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, Strömgren system, Walraven system, Washington system, Cape 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 ±0.028 in EB-V and precision less than ±0.01 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%±0.13, θV=39.7o±2.2; and PV=2.34%±0.07, θV=41.0o±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 Av with the distance,we found evidence of the existence of two absorption layers of dust at distances of ∼250 pc and ∼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, México

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.

May 2016

Probing the cool outer envelope of NGC 6826 and its previous mass-loss history

J. L. Verbena,1,2 S. Jeyakumar,3 K.-P. Schröder,3 and A. Wachter3

1Department of Physics and Astronomy, Brigham Young University, USA

3Departamento de Astronomía, Universidad de Guanajuato, México

Accepted: May 16 2016

Abstract: We have made a direct, quantitative comparison between theoretical and planetary nebula : NGC 6826. For this we observed the optically thin 13CO(J=1-0) and 13CO(J=2-1) rotational transition lines at a projected radial distance from the central star of 60'' and 75''. The observed line strengths and ratios at the inner point and the upper limits at the outer point are consistent with density profiles predicted by mass-loss histories computed from our evolution models, when accounting for the non-LTE radiative transfer and collisional excitation conditions in the envelope.

Analysis of Transfer Maneuvers from Initial Circular Orbit to a Final Circular or Elliptic Orbit

M. A. Sharaf1 and A. S. Saad2,3

1Department of Astronomy, Faculty of Science, King Abdulaziz University, Jeddah, KSA

2Department of Astronomy, National Research Institute of Astronomy and Geophysics, Cairo, Egypt

3Department of Mathematics, Preparatory Year, Qassim University, Buraidah, KSA

Accepted: May 16 2016

Abstract: In the present paper, analysis of the transfer maneuvers from initial circular orbit to a final circular or elliptic orbit was developed to study the problem of impulsive transfers for space missions. It considers planar maneuvers, using newly derived equations. Making use of these equations, comparison of circular and elliptic maneuvers are made. This comparison is important for the mission designers to make useful mappings showing where one maneuver is better than the other. In this aspect, we developed this comparison throughout ten results, together with some graphs to show their meaning.

CD PHOTOMETRY OF THE GLOBULAR CLUSTER NGC 60931

A. Ruelas-Mayorga,2 L. J. Sánchez,2 C. A. Bernal-Herrera,2 A. Nigoche-Netro,3 J. Echevarría,2 and A. M. García2

1Based upon observations acquired at the Observatorio Astronómico Nacional on the Sierra San Pedro Mártir (OAN-SPM), Baja California, México
2Instituto de Astronomía, Universidad Nacional Autónoma de México, Ciudad de México, México

Accepted: May 19 2016

Abstract: In this paper we present photometric CCD observations of the globular cluster NGC 6093 (M80) in filters B, V, R and I. We produce the colour-magnitude diagrams for this object and obtain values for its metallicity [Fe/H], reddening E(V-B), E(V-I) and distance modulus (m-M)0.

An analytic, entraining jet model for a stellar outflow in a stratified environment

A. C. Raga1

1Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Ciudad de México, México

Accepted: May 25 2016

Abstract: We present a model of a steady, entraining, isothermal jet embedded in a stratified environment. This model is appropriate for describing Herbig-Haro (HH) jets in the outer boundaries of molecular clouds. The model has a straightfoward analytic solution which permits an evaluation of the slowing down of the outflow due to the entrainment of environmental material. The solution indicates that the outflow lobe travelling into regions of lower pressure might or not be slowed down (depending on the parameters of the flow) before leaving the molecular cloud. On the other hand, the outflow lobe travelling into regions of increasing environmental pressure is likely to be slowed down quite drastically regardless of the flow parameters. The analytic model presented in this paper gives simple recipes for calculating the slowing down of the two outflow lobes.

Deep VLA observations of nearby star forming regions I: Barnard 59 and Lupus 1

S. A. Dzib,1 L. Loinard,1,2 S.-N. X. Medina,1 L. F. Rodríguez,2 A. J. Mioduszewski,3 and R. M. Torres4

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

3National Radio Astronomy Observatory, Domenici Science Operations Center, NM, USA

Accepted: May 30 2016

Abstract: Barnard 59 and Lupus 1 are two nearby star-forming regions visible from the southern hemisphere. In this manuscript, we present deep ($\sigma$ $\lesssim$ 15 $\mu$Jy) radio observations ($\nu$ = 6 GHz; $\lambda$ = 5 cm) of these regions, and report the detection of a total of 114 sources. Thirteen of these sources are associated with known young stellar objects, nine in Barnard 59 and four in Lupus 1. The properties of the radio emission (spectral index and, in some cases, polarization) suggest a thermal origin for most young stellar objects. Only for two sources (Sz~65 and Sz~67) are there indications for a possible non-thermal origin; more observations will be needed to ascertain the exact nature of the radio emission in these sources. The remaining radio detections do not have counterparts at other wavelengths, and the number of sources detected per unit solid angle is in agreement with extragalactic number counts. This suggests that all radio sources not associated with known young stellar objects are background extragalactic sources.

June 2016

NGC 2440 : A morpho-kinematical model

P.J.A. Lago1 and R.D.D. Costa1

1Instituto da Astronomia, Geofísica e Ciencias Atmosféricas, Universidade de Sao Paulo, Sao Paulo, Brazil

Accepted: June 2 2016

Abstract: This work describes the modelling of the 3D structure and position-velocity (P-V) diagrams of NGC 2440, a well known planetary nebula, aiming to describe the morphology of this object, specially its core. We have used high resolution spectra and P-V diagrams to reproduce the 3D structure of the nebula using SHAPE, a software that allows 3D modelling. HST high angular resolution images were used as reference to the model. The observational data point to a segmented core, and the simulations confirm this assumption; the best model for the nebula is a torus segmented in three pieces. The simulated P-V diagrams agree with the observations. We suggest that the torus was torn apart by interaction with the surrounding medium, either as winds or the radiation field. For the two bipolar lobes, orientation angles to the plane of the sky of $27\pm 5$ and $-5\pm3$ degrees, respectively for the bipolar components with PA of 85 and 35 degrees, were derived. No additional bipolar lobes were required to model the observed features of NGC 2440. A distance of $1.8 \pm 0.5 kpc$ was derived for the nebula using our velocity field for the toroidal structure. These results are the first derived for NGC 2440 from modelling in a 3D environment.

ROTSE1 J164341.65+251748.1: a new W UMa-type eclipsing binary

R. Michel,1 J. Echevarría,2 T.Q. Cang,3 L. Fox-Machado,1 and D. González-Buitrago1

1Instituto de Astronomía, Universidad Nacional Autónoma de México, Ensenada, Baja California, México

Abstract: ROTSE1 J164341.65+251748.1 was photometrically observed in the V band during three epochs with the 0.84-m telescope of the San Pedro M\'artir Observatory in Mexico. Based on additional BVR photometry, we find that the primary star has a spectral type around G0V. The light curve of the system is typical of a W~UMa type binary stars and has an orbital period of $\sim$ 0.323 days. In an effort to gain a better understanding of the binary system and determine its physical properties, we analyzed the light curve with the Wilson and Devinney method. We found that ROTSE1 J164341.65+251748.1 has a mass ratio of $\sim$ 0.34 and that the less massive component is over 230 K hotter than the primary star. The inclination of the system is $\sim$ 84.6 degrees, and the {\bf degree} of over-contact is 11\%. The analysis shows the presence of variable bright spots on the primary star.