A. M. Tolmachev

Russian Academy of Sciences, Moskva, Moscow, Russia

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Publications (29)24.84 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We present the results of our monitoring of the semiregular variable HU Pup in the 1612, 1665, and 1667-MHz OH lines and the 22.235-GHz H2O line. The maser emission in the 1612-MHz satellite line has been detected from this source for the first time. Strong variability of the emission has been observed in all three OH lines, including the radial-velocity drift of the two most intense features. Zeeman splitting components have been found. The longitudinal magnetic field strength has been estimated to be 1.0, 1.6 and 2.7, 3.2 mG in the 1665 and 1667-MHz lines, respectively. Our OH and H2O observations have revealed fairly stable structures in the masing region and have allowed us to estimate the variability period of the maser emission (̃1.5 yr). A possible model of the maser source in HU Pup is discussed.
    03/2014; 40(4).
  • V. V. Krasnov, E. E. Lekht, A. M. Tolmachev
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    ABSTRACT: We present observations of H2O maser emission from the complex region of active star formation Sgr B2 performed in 2005-2012. The observations were carried out with the 22-m radio telescope of the Pushchino Radio Astronomy Observatory. Seven flares with flux densities higher than 1000 Jy were detected. The flares occurred in all three main sites of star formation in Sgr B2, N,M, and S. The highest peak flux densities were 3200 Jy (60.9 km/s), 2350 Jy (69.4 km/s), and 7300 Jy (69.3 km/s) in N, M, and S, respectively. This last flare was the strongest during our monitoring campaign from 1982 to 2012, both in S and in the entire Sgr B2 complex. Possible associations of the flares were determined. High-velocity, short-lived emission was detected at 124-128 km/s. Emission at 127 km/s with a flux density of 23 Jy is associated with region M. Emission at 80.6 and 84.6 km/s, at radial velocities higher than those observed previously, was detected in region S.
    Astronomy Reports 08/2013; 57(8):567-572. · 0.76 Impact Factor
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    ABSTRACT: A catalog of maser spectra in the 1.35-cm water-vapor line towards the maser source NGC 2071 in a region of massive star formation is presented for 1994-2010. The observations were carried out using the 22-m antenna of the Pushchino Radio Astronomy Observatory with a spectral resolution of 0.101 km/s (0.0822 km/s after the end of 2005). Based on the data throughout the monitoring since 1980, two very different cycles of maser activity were found. The first (1980-1992) is characterized by high activity within a broad range of radial velocities. Emission at velocities near 7 km/s predominated in 1980-1986, and emission near 14-16 km/s, in 1987-1992. In 1997-2008, the maser intensity was appreciably lower than in the first activity cycle. Numerous flares of individual emission features were observed. Identifications based on VLA data show that strong flares took place in both maser sources, IRS1 and IRS3. Both sources demonstrated a low level of maser activity during essentially the same epochs (1977, 1995-1997, and the close of 2009 through the beginning of 2010), although the sources are separated by at least 2000 AU.
    Astronomy Reports 01/2011; 55:857-866. · 0.76 Impact Factor
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    ABSTRACT: The results of the search for the ultra-rapid flux fluctuations of the galactic sources of the water-vapour maser emission at a wavelength of 1.35 cm are presented. An observational technique of the search for rapid flux fluctuations on some minute scales has been developed. From 2002 to 2011, a number of observational sessions for 49 maser sources have been carried out with durations from 2 till 7 hours (with spectra exposition from 1 second to 20 minutes). Two-three sessions with the interval of one day have been spent on for the most interesting sources. Some of them were allocated a little that has shown such variability, among which as internal processes in the sources, going in areas the possible reasons of variability were discussed with characteristic scale of the order of 0.1 a.u., and external (up to the theoretical possibility of the resonant influence of the gravitational waves from galactic objects on the area maser radiations). Fast fluctuations of spectra for 12 maser sources on scales in tens minutes and minute (for sources Cep A, GGD4, IRAS 16293-2422, Ori A, W3 (OH), W3 (2), W33B, W43M3, W44C, W49N, W75N, W75S) are found reliably out. A part of them is connected with the linear polarization for some sources (Ori A, W3 (OH), W3 (2), W44C, W49N, W75S) that leads to slow changes of streams (ten minutes) from the polarized spectral details during the sources moving in the sky. The other type of variability is connected with fast movements maser condensation in the space masers (Cep A, GGD4, IRAS 16293-2422, W33B, W43M3, W49N, W75N). The characteristic time of changes of the fluxes of the second type of variability is from 10 minutes to about one hour.
