WARP – Week 1

Captain’s log, stardate: -303916.

Captain Picard boldly utilised the Napoleonic phrase of “divide and conquer” he had heard often during his Starfleet training by cutting the problem in two and tackling each separately. His team had two contingents: The Theoreticians and The Coding Wizards.  

Here is the progress of each of the teams:

The Theoreticians

Our theory team began by deducing conditions which can reduce the number of bodies in a catalogue. Doing this means that we can then use the reduced catalogue to look for metal-poor stars in more detail.

The first step was to find a way to filter out galaxies from data as we just want to look at stars. This was done by uploading the INT data of over 120,000 bodies into TOPCAT and creating subsets containing bodies we deem to be stars and galaxies, using their observed redshift, z, where z=0 for stars and 0.5<z<7.0 for galaxies. We then plotted these subsets on a graph where both axes were magnitude differences (e.g. J-K against B-V) and tried different combinations of colour bands (magnitudes) until we found a plot which gave the best separation of stars and galaxies. The best separation was U-J against J-K so we placed a cut at (where we deemed to be) the best division of groups. This graph is shown below.

Two sets of magnitude differences create a division of stars, in blue, and galaxies, in green, which can be best separated with a cut, ss.

It can be seen on this graph that there is contamination of stars in the galaxies portion (under/to the right of the cut) and vice versa. This contamination is shown for the whole set of data in the figure below.

The contamination of galaxies in the stars portion, and vice versa, from the sample, can be clearly shown over the whole dataset.

Next, we created various subsets to filter out galaxies and data points which had been given extreme values (bodies that are too faint to observe) which were then applied to the whole catalogue and created a graph containing only the possible metal-poor stars.

When the galaxies are filtered out using subsets, only stars are left which we can then use to potentially find metal-poor stars.

The Coding Wizards

Our coding team, consisting of Picard and Lieutenant Commander Data, were the first of our intrepid explorers to encounter a problem, materialising in the form of the code producing totally unrealistic results.

For example, we considered and processed data for a sun-like star (G type, Temperature=5000K) and received absolute magnitudes of approximately -80, which is highly physical. The expected values are about 4.8. We attempted many different ways to resolve this problem such as analysing the units of the produced result to see whether we had made an error when we created the mag output equation, however, there was no such resolution this way.

Upon consulting our mentor D. Sobral, we then checked that our code would produce the correct luminosity of a sun-like star at 10pc. Our value was an order of 18 off the correct value. This allowed us to determine that the cause of our errors was due to the assumption that we had made about the data. We had assumed it would be flux at 10pc and produce absolute magnitude.

Picard and Data believed treachery to be afoot!

Checking the luminosity our data produced for a Sun-like star (assuming the star to be at 10pc) allowed us to determine the ratio between the expected value of luminosity and the value we observed, multiplying our calculated flux by this ratio allowed us to correct for our error and receive sensible results.

Picard and Data’s fears were confirmed as the measurements of flux were found to use units of measurement unlike any found in Federation space, leading to speculations of espionage…

We then processed the data for a variety of stars of varying metallicities, ranging from -5.0 to 0.0 and started to produce theory graphs.

The first attempt at a colour-colour theory graph for spectral types and metallicities.

In conclusion, we had a little bit of a scream, but it all went pretty well for the first week. We’ve all mostly gotten to grips with the software and the code respectively, and we’re all set to keep up the good work next week.

Next week Picard and Data will continue to refine and perfect their data and produce a series of theory colour-colour graphs on the metallically and spectral types of stars. These will be utilised by La Forge, Riker and Troi to determine which of our vast catalogue of bodies could indeed be metal-poor stars.  Guinan, meanwhile, shall delve into the history of metal-poor stars, their inception and their subsequent discovery, for if we are ever to find these elusive celestial inhabitants, we must first truly understand them…

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