The Bulgarian National Astronomical Observatory (NAO) located close to the Rozhen ridge in the Rh... more The Bulgarian National Astronomical Observatory (NAO) located close to the Rozhen ridge in the Rhodope Mountains near Smolyan, is presented with its history, functional characteristics and capabilities. Its latitude of 41◦ 41.5′N gives opportunities to investigate over 80% of the celestial sphere. The altitude of 1750 m lies within the height level that is most populated by observatories (1500-2500m). However, the astroclimate (mean seeing ∼2” and 35-40% clear sky time) is worse than that of the best world sites and corresponds to the mean for the continental Southern Europe. The light pollution near NAO is still the lowest among the Balkan sites, but some problems arise because of the ever growing illumination from the Pamporovo resort and the nearby towns of Smolyan and Chepelare. Equipped with 2-m, 70and 60-cm stellar and 15-cm solar coronograph telescopes, NAO allows observations to be made for a wide range of optical astrophysical investigations: from Solar System bodies to ext...
Symposium - International Astronomical Union, 2004
We present recent X-ray and optical observations of five M-type giants which were detected as str... more We present recent X-ray and optical observations of five M-type giants which were detected as strong X-ray sources. One of these stars, HR 5512, shows short-term variations in both X-ray flux as well as in the shape of the Hα and Ca ii H+K lines, and it rotates much faster than M-type giants usually do. No indication of binarity has been found for this star. We propose that the X-ray emission of HR 5512 is related to a large degree of stellar activity. For two other stars (15 Tri, HR 7547) radial velocity observations seem to indicate spectroscopic binarity.
New measurements of the outer radius of the light echo two years after the peculiar outburst of V... more New measurements of the outer radius of the light echo two years after the peculiar outburst of V838 Mon are presented. Since the outburst maximum (Feb 06 2002) the angular radius rho of the echo increases with the time t as rho˜t^{0.537}, which is close to the theoretically expected law rho˜t^{0.5}. However, the up to now available data cannot allow
The authors present the names of and some myths and beliefs connected with the most popular among... more The authors present the names of and some myths and beliefs connected with the most popular among the Bulgarian people stars and constellations. Only the names of "key" objects that are, due to their position and seasonal visibility, of great importance for the economic calendar and social life have been preserved in people's memory. This importance is illustrated by the legends and the calendar practices of the old Bulgarians. The most impressive are the beliefs connected with the Pleiades, the Great Bear, Orion, Lyra and the Milky Way as well. The authors suppose, and make an attempt to show this, that the roots of some of the preserved astronomical beliefs can be found in the very ancient times (up to 11th - 13th millennia BC).
We report the detection of an unusually high lithium content in HD 232862, a field giant classifi... more We report the detection of an unusually high lithium content in HD 232862, a field giant classified as a G8II star, and hosting a magnetic field. With the spectropolarimeters ESPaDOnS at CFHT and NARVAL at TBL, we have collected high resolution and high signal-to-noise spectra of three giants : HD 232862, KU Peg and HD 21018. From spectral synthesis we have inferred stellar parameters and measured lithium abundances that we have compared to predictions from evolutionary models. We have also analysed Stokes V signatures, looking for a magnetic field on these giants. HD 232862, presents a very high abundance of lithium (ALi = 2.45 +/- 0.25 dex), far in excess of the theoretically value expected at this spectral type and for this luminosity class (i.e, G8II). The evolutionary stage of HD 232862 has been precised, and it suggests a mass in the lower part of the [1.0 Msun ; 3.5 Msun ] mass interval, likely 1.5 to 2.0 solar mass, at the bottom of the Red Giant Branch. Besides, a time variable Stokes V signature has been detected in the data of HD 232862 and KU Peg, pointing to the presence of a magnetic field at the surface of these two rapidly rotating active stars.
Data are presented from the study of two B-V spectra of HD40574. The observational and theoretica... more Data are presented from the study of two B-V spectra of HD40574. The observational and theoretical H-gamma and H-delta profiles are compared. It is found that the star has an effective temperature of 14,000 + or - 150 K and lg g = 3.95 + or - 0.10. HD40574 is classified as a normal B6 IV star. The stellar parameters discussed include rotation, luminosity, mass, radius, distance to the star, evolutionary status, and age.
The possible peculiarity of HD 44907 is examined qualitatively, and more precise physical paramet... more The possible peculiarity of HD 44907 is examined qualitatively, and more precise physical parameters necessary for further study of the chemical composition of its atmosphere are obtained. The results show that HD 44907 has the main properties characteristic of He-weak stars: weakness of the He I lines, slow rotation, and a metallic spectrum which is close to normal. The evolutionary status of HD 44907, according to the mass and luminosity estimates made, is typical for a star with mass approximately equal to 4.5 solar masses in the evolutionary phase of hydrogen burning in its core. This phase has a duration of around 10 to the 8 years, and so the age of HD 44907 is concluded to be less than 100 million years. It is noted that the Geneva system criterion for peculiarity is satisfied quite well for the case of HD 44907.
