Radiative Transfer in Protoplanetary Disks

IR excesses, we can measure a truly independent gas depletion timescale and examine the possibility of gas rich,
dust poor systems. These objects are (initially) only observed in [CII]158µm and [OI]63µm and account for
Gas in Protoplanetary Systems
14% of the Phase I time. A significant fraction of the targets are multiple stars (25%, separations 5-1000 AU),
enabling the survey to be used to study the effect of companions on gas disks. These have not been excluded
to avoid selection bias. Finally the target list has a wide range of X-ray luminosity (10 28 − 10 31 erg s −1 ) and
Hα line strength (W (Hα) =1− 150 ˚A). This allows multivariate analysis of line strengths and ratios, which
is only possible with such a large and unbiased sample, and increases the legacy value. An estimate of the
Statistical survey (≈ 250 disks) : evolution of gas
required number of targets is given by the number of bins of primary parameters (mass, spectral type and age):
Ntargets = Nmass.Nsp.t.Nage.N, whereN is the number in each bin. To investigate effects of other parameters
and dust from young gas-rich protoplanetary disks,
and give a statistically-robust result, we have set Nb = 10. A minimum of 3 logarithmically-spaced bins of
each parameter means we need ∼270 targets. Figure 4 shows the distribution over the primary parameters, and
Table 4 summarises the sample clusters.
to old “dry” debris disks:
Table 4. Target clusters
•Ages 1 – 30Myr, M to A stars, disk dust mass (10-2 - 10-5 Distance Age Total Number Mo)
Group (pc) (Myr) number Phase I
Taurus 140 0.3 − 4 109 48
Upper Sco 145 5 48 2
η Cha 112 5 − 9 17 1
TW Hya 50 8 − 10 13 0
β Pic 30 10 − 20 19 0
Tuc Hor 46 30 18 0
Ae/Be stars 50 − 200 0.5 − 30 50 26
•Well-known star-forming regions (Taurus, TW Hydra, η Cha,
β Pic, Tuc Hor, Upper Sco, Herbig Ae/Be)
•Key far-IR tracers: [OI], [CII], H2O, CO + Phot. at 70 & 160μm