Background Method

This list box chooses the mathematical method used to estimate the sky background level from pixels in the outer annulus. If there are contaminating objects in the background annulus, choose Modal Brightness, which does a good job of rejecting outlying values. If the fields of view is fairly sparse and it is unlikely that any objects contaminate the background annuli of the stars, the other 2 methods may be chosen.

Exposure Time Reference

This parameters selects the time stamp that goes into the Photometry Measurements report. The time of the observation is calculated from the date and time of observation from the image header and the exposure time, following the rule you select here.

Julian Date Type

Select the type of Julian Date to be reported in the photometry table. The options are Heliocentric JD, Geocentric (normal) JD, and Modified Julian Date for both heliocentric and geocentric forms. The selection is listed in the Photometry Report; see Photometric Measurement Definitions.

Julian Date Offset

Enter the value to subtract from Julian Date listed in the photometry Report window. If desired, the number may be fractional, such as 2453000.5. After clicking [Apply] or [Save] the photometry report is updated with the new Julian Date including the offset.

Drawing Mode

This list box provides alternative ways of drawing the photometry markers on objects.

Keywords

Click this button to open the Photometry Keywords dialog. There you setup keyword names used by aperture photometry to load parameters from the image headers.

Verbose Messages

Displays verbose text messages that tell about the photometric measurements.

Calculate Airmass

If checked, the airmass is calculated for each image using the standard header keywords (see Photometric Keywords). If not checked, the airmass for each image is taken from the AIRMASS keyword in the image header.

Note: This option should be set as desired before marking points on the image, becasue the airmass is listed for each measurement. If you change this option after marking any points, you can cause all points to be re-measured by clicking [Re-center] on the Points page.

Inlcude Zero Point Error

Check this box to include the uncertainty (error) in the photometric zero point to the internal error of the measurement. If checked, the reported errors include these two error terms added as the root sum of squares. If you change the checkbox after measurements are made, click to recalculate the errors in the Photometric Measurements Report.

Default Name Format

Enter the Prefix to use for the names of marked stars. A number is appended to this entry to make the default name for each marked object. However, the default name can be overridden using the Edit button on the toolbar.