ALMA observations of the narrow HR 4796A debris ring

作者：Kennedy Grant M; Marino Sebastian; Matra Luca; Panic Olja; Wilner David; Wyatt Mark C; Yelverton Ben

来源：Monthly Notices of the Royal Astronomical Society, 2018, 475(4): 4924-4938.

DOI：10.1093/mnras/sty135

• planet-disc interactions
• circumstellar matter
• stars: individual: HR 4796A
• planetary systems
• Galaxy: formation
• submillimetre: planetary systems

The young A0V star HR 4796A is host to a bright and narrow ring of dust, thought to originate in collisions between planetesimals within a belt analogous to the Solar system's Edgeworth-Kuiper belt. Here we present high spatial resolution 880 mu m continuum images from the Atacama Large Millimeter Array. The 80 au radius dust ring is resolved radially with a characteristic width of 10 au, consistent with the narrow profile seen in scattered light. Our modelling consistently finds that the disc is also vertically resolved with a similar extent. However, this extent is less than the beam size, and a disc that is dynamically very cold (i.e. vertically thin) provides a better theoretical explanation for the narrowscattered light profile, so we remain cautious about this conclusion. We do not detect (CO)-C-12 J=3-2 emission, concluding that unless the disc is dynamically cold the CO+CO2 ice content of the planetesimals is of order a few per cent or less. We consider the range of semi-major axes and masses of an interior planet supposed to cause the ring's eccentricity, finding that such a planet should be more massive than Neptune and orbit beyond 40 au. Independent of our ALMA observations, we note a conflict between mid-IR pericentre-glow and scattered light imaging interpretations, concluding that models where the spatial dust density and grain size vary around the ring should be explored.

• 出版日期2018-4