Download or read book Circumstellar Dust Shells Around Evolved Massive Stars written by and published by . This book was released on 2014 with total page 91 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Extremely Extended Dust Shells Around Evolved Intermediate Mass Stars written by Basil Menzi Mchunu and published by . This book was released on 2011 with total page 312 pages. Available in PDF, EPUB and Kindle. Book excerpt: Intermediate mass stars ( %0 .8 - 8 solar masses), at the asymptotic giant branch phase (AGB) suffer intensive mass loss, which leads to the formation of a circumstellar shell (s) of gas and dust in their circumstellar envelope. At the end of the AGB phase, the mass-loss decreases or stops and the circumstellar envelope begins to drift away from the star. If the velocity of the AGB phase wind has been relatively constant, then dust or molecular emission furthest from the star represents the oldest mass loss, while material closer to the star represents more recent mass loss. Therefore, the history of mass loss during the AGB phase is imprinted on the dust shells of the post-AGB envelope. Thus, by studying the distribution of material in the form of dust emission in the circumstellar shells of late evolved stars (i.e. the post AGB phases are pre - planetary nebula (PPN) and the planetary nebula (PN)) we can gain a better understanding of the mass-loss processes involved in the evolution of intermediate mass stars. I studied two groups of intermediate mass stars, namely six oxygen rich and six carbon rich candidates. In this thesis a study of evolution of intermediate mass stars is confronted by means of observations, in which far - infrared (FIR) images, are used to study the physical properties and the material distribution of dust shells of AGB and post AGB circumstellar envelope. Infrared radiation from thermal dust emission can be used to probe the entire dust shell because, near to mid-infrared radiation arises solely from the hottest regions close to the star; while the outer regions away from the star are cool such that they emit at longer infrared wavelengths. Essentially, radiation in the FIR to sub-millimeter wavelengths is emitted by the entire dust shell and hence can be used to probe the entire dusty envelope. Therefore far-infrared emission by late evolved stars can be used to probe the large scale - structure of AGB and post - AGB circumstellar shells.Our results from space observations indicated the following: The sizes of the circumstellar dust shell observed in oxygen rich stars are within %1 pc. We derived the dust masses derived from far infrared ISO PHT 32 observation of oxygen rich stars that are between 1.7 -- 4 x 10-4 solar masses. These results provides us with a lower limit in the progenitor masses of stars estimated to be within 0.56 -- 0.76 solar masses. These results indicate that the initial main sequence masses fro oxygen rich stars are within 1 - 3.5 solar masses. The time scales derived since the oldest mass was ejected during the evolution of oxygen rich stars are 4 - 13 x 104 years. For the carbon rich stars: The size of the circumstellar dust shells are within 1 - 1.6 pc. The masses of dust in the shells are a approximated to be within 0.1 - 1.44 x 10-4 solar masses. A lower limit to the progenitor masses of carbon rich stars that are between 0.61 - 0.9 solar mass, suggesting that these stars evolved from the main sequence masses between 2. - 6 solar masses.
Download or read book Physics and Chemistry of Circumstellar Dust Shells written by Hans-Peter Gail and published by Cambridge University Press. This book was released on 2013-12-02 with total page 699 pages. Available in PDF, EPUB and Kindle. Book excerpt: Circumstellar dust, the astronomical dust that forms around a star, provides today's researchers with important clues for understanding how the Universe has evolved. This volume examines the structure, dynamics and observable consequences of the dust clouds surrounding highly evolved stars on the Giant Branch. Early chapters cover the physical and chemical basis of the formation of dust shells, the outflow of matter, and condensation processes, while offering detailed descriptions of techniques for calculating dust formation and growth. Later chapters showcase a wide range of modeling strategies, including chemical and radiative transfer and dust-induced non-linear dynamics, as well as the latest data obtained from AGB stars and other giants. This volume introduces graduate students and researchers to the theoretical description for modeling the dusty outflows from cool stars and provides a full understanding of the processes involved.
