arXiv subjects

A. V. Zharova

Publications and source records attributed to A. V. Zharova.

14 recordsLinked to original sources

arXiv2026

The curved jet in the young star FN Tau

In the vicinity of the young star FN Tau, we have detected a microjet and four Herbig-Haro objects, whose positions and kinematics indicate the presence of a bipolar collimated outflow from the star - HH 1267. The stellar jet does not propagate rectilinearly, and we discuss the possibility that the curved shape of the jet, whose axis is inclined to the line of sight at an angle $<20^\circ$, results from the precession of the inner regions of the FN Tau protoplanetary disk. Approximately 60 years ago, the star underwent outbursts with an amplitude of $Δm_{\rm pg} \sim 2^{\rm m}$ lasting several months, which we associate with the onset of the microjet.

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arXiv2026

The eruptive young star IRAS 21204+4913

The results of photometric, polarimetric, and spectroscopic observations are presented for the young star IRAS 21204+4913, whose visible brightness has increased by $\approx 5^{\rm m}$ since October 2025. The star's absorption spectrum in the $0.36 - 0.75 μ$m range resembles those of A - F giants and supergiants, but it also exhibits molecular TiO bands. The brightening was accompanied by a significant increase in the degree of polarization of the stellar radiation (to $\approx 16 \%$ in the I-band), likely due to scattering by dust in an expanding circumstellar shell. The P Cygni profile of the H$α$ line implies a dusty wind velocity of $\approx 300$ km/s. We believe that the outburst of IRAS 21204+4913 is caused by an increase in the accretion rate of protoplanetary disk's matter onto the young star with a mass of $\lesssim 0.5$ M$_\odot$ to $\gtrsim 3\times 10^{-5}$ M$_\odot$ yr$^{-1}$. Furthermore, IRAS 21204+4913 displays several unusual features: the dependence of the width and radial velocity of absorption lines on the excitation potential, emission in the TiO molecular bands, and a comparably bright outburst that occured in 1948. Several T Tauri stars and a group of Herbig-Haro objects are found in the vicinity of the star.

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arXiv2025

On the causes of brightness variability of the young star BP Tau

We have constructed and analysed the secular light curve of BP Tau, a classical T Tauri-type star. Wave-like variations in the average brightness were detected, with an amplitude of $ΔB\approx 0.2$ and characteristic time-scales of several decades. We argue that three deep dimming events $(ΔB \sim 1.5)$, lasting from 1 hour to several days, are caused by the eclipse of a hot (accretion) spot by dust falling onto the star together with gas. Such eclipses, albeit with smaller amplitudes, may explain the absence of a strictly defined periodicity in the brightness variations of BP Tau associated with axial rotation. We also show that within the distance range of 0.1 to 200 AU, BP Tau does not have a companion with a mass exceeding 0.2M$_\odot.$ The causes of brightness and colour index variations on different time-scales are discussed.

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arXiv2025

Optical and X-ray timing analysis of the 2018-2020 outburst and rebrightening of the black-hole transient MAXI J1820+070

We report the results of a comprehensive analysis of the multiwavelength (in optical and X-rays) and multitimescale (from months to tenths of a second) variability of the 2018-2020 outburst of the black hole transient MAXI J1820+070. During the first outburst episode, a detailed analysis of the optical photometry shows a periodicity that evolves over time and stabilises at a frequency of $1.4517(1)$ $1/d$ ($\sim0.5\%$ longer than the orbital period). This super-orbital modulation is also seen in the X-rays for a few days soon after the transition to the high-soft state. We also observed optical Quasi-Periodic Oscillations (QPOs), which correspond to some of the QPOs observed in X-rays at three different epochs when the source was in the low-hard state. In two epochs, optical QPOs with a centroid consistent with half the frequency of the most prominent X-ray QPO can be seen. If the lowest modulation frequency is the one observed in the optical, the characteristic precession frequency of MAXI J1820+070 is lower than that inferred from the `fundamental' QPO in the X-rays. Assuming that QPOs can be generated by Lense-Thirring precession, we calculate the spin of the black hole in the case where the fundamental precession frequency is tracked by the optical emission. We find a relatively slowly spinning black hole with a spin parameter $\lesssim 0.15$. The super-orbital optical and X-ray modulations observed after the disappearance of the QPOs may be triggered by the self-irradiation of the outer disc by a standard inner disc truncated at a few gravitational radii.

