Brian Jackson

Good talk today from Karen Collins, a graduate student in U of Louisville’s Physics program.

Artist’s illustration of KELT-6b, a Saturn-like alien planet announced in June 2013. From http://www.space.com/21431-saturn-like-alien-planet.html.

She spoke about her work in ground-based observations of exoplanet transits, which are impressively simple but amazingly powerful for revealing new planets and telling us about already known planets.

Collins helped discover and confirm the Saturn-sized planet KELT-6 b (pictured at right), in a roughly 8 day orbit around a metal-poor F-type star.

This is a particularly interesting discovery because gas giant planets seem to prefer forming around metal-RICH stars, where there was more material to form planets. But KELT-6 b seems to buck that trend, and this result may point to something unusual about the planet’s formation and history.

Light emitted by the star HD105 and the debris disk orbiting it. From Donaldson+ (2012) — http://adsabs.harvard.edu/abs/2012ApJ…753..147D.

Great talk today from Jessica Donaldson of University of Maryland Astronomy about observing circumstellar debris disks.

These disks represent the fragments from collisions between rocky bodies, themselves orbiting the star and some of which go into forming planets around those stars. Light from the stars heats the dust, and so it emits infrared (IR) radiation that astronomers can distinguish from light emitted from the star (see figure at left).

By studying this IR emission, astronomers attempt to understand how far the dust is from its host star and whether it is in the places where astronomers expect planets to form. The emission can also tell us about the composition of the dust.

Donaldson described her work refining techniques to tease that information out of datasets collected by the Spitzer and Herschel spacecrafts. Her work has suggested, for example, that the dust observed around some stars has a composition similar to that observed in dusty comets orbiting the Sun.

Dr. Andrea Banzatti of the Space Telescope Science Institute visited today and talked about observing infrared (IR) light emitted by water vapor in protoplanetary disks.

Artist illustration of a protoplanetary disk. From http://www.keckobservatory.org/index.php/gallery/detail/milky_way/32.

Planets like the Earth are born in these protoplanetary disks, the gas and dust leftover after a star forms, and by analyzing IR light, Banzatti can estimate how much water there is in a disk and how hot it is.

Water is a key ingredient in planet formation, especially for gas giants like Jupiter, and of course, a key requirement for life. So by learning about how much water is in disks, Banzatti is helping us understanding the earliest stages in planet formation and the origins of life.

Banzatti developed a new technique to study the temperature and abundance of water in disks, and his results suggest that ice grains actually migrate around the disk, in ways that have been expected but not observed.

3D view of the inner part of a collapsing gas cloud, forming a star, where a bundle of twisted magnetic field lines is surrounded at the “waist” by a dense ring. The star is shown as a red dot located near the inner edge of the ring.

Good talk today from Bo Zhao of UVA Astronomy about the effects of magnetic fields on the formation of binary stars.

Binary stars are very common, and about half of all stars have such a celestial companion. Moreover, several exoplanets have now been found in binary star systems. So the formation of these stars touches on many astronomical topics.

Bo described how magnetic fields can control the orbital evolution of binary stars and influence the accretion of mass by the stars. For example, magnetic fields can sculpt the shape of accretion disks around the stars into complex shapes, filaments and strands (as shown at left).

Since these accretion disks mass onto the young stars, understanding their shapes, dynamical evolution, and the effects of magnetic fields on both these are important for understanding the population of binary stars we can see.

Model (top) and observed (bottom) infrared images of the debris disk around HD 15115. From Rodigas+ (2012).

Great talk today in the astronomy seminar from our own Dr. Timothy Rodigas.

Dr. Rodigas talked about several topics related to debris disks around stars. The colors and shapes of these disks can tell us about the compositions of planet-forming materials around the host stars and about the possible presence of otherwise unseen planets.

Without any planets in the system, debris disks are thought to take on very simple shapes, so if an astronomer finds a disk that warped or asymmetric, that can be evidence for a planet gravitationally sculpting the disk.

Dr. Rodigas presented the results of theoretical calculations that showed how the width of a sculpted debris disk can be used to put an upper limit on the mass of a planetary companion — very useful if you’re an astronomer trying to decide where to look for planets.