The sub-mm variability of IRC+10216 and o Ceti

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 µm and 850 µm as part of pointing calibration observations for the James Clerk Maxwell Telescope's SCUBA-2 instrument over a span of 7 years. 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 µm phase folded light curves of IRC+10216 show a time lag of ∼ 540 days 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/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.

Betelgeuse fainter in the sub-millimetre too: an analysis of JCMT and APEX monitoring during the recent optical minimum

“…Using the same logic, we can exclude changes in the sub-mm line emission as a cause of the variations. Similar to CW Leo (Dharmawardena et al 2019a), the CO contribution (the brightest line in these spectral regions) to the measured continuum is at the 5-10% level; short of all the molecular line emission disappearing, the continuum could not change by this amount.…”

“…The CO J=3-2 transition line at 345.7 GHz contaminates SCUBA-2 850 µm observations (Drabek et al 2012;Coudé et al 2016;Dharmawardena et al 2019a). To remove this contamination from our observations, we use an archival CO 3-2 staring observation obtained from the JCMT/Heterodyne Array Receiver Program (HARP) instrument on 2013 December 29.…”

CCAT-prime Collaboration: Science Goals and Forecasts with Prime-Cam on the Fred Young Submillimeter Telescope

“…Magnetic reconnection events in stellar flares have been detected at millimeter and submillimeter wavelengths from low-mass stars (MacGregor et al 2020;Guns et al 2021;Naess et al 2021) and T Tauri stars (Bower et al 2003;Mairs et al 2019) with timescales as short as 15 minutes through a few hours and with multiple detections over 6 days (e.g., a chromospherically active binary whose dwarf star may be about to arrive, or recently has arrived, on the main sequence; Naess et al 2021). Cycles of dust formation and destruction can lead to periodic variability in asymptotic giant branch stars, while free-free emission with origins in the radio photosphere may also contribute (Dharmawardena et al 2019, periods and optical-to-submillimeter lags on a few year timescales).…”