arXiv subjects

N. V. Borisov

Publications and source records attributed to N. V. Borisov.

At least 19 recordsLinked to original sources

arXiv2026

The polar IL Leo in a low accretion state

We performed an optical study of the magnetic period-bouncer candidate IL Leo. Long-term photometric analysis over $\approx 20$ years reveals multiple state transitions. Modelling the ultraviolet and optical spectral energy distribution refined the white dwarf parameters, yielding a mass of $M_\textrm{wd} = 0.74 \pm 0.05 M_{\odot}$ and an effective temperature of $T_\mathrm{eff} = 12700 \pm 360$ K. We analyzed phase-resolved spectroscopy obtained with the 6-m BTA telescope and the VLT during the low state. Orbital variability of the H$α$ emission, inferred from dynamical spectra and Doppler tomograms, suggests that it originates in the accretion stream. Zeeman splitting gives a mean magnetic field of $B = 40.7 \pm 0.5$ MG. Modelling two sets of cyclotron spectra determined a low-state accretion rate of $\dot{M} = (2.5 - 4.1) \times 10^{-13}~M_{\odot}$ yr$^{-1}$ and a magnetic field of $B_\mathrm{m} \approx 41$ MG near magnetic pole.

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arXiv2025

Phase-Resolved Spectroscopy of the Polar V379 Vir with a Brown Dwarf

The polar V379 Vir is a well-known magnetic cataclysmic variable with a brown dwarf donor. Despite numerous studies of this system across various spectral ranges, a detailed investigation of the orbital variability of its optical spectra has not been carried out. In this work, we present an analysis of spectroscopic observations of V379 Vir obtained with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. The orbital variability of the H$α$ emission indicates that the line is most likely formed in the accretion stream near the Lagrangian point L$_1$, rather than on the donor's surface as previously assumed. The analysis of the rotational variability of the Zeeman splitting of hydrogen lines reveals a complex magnetic field topology of the white dwarf, which differs from a simple dipole configuration.

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arXiv2025

The Optical Study of the Eclipsing Polar SDSS J002637.06+242915.6

We have analyzed phase-resolved photometric and spectroscopic observations of the eclipsing polar SDSS J002637.06+242915.6. The light curve has a M-shaped bright phase that was reproduced using a simple model of an accreting magnetic white dwarf. The hydrogen emission lines exhibit a narrow component formed on the irradiated hemispere of the donor. The Doppler tomography revealed differences in the positions of emission regions of hydrogen and HeII $λ$4686 lines. The spectra exhibit a Zeeman absorption triplet of the H$α$ line, formed in the cold halo around the accretion spot at a magnetic field strength of $B = 15.1 \pm 1.3$ MG. The spectra of the bright phase have a red cyclotron continuum, whose orbital variability has been interpreted within a simple model of an accretion spot. The modeling of the cyclotron continuum constrains the white dwarf's magnetic field to $B_{cyc} \lesssim 45$ MG. The analysis of the eclipse light curve and the radial velocities of the irradiated hemisphere yielded estimates for the orbital inclination $77.2^\circ \le i \le 80.6^\circ$, the mass ratio $0.23 \le q \le 0.43$, and the white dwarf mass $0.72 \ge M_1/M_\odot \ge 0.42$.

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arXiv2025

On accretion in the polar V379 Vir

Based on optical and infrared survey data spanning $\approx 20$ years of observations, the long-term variability of the polar V379 Vir with a brown dwarf secondary has been studied. By modeling the spectral energy distribution, we constrain the white dwarf's mass to $M_1 = 0.61 \pm 0.05~M_{\odot}$ and its effective temperature to $T_{eff} = 10930 \pm 350~K$. Near-infrared photometry yields a donor radius of $R_2 = 0.095 \pm 0.018 R_{\odot}$ and temperature $T_{eff} = 1600 \pm 180 K$. Modeling of the cyclotron emission from the accretion spot, detected with the Spitzer infrared telescope, gives an accretion rate of $\dot{M} \approx 3 \times 10^{-13} M_{\odot}/yr$. This rate is consistent with polars in a low accretion state, but significantly higher than expected from wind-driven mass transfer.

