WARP – Week 5

Captain’s log, stardate: -303838.

The Theoreticians

Battered, beaten and severely malnourished by a ship-wide tea shortage, morale among the crew was low, but their noble mission was finally coming to an end.

We plotted a new graph of T against g-i now including O and B stars. We found that there are two lines of best fit on this graph, one for low g-i values and one for high g-i values. In TOPCAT we added a subset that grouped bodies with high g-i values (g-i>-0.4) and found that all but one of our stars fell into this subset so we did not think it was necessary to calculate the line of best fit for the one star in the lower g-i portion. We found that the fit that was best for the high g-i values was a fifth-order polynomial and so created a new column in TOPCAT which calculated the temperatures for our bodies using this equation. With this temperature we created subsets for each star type using the temperature ranges mentioned in last week’s blog.

The crew gazed upon these purest of Milky Way travellers, in awe of their magnitude. Nothing could have prepared them for their sheer elation at the accomplishment of their goal. Starfleet would remember this.

As the Coding Wizards had extended their heatmap, we were given updated metallicities for our bodies and matched these with the data we already had to create one table with all values in. Using this table, we sorted by metallicity and created a naming system of decreasing metallicity named “WARP-” where the most metal-poor body was WARP-1. Using COSMOS Cutouts, we got images of the first 65 bodies (metallicities of less than -3) by inputting their RA and Dec. We attempted to determine whether they were galaxies or stars and found some potentially metal-poor stars!

Here is WARP-1. We know it’s not a single star due to its shape but it could possibly be a binary system and as it was our first (star) baby, we love it the most (don’t tell the others).

An image of WARP-1, what we believe to be a binary star system.

Below are our four best candidates for extremely metal-poor stars. They are all more circular bodies compared to a lot in the dataset, meaning they are more likely to be stars than galaxies which are typically shaped more like an oval.

Images of the four best candidates for extremely metal-poor stars.

The Coding Wizards

We wished to include black bodies in our theoretical plot as this would allow us to further the range of metallicity values used to create our heat map, however reliable and consistent results in NB392-u-(g-i) were not able to be produced. The black body results in g-i however are consistent with what is expected and as such this leads us to the conclusion that an error must arise due to either/both of the NB392 and u filters. A leading theory is that the similarity of said two filters and the lack of any absorption in the model of black bodies is causing the discrepancy.

We completed a refined heat map using the np.polyfit Python function to more clearly define the boundaries between the different metallic items on the plot. The np.polyfit function allowed us to extrapolate our data points such that the layers of metallicities that was expected could be successfully programmed in our code.

By comparing our actual data to the heat map, as shown in below figure, we obtained new values of metallicity and the errors in them.

The final heat map, the method we used to determine the metallicities in our observed stars.

This plot, while slightly unclear, greatly illustrates how our code can determine the possible metallicity of an actual star from the colour change of its magnitudes, by analysing its position upon this heatmap.

We have also created a plot of the number density of stars with respect to their spectral type, showing how dense stars of different metallicities are. The plot is shown below, however work still needs to be done to incorporate errors.

A plot of number density per spectral type where the y-axis is logged for convenience.

We also aim to soon (hopefully) rectify the error in the modelling of black bodies, such as possibly plotting the heatmap with another colour axis, to hopefully remove the error if it is in fact caused by the similarity in u and NB392.

And with that, WARP’s mission was complete. The crew reflected on their journey, a journey fraught with chaos, misery and excitement intertwined, and could not help but be saddened by its end. Picard admired his crew in a way only a captain can: with happiness, pride and an overwhelming sense of faith. Whilst he could not be sure of the voyage upon which they would next embark, he could be safe in the knowledge that his loyal crew would be right there at his side.

Note from Star Trek guy: That’s all from me – thanks for reading! I hope you’ve had as much fun reading these useless little paragraphs as I’ve had writing them. – James (Cdr. William T. Riker)

Note from the communications lead: I wanted to leave this blog saying how nice it has been writing this each week to summarise what we have accomplished. Even though for the past five weeks we have been unsure about what to do on many occasions as well as coming across many errors in our work, it is very satisfying to conclude we have finally found some bodies which we believe to be metal-poor stars! We may be posting over the next few weeks about figures or report writing but here is the end to all of our lab work! – Claire (Cdr. Deanna Troi)

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