Effects of Contamination on 4MOST Stellar Spectra

Sammanfattning

This paper discusses the effects of different types of contamination on 4MOST stellar spectra. Three main types of contamination were tested. These were, a smooth function over the continuum, changing the H-alpha line, and adding telluric contamination. By knowing how much these experiments affected the generated values, it was possible to understand the importance of avoiding overfitting or underfitting the continuum and removing telluric contamination. The effects of these types of contamination were compared to both a signal-to-noise ratio of 100 and 10. This gave insightful information into how long it will be necessary to observe stars to achieve the desired precision. Furthermore, the results were compared to the 4MOST criteria to better understand where to direct focus when trying to increase accuracy. [It was observed that degrading the H-alpha line by 10\% considerably damaged the estimation of $T_{eff}$.] Furthermore, for most elements a longer wavelength of a smooth function over the continuum created the worst estimations. In many cases this was worse than decreasing to a signal-to-noise ratio of 10. Additionally, an alternative method to find the continuum is presented. My method does not sacrifice the number of data points by averaging them, but instead uses a sliding window technique. By knowing what type of spectrum is expected, this method can yield very good results down to below 1K difference between the estimated surface temperature and the true value. The results in this paper are useful for understanding both what makes spectra bad and what to do to prevent these issues. Furthermore, there is no reason to expect that these results would not apply to non-synthetic spectra as well.