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arXiv2025

Gaia 19cwm -- an eclipsing dwarf nova of WZ Sge type with a magnetic white dwarf

The spectral and photometric studies of the cataclysmic variable Gaia 19cwm (or ZTF19aamkwxk) have been performed. Based on the analysis of long-term variability, it is concluded that the object belongs to WZ Sge type stars. The light curves show eclipses recurring with an orbital period of $86.32048 \pm 0.00005$ min, as well as an out-of-eclipse variability with a period of $\approx 6.45$ min. The latter period is stable for $\sim 4$ years and appears to correspond to the rotation of a magnetic white dwarf, i.e., Gaia 19cwm is an intermediate polar. The Gaia 19cwm spectra show photospheric lines of the white dwarf, and Doppler tomograms demonstrate the presence of an accretion disk and a hot spot. Analysis of the eclipse light curve gives an estimates of the white dwarf mass $M_1 = 0.66\pm0.06$ M$_{\odot}$, the donor mass $M_2 = 0.073 \pm 0.015$ M$_{\odot}$, and the orbital inclination $i=83.8 \pm 1.1^{\circ}$. Modeling of the spectral energy distribution gives the white dwarf temperature of $T_{eff}\approx 13000 $ K. The X-ray luminosity $L_X = (1.6 \pm 0.3) \times 10^{31}$ erg/s allows to assign Gaia 19cwm to a small group of low-luminosity intermediate polars.

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arXiv2024

Spectroscopic and photometric study of the new eclipsing polar Gaia23cer

We present the results of the optical study of the new eclipsing polar Gaia23cer. We analyzed the brightness variability of the polar in high ($\langle r \rangle \approx 16.5\mathrm{\,mag}$) and low ($\langle r \rangle \approx 19.2\mathrm{\,mag}$) states. The system has an orbital period $P_{orb} = 102.0665 \pm 0.0015$ min and exhibits deep eclipses with a duration $Δt_{ecl} = 401.30 \pm 0.81$ s. The spectra have a red cyclotron continuum with the Zeeman H$α$ absorption triplet forming in a magnetic field with a strength of $15.2 \pm 1.1$ MG. The source of emission lines has a high radial velocity semiamplitude ($K\approx 450$km/s) and its eclipse lags behind the eclipse of the white dwarf. The mass $M_1=0.79 \pm 0.03 M_{\odot}$ and temperature $T=11350 \pm 650 K$ of the white dwarf have been found by modelling the spectral energy distribution. The eclipse duration corresponds to a donor mass $M_2 = 0.10-0.13M_{\odot}$ and an orbital inclination $i=84.3-87.0^{\circ}$. The donor temperature was estimated to be $T\approx 2900K$ by modelling the elliptical variability and eclipse depth.

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arXiv2023

SDSS J085414.02+390537.3 -- a new asynchronous polar

The asynchrony of the polar SDSS~J085414.02+390537.3 was revealed using the data of ZTF photometric survey. The light curves show a beat period $P_{beat} = 24.6 \pm 0.1$~days. During this period the system changes its brightness by $\sim 3^m$. The periodograms show power peaks at the white dwarf's rotation period $P_{spin} = 113.197 \pm 0.001$~min and orbital period $P_{orb} = 113.560 \pm 0.001$~min with the corresponding polar asynchrony $1-P_{orb}/P_{spin} = 0.3\%$. The photometric behavior of the polar indicates a change of the main accreting pole during the beat period. Based on the Zeeman splitting of the H$β$ line, an estimate of the mean magnetic field strength of the white dwarf is found to be $B = 28.5\pm 1.5$~MG. The magnetic field strength $B \approx 34$~MG near the magnetic pole was found by modeling cyclotron spectra. Doppler tomograms in the H$β$ line demonstrate the distribution of emission sources typical for polars.