Download or read book Physics and Chemistry of Circumstellar Dust Shells written by Hans-Peter Gail and published by Cambridge University Press. This book was released on 2014 with total page 699 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book explores why dust forms around stars, and how to model stellar dust formation and dust-forming environments consistently.
Download or read book Dust and Molecules in Evolved Stars written by I. Cherchneff and published by Springer Science & Business Media. This book was released on 2013-11-11 with total page 392 pages. Available in PDF, EPUB and Kindle. Book excerpt: Dust and molecules are found in a large variety of astrophysical environments, in particular in the circumstellar material ejected by evolved stars. This book brings together the leading astronomers and astrophysicists in the field of molecular astrophysics and stellar physics to discuss the important issues of dust and molecular formation, the role of solids in circumstellar environments, molecules as probes of circumstellar parameters, the stellar contribution to the enrichment of the Galaxy, and the latest observational data in various wavelength domains, in partiular in the infrared with results from the Infrared Space Observatory. The astrophysical senarios include late-type stars, novae, Wolf-Rayet stars, Luminous Blue Variables and supernovae. Audience: Researchers and graduate students in the fields of stellar physics, stellar evolution and astrochemistry.
Download or read book Circumstellar Media in Late Stages of Stellar Evolution written by Robin E. S. Clegg and published by Cambridge University Press. This book was released on 1994-08-25 with total page 364 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the last throes of their lives, how do low- and high-mass stars interact with their immediate surroundings? How does the circumstellar medium affect the shape of a nebula? How are supernovae effected by a dense medium? And what do we understand of how stellar winds interact with their environments? These and many other exciting issues are addressed in these proceedings, from the 34th Herstmonceux conference, held in Cambridge. Highlights of developments in the field covered in this volume include the latest observational results that show how various types of stellar ejecta differ in shape, and a unified view of the physical processes involved; as well as the latest results on the media around supernovae 1987A and 1993J. This timely volume provides review articles that serve both as an excellent introduction for graduate students, and a handy reference for researchers; and up-to-date research papers for those who want to keep abreast of developments in the field.
Download or read book Massive Stars in Starbursts written by Claus Leitherer and published by Cambridge University Press. This book was released on 1991-05-16 with total page 354 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book reviews the importance of massive stars in several areas of astrophysics. Massive stars are objects that are 10-100 times the mass of our Sun. Above ten solar masses, loss through stellar winds begins to have a major impact on the evolution of a star. The upper limit of 100 solar masses is derived from observations. Significant progress has now been achieved in massive star research. New models, along with high quality observations, have improved our understanding of the formation, structure, atmosphere, and evolution of these massive objects. They are formed in violent bursts of star formation and are probably related to the phenomena observed in active galactic nuclei. The workshop at the Space Telescope Science Institute examined the interplay between the astrophysics of massive stars and their location in extragalactic starburst regions. There are eighteen chapters by leading researchers. Each has been carefully edited to ensure that the book is a comprehensive introduction to the theory and observation of massive stars in starburst regions.
Download or read book Evolution of Peculiar Red Giant Stars written by International Astronomical Union. Colloquium and published by Cambridge University Press. This book was released on 1989-06-22 with total page 464 pages. Available in PDF, EPUB and Kindle. Book excerpt: Red giant stars are evolutionarily advanced objects in the closing stages of their nuclear burning lifetime. Observed with increasing spectral coverage they display a variety of unusual phenomena. Many are characterized by peculiar (non-solar) surface chemical compositions which provide otherwise unobtainable clues to interior nucleosynthesis, mixing and evolution. Others may have received their chemical peculiarities by mass transfer from a companion. This book reports on the proceedings of the International Astronomical Union Colloquium 106. It contains discussions on many aspects of these stars, combining theory and observation to interpret these objects in terms of their evolutionary history. There are 20 review papers, 69 abstracts and short contributed papers and a complete transcript of the valuable summary panel discussion. Professional astronomers will find this book useful as a reference work which incorporates current research on the modelling and evolution of these unstable stars.
