Makali'i Instructions

Getting Started in Makali'i

Having started Makali'i, click the [Open] button in the toolbar to display the file opening dialog. Select a FITS file and click [Open]. The image will be displayed in a new window. You can move a mouse over this window to show the x and y co-ordinates in the information bar towards the top left of your screen. The 'counts' value of each individual pixel and the average count value of the overall image will also be displayed here. If the FITS header of the image contains WCS (World Coordinate System) information, that is also displayed (this gives the RA and dec of the cursor's position).

Below is a screencast originally produced in two parts; the first two minutes give a basic introduction to the features of Makali'i and from around 2.15 onwards, you can see how to use Makali'i to perform photometry. You can also download the video to your device (21MB).

From the image taskbar, you can alter the brightness of the image or change the colour mode. The contrast of the image can be adjusted by dragging the triangular sliders (one black, one grey) or by typing the minimum and maximum levels, which are on either side of the triangular sliders. If an image has a high contrast, you can view it more easily by checking the [Log Scale] check box. To adjust this automatically, you can use the [Auto Adjust] button. To change colour, use the [Color Mode] drop down menu, whose default is 'Gray Scale'. Many astronomers prefer the reverse of this as it is easier to view an image with dark stars on a lighter background. This is also an appropriate choice if you are intending on printing this image. There are also 'Zoom in' [+] and 'Zoom out' [-] buttons on this menu.

A 'cut' along a line segment can be made by using the [Graph] button in the tool bar. Using the mouse, a line can be drawn on any part of the image, which will produce a graph of the pixel values along that line. F3 and F4 can be used to hide and display the graphical mode.

From the dropdown menu under 'Image', it is possible to flip the image along a horizontal or vertical axis or rotate it to a specific angle or trim the image. This may be useful since some telescopes produce images that are upside-down when compared with their true orientation as given by an astronomical image database such as Simbad.

Photometry

Aperture photometry allows a measurement of the brightness of an object to be made. It is done by calculating the number of 'counts' within a specific radius having accounted for a sky value. This sky value represents the average amount of background light in that part of the image and is automatically subtracted by the software.

Start by clicking on 'Photometry' from the icon in the top toolbar (or from the dropdown menu in 'Processing') and selecting the 'Aperture' mode. The 'Aperture Photometry' box that opens has some options that you will need to change.

Within 'Radius', [SemiAuto] should be selected. This performs aperture photometry based on the star with star, sky and sky radius specified by the user. The [Find Center] check box should be ticked as this corrects for slightly inaccurate placing of the cursor with respect to the star's centre on the image. The default 'Search Centroid' option of 3 pixels is suitable for most photometry.

[Radius setup] can be used to specify the photometry parameters. The [Default] button returns the values to the default values of Makali'i. [Auto] performs aperture photometry with the star's radius, sky radius, sky radius width and the centroid calculated automatically. This method should not be used since the software will alter the aperture from one star to the next making 'like-for-like' comparisons difficult. The consequences of using differing values for the star's radius can be seen in Figure 2 of this page. For most images, a radius  of 10 - 12 pixels is usually suitable. This is the 'Star' value. It is necessary to change the 'Sky' value first to around 15 pixels and using a 'Sky Radius' of 5 pixels.

[Hide] hides the apertures on the image. [Show] displays all the apertures on the image. To remove apertures (and their associated measurements), you can use the [Remove] or [Remove All] buttons. Pushing the {black triangle} button can hide or display the [Radius] settings within the photometry results page.

You can now measure each star simply by clicking on each one in turn and noting that several values are added to the 'Aperture Photometry' box.

Saving Your Data

Once you are finished with a particular image, you can choose to save your photometry values within the FITS file. You will see "Aperture Photometry result does it save at extension?'' (This is an awkward translation which means "Do you want to save the results of aperture photometry in the extension?''). If you click [Yes], the results of the aperture photometry will be saved and can be reproduced when the image is opened again.

The results of the photometry can also be saved using the [Print] button within the 'Aperture Photometry' box in either .csv or .txt format.

Once you have your photometry stored in this format, you will need to make some calculations to convert these counts into magnitudes from which you can plot your own colour magnitude diagram. Finally, you can upload your data to see how your cluster looks.

Find out how to plot your data.

Read more about photometry.

Upload your data.