Περιγραφή του προβλήματος

Ένα από τα πλέον ενδιαφέροντα και άλυτα, μέχρι πρότινος, προβλήματα της αστροφυσικής ήταν η περιγραφή των φυσικών νόμων που εξελίσσονται στο περιβάλλον μιας παράξενης κατηγορίας αστεριών, των θερμών αστέρων εκπομπής. Η ερευνητική μας ομάδα ασχολήθηκε με αυτό το πρόβλημα επιτυγχάνοντας να παρουσιάσει λύσεις που δίνουν μια πολύ ικανοποιητική απάντηση στο πρόβλημα αυτό. Ας δούμε όμως αναλυτικότερα το πρόβλημα και τη λύση που προτείναμε.
Όπως γνωρίζουμε σήμερα οι αστέρες του ίδιου φασματικού τύπου και τάξης λαμπρότητας εμφανίζουν στα φάσματά τους τις ίδιες γραμμές απορρόφησης.

Όμως, οι παρατηρήσεις μας έδειξαν ότι κάποιοι θερμοί αστέρες εκπομπής, (αστέρες φασματικού τύπου Oe και Be) και κάποιοι κβάζαρ παρουσιάζουν γραμμές απορρόφησης που δεν αναμένονται, σύμφωνα με την κλασσική φυσική θεωρία. Οι παράδοξες αυτές φασματικές αυτές γραμμές ονομάστηκαν Διακριτές Συνιστώσες Απορρόφησης (Discrete Absorption Components - DACs).

Με την πάροδο του χρόνου αποδείχθηκε ότι οι DACs είναι φασματικές γραμμές του ίδιου ιόντος και του ίδιου μήκους κύματος με την κύρια φασματική γραμμή, που παρουσιάζουν διαφορετικές μετατοπίσεις, επειδή δημιουργούνται σε διαφορετικά, ανεξάρτητα πυκνώματα ύλης, τα οποία περιστρέφονται και κινούνται με διαφορετικές ταχύτητες (Danezis 1984, 1987, Danezis et al. 1991, 2003, 2005, 2007 και Lyratzi & Danezis 2004).
Ένα δεύτερο πρόβλημα που παρουσιαζόταν σε πολλά φάσματα θερμών αστέρων εκπομπής και κβάζαρ ήταν ότι κάποιες φασματικές γραμμές τους είχαν πολύπλοκα περιγράμματα και δεν μπορούσαν να αναπαραχθούν θεωρητικά. Έτσι, δεν μπορούσαμε να γνωρίζουμε τις φυσικές συνθήκες που επικρατούσαν στα πυκνώματα ύλης που τις δημιουργούσαν.
Προκειμένου να ερμηνεύσουμε τα πολύπλοκα αυτά περιγράμματα, προτείναμε το φαινόμενο των Δορυφορικών Συνιστωσών Απορρόφησης (Satellite Absorption Components - SACs).

Η λογική ήταν απλή. Αν τα πυκνώματα ύλης που δημιουργούν αυτές τις γραμμές περιστρέφονται με σχετικά μεγάλες ταχύτητες και κινούνται με μικρές ταχύτητες, τότε οι γραμμές που παράγονται έχουν μεγάλο εύρος και μικρή ακτινική μετατόπιση. Ως εκ τούτου, οι φασματικές γραμμές επικαλύπτονται μεταξύ τους όσο και με την κύρια φασματική γραμμή και δεν είναι πλέον διακριτές, με αποτέλεσμα να δημιουργούν ένα πολύπλοκο περίγραμμα.

Η πρότασή μας

Για να γίνει αποδεκτή αυτή η άποψη έπρεπε να επιτύχουμε τη θεωρητική αναπαραγωγή των φασματικών γραμμών που εμφανίζουν DACs ή SACs. Αυτό σημαίνει ότι έπρεπε να υπολογίσουμε τη συνάρτηση γραμμής του πολύπλοκου περιγράμματός τους. Η συνάρτηση γραμμής είναι μια σχέση που συνδέει την ένταση της ακτινοβολίας με το μήκος κύματος και περιέχει, ως παραμέτρους, τις φυσικές συνθήκες που συμβάλλουν στη δημιουργία του περιγράμματος της φασματικής γραμμής. Δεχόμαστε ότι οι τιμές των φυσικών παραμέτρων που δίνουν την καλύτερη αναπαραγωγή του παρατηρούμενου περιγράμματος της φασματικής γραμμής περιγράφουν τις πραγματικές φυσικές συνθήκες που επικρατούν στην περιοχή που δημιουργεί τη συγκεκριμένη φασματική γραμμή.
Μια τέτοια θεωρητική αναπαραγωγή του παρατηρούμενου περιγράμματος της φασματικής γραμμής ήταν αδύνατη μέχρι το 2003, όταν η επιστημονική μας ομάδα πρότεινε μια συνάρτηση γραμμής, ικανή να αναπαράγει την πολύπλοκη δομή των πυκνωμάτων ύλης που βρίσκονται στο περιβάλλον των θερμών αστέρων εκπομπής και κάποιων κβάζαρ.

