Nova Del Spectrum
2012-08-30_844
SC 25 cm F/D = 10
LISA R = 1100
The intensity scale is relative : 1 for range [6050,6100]
The purpose is to obtain an abolute flux calibration in erg/cm2/s
The method is to use a V band photometry to calibrate the spectrum
i.e. computing the absolute value of the continuum at lambda = 5500 angströms
Photometry in V
A photometry with Johnson V filter is obained just before the spectrum
Scope : 66ED
CDD : starlight SXV-H9
Exposure : 9 x 5 seconds
Bias, Dark substracted, flat divided
Photometric reduction
Software : MIRA Pro AP
Reference star : 000-BLC-955 V = 8.004
Check star : 000-BLC-940 V = 7.878
Result : Nova Del = 6.80
Check = 7.88
V = 6.80 +/- 0.02
UT 2013-08-30T19:37:59
Using a Johnson V transmission curve, the spectrum is convolved
Multiplication in ISIS :
Tools>Spectra Processing 1>Profiles arithmetic
The profile shows the (relative) luminosity throw the V filter.
The integrated flux between 4400 and 6600 A is proportional to V magnitude (but also to its value in erg/cm2/s in the Vega System)
Johnson V transmission curve fit
But
What we need is the value of the absolute intensity of a point of the continuum (i.e. 5500 angströms)
We have then to substract the contribution of the emissions lines to the integrated luminosity, according to the method described by Skopal (2003, 2007) in his studies of symbiotics stars (other stars, but same issue with intense emission lines).
This can be done, using "Continuum" in 5. Profile window of ISIS
A smooth continuum is computed (in red)
Perhaps the method should be improved
Using VSpec, we compute :
the integrated (relative) flux of the spectrum between 4400 and 6700 (Fs)
the
integrated (relative) flux of the continuum between 4400 and 6700 (Fc)
Numerical values :
Fs = 211 177
Fc = 174 678
The absolute flux calibrated spectrum will have to be multiplied by a factor Fc/Fs
Fc/Fs = 0.827 (0.83)
The spectrum is calibated in absolute flux with V = 6.80
ISIS>Tools>Spectra processing 3
And corrected for emission lines flux (multiplication by factor 0.83)
ISIS>Tools>Spectra processing
Last but not least, the spectrum must be corrected for interstellar extinction
with E(B-V) = 0.18 (Mubari & al., ATel#5297)
Final calibrated and dereddened spectrum
A measure of H alpha gives 9.9 10E-9 erg/cm2/s
