A world hundreds of light years away: Exoplanets Host Stars
By Lucia Wei
When we are thinking about stars, we usually picture those points of light twinkling in the night sky, including our sun. But what about the stars far beyond our solar system, those that host entire planetary systems of their own? These kinds of stars are called exoplanetary host stars, which refer to stars outside our solar system that host planets and form planetary systems, use an example to illustrate, that it’s just like our sun. The more exoplanet host stars we explore, the more we can predict the future of our galaxy by analyzing their life trajectories. The objective of this article is to analyze data of host stars from the NASA Exoplanet Archive (NASA Exoplanet Archive, 2021) that will be presented in the form of an H-R diagram.
The columns involved in the analysis include stellar effective temperature [K], distance [pc], B (Johnson) magnitude, and V (Johnson) magnitude. stellar luminosity [log (luminosity/solar luminosity)], Luminosities that were originally provided in logarithmic form in the dataset were converted into a linear scale by applying the exponential function. Different spectral types of stars were color-coded to highlight the temperature and luminosity trends of various stellar classifications. The data was processed and analyzed using Python. Data manipulation was performed using the Pandas Library, and the H-R diagram was plotted using Matplotlib.
Data for this article was obtained from NASA's Exoplanet Archive. It contained information on hosts' stars, including luminosity, spectral type, and effective temperature. By plotting the information on an H-R diagram, a clear pattern appeared. A main-sequence star is a diagonal band tending from a hot, bright star in the upper left to a cooler, fainter star in the lower right. Most exoplanet host stars are found along the main sequence, where the prominent diagonal band extends from the upper left (hot and bright stars) to the lower right (cool, dim stars). Additionally, there are few Red Giants and Supergiants in the main sequence; they appear cold and bright. You'll also notice a few stars that fall outside this main sequence. These are the Red Giants and Supergiants, stars that have moved on from their main sequence phase, which appear bright and cool, having expanded greatly in size after exhausting the hydrogen in their cores. (NASA Exoplanet Archive, 2021).
Interestingly, the main sequence stars in this diagram predominantly belong to the F to M spectral types. This is likely because these stars, particularly the ones rich in metals, are more conducive to forming planets, metal elements are crucial for the formation of exoplanets. Host stars with spectral type F and later have richer metal elements in their molecular clouds compared to OBA stars. The planet occurrence rates of gas-giant planets, gas-dwarf planets, and terrestrial planets are about 9.30, 2.03, and 1.72 times higher for metal-rich stars than for metal-poor stars, respectively (Wang & Fischer, 2014). Therefore, they are more likely to form exoplanets Another reason for this is that current observations are focused on finding host stars similar to our solar system, so the results showed up were mostly FGK stars. On the other hand, you might wonder why there are so few OBA stars in the diagram. The reason is that these massive and luminous stars are harder to study using the common methods astronomers employ to detect exoplanets. Both the radial velocity and transit methods are less effective at detecting planets around such stars, which is why they appear less frequently in the data.
The H-R diagram maps the temperature and luminosity of stars and offers important insights into space travel and colonization. It not only helped classify different types of host stars based on their properties but also assisted in predicting their habitable zones. By understanding where a specific star fell in the diagram, astronomers can predict host stars' habitable zones and identify suitable planets for future human colonization.