Extended Dust Emission from Nearby Evolved Stars?

Thavisha E. Dharmawardena, Francisca Kemper, Peter Scicluna, JGA Wouterloot, Alfonso Trejo, S. Srinivasan, Jan Cami, Albert Zijlstra, Jonathan P. Marshall

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    Abstract

    We present James Clerk Maxwell Telescope Sub-millimetre Common-User Bolometer Array 2 (SCUBA-2)
    450

    and
    850μm

    observations of 14 asymptotic giant branch stars (9 O-rich, 4 C-rich, and 1 S-type) and one red supergiant in the solar neighbourhood. We combine these observations with Herschel/PACS observations at
    70

    and
    160μm

    and obtain azimuthally averaged surface-brightness profiles and their point spread function-subtracted residuals. The extent of the SCUBA-2 850
    μm

    emission ranges from 0.01 to 0.16 pc with an average of ∼40 per cent of the total flux being emitted from the extended component. By fitting a modified blackbody to the four-point spectral energy distribution at each point along the residual profile we derive the temperature (T), spectral index of dust emissivity (β), and dust column density (Σ) as a function of radius. For all the sources, the density profile deviates significantly from what is expected for a constant mass-loss rate, showing that all the sources have undergone variations in mass loss during this evolutionary phase. In combination with results from CO line emission, we determined the dust-to-gas mass ratio for all the sources in our sample. We find that, when sources are grouped according to their chemistry, the resulting average dust-to-gas ratios are consistent with the respective canonical values. However, we see a range of values with significant scatter which indicate the importance of including spatial information when deriving these numbers.
    Original languageEnglish
    JournalRoyal Astronomical Society. Monthly Notices
    Volume479
    Issue number1
    Early online date1 Jun 2018
    DOIs
    Publication statusPublished - Sept 2018

    Keywords

    • Stars: AGB and post-AGB
    • Stars: circumstellar matter
    • Stars: mass-loss

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