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SUMMARY:Measuring dust-gas coupling via the gas rotation curve
DTSTART;VALUE=DATE-TIME:20200514T075000Z
DTEND;VALUE=DATE-TIME:20200514T081000Z
DTSTAMP;VALUE=DATE-TIME:20240704T115618Z
UID:indico-contribution-19@meetings.aip.de
DESCRIPTION:Speakers: Giovanni Rosotti (Leiden University)\nALMA is showin
 g that most proto-planetary discs are highly sub-structured and that the m
 ost frequent structure consists in azimuthally symmetric "gaps and rings".
  Rings have attracted a lot of attention since they might be the signature
  of young planets. But rings are extremely important for another reason: t
 hey provide us with a privileged window inside disc physics. Indeed\, as s
 hown by the DSHARP team\, their finite dust width shows that there must be
  some level of dust diffusion\, or else the dust would only collect at the
  pressure maximum. However\, the DSHARP team was only able to place a lowe
 r limit\, and not to measure\, the amount of diffusion\, because they did 
 not have information on the gas distribution. I will show how the analysis
  of the gas rotation curve\, another breakthrough enabled by ALMA observat
 ions of molecular lines\, is a powerful way to measure the width of rings 
 in the gas and therefore allows us to measure the dust-gas coupling\, whic
 h controls the dust ring width. Formally\, the relevant parameter is the r
 atio between the Shakura-Sunyaev α and the dust Stokes number St. I will 
 also discuss the impact of the disc 3D structure on this analysis and show
  that the measurement of ring width is robust towards the details of the v
 ertical structure. At the moment\, there are only two objects with good en
 ough S/N to perform these measurements. In these objects\, I will report g
 as widths larger than in the dust\, consistently with the idea of dust tra
 pping. I will show how the data point to a relatively high degree of dust-
 gas coupling (typical α/St ~ 0.1). Scenarios with very low levels of turb
 ulence and high levels of grain growth can therefore be rejected. Future c
 onstraints on the dust grain size in the rings will help in breaking the d
 egeneracy between St and alpha.\n\nhttps://meetings.aip.de/event/1/contrib
 utions/19/
LOCATION:Leibniz Institute for Astrophysics Potsdam (AIP) Lecture Hall
URL:https://meetings.aip.de/event/1/contributions/19/
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