Το μοντέλο GR

Αρχικά, υπολογίσαμε μια νέα κατανομή, προϋποθέτοντας ότι η κύρια αιτία διεύρυνσης των φασματικών γραμμών είναι η γρήγορη περιστροφή των περιοχών δημιουργίας τους. Τη συνάρτηση αυτή την ονομάσαμε «Κατανομή Περιστροφής».
Σε μια καλύτερη προσέγγιση, λαμβάνοντας υπ’ όψη μας τις τυχαίες κινήσεις των ιόντων στα πυκνώματα ύλης που δημιουργούν τις SACs και DACs, κατασκευάσαμε ακόμα μια νέα κατανομή, η οποία περιλάμβανε ως αίτιο διεύρυνσης των φασματικών γραμμών τόσο την περιστροφή της περιοχής όσο και τις τυχαίες κινήσεις των ιόντων. Τη νέα αυτή κατανομή την ονομάσαμε Γκαουσιανή-Περιστροφική Κατανομή (Gaussian-Rotation distribution - GR distribution).
Με το μοντέλο GR μπορούμε να υπολογίσουμε τις τιμές πολλών φυσικών παραμέτρων των περιοχών που δημιουργούν τις DACs και SACs.
Το μοντέλο GR έχει ελεγχθεί και εφαρμοστεί σε ένα μεγάλο πλήθος φασματικών γραμμών σε φάσματα θερμών αστέρων εκπομπής και κβάζαρ και έχει δώσει σημαντικά αποτελέσματα όσον αφορά την κινηματική και χρονική εξέλιξη αστρικών ατμοσφαιρών συγκεκριμένων θερμών αστέρων εκπομπής και κβάζαρ, όσο και στην περίπτωση στατιστικών μελετών για τη διατύπωση γενικών συμπερασμάτων. Όλα αυτά τα αποτελέσματα έχουν δημοσιευθεί σε διεθνή επιστημονικά περιοδικά με κριτές και σε πρακτικά διεθνών συνεδρίων.

Σύνοψη αποτελεσμάτων;

Συνοπτικά τα αποτελέσματα της έρευνας μας έχουν ως εξής:

1. Ερμηνεύσαμε την προέλευση του φαινομένου DACs και προτείναμε το φαινόμενο SACs για να ερμηνεύσουμε την πολύπλοκη δομή των παρατηρούμενων περιγραμμάτων πολλών φασματικών γραμμών που δημιουργούνται στο περιβάλλον των θερμών αστέρων εκπομπής.

2. Παρατηρήσαμε το ίδιο φαινόμενο σε φάσματα κβάζαρ και δώσαμε μια ερμηνεία ανάλογη με αυτήν των θερμών αστέρων εκπομπής.

3. Παρουσιάσαμε ένα νέο μοντέλο (μοντέλο GR), ικανό να αναπαράγει θεωρητικά τα παρατηρούμενα πολύπλοκα περιγράμματα των φασματικών γραμμών. Για να επιτύχουμε κάτι τέτοιο, επιλύσαμε επιτυχώς τις εξισώσεις διάδοσης ακτινοβολίας και υπολογίσαμε για πρώτη φορά μια συνάρτηση γραμμής.

4. Κατασκευάσαμε δύο νέες συναρτήσεις κατανομής (Rotation distribution και Gauss-Rotation distribution).

5. Κατασκευάσαμε μια πρώτη έκδοση ενός λογισμικού, προκειμένου να αναπαράγουμε τα παρατηρούμενα περιγράμματα και να υπολογίσουμε μια σειρά φυσικών παραμέτρων.

6. Εφαρμόσαμε επιτυχώς το μοντέλο GR σε μεγάλο αριθμό φασματικών γραμμών σε φάσματα θερμών αστέρων εκπομπής και κβάζαρ.

Υπολογίζοντας μια σειρά παραμέτρων για πρώτη φορά, μπορούμε να μελετήσουμε τους φυσικούς νόμους που επικρατούν στις περιοχές που δημιουργούν αυτές τις φασματικές γραμμές.

1. Lyratzi, E., Danezis, E., Popović, L. Č., Antoniou, A., Dimitrijević, M. S. & Stathopoulos, D.: Studying the complex BAL profiles in the BALQSOs spectra, Proceedings of 25th Summer School and International Symposium on the Physics of Ionized Gases (SPIG 2010), held on August, 30 - September, 3, 2010, Donji Milanovac, Serbia.

2. Lyratzi, E., Danezis, E., Popović, L. Č., Dimitrijević, M. S. & Antoniou, A.: Broad Absorption Lines with DACs and SACs in the spectra of PG 0946+301 and PG 1254+047, Proceedings of “JENAM 2010 The European Week of Astronomy and Space Science”, held on September 6-10, 2010, Lisbon, Portugal.

3. Antoniou, A., Danezis, E., Lyratzi, E., Popović, L. Č. & Dimitrijević, M. S.: A statistical study of the UV Mg II resonance lines’ parameters in 20 Be stars, Proceedings of “JENAM 2010 The European Week of Astronomy and Space Science”, held on September 6-10, 2010, Lisbon, Portugal.

4. Danezis, E., Lyratzi, E., Antoniou, A., Popović, L. Č., Dimitrijević, M. S.: Studying the complex spectral line profiles in the spectra of hot emission stars and quasars, Proceedings of the “1^st Workshop: Astrophysical winds and disks, Similar phenomena is stars and quasars”, held September 3-8, 2009, Platamonas, Greece. Edited by Emmanuel Danezis and Evangelia Lyratzi (under publication).

5. Lyratzi, E., Danezis, E., Popović, L. Č., Dimitrijević, M. S., Antoniou, A. & Stathopoulos, D.: Kinematic properties of the Broad Absorption Line Regions in the spectra of quasars, Proceedings of the “1^st Workshop: Astrophysical winds and disks, Similar phenomena is stars and quasars”, held September 3-8, 2009, Platamonas, Greece. Edited by Emmanuel Danezis and Evangelia Lyratzi (under publication).

