Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spectral observations of X Persei: Connection between H-alpha and X-ray
  emission   We present spectroscopic observations of the Be/X-ray binary X Per obtained
during the period 1999 - 2018. Using new and published data, we found that
during "disc-rise" the expansion velocity of the circumstellar disc is 0.4 -
0.7 km/s. Our results suggest that the disc radius in recent decades show
evidence of resonant truncation of the disc by resonances 10:1, 3:1, and 2:1,
while the maximum disc size is larger than the Roche lobe of the primary and
smaller than the closest approach of the neutron star. We find correlation
between equivalent width of H-alpha emission line ($W\alpha$) and the X-ray
flux, which is visible when $15 \: \AA \: < W\alpha \le 40 \: \AA$. The
correlation is probably due to wind Roche lobe overflow.

8
The categories of this paper are: hep-ex
12
The categories of this paper are: nucl-th
31
The categories of this paper are: ao-sci
24
The categories of this paper are: dg-ga
14
The categories of this paper are: math-ph
16
The categories of this paper are: stat
29
The categories of this paper are: funct-an
35
The categories of this paper are: mtrl-th
3
The categories of this paper are: physics
30
The categories of this paper are: q-alg
2
The categories of this paper are: math
4
The categories of this paper are: cond-mat
15
The categories of this paper are: nucl-ex
9
The categories of this paper are: nlin
17
The categories of this paper are: q-fin
18
The categories of this paper are: econ