The Frozen Dome

Normally, if I heard or read the words 'Dome C' I would think they referred to the third dome in a cluster of structures at some observatory. Recently, I've come to learn that Dome C is also the name for one of the coldest places on earth, one of several summits on the Antarctic Ice Shelf.

Ironically, there is still an astronomical link. Dome C is considered to be one of the best potential sites for a new observatory on the face of our planet. For one thing, the Sun never gets higher than 38 degrees above the horizon, so there is a lot of night time for observing from the south polar region. Even better, there is almost no infrared sky glow, the air is extremely dry, there is almost no aerosol or dust, and no light pollution. The Antarctic Plateau is the largest desert on Earth, so there is very little precipitation and a very high percentage of cloud-free time. Surprisingly, the wind is also quite mild at Dome C, averaging a mere 6 mph in winter. That is a good thing, considering the average annual temperature is -55C, with lows of -80C and balmy highs in the -25C range. Who needs wind chill when it's that cold?

Most importantly, the seeing is typically 2.5 times better at Dome C than at the best existing observatories. Star images taken through a telescope at Dome C would be 2.5 times sharper and 6 times brighter.

The image on the left is a simulation of a star field as observed from the best existing observatory sites; the image in the middle is the same star field as observed from Dome C. To see as many stars from a mid-latitude observatory, you would need to build a telescope 2.5 times bigger, which would cost ten times as much, and would give the image on the right, which makes the stars look brighter but doesn't improve the sharpness of the image.

Image and text from 'Exceptional astronomical seeing conditions above Dome C in Antarctica', by
by Jon S. Lawrence, Michael C. B. Ashley, Andrei Tokovinin, and Tony Travouillon, published in Nature, 16 September 2004.

Three interesting papers have been released to the pre-print server arXiv.org describing the PILOT program (the Pathfinder for an International Large Optical Telescope), a proposed observatory on Dome C in Antarctica. The first paper presents an overview of the instrumentation suite and its expected performance, a summary of the key science goals and a discussion of the future of Antarctic astronomy.

Paper 2 describes a series of projects dealing with the distant Universe. One potential project that caught my eye is the search for pair-instability supernovae (PISNe) and gamma-ray burst afterglows. These could be our best glimpses into stars formed in the very early days of the Universe. PISNe are predicted to be the product of super massive stars formed in the early history of the Universe. These stars were formed before there were any heavier elements, so their unique chemical composition and masses resulted in a different kind of final disruption of the supernovae progenitors in this era. The light curves of these PISNe are predicted to be have slower rise times and to stay bright for much longer than SN closer to home. This is pretty cutting edge astrophysics, seeing as how no PISN has ever been found.

PILOT could also examine some of the first evolved galaxies and galaxy clusters to inform us of the processes in the evolution of structure in the Universe. They also propose a large-area weak-lensing survey and a program to obtain supernovae infrared light-curves to examine the nature and evolution of dark energy and dark matter.

The ability to do infra-red astronomy from the planet's surface makes PILOT a good match and essentially the only competition for the James Webb Space Telescope in the coming decade.

Paper 3 presents a series of projects dealing with the nearby Universe. Several projects are proposed that examine stellar populations in nearby galaxies and stellar clusters, to gain insight into the formation and evolution of younger galaxies and stars.

Other projects will investigate the formation processes of stellar and planetary systems. Three projects in the field of exoplanet science are proposed. These include a search for free-floating low-mass planets and dwarfs, a program of follow-up observations of gravitational microlensing events, and a study of infrared light-curves for previously discovered exoplanets.

Free-floating low-mass planets; now there is a category of interesting objects. The plan is to examine nearby star clusters to search for planets not associated with stars down to several Jupiter masses. Why would astronomers be so interested in free floating planets? Because typically, exoplanets light is difficult or impossible to disentangle from the light of their accompanying star. If we can find exoplanets free of the overpowering glare of their host stars we can study the chemical composition and atmospheric properties of these planets.

And finally a study of coronal mass ejections from the Sun, and a monitoring program searching for small-scale Low Earth Orbit satellite debris items are also proposed.

The opportunities to do exciting, results-oriented science exploration and discovery from Antarctica is is almost as mind-numbing as the night time temperatures resident astronomers and technicians will have to bear to perform the work.