6. Antoniou, A., Danezis, E., Lyratzi, E., Popović, L. Č., Dimitrijević, M. S. & Theodossiou, E.: Studying the location of SACs and DACs regions in the environment of hot emission stars, Proceedings of the “1^st Workshop: Astrophysical winds and disks, Similar phenomena is stars and quasars”, held September 3-8, 2009, Platamonas, Greece. Edited by Emmanuel Danezis and Evangelia Lyratzi (under publication).

7. Lyratzi, E., Danezis, E., Popović, L. Č., Dimitrijević, M. S., Antoniou, A.: Ways of creation of DACs and SACs in the spectra of PG 0946+301 and PG 1254+047, 2010, ASPC, 424, 308, Proceedings of the 9th International Conference of the Hellenic Astronomical Society, held September 20-24, 2009 in Athens, Greece. Edited by Kanaris Tsinganos, Despina Hatzidimitriou and Titos Matsakos.

8. Danezis, E., Lyratzi, E., Popović, L. Č., Dimitrijević, M. S., Antoniou, A.: Investigating DACs/SACs Phenomena in Hot Emission Stars and Quasars, 2010, ASPC, 424, 305, Proceedings of the 9th International Conference of the Hellenic Astronomical Society, held September 20-24, 2009 in Athens, Greece. Edited by Kanaris Tsinganos, Despina Hatzidimitriou and Titos Matsakos.

9. Antoniou, A., Danezis, E., Lyratzi, E., Popović, L. Č., Dimitrijević, M. S., Stathopoulos, D.: A New Approach of the GR Model, 2010, ASPC, 424, 187, Proceedings of the 9th International Conference of the Hellenic Astronomical Society, held September 20-24, 2009 in Athens, Greece. Edited by Kanaris Tsinganos, Despina Hatzidimitriou and Titos Matsakos.

10. Danezis, E., Lyratzi, E., Popović, L. Č., Dimitrijević, M. S., Antoniou, A.: Interpreting the complex line profiles in the stellar spectra, 2009, NewAR, 53, 214

11. Lyratzi, E., Popović, L. Č., Danezis, E., Dimitrijević, M. S., Antoniou, A.: Kinematics of the broad absorption line region in QSOs: Rotation and random motion, 2009, NewAR, 53, 179.

12. Antoniou, A., Danezis, E., Lyratzi, E., Popović, L. Č., Dimitrijević, M. S., Theodosiou, E., Stathopoulos, D.: A study of the atmospheric structure of AX Mon (HD 45910), 2009, CoAst, 159, 119, Proceedings of “JENAM 2008 Symposium No 4: Asteroseismology and Stellar Evolution”, held on September 8-12, 2008, edited by Sonja Schuh and Gerald Handler.

13. Antoniou, A., Danezis, E., Lyratzi, E., Nikolaidis, D., Popović, L. Č. & Dimitrijević, M. S.: Kinematical parameters in the coronal and post-coronal regions of the Oe stars, 2008, POBeo, 84, 443, 2008, JPhCS, 133a, 2028, 24th Summer School and International Symposium on the Physics of Ionized Gases, (SPIG 2008), August 25-29, 2008, Novi Sad, Serbia.

14. Lyratzi, E., Danezis, E., Popović, L. Č., Dimitrijević, M. S. & Antoniou, A.: DACs and SACs in the UV Spectrum of the Quasar PG 0946+301, 2008, AIPC, 1058, 323, 19th International Conference on Spectral Line Shapes, (19 ICSLS), June 15 - 20, 2008, Valladolid, Spain.

15. Lyratzi, E., Danezis, E., Popović, L. Č., Dimitrijević, M. S. & Antoniou, A.: Kinematics of Broad Absorption Line Regions of PG 1254+047, 2008, AIPC, 1058, 320, 19th International Conference on Spectral Line Shapes, (19 ICSLS), June 15 - 20, 2008, Valladolid, Spain.

16. Antoniou, A., Danezis, E., Lyratzi, E., Popović, L. Č., Dimitrijević, M. S., Theodosiou, E. & Katsavrias, G.: A Study of the Structure of Different Ionization Potential Regions in the Atmosphere of AX Mon (HD 45910), 2008, AIPC, 1058, 317, 19th International Conference on Spectral Line Shapes, (19 ICSLS), June 15 - 20, 2008, Valladolid, Spain.

17. Antoniou, A., Danezis, E., Lyratzi, E., Popović, L. Č., Dimitrijević, M. S., Theodosiou, E. & Stathopoulos, D.: AX Mon (HD 45910) Kinematical Parameters in the Fe II Spectral Lines as a Function of the Excitation Potential, 2008, AIPC, 1058, 314, 19th International Conference on Spectral Line Shapes, (19 ICSLS), June 15 - 20, 2008, Valladolid, Spain.

18. Danezis, E., Lyratzi, E., Popović, L. Č. & Dimitrijević, M. S., Antoniou, A.: Similarity Between DACs/SACs Phenomena in Hot Emission Stars and Quasars Absorption Lines, 2008, AIPC, 1058, 305, 19th International Conference on Spectral Line Shapes, (19 ICSLS), June 15 - 20, 2008, Valladolid, Spain.

19. Lyratzi, E., Danezis, E., Popović, L. Č., Dimitrijević, M. S. & Antoniou, A.: DACs and SACs phenomena in the C IV emitting regions of QSOs, 2008, POBeo, 84, 483, 24th Summer School and International Symposium on the Physics of Ionized Gases, (SPIG 2008), August 25-29, 2008, Novi Sad, Serbia.

