ABSTRACT
We present a detailed photometric study of the bright cataclysmic variable, BG Triangulum (BG Tri), using ground-based observations mainly from the Rozhen Observatory, the All-Sky Automated ...Survey for Supernovae (ASAS-SN), the Transiting Exoplanet Survey Satellite (TESS) and the Wide Angle Search for Planets (WASP). We report on the discovery of a negative superhump with P−sh = 0.1515(2) d and a co-existing superorbital variation with P = 3.94(53) d in data from 2019 and 2020. A positive superhump with P+sh = 0.1727(14) d is also discovered in data from 2006. The obtained negative superhump deficit ε− = 0.044(1) and the positive superhump excess ε+ = 0.090(9) give us an independent photometric evaluation of the mass ratio (q) of the system, which we find to be q− = 0.37(2) and q+ = 0.40(5), respectively. We also present a study of the quasi-periodic oscillations and stochastic variability (flickering) in BG Tri. The light curves show a rich mixture of simultaneously overlapping quasi-periods ranging from 5 to 25 min. The multicolour (UBVRI) photometric observations from the Rozhen Observatory reveal the typical increase of the flickering amplitudes to the shorter wavelengths. The recently introduced A60 amplitude of the flickering light source in all studied photometric bands is systematically lower when the negative superhump is gone in season 2021.
We analysed the multiband optical behaviour of the BL Lacertae object, S5 0716+714, during its outburst state from 2014 November to 2015 March. We took data on 23 nights at three observatories, one ...in India and two in Bulgaria, making quasi-simultaneous observations in B, V, R, and I bands. We measured multiband optical fluxes, colour, and spectral variations for this blazar on intraday and short time-scales. The source was in a flaring state during the period analysed and displayed intense variability in all wavelengths. R-band magnitude of 11.6 was attained by the target on 2015 January 18, which is the brightest value ever recorded for S5 0716+714. The discrete correlation function method yielded good correlation between the bands with no measurable time lags, implying that radiation in these bands originate from the same region and by the same mechanism. We also used the structure function technique to look for characteristic time-scales in the light curves. During the times of rapid variability, no evidence for the source to display spectral changes with magnitude was found on either of the time-scales. The amplitude of variations tends to increase with increasing frequency with a maximum of ∼22 per cent seen during flaring states in B band. A mild trend of larger variability amplitude as the source brightens was also found. We found the duty cycle of our source during the analysed period to be ∼90 per cent. We also investigated the optical spectral energy distribution of S5 0716+714 using B, V, R, and I data points for 21 nights. We briefly discuss physical mechanisms most likely responsible for its flux and spectral variations.
Reactive oxygen species (ROS) are highly reactive chemical molecules containing oxygen. ROS play an important role in signaling and cell homeostasis at low and moderate concentrations. ROS could be a ...cause of damage to proteins, nucleic acids, lipids, membranes and organelles at high concentrations. There are a lot of cells that can produce ROS to maintain functional activity. It is known that metal nanoparticles can increase production of ROS in cells. However, the effect of cucurbiturils on ROS production is still unknown. In our study, we evaluated production of ROS by the immune (T-, B-lymphocytes, NK-cells) and non-immune cells (red blood cells, platelets), as well as tumor cells line (1301, K562) after treatment with cucurbiturils in vitro. Assessment of reactive oxide species (ROS) were provided by using dihydrorhodamine 123 (DHR 123). Fluorescence intensity and percentage DHR123 were measured by flow cytometry. Platelets, erythrocytes and activated T-helpers were changed the level of ROS production in response to stimulation with cucurbiturils. It was found that the percentage of these ROS-producing cells was reduced by cucurbiturils. Thus, cucurbiturils may affect the production of ROS by cells, but further research is needed in this area.
We report observations of the flickering variability of the symbiotic recurrent nova RS Oph at quiescence in five bands (UBVRI). We find evidence of a correlation between the peak-to-peak flickering ...amplitude (ΔF) and the average flux of the hot component (F
av). The correlation is highly significant, with a correlation coefficient of 0.85 and a p-value of ∼10−20. Combining the data from all wavebands, we find a dependence of the type
$\Delta F \propto F_{{\rm av}}^k$
, with power-law index k = 1.02 ± 0.04 for the UBVRI flickering of RS Oph. Thus, the relationship between the amplitude of variability and the average flux of the hot component is consistent with linearity. The rms amplitude of flickering is on average 8 per cent (±2 per cent) of F
av. The detected correlation is similar to that found in accreting black holes/neutron stars and cataclysmic variables. The possible reasons are briefly discussed. The data are available upon request from the authors.
