Papers by Gagik Tovmassian
Astrophysics, 2010
ABSTRACT By observations with the 1.5m telescope at San Pedro Martir (OAN, UNAM, Mexico) the BVR ... more ABSTRACT By observations with the 1.5m telescope at San Pedro Martir (OAN, UNAM, Mexico) the BVR magnitudes are determined for 66 member galaxies in Shakhbazian Compact Galaxy Groups ShCG 40, ShCG 176, ShCG 270, ShCG 278, ShCG 310, and ShCG 342. Three other groups were observed in two or only in one band. Seven galaxies in ShCG 298 were observed in B and R, six galaxies in ShCG 95 were observed in V, and seven galaxies in ShCG 345 were observed in V and R. The distribution of brightness of observed galaxies is determined. Signs of interaction between galaxies are detected in some groups. Keywordsgalaxies:groups:photometry
Revista mexicana de astronomía y astrofísica
Shakhbazian compact galaxy groups are the most dense configurations known. A few years ago we com... more Shakhbazian compact galaxy groups are the most dense configurations known. A few years ago we commenced a detailed spectral and photometric study of these groups. In this paper we present the investigation results of groups ShCG 31, ShCG 38, ShCG 43, and ShCG 282. The redshifts of member galaxies, the results of the BVR photometry, the surface-brightness profiles, the curves of isophotal twisting, the estimated masses, luminosities, and the mass-to-luminosity ratios of groups, and also some dynamical parameters, as the radial velocity dispersion and the crossing time are presented. The studied ShCGs consist mostly of elliptical and lenticular galaxies. It is shown that some galaxies in groups are in the process of interaction.
Astronomische Nachrichten, 2005
In the course of investigation of Shakhbazian compact groups we studied the group ShCG 191 which ... more In the course of investigation of Shakhbazian compact groups we studied the group ShCG 191 which has been identified also as the Abell cluster A1097. By its richness it may be classified as a rich compact group or a poor cluster. We determined redshifts of 14 objects in the area of the cluster and found that two of the supposed members of the group are stars. Redshifts of 12 galaxies show that the system is gravitationally bound. The V and R magnitudes of 23 member galaxies and their morphological types are determined. We present in this paper also the surface brightness contours of member galaxies in the central area of the cluster, the curves of isophotal twisting and the Fourier parameter a4. It is shown that some galaxies in the cluster are interacting with each other. Physical parameters of the group are close to those of ShCGs.
Astronomy and Astrophysics, 2004
In 1995 we commenced a detailed spectral and photometric study of Shakhbazian compact groups. In ... more In 1995 we commenced a detailed spectral and photometric study of Shakhbazian compact groups. In this paper the results on groups ShCG 181, ShCG 344, ShCG 361, and ShCG 362 are presented. The redshifts of member galaxies in groups and the radial velocity dispersions, the results of the surface photometry in BVR, the profiles of the surface brightness versus semi-major axis a (or a 1/4 ) and the twisting position angle versus semi-major axis of galaxies, virial masses, luminosities and mass-to-luminosity ratios, and the crossing times of groups are given. It is shown that some members of groups are in the process of interaction. On the basis of the results obtained in this and previous works, the general properties of thirteen ShCGs are discussed.
Revista Mexicana de …, 2007
Los grupos compactos de galaxias Shakhbazian son las configuraciones más densas que se conocen. H... more Los grupos compactos de galaxias Shakhbazian son las configuraciones más densas que se conocen. Hace algunos años iniciamos un estudio fotométrico y espectroscópico de estos grupos. En este artículo presentamos los resultados de la investigación en los grupos ShCG 104, ShCG 120, ShCG 243 y ShCG 245. Presentamos los corrimientos al rojo de las galaxias miembro, los resultados de la fotometría R, las curvas de brillo superficial-radio efectivo, las masas estimadas, las luminosidades y las razones masa-luminosidad de los grupos, además de algunos parámetros dinámicos como la dispersión de velocidad radial y el tiempo de cruce. Los ShCGs estudiados consisten principalmente de galaxias elípticas y lenticulares. Se muestra que algunas galaxias en estos grupos están en proceso de interacción.
