February 20, 2017

2017: February March April May

Elements of a gravitational lens by assuming an elliptical galaxy model

U. E. Molina^{1},
P. Viloria^{2},
and I. Steffanell^{3}

^{1}Universidad del Atlántico, Barranquilla, Colombia.

^{2}Universidad de la Costa, CUC, Barranquilla, Colombia.

^{3}Universidad Libre, Barranquilla, Colombia.

ubaldomolina@mail.unialtlantico.edu.co

Received: June 7 2016

Accepted: February 20 2017

Abstract: In this work we study elements for gravitational lenses per galaxies such as the equation of lens, deviation angle, deflection potential and time delay, modeling the distribution of the volumetric mass of the lens in elliptical form. The function of volumetric distribution of mass in the deflecting galaxy $\rho$ has a nucleus with radius $a$ in its core, form-free parameter $b$ ($b>a$), and volumetric density in its nucleus $\rho_{0}$. Through the distribution of volumetric mass density $\rho$, we initially find surface mass density $\Sigma$ (projected on plane of the lens), followed by elements of a gravitational lens which are completely general and expressed in terms of the geometric parameters $a$ and $b$. These are related by the adimensional factor $n=\frac{b}{a}>1$. Results are applied to a galaxy-specific lens system to conduct an analysis based on the temporal delay between two images and to observe the conditions with which parameter $n$ must comply.

LX Leo: A High Mass-Ratio Totally Eclipsing W-type W UMa System

Birol Gürol^{1},
Raúl Michel^{2},
and Chantal Gonzalez^{2}

^{1}Ankara University, Science Faculty, Dept. of Astronomy and Space Sciences, Turkey.

^{2}Instituto de Astronomía, Universidad Nacional Autónoma de México, México.

Received: August 31 2016

Accepted: February 20 2017

Abstract: We present the results of our investigation of the geometrical and physical parameters of the binary system LX Leo. Based on CCD $BVR_c$ light curves, and their analyses with the Wilson-Devinney code, new times of minima and light elements have been determined. According to our solution, the system is a high mass-ratio, totally eclipsing, W-type W UMa system. Combining our photometric solution with the empirical relation for W UMa type systems by \citet{Dimitrow2015}, we derived the masses and radii of the components to be $M_1=0.43 M_\odot$, $M_2=0.81 M_\odot$, $R_1=0.58 R_\odot$ and $R_2=0.77 R_\odot$. In addition, the evolutionary condition of the system is discussed.

On the possibilities of photon-limited tip-tilt compensation in very small telescopes

A. Popowicz^{1}
and V. G. Orlov^{2}

^{1}Silesian University of Technology, Institute of Automatic Control, Akademicka 16, 44-100 Gliwice, Poland.

^{2}Instituto de Astronomía, Universidad Nacional Autónoma de México, México.

Received: November 17 2016

Accepted: March 9 2017

Abstract: The resolution of astronomical images obtained from the ground is severely degraded by the presence of atmosphere. One of the simplest methods for reducing this problem is the tip-tilt compensation. This method is especially valuable for small telescopes, in which it enables reaching the diffraction limit. Unfortunately, the technique requires bright guiding star, which is used for the assessment of the motion of stellar image. In this paper we show how various factors influence possibility of tip-tilt correction performed by very small telescopes ($\leq$ 1 m). We evaluated the impact of: (1) intensity of guiding star, (2) seeing conditions, (3) telescope size and (4) sky background. The resulting characteristics were obtained utilizing the data simulated with the Random Wave Vector method, which accurately reflects all atmospheric distortions of image. Eventually, we compared the centroiding efficiency accounting for the realistic acquisition process performed by the electron multiplying CCDs. The dependencies presented in this paper can be utilized to predict the sky coverage of TT compensation in small telescopes for a wide range of observational conditions.

Analysis of Hansen's Inferior and Superior Partial Anomalies and the Division of the Elliptic Orbit into Two Segments

M. A. Sharaf^{1}
and A. S. Saad^{2,3}

^{1}Astronomy, Space Science and Meteorology Department Faculty of Science, Cairo University, Egypt.

