LECTURER:                           

Julius Koza

TITLE:   

Sensitivity of selected photospheric lines to velocity in quiet Sun

ABSTRACT: 

The solar photospheric spectrum displays wealth of spectral lines
of different diagnostic potential. A recent breakthrough has been 
the identification of simple rules enabling to characterize the
sensitivityof weak photospheric spectral lines to line-of-sight (LOS)
velocity, magnetic field, and temperature by means of their response
functions. We present a study of the sensitivity of selected Ba II,
Cr I, Fe I, and Fe II spectral lines to LOS velocity based on their
response functions in quiet solar photosphere. We examine sensitivity
to velocity of Ba II 4554 A spectral line generally considered to be
an excellent Doppler mapper. We measure depths and widths of line
profiles extracted from solar spectral atlas and synthesized by 1D
model of quiet solar photosphere in LTE approximation. We compute
integrated response functions to velocity and identify their maxima 
to quantify sensitivity of selected spectral lines to velocity. We
show that the sensitivity of the lines to velocity increases not 
only with wavelength, as anticipated from Doppler relation, but
mainly with sharpness of the line profiles given by ratio of their 
depths and widths. The spectral line Fe I 5247 A is the most 
sensitive in our set whereas Fe I and Fe II infrared lines display
very low sensitivity to velocity because of their large thermal
widths. The spectral line Ba II 6497 A shows similarly high
sensitivity as Fe I 5247 A.  The spectral line Ba II 4554 A shows
only medium sensitivity to velocity due to its rather large width 
given by broad hyperfine structure and isotopic split. Largely 
unknown spectral line Ba II 6497 is very promising solar Doppler 
mapper of the future thanks to its high sensitivity to velocity,
very high atomic mass and low effective Lande factor.