B. Yasarsoy - Academia.edu (original) (raw)
Papers by B. Yasarsoy
An investigation of the O-C times has been carried out, using a data set based on the previous pu... more An investigation of the O-C times has been carried out, using a data set based on the previous published times of light maxima, largely enriched by those obtained during an intensive multisite photometric campaign of BL Cam lasting several months.
Gelisen dunyada kirlenen yalnizca dogamiz degil, geceleri gordugumuz gokyuzu de isiklarimiz sayes... more Gelisen dunyada kirlenen yalnizca dogamiz degil, geceleri gordugumuz gokyuzu de isiklarimiz sayesinde kirlenmeye ve daha az yildizi gokyuzunde gormeye basladik. Ozellikle buyuksehirlerde yasayan insanlarin gokyuzundeki bir kac parlak yildizdan daha fazlasini gorememeleri ve karanlik gokyuzune duyulan ihtiyacin artmasindan oturu gunumuzde isik kirliliginin az oldugu gokyuzleri koruma altina alinmaya baslamistir. Bursa Karanlik Gokyuzu Parki, boylesi ihtiyaclarin karsilanmasi ve ulkemizde de karanlik bir gokyuzu bilinci olusturmak icin Bursa Buyukshir Belediyesinin katkilari ile Uludag'da kurulmasi planlanan Turkiye'nin ilk Karanlik Gokyuzu Parkidir.
An investigation of the O-C times has been carried out, using a data set based on the previous pu... more An investigation of the O-C times has been carried out, using a data set based on the previous published times of light maxima, largely enriched by those obtained during an intensive multisite photometric campaign of BL Cam lasting several months. (1 data file).
New Astronomy, 2014
The massive interacting close binary system V729 Cyg (OIa+O/WN9), plausibly progenitor of a Wolf-... more The massive interacting close binary system V729 Cyg (OIa+O/WN9), plausibly progenitor of a Wolf-Rayet system, is studied using new observations gathered over 65 nights and earlier published data. Radial velocity and five colour light curves are analysed simultaneously. Estimated physical parameters of the components are M 1 = 36 ± 3M ⊙ , M 2 = 10 ± 1M ⊙ , R 1 = 27 ± 1R ⊙ , R 2 = 15 ± 0.6R ⊙ , log (L 1 /L ⊙) = 5.59 ± 0.06, and log (L 2 /L ⊙) = 4.65 ± 0.07. We give only the formal 1σ scatter, but we believe systematic errors in the luminosities, of uncertain origin as discussed in the text, are likely to be much bigger. The distance of the Cygnus OB2 association is estimated as 967 ± 48 pc by using our newly obtained parameters.
Monthly Notices of the Royal Astronomical Society, 2012
We report on a multisite photometric campaign on the high-amplitude delta Scuti star V2367 Cyg in... more We report on a multisite photometric campaign on the high-amplitude delta Scuti star V2367 Cyg in order to determine the pulsation modes. We also used high-dispersion spectroscopy to estimate the stellar parameters and projected rotational velocity. Time series multicolour photometry was obtained during a 98-d interval from five different sites. These data were used together with model atmospheres and non-adiabatic pulsation models to identify the spherical harmonic degree of the three independent frequencies of highest amplitude as well as the first two harmonics of the dominant mode. This was accomplished by matching the observed relative light amplitudes and phases in different wavebands with those computed by the models. In general, our results support the assumed mode identifications in a previous analysis of Kepler data.
Astronomy & Astrophysics, 2007
Context. BL Cam is an extreme metal-deficient field high-amplitude SX Phe-type variable where a v... more Context. BL Cam is an extreme metal-deficient field high-amplitude SX Phe-type variable where a very complex frequency spectrum is detected, with a number of independent nonradial modes excited, unusual among the high-amplitude pulsators in the Lower Classical Instability Strip. Aims. An extensive and detailed study has been carried out to investigate the pulsational content and properties of this object. Methods. The analysis is based on 283 h of CCD observations obtained in the Johnson V filter, during a long multisite photometric campaign carried out along the Northern autumn-winter of 2005-2006. Additionally, multicolour BI photometry was also collected to study the phase shifts and amplitude ratios, between light curves obtained in different filters, for modal discrimination of the main excited modes. Results. The detailed frequency analysis revealed a very rich and dense pulsational content consisting of 25 significant peaks, 22 of them corresponding to independent modes: one is the already known main periodicity f 0 = 25.5765 cd −1 (∆V = 153 mmag) and the other 21 are excited modes showing very small amplitudes. Some additional periodicities are probably still remaining in the residuals. This represents the most complex spectrum ever detected in a high-amplitude pulsator of this type. The majority of the secondary modes suspected from earlier works are confirmed here and, additionally, a large number of new peaks are detected. The amplitude of the main periodicity f 0 seems to be stable during decades, but the majority of the secondary modes show strong amplitude changes from one epoch to another. The suspected fundamental radial nature of the main periodicity of BL Cam is confirmed, while the secondary peak f 1 = 25.2523 cd −1 is identified as a nonradial mixed mode g 4 with = 1. The radial double-mode nature, claimed by some authors for the main two frequencies of BL Cam, is not confirmed. Nevertheless, the frequency f 6 = 32.6464 cd −1 could correspond to the first radial overtone.
