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Papers by Emmanuel Danezis
AIP Conference Proceedings, 2006
Several Non-LTE models (very bad reproduction). 2. Non-LTE specialized models (e.g. PHOENIX) havi... more Several Non-LTE models (very bad reproduction). 2. Non-LTE specialized models (e.g. PHOENIX) having very complicated codes that may reproduce the peculiar profiles in some cases. There are some models to reproduce such peculiar profiles.
In this paper we present a study of the UV SiIV resonance lines of 50 BeV stars’ spectra, using t... more In this paper we present a study of the UV SiIV resonance lines of 50 BeV stars’ spectra, using the model proposed by Danezis et al. (2002b, 2003). This model is based on the idea of independent density layers in the regions where the spectral lines that present SACs (DACs) are created. We calculated the apparent rotation (Vrot) and expansion/contraction velocities (Vexp) of these density regions, as well as their ξ value, which is an expression of the optical depth. We also present the relation among these parameters and their evolution with the spectral subtype.
cc.uoa.gr
... V., Stathopoulou, M., Theodossiou, E., Kosionidis, A., Drakopoulos, C., Christou G. & Kou... more ... V., Stathopoulou, M., Theodossiou, E., Kosionidis, A., Drakopoulos, C., Christou G. & Koutsouris, P.: 2003, Ap&SS, 284, 1119 Iben, I.:1967, Ann. Rev. A&A 5, 571 Jeffers, HM, van de Box, WH & Greeby, FM: 1963, Index Catalogue of Visual Double Star, Publ. Link Obs. 21 Kelly, ...
DACs and SACs phenomena in Hα line of 120 Be stars In this study we apply the method proposed by ... more DACs and SACs phenomena in Hα line of 120 Be stars In this study we apply the method proposed by Danezis et al. (2003, 2005) on the stellar spectrographs of 120 Be stars, and we examine the variations of the physical parameters, stated below, as a function of the spectral subtype and the luminosity class. We found that in the Be-type stellar atmospheres, there are two regions that can produce the Hα Satellite Absorption Components (SACs or DACs). The first one lies in the chromosphere and the second one in the cool extended envelope. With the above method we calculate: a) For the chromospheric absorption components: the optical depth as well as the rotational and radial velocities of the independent regions of matter which produce the main and the satellites components. b) For the emission and absorption components which are created in the cool extended envelope: the FWHM, the optical depth and the radial velocities of the independent regions of matter which produce the main and the...
Spectral lines of Oe and Be stars present DACs or SACs In this paper we study the N V line profil... more Spectral lines of Oe and Be stars present DACs or SACs In this paper we study the N V line profiles of a sample of 20 Oe stars (from O4 to O7 spectral subtype). Using the model given by Danezis et al. (2003, 2005a,b) we found that the line shapes are very complex and that they can be fitted by a multi-component N V region. In the sample the region may be divided into two to five subregions which show different kinematical and physical parameters. We give the kinematical parameters of subregions where the N V resonance lines (λλ 1238.81, 1242.804 Å) are formed.
Open Astronomy, 2011
Using the GR model, we analyze the ultraviolet Si IV resonance lines in the spectra of 19 Be star... more 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 velocities, the random velocities of the ion thermal motions, as well as the absorbed energy and the logarithm of the column density of the independent regions of matter which produce the main and the satellite components of the studied spectral lines.
Open Astronomy, 2011
Most of the Broad Absorption Lines (BALs) in quasars show very complex profiles. An idea to expla... more 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 in the spectra of a group of high ionization BAL quasars, using the Gauss-Rotation model.
Open Astronomy, 2011
Using the GR model, we analyze the UV Mg II resonance lines in the spectra of 20 Be stars of diff... more 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 the effective temperature for the studied stars are determined.
AIP Conference Proceedings, 2007
AIP Conference Proceedings, 2007
In order to explain the peculiarity of the line profiles in the spectra of hot emission stars, ou... more In order to explain the peculiarity of the line profiles in the spectra of hot emission stars, our team proposes and uses the DACs (Bates & Halliwell, 1986) and SACs (Danezis et al. 2005) theory. These spectral lines are named Discrete Absorption Components (DACs) when they are discrete (Bates, B.
AIP Conference Proceedings, 2004
Some Hot Emission Stars and AGNs present peculiar spectral line profiles which are due to DACs an... more 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 phenomena. At first we present a theoretic ad hoc picture for the structure of the plasma that surrounds the specific category of hot emission stars that present DACs or SACs. Then we present the mathematical model that we constructed, which is based on the properties of the above ad hoc theoretical structure. Finally, we present some results from our statistical studies that prove the consistency of our model with the classical physical theory.
Hot emission stars (Oe and Be stars) present complex spectral line profiles, which are formed by ... more 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 independent and successive absorbing or emitting density regions of matter. Here we are testing a new approach of the GR model, which supposes that the independent density regions are not successive. We use this new approach in the spectral lines of some Oe and Be stars and we compare the results of this method with the results deriving from the classical GR model that supposes successive regions.
