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diff --git a/src/slalib/sun67.htx/node225.html b/src/slalib/sun67.htx/node225.html new file mode 100644 index 0000000..ce716c7 --- /dev/null +++ b/src/slalib/sun67.htx/node225.html @@ -0,0 +1,143 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN"> +<!--Converted with LaTeX2HTML 97.1 (release) (July 13th, 1997) + by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds +* revised and updated by: Marcus Hennecke, Ross Moore, Herb Swan +* with significant contributions from: + Jens Lippman, Marek Rouchal, Martin Wilck and others --> +<HTML> +<HEAD> +<TITLE>Radial Velocity and Light-Time Corrections</TITLE> +<META NAME="description" CONTENT="Radial Velocity and Light-Time Corrections"> +<META NAME="keywords" CONTENT="sun67"> +<META NAME="resource-type" CONTENT="document"> +<META NAME="distribution" CONTENT="global"> +<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso_8859_1"> +<LINK REL="STYLESHEET" HREF="sun67.css"> +<LINK REL="next" HREF="node226.html"> +<LINK REL="previous" HREF="node224.html"> +<LINK REL="up" HREF="node197.html"> +<LINK REL="next" HREF="node226.html"> +</HEAD> +<BODY > +<BR> <HR> +<A NAME="tex2html2703" HREF="node226.html"> +<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next_motif.gif"></A> +<A NAME="tex2html2701" HREF="node197.html"> +<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up_motif.gif"></A> +<A NAME="tex2html2695" HREF="node224.html"> +<IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="previous_motif.gif"></A> <A HREF="sun67.html#stardoccontents"><IMG ALIGN="BOTTOM" BORDER="0" + SRC="contents_motif.gif"></A> +<BR> +<B> Next:</B> <A NAME="tex2html2704" HREF="node226.html">Focal-Plane Astrometry</A> +<BR> +<B>Up:</B> <A NAME="tex2html2702" HREF="node197.html">EXPLANATION AND EXAMPLES</A> +<BR> +<B> Previous:</B> <A NAME="tex2html2696" HREF="node224.html">Ephemerides</A> +<BR> <HR> <P> +<P><!--End of Navigation Panel--> +<H2><A NAME="SECTION000519000000000000000"> +Radial Velocity and Light-Time Corrections</A> +</H2> +When publishing high-resolution spectral observations +it is necessary to refer them to a specified standard of rest. +This involves knowing the component in the direction of the +source of the velocity of the observer. SLALIB provides a number +of routines for this purpose, allowing observations to be +referred to the Earth's centre, the Sun, a Local Standard of Rest +(either dynamical or kinematical), the centre of the Galaxy, and +the mean motion of the Local Group. +<P> +The routine +sla_RVEROT +corrects for the diurnal rotation of +the observer around the Earth's axis. This is always less than 0.5 km/s. +<P> +No specific routine is provided to correct a radial velocity +from geocentric to heliocentric, but this can easily be done by calling +sla_EVP +as follows (array declarations <I>etc</I>. omitted): +<P><PRE> + : + * Star vector, J2000 + CALL sla_DCS2C(RM,DM,V) + + * Earth/Sun velocity and position, J2000 + CALL sla_EVP(TDB,2000D0,DVB,DPB,DVH,DPH) + + * Radial velocity correction due to Earth orbit (km/s) + VCORB = -sla_DVDV(V,DVH)*149.597870D6 + : +</PRE> +<P> +The maximum value of this correction is the Earth's orbital speed +of about 30 km/s. A related routine, +sla_ECOR, +computes the light-time correction with respect to the Sun. It +would be used when reducing observations of a rapid variable-star +for instance. +Note, however, that the accuracy objectives for pulsar work are +beyond the scope of these SLALIB routines, and even the superior +sla_EVP +routine is unsuitable for arrival-time calculations of better +than 25 millisecond accuracy. +<P> +To remove the intrinsic <IMG WIDTH="36" HEIGHT="14" ALIGN="BOTTOM" BORDER="0" + SRC="img324.gif" + ALT="$\sim20$"> km/s motion of the Sun relative +to other stars in the solar neighbourhood, +a velocity correction to a +<I>local standard of rest</I> (LSR) is required. There are +opportunities for mistakes here. There are two sorts of LSR, +<I>dynamical</I> and <I>kinematical</I>, and +multiple definitions exist for the latter. The +dynamical LSR is a point near the Sun which is in a circular +orbit around the Galactic centre; the Sun has a ``peculiar'' +motion relative to the dynamical LSR. A kinematical LSR is +the mean standard of rest of specified star catalogues or stellar +populations, and its precise definition depends on which +catalogues or populations were used and how the analysis was +carried out. The Sun's motion with respect to a kinematical +LSR is called the ``standard'' solar motion. Radial +velocity corrections to the dynamical LSR are produced by the routine +sla_RVLSRD +and to the adopted kinematical LSR by +sla_RVLSRK. +See the individual specifications for these routines for the +precise definition of the LSR in each case. +<P> +For extragalactic sources, the centre of the Galaxy can be used as +a standard of rest. The radial velocity correction from the +dynamical LSR to the Galactic centre can be obtained by calling +sla_RVGALC. +Its maximum value is 220 km/s. +<P> +For very distant sources it is appropriate to work relative +to the mean motion of the Local Group. The routine for +computing the radial velocity correction in this case is +sla_RVLG. +Note that in this case the correction is with respect to the +dynamical LSR, not the Galactic centre as might be expected. +This conforms to the IAU definition, and confers immunity from +revisions of the Galactic rotation speed. +<P> +<BR> <HR> +<A NAME="tex2html2703" HREF="node226.html"> +<IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="next_motif.gif"></A> +<A NAME="tex2html2701" HREF="node197.html"> +<IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="up_motif.gif"></A> +<A NAME="tex2html2695" HREF="node224.html"> +<IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="previous_motif.gif"></A> <A HREF="sun67.html#stardoccontents"><IMG ALIGN="BOTTOM" BORDER="0" + SRC="contents_motif.gif"></A> +<BR> +<B> Next:</B> <A NAME="tex2html2704" HREF="node226.html">Focal-Plane Astrometry</A> +<BR> +<B>Up:</B> <A NAME="tex2html2702" HREF="node197.html">EXPLANATION AND EXAMPLES</A> +<BR> +<B> Previous:</B> <A NAME="tex2html2696" HREF="node224.html">Ephemerides</A> +<BR> <HR> <P> +<P><!--End of Navigation Panel--> +<ADDRESS> +<I>SLALIB --- Positional Astronomy Library<BR>Starlink User Note 67<BR>P. T. Wallace<BR>12 October 1999<BR>E-mail:ptw@star.rl.ac.uk</I> +</ADDRESS> +</BODY> +</HTML> |