Betelgeuse, the nearest red supergiant star to Earth, underwent an unusually deep minimum at optical wavelengths during its most recent pulsation cycle. We present submillimeter observations taken by ...the James Clerk Maxwell Telescope and Atacama Pathfinder Experiment over a time span of 13 yr including the optical dimming. We find that Betelgeuse has also dimmed by ∼20% at these longer wavelengths during this optical minimum. Using radiative-transfer models, we show that this is likely due to changes in the photosphere (luminosity) of the star as opposed to the surrounding dust, as was previously suggested in the literature.
ABSTRACT
The thermal emission of dust is one of the most important tracers of the interstellar medium: multiwavelength photometry in the far-infrared (FIR) and submillimetre (submm) can be fitted ...with a model, providing estimates of the dust mass. The fit results depend on the assumed value for FIR/submm opacity, which in most models – due to the scarcity, until recently, of experimental measurements – is extrapolated from shorter wavelengths. Lab measurements of dust analogues, however, show that FIR opacities are usually higher than the values used in models and depend on temperature, which suggests that dust mass estimates may be biased. To test the extent of this bias, we create multiwavelength synthetic photometry for dusty galaxies at different temperatures and redshifts, using experimental results for FIR/submm dust opacity and then we fit the synthetic data using standard dust models. We find that the dust masses recovered by typical models are overestimated by a factor of 2–20, depending on how the experimental opacities are treated. If the experimental dust samples are accurate analogues of interstellar dust, therefore, current dust masses are overestimated by up to a factor of 20. The implications for our understanding of dust, both Galactic and at high redshift, are discussed.
ABSTRACT
We report H α filter photometry for 197 Northern hemisphere planetary nebulae (PNe) obtained using imaging data from the IPHAS survey. H α+N ii fluxes were measured for 46 confirmed or ...possible PNe discovered by the IPHAS survey and for 151 previously catalogued PNe that fell within the area of the northern Galactic Plane surveyed by IPHAS. After correcting for N ii emission admitted by the IPHAS H α filter, the resulting H α fluxes were combined with published radio free–free fluxes and H β fluxes, in order to estimate mean optical extinctions to 143 PNe using ratios involving their integrated Balmer line fluxes and their extinction-free radio fluxes. Distances to the PNe were then estimated using three different 3D interstellar dust extinction mapping methods, including the IPHAS-based h-mead algorithm of Sale (2014). These methods were used to plot dust extinction versus distance relationships for the lines of sight to the PNe; the intercepts with the derived dust optical extinctions allowed distances to the PNe to be inferred. For 17 of the PNe in our sample reliable GaiaDR2 distances were available and these have been compared with the distances derived using three different extinction mapping algorithms as well as with distances from the nebular radius versus H α surface brightness relation of Frew et al. (2016). That relation and the h-mead extinction mapping algorithm yielded the closest agreement with the Gaia DR2 distances.
ABSTRACT
We present the highest resolution single-dish submillimetre observations of the detached shell source U Antliae to date. The observations were obtained at $450$ and $850\,{\mu}{\rm m}$ with ...SCUBA-2 instrument on the James Clerk Maxwell Telescope as part of the Nearby Evolved Stars Survey. The emission at $850\,{\mu}{\rm m}$ peaks at 40 arcsec with hints of a second peak seen at ∼20 arcsec. The emission can be traced out to a radius of 56 arcsec at a 3σ level. The outer peak observed at $850\,{\mu}{\rm m}$ 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 that gave rise to the detached shell occurred 3500 ± 500 yr ago.
The sub-mm variability of IRC+10216 and o Ceti Dharmawardena, Thavisha E; Kemper, Francisca; Wouterloot, Jan G A ...