Astronomy and Astrophysics, 2010
Context. Short-period high-amplitude pulsating stars of Population I (δ Sct stars) and II (SX Phe... more Context. Short-period high-amplitude pulsating stars of Population I (δ Sct stars) and II (SX Phe variables) exist in the lower part of the classical (Cepheid) instability strip. Most of them have very simple pulsational behaviours, only one or two radial modes being excited. Nevertheless, BL Cam is a unique object among them, being an extreme metal-deficient field high-amplitude SX Phe variable with a large number of frequencies. Based on a frequency analysis, a pulsational interpretation was previously given. Aims. We attempt to interpret the long-term behaviour of the residuals that were not taken into account in the previous Observed-Calculated (O-C) short-term analyses. Methods. An investigation of the O-C times has been carried out, using a data set based on the previous published times of light maxima, largely enriched by those obtained during an intensive multisite photometric campaign of BL Cam lasting several months. Results. In addition to a positive (161 ± 3) × 10 −9 yr −1 secular relative increase in the main pulsation period of BL Cam, we detected in the O-C data short-(144.2 d) and long-term (∼3400 d) variations, both incompatible with a scenario of stellar evolution. Conclusions. Interpreted as a light travel-time effect, the short-term O-C variation is indicative of a massive stellar component (0.46 to 1 M) with a short period orbit (144.2 d), within a distance of 0.7 AU from the primary. More observations are needed to confirm the long-term O-C variations: if they were also to be caused by a light travel-time effect, they could be interpreted in terms of a third component, in this case probably a brown dwarf star (≥0.03 M), orbiting in ∼3400 d at a distance of 4.5 AU from the primary.
An investigation of the O-C times has been carried out, using a data set based on the previous pu... more An investigation of the O-C times has been carried out, using a data set based on the previous published times of light maxima, largely enriched by those obtained during an intensive multisite photometric campaign of BL Cam lasting several months.
Gelisen dunyada kirlenen yalnizca dogamiz degil, geceleri gordugumuz gokyuzu de isiklarimiz sayes... more Gelisen dunyada kirlenen yalnizca dogamiz degil, geceleri gordugumuz gokyuzu de isiklarimiz sayesinde kirlenmeye ve daha az yildizi gokyuzunde gormeye basladik. Ozellikle buyuksehirlerde yasayan insanlarin gokyuzundeki bir kac parlak yildizdan daha fazlasini gorememeleri ve karanlik gokyuzune duyulan ihtiyacin artmasindan oturu gunumuzde isik kirliliginin az oldugu gokyuzleri koruma altina alinmaya baslamistir. Bursa Karanlik Gokyuzu Parki, boylesi ihtiyaclarin karsilanmasi ve ulkemizde de karanlik bir gokyuzu bilinci olusturmak icin Bursa Buyukshir Belediyesinin katkilari ile Uludag'da kurulmasi planlanan Turkiye'nin ilk Karanlik Gokyuzu Parkidir.
An investigation of the O-C times has been carried out, using a data set based on the previous pu... more An investigation of the O-C times has been carried out, using a data set based on the previous published times of light maxima, largely enriched by those obtained during an intensive multisite photometric campaign of BL Cam lasting several months. (1 data file).
New Astronomy, 2014
The massive interacting close binary system V729 Cyg (OIa+O/WN9), plausibly progenitor of a Wolf-... more The massive interacting close binary system V729 Cyg (OIa+O/WN9), plausibly progenitor of a Wolf-Rayet system, is studied using new observations gathered over 65 nights and earlier published data. Radial velocity and five colour light curves are analysed simultaneously. Estimated physical parameters of the components are M 1 = 36 ± 3M ⊙ , M 2 = 10 ± 1M ⊙ , R 1 = 27 ± 1R ⊙ , R 2 = 15 ± 0.6R ⊙ , log (L 1 /L ⊙) = 5.59 ± 0.06, and log (L 2 /L ⊙) = 4.65 ± 0.07. We give only the formal 1σ scatter, but we believe systematic errors in the luminosities, of uncertain origin as discussed in the text, are likely to be much bigger. The distance of the Cygnus OB2 association is estimated as 967 ± 48 pc by using our newly obtained parameters.
