Dr. Gail Zasowski — “Near-IR Explorations of the Diffuse Interstellar Medium”

Posted by admin on November 8, 2013
Posted in: DTM Astronomy Seminar.
Relative strengths of known diffuse interstellar bands. From http://en.wikipedia.org/wiki/File:Diffuse_Interstellar_Bands.gif.

Relative strengths of known diffuse interstellar bands. From http://en.wikipedia.org/wiki/File:Diffuse_Interstellar_Bands.gif.

We had a great talk today from Dr. Gail Zasowski of Johns Hopkins University Astronomy. She talked about mysterious spectral features called diffuse interstellar bands (or DIBS).

Illustrated at left, DIBs are spectral absorption features that pop up when astronomers point their telescopes in almost any direction in the sky. The DIBs are probably created by some type of molecule (or molecules) that abounds throughout our galaxy, but astronomers and astrochemists haven’t figure out what it is yet, even after decades of work.

Dr. Zasowski described how the DIBs could be identified in the vast collection of spectra from the APOGEE project and then used to map structure in the Milky Way. It goes to show that, just because we don’t know what exactly we’re looking at, it doesn’t mean astronomers can’t use the information to learn about the universe.

“Focusing the Hard X-ray Universe” — Dr. Daniel Wik

Posted by admin on October 4, 2013
Posted in: DTM Astronomy Seminar.
NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, has captured these first, focused views of the supermassive black hole at the heart of our galaxy in high-energy X-ray light. Taken from wikipedia.

NASA’s Nuclear Spectroscopic Telescope Array, or NuSTAR, has captured these first, focused views of the supermassive black hole at the heart of our galaxy in high-energy X-ray light. Taken from wikipedia.

Dr. Daniel Wik visited DTM this morning to give a talk about NASA’s NuSTAR mission, an X-ray telescope in low-Earth orbit designed to study some of the most exotic and energetic phenomena in the universe.

For example, the image at left shows observations taken by NuSTAR of the center of our galaxy. In recent years, astronomers have learned that a supermassive blackhole looms at the center of our galaxy, gobbling up gas.

The images at left show a flare bursting from the galactic center, made of gas heated to 180 million degrees Fahrenheit (100 million degrees Celsius) as the black hole sucked material down into its deep, dark center.

“Recent Results on Exoplanets and Brown Dwarfs” — Prof. Chris Tinney

Posted by admin on October 3, 2013
Posted in: DTM Seminar.
This image of the brown dwarf binary CFBDSIR 1458+10 was obtained using the Laser Guide Star (LGS) Adaptive Optics system on the Keck II Telescope in Hawaii.

This image of the brown dwarf binary CFBDSIR 1458+10 was obtained using the Laser Guide Star (LGS) Adaptive Optics system on the Keck II Telescope in Hawaii. Taken from wikipedia.org.

Good DTM seminar today by Prof. Chris Tinney, presenting a long and fascinating list of results from exoplanetary astronomy.

Among many projects his group is working on at the University of New South Wales, they are observing potential planet-hosting stars for the radial velocity signals of gas giant planets in orbits with long periods, comparable to Jupiter’s period of 12 years. Such planets require long observational baselines to find because you must observe the planet-hosting star for at least one orbital period, 12 years, to conclusively say that you’ve found such a planet. As a result, there aren’t too many long-period exoplanets known.

His group is also looking for brown dwarfs, exotic objects that aren’t quite stars but aren’t quite planets either. Brown dwarfs have masses large enough (probably greater than 13 times Jupiter’s mass) that they can fuse deuterium in their interiors — unlike planets — but small enough that they don’t fuse the lighter isotope, hydrogen — unlike stars.

“Plasma Physics to Space Weather on Distant Worlds” — Dr. Rachel Osten

Posted by admin on September 26, 2013
Posted in: DTM Seminar.

Today we had a great DTM seminar by Rachel Osten from the Space Telescope Science Institute (STScI). She talked about stellar activity and coronal mass ejections (CMEs).

A coronal mass ejection in time-lapse imagery obtained with the LASCO instrument. The Sun (center) is obscured by the coronagraph's mask.

A coronal mass ejection in time-lapse imagery obtained with the LASCO instrument. The Sun (center) is obscured by the coronagraph’s mask.

Osten pointed out that these huge eruptions from stars are important for several reasons. For example, the energy and frequency of CMEs depend on several properties of stars, including their age, rotation rates, and magnetic fields. In general, as stars age, their rotation rates drop, usually reducing the strength of their magnetic fields and the amount of CME activity. And so learning about CMEs can tell us about stellar evolution.