AIP Conference Proceedings, 2006
Several Non-LTE models (very bad reproduction). 2. Non-LTE specialized models (e.g. PHOENIX) havi... more Several Non-LTE models (very bad reproduction). 2. Non-LTE specialized models (e.g. PHOENIX) having very complicated codes that may reproduce the peculiar profiles in some cases. There are some models to reproduce such peculiar profiles.
In this paper we present a study of the UV SiIV resonance lines of 50 BeV stars’ spectra, using t... more In this paper we present a study of the UV SiIV resonance lines of 50 BeV stars’ spectra, using the model proposed by Danezis et al. (2002b, 2003). This model is based on the idea of independent density layers in the regions where the spectral lines that present SACs (DACs) are created. We calculated the apparent rotation (Vrot) and expansion/contraction velocities (Vexp) of these density regions, as well as their ξ value, which is an expression of the optical depth. We also present the relation among these parameters and their evolution with the spectral subtype.
cc.uoa.gr
... V., Stathopoulou, M., Theodossiou, E., Kosionidis, A., Drakopoulos, C., Christou G. & Kou... more ... V., Stathopoulou, M., Theodossiou, E., Kosionidis, A., Drakopoulos, C., Christou G. & Koutsouris, P.: 2003, Ap&SS, 284, 1119 Iben, I.:1967, Ann. Rev. A&A 5, 571 Jeffers, HM, van de Box, WH & Greeby, FM: 1963, Index Catalogue of Visual Double Star, Publ. Link Obs. 21 Kelly, ...
DACs and SACs phenomena in Hα line of 120 Be stars In this study we apply the method proposed by ... more DACs and SACs phenomena in Hα line of 120 Be stars In this study we apply the method proposed by Danezis et al. (2003, 2005) on the stellar spectrographs of 120 Be stars, and we examine the variations of the physical parameters, stated below, as a function of the spectral subtype and the luminosity class. We found that in the Be-type stellar atmospheres, there are two regions that can produce the Hα Satellite Absorption Components (SACs or DACs). The first one lies in the chromosphere and the second one in the cool extended envelope. With the above method we calculate: a) For the chromospheric absorption components: the optical depth as well as the rotational and radial velocities of the independent regions of matter which produce the main and the satellites components. b) For the emission and absorption components which are created in the cool extended envelope: the FWHM, the optical depth and the radial velocities of the independent regions of matter which produce the main and the...
Spectral lines of Oe and Be stars present DACs or SACs In this paper we study the N V line profil... more Spectral lines of Oe and Be stars present DACs or SACs In this paper we study the N V line profiles of a sample of 20 Oe stars (from O4 to O7 spectral subtype). Using the model given by Danezis et al. (2003, 2005a,b) we found that the line shapes are very complex and that they can be fitted by a multi-component N V region. In the sample the region may be divided into two to five subregions which show different kinematical and physical parameters. We give the kinematical parameters of subregions where the N V resonance lines (λλ 1238.81, 1242.804 Å) are formed.
Open Astronomy, 2011
Using the GR model, we analyze the ultraviolet Si IV resonance lines in the spectra of 19 Be star... more 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 velocities, the random velocities of the ion thermal motions, as well as the absorbed energy and the logarithm of the column density of the independent regions of matter which produce the main and the satellite components of the studied spectral lines.
Open Astronomy, 2011
Most of the Broad Absorption Lines (BALs) in quasars show very complex profiles. An idea to expla... more 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 in the spectra of a group of high ionization BAL quasars, using the Gauss-Rotation model.
Open Astronomy, 2011
Using the GR model, we analyze the UV Mg II resonance lines in the spectra of 20 Be stars of diff... more 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 the effective temperature for the studied stars are determined.
AIP Conference Proceedings, 2007
AIP Conference Proceedings, 2007
In order to explain the peculiarity of the line profiles in the spectra of hot emission stars, ou... more In order to explain the peculiarity of the line profiles in the spectra of hot emission stars, our team proposes and uses the DACs (Bates & Halliwell, 1986) and SACs (Danezis et al. 2005) theory. These spectral lines are named Discrete Absorption Components (DACs) when they are discrete (Bates, B.
AIP Conference Proceedings, 2004
Some Hot Emission Stars and AGNs present peculiar spectral line profiles which are due to DACs an... more 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 phenomena. At first we present a theoretic ad hoc picture for the structure of the plasma that surrounds the specific category of hot emission stars that present DACs or SACs. Then we present the mathematical model that we constructed, which is based on the properties of the above ad hoc theoretical structure. Finally, we present some results from our statistical studies that prove the consistency of our model with the classical physical theory.
Hot emission stars (Oe and Be stars) present complex spectral line profiles, which are formed by ... more 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 independent and successive absorbing or emitting density regions of matter. Here we are testing a new approach of the GR model, which supposes that the independent density regions are not successive. We use this new approach in the spectral lines of some Oe and Be stars and we compare the results of this method with the results deriving from the classical GR model that supposes successive regions.