SIMPS: Search Into Metal-Poor Stars

Week 1

The first week was mainly getting to grips with what we plan to do with our project. Our theory lead, James, along with Paula and Joshua, hit the internet to search through the vastness of astrophysics papers in order to gain deeper understanding of what metal-poor stars are, why they form and what that implies about the early Universe. There were many papers available (some even referenced Sobral’s work!) and a lot of reading to do, but our theorists gathered the knowledge we would need to embark on our journey.

During our first lab session, Joshua and Paula got to work on our introduction for the final report (to lessen the workload later), whilst myself, Joe and James looked at how WARP cut the catalogue down to their potential candidates. This allowed us to get to grips with the software we will need, whilst familiarising ourselves with the contents of the COSMOS catalogue. We decided to use the WARP conditions and worked on TOPCAT to make the cuts. The first few cuts went without a hitch and we had the source numbers that WARP had gotten. However, we ran into some issues when working through the error conditions; we were ending with 628 sources, whereas WARP had 338. Although this wouldn’t be affecting any results that we would be reaching, it was interesting as the difference seemed so large. After consultation with David, we concluded that there may have been a mistake on either parties end. We reminded ourselves that the point wasn’t to get the same results as WARP, but to familiarise ourselves with the data and software. We produced an on-sky graph of the 628 sources we arrived at.

Figure 1: On-sky positions of the sources. White gaps are due to missing data and omission of very bright sources.

Joe, our code lead, then got to work on coding an algorithm that would produce stellar spectra for 81 candidates (identified by LAMPSS and WARP, of which they concluded 23 were metal-poor stars) and compare them to various model stellar spectra and give the best model for each candidate. There are 85 models, organised by metallicity and temperature , respectively. When looking at the low resolution spectra, we found that many appeared to be potentially galactic in nature(the spectra trended up, rather than down), meaning many of the 81 candidates may not be stars.

Our lab concluded with the algorithm partially complete. Joe went away and worked on it, but we ran into an issue with comparing the spectra to the models. We talked to David and he suggested we log the flux axes on both the model and the stars to make comparisons. More algorithm work was needed!