RMxAA: Abstracts of Accepted Papers for Volume 52 Number 2

March 3, 2016

2016: March April May June

March 2016

The Scale of Reddening for Classical Cepheid Variables

D. G. Turner1

1Saint Mary's University, Halifax, NS, Canada

Accepted: March 3 2016

Abstract: Field reddenings are summarized for 68 Cepheids and used for comparison with other published reddening scales: from reddening-independent indices, photometry on the Lick six-color system, Str\"{o}mgren system, Walraven system, Washington system, Cape {\it BVI} system, DDO system, and Geneva system, IRSB studies, and Cepheid spectroscopy, old and new. Reddenings from period-color relations are least reliable; photometric color excesses vary in precision, accuracy depending on methodology and calibration sample. The accuracy and precision of published Cepheid reddening scales are revealed, leading to a new system of standardized reddenings for 198 variables, of average uncertainty $\pm0.028$ in E$_{B-V}$ and precision less than $\pm0.01$ for many. The color excesses are used to map the dependence of intrinsic color on pulsation period, the results contradicting ideas about the period dependence of dispersion in Cepheid effective temperatures.

The influence of galaxy interactions on some parameters of galaxies

Xin-Fa Deng,1 Xiao-Ping Qi,1 Peng Jiang,1 Jun Song,1 and Ying-Ping Ding1

1School of Science, Nanchang University, Jiangxi, China

Accepted: March 14 2016

Abstract: From two volume-limited main galaxy samples of the Sloan Digital Sky Survey Data Release 10 (SDSS DR10), we extracted paired galaxies and isolated galaxies and performed comparative studies between them to explore the influence of galaxy interactions on age, stellar velocity dispersion and K-band luminosity. Paired galaxies have preferentially larger stellar velocity dispersions and are preferentially older than isolated galaxies. We also noted apparent differences in the K-band luminosity distribution between paired galaxies and isolated galaxies in the luminous volume-limited main galaxy sample: paired galaxies are preferentially more luminous than isolated galaxies, whereas this difference in the faint volume-limited main galaxy sample is very small.

April 2016

Optical polarization study towards the open cluster NGC 62491

M. M. Vergne,2,3,4 Ana Maria Orsatti,3,4 Carlos Feinstein,2,3,4 E. Irene Vega,2,4 and Ruben E. Martínez2,3

1Based on observations obtained at Complejo Astronómico El Leoncito, operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the Universities of La Plata, Córdoba, and San Juan

2Facultad de Ciencias Astronómicas y Geofísicas, Observatorio Astronómico, La Plata, Argentina

3Instituto de Astrofísica de La Plata (UNLP - CONICET), Facultad de Ciencias Astronómicas y Geofísicas, Argentina

4Member of the Carrera del Investigador Científico, CONICET, Argentina

Accepted: April 12 2016

Abstract: We present (UBVRI) multicolor linear polarimetric data of 30 of the brightest stars in the region of the open cluster NGC 6249. The cluster members are found to be part of two subgroups with average polarization and orientation of the electric vector as PV= 1.7 $\% \pm 0.13$, $\theta_{V}$ = 39.7$^{o}$ $\pm$ 2.2; and $P_{V}$ = 2.34 $\%$ $\pm$ 0.07, $\theta_{V}$ = 41.0$^{o}$ $\pm$ 1.2, respectively. This difference in polarization may be the consequence of the presence of an U-shaped dark absorbing zone seen on the central region and, probably, it is located in front of or inside the cluster. From the study of the evolution of the $A_v$ with the distance,we found evidence of the existence of two absorption layers of dust at distances of $\sim$ 250 pc and $\sim$ 600 pc. By comparing the polarimetric parameters of NGC~6249 and the nearby cluster NGC~6250, some coincidences are found.

The abundance discrepancy factor and t2 in nebulae: are non-thermal electrons the culprits?

G. J. Ferland,1 W. J. Henney,2 C. R. O'Dell,3 and M. Peimbert4

1Department of Physics and Astronomy, University of Kentucky, Lexington, KY, USA

2Centro de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Morelia, Michoacán, México

3Department of Physics and Astronomy, Vanderbilt University, Nashville, TN, USA

4Instituto de Astronomía, Universidad Nacional Autónoma de México, Ciudad de México, M\'exico

Accepted: April 25 2016

Abstract: Photoionization produces supra-thermal electrons, electrons with much more energy than is found in a thermalized gas at electron temperatures characteristic of nebulae. The presence of these high energy electrons may solve the long-standing t2/ADF puzzle, the observations that abundances obtained from recombination and collisionally excited lines do not agree, and that different temperature indicators give different results, if they survive long enough to affect diagnostic emission lines. The presence of these non-Maxwellian distribution electrons are usually designated by the term kappa. Here we use well established methods to show that the distance over which heating rates change are much longer than the distance supra thermal electrons can travel, and that the timescale to thermalize these electrons are much shorter than the heating or cooling timescales. These estimates establish that supra thermal electrons will have disappeared into the Maxwellian velocity distribution long before they affect the collisionally excited forbidden and recombination lines that are used for deriving abundances relative to hydrogen. The electron velocity distribution in nebulae should be closely thermal.