    Odessa Astronomical Publications. 01/2011;
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    ABSTRACT: Results of a search for ultrarapid flux fluctuations of galactic sources of maser emission in the water-vapour line at a wavelength of 1.35~cm are presented. An observational technique of a search for ultrarapid flux fluctuations has been developed. From 2002 to 2008 a number of observational sessions for about 30 maser sources have been carried out. Several of them have demonstrated such a variability. Possible mechanisms of the variability are discussed, among them internal processes within the sources themselves as well as external ones, including the theoretical possibility of a resonant effect of gravitational waves from galactic objects on the masering region. Clear evidence for the presence of such a variability has been found in several sources (Cep~A, W43M3, W49N, W33B). This variability appears not permanently, but only certain states of particular H_2O masers. Of major interest is the behaviour of Cep~A in some observational sessions: this source can turn from the state of relative stability to the state of variability by as much as tens per cent in some features on timescales of tens of minutes.
    Astronomical and Astrophysical Transactions 01/2011;
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    ABSTRACT: Results of a search for ultra rapid flux fluctuations of galactic sources of maser emission in the water-vapor line at a wavelength of 1.35 cm. An observational technique of a search for ultra rapid flux fluctuations has been developed. From 2002 to 2009 a number of observational sessions for about 40 maser sources have been carried out. Several of them have demonstrated such a variability. Possible mechanisms of the variability are discussed, among them internal processes within the sources themselves as well as external ones, including the theoretical possibility of a resonant effect of gravitational waves from galactic objects on the maser region. Clear evidence for the presence of such a variability has been found in several sources (Cep A, W43M3, W49N, W33B). This variability appears not permanently, but only certain states of particular H2O masers. In some sources (Ori A, W3 OH, W49N) demonstrated any variations by linear polarization of signal.
    Journal of Physics Conference Series 01/2010; 1206:346.
  • E. E. Lekht, V. I. Slysh, A. M. Tolmachev
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    ABSTRACT: Results of a multi-faceted study of the H2O maser emission in the region ON2 N carried out on the Very Large Array (VLA, NRAO) and 22-m radio telescope of the Pushchino Radio Astronomy Observatory are reported. The envelope around the ultracompact HII region is fairly extended and has a composite, strongly fragmented structure. The maser emission zone consists of single spots and spot clusters arranged along an arc, which is associated with a ram shock front. This shock front is nonsta-tionary, and its position changes with time. The front position probably depends on the state of activity of the central star. There can be turbulent motions of material in clusters as well as individual maser spots (such as turbulent vortices). In the turbulent-vortex model, the size of an H2O maser spot is estimated to be 0.07–0.1 AU. Flux-correlated radial-velocity drifts of emission features have been detected, which can be accompanied by spatial displacement (proper motion) of maser spots.
    Astronomy Reports 01/2010; 54(6):509-513. · 0.76 Impact Factor
  • Radio Physics and Radio Astronomy. 01/2008; 13(3):86.
  • M. I. Pashchenko, A. M. Tolmachev, E. E. Lekht
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    ABSTRACT: Results of monitoring of the H2O maser observed toward the infrared source IRAS 21078+5211 in the giant molecular cloud Cygnus OB7 are presented. The observations were carried out on the 22-m radio telescope of the Pushchino Radio Astronomy Observatory (Russia) from April 1992 to March 2006. Five cycles of maser activity at various levels were observed. In the periods of highest activity, the spectrum of the H2O maser emission extended from −43 to 12 km/s. During strong flares, the flux densities in some emission features reached nearly 600 Jy. The protostar has a small peculiar velocity with respect to the CO molecular cloud (∼2 km/s). Based on the character of the radial-velocity variations and the tendency for the linewidth to increase with the flux, it is concluded that the medium is strongly fragmented and that there is a small-scale turbulent outflow of ga in the H2O maser region, which may impede the formation of an HII region. The asymmetric distribution of the maser components in V LSR, the difference in the average linewidths of the central and lateral clusters of components, and the fairly high radial velocities relative to the molecular cloud (especially during periods of the highest maser activity) suggest that the maser spots belong to different clusters and different structures of the source: a disk and bipolar outflow.
