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S. A. Lamzin

Publications and source records attributed to S. A. Lamzin.

At least 19 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.

astro-ph.SR↗
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 influence of component orbital motion on the photometric variability of DF Tau

Based on the analysis of the long-term light curve of the young binary DF Tau spanning approximately 125 years, we infer that its brightness variations are associated with changes in the accretion rate from the circumstellar protoplanetary disk onto the primary. We have also substantially improved the orbital parameters of DF Tau, which enables us to align its secular light curve with the evolution of the binary's component separation. The relationship between the long-term brightness variations and the orbital motion of DF Tau, if present, appears to be inconsistent with theoretical predictions. Notably, similar discrepancies between theory and observations are also seen in other young binary systems. Furthermore, the source of the polarized radiation in the optical range is found to be located at a distance of $\lesssim 0.5^{\prime\prime}$ from the star, with the polarization variability showing no dependence on the orbital phase.

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arXiv2025

The jet and circumstellar environment of the young binary DF Tau

Jets and disc winds play an important role in the evolution of protoplanetary discs and the formation of planetary systems. However, there is still a lack of observational data regarding the presence and parameters of outflows, especially for close young binaries. In this study, we aim to find the HH flow near the young sub-arcsecond binary DF Tau and explore its morphology. Narrow-band H$α$ and H$_2$ 2.12 $μ$m imaging and spectroscopic observations of DF Tau and its vicinity were performed. We have discovered several emission nebulae near the binary, which likely result from the interaction of gas outflow from the binary components with the surrounding medium. The outflow appears to occur both in the form of jets, generating numerous Herbig-Haro objects (HH 1266 flow), and as a weakly collimated wind responsible for the formation of the ring-like nebula around the binary and the rim of the cometary globule. We have found that the angle between the jet and the counter-jet is $168^\circ$ and discuss the complex morphology of the HH flow.

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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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arXiv2024

The jet of BP Tau

A strong global magnetic field of young low-mass stars and a high accretion rate are the necessary conditions for the formation of collimated outflows (jets) from these objects. But it is still unclear whether these conditions are also sufficient. We aim to check whether BP Tau, an actively accreting young star with a strong magnetic field, has a jet. We carried out narrowband SII 672 nm imaging and spectroscopic observations of BP Tau and its vicinity. We find that BP Tau is a source of a Herbig-Haro flow (assigned number HH 1181), which includes two HH objects moving from the star in opposite directions and a micro- (counter-) jet of ~ 1" projected length. The flow is oriented along position angle $59 \pm 1$ degree.

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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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arXiv2023

Laboratory modeling of jets from young stars using plasma focus facilities

Jets from young stars are used as an example to review how laboratory modeling enables advancement in understanding the main physical processes responsible for the formation and stability of these amazing objects. The discussion focuses on the options for modeling jet emissions in a laboratory experiment at the PF-3 facility at the National Research Center Kurchatov Institute. Many properties of the flows obtained using this experimental setup are consistent with the main features of jets from young stars.

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arXiv2017

The jet of the young star RW Aur A and related problems

Comparing the images of the jet of the young star RW Aur A, separated by a period of 21.3 years, we found that the outermost jet's knots have emerged $\approx 350$ yr ago. We argue that at that moment the jet itself has appeared and intensive accretion onto the star has began due to the rearrangement of its protoplanetary disk structure caused by the tidal effect of the companion RW Aur B. More precisely, we assume that the increase of accretion is a response to changing conditions in the outer disk regions, which followed after the sound wave, generated by these changes, crossed the disk in a radial direction. The difference in the parameters of the blue and red lobes of the RW Aur A jet, according to our opinion, is a result of the asymmetric distribution of the circumstellar matter above and below the disk, due to a fly-by of the companion. It was found from the analysis of RW Aur historical light curve that deep and long $(Δt>150$ days) dimmings of RW Aur A observed after 2010 yr, had no analogues in the previous 110 years. We also associate the change in the character of the photometric variability of the star with the rearrangement of the structure of inner $(r<1$ a.u.) regions of its protoplanetary disk and discuss why these changes began only 350 years after the beginning of the active accretion phase.

