star HD 93521, during a period of 16 years, applying the model proposed by Danezis et al. (2005). We found that the spectral lines consist of one or more Satellite Absorption Components (SACs or DACs) which construct the whole spectral profile. In this paper we present the time scale variation of the radial velocities.

The DACs and SACs Effects From Stars to Quasars. Some First General Notices

In this paper we present a statistical study of the Hα line profiles of 120 Be‐type stars using the model proposed by Danezis et al. (2003) and Lyratzi & Danezis (2004). This model proposes that the density layers which produce the Hα line lie in different regions in the stellar atmosphere. In the Be‐type stellar atmospheres, there are two regions that can produce the Hα satellite components. The first one lies in the chromosphere and the second one in the cool extended envelope. By fitting the Hα line profiles with the line function of the proposed model we are able to calculate: a) For the chromospheric absorption components we calculated the rotational and radial velocities as well as the optical depth. b) For the emission and absorption components which are created in the cool extended envelope we calculated the radial velocities, the FWHM and the optical depth. Finally, we present the relation between these parameters with the spectral subtype and the luminosity class.