    Astronomy Reports 01/2008; 52(3):211-225. · 0.76 Impact Factor
  • E. E. Lekht, M. I. Pashchenko, A. M. Tolmachev
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    ABSTRACT: Results of monitoring of H2O maser in the infrared source IRAS 20126+4104, which is associated with a cool molecular cloud, are presented. The observations were carried out on the 22-meter radio telescope of the Pushchino Radio Astronomy Observatory (Russia) between June 1991 and January 2006. The spectrum of the H2O maser emission extends from − 16.7 to 4.8 km/s and splits into separate groups of emission features. Cyclic variations of the integrated maser flux with a period from 3.4 to 5.5 years were detected, together with strong flares of up to 220 Jy in individual emission features. It is shown that large linewidths in periods of high maser activity are due to small-scale turbulent motions of the material. An expanding envelope around a young star is accepted as a model for the source. The protostar has a small peculiar velocity with respect to the molecular cloud (∼2 km/s). Individual emission features form organized structures, including multi-link chains.
    Astronomy Reports 01/2007; 51(7):531-541. · 0.76 Impact Factor
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    ABSTRACT: Since 1980 variability of a sample of H2O maser sources has been monitored on the 22-metre radio telescope in Pushchino, Russia. The interval between successive observational sessions is 1–2 months. The sample includes 125 maser sources in star-forming regions (SFR) and late-type variable stars. Twenty-six-year time series of H2O line profiles have detected flares and velocity drift of spectral features. Very fast variations in the H2O maser flux (Δt 1 hour) have been detected in several SFR sources, in particular, W33B. Variations of circumstellar H2O masers in late-type stars correlate with visual light curves with a time lag of 0.3-0.4P (P is the star's period). Exceptionally strong H2O maser flares were recorded in SFR sources (Sgr B2 and others) and in the stars W Hya, R Cas and U Ori. Models for H2O maser variability are reviewed. For stellar masers shock-wave excitation of H2O line variability is discussed.
    Proceedings of the International Astronomical Union 01/2007; 3.
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    ABSTRACT: We present the results of a variability study of some H2O maser-emission components of Sgr B2, which is located in an active star-forming region. Our monitoring was conducted in 1982–2004 with the 22-m radio telescope of the Pushchino Radio Astronomy Observatory. We analyze brightness variations for the strongest groups of emission features in the H2O spectra, mainly during periods of maser flaring activity. Each of these groups contains many components, whose radial velocities and fluxes we determined. Most of the components displayed radial-velocity drifts. We detected a correlation between the flux and radial-velocity variations for some of the components. Variability of the emission can be explained in a model in which the maser spots form elongated chains and filaments with radial-velocity gradients. During H2O flares, the flux increases of some maser spots were accompanied by acceleration, while flux decreases were accompanied by deceleration of their motion in the dense circumstellar matter. Spectral groups of emission features are probably spatially compact structures.
    Astronomy Reports 01/2007; 51(1):19-26. · 0.76 Impact Factor
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    ABSTRACT: The results of a search for ultrarapid variability of galactic water maser sources at the wavelength 1.35 cm on a timescale of several minutes to 1 h are reported. A special observational technique was developed. Using this technique, several observational sessions for more than 30 maser sources were carried out from 2002 to 2006. Among those, several sources that have shown such variability were found. The causes of this are discussed. The most interesting of these causes are internal processes within the sources ongoing in regions with a characteristic size of about 0.1 AU. Clear evidence for such a variability type was found in at least two sources: W49N and W33B. Variability of this kind displays itself only in certain states of the water masers.