Constructing, operating and maintaining a telescope at the bottom of the world under these conditions will be another great story. Now that I know about Dome C and PILOT, I'll keep an ear to the ground and let you know when there are new developments.

Extrasolar Asteroids and Ophiuchans

As promised, the full length interview with Steve Howell from NOAO and the Kepler mission is now online at Slacker Astronomy dot org.

The Kepler mission is designed to discover Earth-like planets around other stars. The Kepler space telescope will stare at a field bordering Cygnus and Lyra for three to five years, continuously monitoring over 150,000 stars for exoplanet transits. According to a recent paper from Howell and collaborators, Kepler should also be able to detect asteroids orbiting white dwarfs.

And just for fun, Steve and I talk about the long lost astrological sign Ophiuchus.

Impressions from the 215th AAS Meeting in Washington, DC

The American Astronomical Society held its 215th annual meeting in Washington DC January 3-7. Now with the talks all done, the posters taken down and the tables and chairs packed away, I thought I�d give a brief overview of my own impressions from the meeting.

I think everyone who went to the meeting was eagerly anticipating the first results from the Kepler mission. They did not disappoint. Five new exoplanets, a mysterious, possibly new type of object too hot to be a planet, but not a star, (or is it?), reports on the excellent performance of the detectors and space craft, and asteroseismological results, all from the first months of observations.

"Kepler is working so amazingly well," says Berkeley's Geoff Marcy, a member of the Kepler science team, "that the light curves look like they come from a textbook, not a real instrument."

What I found even more impressive was the immediate release of science papers by the team, with a dozen significant papers hitting the astro-ph server within hours of being announced at the AAS meeting. The mission scientists were ready and loaded for bear right out of the shoot. We are gong to be hearing about results from this exciting mission for years and years.

The Hubble Space Telescope is in good hands. Dr. John M. Grunsfeld was appointed Deputy Director of the Space Telescope Science Institute (STScI) in Baltimore, Md. on January 4th. STScI is the science operations center for NASA's Hubble Space Telescope and the James Webb Space Telescope planned for launch in 2014.

If John�s name sounds familiar it�s because he�s a veteran of five space flights, including three servicing missions to the Hubble. He�s logged over 835 hours in space, including eight space walks, totaling nearly 60 hours. He succeeds Dr. Michael Hauser, who stepped down in October.

There were plenty of new science results presented at AAS demonstrating that Hubble has been reborn again, and is in fact better than ever. Images of the earliest galaxies ever recorded were among the hot Hubble news this week. "We're just at the beginning of this story," said Grunsfeld. "It's incredibly thrilling to see these new instruments working and delivering results."

One of my favorite 2009-2010 stories is the enigmatic variable star epsilon Aurigae. Epsilon Aur made the news at AAS on several fronts. Talks from some of my colleagues on results from the Citizen Sky project were given on Tuesday, and results from observations in the far ultra-violet using the Spitzer Space Telescope were also big news.

Observations by Dr. Don Hoard and collaborators using Spitzer revealed the presence of a disk about 8 astronomical units in diameter, as expected. What was unexpected was that it consists of relatively large particles mostly the size of sand grains, not the usual microscopically fine space dust. Observations also indicate the presence of a smaller, very hot star at the center of the disk, probably spectral type B.

Hoard and his colleagues have proposed a new model to explain these observations. A key element is that the primary, a bright F supergiant, is much less massive than previously thought. In their model the primary started off at around 10 solar masses (as opposed to the 15 or 20 previously assumed) and has since blown off much of that via its stellar wind. The B star companion has only about 6 solar masses, and shines much dimmer. According to Hoard and colleagues, the dark disk is not that of a newborn star still accreting material. The disk is made of material that the B star gravitationally captured from the evolved primary�s wind.

"It was amazing how everything fell into place so neatly," said collaborator Steve Howell of the National Optical Astronomy Observatory. "All the features of this system are interlinked, so if you tinker with one, you have to change another. It's been hard to get everything to fall together perfectly until now."