20. Danezis, E., Lyratzi, E., Popović, L. Č., Antoniou, A. & Dimitrijević, M. S.: The very broad lines in the UV spectra of hot emission stars - A possible explanation, 2008, POBeo, 84, 463, 24th Summer School and International Symposium on the Physics of Ionized Gases, (SPIG 2008), August 25-29, 2008, Novi Sad, Serbia.

21. Antoniou, A., Danezis, E., Lyratzi, E., Popović, L. Č., Dimitrijević, M. S., Theodossiou, E. & Stathopoulos, D.: A study of AX Mon (HD 45910) kinematical parameters of the Fe II density regions, 2008, POBeo, 84, 455, 24th Summer School and International Symposium on the Physics of Ionized Gases, (SPIG 2008), August 25-29, 2008, Novi Sad, Serbia.

22. Danezis, E., Lyratzi, E., Popović, L. Č., Dimitrijević, M. S. & Antoniou, A.: DACs/SACs phenomena in astrophysical spectra, Joint European and National Astronomical Meeting (JENAM 2008), September 8-12, 2008, Vienna, Austria.

23. Lyratzi, E., Danezis, E., Popović, L. Č., Dimitrijević, M. S. & Antoniou, A.: An analysis of C IV and Si IV lines in the spectra of the quasars PG 0946+301 and PG 1254+047, Joint European and National Astronomical Meeting (JENAM 2008), September 8-12, 2008, Vienna, Austria.

24. Antoniou, A., Danezis, E., Lyratzi, E., Popović, L. Č., Dimitrijević, M. S. & Katsavrias, G.: The structure of atmospherical layers of AX Mon (HD 45910), Joint European and National Astronomical Meeting (JENAM 2008), September 8-12, 2008, Vienna, Austria.

25. Antoniou, A., Danezis, E., Lyratzi, E., Nikolaidis, D., Popović, L. Č. & Dimitrijević, M. S.: Investigation of the post coronal density regions of Oe stars, through the N V UV resonance lines, 2007, AIPC, 938, 210, VI Serbian Conference on Spectral Line Shapes in Astrophysics (VI SCSLSA), June 2007, Sremski Karlovci, Serbia.

26. Antoniou, A., Danezis, E., Lyratzi, E., Nikolaidis, D., Popović, L. Č. & Dimitrijević, M. S.: The N IV density regions in the spectra of 20 Oe stars, 2007, AIPC, 938, 206, VI Serbian Conference on Spectral Line Shapes in Astrophysics (VI SCSLSA), June 2007, Sremski Karlovci, Serbia.

27. Antoniou, A., Danezis, E., Lyratzi, E., Nikolaidis, D., Popović, L. Č. & Dimitrijević, M. S.: Long term variability of the coronal and post-coronal regions of the Oe star HD 149757 (zeta Oph), 2007, AIPC, 938, 198, VI Serbian Conference on Spectral Line Shapes in Astrophysics (VI SCSLSA), June 2007, Sremski Karlovci, Serbia.

28. Antoniou, A., Danezis, E., Lyratzi, E., Nikolaidis, D., Popović, L. Č. & Dimitrijević, M. S.: A statistical study of physical parameters of the C IV density regions in 20 Oe stars, 2007, AIPC, 938, 194, VI Serbian Conference on Spectral Line Shapes in Astrophysics (VI SCSLSA), June 2007, Sremski Karlovci, Serbia.

29. Lyratzi, E., Danezis, E., Dimitrijević, M. S., Popović, L. Č., Nikolaidis, D. & Antoniou, A.: The Evolution of Some Physical Parameters in the DACs/SACs Regions in Be Stellar Atmospheres, 2007, AIPC, 938, 176, VI Serbian Conference on Spectral Line Shapes in Astrophysics (VI SCSLSA), June 2007, Sremski Karlovci, Serbia.

30. Danezis, E., Antoniou, A., Lyratzi, E., Popović, L. Č., Dimitrijević, M. S. & Nikolaidis, D.: The DACs and SACs Effects From Stars to Quasars. Some First General Notices, 2007, AIPC, 938, 119, VI Serbian Conference on Spectral Line Shapes in Astrophysics (VI SCSLSA), June 2007, Sremski Karlovci, Serbia. (Προσκεκλημένη ομιλία).

31. Chatzichristou, E. T., Danezis, E., Popović, L. Č., Lyratzi, E. & Dimitrijević, M. S.: Studying the complex absorption and emission lines in AGN spectra, 2007, AIPC, 938, 65, VI Serbian Conference on Spectral Line Shapes in Astrophysics (VI SCSLSA), June 2007, Sremski Karlovci, Serbia.

32. Danezis, E., Nikolaidis D., Lyratzi, E., Popović, L. Č., Dimitriević, M. S., Antoniou, A. & Theodosiou, E.: A new model for the structure of DACs and SACs regions in Oe and Be stellar atmospheres, 2007, PASJ, 59, 827.

33. Antoniou, A., Danezis, E., Lyratzi, E., Nikolaidis, D., Popović, L. Č. & Dimitrijević, M. S.: Hyper Ionization Phenomena In The N V Region Of 20 Oe Stars, 2006, IAUJD, 4E, 7, 2007, uasb.conf, 155, XXVIth IAU General Assembly, 2006, August 14-25, Prague, Czech Republic.