Monthly Notices of the Royal Astronomical Society, 2012
We report on a multisite photometric campaign on the high-amplitude delta Scuti star V2367 Cyg in... more We report on a multisite photometric campaign on the high-amplitude delta Scuti star V2367 Cyg in order to determine the pulsation modes. We also used high-dispersion spectroscopy to estimate the stellar parameters and projected rotational velocity. Time series multicolour photometry was obtained during a 98-d interval from five different sites. These data were used together with model atmospheres and non-adiabatic pulsation models to identify the spherical harmonic degree of the three independent frequencies of highest amplitude as well as the first two harmonics of the dominant mode. This was accomplished by matching the observed relative light amplitudes and phases in different wavebands with those computed by the models. In general, our results support the assumed mode identifications in a previous analysis of Kepler data.
Astronomy & Astrophysics, 2007
Context. BL Cam is an extreme metal-deficient field high-amplitude SX Phe-type variable where a v... more Context. BL Cam is an extreme metal-deficient field high-amplitude SX Phe-type variable where a very complex frequency spectrum is detected, with a number of independent nonradial modes excited, unusual among the high-amplitude pulsators in the Lower Classical Instability Strip. Aims. An extensive and detailed study has been carried out to investigate the pulsational content and properties of this object. Methods. The analysis is based on 283 h of CCD observations obtained in the Johnson V filter, during a long multisite photometric campaign carried out along the Northern autumn-winter of 2005-2006. Additionally, multicolour BI photometry was also collected to study the phase shifts and amplitude ratios, between light curves obtained in different filters, for modal discrimination of the main excited modes. Results. The detailed frequency analysis revealed a very rich and dense pulsational content consisting of 25 significant peaks, 22 of them corresponding to independent modes: one is the already known main periodicity f 0 = 25.5765 cd −1 (∆V = 153 mmag) and the other 21 are excited modes showing very small amplitudes. Some additional periodicities are probably still remaining in the residuals. This represents the most complex spectrum ever detected in a high-amplitude pulsator of this type. The majority of the secondary modes suspected from earlier works are confirmed here and, additionally, a large number of new peaks are detected. The amplitude of the main periodicity f 0 seems to be stable during decades, but the majority of the secondary modes show strong amplitude changes from one epoch to another. The suspected fundamental radial nature of the main periodicity of BL Cam is confirmed, while the secondary peak f 1 = 25.2523 cd −1 is identified as a nonradial mixed mode g 4 with = 1. The radial double-mode nature, claimed by some authors for the main two frequencies of BL Cam, is not confirmed. Nevertheless, the frequency f 6 = 32.6464 cd −1 could correspond to the first radial overtone.
Astronomy and Astrophysics, 2010
Context. Short-period high-amplitude pulsating stars of Population I (δ Sct stars) and II (SX Phe... more Context. Short-period high-amplitude pulsating stars of Population I (δ Sct stars) and II (SX Phe variables) exist in the lower part of the classical (Cepheid) instability strip. Most of them have very simple pulsational behaviours, only one or two radial modes being excited. Nevertheless, BL Cam is a unique object among them, being an extreme metal-deficient field high-amplitude SX Phe variable with a large number of frequencies. Based on a frequency analysis, a pulsational interpretation was previously given. Aims. We attempt to interpret the long-term behaviour of the residuals that were not taken into account in the previous Observed-Calculated (O-C) short-term analyses. Methods. An investigation of the O-C times has been carried out, using a data set based on the previous published times of light maxima, largely enriched by those obtained during an intensive multisite photometric campaign of BL Cam lasting several months. Results. In addition to a positive (161 ± 3) × 10 −9 yr −1 secular relative increase in the main pulsation period of BL Cam, we detected in the O-C data short-(144.2 d) and long-term (∼3400 d) variations, both incompatible with a scenario of stellar evolution. Conclusions. Interpreted as a light travel-time effect, the short-term O-C variation is indicative of a massive stellar component (0.46 to 1 M) with a short period orbit (144.2 d), within a distance of 0.7 AU from the primary. More observations are needed to confirm the long-term O-C variations: if they were also to be caused by a light travel-time effect, they could be interpreted in terms of a third component, in this case probably a brown dwarf star (≥0.03 M), orbiting in ∼3400 d at a distance of 4.5 AU from the primary.