RevMexAA: Abstracts of Accepted Papers for Volume 48 Number 2

June 19, 2012

2012: June April March

June 2012

The expansion of a stellar wind bubble within a non-singular, stratified core

J. Rodríguez-Ramírez and A. C. Raga

Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, México, D. F., Mexico

Received: 2012 May 30
Accepted: 2012 June 19

Abstract: We study the expansion of a non-radiative bubble (driven by the wind from a massive star) into an environment with a non-singular, self-gravitating isothermal sphere density stratification. For this stratification, we derive the equation of motion for the outer radius of the bubble (using the assumptions of the classical analytic model for expanding bubbles, but allowing the outer shock to have the appropriate strong/weak shock transition). The model equation has a single dimensionless parameter, that determines whether or not the outer shock becomes weak. For small values of this parameter, the bubble expands in approximate pressure equilibrium with the surrounding environment, and for large values of the dimensionless parameter the bubble always pushes out a strong shock. We derive analytic solutions for both of these limits, and a more complex solution for the transition between them. We find that O star bubbles within dense molecular cloud cores (possibly associated with some of the observed ultracompact HII regions) are in the “strong shock” limit. Our corresponding analytic solution therefore can be used to model the kinematical properties of ultracompact HII regions.

Discovery of New Faint Northern Galactic Planetary Nebulae

Agnès Acker,1 Henry M. J. Boffin,2 Nicolas Outters,3 Brent Miszalski,4,5 Laurence Sabin,6 Pascal Le Dû,7 and Filipe Alves8

1Observatoire de Strasbourg, France
2ESO, Chile
3Orange Observatory, France
4South African Astronomical Observatory, South Africa
5Southern African Large Telescope Foundation, South Africa
6Instituto de Astronomía, Universidad Nacional Autónoma de México, Ensenada, B. C., Mexico
7Porspoder, France
8CROW-Portalegre, Atalaia Group, Portugal

Received: 2012 March 15
Accepted: 2012 June 14

Abstract: We present the discovery of 6 nebular objects made by amateur astronomers. Four of these discoveries are clearly planetary nebulae (PNe), one is a possible PN, and another is a likely H II region. The bipolar nebula Ou4 presents the largest angular extent ever found: over one degree on the sky! We consider various scenarios that could explain such a nebula. Ou4 could be one of the nearest PNe known, though its possible PN nature will need confirmation.

April 2012

New Analytical Results for Poissonian and non-Poissonian Statistics of Cosmic Voids

L. Zaninetti

Dipartimento di Fisica, Universita degli Studi di Torino, Italy

Received: 2012 January 10
Accepted: 2012 April 10

Abstract: Stereology allows shifting from the 3D distribution of the volumes of Poissonian Voronoi Diagrams to their 2D cross-sections. The basic assumption is that the 3D statistics of the volumes of the voids in the local Universe has a distribution function of the gamma-type. The standard rule of conversion from 3D volumes to 2D circles, adopting the standard rules of stereology, produces a new probability density function of the radii which contains the Meijer G-function. A non-Poissonian distribution of volumes is also considered. The distribution of the 3D radii of the Sloan Digital Sky Survey Data Release 7 is best fitted by a non-Poissonian distribution in volumes as given by the Kiang function with argument of about two.

New analytic and quasi-analytic solutions for wind-driven compact HII regions

A. C. Raga,1 J. Cantó,2 and L. F. Rodríguez3

1Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, México, D. F., Mexico
2Instituto de Astronomía, Universidad Nacional Autónoma de México, México, D. F., Mexico
3Centro de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Morelia, Michoacán, Mexico

Received: 2012 February 10
Accepted: 2012 April 3

Abstract: Ultracompact HII regions are in a regime of approximate pressure balance with the surrounding, dense molecular clouds. In this paper, we apply a newly developed “thick shell” formalism to the case of an expanding HII region energized by both the photoionizing radiation and the wind from the central stellar source. The resulting model leads to analytic and quasi-analytic solutions that have a transition to a regime (absent in the classical “wind-driven bubble” analytic solutions) in which the hot, stellar wind bubble expands quasi-statically, in approximate pressure equilibrium with the surrounding ISM. This regime is relevant for the observed ultracompact HII regions. We present the time-evolution of the radius and the thickness of the expanding HII shell for different values of a single, dimensionless parameter that determines the characteristics of the solution.

March 2012

Chemical abundance of late-type spiral galaxies at the SDSS

A. M. Hidalgo-Gámez, A. Moranchel-Basurto, and A. F. González-Fajardo

Escuela Superior de Física y Matemáticas, Instituto Politécnico Nacional, México, D. F., Mexico

Received: 2012 February 8
Accepted: 2012 March 22

Abstract: Oxygen abundances have been determined for a total of 15 late-type spiral galaxies. The intensities of the emission lines were determined from the spectra retrieved from the SDSS data-base. Only three galaxies have abundances previously reported in the literature. For four of them the forbidden oxygen line was detected in the spectra but the Te determined for three of them is larger than 20,000 K. The chemical abundances for the other galaxies were determined with the semi-empirical methods. The values indicate that, in general, the oxygen abundance of dS galaxies is smaller than for Sm ones.

Speckle Interferometry at the Observatorio Astronómico Nacional. IV

V. G. Orlov, V. V. Voitsekhovich, and C. A. Guerrero

Instituto de Astronomía, Universidad Nacional Autónoma de México, México, D. F., Mexico

Received: 2012 February 10
Accepted: 2012 March 12

Abstract: We present speckle interferometric measurements of binary stars performed during September and October of 2009 with the 2.1 m telescope of the Observatorio Astronómico Nacional at SPM (Mexico). We report here the results of 200 measurements of 196 pairs with a primary limiting magnitude of V=12.3. The measured angular separations range from 0”.115 to 5”.26. Ninety seven pairs have separations less than 1”. The mean error in separation is 0”.03 and 1.5 in position angle. The usual 180 ambiguity was corrected for a majority of position angles by comparison with observations performed by other observers.

The Filamentary Multi-polar Planetary Nebula NGC 5189

L. Sabin,1 R. Vázquez,1 J. A. López,1 Ma. T. García-Díaz,1 and G. Ramos-Larios2

1Instituto de Astronomía, Universidad Nacional Autónoma de México, Ensenada, B. C., Mexico
2Instituto de Astronomía y Meteorología, Departamento de Física, CUCEI, Universidad de Guadalajara, Jalisco, Mexico

Received: 2011 December 29
Accepted: 2012 March 5

Abstract: We present a set of optical and infrared images combined with long-slit, medium and high dispersion spectra of the southern planetary nebula (PN) NGC 5189. The complex morphology of this PN is puzzling and has not been studied in detailed so far. Our investigation reveals the presence of a new dense and cold infrared torus (alongside the optical one) which probably generated one of the two optically seen bipolar outflows and which might be responsible for the twisted appearance of the optical torus via an interaction process. The high-resolution MES-AAT spectra clearly show the presence of filamentary and knotty structures as well as three expanding bubbles. Our findings therefore suggest that NGC 5189 is a quadrupolar nebula with multiple sets of symmetrical condensations in which the interaction of outflows has determined its complex morphology.