Subsections

• 8.6.1 PHT-S spectrum in wavelength units for point sources
  • Ancillary data needed
• 8.6.2 PHT-S spectrum for extended sources
  • Ancillary data needed
• 8.6.3 Write spectroscopy products

8.6 Spectroscopy with PHT40

The processing of PHT-S data during Derive_SPD created PHT-S spectra where for each pixel the flux density is given in Jy. In Derive_AAR the PHT-SS and PHT-SL detector arrays are processed separately in line with the separate treatment in SPD. Due to the relatively few PHT-S raster maps collected during the mission, no raster images with PHT-S are produced.

8.6.1 PHT-S spectrum in wavelength units for point sources

Operation:  Derive a PHT-S spectrum in $F_{\lambda}$

The PHT-S flux density $F_{\nu}(i)$ in frequency units of Jy of detector array element $i$ with uncertainty ${\Delta}F_{\nu}(i)$ is converted to wavelength units according to:

$$F_{\lambda}(i) = \frac {10^{-32}c}{\lambda^2(i)} F_{\nu}(i) ~~~~~~~~~~~~~~{\rm [W\,m^{-2}{\mu}m^{-1}]}$$ (8.17)

$${\Delta}F_{\lambda}(i) = \frac {10^{-32}c}{\lambda^2(i)} {\Delta}F_{\nu}(i)$$ (8.18)

where,

• $F_{\lambda}(i)$ in ${\rm W\,m^{-2}{\mu}m^{-1}}$ is the flux density in wavelength units, and
• ${\Delta}F_{\lambda}(i)$ the corresponding uncertainty;
• $\lambda(i)$ in $\mu$m is the centre wavelength of a pixel;
• $c$ = 299792500 m/s is the speed of light used in OLP.

This conversion is applied to

• PHT40 point source observations in staring mode, and
• the chopped source and the chopped (source+background) spectrum of PHT40 point source observations in chopped mode.

Ancillary data needed

The values for $\lambda(i)$ are stored in Cal-G file PSPECAL, see Section14.19.1.

8.6.2 PHT-S spectrum for extended sources

Operation:  Derive a PHT-S spectrum for extended sources.

The PHT-S flux density $F_{\nu}(i)$ in frequency units of Jy of detector array element $i$ with uncertainty ${\Delta}F_{\nu}(i)$ is converted to surface brightness:

$$I_{\lambda}(i) = \frac {10^{-26}c}{\lambda(i)^2} F_{\nu}(i) \frac {C^{p}_{ave}(i)}{C^{e}_{ave}(i)} ~~~~~~~~~~~~~~{\rm [W\,m^{-2}{\mu}m^{-1}sr^{-1}]}$$ (8.19)

$${\Delta}I_{\lambda}(i) = \frac {10^{-26}c}{\lambda(i)^2} {\Delta}F_{\nu}(i)\frac {C^{p}_{ave}(i)}{C^{e}_{ave}(i)}$$ (8.20)

where

• $I_{\lambda}(i)$ in ${\rm W\,m^{-2}{\mu}m^{-1}sr^{-1}}$ is the surface brightness for a given detector array element $i$, and
• ${\Delta}I_{\lambda}(i)$ is the corresponding uncertainty;
• $\lambda(i)$ in $\mu$m is the central wavelength of a PHT-S detector pixel;
• $C^p_{ave}(i)$ in Vs$^{-1}$/Jy is the average spectral response function for the conversion from signal in Vs$^{-1}$ to point source flux density in Jy;
• $C^e_{ave}(i)$ in (Vs$^{-1}$)/(MJysr$^{-1}$) is the average spectral response function for the conversion from signal in Vs$^{-1}$ to surface brightness in MJysr$^{-1}$;
• ${\rm c}$ = 299792500 ms$^{-1}$ is the speed of light.

This conversion is applied to

• extended source PHT40 observations in staring mode,
• each raster pointing in PHT40 raster mode.

Ancillary data needed

The values for $\lambda(i)$, $C^p_{ave}(i)$, and $C^e_{ave}(i)$ are stored in Cal-G file PSPECAL, see Section14.19.1.

8.6.3 Write spectroscopy products

Operation:  Write spectroscopy products.

To maintain the separation between the short wavelength and long wavelength PHT-S detector arrays SS and SL, the different array data are stored in separate products.

Detailed product descriptions can be found in Sections 13.4, 13.4.11 (product PSAP), 13.4.12 (product PLAP), 13.4.13 (product PSAE), 13.4.14 (product PLAE), 13.4.15 (product PSAS), 13.4.16 (product PLAS), for the PHT-SS and SL point source, extended source and raster products, respectively.