Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: PAH emission from Herbig AeBe stars   We present spectra of a sample of Herbig Ae and Be (HAeBe) stars obtained
with the Infrared Spectrograph on the Spitzer Space Telescope. All but one of
the Herbig stars show emission from polycyclic aromatic hydrocarbons (PAHs) and
seven of the spectra show PAH emission, but no silicate emission at 10 microns.
The central wavelengths of the 6.2, 7.7--8.2, and 11.3 micron emission features
decrease with stellar temperature, indicating that the PAHs are less
photo-processed in cooler radiation fields. The apparent low level of photo
processing in HAeBe stars, relative to other PAH emission sources, implies that
the PAHs are newly exposed to the UV-optical radiation fields from their host
stars. HAeBe stars show a variety of PAH emission intensities and ionization
fractions, but a narrow range of PAH spectral classifications based on
positions of major PAH feature centers. This may indicate that, regardless of
their locations relative to the stars, the PAH molecules are altered by the
same physical processes in the proto-planetary disks of intermediate-mass
stars. Analysis of the mid-IR spectral energy distributions indicates that our
sample likely includes both radially flared and more flattened/settled disk
systems, but we do not see the expected correlation of overall PAH emission
with disk geometry. We suggest that the strength of PAH emission from HAeBe
stars may depend not only on the degree of radial flaring, but also on the
abundance of PAHs in illuminated regions of the disks and possibly on the
vertical structure of the inner disk as well.

20
The categories of this paper are: acc-phys
1
The categories of this paper are: cs
18
The categories of this paper are: econ
5
The categories of this paper are: gr-qc
32
The categories of this paper are: atom-ph
17
The categories of this paper are: q-fin
31
The categories of this paper are: ao-sci
19
The categories of this paper are: eess
35
The categories of this paper are: mtrl-th
21
The categories of this paper are: adap-org
7
The categories of this paper are: hep-th
16
The categories of this paper are: stat
26
The categories of this paper are: bayes-an
28
The categories of this paper are: alg-geom
22
The categories of this paper are: chao-dyn
27
The categories of this paper are: comp-gas