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arXiv2024

ZZ Tau IRS: a low mass UX Ori type star with strong wind

The results of photometric, polarimetric and spectroscopic observations of the young star ZZ Tau IRS in the visible and near-infrared bands are presented. Against the continuum of an M spectral type star about 50 emission lines of allowed (HI, HeI, NaI, SII) and forbidden (OI, OII, OIII, NI, NII, SII, CaII, FeII, NiII) transitions were identified. It was found that from the autumn of 2020 to the beginning of 2023, the brightness of the star in the visible region decreased $(ΔI \approx 1.5^m),$ and then began to return to initial level. As the visible brightness of the star declined, its colour indices decreased in the visible region, but increased in the near-IR bands. At light minimum, the degree of polarization in the $I$ band reached $\approx$ 13%, and the equivalent widths of e.g. the H$α$ and [SII] 6731 A lines increased to 376 and 79 A, respectively. Arguments are given in favour of ZZ Tau IRS being a UX Ori type star, and its variability being due to eclipses by dust clouds, which are inhomogeneities in the dusty disc wind. Forbidden lines are formed both in the disc wind and in the jet, the axis of which is oriented along PA$=61\pm 3$ degrees. The jet mass-loss rate is $>5 \times 10^{-10}$ M$_\odot$/yr, what is abnormally large for a star with a mass of $<0.3$ M$_\odot.$ Apparently, the disc wind of ZZ Tau IRS is not axially symmetric, probably due to the azimuthal asymmetry of the protoplanetary disc found earlier from ALMA observations.

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arXiv2018

New variable Stars from the Photographic Archive: Semi-automated Discoveries, Attempts of Automatic Classification, and the New Field 104 Her

Using 172 plates taken with the 40-cm astrograph of the Sternberg Astronomical Institute (Lomonosov Moscow University) in 1976-1994 and digitized with the resolution of 2400 dpi, we discovered and studied 275 new variable stars. We present the list of our new variables with all necessary information concerning their brightness variations. As in our earlier studies, the new discoveries show a rather large number of high-amplitude Delta Scuti variables, predicting that many stars of this type remain not detected in the whole sky. We also performed automated classification of the newly discovered variable stars based on the Random Forest algorithm. The results of the automated classification were compared to traditional classification and showed that automated classification was possible even with noisy photographic data. However, further improvement of automated techniques is needed, which is especially important having in mind the very large numbers of new discoveries expected from all-sky surveys.

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arXiv2016

Luminous Red Nova 2015 in the Galaxy M101

We present the results of the study of the red nova PSN J14021678+5426205 based on the observations carried out with the Russian 6-m telescope (BTA) along with other telescopes of SAO RAS and SAI MSU. To investigate the nova progenitor, we used the data from the Digital Sky Survey and amateur photos available on the internet. In the period between April 1993 and July 2014, the brightness of the progenitor gradually increased by 2.2 mag in the V band. At the peak of the first outburst in mid-November of 2014, the star reached an absolute visual magnitude of -12.75 mag but was discovered later, in February 2015, in a repeated outburst at the absolute magnitude of -11.65 mag. The amplitude of the outburst was minimum among the red novae, only 5.6 mag in the V band. The H alpha emission line and the continuum of a cool supergiant with a gradually decreasing surface temperature were observed in the spectra. Such process is typical for red novae, although the object under study showed extreme parameters: maximum luminosity, maximum outburst duration, minimum outburst amplitude, unusual shape of the light curve. This event is interpreted as a massive OB star system components merging accompanied by the formation of a common envelope and then the expansion of this envelope with minimal energy losses.