The Astrophysical Journal, 2010
We present infrared JHK photometry of the cataclysmic variable SDSS J123813.73-033933.0 and analy... more We present infrared JHK photometry of the cataclysmic variable SDSS J123813.73-033933.0 and analyze it along with optical spectroscopy, demonstrating that the binary system is most probably comprised of a massive white dwarf with T eff = 12000 ± 1000 K and a brown dwarf of spectral type L4. The inferred system parameters suggest that this system may have evolved beyond the orbital period minimum and is a bounce-back system. SDSS J123813.73-033933.0 stands out among CVs by exhibiting the cyclical variability that called brightenings. These are not related to specific orbital phases of the binary system and are fainter than dwarf novae outbursts, that usually occur on longer timescales. This phenomenon has not been observed extensively and, thus, is poorly understood. The new time-resolved, multi-longitude photometric observations of SDSS J123813.73-033933.0 allowed us to observe two consecutive brightenings and to determine their recurrence time. The period analysis of all observed brightenings during 2007 suggests a typical timescale that is close to a period of ∼ 9.3 hours. However, the brightenings modulation is not strictly periodic, possibly maintaining coherence only on timescales of several weeks. The characteristic variability with double orbital frequency that clearly shows up during brightenings is also analyzed.
We present X-ray observations of the close binary nucleus of the planetary nebula PN G135.9+55.9 ... more We present X-ray observations of the close binary nucleus of the planetary nebula PN G135.9+55.9 obtained with the XMM satellite. The nebula is the most oxygen-poor PN known to date and is located in the Galactic halo. It is known to harbor a close binary nucleus of which only one component can be observed in optical-UV range. New X-ray observations
Astronomy and Astrophysics, 2010
The chemical composition of TS 01, the most oxygen-deficient planetary nebula. AGB nucleosynthesi... more The chemical composition of TS 01, the most oxygen-deficient planetary nebula. AGB nucleosynthesis in a metal-poor binary star ABSTRACT The planetary nebula TS 01 (also called PN G 135.9+55.9 or SBS 1150+599A) with its record-holding low oxygen abundance and its double degenerate close binary core (period 3.9 h) is an exceptional object located in the Galactic halo. We have secured observational data in a complete wavelength range to pin down the abundances of half a dozen elements in the nebula. The abundances are obtained via detailed photoionization modelling which takes into account all the observational constraints (including geometry and aperture effects) using the pseudo-3D photoionization code Cloudy_3D. The spectral energy distribution of the ionizing radiation is taken from appropriate model atmospheres. Incidentally we find from the new observational constraints that both stellar components contribute to the ionization: the "cool" one provides the bulk of hydrogen ionization, while the "hot" one is responsible for the presence of the most highly charged ions, which explains why previous attempts to model the nebula experienced difficulties. The nebular abundances of C, N, O, and Ne are found to be 1/3.5, 1/4.2, 1/70, and 1/11 of the solar value respectively, with uncertainties of a factor 2. Thus the extreme O deficiency of this object is confirmed. The abundances of S and Ar are less than 1/30 of solar. The abundance of He relative to H is 0.089 ± 0.009. Standard models of stellar evolution and nucleosynthesis cannot explain the abundance pattern observed in the nebula. To obtain an extreme oxygen deficiency in a star whose progenitor has an initial mass of about 1 M requires an additional mixing process, which can be induced by stellar rotation and/or by the presence of the close companion. We have computed a stellar model with an initial mass of 1 M , appropriate metallicity, and initial rotation of 100 km s −1 , and find that rotation greatly improves the agreement between the predicted and observed abundances.
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Papers by Gagik Tovmassian