Week 1: A Strange Trimester

Hello everyone and welcome to the first week of my SRP blog! The past week has been a very interesting experience; the thought of my last trimester at BASIS being outside of BASIS is more intimidating than liberating. Nonetheless, week 1 was slow but productive. I've begun reading the literature I chose regarding the SRP, as well as other sources provided to me. Besides that, I've also started reviewing the terms I would need to know to understand how to play around with the HR diagram.

Dr. Rieke provided me with a website interface for plotting and manipulating isochrones by inputting various parameters and selecting specific photometric systems. The nomenclature of the input fields as well as what each parameter does is something I will have to learn. My main goal for the next three weeks is to experiment with different systems and to find out how the HR diagram works.

Here's the interface for anybody who's interested: http://stev.oapd.inaf.it/cgi-bin/cmd

I am planning to talk about the underlining terms and tools I will be working with for the duration of my project on this blog. As this is the first week, I find it fitting to discuss the Hertzsprung-Russell diagram, as it is the most important figure in my research.

The Hertzsprung-Russell diagram was created by Henry Norris Russell and Ejnar Hertzsprung in 1910. The HRD is a scatter plot which consists of points representing different stars. The y-axis of this graph is labeled luminosity or absolute magnitude, which are both measurements of hypothetical brightness as seen from the Earth. Luminosity increases as we move up the graph. The x-axis features the temperature of the star in Kelvin, which also means it shows what spectral type the star is. The temperature and spectral type can be predicted by recording the color of the star. What we know from black-body radiation tells us that light radiated at a shade of blue is a higher temperature than light radiated at a shade of red. Temperature increases as we move to the left of the graph.

The Y-axis sports the luminosity and absolute magnitude, while the X-axis sports the color, temperature, and spectral class of the star. Different bands of stars are visible through purple lines on the scatter plot.

This is the most basic description of the Hertzsprung-Russel diagram. There are other components and features of the HRD that help us understand star evolution. Regions of the scatter plot are designated as different stellar bands, such as white dwarfs, supergiants, giants, and the main sequence. Negatively sloped diagonal lines can be plotted across the HRD which represent different solar radii (in relation to our sun); the higher up the line on the graph, the bigger the solar radius.

The stellar bands can be seen on the graph. The solar radii are the diagonal lines seen throughout the scatter plot. It's important to note the classes of stars on the X-axis along with photometric colors and temperature.

The most important component of the HRD and the one which is the focus of this project is the isochrone. An isochrone is a curve on the HRD which represents a population of stars which are the same age. Stars switch between isochrones throughout their lives as they fuse hydrogen and near their stellar endpoint (be it black holes, white dwarfs, or neutron stars). Isochrones are important tools in predicting the ages of stars, as they are used as theoretical standpoints that can later be compared to open clusters (clusters of stars all born at relatively the same time) to conclude the validity of the isochrone as an accurate representation.

An example of 3 different isochrones plotted on a segment of the HRD with each color being its own isochrone. Every plotted point on the graph is a separate star. The color spectrum can be seen on the x-axis, and the magnitude can be seen on the y-axis.

That's it for this week folks. I look forward to week 2, as that is the week when I begin my internship at Steward. I'll see everyone next week!