When a star fires off a CME, it typically flares or brightens a bit (see figure at right), and since we can’t see stars other than our Sun up close, we can use the temporary brightening of those stars to study their flare activity. Osten talked about one of her projects to use data from the Hubble Space Telescope to look for flare activity for many stars near the constellation Sagittarius.

That project had a surprising result: many stars that were thought to be older than the Sun actually showed MORE flare activity than they should have. This result might mean these stars actually have previously unknown binary companions that kept the stars spinning quickly and thereby keeping their flare activity up.

Stellar flares may also be important for planetary habitability. For example, a big stellar flare can actually disrupt the atmosphere of an Earth-like planet, perhaps even removing all of the life-protecting ozone.

 

 

“Constraints on Venus Tectonics from Deformation Experiments” — Dr. Steve Mackwell

Posted by admin on September 20, 2013
Posted in: DTM Seminar.
Comparison of Venus' and Earth's topography. For Venus, orange represents the topographic highs, blue the lows. For the Earth, red represents the highs and blue the lows.

Comparison of Venus’ and Earth’s topography. For Venus, orange represents the topographic highs, blue the lows. For the Earth, red represents the highs and blue the lows.

Today I saw an interesting talk about Venusian geophysics by Dr. Steve Mackwell.

Dr. Mackwell talked about how mountains, volcanoes, craters, and fractures in Venus’ surface allow scientists to infer the tectonic history of Venus.

For example, unlike the Moon, there aren’t that many craters on the surface of Venus, which should have accumulated with time as more and more asteroids and comets struck the surface. This lack of craters (along with widespread, large-scale volcanic features) suggest that Venus underwent a tremendous volcanic upheaval about a half billion years ago, during which global volcanic eruptions almost completely re-surfaced the planet.

Dr. Mackwell also discussed how his lab experiments in rock mechanics (in which he squeezes and heats rocks to determine their physical properties) have contributed to our understanding of Venus’ history.

For example, the flow of heat from Venus’ interior drives its geophysical activity and plays a key role in determining the strength of the rocks underlying the surface topography. Understanding the relationship between internal heat flow and rock strength, however, requires lab experiments such as Dr. Mackwell’s.

“Massive Star Formation Theory” — Prof. Jonathan Tan

Posted by admin on September 13, 2013
Posted in: Other Seminars.
This is an enlarged image of the region around the Kleinman-Low nebula in the Orion cloud located 1500 light years away. This image is taken in light at 2.12 micron at the Subaru telescope, which is emitted by warm molecular hydrogen gas with an absolute temperature of 2000 K.

This is an enlarged image of the region around the Kleinman-Low nebula in the Orion cloud located 1500 light years away, where a massive star may be in the process of forming. This image was taken in light at 2.12 micron at the Subaru telescope, which is emitted by warm molecular hydrogen gas with an absolute temperature of 2000 K.

I saw an interesting colloquium talk today at the National Radio Astronomy Observatory, given by Prof. Jonathan Tan about formation of massive stars.

Many details about the formation process for massive stars remain unclear, and Prof. Tan described that the stars may either form through the merger of many small, low-mass stellar cores or by direct accretion of massive quantities of gas.

And big questions about these processes remain. For example, what spurs the initial collapse of a gas cloud into star? How exactly is the mass accreted, and what forces dominate that accretion? How long do all these processes take?

Prof. Tan described observations of clumps of gas and dust in the galaxy, including observations from the world’s largest radio telescope, the ALMA array, and how these observations may provide constraints on the star formation processes.

 

Looking for Very Short-Period Planets with a Re-Purposed Kepler Mission

Posted by admin on September 10, 2013
Posted in: Brian's publications.
Synthetic data for the new pointing capabilities of Kepler. The red points show when the planet is transiting.

Synthetic data for the new pointing capabilities of Kepler, showing the expected brightness variations for a planet hosting a star that transits (i.e., the planet passes in front of the star, blocking out some of the light). The red points show when the planet is transiting.

Recently, the Kepler mission announced that two reaction wheels on the spacecraft have failed, and so the telescope won’t be able to point as accurately as before. As a result, data from the telescope will suffer from large instrumental variations (see figure at right), and so it will be difficult to detect Earth-like planets. However, the telescope may be able to detect other kinds of planets and study other astronomical phenomena.

