University of Hertfordshire Research Archive

        JavaScript is disabled for your browser. Some features of this site may not work without it.

        Browse

        All of UHRABy Issue DateAuthorsTitlesThis CollectionBy Issue DateAuthorsTitles

        Arkivum Files

        My Downloads
        View Item 
        • UHRA Home
        • University of Hertfordshire
        • Research publications
        • View Item
        • UHRA Home
        • University of Hertfordshire
        • Research publications
        • View Item

        Ejecta and the Late Stages of Stellar Evolution

        View/Open
        901645.pdf (PDF, 602Kb)
        Author
        Gledhill, T.
        Attention
        2299/1433
        Abstract
        The late stages of stellar evolution are characterised by prodigious mass-loss, particularly on the Asymptotic Giant Branch (AGB), resulting in the build up of a circumstellar envelope of gas and dust. In this way, the majority of stars (» 0:8 M¯ < M < » 8 M¯) will have shed their excess mass by the end of the AGB, allowing them to evolve to hotter temperatures to become the central stars of planetary nebulae (PN). With the expulsion of so much dust into the circumstellar environment, polarization (and polarimetry) becomes a key techmique in the study of these objects. At wavelengths shortwards of 5 ¹m, AGB and post-AGB objects (those in transition to the PN phase are often termed proto-PN) are seen predominantly by dust-scattered light, and are therefore polarized. Imaging polarimetry may be used to investigate the geometry of the dust shells, the distribution of dust therein (and hence the massloss rate evolution on the AGB) and also the nature of the scattering particles themselves (the dust grains). A particularly enduring puzzle concerns the origin of the complex structures seen in PN, which originate from what are presumed to be spherically symmetric outflows on the AGB. Polarimetry is the natural tool with which to search for and investigate the origin of asymmetric structure, such as bipolar outflows, which reveal themselves in the form of significant net linear polarization. At wavelengths longer than 5 ¹m, thermal emission from warm (150 K) dust prevails. This too may be polarized, if the grains are non-spherical and aligned, for example by a magnetic field. The possible role of magnetic fields in driving and collimating asymmetric outflows from evolved stars, in the form of magnetised winds, has received recent attention, and a number of theoretical models have been proposed. The ability of polarimetry to detect these fields and to determine their structure will offer vital observational tests for the models. An alternative approach to determining field configurations and strengths is the use of polarimetric imaging of maser emission at radio wavelengths. The use of polarimetry in studies of evolved stars and their ejecta, over a wide range of wavelengths and spatial resolutions will be reviewed.
        Publication date
        2005
        Published in
        In: Astronomical Polarimetry: Current Status and Future Directions - ASP Conf Series 343
        Other links
        http://hdl.handle.net/2299/1433
        Metadata
        Show full item record
        Keep in touch

        © 2019 University of Hertfordshire

        I want to...

        • Apply for a course
        • Download a Prospectus
        • Find a job at the University
        • Make a complaint
        • Contact the Press Office

        Go to...

        • Accommodation booking
        • Your student record
        • Bayfordbury
        • KASPAR
        • UH Arts

        The small print

        • Terms of use
        • Privacy and cookies
        • Criminal Finances Act 2017
        • Modern Slavery Act 2015
        • Sitemap

        Find/Contact us

        • T: +44 (0)1707 284000
        • E: ask@herts.ac.uk
        • Where to find us
        • Parking
        • hr
        • qaa
        • stonewall
        • AMBA
        • ECU Race Charter
        • disability confident
        • AthenaSwan