^{2}Department of Astronomy, National Research Institute of Astronomy and Geophysics, Cairo, Egypt.

^{3}Department of Mathematics, Preparatory Year, Qassim University, Buraidah, KSA.

Received: January 6 2017

Accepted: March 14 2017

Abstract: In this paper, a novel analysis was established to prove how Hansen's inferior and superior partial anomalies $k$ and $k_1$ can divide the elliptic orbit into two segments. The analyses depends on the departures of $r$ (for $k$) and $1/r$ (for $k_1$) from their minima. By these departures, we can find: (i) Transformations relating the eccentric anomaly to $k$ and the true anomaly to $k_1$. (ii) Expressions for $k$ and $k_1$ in terms of the orbital elements. (iii) Interpretation and the intervals of definition of two modulus (X, S) related to $k$ and $k_1$. (iv) The extreme values of $r$ and the elliptic equations in terms of $k$ and $k_1$. (v) For $r'$ and $r''$, the modulus $X$ is a measure of the asymmetry of $r'$ (or $r''$) from $r''$ (or $r'$), while the modulus $S_{12}$ is a measure of the asymmetry of $r'$ and $r''$ from the minimum value of $r$. (vi) Description of the segments represented by $k$ and $k_1$. (vii) Relative position of the radius vector at $k=0^{\circ}$ and $k_1=180^{\circ}$.

The formation of double working surfaces in periodically variable jets

A. C. Raga^{1}
and J. Cantó^{2}

^{1}Instituto de Ciencias Nucleares, UNAM, México.

^{2}Instituto de Astronomía, UNAM, México.

Received: November 10 2016

Accepted: March 17 2017

Abstract: It is a well known result that a periodic ejection variability in a hypersonic jet results in the production of a train of internal working surfaces (one working surface produced by each period of the ejection variability) travelling down the jet beam. This mechanism has been successfully applied to model the knot structures of Herbig-Haro (HH) jets. In this paper we explore the possibility of producing more than one working surface with each ejection variability period. We derive the mathematical criteria that have to be satisfied by the functional form of an ejection velocity variability that produces double working surfaces, and study a family of functions with appropriate properties.

A new mechanism for the near-IR variability in the transitional disk of GM Aur

E. Nagel^{1},
R. Álvarez-Meraz^{1},
and F. Rendón^{1}

^{1}Departamento de Astronomía, Universidad de Guanajuato, México.

Received: September 7 2016

Accepted: April 4 2017

Abstract: An ubiquitous feature of the stellar systems, particularly the transitional disks is their variability in the full range of wavelengths. The contribution for the near-infrared part of the spectrum mainly comes from the inner region of the disk, where the gas and the dust are heated strong enough in order to reach an appropriate temperature. Here, we present a new physical mechanism able to explain the near-infrared variability in some transitional disks. The main process is the intermittently formation of a sublimation wall due to an instability between the magnetic field of the star and the innermost disk region. When the wall is present it contributes to the spectrum but also shadows part of the material beyond its location. Using this mechanism, we present a model to explain the near-infrared variability in the transitional disk around GM Aur.

Observations and light curve solutions of six deep-contact W UMa binaries

Diana P. Kjurkchieva^{1},
Velimir A. Popov^{1,2},
Doroteya L. Vasileva^{1},
and Nikola I. Petrov^{3}

^{1}Department of Physics, Shumen University.

^{2}IRIDA Observatory, Rozhen NAO, Bulgaria.

^{3}Institute of Astronomy and NAO, Bulgarian Academy of Sciences.

