Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spectral luminosity indicators in SNe Ia - Understanding the R(SiII)
  line strength ratio and beyond   SNe Ia are good distance indicators because the shape of their light curves,
which can be measured independently of distance, varies smoothly with
luminosity. This suggests that SNe Ia are a single family of events. Similar
correlations are observed between luminosity and spectral properties. In
particular, the ratio of the strengths of the SiII \lambda 5972 and \lambda
6355 lines, known as R(SiII), was suggested as a potential luminosity
indicator. Here, the physical reasons for the observed correlation are
investigated. A Monte-Carlo code is used to construct a sequence of synthetic
spectra resembling those of SNe with different luminosities near B maximum. The
influence of abundances and of ionisation and excitation conditions on the
synthetic spectral features is investigated. The ratio R(SiII) depends
ssentially on the strength of SiII \lambda 5972, because SiII \lambda 6355 is
saturated. In less luminous objects, SiII \lambda 5972 is stronger because of a
rapidly increasing SiII/SiIII ratio. Thus, the correlation between R(SiII) and
luminosity is the effect of ionisation balance. The SiII \lambda 5972 line
itself may be the best spectroscopic luminosity indicator for SNe Ia, but all
indicators discussed show scatter which may be related to abundance
distributions.

2
The categories of this paper are: math
18
The categories of this paper are: econ
14
The categories of this paper are: math-ph
0
The categories of this paper are: hep-ph
9
The categories of this paper are: nlin
15
The categories of this paper are: nucl-ex
25
The categories of this paper are: patt-sol
12
The categories of this paper are: nucl-th
13
The categories of this paper are: quant-ph
27
The categories of this paper are: comp-gas
31
The categories of this paper are: ao-sci
37
The categories of this paper are: supr-con
10
The categories of this paper are: q-bio
26
The categories of this paper are: bayes-an
11
The categories of this paper are: hep-lat
28
The categories of this paper are: alg-geom