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arXiv2016

Photometry and spectroscopy of SN 2015bh in the galaxy NGC 2770

We present medium-resolution spectroscopy and multicolor photometry for the optical transient PSN J09093496+3307204 (SN 2015bh) in the galaxy NGC 2770, which has transferred into the supernova phase. The observations were carried out between February 2015 to May 2016. Both at the phase of the SN impostor (2015a) and at the supernova phase (2015b), besides Balmer emissions, the strong Fe II emissions are seen in the spectrum; so, these spectra resemble those of Williams Fe II type classical novae. The star is located near the edge of a dark nebula and notably absorbed (Av = 1.14 +/-0.15 mag). Taking into account this absorption, we determined maximum absolute magnitudes of Mv = -15.0 +/-0.3 mag at the 2015a phase and of Mv = -18.14 +/-0.30 mag at the 2015b phase. The light curve at the 2015b phase is similar to those of SN IIL. The supernova progenitor is a luminous blue variable (LBV) star with the powerful Hα emission. We considered several hypotheses of supernovae explosions following optical transients related with LBV. The hypothesis of core collapse of an evolved massive star interrupting the process of its merging with massive companion in a binary system (a failed luminous red nova) was chosen as the preferable one for this event.

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arXiv2015

Orbital motions and light curves of young binaries XZ Tau and VY Tau

The results of our speckle interferometric observations of young binaries VY Tau and XZ Tau are presented. For the first time, we found a relative displacement of VY Tau components as well as a preliminary orbit for XZ Tau. It appeared that the orbit is appreciably non-circular and is inclined by $i \lesssim 47^o$ from the plane of the sky. It means that the rotation axis of XZ Tau A and the axis of its jet are significantly non-perpendicular to the orbital plane. We found that the average brightness of XZ Tau had been increasing from the beginning of the last century up to the mid-thirties and then it decreased by $ΔB > 2$ mag. The maximal brightness has been reached significantly later on the time of periastron passage. The total brightness of XZ Tau's components varied in a non-regular way from 1970 to 1985 when eruptions of hot gas from XZ Tau A presumably had occurred. In the early nineties the variations became regular following which a chaotic variability had renewed. We also report that a flare activity of VY Tau has resumed after 40 yr pause, parameters of the previous and new flares are similar, and the flares are related with the A component.

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arXiv2013

A family of cometary globules at the periphery of Cyg OB1: the star HBHA 3703-01 and the reflection nebula GM 2-39

The interstellar medium in the region of a family of cometary globules including the reflection nebula GM 2-39 has been analyzed basing on our observations with the slit spectrograph, the results of our previous observations with a Fabry-Perot interferometer in the H-alpha line, Spitzer archival data together with CO microwave data. The structure of globules' IR emission, velocity field of ionized gas in the H-alpha line and of molecular gas in the CO line have been considered. We have detected a CO cavern around the eastern globules and faint high-velocity H-alpha features of surrounding gas. The most probable sources of ionizing radiation and wind of the Cyg OB1 association responsible for the globules' formation are proposed. Based on our multicolour photometry, it has been found that the brightest compact source in the southern 'head' of the cometary globule - the star HBHA 3703-01 (IRAS 20153+3850) - is a B(5-6)V star with E(B-V)=1.18 mag. The strong and broad H-alpha emission line was revealed in its spectrum. The spectral energy distribution of HBHA 3703-01 in the 0.44-24 micron range has been modeled. It is shown that the star has a hot dust envelope with T(dust)=1400 K and tau(V)=1.1. Besides, the star HBHA 3703-01 illuminates the encompassing diffuse nebula GM 2-39 with a diameter of about 30 arcsec. With regard to all obtained observational data for HBHA 3703-01, this object may be classified as the Herbig Ae/Be star.

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arXiv2011

GSC 2576-02071 and GSC 2576-01248: two Algol-type eclipsing binaries studied using CCD observations and historical photographic data

An initial investigation of two poorly studied eclipsing binaries separated by ~3' in the sky is presented. The first star (GSC 2576-01248) was discovered by the TrES exoplanet search project. The second one (GSC 2576-02071) was identified by the authors during CCD observations of GSC 2576-01248. We combine our dedicated CCD photometry with the archival TrES observations and data from the digitized photographic plates of the Moscow collection to determine periods of the two variable stars with high precision. For GSC 2576-01248, addition of historical photographic data provides a major improvement in accuracy of period determination. No evidence for period change in these binary systems was found. The lightcurve of GSC 2576-01248 is characterized by a prominent variable O'Connell effect suggesting the presence of a dark starspot and asynchronous rotation of a binary component. GSC 2576-02071 shows a shift of the secondary minimum from the phase =0.5 indicating a significant orbit eccentricity.