Download or read book New Worlds New Horizons in Astronomy and Astrophysics written by National Research Council and published by National Academies Press. This book was released on 2011-02-04 with total page 324 pages. Available in PDF, EPUB and Kindle. Book excerpt: Driven by discoveries, and enabled by leaps in technology and imagination, our understanding of the universe has changed dramatically during the course of the last few decades. The fields of astronomy and astrophysics are making new connections to physics, chemistry, biology, and computer science. Based on a broad and comprehensive survey of scientific opportunities, infrastructure, and organization in a national and international context, New Worlds, New Horizons in Astronomy and Astrophysics outlines a plan for ground- and space- based astronomy and astrophysics for the decade of the 2010's. Realizing these scientific opportunities is contingent upon maintaining and strengthening the foundations of the research enterprise including technological development, theory, computation and data handling, laboratory experiments, and human resources. New Worlds, New Horizons in Astronomy and Astrophysics proposes enhancing innovative but moderate-cost programs in space and on the ground that will enable the community to respond rapidly and flexibly to new scientific discoveries. The book recommends beginning construction on survey telescopes in space and on the ground to investigate the nature of dark energy, as well as the next generation of large ground-based giant optical telescopes and a new class of space-based gravitational observatory to observe the merging of distant black holes and precisely test theories of gravity. New Worlds, New Horizons in Astronomy and Astrophysics recommends a balanced and executable program that will support research surrounding the most profound questions about the cosmos. The discoveries ahead will facilitate the search for habitable planets, shed light on dark energy and dark matter, and aid our understanding of the history of the universe and how the earliest stars and galaxies formed. The book is a useful resource for agencies supporting the field of astronomy and astrophysics, the Congressional committees with jurisdiction over those agencies, the scientific community, and the public.
Download or read book Evolution of Massive Stars written by D. Vanbeveren and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 472 pages. Available in PDF, EPUB and Kindle. Book excerpt: Massive stars occupy an exceptional place in general astrophysics. They trigger many if not all of the important processes in galactic evolution whereas due to their intrinsic brightness, they offer the (only until now) possibility to study the stellar content and stellar behaviour in distant galaxies. The last, say, 25 years, massive stars have been the subject of numerous meetings discussing the influence of massive stars on population synthesis, the number distribution of different types of massive stars, the LBV phenomenon, WR stars, X-ray binaries, stellar winds in massive stars, chemical pecularities in massive stars, supernova explosions of massive stars and the important SN1987A event, the influence of massive stars and chemical evolution of galaxies. It is clear that without a theory of stellar evolution, the study of these topics loses a lot of its significance. Massive star evolution therefore got a chance in these meetings, but rarely as a prime subject. The state of the art, the physical processes and the uncertainties in stellar evolution were barely touched. Even more, the influence of close binaries in all these massive star meetings slowly disappeared the last, say, 13 years without any scientific justification, although a significant fraction of stars occurs in close binaries with periods small enough so that both components will interact during their evolution. Denying the binaries or not discussing their influence on results and conclusions, makes the latter very uncertain or even completely unreliable.
Download or read book Astrophysics and Space Science written by L.B.F.M. Waters and published by Springer Science & Business Media. This book was released on 1998-08-31 with total page 562 pages. Available in PDF, EPUB and Kindle. Book excerpt: This conference proceedings contains review papers and contributed papers discussing early results from the Infrared Space Observatory (ISO) on the subject of stellar evolution. Three topics have been emphasized in the book: young stellar objects and Vega-type stars, circumstellar matter of massive stars, and late stages of stellar evolution. The very rich harvest of new results from ISO is demonstrated by the many discoveries of new solid state and molecular bands in the spectra of stars and circumstellar shells, and by spectacular images of circumstellar and interstellar matter. The book is intended for professional astronomers and students.