Page 1. Bulgarian astronomy: From John Exarch till nowadays Dimitar Z. Kolev Institute of Astrono... more Page 1. Bulgarian astronomy: From John Exarch till nowadays Dimitar Z. Kolev Institute of Astronomy and NAO, Bulgarian Academy of Sciences dzkolev@abv.bg (Invited conference contribution) Abstract. This paper presents ...
Romanian Astronomical Journal Supplement, Vol. 16, Proceedings of the Scientific Session, Scienti... more Romanian Astronomical Journal Supplement, Vol. 16, Proceedings of the Scientific Session, Scientific Programs and Astronomy Education in See and Ukraine, Bucharest, Romania, 16--17 September 2005. Edited by Magda Stavinschi and Vasile Mioc., p. 255
... Интересът към небето наистина е изиграл огромна роля във формира- нето на човешкатакултура. .... more ... Интересът към небето наистина е изиграл огромна роля във формира- нето на човешкатакултура. ... на гръцкия зодиак и с явна астрологична насоченост, на звездната карта са изобразени в оригиналния им вид и редица египетски съзвездия Хипопотама, Би ...
We have obtained high-dispersion blue spectograms and BV photometry of the high-latitude F-superg... more We have obtained high-dispersion blue spectograms and BV photometry of the high-latitude F-supergiant HR 4912=HD 112374. As a result of our curve-of-growth analysis we conclude that it appears to have the parameters of a F-supergiant with slight metal deficiency ([Fe/H]=-0.7). The latter depends much upon the derived temperature of HR 4912, hence we pay special attention to this problem. Our
... We are most grateful to Piotr Ligeza on the one side, and to Regina Rudawska and Roman Hirsch... more ... We are most grateful to Piotr Ligeza on the one side, and to Regina Rudawska and Roman Hirsch on the other side, for their contribution of ... Biul., 75, 31 [NASA ADS] (In the text); Gimenez, A., &Zamorano, J. 1985, Ap&SS, 114, 259G [NASA ADS] (In the text); Kim, Y., Demarque, P ...
The Bulgarian National Astronomical Observatory (NAO) located close to the Rozhen ridge in the Rh... more The Bulgarian National Astronomical Observatory (NAO) located close to the Rozhen ridge in the Rhodope Mountains near Smolyan, is presented with its history, functional characteristics and capabilities. Its latitude of 41◦ 41.5′N gives opportunities to investigate over 80% of the celestial sphere. The altitude of 1750 m lies within the height level that is most populated by observatories (1500-2500m). However, the astroclimate (mean seeing ∼2” and 35-40% clear sky time) is worse than that of the best world sites and corresponds to the mean for the continental Southern Europe. The light pollution near NAO is still the lowest among the Balkan sites, but some problems arise because of the ever growing illumination from the Pamporovo resort and the nearby towns of Smolyan and Chepelare. Equipped with 2-m, 70and 60-cm stellar and 15-cm solar coronograph telescopes, NAO allows observations to be made for a wide range of optical astrophysical investigations: from Solar System bodies to ext...
Symposium - International Astronomical Union, 2004
We present recent X-ray and optical observations of five M-type giants which were detected as str... more We present recent X-ray and optical observations of five M-type giants which were detected as strong X-ray sources. One of these stars, HR 5512, shows short-term variations in both X-ray flux as well as in the shape of the Hα and Ca ii H+K lines, and it rotates much faster than M-type giants usually do. No indication of binarity has been found for this star. We propose that the X-ray emission of HR 5512 is related to a large degree of stellar activity. For two other stars (15 Tri, HR 7547) radial velocity observations seem to indicate spectroscopic binarity.
New measurements of the outer radius of the light echo two years after the peculiar outburst of V... more New measurements of the outer radius of the light echo two years after the peculiar outburst of V838 Mon are presented. Since the outburst maximum (Feb 06 2002) the angular radius rho of the echo increases with the time t as rho˜t^{0.537}, which is close to the theoretically expected law rho˜t^{0.5}. However, the up to now available data cannot allow
The authors present the names of and some myths and beliefs connected with the most popular among... more The authors present the names of and some myths and beliefs connected with the most popular among the Bulgarian people stars and constellations. Only the names of "key" objects that are, due to their position and seasonal visibility, of great importance for the economic calendar and social life have been preserved in people's memory. This importance is illustrated by the legends and the calendar practices of the old Bulgarians. The most impressive are the beliefs connected with the Pleiades, the Great Bear, Orion, Lyra and the Milky Way as well. The authors suppose, and make an attempt to show this, that the roots of some of the preserved astronomical beliefs can be found in the very ancient times (up to 11th - 13th millennia BC).