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arXiv2010

The progenitor and remnant of the helium nova V445 Puppis

V445 Pup was a peculiar nova with no hydrogen spectral lines during the outburst. The spectrum contained strong emission lines of carbon, oxygen, calcium, sodium, and iron. We have performed digital processing of photographic images of the V445 Pup progenitor using astronomical plate archives. The brightness of the progenitor in the B band was 14.3 mag. It was a periodic variable star, its most probable period being 0.650654+/-0.000011 day. The light curve shape suggests that the progenitor was a common-envelope binary with a spot on the surface and variable surface brightness. The spectral energy distribution of the progenitor between 0.44 and 2.2 micrometers was similar to that of an A0V type star. After the explosion in 2001, the dust was formed in the ejecta, and the star became a strong infrared source. This resulted in the star's fading below 20 mag in the V band. Our CCD BVR observations acquired between 2003 and 2009 suggest that the dust absorption minimum finished in 2004, and the remnant reappeared at the level of 18.5 mag V. The dust dispersed but a star-like object was absent in frames taken in the K band with the VLT adaptive optics. Only expanding ejecta of the explosion were seen in these frames till March 2007. No reddened A0V type star reappeared in the spectral energy distribution. The explosion of V445 Pup in 2000 was a helium flash on the surface of a CO-type white dwarf. Taking into account the results of modern dynamic calculations, we discuss the possibility of a white-dwarf core detonation triggered by the helium flash and the observational evidence for it. Additionally, the common envelope of the system was lost in the explosion. Destruction in the system and mass loss from its components exclude the future SN Ia scenario for V445 Pup.

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arXiv2010

MN112: a new Galactic candidate Luminous Blue Variable

We report the discovery of a new Galactic candidate Luminous Blue Variable (cLBV) via detection of an infrared circular nebula and follow-up spectroscopy of its central star. The nebula, MN112, is one of many dozens of circular nebulae detected at $24 μ$m in the {\it Spitzer Space Telescope} archival data, whose morphology is similar to that of nebulae associated with known (c)LBVs and related evolved massive stars. Specifically, the core-halo morphology of MN112 bears a striking resemblance to the circumstellar nebula associated with the Galactic cLBV GAL 079.29+00.46, which suggests that both nebulae might have a similar origin and that the central star of MN112 is a LBV. The spectroscopy of the central star showed that its spectrum is almost identical to that of the bona fide LBV P Cygni, which also supports the LBV classification of the object. To further constrain the nature of MN112, we searched for signatures of possible high-amplitude ($\ga 1$ mag) photometric variability of the central star using archival and newly obtained photometric data covering a 45 year period. We found that the B magnitude of the star was constant ($\simeq$ 17.1$\pm$0.3 mag) over this period, while in the I band the star brightened by $\simeq 0.4$ mag during the last 17 years. Although the non-detection of large photometric variability leads us to use the prefix `candidate' in the classification of MN112, we remind that the long-term photometric stability is not unusual for genuine LBVs and that the brightness of P Cygni remains relatively stable during the last three centuries.

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arXiv2008

Warped polar ring in the Arp 212 galaxy

The Fabry-Perot scanning interferometer mounted on the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences is used to study the distribution and kinematics of ionized gas in the peculiar galaxy Arp 212 (NGC 7625, III Zw 102). Two kinematically distinct subsystems - the inner disk and outer emission filaments, are found within the optical radius of the galaxy. The first subsystem, at galactocentric distances r<3.5 kpc, rotates in the plane of the stellar disk. The inner part of the ionized-gas disk (r<1.5-2 kpc) exactly coincides with the previously known disk consisting of molecular gas. The second subsystem of ionized gas is located at galactocentric distances 2-6 kpc. This subsystem rotates in a plane tilted by a significant angle to the stellar disk. The angle of orbital inclination in the outer disk increases with galactocentric distance and reaches 50 degrees at r=6 kpc. The ionized fraction of the gaseous disk does not show up beyond this galactocentric distance, but we believe that the HI disk continues to warp and approaches the plane that is polar with respect to the inner disk of the galaxy. Hence Arp 212 can be classified as a galaxy with a polar ring (or a polar disk). The observed kinematics of the ionized and neutral gas can be explained assuming that the distribution of gravitational potential in the galaxy is not spherically symmetric. Most probably, the polar ring have formed via accretion of gas from the dwarf satellite galaxy UGC 12549.

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