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arXiv2023

Optical study of the polar BM CrB in low accretion state

This paper presents a spectral and photometric study of the poorly studied polar BM CrB. Three states of the polar brightness and signs of transition from one-pole to two-pole accretion mode were found by an analysis of ZTF data. It is shown that the transition from the low state to the high state changes the longitude of the main accretion spot (by $\approx 17^{\circ}$) and increases its elongation (by $\approx 10^{\circ}$). The spectra contain Zeeman absorptions of the H$α$ line which are formed at a magnetic field strength of $15.5\pm1$ MG. These absorptions are likely produced by a cold halo extending from the accretion spot at $\approx {^1/_4}$ of the white dwarf radius. Modeling of the behavior of the H$α$ emission line shows that the main source of emission is the part of the accretion stream near the Lagrangian point L$_1$, which is periodically eclipsed by the donor star. The spectra exhibit a cyclotron component formed in the accretion spot. Its modeling by a simple accretion spot model gives constraints on the magnetic field strength $B=15-40$ MG and the temperature $T_e\gtrsim15$ keV.

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arXiv2022

On accretion in the eclipsing polar BS Tri

We analyze spectroscopic and photometric observations of the eclipsing polar BS Tri. The polar's light curve shape variations can be interpreted by changing contributions of the accretion stream to the integral radiation of the system. Based on the radial velocity curves of the irradiated part of the secondary, we refine the masses of the system components, $M_1 = 0.60 \pm 0.04 M_{\odot}$, $M_2 \approx 0.12 M_{\odot}$, and the orbital inclination, $i=85\pm 0.5^{\circ}$. The polar's spectra reveal cyclotron harmonics forming in an accretion spot with a magnetic field strength of $B=22.7 \pm 0.4$ MG and an average temperature of $T \sim 10$ keV. In addition to the cyclotron harmonics, the BS Tri spectra contain Zeeman components of H$α$ line, which are probably formed in the cool halo near the accretion spot. The orientation of the magnetic dipole and the coordinates of the accretion spot are estimated by modeling the light curves of the polar. We show that for a satisfactory description of the BS~Tri light curves we have to take into account the variability of the spot's optical depth along the line of sight. Doppler maps of BS Tri show a part of the accretion stream with a trajectory close to ballistic near the Lagrange point L$_1$, and another part of the stream moving along the magnetic field lines. The estimate of the stagnation region position found from the Doppler tomograms is consistent with the photometric estimates of the accretion spot position.

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arXiv2020

Possibilities of Using Middle-Band Filters to Search for Polar Candidates

We present a method for searching for polar candidates using mid-band filters. One of the spectral singularities of polars is the $HeII \lambda4686$Å~ strong emission line. We selected the Edmund Optics filters with central wavelengths of 470, 540, and 656 nm and a transmission bandwidth of 10 nm. These filters cover the regions of the $HeII \lambda4686$Å~ line, continuum, and the $H_α$ line respectively. We constructed a color diagram based on the available spectra of polars and objects with a zero redshift from the SDSS archive. We show that most polars make a group with unique color indices. In practice, the method is implemented in SAO RAS at the Zeiss-1000 telescope with a new multi-mode photometer-polarimeter (MMPP). Approbation of the method with the known polars allowed us to develop two criteria to select candidates with an efficiency of up to 75\%.

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arXiv2017

Photometric and Polarimetric Observations of a New Polar USNO-A2.0 0825-18396733

We present photometric and polarimetric observations of a new magnetic cataclysmic variable, presumably a polar, USNO-A2.0 0825-18396733. The photometric observations were carried out with the SAO RAS Zeiss-1000 telescope, and the polarimetry was performed with the 6-m BTA telescope. The redefined orbital period P = 0:d08481(2); the brightness of the system varied from 17:5 to 20:0 in the Rc filter. Polarimetric observations of the object in the V filter revealed strong variable circular polarization: -2% to over -31%. This indicates that the variable USNO-A2.0 0825-18396733 is a polar.

