Artigos gratuitos em astrofísica e ciência espacial

terça-feira, março 31, 2009

Astrophysics and Space Science
An International Journal of Astronomy, Astrophysics and Space Science
Editor-in-Chief: Michael A. Dopita
ISSN: 0004-640X (print version)
ISSN: 1572-946X (electronic version)
Journal no. 10509
Springer Netherlands

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A milestone paper providing a magisterial summary of a complete subdiscipline in Astrophysics

M. Catelan
Horizontal branch stars: the interplay between observations and theory, and insights into the formation of the Galaxy

(1) Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 782-0436 Santiago, Chile
Received: 24 October 2008 Accepted: 19 January 2009 Published online: 12 February 2009


We review and discuss horizontal branch (HB) stars in a broad astrophysical context, including both variable and non-variable stars. A reassessment of the Oosterhoff dichotomy is presented, which provides unprecedented detail regarding its origin and systematics. We show that the Oosterhoff dichotomy and the distribution of globular clusters in the HB morphology-metallicity plane both exclude, with high statistical significance, the possibility that the Galactic halo may have formed from the accretion of dwarf galaxies resembling present-day Milky Way satellites such as Fornax, Sagittarius, and the LMC—an argument which, due to its strong reliance on the ancient RR Lyrae stars, is essentially independent of the chemical evolution of these systems after the very earliest epochs in the Galaxy’s history. Convenient analytical fits to isochrones in the HB type–[Fe/H] plane are also provided. In this sense, a rediscussion of the second-parameter problem is also presented, focusing on the cases of NGC 288/NGC 362, M13/M3, the extreme outer-halo globular clusters with predominantly red HBs, and the metal-rich globular clusters NGC 6388 and NGC 6441. The recently revived possibility that the helium abundance may play an important role as a second parameter is also addressed, and possible constraints on this scenario discussed. We critically discuss the possibility that the observed properties of HB stars in NGC 6388 and NGC 6441 might be accounted for if these clusters possess a relatively minor population of helium-enriched stars. A technique is proposed to estimate the HB types of extragalactic globular clusters on the basis of integrated far-UV photometry. The importance of bright type II Cepheids as tracers of faint blue HB stars in distant systems is also emphasized. The relationship between the absolute V magnitude of the HB at the RR Lyrae level and metallicity, as obtained on the basis of trigonometric parallax measurements for the star RR Lyr, is also revisited. Taking into due account the evolutionary status of RR Lyr, the derived relation implies a true distance modulus to the LMC of (m–M)0=18.44±0.11. Techniques providing discrepant slopes and zero points for the M V (RRL)–[Fe/H] relation are briefly discussed. We provide a convenient analytical fit to theoretical model predictions for the period change rates of RR Lyrae stars in globular clusters, and compare the model results with the available data. Finally, the conductive opacities used in evolutionary calculations of low-mass stars are also investigated.

Keywords Galaxies: Local Group - Galaxy: formation - Galaxy: globular cluster: general - Stars: evolution - Stars: Hertzsprung-Russell diagram - Stars: horizontal-branch - Stars: variables: other

M. Catelan is John Simon Guggenheim Memorial Foundation Fellow.

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Laying out the observational evidence for the building blocks of life in space:
Sun Kwok
Organic matter in space: from star dust to the Solar System

(1) Faculty of Science, The University of Hong Kong, Hong Kong, China
Received: 30 November 2008 Accepted: 9 December 2008 Published online:19 December 2008


Organic compounds of high degree of complexity are now known to be widespread in the Universe, ranging from objects in our Solar System to distant galaxies. Through the techniques of millimeter-wave spectroscopy, over 140 molecules have been identified through their rotational transitions. Space infrared spectroscopy has detected the stretching and bending modes of compounds with aromatic and aliphatic structures. Analyses of samples of meteorites, comets, asteroids, and interplanetary dust also revealed a rich content of organic substances, some of which could be of extra-solar origin. We review the current state of understanding of the origin, evolution, nature, and distribution of organic matter in space. Also discussed are a number of unexplained astronomical phenomena whose origins could be traced to organic carriers.

Keywords Solar System - Stellar evolution - Infrared spectroscopy - Organic matter

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Examining the various prevailing hypotheses on how life arose on earth:
Ashwini Kumar Lal
Origin of Life

(1) Ministry of Statistics and Programme Implementation, Sardar Patel Bhawan, Parliament Street, New Delhi, 110001, India

Received: 16 April 2008 Accepted: 15 July 2008 Published online: 10 October 2008


The evolution of life has been a big enigma despite rapid advancements in the field of astrobiology, microbiology and genetics in recent years. The answer to this puzzle is as mindboggling as the riddle relating to evolution of the universe itself. Despite the fact that panspermia has gained considerable support as a viable explanation for origin of life on the earth and elsewhere in the universe, the issue, however, remains far from a tangible solution. This paper examines the various prevailing hypotheses regarding origin of life-like abiogenesis, RNA world, iron–sulphur world and panspermia, and concludes that delivery of life-bearing organic molecules by the comets in the early epoch of the earth alone possibly was not responsible for kick-starting the process of evolution of life on our planet.

Keywords Abiogenesis - Panspermia - LUCA - Microbes - Thermophiles - Extremophiles - Cyanobacteria - DNA - RNA - RNA world - Iron–sulphur world - Miller–Urey experiment – Comets

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Probing stellar winds at Ultraviolet wavelengths:
A. Herrero 1, M. Garcia 2 and F. Najarro 3
Outflows from massive blue stars

(1) Departamento de Astrofísica, Avda Francisco Sánchez 2, 38206 La Laguna, Spain
(2) Instituto de Astrofísica de Canarias, C/ Vía Láctea s/n, 38200 La Laguna, Spain
(3) Departamento de Astrofísica Molecular e Infrarroja, Instituto de Estructura de la Materia, CSIC, C/ Serrano 117, 28000 Madrid, Spain

Received: 21 April 2008 Accepted: 23 December 2008 Published online: 4 February 2009


We present in this contribution a revision of the origin, main properties and open issues in the field of winds of massive blue stars, with a particular emphasis in the ultraviolet observations

Keywords Stars: massive - Stars: mass-loss - Stars: atmospheres - Stars: UV

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