October 2013

Effect of a stellar companion on the modeling of HD 142527 infrared SED

E. Nagel

Departamento de Astronomía, Universidad de Guanajuato, Guanajuato, Mexico

Accepted: 2013 October 16

Abstract: The discovery of a companion of the Herbig Ae/Be star HD 142527 motivates the study of the effect that it produces on the SED. The main change on the system configuration is the formation of a gap in the disk. Due to this change, a wall (outer edge of the gap), which is frontally illuminated by stellar radiation is formed. We present a model for the SED, considering all the components: a disk with two gaps (one produced by the stellar companion and the other by potential planets), three walls (two associated with the gaps and the other with dust sublimation), and optically thin streams of material in the gaps and the stars. The optically thin material required to fit the spectrum is located in a halo, but also inside the gaps. The modeled halo is smaller than the one considered in a previous model of the system.

Temporal Properties of Brightest Speckle

V. V. Voitsekhovich and V. G. Orlov

Instituto de Astronomía, Universidad Nacional Autónoma de México, Mexico

Accepted: 2013 October 14

Abstract: The experimental results related to the temporal properties of brightest speckle are presented. The analysis of the data shows that the live time of brightest speckle defined as a correlation time at the one-half height of the temporal correlation function is about 20 ms. The shortest live time which we observed is about 7 ms while the longest one is about 70 ms. The comparison of the results obtained in three filters allows to conclude that the live time of brightest speckle decreases with the decreasing of the wavelength. Also a comparison of the live time of brightest speckle to the correlation time of image centroid is performed. The comparison result shows that the correlation time of image centroid is approximately 10 times longer than the live time of brightest speckle.

A Hydrodynamical Mechanism for Generating Astrophysical Jets

X. Hernández,1 P. L. Rendón,2 R. G. Rodríguez-Mota,2 and A. Capella3

1Instituto de Astronomía, Universidad Nacional Autónoma de México, Mexico
2Centro de Ciencias Aplicadas y Desarrollo Tecnológico, Universidad Nacional Autónoma de México, Mexico
3Instituto de Matemáticas, Universidad Nacional Autónoma de México, Mexico

Accepted: 2013 October 11

Abstract: Whenever in a classical accretion disk the thin disk approximation fails interior to a certain radius, a transition from Keplerian to radial infalling trajectories should occur. We show that this transition is actually expected to occur interior to a certain critical radius, provided surface density profiles are steeper than Σ(R) ∝ R-1/2, and further, that it probably corresponds to the observationally inferred phenomena of thick hot walls internally limiting the extent of many stellar accretion disks. Infalling trajectories will lead to the convergent focusing and concentration of matter towards the very central regions, most of which will simply be swallowed by the central object. We show through a perturbative hydrodynamical analysis, that this will naturally develop a well collimated pair of polar jets. A first analytic treatment of the problem described is given, proving the feasibility of purely hydrodynamical mechanisms of astrophysical jet generation.

September 2013

uvby-β Photoelectric Photometry and membership determination of the Open Cluster NGC 2353

J. Segura,1 A. Juárez,2 and J. H. Peña3

3Instituto de Astronomía, Universidad Nacional Autónoma de México, Mexico

Accepted: 2013 October 7

Abstract: From uvby-β photoelectric photometry of the open cluster NGC 2353 (55 stars) we were able to determine membership of the stars to the cluster and fix its age and reddening.

A near infrared test for two recent luminosity functions for galaxies

L. Zaninetti

Dipartimento di Fisica, Università degli Studi di Torino, Italy

Accepted: 2013 September 13

Abstract: Two recent luminosity function (LF) for galaxies are reviewed and the parameters which characterize the near infrared are fixed. A first LF is a modified Schechter LF with four parameters. The second LF is derived from the generalized gamma and has four parameters. The formulas which give the number of galaxies as function of the redshift are reviewed and a special attention is given to the position of the photometric maximum which is expressed as function of a critical parameter or the flux of radiation or the apparent magnitude. A simulation of the 2MASS Redshift Survey is given in the framework of the non Poissonian Voronoi Tessellation.

New Radio Continuum Observations of the Compact Source Projected Inside NGC 6334A

L. F. Rodríguez,1,2 J. M Masqué,1 S. A. Dzib,1 L. Loinard,1 and S. E. Kurtz1