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arXiv2016

Voracious vortexes in cataclysmic variables. A multi-epoch tomographic study of HT Cassiopeia

We present multi-epoch, time-resolved optical spectroscopic observations of the dwarf nova HT Cas, obtained during 1986, 1992, 1995 and 2005 with the aim to study the properties of emission structures in the system. We determined that the accretion disc radius, measured from the double-peaked emission line profiles, is persistently large and lies within the range of 0.45-0.52a, where a is the binary separation. This is close to the tidal truncation radius r_max=0.52a. This result contradicts with previous radius measurements. An extensive set of Doppler maps has revealed a very complex emission structure of the accretion disc. Apart from a ring of disc emission, the tomograms display at least three areas of enhanced emission: the hot spot from the area of interaction between the gas stream and the disc, which is superposed on the elongated spiral structure, and the extended bright region on the leading side of the disc, opposite to the location of the hot spot. The position of the hot spot in all the emission lines is consistent with the trajectory of the gas stream. However, the peaks of emission are located in the range of distances 0.22-0.30a, which are much closer to the white dwarf than the disc edge. This suggests that the outer disc regions have a very low density, allowing the gas stream to flow almost freely before it starts to be seen as an emission source. We have found that the extended emission region in the leading side of the disc is always observed at the very edge of the large disc. Observations of other cataclysmic variables, which show a similar emission structure in their tomograms, confirm this conclusion. We propose that the leading side bright region is caused by irradiation of tidally thickened sectors of the outer disc by the white dwarf and/or hot inner disc regions.

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arXiv2015

Spectropolarimetric monitoring of active galaxy 3C390.3 with 6m telescope SAO RAS in the period 2009-2014

Here we present the spectropolarimetric observations of the radio loud active galaxy 3C 390.3 in the period 2009-2014 (24 epochs). The galaxy has been observed with the 6-meter telescope of SAO RAS using the SCORPIO spectropolarimeter. We explore the variability and lags in the polarized light of the continuum and broad H$α$ line. We give the Stokes parameters $Q, U$, degree of linear polarization $P$ and the position angle of the polarization plane, $φ$, for 24 epochs. We find a small lag~(10-40 days) between the unpolarized and polarized continuum that is significantly smaller than the estimated lags for the unpolarized broad emission lines (lag(H$α$)$\sim$138-186 and lag(H$β$)$\sim$60-79 days). This shows that the region of the variable polarized continuum is significantly smaller than the broad line region, indicating that a part of the polarized continuum is coming from the jet. The lag of the polarized light in the H$α$ line (89-156 days) indicates an additional component to the disc one that has an outflowing velocity of $\sim$-1200 km s$^{-1}$. This region seems to depolarize the polarized broad H$α$ line emitted from the disc and scattered in the inner part of the torus.

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arXiv2014

Variability in Spectropolarimetric properties of Sy 1.5 galaxy Mrk 6

Here we present an analysis of spectro-polarimetric observations of type 1.5 AGN Mrk 6, performed with 6m telescope SAO RAN in 12 epochs (2010 -- 2013). Additionally, the inter-stellar mater (ISM) polarization has been observed and its contribution to the AGN spectral polarization is taken into account. We measured Stokes parameters and determined the polarization parameters in 12 spectra with and without correction for the ISM polarization. We estimated the time lag between the unpolarized and polarized continuum flux variation of about ~2 days, that indicates a compact scattering region which contributes to the polarized continuum variability. The polarization in Hα is complex, showing three prominent components in the BLR, one redshifted around +3000 km/s that corresponds to the red shoulder in Hα, and two blue-shifted around -2000 km/s and -6000 km/s. We found that the ISM polarization has a very significant influence on the measured AGN polarization parameters. After correcting the observations for the ISM polarization we were able to detect the Keplerian motion in the BLR. We give a new method for the black hole mass estimation using spectro-polarimetric observation in the line profile, finding the black hole mass in Mrk 6 of $M_{BH} \sim 1.53 \cdot 10^8 M_{\odot}$, that is in a good agreement with reverberation estimates.

