Evangelia Lyratzi

Evangelia Lyratzi
National and Kapodistrian University of Athens | uoa · Department of Astrophysics, Astronomy and Mechanics

PhD

About

111
Publications
3,683
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164
Citations
Citations since 2016
3 Research Items
22 Citations
20162017201820192020202120220246810
20162017201820192020202120220246810
20162017201820192020202120220246810
20162017201820192020202120220246810

Publications

Publications (111)
Article
In this article, we study the variability of Si iv and C iv broad absorption lines (BALs) between two different epochs in the case of 10 broad absorption-line quasi-stellar objects (BALQSOs). By performing multicomponent analysis of Si iv and C iv broad absorption troughs, we analyse each BAL trough to find the individual and uniquely determined nu...
Article
ASTA is a new spectral analysis software aiming to serve the growing need of an integrated computing environment which will implement efficiently the demanding process of multicomponent analysis. It is a cutting-edge spectral multicomponent analysis software for displaying, fitting and analyzing astronomical spectra of complex emission and absorpti...
Article
In this paper we analyze the C IV and Si IV broad absorption troughs of two BALQSOs (J101056.69+355833.3, J114548.38+393746.6) to the individual components they consist of. By analyzing a BAL trough to its components we have the advantage to study the variations of the individual absorbing systems in the line of sight and not just the variations of...
Article
Full-text available
Broad Absorption Line QSOs (BALQSOs) are a subtype of radio-quite QSOs that exhibit complex and unusually broad (FWHM ≥ 2,000 km/s) absorption lines. The existence of these lines in BALQSO spectra raises some questions with respect to the properties, the physical conditions and kinematics of the BAL material as well as the morphology of BAL troughs...
Article
Full-text available
In this paper, using the Gauss - Rotation model (GR model), we analyse the UV C IV resonance lines in the spectra of 20 Oe stars of different spectral subtypes, in order to detect the structure of C IV region. We study the presence and behaviour of absorption clouds and analyse their characteristics. From this analysis we can calculate the values o...
Conference Paper
Full-text available
We investigate the physical conditions and kinematics of broad absorption line region clouds of Si IV in 21 HiBAL Quasars. We use the Danezis et al. method [1], [2], [3] in order to fit and analyze the broad absorption troughs of Si IV resonance lines in the UV region of the electromagnetic spectrum. We find that the BAL flow is not smooth but inst...
Data
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 as well as their kinematical characteristics. Namely, our objective is to check whether there exists a common phy...
Data
Full-text available
In this review we present our recent investigation of the complex absorption lines in spectra of hot emission stars. The lines are created in a material ejected from stars (here we call it density regions around the objects). Particularly we present a model (GR model) which is developed to study satellite or discrete absorption components (SACs or...
Article
Full-text available
Using the GR model, we analyze the UV Si IV resonance lines in the spectra of 68 Be stars of different spectral subtypes, in order to detect the structure of Si IV region. We calculated the values of the rotational, radial and random velocities as well as the absorbed energy of each one of the λλ 1393.755, 1402.778 Å Si IV resonance lines and we pr...
Article
Full-text available
Using the GR model, we analyze the ultraviolet Si IV resonance lines in the spectra of 19 Be stars of different spectral subtypes, in order to detect the presence of absorption components and to analyze their characteristics. From this analysis we can calculate the values of a group of physical parameters, such as the apparent rotational and radial...
Article
Full-text available
Using the GR model, we analyze the UV Mg II resonance lines in the spectra of 20 Be stars of different spectral subtypes, in order to detect the presence of satellite or discrete absorption components. The values of some physical parameters -- rotational, radial and random velocities, as well as the FWHM and the absorbed energy, as a function of th...
Article
Full-text available
Most of the Broad Absorption Lines (BALs) in quasars show very complex profiles. An idea to explain these profiles is that the dynamical systems of broad line regions are not homogeneous but consist of a number of dense regions or ion populations with different physical parameters. This approach is used to study the ultraviolet CIV resonance lines...
Data
Full-text available
