The rotation velocity, V, is determined from a terminal velocity V_t in
the usual way:

but corrected for a dispersion factor sigma. The terminal velocity is defined by the velocity at which the intensity becomes equal toV = (V_t - V_sys)/sin(i) - sigma

where I_max is the maximum intensity in the map, and I_lc the lowest contour (usually 3 times the noise in the PV diagram). Both eta and I_lc can be set via parameters to the program. Typical values for eta = 0.2 - 0.5.I_t = sqrt( (eta*I_max)^2 + (I_lc)^2 )

In addition, this program will also perform the usual peak fit, gaussian fit, and simple first moment analysis. See OUTPUT below for the output format. For lower inclinations, the envelope tracing method should give simular results to the other methods.

MET = Modified Envelope Tracing method (Gentile et al.,
see below)

where sigma is really the quadrature sum of three components representing the ISM, instrumental resolution and beam smearing.V = [ |V_t - V_sys| - 0.5 sqrt(sigma^2 * 8ln2) ] / sin(i)

WAMET = WArped Modified

Envelope-Tracing method

**in=**- Input image file - must be an PV
*image(5NEMO)*with position along the 1st axis, and velocity along the 2nd. Units are not important. Use**ccdsub reorder=xzy**for an X-Y-VZ cube to be properly reordered. No default. **eta=**- [0..1] weight factor for I_max adding to I_lc. [Default: 0.2]
**ilc=**- Lowest Contour value. Normally taken as something like 3 times the noise level. [Default: 0]
**sign=-1|1**- Designates rotation of the galaxy. This is only important for tracing the ’right’ part of the PV diagram. sign=1 is meant for PV diagrams where the approaching side is for positive positions. By using the "wrong" value of sign you can find out something about the radial extent of the tracer, as for large radii this would cause small values of dV/dR. For a known rotation curve using sign=1 one could determine the radial extent from sign=-1. [Default: 1]
**sigma=**- Velocity dispersion correction factor. This includes both the observational resolution as well as the velocity dispersion of the tracer component that is being observed. [Default: 0]
**clip=**- Clipping values to aid removing noisy values around 0. If value(s) given, signal will be clipped as follows: if one value given, clipping occurs between -clip and clip. If two numbers given, clipping occurs between clip(1) and clip(2) . Default: None
**vsys=**- Systemic velocity of the galaxy. Since the velocity axis (assumed to be the 2nd or Y-axis), this number is simply subtraced from each velocity determination. [Default: 0]
**inc=**- Inclination of the galaxy. Each rotation speed is corrected by sin(inc). [Default: 90]
**center=**- Center of the galaxy along the Position axis. [Default: 0]
**rotcur=t|f**- Should a folded rotation curve be tabulated? If so, negative positions will have both position and velocity with a positive sign, thus creating two rotation curves, receding and approaching, which can be plotted on top of each other and compared. [Default: false]
**out=**- Output file in case input file was a cube and output is now a map, not a table.
**mode=**- Which of the output modes (see OUTPUT below) will be used for the output map. [Default: 2]

1position from the P-axis of the PV diagram 2envelope tracing (corrected with vsys, sini, and sigma) 3first moment (sum(I*v)/sum(I)) (corrected with vsys, sini) 4velocity at peak of signal 5velocity at peak of parabolic fit of 3 points at peak signal 6gaussian fit 7half gaussian fit 8half gaussian fit, with for MET correction

The MET mode is still not very robust, clipping helps.

Sancisi & Allen 1979 Sofue, Y. 1996 ApJ 458, 120 Sofue et al 1997 PASJ 49, 17 Sofue et al 523, 136 Sofue et al (1997AJ....114.2428S) Gentile et al. (2004MNRAS.351..903G) - MET/WAMET method

src/image/rotcursources

5-May-01V1.0 CreatedPJT 6-may-01V1.1 clip=, interpolated to find tracePJT 18-mar-09V1.3 added rotcur=PJT 9-jun-09V1.4 implemented MET=PJT