Download or read book Using Infrared Observations of Circumstellar Dust Around Evolved Stars to Test Dust Formation Hypothesis written by Suklima Guha Niyogi and published by . This book was released on 2011 with total page 214 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Birth and Evolution of Massive Stars and Stellar Groups written by Wilfried Boland and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 392 pages. Available in PDF, EPUB and Kindle. Book excerpt: Proceedings of a Symposium held in Dwingeloo, The Netherlands, September 24-26, 1984 in honour of Adriaan Blaauw on the occasion of his 70th birthday
Download or read book Milliarcsecond studies of circumstellar dust shells around late type stars using lunar occultations written by David Andrew Wilson and published by . This book was released on 2002 with total page 128 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Wolf Rayet Stars written by Karel A. van der Hucht and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 598 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this IAU Symposium on Wolf--Rayet stars, binary aspects received ample attention, notably because of the recognition that many observations of spectral and photometric variability at all accessible wavelengths are related to colliding winds or other forms of wind interaction. The basic structure of the conference and its proceedings is basic parameters and general properties of WR stars; state of the art model atmospheres for WR stars, anisotropic mass loss and disk formation of WR stars, properties of WR binaries; influence of stellar winds on mass transfer in hot massive binary evolution; dust formation near WR stars and other circumstellar phenomena; and hydrodynamics and high-energy physics of colliding winds in WR+O binaries and of WR winds interacting with compact objects. Within this framework 20 invited reviews, 38 invited oral contributions, and 76 poster papers were presented at the Symposium, entertaining 111 astronomers from 24 countries. These proceedings provide up-to-date information on all aspects of Wolf--Rayet atmospheres, binaries, and colliding winds.
Download or read book Circumstellar Structure Around Evolved Stars in the Cygnus X Star Formation Region written by and published by . This book was released on 2010 with total page 13 pages. Available in PDF, EPUB and Kindle. Book excerpt: We present observations of newly discovered 24 micron circumstellar structures detected with MIPS around three evolved stars in the Cygnus-X star-forming region. One of the objects, BD+43 3710, has a bipolar nebula, possibly due to an outflow or a torus of material. A second, HBHA 4202-22, a Wolf-Rayet candidate, shows a circular shell of 24 micron emission suggestive of either a limb-brightened shell or disk seen face-on. No diffuse emission was detected around either of these two objects in the Spitzer 3.6-8 micron IRAC bands. The third object is the luminous blue variable candidate G79.29+0.46. We resolved the previously known inner ring in all four IRAC bands. The 24 micron emission from the inner ring extends ~1 deg. 2 beyond the shorter wavelength emission, well beyond what can be attributed to the difference in resolutions between MIPS and IRAC. Additionally, we have discovered an outer ring of 24 micron emission, possibly due to an earlier episode of mass loss. For the two shell stars, we present the results of radiative transfer models, constraining the stellar and dust shell parameters. The shells are composed of amorphous carbon grains, plus polycyclic aromatic hydrocarbons in the case of G79.29+0.46. Both G79.29+0.46 and HBHA 4202-22 lie behind the main Cygnus-X cloud. Although G79.29+0.46 simply may be on the far side of the cloud, HBHA 4202-22 is unrelated to the Cygnus-X star formation region.
Download or read book Asymptotic Giant Branch Stars written by Harm J. Habing and published by Springer Science & Business Media. This book was released on 2004 with total page 578 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book deals with stars during a short episode before they undergo a ma jor, and fatal, transition. Soon the star will stop releasing nudear energy, it will become a planetary nebula for abrief but poetic moment, and then it will turn into a white dwarf and slowly fade out of sight. Just before this dramatic change begins the star has reached the highest luminosity and the largest diameter in its existence, and while it is a star detectable in galaxies beyond the Local Group, its structure contains already the inconspicuous white dwarf it will become. It is called an "asymptotic giant branch star" or "AGB star". Over the last 30 odd years AGB stars have become a topic of their own although individual members of this dass had already been studied for cen turies without realizing what they were. In the early evolution, so called "E-AGB"-phase, the stars are a bit bluer than, but otherwise very similar to, what are now called red giant branch stars (RGB stars). It is only in the sec ond half of their anyhow brief existence that AGB stars differ fundamentally from RGB stars.
