arXiv subjects

R. K. Zamanov

Publications and source records attributed to R. K. Zamanov.

At least 19 recordsLinked to original sources

arXiv2026

Is Mira B a low mass white dwarf?

We report photometric observations in Johnson B and V bands of the short term variability (flickering) of Mira (omicron Ceti). The observations were performed during 7 nights in the period August - October 2025, in the course of the last minimum of the Mira pulsations. The observed peak-to-peak amplitude of the flickering is 0.11-0.28 mag in B band. For the flickering source we find luminosity in the range 0.10-0.46 L_sun. Using the amplitude-flux relation, we estimate an average luminosity of the accretion disc L_d = 0.91 +/- 0.28 L_sun. Assuming that the white dwarf accretes material through Wind Roche Lobe Overflow (WRLOF), we find that Mira B is a low mass white dwarf with M_wd = 0.24 +/- 0.04 M_sun accreting at a rate 6.8x10^{-9} M_sun/yr. This value of the mass is in the range of the extremely low mass white dwarfs. The data are available on Zenodo: zenodo.org/records/18756532

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arXiv2025

Photometry with the new 1.5-meter telescope of the Rozhen Observatory

The new 1.5~m telescope (AZ1500) is operating at the National Astronomical Observatory Rozhen, Bulgaria. This paper gives an overview of the telescope and presents a snapshot of the current performance. Science observations are under way, and we give brief highlights from a number of programs that have been enabled.

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arXiv2025

Red giant component of the recurrent nova T Coronae Borealis

We performed simultaneous V band photometry and spectroscopic observations of the recurrent nova T CrB and estimate the V band magnitude of the red giant. We find for the red giant of T CrB apparent and absolute V-band magnitudes m_V = 10.17 +/- 0.06 and M_V = +0.14 +/- 0.08, respectively. At the maximum of the ellipsoidal variation when these values are obtained, its absolute V-band magnitude is similar but fainter than the typical M4/5III giants. The data are available on : zenodo.org/records/15174720

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arXiv2024

Pre-outburst signal in the light curves of the recurrent novae RS Oph and T CrB

Pre-outburst signal (a decrease of the optical brightness) just before the outburst is clearly detected in the observations of the T CrB obtained before and during the 1946 outburst. A similar decrease is also visible in the light curve of RS Oph during the 2021 outburst. We suppose that this is due to formation of a thick, dense envelope around the white dwarf, and we estimate its size (1000 - 2000 km), mass (5.10$^{-8}$ - 6.10$^{-7}$ M$_\odot$) and average density (5 - 16 g cm$^{-3}$).

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arXiv2024

Evolution of the optical emission lines and the X-ray emission during the super-active stage of T CrB

T CrB is a symbiotic star that experiences nova outbursts every $\sim$ 80~yr. The next, long-anticipated nova outburst should occur during the 2024-2026 period. Here, we present results of high-resolution optical spectroscopy of T CrB in the period 2016 - 2023. In these spectra, we measured the equivalent widths of the H$α$, H$β$, HeI and HeII emission lines. The maximum equivalent width (EW) was recorded on May 2021, when the EW of $Hα$ reached -44.6 Åand H$β$ = -21.5 Å. At the other extreme, the minimum of EW($Hα$)= -2.9 Åwas recorded in October 2023. After October 2023, the B-band emission brightened, suggesting a re-appearance of the orbital modulation. In addition to the optical data, we study the X-ray behaviour in the same period. We find a strong correlation between $EW(Hα)$ and X-ray flux with a correlation coefficient -0.78 and a significance of 2.6$\times 10^{-5}$.

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arXiv2024

Size of the accretion disc in the recurrent nova T CrB

We present high resolution (0.06 A/px) spectroscopic observations of the recurrent nova T Coronae Borealis obtained during the last 1.5 years (September 2022 -- January 2024), with the 2.0m RCC telecope of the Rozhen National Astronomical Observatory, Bulgaria. Double-peaked emission is visible in the H-alpha line after the end of the superactive state. We subtract the red giant contribution and measure the distance between the peaks ($Δv_a$) of the line. For the period July 2023 -- January 2024, we find that $Δv_a$ is in range $90 < Δv_a < 120$ km/s. Assuming that the emission is from the accretion disc around the white dwarf, we find average radius of the accretion disc $R_{disc} = 89 \pm 19$ R$_\odot$, which is approximately equal to the Roche lobe size of the white dwarf. Our results indicate that tidal torque plays an important role but that the disc can extend up to the Roche lobe of the accreting star.

