Measure the line-of-sight (LOS) Doppler shift.¶
In the fisspy package, we supply the Doppler velocity measurement which is called lambdameter (=bisector). This lambameter method is useful when you derive the LOS Doppler velocity or intensity at a certain formation height defined by the half-width of the chord. It is also embedded in the fisspy.read.FISS class, so you can quickly draw the Doppler map using the 'vshow' method.
Here we can show how to use this code.
# preparing the data
import fisspy
a = fisspy.read.FISS('./FISS_20140603_170841_A1_c.fts', wvCalibMethod='photo')
wc, ic = fisspy.analysis.lambdameter(a.wave, a.data, hw=0.1)
where 'wc' represents the central wavelength of the lambdameter chord and 'ic' is the intensity of the chord. Using the definition of the Doppler velocity, you can draw the Doppler velocity map like this:
href = 6562.817
v = (wc-href)/href*3e5 # unit of km/s
import matplotlib.pyplot as plt
plt.imshow(v, plt.cm.RdBu_r, origin='lower', clim=[-5,5])
<matplotlib.image.AxesImage at 0x168bfb190>
You can also draw the Doppler intensity map like this:
plt.imshow(ic, fisspy.cm.ha, origin='lower')
<matplotlib.image.AxesImage at 0x168ab6460>
You can also derive the LOS velocity for the emission line or photospheric line putting the initial guess of 'iwc'. Here we show how to measure the velocity of the Ti II photospheric line of 6559.56 Å.
pwc, pic = fisspy.analysis.lambdameter(a.wave, a.data, iwc=6559.56, wvRange=[6559.2,6559.7])
pv = (pwc-6559.56)/6559.56*3e5
plt.imshow(pv, plt.cm.RdBu_r, origin='lower', clim=[-1,1])
<matplotlib.image.AxesImage at 0x1689cb430>
Please see the details in here.