34. Antoniou, A., Danezis, E., Lyratzi, E., Nikolaidis, D., Popović, L. Č. & Dimitrijević, M. S.: Hyper Ionization Phenomena In The N IV Region Of 20 Oe Stars, 2006, IAUJD, 4E, 6, 2007, uasb.conf, 149, XXVIth IAU General Assembly, 200680ugust 14-25, Prague, Czech Republic.

35. Antoniou, A., Danezis, E., Lyratzi, E., Nikolaidis, D., Popović, L. Č. & Dimitrijević, M. S.: Hyper Ionization Phenomena In The C IV Region Of 20 Oe Stars, 2006, IAUJD, 4E, 5, 2007, uasb.conf, 143, XXVIth IAU General Assembly, 2006, August 14-25, Prague, Czech Republic.

36. Lyratzi, E., Danezis, E., Antoniou, A., Nikolaidis, D., Popović, L. Č. & Dimitrijević, M. S.: The complex structure of the Si IV λλ 1393.755, 1402.77 Å regions of 68 Be-type stars, 2006, IAUJD, 4E, 10, 2007, uasb.conf, 137, XXVIth IAU General Assembly, 2006, August 14-25, Prague, Czech Republic.

37. Lyratzi, E., Danezis, E., Antoniou, A., Nikolaidis, D., Popović, L. Č. & Dimitrijević, M. S.: Study of Hα regions in 120 Be-type stars, 2006, IAUJD, 4E, 9, 2007, uasb.conf, 131, XXVIth IAU General Assembly, 2006, August 14-25, Prague, Czech Republic.

38. Danezis, E., Antoniou, A., Lyratzi, E., Nikolaidis, D., Popović, L. Č., Dimitrijević, M. S. & Theodossiou, E.: Long term variability of the coronal and post-coronal C IV region of the Oe star HD 93521, 2006, IAUJD, 4E, 4, 2007, uasb.conf, 113, XXVIth IAU General Assembly, 2006, August 14-25, Prague, Czech Republic.

39. Nikolaidis, D., Danezis, E., Lyratzi, E., Popović, L. Č., Dimitrijević, M. S., Antoniou, A. & Theodossiou, E.: A New Approach For DACs And SACs Phenomena In The Atmospheres Of Hot Emission Stars, 2006, IAUJD, 4E, 11, 2007, uasb.conf, 107, XXVIth IAU General Assembly, 2006, August 14-25, Prague, Czech Republic.

40. Lyratzi, E., Danezis, E., Popović, L. Č., Dimitijević, M. S. & Nikolaidis D.: The complex structure of the MgII λλ 2795.523, 2802.698 A regions of 64 Be stars, 2007, PASJ, 59, 357.

41. Danezis, E., Popović, L. Č., Lyratzi, E. & Dimitriević, M. S.: The peculiar absorption and emission phenomena from stars to quasars, 2006, AIPC, 876, 373, 23rd Summer School and International Symposium on the Physics of Ionized Gases, (SPIG 2006), 2006, August 28 - September 1, Kopaonik, Serbia (Προσκεκλημένη ομιλία).

42. Danezis, E., Lyratzi, E., Nikolaidis, D., Antoniou, A., Popović, L. Č. & Dimitrijević, M. S.: The SACs Broadening, 23rd Summer School and International Symposium on the Physics of Ionized Gases (SPIG 2006), August 28 - September 1, 2006, Kopaonik, Serbia.

43. Lyratzi, E., Danezis, E., Nikolaidis, D., Antoniou, A., Popović, L. Č., Dimitrijević, M. S. & Theodossiou, E.: The Photospheric And The Respective Si IV Regions' Rotational Velocities In 27 Be Stars, 23rd Summer School and International Symposium on the Physics of Ionized Gases, (SPIG 2006), August 28 - September 1, 2006, Kopaonik, Serbia.

44. Nikolaidis, D., Danezis, E., Lyratzi, E., Popović, L. Č., Antoniou, A. Dimitrijević, M. S. & Theodossiou, E.: A Study Of DACs And SACs Regions In The Atmospheres Of Hot Emissions Stars, 23rd Summer School and International Symposium on the Physics of Ionized Gases, (SPIG 2006), August 28 - September 1, 2006, Kopaonik, Serbia.

45. Antoniou, A., Danezis, E., Lyratzi, E., Nikolaidis, D., Popović, L. Č., Dimitrijević, M. S. & Theodossiou, E.: The Photospheric And The Respective C IV Regions' Rotational Velocities In 20 Oe Stars, 23rd Summer School and International Symposium on the Physics of Ionized Gases, (SPIG 2006), August 28 - September 1, 2006, Kopaonik, Serbia.

46. Lyratzi, E., Danezis, E., Nikolaidis, D., Antoniou, A., Popović, L. Č. & Dimitijević, M. S.: A new approach for the structure of Ha regions in 120 Be stars, 2006, AIPC, 848, 402, RECENT ADVANCES IN ASTRONOMY AND ASTROPHYSICS: 7th International Conference of the Hellenic Astronomical Society, September 2005, Kefallinia Island, Greece.

47. Danezis, E., Nikolaidis, D., Lyratzi, E., Popović, L. Č., Dimitijević, M. S. & Antoniou, A.: A new modelling approach for DACs and SACs regions in the atmospheres of hot emission stars, 2006, AIPC, 848, 380, RECENT ADVANCES IN ASTRONOMY AND ASTROPHYSICS: 7th International Conference of the Hellenic Astronomical Society, September 2005, Kefallinia Island, Greece.