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arXiv2023

Macro-flickering of AQ Mensae on the daily time-scales: Parameters and quasi-period modes

We analyzed TESS photometric data of the flickering-active cataclysmic star AQ Men in 2018--2019. We processed 7 sectors with 14 light curves (LCs) inside them, with a time resolution of 2 min. Aiming to study the "macro-flickering", with quasi periods (QPs) between 10 and 100 hours, we processed LCs after 55 time reduced, with a time resolution of 1.83 hours. The method, developed earlier by us, includes comparing the LCs by their statistical and fractal parameters, as well as revealing QPs by minima of structure functions and relevant maxima of autocorrelation functions. We distinguish the known high state of AQ Men, in the sectors ## 01, 05, 08, 12, 13, as well as the low state, in sectors #19, #20. In the low state the LCs show noticeable eclipses with period 3.4 h, lower average fluxes, higher scatters, and additional QPs. By its statistical and fractal parameters, the macro-flickering of AQ Men in the high state is similar to the ordinary flickering of 3 symbiotic binaries, studied by us earlier (see below). We found 92 QPs in the range of 20--70 h. We reveal 3 QP modes, at 20.9 h, 32.5 h and 54.1 h (1.149, 0.738 and 0.434 c/d; Fig. 7) within a standard error about 10%. The last mode is the most populated one and seems to be a manifestation of the superorbital period. Other 4 QP modes of AQ Men are added from the literature. The regularity of these 7 QP modes follows a power function with a base 1.57 and standard deviation 6.4% (Fig. 8). This power model prognosticates 5 other QP modes: 3 internal and 2 external (Table 2). The bases of the power regularity models for the flickering of the symbiotic binaries RS Oph, T CrB, and MWC 560 (however in the time scale of minutes) are 1.55, 2.0, and 1.34, respectively (Table 1). For unknown reasons in these 4 cases we find (i) regularities with (ii) different bases.

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arXiv2023

BV photometric observations of the flickering of the dwarf nova RX And

We report photometry of the intranight variability of the dwarf nova RX And in two bands (B and V). The observations are carried out during three nights in November-December 2022 at the 50/70~cm Schmidt telescope of the Rozhen National Astronomical Observatory. The observations indicate that the amplitude of the flickering is about 0.5 mag in B band when the star is in faint state (m_V=13.5), but it is considerably lower (less than 0.1 mag) when the star is bright (m_V=10.9). The mass accretion rate in high state is estimated to be $1.2 \times 10^{-9}$ M$_\odot$ yr$^{-1}$. Combining our data and GAIA distances we find for the mass donor in RX~And spectral type K6V-K7V. The data are available upon request from the authors.

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arXiv2023

Optical spectroscopy of Be stars: peak separation of Balmer emission lines

The Be stars display variable optical emission lines originating in the circumstellar disc. Here we analyse high resolution spectroscopic observations of Be stars and the distance between the peaks of H-alpha, H-beta, and H-gamma emission lines ($ΔV_α$, $ΔV_β$, and $ΔV_γ$ respectively). Combining published data, spectra from the ELODIE archive (obtained in the period 1998 -- 2003) and Rozhen spectra (obtained 2015 -- 2023) of 93 Be stars, we find a set of relations connecting $ΔV_α$, $ΔV_β$ and $ΔV_γ$. They are effective for $30 \le ΔV_α\le 500$ km s$^{-1}$, $80 \le ΔV_β\le 600$ km s$^{-1}$, and $40 \le ΔV_γ\le 300$ km s$^{-1}$. The new equations are in the form $y=ax + b$ and are valid for a wider velocity range than in previous studies.

