College of Arts and Science Hosts First Speaker of the Spring

Dr. J. Andrews discusses the spectra of star Eta Carinae before its eruption

On Jan. 23, 2020 the College of Arts and Sciences at the Prescott campus of Embry-Riddle Aeronautical University hosted speaker Dr. Jennifer Andrews from the University of Arizona to speak about the spectra of the star Eta Carinae before its great eruption in the 1800s. Dr. Andrews does research at the Steward Observatory at the University of Arizona campus. Presenting with a PowerPoint and ample information, she spoke about what is considered “one of the most exciting and enigmatic massive stars in the Milky Way,” per her abstract. 

Dr. Andrews began the talk discussing the background behind star formation and death, going into where massive stars and supernovae were located on the Hertzsprung-Russell (H-R) diagram. Revealing incredible facts about how massive stars can evolve, Dr. Andrews shared that her “work is on how to look at supernovae and find out where it was on the H-R diagram before.” Dr. Andrews also addressed more background information on the origin of some Solar System elements. Solar System elements are the larger elements on the periodic table of elements, typically found in explosions of large and massive stars. 

With this context out of the way, Dr. Andrews moved into the purpose of her talk, which was to delve into why the star Eta Carinae looks the way it does today and learn about its great explosion – or attempt at one. This was mentioned because the star didn’t completely explode, as revealed by its spectra. 

Moving into the data behind Eta Carinae, Dr. Andrews showed the audience a light curve of the star over time, which included when the brightness of the star was perceived to have spiked and when the brightness was perceived to have dimmed. This light curve showed when the great eruption was determined to have occurred in the mid-1800s. Dr. Andrews also added that the star “lost about 10 to 20 Earth masses of material during the explosion.” She noted, as well, that the light curve was also a reflection of the progression of modern astronomy and the advancement of observation techniques.

Next, Dr. Andrews moved into light echoes, stating that they were like “time machines.” This is because, with light echoes, astronomers can learn what happened to the stars in the past. The light echoes are produced by dust clouds reflecting light to Earth. Graphical ellipses were used to show how the light echoes worked and Dr. Andrews explained how data is collected from the light echoes. The collected data is analyzed by looking at its spectra to figure out what exactly happened at particular times in the history of the star. This also helps in aligning the timeline of the star to the light curve data that had been collected since the early 1800s or, in the words of Dr. Andrews, using “light curves and spectra to see the physics that’s happening.”

Based on all of these observations and research into Eta Carinae, Dr. Andrews stated that “in fact, maybe Eta [Carinae] started out as a tertiary system.” According to Dr. Andrews, the data says that this is a plausible hypothesis and showed her audience an accompanying graphic of how the explosion may have occurred. 

Dr. Andrews is currently working on identifying what happened before the explosion using the light curves. From the light echoes, she maps out a possible light curve and tries to match it to the logged light curve of brightness from other astronomers, former and current. In turn, this research can be used to understand other stars as well. Dr. Andrews shared that the light echoes can be helpful for better understanding of ancient events. The talk closed with applause and many questions that shared how engaged the audience was at the first talk of the Science Spring Speaker Series.

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