Megan M. Kiminki
(formerly Megan M. Bagley)
My Ph.D. research with Nathan Smith revolves around massive stars, how they form, how they move, and how they impact their environment throughout their lives. Massive stars provide a lot of "feedback" to their surroundings in the form of energetic UV radiation, kinetic energy from stellar winds, and, most dramatically, supernovae.
Proper Motions of Eta Carinae's Outer Ejecta
Eta Carinae (η Car) is a Luminous Blue Variable, a very massive star nearing the end of its life that occasionally erupts in spectacular fashion. It is surrounded by material ejected from the star, including the massive, bipolar Homunculus, which was produced in η Car's Great Eruption of the 1840s. No theory has yet been able to fully explain the Great Eruption; we don't know whether η Car's behavior is normal for a very massive star, or if it is unique.
We've measured the proper motions of the outermost ejecta around η Car using eight epochs of Hubble Space Telescope images observed over 21 years. Through these data, we've learned that η Car erupted before, in the 1200s A.D. and likely also in the 1500s. Theories for the cause of this star's dramatic events must therefore account for their repetition and several-hundred-year timescale.
Star Formation in the Carina Nebula
Eta Carinae's home, the Carina Nebula, is one of the richest clusters within easy observational reach in our galaxy. The energy from many dozens of massive stars has eroded the neighboring molecular gas into dramatic pillars in which new generations of stars are forming.
Intriguingly, Carina's massive stars are found in several dense clusters, as expected, but also in a relatively distributed population across the 40-parsec region. Were they born in these positions, or did they migrate from birthplaces in the dense clusters? I am measuring their kinematics to find out.
Another question posed by the Carina Nebula is whether the new star formation was directly triggered by massive star feedback, or whether the erosion of the pillars merely revealed processes that were already ongoing. To tackle this question, I am looking at the relative three-dimensional motions of the young stars, massive stars, and gas structures that make up one of the pillars.
Massive Stars Across W3
The W3/W4 star-forming region, also known as the Heart Nebula, is another region where massive stars are thought to be playing a key role in driving star formation. An expanded bubble of ionized gas, heated by a star cluster in W4, has pushed into the W3 molecular cloud, compressing its gas into a dense layer. A string of small, young star clusters in that dense layer appear to have formed as a direct result of the compression.
However, our spectroscopic survey of W3 revealed a more extensive population of massive and intermediate-mass stars, suggesting that star formation had begun unprompted in the less-dense parts of the cloud roughly 8–10 million years ago. Massive star feedback does seem to have sped up the star-formation rate in the last 3–5 million years, but it is not the sole trigger of star formation in W3.
Learn more about this project in our 2015 ApJ paper.