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arXiv2023

Mass outflow from the symbiotic binary RS Oph during its 2021 outburst

RS Oph is a symbiotic recurrent nova containing a massive white dwarf with heavy mass loss during activity. In August 2021, it underwent its seventh optical eruption since the end of the 19th century. The goal of this work is to analyse the structure of the outflows from the outbursting object. Based on broad-band $U$, $B$, $V$, $R_{\rm C}$, and $I_{\rm C}$ photometry and high-resolution H$α$ spectroscopy obtained at days 11--15 of the outburst, we derived some parameters of the system's components and outflows and their changes during our observation. The effective temperature of a warm shell (pseudophotosphere) produced by the ejected material and occulting the hot component of the system was $T_{eff}=15000\pm1000$ K and the electron temperature of the nebula was $T_{e}=17000\pm3000$ K throughout the observations. The effective radius of the pseudophotosphere was $R_{ eff}=13.3\pm2.0$ R$_{\odot}$ and the emission measure of the nebula $EM=(9.50\pm0.59) $10$^{61}$ cm$^{-3}$ for day 11 and $R_{eff}=10.3\pm1.6$ R$_{\odot}$ and $EM=(5.60\pm0.35)$10$^{61}$ cm$^{-3}$ for day 15. To provide this emission measure, the bolometric luminosity of the outbursting object must exceed its Eddington limit. The mass-loss rate of the outbursting object through its wind is much greater than through its streams. The total rate (from wind + streams) was less than $(4-5)$ 10$^{-5}$ (d/1.6kpc)$^{3/2}$ M$_{\odot}$yr$^{-1}$. The streams are not highly collimated. Their mean outflowing velocities are $\upsilon_{b}=-3680\pm60$ km s$^{-1}$ for the approaching stream and $\upsilon_{r}=3520\pm50$ km s$^{-1}$ for the receding one if the orbit inclination is 50$^\circ$.

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arXiv2022

The hidden symbiotic star SU Lyn -- detection of flickering in U band

We report photometric observations of the hidden symbiotic star SU Lyn in the optical bands. In five nights we detect a weak flickering in U band with amplitude of about 0.05 magnitudes. No intranight variations are found in B, V, g' and r' bands. This is one more indication that the secondary component is a white dwarf accreting at low accretion rate. We also searched for intranight variability of a dozen related object (RR Boo, RT Boo, AM Cyg, AG Peg, BF Cyg, NQ Gem, StHa190, V627 Cas, XX Oph, FS Cet and Y Gem) in which no variability above the observational errors is detected.

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arXiv2022

Optical spectroscopy of the Be/black hole binary MWC656 -- interaction of a black hole with a circumstellar disc

We present new spectroscopic observations of the Be/black hole binary MWC 656 obtained during the period 2015 - 2021. We measure the equivalent width of H$α$ (EW$_α$), H$β$ ($EW_β$), and the distance between the peaks of H$α$ ($ΔV_α$), H$β$ ($ΔV_β$), and FeII ($ΔV_{FeII}$) lines. Combining new and old data, we find that: - the density of the circumstellar disc of MWC 656 ($ΔV_α$ versus $EW_α$ diagram) is similar to the Be stars. For the Be stars we find the relation $ΔV_β= 0.999 ΔV_α+ 62.4$ km s$^{-1}$, and the position of MWC~656 corresponds to the average behaviour of the Be stars. This means that the presence of the black hole does not change the overall structure of the circumstellar disc. - the periodogram analysis indicates modulation of $EW_α$ with a period $60.4 \pm 0.4$ days, which is identical to the binary orbital period. The maxima of $EW_α$ and $EW_β$ are around periastron (phase zero). - around orbital phase zero, $ΔV_β$ and $ΔV_{FeII}$ decrease by about $30$ km s$^{-1}$. This suggests that we observe an increase of the circumstellar disc size induced by the periastron passage of the black hole and that the entire circumstellar disc pulsates with the orbital period with relative amplitude of 10-20%. The observations also indicate, that the reason for the black hole in MWC 656 to be in deep quiescence is a very low efficiency of accretion ($\sim 2 \times 10^{-6}$).

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arXiv2021

The symbiotic binary ZZ CMi: intranight variability and suggested outbursting nature

We present photometric and spectral observations of the symbiotic star ZZ CMi. We detect intranight variability - flickering and smooth variations in U band. The amplitude of the flickering is about 0.10-0.20 mag in U band. In the B band the variability is lower, with amplitude less than 0.03 mag. We also detect variability in the H-alpha and H-beta emission lines, and find an indication for outflow with velocity of about 120-150 km/s. The results indicate that ZZ CMi is an accretion powered symbiotic containing an M4-M6 III cool component with an white dwarf resembling recurrent novae and jet-ejecting symbiotic stars. [The data are available on www.astro.bas.bg/~rz/ZZCMi/ZZCMi.tar.gz]

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arXiv2021

H-alpha spectroscopy of the recurrent nova RS Oph during the 2021 outburst

We report spectroscopic observations of the $Hα$ emission line of the recurrent nova RS~Oph obtained between 12 and 23 August 2021 during the recent outburst. On the basis of the sharp P~Cyg profile superimposed onto the strong H-alpha emission, we estimate that the outflowing velocity of the material surrounding RS Oph is in the range 32 km/s < V_{out} < 68 km/s. The new GAIA distance indicates that the red giant should be probably classified in between II and III luminosity class. The spectra are available upon request from the authors and on Zenodo.

