Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Be and Bn stars: Balmer discontinuity and stellar-class relationship   A significant number of Be stars show a second Balmer discontinuity (sBD)
attributed to an extended circumstellar envelope (CE). The fast rotational
velocity of Be stars undoubtedly plays a significant role in the formation of
the CE. However, Bn stars, which are also B-type rapidly rotating stars, do not
all present clear evidence of being surrounded by circumstellar material. We
aim to characterize the populations of Be and Bn stars, and discuss the
appearance of the sBD as a function of the stellar parameters. We expect to
find new indices characterizing the properties of CEs in Be stars and
properties relating Be and Bn stars. Correlations of the aspect and intensity
of the sBD and the emission in the H$\alpha$ line with the stellar parameters
and the $V\!\sin i$ are presented. Some Bn stars exhibit the sBD in absorption,
which may indicate the presence of rather dense CEs. Six Bn stars show emission
in the H$\alpha$ line, so they are reclassified as Be stars. The sBD in
emission appears in Be stars with $V\!\sin i \lesssim 250$ km\,s$^{-1}$, and in
absorption in both Be and Bn stars with \mbox{$V\!\sin i \gtrsim 50$
km\,s$^{-1}$}. Low-mass Be and Bn stars share the same region in the
Hertzsprung-Russell diagram. The distributions of rotational to critical
velocity ratios of Be and Bn stars corresponding to the current stellar
evolutionary stage are similar, while distributions inferred for the zero-age
main sequence have different skewness. We found emission in the H$\alpha$ line
and signs of a CE in some Bn stars, which motivated us to think that Bn and Be
stars probably belong to the same population. It should be noted that some of
the most massive Bn stars could display the Be phenomenon at any time. The
similarities found among Be and Bn stars deserve to be more deeply pursued.

23
The categories of this paper are: solv-int
15
The categories of this paper are: nucl-ex
25
The categories of this paper are: patt-sol
10
The categories of this paper are: q-bio
37
The categories of this paper are: supr-con
28
The categories of this paper are: alg-geom
13
The categories of this paper are: quant-ph
24
The categories of this paper are: dg-ga
20
The categories of this paper are: acc-phys
5
The categories of this paper are: gr-qc
30
The categories of this paper are: q-alg
19
The categories of this paper are: eess
29
The categories of this paper are: funct-an
1
The categories of this paper are: cs
3
The categories of this paper are: physics
16
The categories of this paper are: stat