Analyzing the metallicities of Hot Jupiters in orbit around low-metallicity Population I stars and potential theories regarding their origin and propagation

Hot Jupiters are large exoplanets similar to the size of Jupiter with relatively short periods of orbit around their star. Though it has been recognized as a common phenomenon that Hot Jupiters are found around high-metallicity stars, it has been proposed that this is simply due to the greater ease of discovering exoplanets orbiting those stars due to their stronger spectral lines, or due to the greater chance of core accretion of gas giants near more metallic stars. In those scenarios, it would be quite possible that a greater number of undiscovered Hot Jupiters exist orbiting around stars with lower metallicity. However, since there have not been any Hot Jupiters discovered around a Population II star to date, it is necessary to define some boundaries in regards to this exploration. Here we (1) determine the abundances of Hot Jupiters in orbit around low-metallicity Population I stars, and (2) analyze the relationship between metallicity of a host star and the mass of orbiting Hot Jupiters. For the purpose of this paper, we chose to specifically examine low-metallicity Population I stars (defined in our study as having stellar metallicities less than or equal to 0 dex compared to the Sun). We set the upper limit to 0 as it gives us an objective way to define low-metallicity Population I stars. To compile the data used for this analysis, we used the NASA Exoplanet Archive and placed filters on certain parameters to limit the scope specifically to exoplanets with periods between 1.3 and 111 days, inclusive and masses of 0.36 to 11.8 Jupiter masses, inclusive (essentially eliminating planets that did not fit the Hot Jupiter parameter), as well as the metallicity parameter, <= 0 for the Stellar metallicity. We find that prior results are supported in that the abundance of Hot Jupiters increases rapidly with increasing metallicity. However, a key finding of our study was that the mass of Hot Jupiters around a home star has a weak association or even a slightly negative correlation with increasing metallicity. This means that lower-metallicity stars may actually be able to sustain high-mass gas giants despite their lower ability to provide a more metallic planetary core for core accretion. The presence of Hot Jupiters around low-metallicity stars is a significant point of inquiry as the conventional perspective has been that high-metallicity stars help facilitate creation of metal-rich planetary cores, which aid in core accretion in gas giants. If these processes are still possible to a certain efficiency in satellites of low-metallicity stars, there may be potential alternate explanations for exoplanetary formation. Moreover, it is important to note that optimization of exoplanetary detection methods to prevent some of the discrepancies faced in regards to demographics of the home star of a Hot Jupiter. Future analyses with a greater sample set of exoplanets, once they are discovered, would likely bring fruitful results in pursuit of these objectives.