Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The inner regions of protoplanetary disks   To understand how planetary systems form in the dusty disks around
pre-main-sequence stars a detailed knowledge of the structure and evolution of
these disks is required. While this is reasonably well understood for the
regions of the disk beyond about 1 AU, the structure of these disks inward of 1
AU remains a puzzle. This is partly because it is very difficult to spatially
resolve these regions with current telescopes. But it is also because the
physics of this region, where the disk becomes so hot that the dust starts to
evaporate, is poorly understood. With infrared interferometry it has become
possible in recent years to directly spatially resolve the inner AU of
protoplanetary disks, albeit in a somewhat limited way. These observations have
partly confirmed current models of these regions, but also posed new questions
and puzzles. Moreover, it has turned out that the numerical modeling of these
regions is extremely challenging. In this review we give a rough overview of
the history and recent developments in this exciting field of astrophysics.

23
The categories of this paper are: solv-int
7
The categories of this paper are: hep-th
22
The categories of this paper are: chao-dyn
3
The categories of this paper are: physics
21
The categories of this paper are: adap-org
32
The categories of this paper are: atom-ph
30
The categories of this paper are: q-alg
18
The categories of this paper are: econ
33
The categories of this paper are: plasm-ph
10
The categories of this paper are: q-bio
36
The categories of this paper are: cmp-lg
24
The categories of this paper are: dg-ga
17
The categories of this paper are: q-fin
25
The categories of this paper are: patt-sol
31
The categories of this paper are: ao-sci
12
The categories of this paper are: nucl-th