August 20, 2014
Newly-Released Hypatia Catalog Offers Glimpse Into The Lives Of Stars
April Flowers for redOrbit.com - Your Universe Online
The largest catalog ever assembled for stellar compositions was unveiled this week by Arizona State University (ASU) alumna Natalie Hinkle. Hinkle, who graduated in 2012 from ASU with a doctorate in astrophysics, named her project the Hypatia Catalog after one of the first female astronomers who lived ~350 AD in Alexandria. The catalog is described in an upcoming issue of The Astronomical Journal.
The new catalog is critical to understanding the properties of stars, the mechanism of their formation, and the possible connections with orbiting planets. Hinkle's results revealed that the composition of nearby stars isn't nearly as uniform as once believed.
Physically sampling a star is impossible, so researchers use the star's light to determine its composition in a process called spectroscopy. Because spectroscopy allows scientists to gain information about the temperature, density, composition and important physical processes of an astronomical object, it is one of the most important tools an astronomer has.
The Hypatia Catalog is a digital compilation of spectroscopic abundance data from 84 literature sources. It encompasses 50 elements across 3,058 stars within 500 lightyears of our Sun. Essentially, the catalog is a listing of the composition of the stars, but only those relatively near the Sun, and only those like the Sun (F, G and K-type stars).
"This catalog can hopefully be used to guide a better understanding of how the local neighborhood has evolved," Natalie Hinkel, who is now a postdoctoral fellow at San Francisco State University (SFSU), explained.
To compile such a comprehensive accumulation of other researchers' work required Hinkle do to extensive background research. The first fifty datasets alone took nearly six months, while the total project was nearly two years in the making. The catalog was started as part of Hinkle's dissertation at ASU and underwent editing and revision while she was at SFSU.
Hinkle used Vizier, a database where researchers can post their astronomical data, as a starting point. Not everyone posts to Vizier, however, meaning that Hinkle had to transcribe the data from many studies by hand.
Hinkle envisions a wide number of applications for the Hypatia Catalog, including use by astronomers who are searching for stars that host exoplanets.
"Since 1997, we've known that stars with giant, Jupiter-like planets have quite a bit of iron in them. This result has been reproduced dozens of times. However, with a catalog of this magnitude, we can now study literally all of the other elements measured in stars in great detail to see if there are relationships between the presence of a planet (gaseous or terrestrial) and the element abundances," said Hinkel.
Another application with great promise is the ability to compare the abundances of stars that rotate slowly with those that rotate quickly. This would allow researchers to determine if there is an association between chemical composition and rotation speeds.
While compiling her work, Hinkle noticed that the stars in our solar neighborhood had unexpected compositions. The Sun, and the vast majority of the Milky Way's young stars are in the disk at the center of the galaxy. The stars all rotate in the direction of the disk's rotation, as well as make small, random movements.
"You can think of this like a swarm of bees: While the swarm in general moves, the bees themselves are going in all different directions. Because of this motion within the disk, the stars are considered to be well mixed – like a tossed salad. Therefore, you don't expect to see, for example, a whole tomato in your salad – or many stars that have similar abundances in close proximity to each other," explains Hinkel.
Hinkle was surprised to find, however, that the nearby "solar salad" isn't really mixed, it is layered. It has lettuce at the bottom, chunks of tomato in the middle (where the middle of the galactic plane is), and lettuce again at the top—at least, if you think of stars that all have high abundances of quite a few elements as lettuce, and stars that have low abundances of those same elements as tomatoes.
"Given all of the motion in the galaxy, this was a very unexpected result. But it's also very exciting," says Hinkel.
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