Received: February 20 2017

Accepted: April 7 2017

Abstract: Photometric observations in Sloan $g'$ and $i'$ bands of W UMa binaries V0637 Peg, V0473 Cam, CSS J153314.8+560527, CSS J075258.0+382035, V0416 Gem and NSVS 6859986 are presented. Their periods are in the range of 0.26--0.43 d. The light curve solutions revealed that the components of each target are almost equal in temperature. The stellar components are of G and K spectral types and undergo total eclipses. All targets have deep-contact configurations with fillout factor $f \geq$ 0.5. NSVS 6859986 has one of the biggest value determined until now, $f = $ 0.84. We studied the empirical dependencies of fillout factor on the stellar parameters (temperature, period, mass ratio, relative component radii, and luminosity ratio) for a sample of around thirty stars. They are consistent with the theoretical predictions but there are deviations from the common trends.

Approximate Analytical Solutions to the Relativistic Isothermal Gas Spheres

A. S. Saad^{1,2},
M. I. Nouh^{1,3},
A. A. Shaker^{1},
and T. M. Kamel^{1}

^{1}Department of Astronomy, National Research Institute of Astronomy and Geophysics, Cairo, Egypt.

^{2}Department of Mathematics, Preparatory Year, Qassim University, Buraidah, KSA.

^{3}Department of Physics, College of Science, Northern Border University, Arar, KSA.

Received: February 22 2017

Accepted: May 11 2017

Abstract: In this paper, we introduce a novel analytical solution to Tolman-Oppenheimer-Volkoff (TOV) equation, which is ultimately a hydrostatic equilibrium equation derived from the general relativity in the framework of relativistic isothermal spheres. To improve the convergence radii of the obtained series solutions, a combination of Euler-Abel transformation and Padé approximation has been done. The solutions are given in ξ-θ and ξ-ν phase planes taking into account the general relativistic effects σ = 0.1, 0.2 and 0.3. A Comparison between the results obtained by the suggested approach and the numerical one indicates a good agreement with a maximum relative error of order 10^{-3}, which establishes the validity and accuracy of the method. The proposed procedure accelerated the power series solution with about ten times than of traditional one. An application to a neutron star has been done.

Detecting the Growth of Structures in Pure Stellar Disk Models

D. Valencia-Enriquez^{1},
I. Puerari^{1},
and L. Chaves-Velasquez^{1}

^{1}Instituto Nacional de Astrofísica, Óptica y Electrónica, INAOE, México.

Received: January 30 2017

Accepted: May 19 2017

Abstract: We performed a series of 3D N-body simulations where the initial conditions were chosen to get two sets of models; unbarred and barred ones. In this work, we analyze the growth of spirals and/or bar structures using 1D and 2D Fourier Transforms FT methods. Spectrograms and diagrams of the amplitude of the Fourier coecients as a function of time, radius and pitch angle show that the general morphology of our modeled galaxies is due to the superposition of structures with diã„¦ent values of pitch angle and number of arms. Also, we studied the orbits in a bar reference frame in models where a bar is formed. A geometric classication of the orbits shows that the bar potential and the Lagrangian points L_{4} and L_{5} catch approximately one-third of the total disk mass.

Planetary Influence in the Gap of a Protoplanetary Disk: The Structures Formation and an Application for V1247 Ori

R. Alvarez-Meraz^{1},
E. Nagel^{1},
F. Rendon^{1},
and O. Barragan^{1,2}

^{1}Departamento de Astronomía, Universidad de Guanajuato, Guanajuato, Gto 36240, México.

^{2}Dipartimento di Fisica, Universit'a di Torino, via P. Giuria 1, 10125 Torino, Italy.

Received: October 11 2016

Accepted: May 2017

Abstract: We present a set of hydrodynamical models of a planetary system embedded in a protoplanetary disk, in order to extract the number of all dust structures in the disk, their masses and sizes, within optical depth ranges τ≤0.5, 0.5<τ<2 and τ≥2. The study of structures shows: 1) an increase in the number of planets infers an increase in the creation rate of massive structures; 2) a lower planetary mass accretion corresponds to slower time effects for optically thin structures; 3) an increase in the number of planets allows a faster evolution of the structures in the Hill Radius for the different optical depth ranges for the inner planets. An ad-hoc simulation was run using the available information of the stellar system V1247 Ori, leading us to present a model with a planetary system which explains the SED and consistent with interferometric observations of structures.