Monthly notices of the Royal Astronomical Society,
11/2019, Volume:
489, Issue:
3
Journal Article
Peer reviewed
Open access
Abstract
We present the sub-mm variability of two of the most well-studied AGB stars, IRC + 10216 and o Ceti. The data are obtained at $450$ and $850\,{\mu {\rm m}}$ as part of pointing calibration ...observations for the James Clerk Maxwell Telescope’s SCUBA-2 instrument over a span of 7 yr. The periods are derived using non-parametric methods, Gatspy Supersmoother and P4J, in order not to assume an underlying shape to the periodicity. These were compared to two Lomb–Scargle parametric methods. We find that for both sources and wavelengths the periods derived from all methods are consistent within 1σ. The $850\,{\mu {\rm m}}$ phase folded light curves of IRC + 10216 show a time lag of ∼540 d compared to its optical counterpart. We explore the origins of the sub-mm variability and the phase lag using radiative transfer models. Combining the modelling with findings in the literature, we find that the sub-mm emission and phase lag can be partially attributed to the dust formation or destruction cycle. A second, unknown mechanism must be invoked; we defer an investigation of the origin and nature of this mechanism to a future work.
The thermal emission of dust is one of the most important tracers of the interstellar medium: multi-wavelength photometry in the far-infrared (FIR) and submillimeter (submm) can be fitted with a ...model, providing estimates of the dust mass. The fit results depend on the assumed value for FIR/submm opacity, which in most models - due to the scarcity, until recently, of experimental measurements - is extrapolated from shorter wavelengths. Lab measurements of dust analogues, however, show that FIR opacities are usually higher than the values used in models and depend on temperature, which suggests that dust mass estimates may be biased. To test the extent of this bias, we create multi-wavelength synthetic photometry for dusty galaxies at different temperatures and redshifts, using experimental results for FIR/submm dust opacity, then we fit the synthetic data using standard dust models. We find that the dust masses recovered by typical models are overestimated by a factor 2 to 20, depending on how the experimental opacities are treated. If the experimental dust samples are accurate analogues of interstellar dust, therefore, current dust masses are overestimated by up to a factor 20. The implications for our understanding of dust, both Galactic and at high redshift, are discussed.
Betelgeuse is the nearest Red Supergiant star and it underwent an unusually deep minimum at optical wavelengths during its most recent pulsation cycle. We present submillimetre observations taken by ...the James Clerk Maxwell Telescope and Atacama Pathfinder Experiment over a time span of 13 years including the optical dimming. We find that Betelgeuse has also dimmed by \sim20\% at these longer wavelengths during this optical minimum. Using radiative-transfer models, we show that this is likely due to changes in the photosphere (luminosity) of the star as opposed to the surrounding dust as was previously suggested in the literature.
We report H$\alpha$ filter photometry for 197 northern hemisphere planetary
nebulae (PNe) obtained using imaging data from the IPHAS survey. H$\alpha$+N
II fluxes were measured for 46 confirmed or ...possible PNe discovered by the
IPHAS survey and for 151 previously catalogued PNe that fell within the area of
the northern Galactic Plane surveyed by IPHAS. After correcting for N II
emission admitted by the IPHAS H$\alpha$ filter, the resulting H$\alpha$ fluxes
were combined with published radio free-free fluxes and H$\beta$ fluxes, in
order to estimate mean optical extinctions to 143 PNe using ratios involving
their integrated Balmer line fluxes and their extinction-free radio fluxes.
Distances to the PNe were then estimated using three different 3D interstellar
dust extinction mapping methods, including the IPHAS-based H-MEAD algorithm of
Sale (2014). These methods were used to plot dust extinction versus distance
relationships for the lines of sight to the PNe; the intercepts with the
derived dust optical extinctions allowed distances to the PNe to be inferred.
For 17 of the PNe in our sample reliable Gaia DR2 distances were available and
these have been compared with the distances derived using three different
extinction mapping algorithms as well as with distances from the nebular radius
vs. H$\alpha$ surface brightness relation of Frew et al. (2016). That relation
and the H-MEAD extinction mapping algorithm yielded the closest agreement with
the Gaia DR2 distances.
PDF