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arXiv2012

Investigation of the new cataclysmic variable 1RXS J180834.7+101041

We present the results of our photometric and spectroscopic studies of the new eclipsing cataclysmic variable star 1RXS J180834.7+101041. Its spectrum exhibits double-peaked hydrogen and helium emission lines. The Doppler maps constructed from hydrogen lines show a nonuniform distribution of emission in the disk similar to that observed in IP Peg. This suggests that the object can be a cataclysmic variable with tidal density waves in the disk. We have determined the component masses (M_WD =0.8 \pm 0.22 M_sun and M_RD =0.14 \pm 0.02 M_sun) and the binary inclination (i =78 \pm 1.5 deg) based on well-known relations between parameters for cataclysmic variable stars. We have modeled the binary light curves and showed that the model of a disk with two spots is capable of explaining the main observed features of the light curves.

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arXiv2011

Optical spectroscopy of MT Dra in 2006 and 2009

We present low-resolution phase-resolved spectra of the polar MT Dra during its high states in 2006 and 2009. Balmer series, He I and He II 4686 Å emission lines have complex shapes and show similar profile variations over an orbital cycle. The radial velocities vary with orbital period and display motions of the gas falling close to the magnetic poles of the white dwarf.

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arXiv2011

Spectropolarimetric Observations of Active Galactic Nuclei with the 6-m BTA Telescope

We present the results of our spectropolarimetric observations for a number of active galactic nuclei (AGNs) carried out at the 6-m telescope with the SCORPIO focal reducer. The derived wavelength dependences of the polarization have been analyzed by taking into account the Faraday rotation of the polarization plane on the photon mean free path in a magnetized accretion disk. As a result, based on traditional accretion disk models, we have determined the magnetic field strength and distribution and a number of physical parameters of the accreting plasma in the region where the optical radiation is generated.

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arXiv2010

Modeling of the spectral energy distribution of the cataclysmic variable TT Ari and evaluation of the system parameters

The spectral energy distribution (SED) of the TT Ari system, which is well known from published IUE and optical photometric observations, was modeled by a steady-state accretion α-disc around a white dwarf. Parameters of the system were derived from time-resolved optical spectral observations in the bright state that we obtained in Sep. 1998. The radial velocity semi-amplitude of the white dwarf (33.8 +/- 2.5 km/s) and corresponding mass function (f(M) = 5.5 +/- 1.2 *10^{-4}~ M_sun) were derived from the motion of the emission components of Balmer lines. The mass ratio q (\approx 0.315) was evaluated from the fractional period excess of the superhump period over the orbital period ε(\approx 0.085), and a secondary mass range (0.18 - 0.38 M_sun) was estimated from the orbital period. Therefore, the white dwarf mass range is 0.57 - 1.2 M_sun and the inclination angle of the system to the line of sight is 17 - 22.5 degrees. The adopted distance to the system is 335 +/- 50 pc. To fit the observed SED it is necessary to add a thermal spectrum with T \approx 11600 K and luminosity \approx 0.4 L_disk to the accretion disc spectrum. This combined spectrum successfully describes the observed Balmer lines absorption components. Formally the best fit of the HeI 4471 line gives minimum masses of the components (M_RD = 0.18 M_sun and M_WD = 0.57 M_sun), with the corresponding inclination angle i = 22.1 deg and mass-accretion rate \dot M = 2.6 * 10^{17} g/s.

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