We report the detection of an unusually high lithium content in HD 232862, a field giant classifi... more We report the detection of an unusually high lithium content in HD 232862, a field giant classified as a G8II star, and hosting a magnetic field. With the spectropolarimeters ESPaDOnS at CFHT and NARVAL at TBL, we have collected high resolution and high signal-to-noise spectra of three giants : HD 232862, KU Peg and HD 21018. From spectral synthesis we have inferred stellar parameters and measured lithium abundances that we have compared to predictions from evolutionary models. We have also analysed Stokes V signatures, looking for a magnetic field on these giants. HD 232862, presents a very high abundance of lithium (ALi = 2.45 +/- 0.25 dex), far in excess of the theoretically value expected at this spectral type and for this luminosity class (i.e, G8II). The evolutionary stage of HD 232862 has been precised, and it suggests a mass in the lower part of the [1.0 Msun ; 3.5 Msun ] mass interval, likely 1.5 to 2.0 solar mass, at the bottom of the Red Giant Branch. Besides, a time variable Stokes V signature has been detected in the data of HD 232862 and KU Peg, pointing to the presence of a magnetic field at the surface of these two rapidly rotating active stars.
Data are presented from the study of two B-V spectra of HD40574. The observational and theoretica... more Data are presented from the study of two B-V spectra of HD40574. The observational and theoretical H-gamma and H-delta profiles are compared. It is found that the star has an effective temperature of 14,000 + or - 150 K and lg g = 3.95 + or - 0.10. HD40574 is classified as a normal B6 IV star. The stellar parameters discussed include rotation, luminosity, mass, radius, distance to the star, evolutionary status, and age.
The possible peculiarity of HD 44907 is examined qualitatively, and more precise physical paramet... more The possible peculiarity of HD 44907 is examined qualitatively, and more precise physical parameters necessary for further study of the chemical composition of its atmosphere are obtained. The results show that HD 44907 has the main properties characteristic of He-weak stars: weakness of the He I lines, slow rotation, and a metallic spectrum which is close to normal. The evolutionary status of HD 44907, according to the mass and luminosity estimates made, is typical for a star with mass approximately equal to 4.5 solar masses in the evolutionary phase of hydrogen burning in its core. This phase has a duration of around 10 to the 8 years, and so the age of HD 44907 is concluded to be less than 100 million years. It is noted that the Geneva system criterion for peculiarity is satisfied quite well for the case of HD 44907.
Page 1. Bulgarian astronomy: From John Exarch till nowadays Dimitar Z. Kolev Institute of Astrono... more Page 1. Bulgarian astronomy: From John Exarch till nowadays Dimitar Z. Kolev Institute of Astronomy and NAO, Bulgarian Academy of Sciences dzkolev@abv.bg (Invited conference contribution) Abstract. This paper presents ...
Romanian Astronomical Journal Supplement, Vol. 16, Proceedings of the Scientific Session, Scienti... more Romanian Astronomical Journal Supplement, Vol. 16, Proceedings of the Scientific Session, Scientific Programs and Astronomy Education in See and Ukraine, Bucharest, Romania, 16--17 September 2005. Edited by Magda Stavinschi and Vasile Mioc., p. 255
... Интересът към небето наистина е изиграл огромна роля във формира- нето на човешкатакултура. .... more ... Интересът към небето наистина е изиграл огромна роля във формира- нето на човешкатакултура. ... на гръцкия зодиак и с явна астрологична насоченост, на звездната карта са изобразени в оригиналния им вид и редица египетски съзвездия Хипопотама, Би ...
We have obtained high-dispersion blue spectograms and BV photometry of the high-latitude F-superg... more We have obtained high-dispersion blue spectograms and BV photometry of the high-latitude F-supergiant HR 4912=HD 112374. As a result of our curve-of-growth analysis we conclude that it appears to have the parameters of a F-supergiant with slight metal deficiency ([Fe/H]=-0.7). The latter depends much upon the derived temperature of HR 4912, hence we pay special attention to this problem. Our
... We are most grateful to Piotr Ligeza on the one side, and to Regina Rudawska and Roman Hirsch... more ... We are most grateful to Piotr Ligeza on the one side, and to Regina Rudawska and Roman Hirsch on the other side, for their contribution of ... Biul., 75, 31 [NASA ADS] (In the text); Gimenez, A., &Zamorano, J. 1985, Ap&SS, 114, 259G [NASA ADS] (In the text); Kim, Y., Demarque, P ...
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