Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Debris disks with multiple absorption features in metallic lines:
  circumstellar or interstellar origin?   Debris disks are second generation dusty disks thought to be devoid of gas.
However, this idea has been challenged in the last years by gas detections in
some systems. We compiled a database of 301 debris disks and collected
high--resolution optical spectra for $\sim77\%$ of them. From the analysis of
these data we identified a group of 23 debris disks presenting several
absorption features superimposed to the photospheric Ca II and Na I doublets.
These absorptions could be due to circumstellar material or interstellar
clouds. In order to discriminate between the two scenarios, we characterized
each feature in terms of its radial velocity, equivalent width and column
density. Additionally, we searched in the literature for local clouds in the
line of sight of the stars, and looked for the presence of similar absorption
features in nearby stars. Our study concludes that while all the objects
present interstellar absorptions in their spectra, three objects show features
more compatible with circumstellar origin: HD 110058 presents a stable
circumstellar absorption, while HR 4796 and c Aql present variable absorption
features likely due to exocometary activity. The minute-scale variability we
detect towards c Aql is the shortest of this kind detected so far. The
detection of circumstellar features in these objects is consistent with their
near edge-on inclinations. We also provide evidence challenging previous claims
of circumstellar gas detections for HR 6507. Given the properties of the
sample, we speculate that transient gaseous events must be a common phenomenon
among debris disks.

1
The categories of this paper are: cs
30
The categories of this paper are: q-alg
17
The categories of this paper are: q-fin
5
The categories of this paper are: gr-qc
31
The categories of this paper are: ao-sci
27
The categories of this paper are: comp-gas
11
The categories of this paper are: hep-lat
26
The categories of this paper are: bayes-an
34
The categories of this paper are: chem-ph
24
The categories of this paper are: dg-ga
32
The categories of this paper are: atom-ph
2
The categories of this paper are: math
15
The categories of this paper are: nucl-ex
35
The categories of this paper are: mtrl-th
0
The categories of this paper are: hep-ph
25
The categories of this paper are: patt-sol