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Point Source

If we consider for example a point source with a uniform emission of magnitude 15, in K band, being the sky airmass 1.2, and a seeing of 0.5, using a slit width of 2 arcsec, in low resolution, with the red grism inserted, and the large field, for an integration time, we could get:


\begin{displaymath}M_{K}=15\Longrightarrow Z_{K}=9.4367\Longrightarrow
F=3.65847422794\cdot 10^{-16}
~J\cdot s^{-1}\cdot m^{-2}\cdot \mu m^{-1}
\end{displaymath}

where we have used data in Tab. 2.3 and eq. (2.5), (2.6) and expressed the result in Joule units.

Using eq. (2.7):


\begin{displaymath}P=\frac{h\cdot c}{\lambda}=0.90\overline{27}\cdot10^{-20} J\slash ph\hbox{ at $\lambda=2.2~\mu m$}
\end{displaymath}


\begin{displaymath}\displaystyle\left(\frac{F}{P}\right)_{Obj}=4.05269048412\cdot 10^{3}
~ph\cdot s^{-1}\cdot m^{-2}\cdot\mu m^{-1}
\end{displaymath}


\begin{displaymath}\Delta_{S}=1.01\cdot 10^{-3} ~\mu m\slash bin
\end{displaymath}


S=8.9  m2


T=60  s


E=0.25

With the previously specified parameter we can get from formulae in Tab. 2.1:


\begin{displaymath}N_{Obj}=\frac{F\cdot \Delta_{S}\cdot T\cdot E\cdot S}{P}= 546.444521425 ~cnts\slash bin
\end{displaymath} (2.11)

The ETC for FORS1 with the input parameter as specified above predicts NETC=515 cntsbin.


next up previous contents
Next: Sky Up: SOFI-Spectroscopy Previous: SOFI-Spectroscopy
Pascal Ballester
1999-07-29