A study of Si II and S II features in spectra of Type Ia supernova. (arXiv:2104.02875v1 [astro-ph.HE])

A study of Si II and S II features in spectra of Type Ia supernova. (arXiv:2104.02875v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Zhao_X/0/1/0/all/0/1">Xulin Zhao</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Maeda_K/0/1/0/all/0/1">Keiichi Maeda</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wang_X/0/1/0/all/0/1">Xiaofeng Wang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sai_H/0/1/0/all/0/1">Hanna Sai</a>

We studied the spectral features of Si II $lambdalambda$4130, 5972, 6355
and S II W-trough for a large sample of Type Ia supernovae (SNe Ia). We find
that in NV (Normal-Velocity) subclass of SNe Ia, these features tend to reach a
maximum line strength near maximum light, except for Si II $lambda$5972.
Spectral features with higher excitation energy, such as S II W-trough, are
relatively weak and have relatively low velocity. SNe Ia with larger
$Delta$m$_{15}$($B$) tend to have lower velocities especially at phases after
maximum light. NV SNe show a trend of increasing line strength with increasing
$Delta$m$_{15}$($B$), while 91T/99aa-like SNe show an opposite trend. Near
maximum light, the absorption depth of Si II $lambda$5972 shows the strongest
correlation with $Delta$m$_{15}$($B$), while at early times the sum of the
depths of Si II $lambdalambda$4130 and 5972 shows the strongest correlation
with $Delta$m$_{15}$($B$). The overall correlation between velocity and line
strength is positive, but within NV SNe the correlation is negative or
unrelated. In normal SNe Ia, the velocity-difference and depth-ratio of a
longer-wavelength feature to a shorter-wavelength feature tend to increase with
increasing $Delta$m$_{15}$($B$). These results are mostly well explained with
atomic physics, but some puzzles remain, possibly related to the effects of the
saturation, line competition or other factors.

We studied the spectral features of Si II $lambdalambda$4130, 5972, 6355
and S II W-trough for a large sample of Type Ia supernovae (SNe Ia). We find
that in NV (Normal-Velocity) subclass of SNe Ia, these features tend to reach a
maximum line strength near maximum light, except for Si II $lambda$5972.
Spectral features with higher excitation energy, such as S II W-trough, are
relatively weak and have relatively low velocity. SNe Ia with larger
$Delta$m$_{15}$($B$) tend to have lower velocities especially at phases after
maximum light. NV SNe show a trend of increasing line strength with increasing
$Delta$m$_{15}$($B$), while 91T/99aa-like SNe show an opposite trend. Near
maximum light, the absorption depth of Si II $lambda$5972 shows the strongest
correlation with $Delta$m$_{15}$($B$), while at early times the sum of the
depths of Si II $lambdalambda$4130 and 5972 shows the strongest correlation
with $Delta$m$_{15}$($B$). The overall correlation between velocity and line
strength is positive, but within NV SNe the correlation is negative or
unrelated. In normal SNe Ia, the velocity-difference and depth-ratio of a
longer-wavelength feature to a shorter-wavelength feature tend to increase with
increasing $Delta$m$_{15}$($B$). These results are mostly well explained with
atomic physics, but some puzzles remain, possibly related to the effects of the
saturation, line competition or other factors.

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