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arXiv2017

ASTRONIRCAM - infrared camera-spectrograph for Sternberg institute 2.5 METER TELESCOPE

ASTRONIRCAM is a cryogenic-cooled slit spectrograph for the spectral range 1-2.5 mkm installed at the Nasmyth focus of the 2.5-meter telescope of the Caucasian observatory of Sternberg Astronomical Institute of Lomonosov Moscow State University. The instrument is equipped with the HAWAII-2RG 2048x2048 HgCdTe array. Grisms are used as dispersive elements. In the photometric mode ASTRONIRCAM allows for extended astronomical object imaging in the field of view of 4.6x4.6 arc minutes with the 0.269 arcsec/pixel scale in standard photometric bands J, H, K and Ks as well as in narrow-band filters CH_4, [Fe II], H_2 v=1-0 S(1), Br_gamma and CO. In the spectroscopic mode, ASTRONIRCAM takes spectra of extended or point-like sources with spectral resolution R=lambda/Delta lambda <= 1200. The general design, optical system, detector electronics and readout, amplification and digitization scheme are considered. The conversion factor GAIN measurement results are described as well as its dependence on the accumulated signal (non-linearity). The full transmission of the atmosphere-to-detector train ranges from 40 to 50\% in the wide-band photometry mode. The ASTRONIRCAM sensitivity at the 2.5-m telescope is characterized by the limiting J=20, K=19 star magnitudes measured with the 10% precision and 15 minutes integration at the 1 arcsec atmospheric seeing conditions. The references to first results published on the base of ASTRONIRCAM observations are given.

astro-ph.IM↗
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

The Structure of Shock Waves in the Case of Accretion onto Low-Mass Young Stars

A physical analysis and mathematical formulation of the structure of an accretion shock wave in the case of young stars are given. Some results are presented, and the dependence of the structure of the shock on various parameters is investigated. In the general case, the relative intensities and profiles of lines in the spectra of T Tauri stars should depend on the velocity and density of the infalling gas, as well as on the accretion geometry. The calculation results may serve as a base for elucidating the nature of the activity of young stars.

astro-ph.SR↗
arXiv2013

Results of magnetic field measurements in young stars DO Tau, DR Tau, DS Tau

Results of measurements of the longitudinal magnetic field in a hot accretion spot in three classical T Tauri stars (CTTS) are presented. The magnetic field in the formation region of the narrow component of the emission line HeI 5876 Å was found for each star in our sample at a level of more than 2σ. In case of DS Tau we have found the field in the narrow components of NaI D lines, which was equal to +0.8 \pm 0.3 kG, i.e. it was equal to the field measured on the narrow component of HeI 5876 Å. Our results indicate that the magnetic field in the hot spots can be studied for CTTS down to 13^m that allow in the future to double a number of CTTS with measured field in the accretion zone.

astro-ph.SR↗
arXiv2013

A non-LTE modeling of narrow emission components of He and Ca lines in optical spectra of CTTS

A spectrum of a hot spot, produced by radiation of accretion shock at T Tauri star's surface, has been calculated taking into account non-LTE effects for HeI, HeII, CaI and CaII, using LTE-calculations of spot's atmospheric structure, calculated by Dodin & Lamzin (2012). Assuming that pre-shock gas number density N_0 and its velocity V_0 are the same across the accretion column, we calculated spectra of a system "star + round spot" for a set of N_0, V_0 values and parameters, which characterized the star and the spot. It has been shown that theoretical spectra with an appropriate choice of the parameters reproduce well observed veiling of photospheric absorption lines in optical band as well as profiles and intensities of so-called narrow components of HeII and CaI emission lines in spectra of 9 stars. We found that the accreted gas density N_0>10^{12} cm^{-3} for all considered stars except DK Tau. Observed spectra of 8 stars were succesfully fitted, asuming solar abundance of calcium, but it appeared possible to fit TW Hya spectrum only under assumption that calcium abundance in accreted gas was three times less than solar. We derive spot's parameters by comparison of theoretical and observed spectra, normalised to continuum level, so our results are independent on unknown value of interstellar extinction. We have found that the predicted flux in CaII lines is less than observed one, but this discrepancy can be resolved if not only high-density but also lower density gas falls onto the star. Theoretical equivalent widths as well as relative intensities of He\,I subordinate lines disagree significantly with observations, presumbly due to a number of reasons: necessity to take into account non-LTE thermal structure of upper layers of a hot spot, poorly known collisional atomic data for HeI upper levels and inhomogeneity of the hot spot.

