arXiv subjects

B. E. Zhilyaev

Publications and source records attributed to B. E. Zhilyaev.

16 recordsLinked to original sources

arXiv2025

Small-scale variability in the spectrum of Vega

We reported the results of observations of small-scale variability in the hydrogen Balmer lines in Vega. Spectral observations were carried out with low-resolution spectrograph (R $\simeq$ 600) installed in the Main Astronomical Observatory, Ukraine. Spectra were obtained with a time resolution in the second range. It has been found that Vega shows variations in the hydrogen lines $H_β $, $H_γ $, $H_{ δ} $. This can be interpreted that their variations are non-radial pulsations. The characteristic time of the observed variations ranges from 300 to 1200 sec. The horizontal scale for oscillating elements is about 800 Mm, which is comparable to the solar radius. The radial velocity of the variations is about 36 km/s.

astro-ph.SR↗

arXiv2022

Unidentified aerial phenomena II. Evaluation of UAP properties

NASA commissioned a research team to study Unidentified Aerial Phenomena (UAP), observations of events that cannot scientifically be identified as known natural phenomena. The Main Astronomical Observatory of NAS of Ukraine conducts an independent study of UAP also. For UAP observations, we used two meteor stations installed in Kyiv and in the Vinarivka village in the south of the Kyiv region. Two-side monitoring of the daytime sky led to the detection of two luminous objects at an altitude of 620 and 1130 km, moving at a speed of 256 and 78 km/s. Colorimetric analysis showed that the objects are dark: B - V = 1.35, V - R = 0.23. The size of objects is estimated to be more than 100 meters. The detection of these objects is an experimental fact. Estimates of their characteristics follow from observational data. The authors do not interpret these objects. Daytime sky monitoring in Kyiv with multi-color DSLR camera at a rate of 30 frames per second in August and September 2018 and in Vinarivka with a multi-color CMOS camera in October 2022 revealed several cases of dark objects (phantoms). The time of their existence is, as a rule, a fraction of a second. These are oval-shaped objects ranging in size from 20 to 100 meters with speeds from 2 to 30 km/s.

physics.pop-ph↗

arXiv2022

Unidentified aerial phenomena I. Observations of events

NASA commissioned a research team to study Unidentified Aerial Phenomena (UAP), observations of events that cannot scientifically be identified as known natural phenomena. The Main Astronomical Observatory of NAS of Ukraine conducts an independent study of UAP also. For UAP observations, we used two meteor stations. Observations were performed with colour video cameras in the daytime sky. We have developed a special observation technique, for detecting and evaluating UAP characteristics. According to our data, there are two types of UAP, which we conventionally call: (1) Cosmics, and (2) Phantoms. We note that Cosmics are luminous objects, brighter than the background of the sky. Phantoms are dark objects, with contrast from several to about 50 per cent. We observe a significant number of objects whose nature is not clear. Flights of single, group and squadrons of the ships were detected, moving at speeds from 3 to 15 degrees per second. Some bright objects exhibit regular brightness variability in the range of 10 - 20 Hz. We use colourimetry methods to determine of distance to objects and evaluate their colour characteristics. Objects RGB colours of the Adobe colour system had converted to the Johnson BVR astronomical colour system using the colour corrections. Phantom shows the colour characteristics inherent in an object with zero albedos. It is a completely black body that does not emit and absorbs all the radiation falling on it. We see an object because it shields radiation due to Rayleigh scattering. An object contrast makes it possible to estimate the distance using colourimetric methods. Phantoms are observed in the troposphere at distances up to 10 - 12 km. We estimate their size from 3 to 12 meters and speeds up to 15 km/s.

astro-ph.IM↗

arXiv2022

Optical Flare Search on the RS CVn-type flare stars AR Lacertae

We present the results of fast spectrophotometry of flares on the RS CVn-type star AR Lac with a time resolution of 34 s and a spectroscopic resolution R $\sim $ 1300. The observations were performed on July 21-22, 2021 with the 2.0 m Karl Zeiss telescope at the Terskol Observatory. During the flares, an additional emission appeared in the spectrum of AR Lac at wavelengths nearby Ca II H\&K ($λ$ = 3933, 3968 Å), nearby Si IV lines ($λ$ = 4089, 4116 Å). Variations in these lines range from 2 to 5\%. We have estimated the UBV magnitudes from spectrograms through a mathematical convolution of the spectra with the filter transmission curves. The flare amplitudes in the UBV band up to 0.8 magnitudes were discovered. A detailed colorimetric analysis has allowed important parameters of the flares on AR Lac to be estimated: the temperatures at maximum light and their sizes. The color-color $(U-B)$ - $(B-V)$ diagrams confirm that all the flares at maximum light radiate as a blackbody. The temperatures at maximum light were up to 12000 $\pm $ 300 K. Based on our colorimetric analysis, we have estimated the linear sizes of the flares at maximum light. The linear size of the flares at the maximum luminosity is approximately 2\% of the radius of the star.