    Astronomical and Astrophysical Transactions 10/2006; 25(5-6):393-398.
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    ABSTRACT: Results of long-term monitoring of circumstellar water maser sources in red supergiants are reviewed. The observations were carried out in 1980-2006 on the RT-22 radio telescope at Pushchino Radio Astronomy Observatory. We discuss the results for the semiregular variable M-supergiant VX Sgr and non-variable M-supergiant IRC-10414. In addition to our single-dish data, very-long-baseline interferometry results are invoked. VX Sgr and IRC-10414 display a characteristic water line profile, which suggests the presence of a rotating circumstellar disc and a bipolar outflow.
    Astronomical and Astrophysical Transactions 09/2006; 25:399-403.
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    ABSTRACT: Context.The results of monitoring of the water-vapour maser in the 1.35-cm line toward ON2 in 1995–2004 are reported.Aims.The main goal was to study variations of the H$_2$O maser emission on a long (10 years) time interval, in particular, velocity drifts and correlation between fluxes in various spectral features.Methods.The observations were carried out on the RT-22 radio telescope of Pushchino Radio Astronomy Observatory.Results.The emission of the northern component (ON2 N) took place in a broad interval of radial velocities, from -12 to 9 km s$^{-1}$. The total H$_2$O emission has two variability components: slow and flaring. The period of the former component is most likely between 25 and 30 years. The flaring component has a cyclic character with a period from 1.1 to 2.6 years. The alternation of the activity cycles was accompanied by changes in the velocity structure of the H$_2$O spectra. There is good correlation between the variations in the integrated flux and velocity centroid, as well as between the emissions in various segments of the H$_2$O spectrum. We suggest that long-term variations and oscillations of the water-maser emission can be related to the non-stationarity and anisotropy of bipolar molecular outflow from the B-type star in the ultracompact H II region.
    http://dx.doi.org/10.1051/0004-6361:20053495. 01/2006;
  • E. E. Lekht, V. A. Munitsyn, A. M. Tolmachev
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    ABSTRACT: We analyze our monitoring data for the water-vapor maser in the source W31(2), associated with a region of vigorous star formation, a cluster of OB stars. The monitoring was performed with the 22-m radio telescope at Pushchino Radio Astronomy Observatory during 1981–2004. The variability of the H2O maser in W31(2) was found to be cyclic, with a mean period of 1.9 yr. Two flares were most intense (superflares): in 1985–1986 and 1998–1999. In each activity cycle, we observed up to several short flares, subpeaks. The fluxes of many emission features during the flares were correlated. We also observed successive activation of individual emission features in order of increasing or decreasing radial velocity, suggesting an ordered structure and, hence, a radial-velocity gradient of the medium. There is a clear correlation of the emission peaks of the main components in the spectra at radial velocities of −1.7, −1.3, 0.5, and 1.3 km s−1 with activity cycles and of the emission at VLSR −1 with short flares. During the superflares, the emission in the low-velocity part of the H2O spectrum and a number of other phenomena related to coherent maser-emission properties were suppressed. The maser spots are assumed to form a compact structure, to have a common pumping source, and to be associated with an accretion flow onto the cluster of OB stars.
    Astronomy Letters 01/2005; 31(5):315-326. · 0.93 Impact Factor
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    ABSTRACT: We present the results from observing the circumstellar maser emission of the M-type supergiant S Per in the 6{16}-5{23} water-vapour line at 1.35 cm. The observations were carried out in 1981-2002 (JD=2 444 900-2 452 480) on the RT-22 radio telescope of the Pushchino Radio Astronomy Observatory, Astrospace Center of the Lebedev Institute of Physics, Russian Academy of Sciences. The H2O spectra obtained represent an unprecedented long, uniform dataset on this star. We discuss the properties of the optical and maser variations of S Per, together with particulars of the available VLBI maps. The close relation between maser and optical variations favors a model in which mass-loss is episodic. Changes observed in the total H2O line flux follow the visual light curve with a delay of 0.01 to 0.5P, where P≈ 800 d is the mean light cycle for S Per. The feature at VLSR=-44 km s-1 flared in July 1988, which seemed to be the response of the maser to an unusually bright optical maximum. The position of the -44-km s-1 feature on the VLBI maps coincides with the direction toward the optical stellar disc, which can be explained by amplification of enhanced stellar continuum by the H2O line.