In response to a request from Kepler for new ideas of what to do with the telescope, I wrote about an idea to search for very short-period (less than 1 day) planets. A re-purposed Kepler mission could continue the search for nearly Earth-sized planets in very short-period orbits. Our recent work revealed more than a dozen such planetary candidates, and a more complete and focused survey is likely to reveal more.

A Circumstellar Disk Imaged in Silhouette with Adaptive Optics — Follette+ (2013); Tidal Dissipation in Giant Planets — Storch & Lai (2013)

Posted by admin on September 3, 2013
Posted in: Journal Club.
Part of Figure 1 from Follette et al. (2013), comparing the Hubble (HST) image (top) to their image (bottom) of the protoplanetary disk.

Part of Figure 1 from Follette et al. (2013), comparing the Hubble (HST) image (top) to their image (bottom) of the protoplanetary disk.

Today in journal club, we discussed two papers.

The first one was Follette+ (2013), which presented the first images of a protoplanetary disk taken using a new adaptive optics instrument on the Magellan telescope.

This disk (shown at right) is a collection of gas and dust orbiting a young star, only a few million years old. Studying these kinds of young disks help astronomers understand what the early solar system was like, when our planets were still forming.

In addition to providing new images of this disk, this paper also presented evidence that, although the disk is young, the accumulation of dust particles that gives rise to planets may already be underway. This result means that, although astronomers have thought this particular disk may show us the very earliest conditions in a protoplanetary disk, instead this disk may be fairly far along in its evolution and the process of planet formation.

The second paper we discussed was Storch & Lai (2013), which studied the origin of hot Jupiters — gas giant planets (like Jupiter) but orbiting hundreds of times closer to their host stars than the Earth does the Sun.

The origins of these planets are still unclear, but they are so close to their stars that they undergo very strong tidal interactions. These tidal interactions distort the shapes of the planets, dissipating orbital energy within the planets’ interiors and causing the orbits to shrink over time.

Determining the rates and processes of tidal dissipation are key to understanding the origins and fates of these planets: Too much tidal dissipation will overheat the planets’ interiors and blow them up; too little, and the planets wouldn’t reside in the orbits in which we see them today.

Storch & Lai (2013) include the effects of dissipation within the planets’ icy and rocky cores, which they show can help explain the origins of the planets.

“Catastrophic evaporation of rocky planets” — Perez-Becker & Chiang (2013); “Kepler and the Kuiper Belt” — Gaudi (2004)

Posted by admin on August 27, 2013
Posted in: Journal Club.
Figure 4 from Perez-Becker & Chiang (2013), showing the how the mass loss rate depends on the amount of dust in the atmosphere (x_dust).

Figure 4 from Perez-Becker & Chiang (2013), showing the how the mass loss rate depends on the amount of dust in the atmosphere (x_dust).

Today in Journal Club, we discussed a paper by Perez-Becker & Chiang (2013).

This paper looked at the mass lost by a rocky extrasolar planet so close to its host star that its surface is melted and a liquid rock lake has formed on the planet’s day side. This work was motivated by Rappaport et al. (2012), which claimed to have discovered a roughly Mercury-sized extrasolar planet candidate orbiting the star KIC 12557548 in data from the Kepler mission. The planet seems to be disintegrating and may disappear in the next few million years.

An atmosphere of rocky vapor likely forms over the liquid rock lake and can actually escape from the planet, owing to the planet’s very low surface gravity. As the gas escapes, it cools (through adiabatic expansion) and can potentially condense into little dust grains, which are then swept out into space by the escaping gas. This putative cloud of dust can help explain some of the observations from Rappaport et al. (2012).

As interesting as the paper is, though, it raises some big questions that we talked about in journal club. For example, the dust should be strongly heated by the starlight and should reach high temperatures (> 2000 K or 3140 degrees F). If the planet’s surface is hot enough that the rocky surface evaporates, why doesn’t the dust also evaporate?

Unfortunately, the star KIC 12557548 is very dim, so it’s hard to observe with other telescopes and learn more about the planet candidate. However, the upcoming TESS mission will probably find more planets like this one, and so we might be able to see other rocky planets that are disintegrating before our eyes.

We also discussed an older paper by Gaudi (2004), which predicts that the Kepler mission might have observed a handful of stellar occultations by Kuiper belt objects (KBOs). During such an occultation, a KBO will block out the light from a background star in a way that depends on its size and how far it is from the Sun. Since Kepler has been staring at about 150,000 stars over 3.5 years, there’s a good chance that a few of those stars were occulted by KBOs. Unfortunately, because Kepler wasn’t designed to look for such signals, it might be very hard to spot them in the data.