Most of the Broad Absorption Lines (BALs) in quasars show very complex profiles. An idea to explain these profiles is that the dynamical systems of broad line regions are not homogeneous but consist of a number of dense regions or ion populations with different physical parameters. This approach is used to study the ultraviolet C IV resonance lines...
Article
Full-text available
Most of Broad Absorption Lines (BALs) in quasars (QSOs) present very complex profiles. This means that we cannot fit them with a known physical distribution. An idea to explain these profiles is that the dynamical systems of Broad Line Regions (BLRs) are not homogeneous but consist of a number of density regions or ion populations with different ph...
Article
Full-text available
According to the GR model, the Broad Absorption Line Region (BALR), lie in a disk around the quasar and is composed of a number of successive independent absorbing density regions that have different apparent rotational and radial velocities. By fitting the observed absorption lines with GR model, we can calculate some basic kinematical pa- rameter...
Article
Full-text available
Hot emission stars (Oe and Be stars) present complex spectral line profiles, which are formed by a number of DACs and/or SACs. In order to explain and reproduce theoretically these complex line profiles we use the GR model (Gauss-Rotation model). This model presupposes that the regions, where the spectral lines are created, consist of a number of i...
Article
Full-text available
Some Hot Emission Stars and AGNs present peculiar spectral line profiles which are due to DACs and SACs phenomena. The origin and the mechanisms which are responsible for the creation of DACs/SACs is an important problem that has been studied by many researchers. This paper is a review of our efforts to study the origin and the mechanisms of these...
Article
Full-text available
We use the GR model in order to fit broad spectral lines (absorption and emission) of several BAL QSOs. According to this motdel, we assume that the Broad Line Regions (BLR), which originate in a disk wind, are composed of a number of successive independent absorbing density layers, which may have different random, rotational and radial velocities....
Article
Assuming that the Broad Absorption Line Region – BALR (originated in a disk wind) is composed of a number of successive independent absorbing density layers, which have apparent rotational and radial velocities and where ions have random velocities, we applied a model in order to obtain the kinematical parameters of BALR, by fitting the broad absor...
Article
a b s t r a c t In this review we present our recent investigation of the complex absorption lines in spectra of hot emis-sion stars. The lines are created in a material ejected from stars (here we call it density regions around the objects). Particularly we present a model (GR model) which is developed to study satellite or discrete absorption com...
Article
Full-text available
In this paper we apply the GR model to find kinematic parameters (radial, rotational and random velocities) as well as FWHM, the absorbed energy and the Gaussian Typical Deviation (sigma) for a group of Fe II spectral lines from AX Mon spectra obtained with IUE. In order to find possible stratification in the Fe II absorbing region of AX Mon we pre...
Data
a b s t r a c t In this review we present our recent investigation of the complex absorption lines in spectra of hot emis-sion stars. The lines are created in a material ejected from stars (here we call it density regions around the objects). Particularly we present a model (GR model) which is developed to study satellite or discrete absorption com...
Article
Full-text available
In this progress report we present the main results of our research. Using a new model we studied the kinematical parameters such as the random velocities of the ions, which create the spectral lines of C IV, N IV and N V in the spectra of 20 Oe stars, as well as the rotational and radial velocities of the regions, where the above ions are created....
Article
Full-text available
In the UV spectrum of AX Mon (HD 45910) we observe a series of spectral lines with complex structure and peculiar profiles. This peculiarity is due to SACs or DACs. In this paper, using the GR model, we study the complex profile of Fe II spectral lines and we calculate the relation of some kinematical parameters of the regions that create the DACs/...
Article
Full-text available
The complex structure and the peculiar profiles of some spectral lines are common in the UV spectrum of AX Mon (HD 45910). The observed peculiar profiles are composed by a number of SACs or DACs. In this paper, using the GR model, we study the complex profile of the Al II (lambda 1670.81 A˚), Al III (lambdalambda 1854.722, 1867.782 A˚), M...
Article
Full-text available