astro-ph.SR↗

arXiv2022

Detection of C2, CN and CH radicals in the spectrum of the transiting hot Jupiter HAT-P-1b

In this paper we report spectroscopy of the transiting hot Jupiter HAT-P-1b. The HAT-P-1b is a giant ($R = 1.2 RJ$), low-mean density transiting extrasolar planet in a visual binary system, composed of two sun-like stars. The host star HAT-P-1b known as ADS 16402 B is a G0V C dwarf (V = 9.87). We revealed optical emission of $C_{2}$, $CN$ and $CH$ radicals in the spectrum of the hot Jupiter HAT-P-1b. We discovered radial pulsation of the hot Jupiter HAT-P-1b with a period of about 1900 sec.

astro-ph.EP↗

arXiv2021

Meteor colorimetry with CMOS cameras

This article describes our approach to quantifying the characteristics of meteors such as temperature, chemical composition, and others. We are using a new approach based on colourimetry. We analyze an image of Leonid meteor-6230 obtained by Mike Hankey in 2012. Analysis of the temporal features of the meteoroid trail is performed. For determining the meteor characteristics we use the "tuning technique" in combination with a simulation model of intrusion. The progenitor of the meteor was found as an object weighing 900 kg at a speed of 36.5 km/s. The meteoroid reached a critical value of the pressure at an altitude of about 29 km in a time of about 4.6 sec with a residual mass of about 20 kg, and a residual speed of about 28 km/s. At this moment, a meteoroid exploded and destroyed. We use the meteor multicolour light curves revealed from a DSLR image in the RGB colour standard. We switch from the RGB colour system to Johnson's RVB colour system introducing colour corrections. This allows one to determine the colour characteristics of the meteor radiation. We are using a new approach based on colourimetry. Colourimetry of BGR three-beam light curves allows the identification of the brightest spectral lines. Our approach based on colourimetry allows direct measurements of temperature in the meteor trail. We find a part of the trajectory where the meteoroid radiates as an absolutely black body. The R/G and B/G light curves ratio allow one to identify the wavelengths of the emission lines using the transmission curves of the RGB filters. At the end of the trajectory, the meteoroid radiates in the lines Ca II H, K 393, 397 nm, Fe I 382, 405 nm, Mg I 517 nm, Na I 589 nm, as well as atmospheric O I 779 nm.

astro-ph.EP↗

arXiv2013

Performance of commercial CMOS cameras for high-speed multicolor photometry

We present some results of testing of commercial color CMOS cameras for astronomical applications. CMOS sensors allow to perform photometry in three filters simultaneously that gives a great advantage compared with monochrome CCD detectors. The Bayer BGR colour system realized in CMOS sensors is close to the Johnson BVR system. We demonstrate transformation from the Bayer color system to the Johnson one. Our photometric measurements with color CMOS cameras coupled to small telescopes (11 - 30 inch) reveal that in video mode stars up to V $\sim$ 9 can be shot at 24 frames per second. Using a high-speed CMOS camera with short exposure times (10 - 20 ms) we can perform an imaging mode called "lucky imaging". We can pick out high quality frames and combine them into a single image using "shift-and-add" technique. This allows us obtain an image with much higher resolution than would be possible shooting a single image with long exposure. For image selection we use the Strehl-selection method. We demonstrates advantage of the lucky imaging technique in comparison with long exposure shooting. The FWHM of the blurred image caused by atmosphere turbulence can be decreased twice and more.

astro-ph.IM↗

arXiv2012

High-speed multicolor photometry with CMOS cameras

We present the results of testing the commercial digital camera Nikon D90 with a CMOS sensor for high-speed photometry with a small telescope Celestron 11" on Peak Terskol. CMOS sensor allows to perform photometry in 3 filters simultaneously that gives a great advantage compared with monochrome CCD detectors. The Bayer BGR color system of CMOS sensors is close to the Johnson BVR system. The results of testing show that we can measure the stars up to V $\simeq$ 14 with the precision of 0.01 mag. Stars up to magnitude V $\sim$ 10 can shoot at 24 frames per second in the video mode.

