The Universe full of hydrogen and … a new feature in LabPlot

The Universe is full of the hydrogen and one of its emission lines that is very important in astronomy is caused by the hyper-fine interaction. This electromagnetic radiation has the frequency of ca. 1420.4MH which corresponds to the vacuum wavelength of ca. 21cm.

Observations performed at this wavelength reveal many structures in the Universe. The following plot shows the results of such observations in the Milky Way:

Hydrogen in the Milky Way

The background image used here represents an all-sky survey with radio telescopes at the wavelength of 21 cm. the image uses false colors to show the information and the plane of our Milky Way galaxy is the lighter stripe running horizontally through the center.

The curve shows the intensities observed at longitude 90° and latitude 0° (galactic coordinates). The first peak with the greatest intensity corresponds to the emission in the local hydrogen cloud, while the two peaks with smaller intensities are mapped to clouds in the Perseus and Outer arms, respectively (data taken from here). Because of their velocities relative to us and because of the Doppler-Effect, the frequencies for these two spiral arms appear to be blue-shifted. See link 1, link 2, link 3 and link 4 if you want to read more about this.

Besides the very interesting results shown here, this plot also shows a new feature in LabPlot: the Info Element.

This Info Element allows you to annotate values and positions in a plot. You specify the value that needs to be highlighted/annotated and the position of the text label, as well as the properties of the lines (the connection line and the vertical line, if needed) can be freely changed. The Info Element sticks to the specified position during the navigation in the data.

The new Info Element is also easy to use when the same position needs to be annotated for multiple curves in the plot. To do this, select the curves and specify which curve to use to connect the line to. The final result can look something like what you see in the following plot:

Helium Rydberg-Spectrum
This image shows the Rydberg-spectrum of helium trapped in a magneto-optical trap. The selection of curves, as well as all the other properties of the Info Element, is performed in the Properties Explorer of the selected object:

Info-Element Properties
Here, we asked to place the “markers” on all three curves showing the data for three different configurations (pulse duration) of the laser.

The properties of the text shown in the Info Element are modified in a similar fashion to the properties of the usual text labels, but include the additional syntax for “placeholders” for x- and y-values:

Info-Element Text Properties
Note how the x-value and the corresponding y-values of the selected curves are referenced here via the &(x) and &(curve_name) syntax respectively. There is no need for you to manually read off the the values, as LabPlot does this automatically for the current position of the Info Element in case the values are referenced via this syntax. With this, the Info Element can be considered as an additional method to define the plot legend.

Finally, the properties of the connection and of the vertical lines are modified similarly to other line objects on the worksheet:

Info-Element Lines Properties
The Info Element has already reached LabPlot’s master branch and will be part of the next release 2.9. If you’d like to use it now and test it and provide feedback, please grab the nightly builds available for all supported platforms. See download section for details.

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