publications

The Nearby Evolved Stars Survey: I. JCMT/SCUBA-2 Sub-millimetre detection of the detached shell of U Antliae

July 2019. ADS: 2019MNRAS.tmp.2246D

Dharmawardena, Thavisha E.; Kemper, Francisca; Srinivasan, Sundar; Scicluna, Peter; Marshall, Jonathan P.; Wouterloot, Jan G. A.; Greaves, Jane; Goldman, Steven R.; van Loon, Jacco Th; Matsuura, Mikako; McDonald, Iain; He, Jinhua; Zijlstra, Albert A.; Toalá, Jesús A.; Wallström, Sofia H. J.; Kim, Hyosun; Trejo, Alfonso; Ventura, Paolo; Lagadec, Eric; Boyer, Martha L.; Liu, Tie; Rau, Gioia; Izumiura, Hideyuki; Cami, Jan; Holland, Wayne; Jones, Olivia; Shinnaga, Hiroko

We present the highest resolution single-dish submillimetre observations of the detached shell source U Antliae to date. The observations were obtained at 450 {μ m} and 850 {μ m} with SCUBA-2 instrument on the James Clerk Maxwell Telescope as part of the Nearby Evolved Stars Survey. The emission at 850 {μ m} peaks at 40″ with hints of a second peak seen at ̃20″. The emission can be traced out to a radius of 56″ at a 3σ level. The outer peak observed at 850 {μ m} aligns well with the peak observed at Herschel/PACS wavelengths. With the help of spectral energy distribution fitting and radiative transfer calculations of multiple-shell models for the circumstellar envelope, we explore the various shell structures and the variation of grain sizes along the in the circumstellar envelope. We determine a total shell dust mass of (2.0 ± 0.3) × 10-5 M and established that the thermal pulse which gave rise to the detached shell occurred 3500 ± 500 years ago.

Extended Dust Emission from Nearby Evolved Stars

August 2018. ADS: 2018MNRAS.479..536D

Dharmawardena, Thavisha E.; Kemper, Francisca; Scicluna, Peter; Wouterloot, Jan G. A.; Trejo, Alfonso; Srinivasan, Sundar; Cami, Jan; Zijlstra, Albert; Marshall, Jonathan P.

We present James Clerk Maxwell Telescope Sub-millimetre Common-User Bolometer Array 2 (SCUBA-2) 450 and 850 {μ} m 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 160 {μ} m and obtain azimuthally averaged surface-brightness profiles and their point spread function-subtracted residuals. The extent of the SCUBA-2 850 {μ} m 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.