There is some controversy about this and still a lot to be learned. Arne Henden, director of the American Association of Variable Star Observers, (and my boss), emphasizes that the mystery of epsilon Aurigae has not been solved yet. �We�re nearing the middle of the eclipse, and lots of interesting things will happen over the next year. There are still things about this system we don�t understand.�

The blogosphere was alive and kicking throughout the meeting. New media coverage of the fast breaking news was phenomenal. First and foremost, I have to thank and congratulate Pamela Gay and Fraser Cain for the excellent coverage of the press conferences and many of the invited talks on Astronomy Cast Live. I wasn�t able to attend the meeting, but thanks to the live coverage I feel like I got to see a lot of the events I would have wanted to cover if I was there in the flesh. I was able to watch new NASA Deputy Director, John Grunsfeld, live and share in the audience�s approval and excitement. The 21st century will see a lot more remote coverage of science news, and Astronomy Cast Live is showing the way.

Twitter was also abuzz with tweets coming directly from attendees. There was a wave of tweets rolling in as Charlie Bolden, the new NADSA administrator, gave the keynote address to a packed house. Every time he made an applause-worthy or controversial statement, Twitter lit up with quotes and comments from people in the conference room.

Bloggers from Universe Today and elsewhere covered all the big stories and had blogs posted by the end of the day on everything exciting and new.

The print press was also there in full force. I have to admit, Bob Naeye, the Editor in Chief of Sky and Telescope magazine impressed me at the press conferences with his knowledgeable and penetrating questions. He appeared well versed in what ever the topic of the moment was, from Gamma-Ray Bursts to stellar evolution to exoplanet searches and results. Bob was everywhere, asking multiple questions of numerous speakers at just about every press conference I witnessed.

By and large, scientists are doing better than ever at getting the word out about the scientific method, the universe we live in and the �secret lives of astronomers�. There are still those PhDs who can�t give a presentation, and should take a public speaking 101 course, but every discipline has people who just suck in front of a microphone. I give a big Simo-wag-of-the-finger to those astronomers who come ill prepared to give a talk or stammer through press conferences; you know who you are. Fortunately, they are the small minority.

I think the 3,000 people attending this meeting would agree that most of these astronomers are succeeding admirably informing the public and each other in entertaining and enlightening ways. The AAS is not a bunch of geeky nerds with pocket protectors in lab coats. They are real people doing real science in the real world, really well. Really!

The Planet With a Tail

Today there is a new tail to add to the tale of astronomical tails. This one belongs to a planet.

Comet McNaught Credit: Robert McNaught

You're all familiar with the beautiful tails that comets display as the go around the Sun. Energy from our star ionizes particles and strips dust away from the comet's nucleus to form these sometimes magnificent tails.

Mira, one of the most famous variable stars, also sports a tail. Mira is an old evolved red giant star that is losing massive amounts of surface material as it hurdles along through space. This tail material, imaged for the first time in 2007, has been released over the past 30,000 years. Coincidentally, Mira happens to reside inside the tail of the constellation Cetus the Whale.

Image credit: NASA/JPL-Caltech

The common factor in the formation of these tails is a strong stellar wind emanating from the star; our Sun in the case of comets, and the wind from the red giant Mira in the case of the variable star.

Now astronomers have discovered evidence for a planet sporting a tail caused by this same phenomena, the stellar wind of the star  HD 209458. The gas giant planet, named HD 209458b, is orbiting so close to its star that it only takes three and a half days to orbit the star.  As a result of this uncomfortable proximity its super-heated atmosphere is being blown off into space. Observations taken with Hubble's Cosmic Origins Spectrograph (COS) suggest this cast-off atmospheric material is accumulating behind the scorched planet forming a comet-like tail.

 Image credit: NASA, ESA, and G. Bacon (STScI)

"Since 2003 scientists have theorized the lost mass is being pushed back into a tail, and they have even calculated what it looks like," said astronomer Jeffrey Linsky of the University of Colorado in Boulder, leader of the COS study. "We think we have the best observational evidence to support that theory. We have measured gas coming off the planet at specific speeds, some coming toward Earth. The most likely interpretation is that we have measured the velocity of material in a tail."

The star is not just blowing off the top layers of the atmosphere either. COS detected carbon and silicon in the planet's super-hot, 2,000-degree-Fahrenheit atmosphere. This means the parent star is heating the entire atmosphere, dredging up heavier elements and allowing them to escape the planet along with the lighter gases.

Considering the continuous loss of material into space, how long before this planet simply evaporates? "It will take about a trillion years for the planet to evaporate," answered Linsky.