Using the 2 m telescope of the Bulgarian National Astronomical Observatory at Rozhen, observations of 271 double or multiple stars were carried out during seven nights in 2013 and 2014. This is the ...eighth series of measurements of CCD frames of double and multiple stars obtained at Rozhen. Also in 2013 and 2014, using the 0.6 m telescope of the Serbian Astronomical Station on the mountain of Vidojevica, observations of 343 double or multiple stars were carried out during 21 nights. This is the third series of measurements of CCD frames of double and multiple stars obtained at this station. In this paper, we present the results for the position angle and angular separation for 721 pairs and residuals for 126 pairs with published orbital elements or linear solutions. These observations have angular separations in the range from 1".24 to 202".30, with a median angular separation of 7".17. We also present eight linear solutions that have been calculated for the first time.
Results of CCD observations of 154 double or multiple stars, made with the 2 m telescope of the Bulgarian National Astronomical Observatory at Rozhen over five nights in 2015, are presented. This is ...the ninth series of measurements of CCD frames obtained at Rozhen. We also present results of CCD observations of 323 double or multiple stars made with the 0.6 m telescope of the Serbian Astronomical Station on the mountain of Vidojevica over 23 nights in 2015. This is the fourth series of measurements of CCD frames obtained at this station. This paper contains the results for the position angle and angular separation for 801 pairs and residuals for 127 pairs with published orbital elements or linear solutions. The angular separations are in the range from 1 52 to 201 56, with a median angular separation of 8 26. We also present eight pairs that are measured for the first time and linear elements for five pairs.
Using the 2 m telescope of the Bulgarian National Astronomical Observatory at Rozhen, observations of 246 double or multiple stars were carried out during six nights in 2012. This is the seventh ...series of measurements of CCD frames of double and multiple stars obtained at Rozhen. Also in 2012, using the 0.6 m telescope of the Serbian Astronomical Station on the mountain of Vidojevica, observations of 117 double or multiple stars were carried out during five nights. This is the second series of measurements of CCD frames of double and multiple stars obtained at this station. In this paper we present the results for the position angle and angular separation for 453 pairs and residuals for 105 pairs with published orbital elements or linear solutions. These observations have angular separations in the range from 1".50 to 178".12, with a median angular separation of 8".13. We also present the recalculated linear solution for one pair and three linear solutions that have been calculated for the first time.
We report the results of quasi-simultaneous two-filter optical monitoring of two high-energy peaked blazars, 1ES 1959+650 and 1ES 2344+514, to search for microvariability and short-term variability ...(STV). We carried out optical photometric monitoring of these sources in an alternating sequence of B and R passbands, and have 24 and 19 nights of new data for these two sources, respectively. No genuine microvariability (intranight variability) was detected in either of these sources. This non-detection of intranight variations is in agreement with the conclusions of previous studies that high-energy peaked BL Lacs are intrinsically less variable than low-energy peaked BL Lacs in the optical bands. We also report the results of STV studies for these two sources between 2009 July and 2010 August. Genuine STV is found for the source 1ES 1959+650 but not for 1ES 2344+514. We briefly discuss possible reasons for the difference between the intranight variability behaviour of high- and low-energy peaked blazars.
We performed high-resolution optical spectroscopy and X-ray observations of the recently identified Mira-type symbiotic star EF Aql. Based on high-resolution optical spectroscopy obtained with SALT, ...we determine the temperature (~55 000 K) and the luminosity (~5.3 L⨀) of the hot component in the system. The heliocentric radial velocities of the emission lines in the spectra reveal possible stratification of the chemical elements. We also estimate the mass-loss rate of the Mira donor star. Our Swift observation did not detect EF Aql in X-rays. The upper limit of the X-ray observations is 10(exp -12) erg cm(exp -2) s(exp -1), which means that EF Aql is consistent with the faintest X-ray systems detected so far. Otherwise, we detected it with the UVOT instrument with an average UVM2 magnitude of 14.05. During the exposure, EF Aql became approximately 0.2 UVM2 magnitudes fainter. The periodogram analysis of the V-band data reveals an improved period of 320.4±0.3 d caused by the pulsations of the Mira-type donor star. The spectra are available upon request from the authors.
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