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arXiv2021

UBVRI observations of the flickering of the dwarf nova RX And

We report observations of the flickering variability of the dwarf nova RX And in five bands (UBVRI) on two nights. On 25 October 2019 the brightness of the star was $B\approx 13.9$ mag, the amplitude of the flickering was 0.47 mag, and we estimate for the flickering source temperature $T_{fl} = 10700 \pm 400$ K, and radius $R_{fl} =0.046 \pm 0.004$ $R_\odot$. On 2 January 2020, the star was about 3 magnitudes brighter ($B \approx 10.7$), the amplitude of the flickering was significantly lower (0.07 mag) and we derive for the flickering source $T_{fl} = 9600 \pm 700$ K, and radius $R_{fl} = 0.098 \pm 0.009$ $R_\odot$. The results indicate that 3 magnitudes brightening of the star doubled the radius of the flickering source. The data are available upon request from the authors.

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arXiv2021

Radius, rotational period and inclination of the Be stars in the Be/gamma-ray binaries MWC 148 and MWC 656

Using TESS photometry and Rozhen spectra of the Be/gamma-ray binaries MWC 148 and MWC 656, we estimate the projected rotational velocity ($ {v} \sin i$), the rotational period (P$_{\rm rot}$), radius (R$_{\rm 1}$), and inclination ($i$) of the mass donor. For MWC 148 we derive P$_{\rm rot} = 1.10 \pm 0.03$~d, R$_{\rm 1}= 9.2 \pm 0.5$~R$_\odot$, $i = 40^\circ \pm 2^\circ$, and $ {v} \sin i =272 \pm 5$~km~s$^{-1}$. For MWC 656 we obtain P$_{\rm rot} = 1.12 \pm 0.03$~d, R$_{\rm 1}= 8.8 \pm 0.5$~R$_\odot$, $i = 52^\circ \pm 3^\circ$, and $ {v} \sin i =313 \pm 3$~km~s$^{-1}$. For MWC 656 we also find that the rotation of the mass donor is coplanar with the orbital plane.

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arXiv2020

An eccentric wave in the circumstellar disc of the Be/X-ray binary X Persei

We present spectroscopic observations of the Be/X-ray binary X Per obtained during the period December 2017 - January 2020 (MJD~58095 - MJD~58865). In December 2017 the $Hα$, $Hβ$, and HeI 6678 emission lines were symmetric with violet-to-red peak ratio $V/R \approx 1$. During the first part of the period (December 2017 - August 2018) the V/R-ratio decreased to 0.5 and the asymmetry developed simultaneously in all three lines. In September 2018, a third component with velocity $\approx 250$~km~s$^{-1}$ appeared on the red side of the HeI line profile. Later this component emerged in $Hβ$, accompanied by the appearance of a red shoulder in $Hα$. Assuming that it is due to an eccentric wave in the circumstellar disc, we find that the eccentric wave appeared first in the innermost part of the disc, it spreads out with outflowing velocity $v_{wave} \approx 1.1 \pm 0.2 $~km~s$^{-1}$, and the eccentricity of the eccentric wave is $e_{wave} \approx 0.29 \pm 0.07$. A detailed understanding of the origin of such eccentricities would have applications to a wide range of systems from planetary rings to AGNs.

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arXiv2020

Interstellar extinction toward symbiotic stars

Using diffuse interstellar bands (DIBs) at 5780 A, 5797 A and 6613 A, visible in the high resolution spectra, and measuring their equivalent widths, we estimate the interstellar extinction toward seven symbiotic stars. We find $E_{B-V}$= $1.28 \pm 0.10$ for AS 289, $E_{B-V}$= $1.55 \pm 0.10$ for BI Cru, $E_{B-V}$= $0.63 \pm 0.10$ for HD330036, $E_{B-V}$= $0.33 \pm 0.05$ for V2756 Sgr, $E_{B-V}$= $0.30 \pm 0.05$ for V2905 Sgr, $E_{B-V}$= $1.52 \pm 0.11$ for V417 Cen, $E_{B-V}$= $0.81 \pm 0.10$ for PN Sa 3-22. The derived values are in agreement with the extinction through the Galaxy.

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