In this paper we study the Lyα spectral line and the N V, Si IV and C IV resonance lines in the UV spectrum of the Broad Absorption Line Quasar (BAL QSO) PG 1254+047. We found that the studied Broad Absorption Lines (BALs) of this quasar are created by a number of Satellite Absorption Components (SACs). We calculated some kinematical parameters...
Article
Full-text available
In this paper we study the C IV and Si IV resonance lines in the UV spectrum of the Broad Absorption Line Quasar (BAL QSO) PG 0946+301. The studied Broad Absorption Lines (BALs) are mainly created by a number of Satellite Absorption Components (SACs). However, the C IV doublet of PG 0946+301 is one of the very few lines that present clearly the DAC...
Article
Full-text available
In the spectra of Hot Emission Stars and AGNs we observe some peculiar profiles that result from dynamical processes such as accretion and/or ejection of matter from these objects. In this paper we indicate that DACs and SACs phenomena, can explain the spectral lines peculiarity in Hot Emission Stars and AGNs. We also try to connect the physical pr...
Article
Full-text available
Introduction: As it is already known, the spectra of many Oe and Be stars present Discrete Absorption Components (DACs) which, due to their profiles' width as well as the values of the radial velocities, create a complicated profile of the main spectral lines (Bates & Halliwell, 1986). In this poster paper we detect the presence of this phenomenon...
Article
Full-text available
In this paper we study the C IV resonance lines in the UV spectra of 5 Broad Absorption Line Quasars (BAL QSOs). We found that the Broad Absorption Lines (BALs) that we analyzed in the spectra of some BAL QSOs, are created by a number of Satellite Absorption Components (SACs). We calculated the kinematical parameters such as the apparent rotational...
Article
Full-text available
In some cases, the UV spectral lines of hot emission stars and quasars have very large widths that can not be explained as the consequence of rotational or random velocities. In this paper we present a new idea to explain this phenomenon.
Article
Full-text available
The UV spectrum of AX Mon (HD 45910) presents a series of complex structure spectral lines, that present SACs or DACs. In this paper, using the GR model, we study the complex profile of Fe II spectral lines and we calculate the relation of some physical parameters with the excitation potential.
Article
Full-text available
Some spectra of AGN present peculiar line profiles, resulting from dynamical processes such as accretion to and∕or ejection of matter from the central source. In this paper we explore the idea that Discrete or Satellite Absorption Compoments (DASs∕SACs, respectively) might be responsible for the absorption line peculiarities in at least some AGN. W...
Article
Full-text available
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 th...
Article
Full-text available
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...
Article
Full-text available
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...
Article
Full-text available
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 (lambdalambda 2795.523, 2802.698 Å), SiIV (lambdalambda 1393.755, 1402.77 Å), and Halpha (lambda 6562,...
Article
Full-text available
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 Wi...
Article
Full-text available
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 kinematic...
Article
Full-text available
Introduction: As it is already known, the spectra of many Oe and Be stars present Discrete Absorption Components (DACs) which, due to their profiles' width as well as the values of the radial velocities, create a complicated profile of the main spectral lines (Bates & Halliwell, 1986). In this poster paper we detect the presence of this phenomenon...
Article
Full-text available
SACs in the C IV regions of HD 93521 We examine the timescale changes of C IV spectral lines of the Oe star HD 93521, during a period of 16 years, applying the model proposed by Danezis et al. (2003, 2005a, b). We found that the spectral lines consist of one or more Satellite Absorption Components (SACs or DACs) which construct the whole spectral p...
Article
Full-text available
Introduction: As it is already known, the spectra of many Oe and Be stars present Discrete Absorption Components (DACs) which, due to their profiles' width as well as the values of the radial velocities, create a complicated profile of the main spectral lines (Bates & Halliwell, 1986). In this poster paper we detect the presence of this phenomenon...
Article
Full-text available
Here is studied the presence of absorption components shifted to the violet or the red side of the main spectral line (satellite, or discrete absorption components, i.e. SACs or DACs), in Mg II resonance lines' regions in Be stars and their kinematical characteristics. Namely our objective is to check if exists a common physical structure for the a...