astro-ph.IM↗

arXiv2011

Detection of high-frequency variability in chromospherically active stars

We have carried out high-speed photometry of three chromospherically active stars, BD +15 3364, II Peg, and SAO 52355 with the Zeiss 2-m telescope, as well as low-resolution spectroscopy of SAO 52355 with the Zeiss-600 telescopes at Peak Terskol. BD +15 3364 is known as chromospherically active star of the spectral type G0. II Peg is the RS CVn binary. It has a spectral type K2IV-Ve. SAO 52355 is a field star of the spectral type K0 III. The X-ray observations taken by Ginga and ROSAT indicate in II Peg and SAO 52355 coronae plasma temperatures as high as $10^{7}$ K. These two stars are supposed to have high-powered chromospheres. Photometric observations of all three stars show high-frequency variations in brightness in the UBV bands at subsecond range. Intensity variations are found peaked at frequency around about 0.5 Hz, spanning the range up to 1.5 Hz for BD +15 3364, II Peg, and up to about 35 Hz for SAO 52355. The relative power of fluctuations reaches ($10^{-3.7} - 10^{-4.2}$) in the UBV bands. Spectroscopic monitoring of SAO 52355 showed variations of emission in the Balmer lines and in the CaII H, K lines at time intervals ranging from seconds to minutes. From the power spectrum data one can find that variations in the intensities of the CaII H, K and $H_γ$ lines are 3.2% and 1.5%, respectively. This allows us to assert the existence of intense microflaring activity in these stars.

astro-ph.SR↗

arXiv2008

The last stages of evolution of close binaries composed of compact companions

Gamma-ray bursts (GRB) are the most powerful transient phenomena in the Universe. Nowadays dozens of speculations on the origin of GRB were undertaken, but so far a single model for the origin of, in particular, short GRBs does not exist. The black hole (BH) - neutron star (NS) coalescence is a promising candidate source for short GRBs. Most of binary mergers numerical simulations were carried out with the purpose of investigating the emission of gravitational waves. Such a scenario consists of an inspiral, merging and ringdown phase. In this paper we present the comparison of the observational results and analytical predictions for a test particle in a quasicircular orbit around the BH. The emission of gravitational waves causes a rapid decrease of the orbital radius and a rise of a {\it chirp} of radiation. Matter orbiting the black hole would be expected to produce high-frequency oscillations (HFO). Timescales of the coalescence process are of the order of milliseconds and oscillation frequencies of hundreds Hz for a system with a solar mass BH companion. We report on the detection of HFO in two short gamma-ray bursts in this paper. The frequencies and durations of the oscillations are in agreement with the predicted values. A {\it chirp} phenomenon is identified also. We therefore argue in favor of BH-NS mergers as a scenario for the production of short gamma-ray bursts.

astro-ph↗

arXiv2008

Bispectral technique for reconstruction the astronomical images with an intensity interferometer

An extension may be proposed to the intensity interferometer of Hanbury Brown and Twiss to provide the Fourier phase measurement by the use of third-order intensity correlations. It is well known that interferometric reconstruction of astronomical images can be obtained from second-order correlations only when a priory information is used about the object. The third-order intensity correlations contain information about the Fourier phase and need no such assumptions. In the ordinary way we can make measurements of the second-order intensity correlations with an intensity interferometer. We can also calculate the third-order intensity correlations from the data set of measured intensities for each distance triplet. After that we can reconstruct the Fourier phase from third-order correlations by using bipectral technique. When this is combining with the Fourier magnitude obtained from the second-order intensity correlations, we have the ultimate Fourier transform of the source brightness distribution. An inverse Fourier transform recovers the source image.

astro-ph↗

arXiv2007

Ukrainian Synchronous Network of small Internet Telescopes as rapid action instrument for transient objects

UNIT (The Ukrainian synchronous Network of small Internet Telescopes) is a system of automated telescopes that search for simultaneous optical activity of transient objects associated with variable stars, small bodies of the Solar system, Near-Earth objects (NEOs), gamma ray bursts, etc. Their instruments are sensitive down to $M_{V} \approx 18$ and require an average of 60 seconds to obtain the first images of the transient events after the alarm or GCN notice. Telescopes of UNIT are equipped with fast CCD cameras to study astrophysics on the timescales up to tens Hz. UNIT will be operating by the middle of 2008.

astro-ph↗

arXiv2007

Detection of an oscillatory phenomenon in optical transient counterpart of GRB090522C from observations on Peak Terskol