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arXiv2012

Interpretation of the Veiling of the Photospheric Spectrum for T Tauri Stars in Terms of an Accretion Model

The problem on heating the atmospheres of T Tauri stars by radiation from an accretion shock has been solved. The structure and radiation spectrum of the emerging so-called hot spot have been calculated in the LTE approximation. The emission not only in continuum but also in lines has been taken into account for the first time when calculating the spot spectrum. Comparison with observations has shown that the strongest of these lines manifest themselves as narrow components of helium and metal emission lines, while the weaker ones decrease significantly the depth of photospheric absorption lines, although until now, this effect has been thought to be due to the emission continuum alone. The veiling by lines changes the depth of different photospheric lines to a very different degree even within a narrow spectral range. Therefore, the nonmonotonic wavelength dependence of the degree of veiling r found for some CTTS does not suggest a nontrivial spectral energy distribution of the veiling continuum. In general, it makes sense to specify the degree of veiling r only by providing the set of photospheric lines from which this quantity was determined. We show that taking into account the contribution of lines to the veiling of the photospheric spectrum can cause the existing estimates of the accretion rate onto T Tauri stars to decrease by several times, with this being also true for stars with a comparatively weakly veiled spectrum. Neglecting the contribution of lines to the veiling can also lead to appreciable errors in determining the effective temperature, interstellar extinction, radial velocity, and vsin(i).

astro-ph.SR↗
arXiv2012

Reverse Rotation of the Accretion Disk in RW Aur A: Observations and a Physical Model

Speckle interferometry of the young binary system RW Aur was performed with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences using filters with central wavelengths of 550 nm and 800 nm and pass-band halfwidths of 20 nm and 100 nm, respectively. The angular separation of the binary components was 1.448"{\pm}0.005 and the position angle of the system was 255.9°{\pm}0.3° at the observation epoch (JD 2 454 255.9). We find using published data that these values have been changing with mean rates of +0.002"/yr and +0.02°/yr, respectively, over the past 70 years. This implies that the direction of the orbital motion of the binary system is opposite to the direction of the disk rotation in RW Aur A. We propose a physical model to explain the formation of circumstellar accretion disks rotating in the reverse direction relative to young binary stars surrounded by protoplanetary disks. Our model can explain the characteristic features of the matter flow in RW Aur A: the high accretion rate, small size of the disk around the massive component, and reverse direction of rotation.

astro-ph.SR↗
arXiv2011

Magnetic field of young star RW Aur

Results of longitudinal magnetic field B_z measurements for young star RW Aur A are presented. We found that B_z in the formation region of HeI 5876 line's narrow component varies from -1.47 \pm 0.15 kG to +1.10 \pm 0.15 kG. Our data are consistent with a stellar rotational period of \simeq 5.6^d and with a model of two hotspots with an opposite polarity of magnetic field and with a difference in a longitude about 180^o. The spot with B_z<0 is located at the hemisphere above the midplane of RW Aur's accretion disc and the spot with B_z>0 is below the midplane. The following upper limits for B_z (at 3σ level) were found after averaging of all our observations: 180 G for photosperic lines, 220 G and 230 G for formation regions of H_α and [OI] 6300 lines respectively. Upper limit 600 G were found in the region where broad components of emisson lines form. For two cases out of 11 we observed the field in a formation region of a blue absorption wing of NaI D lines i.e. in an outflow: B_z= -180 \pm 50 G and -810 \pm 80 G. Radial velocity of RW Aur's photospheric lines averaged over all our observations is about + 10.5 km/s what is 5.5 km/s less than value derived ten years earlier by Petrov et al. (2001). In this connection, we discuss a possibility that RW Aur is not a binary but a triple system.

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