48. Antoniou, A., Danezis, E., Lyratzi, E., Nikolaidis, D., Popović, L. Č., Dimitijević, M. S. & Theodossiou, E.: Long Term Variability of the Radial Velocities in the Coronal and Post-coronal Regions of the Oe Star HD 93521, 2006, AIPC, 848, 370, RECENT ADVANCES IN ASTRONOMY AND ASTROPHYSICS: 7th International Conference of the Hellenic Astronomical Society, September 2005, Kefallinia Island, Greece.

49. Lyratzi, E., Danezis, E., Nikolaidis, D., Popović, L. Č., Dimitriević, M. S., Theodossiou, E. & Antoniou, A.: A new approach for the structure of Ηα regions in 120 Be stars, 2005, MSAIS, 7, 114, 5th Serbian Conference on Spectral Lines Shapes in Astrophysics (V SCSLSA), June 2005, Vrsać, Serbia. (Προσκεκλημένη ομιλία).

50. Danezis, E., Nikolaidis, D., Lyratzi, E., Popović, L. Č., Dimitriević, M. S., Theodossiou, E. & Antoniou, A.: A new modelling approach for DACs and SACs regions in the atmospheres of hot emission stars, 2005, MSAIS, 7, 107, 5th Serbian Conference on Spectral Lines Shapes in Astrophysics (V SCSLSA), June 2005, Vrsać, Serbia. (Προσκεκλημένη ομιλία).

51. Popović, L. Č., Dimitrijević, M. S., Mediavilla, E., Danezis, E., Lyratzi, E., Bon, E., Ilić, D., Jovanović, P., Theodossiou, E. & Dačić, M.: Some spectroscopic methods for astrophysical plasma research, 2004, AIPC, 740, 497, 22nd Summer School and International Symposium on the Physics of Ionized Gases (SPIG 2004), 2004, August, 23 - 27, National Park "TARA", Serbia and Montenegro. (Προσκεκλημένη ομιλία) (right click here and select "Save Target As..." to download .pdf file)

52. Lyratzi, Ε., & Danezis, E.: SACs and DACs phenomena in the atmospheres of hot emission stars, 2004, AIPC, 740, 458, 22nd Summer School and International Symposium on the Physics of Ionized Gases (SPIG 2004), 2004, August, 23 - 27, National Park "TARA", Serbia and Montenegro. (Προσκεκλημένη ομιλία) (right click here and select "Save Target As..." to download .pdf file)

53. Danezis, E., Koutroumanou, M., Lyratzi, Ε., Theodossiou, E., Stathopoulou, M., Nikolaidis, D., Antoniou, A., Drakopoulos, C. & Soulikias, A.: Discontinuous structure of SiIV regions in the Oe star's λ Orionis atmosphere, 2004, hell.conf, 117, 6th Astronomical Conference of the Hellenic Astronomical Society, September 2005, Athens, Greece.

54. Lyratzi, Ε., Danezis, E., Stathopoulou, M., Theodossiou, E., Nikolaidis, D., Antoniou, A., Drakopoulos, C., Soulikias, A. & Koutroumanou, M.: Discontinuous phenomena in SiIV regions of BeV stars, 2004, hell.conf, 116L, 6th Astronomical Conference of the Hellenic Astronomical Society, September 2005, Athens, Greece.

55. Danezis, E., Antoniou, A., Lyratzi, Ε., Theodossiou, E., Stathopoulou, M., Nikolaidis, D., Drakopoulos, C., Soulikias, A. & Koutroumanou, M.: Discontinuous structure and SACs phenomena in the Oe star's HD 175754 atmosphere, 2004, hell.conf, 116D, 6th Astronomical Conference of the Hellenic Astronomical Society, September 2005, Athens, Greece.

56. Lyratzi, Ε., Danezis, E., Stathopoulou, M., Theodossiou, E., Nikolaidis, D., Antoniou, A., Drakopoulos, C., Soulikias, A. & Koutroumanou, M.: Discontinuous phenomena in MgII regions of BeV stars, 2004, hell.conf, 115L, 6th Astronomical Conference of the Hellenic Astronomical Society, September 2005, Athens, Greece.

57. Danezis, E., Lyratzi, Ε., Nikolaidis, D., Theodossiou, E., Stathopoulou, M., Drakopoulos, C. & Soulikias, A.: Discontinuous structures in early type stars' atmospheres, 2004, hell.conf, 115D, 6th Astronomical Conference of the Hellenic Astronomical Society, September 2005, Athens, Greece.

58. Lyratzi, Ε., Danezis, E., Popović, L. Č., Dimitrijević, M. S., Nikolaidis, D., Soulikias, A., Antoniou, A. & Stathopoulou, M.: The complex structure of the SiIV λλ 1393.73, 1402.73 A regions of 57 BeV stars, JENAM 2004, Spetember, 13-17, 2004, Granada, Spain. (right click here and select "Save Target As..." to download .pdf file)

59. Danezis, E., Antoniou, A., Popović, L. Č., Dimitrijević, M. S., Lyratzi, Ε., Nikolaidis, D., Soulikias, A. & Theodossiou, E.: Satellite Absorption Components of the UV spectral lines SiIV, CIV, NV, and NIV in the atmosphere of the Oe star HD 175754, JENAM 2004, Spetember, 13-17, 2004, Granada, Spain. (right click here and select "Save Target As..." to download .pdf file)

60. Danezis, E., Lyratzi, Ε., Popović, L. Č., Dimitrijević, M. S., Christou, G., Soulikias, A. & Antoniou, A.: Satellite Absorption Components of the UV spectral lines SiIV, CIV, NV, and NIV in the atmosphere of the Oe star HD 66811 (ζPup), JENAM 2004, September, 13-17, 2004, Granada, Spain. (right click here and select "Save Target As..." to download .pdf file).

