Continuum and CO J=3-2 Emission from the Pluto- Charon System.
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Continuum and CO J=3-2 Emission from the Pluto-Charon System
Left: Submillimeter Array (SMA) aperture synthesis images of1400μm(220GHz) continuum emission Pluto and Charon (Gurwell and Butler. 2005). These observations were made with the most extended SMA configuration, achieving a synthesized beam of ~ 0.4” FWHM. During Early Science, ALMA will achieve similar angular resolution in Band 9 (690 GHz) with integration times of ~2.5 hours required to obtain similar uv-coverage.
Science Goal: To observe the CO line on Pluto and to measure the fluxes of both Pluto and Charon.
Receivers: Bands 7 and 9 (345 GHz and 690 GHz)
Angular Resolution: 0".4 (Band 9) to 0”.7 (Band 7), assuming a maximum baseline of 250m. The typical separation of Pluto and Charon is ~0”.9 so the two will be well-resolved at 690GHz but barely so, if at all at 345GHz. Fluxes are expected to be 100 and 20 mJy for Pluto at the two frequencies, and 40% of that for Charon. The predicted intensity of the CO line is scores of mJy in a 1 km/s line. This should be detectable in a few hours of integration.
Spectral Resolution:0.2 km/s (244kHz) at 345 GHz.
Continuum Sensitivity: 0.03 mJy and.12mJy for Bands 7, and 9, respectively. These are the expected point source sensitivities needed for5σ detections of Nix and Hydra in each band, if the radii are near 150km.
Line Sensitivity: 1 mJy km/s Band 7. The excited line at 690 GHz is expected to be too weak given the 40K temperature expected for the surface.
Observing Time: Using the ALMA integration time calculator with 16 12 m antennas and 4 GHz bandwidth, these point source sensitivities can be achieved in 40m (CO3-2 Band 7),1h for the simultaneously observed 345 GHz continuum, and 2h (Band 9). Observations of the CO line in Pluto, and of the continuum emission from Pluto and Charon (and perhaps Nix and Hydra) a total of 3 hours of observation in good weather. Pluto is well-placed for winter observation.
In the future: As ALMA’s maximum baseline length increases, the disks in this example can be resolved at all wavelengths, with matched angular resolution if desired. With greater angular resolution, the science case presented here can be expanded to study the variation of the dust SED as a function of disk radius, and to look for holes in emission which may indicate the presence of gaps in the disks. The resolved disks will require a greater amount of observing time, both for sensitivity (using the surface brightness rather than point source mode with the ALMA integration time calculator), and to increase the uv-coverage, as we have done here for Band 9. The number of antennas will increase during Early Science, however, reducing the amount of time required to obtain the same uv-coverage. To match the Band 9 angular resolution of 0.4” discussed above at Band 3 requires a maximum baseline of 1.5 km.
Place holder for real OT screen capture.