SPECTROSCOPIC section

The SPECTROSCOPIC section is revised as follows:

• from the first copy of all the input header of $obs$ into $S_{\ensuremath{\mathrm{out}}}$, the spectroscopic section inherits the $obs$ values, in particular the rest and image frequencies.
• the number of channels is set to the appropriate value (according to the COMPOSITE or INTERSECT mode) computed at section .

Then, depending on the alignment rule, another set of values can be set:

• in case of channel alignment (SET ALIGN CHANNEL), no more values of this section are redefined.

• in case of frequency alignment (SET ALIGN FREQUENCY), the frequency and associated velocity parameters are set:
  • the output frequency resolution $f_{\ensuremath{\mathrm{res}},S_{\ensuremath{\mathrm{out}}}}$ is set to the value computed at Eq. ,
  • the output frequency offset $f_{\ensuremath{\mathrm{off}},S_{\ensuremath{\mathrm{out}}}}$ is set to $f_{\ensuremath{\mathrm{off}},S_{\ensuremath{\mathrm{in}}}}$,
  • the reference channel associated to $f_{\ensuremath{\mathrm{off}}}$ is set to $(f_{\ensuremath{\mathrm{off}},S_{\ensuremath{\mathrm{out}}}} - x_{\ensuremath{... ...\mathrm{out}}}}) / f_{\ensuremath{\mathrm{res}},S_{\ensuremath{\mathrm{out}}}}$ where $x_{\ensuremath{\mathrm{val}}}$ is the frequency value at channel $0$⁵, computed at Eq. ,
  • then the velocity resolution $v_{\ensuremath{\mathrm{res}},S_{\ensuremath{\mathrm{out}}}}$ is set to $-c \times f_{\ensuremath{\mathrm{res}},S_{\ensuremath{\mathrm{out}}}} / f_{\ensuremath{\mathrm{rest}},S_{\ensuremath{\mathrm{out}}}}$ where $c$ is the speed of light and $f_{\ensuremath{\mathrm{rest}}}$ the rest frequency,
  • and the velocity offset $v_{\ensuremath{\mathrm{off}},S_{\ensuremath{\mathrm{out}}}}$ is set to $v_{\ensuremath{\mathrm{off}},S_{\ensuremath{\mathrm{in}}}}$

• in case of velocity alignment SET ALIGN VELOCITY, the velocity and associated frequency parameters are set to:
  • the output velocity resolution $v_{\ensuremath{\mathrm{res}},S_{\ensuremath{\mathrm{out}}}}$ is set to the value computed at Eq. ,
  • the output velocity offset $v_{\ensuremath{\mathrm{off}},S_{\ensuremath{\mathrm{out}}}}$ ⁶ is set to $v_{\ensuremath{\mathrm{off}},S_{\ensuremath{\mathrm{in}}}}$,
  • the reference channel is set to $(v_{\ensuremath{\mathrm{off}},S_{\ensuremath{\mathrm{out}}}}-x_{\ensuremath{\ma... ...{\mathrm{out}}}}) / v_{\ensuremath{\mathrm{res}},S_{\ensuremath{\mathrm{out}}}}$ where $x_{\ensuremath{\mathrm{val}}}$ is the velocity value at channel $0$, computed at Eq. ,
  • then the frequency resolution $f_{\ensuremath{\mathrm{res}},S_{\ensuremath{\mathrm{out}}}}$ is set to $- f_{\ensuremath{\mathrm{rest}},S_{\ensuremath{\mathrm{out}}}} \times v_{\ensuremath{\mathrm{res}},S_{\ensuremath{\mathrm{out}}}} / c$,
  • and the frequency offset $f_{\ensuremath{\mathrm{off}},S_{\ensuremath{\mathrm{out}}}}$ is set to $f_{\ensuremath{\mathrm{off}},S_{\ensuremath{\mathrm{in}}}}$