Line Widths

If the line width is less than 900 km/s when using the LWS01 or LWS02 observing modes or the line width is less than 30 km/s when using the LWS03 or LWS04 modes, then the parameter "Line Width" should be entered as "0" as input to the PGA-MDB software and to the time estimator (lws-te) software. This is because the resolution element is seeing all of the flux of the line.

If, on the otherhand, the line is resolved, then the linewidth in microns (given by:

linewidth = [ delta_v (km/s) / 3x10^5 km/s ] x lambda

where delta_v is the linewidth in km/s and lambda) should be entered.

The time estimator and the PH compute the flux from a resolved line in the following manner:

Flux[observed] = Flux[emitted] x 1 / SQRT [ 1 + ( linewidth / res )**2 ]

where res = the LWS resolution element in microns. (For LWS01 and LWS02 res is 0.29 um or 0.6 um, depending on if one is working shortward or longward of 90.5 um, respectively. For LWS03 and LWS04, res is found in Table 3, pg. 20 of the LWS Manual.)

This formulation assumes the line to be Gaussian and to be convolved by a Gaussian resolution element. The widths add in quadrature, and the ratio of the old to the new width scales the observed flux.