    Astronomy and Astrophysics 01/2005; 437:127-133. · 5.08 Impact Factor
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    ABSTRACT: Results of a study of a strong flare of H2O maser emission in the star-forming region Sgr B2(M) in 2004 are reported. The observations were carried out on the 22-m radio telescope of the Pushchino Radio Astronomy Observatory. The main emission, with its flux density reaching 3800 Jy, was concentrated in a narrow radial-velocity interval (about 3 km/s) and was most likely associated with the compact group r, while the emission at V LSR > 64 km/s came from group q. After 1994, the variations of the H2O maser emission in Sgr B2(M) became cyclic with a mean period of 3 years.
    Astronomy Reports 01/2005; 49(10):777-782. · 0.76 Impact Factor
  • E. E. Lekht, V. A. Munitsyn, A. M. Tolmachev
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    ABSTRACT: A catalog of water-vapor maser spectra at 1.35 cm for the sourceW31(2), which is associated with an active star-forming region, is presented. The observations were carried out in 1981–2003 on the 22-m antenna of the Pushchino Radio Astronomy Observatory with a spectral resolution of 0.101 km/s. The mean interval between observations was about 1.5 months. The total velocity range in which emission was observed during the monitoring is from −14 to +14 km/s. The spectrum is strongly variable and contains a large number of emission features. Two strong flares with an interval between their emission maxima (integrated flux) of about 12 years (1985–1986 and 1998–1999) were observed, as well as fast variations on a timescale of 0.5–2 years with amplitudes of up to 600 Jy km/s. No long-period component of the variations was found. A drift of the velocity centroid has been detected; it is well approximated by a third-power polynomial corresponding to a period of about 31–33 years. The two strong flares fall on different phases of this curve: the first (1985–1986) is located near the minimum, while the second (1998–1999) is at the maximum. The observed character of the variability of the emission is well explained by the existing model for the region of G10.6-0.4. The drift of the velocity centroid is probably associated with the nonstationary accretion of material onto an HII region formed by a cluster of OB stars.
    Astronomy Reports 12/2004; 49(1):44-56. · 0.76 Impact Factor
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    ABSTRACT: A catalog of λ=1.35 cm water-vapor maser spectra in Sgr B2 obtained in 1992–2003 is presented; this supplements our results for earlier observations in 1982–1992. Sgr B2 was monitored using the 22 m radio telescope of the Pushchino Radio Astronomy Observatory. The whole monitoring dataset for 1982–2003 has been analyzed. The emission received is a superposition of radiation from various parts of the entire Sgr B2 region, but the main contribution is made by two sources: Sgr B2(M) and Sgr B2(N). The monitoring did not reveal any long-term component of the integrated maser flux variations with a period shorter than 20 years. The flare component of the flux variability and a short-period component with a mean period of two years have been found. The latter are correlated with variations of the velocity centroid, supporting the reality of the short-period variations. It is likely that all the various types of variations are inherent to both Sgr B2(M) and Sgr B2(N), and represent a superposition of the variations occurring in each of these sources. There is an alternation of maxima of the emission from Sgr B2(M) and Sgr B2(N).
    Astronomy Reports 11/2004; 48(12):965-978. · 0.76 Impact Factor

Publication Stats

37 Citations
24.84 Total Impact Points

Institutions

  • 2003–2011
    • Russian Academy of Sciences
      • • Space Research Institute
      • • Department of Radio Astronomy
      Moskva, Moscow, Russia
  • 2006
    • Lomonosov Moscow State University
      • Shternberg Astronomical Institute
      Moscow, Moscow, Russia
  • 2003–2004
    • Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE)
      Cholula de Riva dabia, Puebla, Mexico