61. Lyratzi, Ε., Danezis, E., Popović, L. Č., Dimitrijević, M. S., Nikolaidis, D., Thiedossiou, E., Soulikias, A. & Antoniou, A.: The complex structure of the MgII λλ 2795.523, 2802.698 A regions of 64 Be stars, 17th International Conference on Spectral Line Shapes (17th ICSLS), June 21-25, 2004, Paris, France.

62. Lyratzi, Ε., Danezis, E., Popović, L. Č., Dimitrijević, M. S., Nikolaidis, D., Theiodossiou, E., Soulikias, A. & Antoniou, A.: The complex structure of the SiIV λλ 1393.73, 1402.73 A regions of 42 BeV stars, 17th International Conference on Spectral Line Shapes (17th ICSLS), June 21-25, 2004, Paris, France.

63. Popović, L. Č., Danezis, E., Lyratzi,E., Dimitrijević, M. S. & Theodossiou E.: A model for the Broad Absorption Line Region in BAL-QSOs, The conference of Euro-asian astronomical society, Russian Astronomical conference, July, 2 - 10, 2004, Moscow, Russia.

64. Danezis, E., Lyratzi, Ε., Nikolaidis, D., Stathopoulou, M., Theodossiou, E., Drakopoulos, C., Soulikias, A. & Antoniou, A.: On modeling SACs regions in early type atmospheres, 2003, POBeo, 76, 179, IV Serbian Conference on Spectral Lines Shapes (IV SCSLS), 2003, October 10-15, Arandjelovac, Serbia.

65. Danezis, E., Antoniou, A., Lyratzi, Ε., Theodossiou, E., Stathopoulou, M., Nikolaidis, D., Drakopoulos, C., Soulikias, A. & Koutroumanou, M.: The complex coronal structure of the Oe star HD 175754, 2003, POBeo, 76, 175, IV Serbian Conference on Spectral Lines Shapes (IV SCSLS), 2003, October 10-15, Arandjelovac, Serbia.

66. Lyratzi, Ε., Danezis, E., Stathopoulou, M., Theodossiou, E., Nikolaidis, D., Drakopoulos, C. & Soulikias, A.: The complex structure of the MgII regions of 40 Be V stars, 2003, POBeo, 76, 27, IV Serbian Conference on Spectral Lines Shapes (IV SCSLS), 2003, October 10-15, Arandjelovac, Serbia (Προσκεκλημένη ομιλία).

67. Danezis, E., Lyratzi, E., Nikolaides, D., Theodossiou, E., Stathopoulou, M., Christou, G., Drakopoulos, C., Kosionidies, A. & Soulikias, A.: Applications of a New Model of Density Layers of Matter in the Expanding Gaseous Envelope of Oe and Be Stars, 2003, IAUS, 210P, E29, 210th Symposium of the International Astronomical Union, June 2002, Uppsala, Sweden.

68. Danezis, E., Nikolaides, D., Lyratzi, E., Stathopoulou, M., Theodossiou, E., Kosionidies, A., Drakopoulos, C., Christou, G. & Koutsouris, P.: A new model of density layers of matter to the expanding gaseous envelope of Oe and Be stars, 2003, IAUS, 210P, E3, 210th Symposium of the International Astronomical Union, June 2002, Uppsala, Sweden.

69. Danezis E., Nikolaidis D., Lyratzi Ε., Stathopoulou M., Theodossiou E., Kosionidis A., Drakopoulos C., Christou G. & Koutsouris P.: Α New Model for the Structure of the DACs Regions in the Oe and Be stars, 2003, Ap&SS, 284, 1119. (right click here and select "Save Target As..." to download .pdf file)

70. Danezis, E., Lyratzi, Ε., Nikolaidis, D., Theodossiou, E., Stathopoulou, M., Drakopoulos, C. & Soulikias, A.: SACs phenomena in early type stars, JENAM 2003, August 25 - 31, 2003 Budapest, Hungary.

71. Lyratzi, Ε., Danezis, E., Stathopoulou, M., Theodossiou, E., Nikolaidis, D., Antoniou, A., Drakopoulos, C., Soulikias, A. & Koutroumanou, M.: SACs phenomena in MgII regions of 40 BeV stars, JENAM 2003, August 25 - 31, 2003 Budapest, Hungary.

72. Lyratzi, Ε., Danezis, E., Stathopoulou, M., Theodossiou, E., Nikolaidis, D., Antoniou, A., Drakopoulos, C., Soulikias, A. & Koutroumanou, M.: SACs phenomena in SiIV regions of 42 BeV stars, JENAM 2003, August 25 - 31, 2003 Budapest, Hungary. (right click here and select "Save Target As..." to download .pdf file)

73. Danezis, E., Antoniou, A., Lyratzi, Ε., Theodossiou, E., Stathopoulou, M., Nikolaidis, D., Drakopoulos, C., Soulikias, A. & Koutroumanou, M.: The complex structure of hyperionization regions of the Oe star HD 175754, JENAM 2003, August 25 - 31, 2003 Budapest, Hungary. (right click here and select "Save Target As..." to download .pdf file)

74. Danezis, E., Koutroumanou, M., Lyratzi, Ε., Theodossiou, E., Stathopoulou, M., Nikolaidis, D., Antoniou, A., Drakopoulos, C. & Soulikias, A.: The complex structure of SiIV regions of the Oe star λ Orionis, JENAM 2003, August 25 - 31, 2003 Budapest, Hungary. (right click here and select "Save Target As..." to download .pdf file)