22 Sep 2005 Swift-BAT triggered and located GRB050922C. The light curve shows the intense broad peak with $T_{90}$ of $(5 \pm 1)$ s. The Nordic Optical Telescope has obtained spectra of the afterglow with several absorption features corresponding to a redshift of $z = 2.17 \pm 0.03$. Observation of optical transient of GRB050922C was carried out in the R-band with the 60-cm telescope equipped with a CCD on Peak Terskol (North Caucasus). The OT magnitude was fading from R $\approx 16$ to $\approx 17.5$. Detection of an oscillatory phenomenon in the R post-burst light curve is described in this work. Analysis of the R data reveals coherent harmonic with a period of $0.0050 \pm 0.0003$ days (7.2 min) during observing run of about 0.05 days ($\sim 70$ min). Amplitude of oscillations is about 0.05 magnitude. The simplest model suggests that GRB050922C may result from tidal disruption of a white dwarf star by a black hole of about one thousand solar mass. The periodicity in the light curve can be identified with relativistic precession of an accretion disc.

astro-ph↗

arXiv2007

Singular Sources of Energy in Stars and Planets

If primordial low-mass black holes (PBH) exist in the Universe than many of stars and planetary bodies appear to be infected by them. This is also true in regard to the Sun and likely Jupiter and Saturn. The availability of even the very low-mass inner relativistic reactor may lead to essential changes in evolution scenario of a celestial body on its lifetime scale. Black holes in stellar interior may be found either in consequence of captures process or incorporation during the formation of a star from interstellar clouds. Surprisingly that in the equilibrium state a PBH growth is a long-lived process with e-folding rise time of billion years. One can envision a PBH orbiting inside the Sun. Our considerations showed that the PBH experiences very little friction in passing through the stellar matter. If the BH mass is above 10^{-5}M_{sun} the major contribution to the luminosity comes from the relativistic gravitational reactor. In such a case a star evolves towards the Eddington limit. This should lead to considerable expansion of a star and a global stability loss. Microscopic PBHs can exist in the interior of planetary bodies too. To produce the required excess of thermal energy on Jupiter and Saturn the masses of PBH captured are assumed to be reached of 4 10^{19} and 7 10^{18} g, respectively. These microscopic objects are comparable to the hydrogen atom in size. One can envision even a planet with the PBH acting as the self-sufficient source of heating. Such a planet does not need a sun to maintain animal life on its surface. This may last eons.

astro-ph↗

arXiv2007

Gamma-Ray Bursts as Manifestation of Collisions of Primordial Black Holes with Stars

Using the BATSE survey data I find that quite small fraction of GRBs numbering 37 sources seems to emit the radiation similar to thermal bremsstrahlung in the range 20 to 300 keV. I suggest that these bursts may perhaps occur from collision of stars with primordial black holes (PBH). These objects are relic of a hot matter in the early Universe. PBH in the vicinity of stars may be found in consequence of incorporation processes during the formation of stars from interstellar clouds. At present they can form the gravitationally captured haloes around stars like the family of solar comets. The comet paradigm has been used to understand various aspects of PBH. Comet collisions with the Sun and planets are ordinary events in solar system history. On the analogy, one can support the view that PBH collisions with the parent star may be quite frequent events in its history, too. PBHs are the engines driving gamma-ray bursts when collide with the stars. Entering a stellar atmosphere, PBH is supposed to produce the gamma-ray burst due to accretion with duration from a few tenths of second to a few seconds. It can exhibit the main qualitative features of some GRBs. Their masses are estimated in the range from thousandths to hundredths of the solar mass. I found that these burst sources are isotropically distributed on the sky and are seen from a distance up to 50 ps. In this context one may expect that some short GRBs are observable signatures of primordial black holes in the Universe.

astro-ph↗

arXiv2005

Fast Optical Photometry of Galaxies: Observations of Short-Lived Flare Events

We have monitored two bright galaxies, M85 and NGC7331, on timescales as short as 0.01s. In the optical, we discovered an unusual burst coincident with the galaxy M85. We registered a sudden onset with a characteristic time of less than 10ms with subsequent quasi-exponential decay within approximately 1s and an amplitude of 2.5mag in the V-band. In the course of high-speed monitoring with two Crimean telescopes operated synchronously, in both independent instruments we have registered one coincident event occurring in NGC7331 with a duration of ~0.6s. The amplitudes range from ~3mag to ~0.3mag in the U-band and I-band, respectively. Merging of an intermediate-mass black hole with a small black hole or normal star seems to be the most plausible mechanism responsible for short bursts. Our observations support the hypothesis concerning the existence of intermediate-mass black holes in the centers of galaxies and in dense globular clusters.

astro-ph↗