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, Letnik:
489, Številka:
3
Journal Article
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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.
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.
How stellar feedback from high-mass stars (e.g., H ii regions) influences the surrounding interstellar medium and regulates new star formation is still unclear. To address this question, we observed ...the G9.62+0.19 complex in 850 m continuum with the James Clerk Maxwell Telescope/POL-2 polarimeter. An ordered magnetic field has been discovered in its youngest clump, the G9.62 clump. The magnetic field strength is determined to be ∼1 mG. Magnetic field plays a larger role than turbulence in supporting the clump. However, the G9.62 clump is still unstable against gravitational collapse even if thermal, turbulent, and magnetic field support are taken into account together. The magnetic field segments in the outskirts of the G9.62 clump seem to point toward the clump center, resembling a dragged-in morphology, indicating that the clump is likely undergoing magnetically regulated global collapse. However, the magnetic field in its central region is aligned with the shells of the photodissociation regions and is approximately parallel to the ionization (or shock) front, indicating that the magnetic field therein is likely compressed by the expanding H ii regions that formed in the same complex.
We present results from an initial survey of the 2(12)-1(11) transition of formaldehyde (H2CO) at 140.8 GHz in giant molecular clouds in the far outer Galaxy (RG >or= 16 kpc). Formaldehyde is a key ...prebiotic molecule that likely plays an important role in the development of amino acids. Determining the outermost extent of the H2CO distribution can constrain the outer limit of the Galactic Habitable Zone, the region where conditions for the formation of life are thought to be most favorable. We surveyed 69 molecular clouds in the outer Galaxy, ranging from 12 to 23.5 kpc in galactocentric radius. Formaldehyde emission at 140.8 GHz was detected in 65% of the clouds. The H2CO spectral line was detected in 26 of the clouds with RG > 16 kpc (detection rate of 59%), including 6 clouds with RG > 20 kpc (detection rate of 55%). Formaldehyde is readily found in the far outer Galaxy-even beyond the edge of the old stellar disk. Determining the relatively widespread distribution of H2CO in the far outer Galaxy is a first step in establishing how favorable an environment this vast region of the Galaxy may be toward the formation of life.
Abstract
The Submillimetre Common User Bolometer Array 2 (SCUBA-2) is the James Clerk Maxwell Telescope’s continuum imager, operating simultaneously at 450 and 850
μ
m. SCUBA-2 was commissioned in ...2009–2011, and since that time, regular observations of point-like standard sources have been performed whenever the instrument is in use. Expanding the calibrator observation sample by an order of magnitude compared to previous work, in this paper we derive updated opacity relations at each wavelength for a new atmospheric extinction correction, analyze the Flux Conversion Factors used to convert instrumental units to physical flux units as a function of date and observation time, present information on the beam profiles for each wavelength, and update secondary calibrator source fluxes. Between 07:00 and 17:00 UTC, the portion of the night that is most stable to temperature gradients that cause dish deformation, the total flux uncertainty and the peak flux uncertainty measured at 450
μ
m are found to be 14% and 17%, respectively. Measured at 850
μ
m, the total flux and peak flux uncertainties are 6% and 7%, respectively. The analysis presented in this work is applicable to all SCUBA-2 projects observed since 2011.
We have obtained CO(J = 2−1) spectra of nine face-on low surface brightness galaxies using the JCMT 15 m telescope and observed H images using the 2.16 m telescope of NAOC. As no CO has been ...detected, only upper limits on the H2 masses are given. The upper limits of total molecular hydrogen masses are about . Their star-formation rates are mainly lower than yr−1 and star-formation efficiencies are lower than yr−1. Our results show that the absence of molecular gas content is the direct reason for the low star-formation rate. The low star-formation efficiency probably resulted from the low efficiency of H i gas transforming to H2 gas.
Far Outer Galaxy H II Regions Rudolph, Alexander L.; Brand, Jan; de Geus, Eugene J. ...
The Astrophysical journal,
02/1996, Letnik:
458
Journal Article
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