75. Lyratzi E., Danezis E., Nikolaidis D., Theodossiou E., Stathopoulou M., Drakopoulos C., Soulikias A. & Koutsouris P.: The complex structure of the expanding gaseous envelope of the Be star HD45910 (AX Mon), 210th Symposium of the International Astronomical Union, June 2002, Uppsala, Sweden. (right click here and select "Save Target As..." to download .pdf file)

76. Lyratzi E., Danezis E., Nikolaides D., Theodossiou E., Stathopoulou M., Kyriakopoulou A. & Soulikias A.: The complex structure of Ha region in the gaseous envelope of Be V stars, 210th Symposium of the International Astronomical Union, June 2002, Uppsala, Sweden. (right click here and select "Save Target As..." to download .pdf file)

77. Danezis E., Lyratzi E., Nikolaides D., Theodossiou E., Stathopoulou M., Christou G. & Soulikias A.: The complex structure of MgII region in the gaseous envelope of Be V stars, 210th Symposium of the International Astronomical Union, June 2002, Uppsala, Sweden. (right click here and select "Save Target As..." to download .pdf file)

78. Danezis E., Lyratzi E., Christou G., Theodossiou E., Stathopoulou M., Nikolaides D. & Kyriakopoulou A.: Hyperionisation and emission phenomena in the coronal an post-coronal region of the moving atmosphere of the Oe star HD66811 (ζPup), 210th Symposium of the International Astronomical Union, June 2002, Uppsala, Sweden. (right click here and select "Save Target As..." to download .pdf file)

79. Lyratzi, E., Danezis, E., Nikolaidis, D., Theodossiou, E., Stathopoulou, M., Drakopoulos, Ch. & Bourma, P.: Application of a new model of density shells of matter to the expanding gaseous envelope of the star HD 45910 (AXMonocerotis), 2001, hell.confE, 67, 5th Hellenic Astronomical Conference, September 2001, Crete, Greece. (right click here and select "Save Target As..." to download .pdf file)

80. Danezis, E., Nikolaides, D., Lyratzi, E., Stathopoulou, M., Theodossiou, E., Kyriakopoulou, A., Christou, G., Kossionides, A. & Drakopoulos, C.: The complex structure of the expanding gaseous envelope of the star HD 164794 (9Sagittarii), 2001, hell.confE, 66, 5th Hellenic Astronomical Conference, September 2001, Crete, Greece. (right click here and select "Save Target As..." to download .pdf file)

81. Danezis, E., Lyratzi, E., Theodossiou, E., Nikolaidis, D., Stathopoulou, M., Kiriakopoulou, A., Ghristou, G. & Drakopoulos, Ch.: Application of a new model of density shells of matter to the expanding gaseous envelope of the star HD 175754, 2001, hell.confE, 65, 5th Hellenic Astronomical Conference, September 2001, Crete, Greece. (right click here and select "Save Target As..." to download .pdf file)

82. Danezis, E., Nikolaidis, D., Lyratzi, E., Stathopoulou, M., Theodossiou, E., Kosionidis, Α., Drakopoulos, Ch. & Soulikias, A.: Phenomena of hyperionization and emission in the gaseous envelope of the star λ Orionis, 2001, hell.confE, 64, 5th Hellenic Astronomical Conference, September 2001, Crete, Greece. (right click here and select "Save Target As..." to download .pdf file)

83. Danezis, E., Christou, G., Stathopoulou, M., Theodossiou, E., Nikolaidis, D., Lyratzi, E., Drakopoulos, Ch., Bourma, E. & Soulikias, A.: Phenomena of hyperionization and emission in the gaseous envelope of the star HD 66811 (ζ Puppis), 2001, hell.confE, 63, 5th Hellenic Astronomical Conference, September 2001, Crete, Greece. (right click here and select "Save Target As..." to download .pdf file)

84. Danezis E., Kiriakopoulou A., Nikolaidis D., Theodossiou E., Stathopoulou M., Lyratzi E., Ghristou G. & Kosionidis A.: A final consideration of the developing velocity fields in the gaseous envelope of the star HD 50138, 2001, hell.confE, 62, 5th Hellenic Astronomical Conference, September 2001, Crete, Greece. (right click here and select "Save Target As..." to download .pdf file)

85. Danezis E., Nikolaidis D., Theodossiou E., Kosionidis A., Stathopoulou M., Lyratzi V., Draakopoulos C. & Bourma P.: A simple model for the complex structure of moving atmospheric shells in Oe and Be stars. The example of HD 36861, some first conclusions. JENAM 2000, May 29-June 3, 2000 Moscow, Russia. (click here for Abstract)

86. Danezis E., Nikolaidis D., Theodossiou E., Kosionidis A., Stathopoulou M., Lyratzi V., Draakopoulos C. & Bourma P.: A simple model for the complex structure of moving atmospheric shells in Oe and Be stars. The example of HD 66811, some first conclusions. JENAM 2000, May 29-June 3, 2000 Moscow, Russia. (click here for Abstract)

87. Danezis E., Nikolaidis D., Theodossiou E., Kosionidis A., Stathopoulou M., Lyratzi V., Draakopoulos C. & Bourma P.: A simple model for the complex structure of moving atmospheric shells in Oe and Be stars. The example of HD 152408, some first conclusions. JENAM 2000, May 29-June 3, 2000 Moscow, Russia. (click here for Abstract)