Would You Believe a Million Pieces?

Thursday, May 11th, 2006 at 11:27 AM by Dave

(Click on image for full-size version.) An infrared light image of Comet 73P/Schwassman-Wachmann 3 taken by the Spitzer Space Telescope. It clearly shows the comet is falling apart as it swings through the inner solar system. (Courtesy: Spitzer Space Science Center)

In a followup to my previous post on Comet 73P/Schwassman-Wachmann 3, the latest image from the Spitzer Space Telescope shows innumerable pieces that have broken off from Comet 73P/Schwassman-Wachmann 3. The Spitzer Space Telescope is an infrared telescope meaning it sees infrared light, which has wavelengths just a bit longer than the visible portion of the electromagnetic spectrum you or I can see with our eyes. Sunlight heats the pieces of the comet, causing them to radiate infrared light, so they can be detected by this telescope. The tails from the pieces trail away from the Sun, showing us the solar direction.

There are at least 36 major pieces of this comet. However, dust, pebbles, and boulder-sized peices eminate from the larger pieces as sun light melts the comet. This cometary debris will form spectacular meteor showers in the year 2022 when the Earth is expected to pass through this debris.

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“Breaking Up Is Not Hard To Do”

Tuesday, April 25th, 2006 at 10:23 AM by Dave

Or, so it would seem for Comet 73P/Schwassmann-Wachmann 3. It has now broken into more than 30 pieces. It is going to be approaching its closest point to the Earth from May 12 through May 28 at a distance of 5.5 million miles.

During the expected perihelion, the closest point to the Sun (just inside the Earth’s orbit), on June 6, the comet is expected to disintegrate into 30 additional pieces. During this time the Hubble Space Telescope, the Spitzer infrared space telescope, along with Aricebo and Goldstone radars will closely observe this comet.

Back on March 31, I reported that the comet had only 8 fragments but seemed to be tending towards further fragmentation. Obviously, that seems to be the case.

Astronomers expect to examine this comet closely to discover the cometary break up process and shed some light on why some comets do so.

Please look up Sky & Telescope’s news articles on this comet:
http://skyandtelescope.com/observing/objects/comets/article_1704_1.asp

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Coming Down off the Mountain

Tuesday, April 11th, 2006 at 03:31 PM by Administrator

Well, our observing run at CTIO is a success. It got a little dicey toward the end with the moonlight just flooding the sky making us have to spend 4 and a half hours in a field we had to spend only 1 hour on the first night, but we got all the fields we wanted to get observed at CTIO (and couldn’t see from Kitt Peak in Arizona, where we will continue this project next month). Although conditions were completely cloudless the entire run (a condition astronomers call “photometric”), we did have a problem with large amounts of seeing (a way of quantifying “twinkling”) on Sunday night, so we may have to re-shoot those fields in the future.

My last night on the mountain, the sky was bright with moonlight and remained so all night, so we were not really able to do any more observations of our fields (without spending essentialy the entire night on one field), so we concentrated on shooting standard stars whose brightness is known, so we can calibrate all our data. This is something we do every night, but it is not a bad idea to have as much data as possible. Since we couldn’t shoot any of our fields between these standards measurements, I targeted the 1-meter at some of the southern skies more interesting sights, including:

• Eta Carinae: Since Dr. Humphreys (who I am observing with) has spent much of her professional career investigating this extremely massive star (likely the most massive in the Milky Way), we targetted it. It saturated the detector in 0.3 seconds, the shortest possible exposure time, but we could see the famous Homunculus nebulae surrounding the star! For much more informationon Eta Carinae go to the Eta Car Treasury Project website.
• 30 Doradus: Also known as the Tarantula nebula because of its appearance, this is one of the of largest star forming regions known.  Essentually a very big version of the more famous Orion Nebula, it resides in the Large Magellanic Cloud and is the home of many relatively young (only a few million years old) high-mass stars (as well as many more recently formed low mass stars).  If you want to get a feel for what we saw, look at Astronomy Picture of the Day for January 6, 2006.
• Omega Centauri: This is one of the Globular Clusters surrounding our galaxy. It happens to be noted for having stars whose spectra indicate higher levels of processed materials (atoms heavier than Helium) indicating it is one of the younger globular clusters orbiting the Milky Way galaxy. I shot images of it in U (near UV), B (Blue), V (Visual), and R (Red), which I hope to use to construct an astronomy lab (or two) on determining the stellar populations of globular clusters.  If Omega Centauri was also Astronomy Picture of the Day for April 16, 2002.
• Centaurus A: This is a dramatic galaxy in radio waves that also happens to be dramatic in the optical. It is a giant elliptical galaxy that has dust lanes cutting across it. I also took multi-bandpass images of this galaxy for use in an astronomical observing class.  Again, you can get a feel for what we saw on Astronomy Picture of the Day, this time for August 6, 2003.
• NGC 3663: This spiral galaxy has the distinction of currently hosing Supernova 2006ax, a Type Ia supernova. The supernova was discovered on March 20 by the Lick Observatory Supernova Search team and I can tell you that as of last night, it still outshown the rest of the galaxy.

After the night was done, we backed up all the data onto DVDs and a portable hard drive (it was over 40 Gigabytes of images, just over 1000 images) and went to sleep. I got up in time to do some laundry (yes, the mundane aspects of living do catch up with you), packed, and came down in the carry-all. Tonight we will unwind at a local Pizza shop in La Serena, then tomorrow we fly home. I am looking forward to being home with my family, but this was quite an adventure.

And the adventure doesn’t quite end… last night I found I will be observing at the 90-inch Bok telescope on Kitt Peak in Arizona in late May as a continuation of this project. My summer student and I will be very busy this summer turning these images into a measurement of the distributionon of thick disk stars in the Galaxy.

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Report from CTIO: I saw the Magellanic Clouds last night!

Friday, April 7th, 2006 at 03:27 PM by Administrator

(Click on image for full-size version.) This is an image of the center of the Milky Way and The Magellanic Clouds over the CTIO 4-m telescope. I did not take this picture and the orientation of the sky is a bit different right now (the Magellanic Clouds are lower), but it gives you a small taste of the grandeur of what I am seeing here. And it was taken some right outside the telescope I am using. (Courtesy: NOAO)

Well, our second night of observing at the Smarts/Yale 1-meter at Cerro Tololo Inter-American Observatory in Chile went well except for about 25 minutes lost when we started seeing out of focus shadows on the images. It turned out we had a bit of lose tape inside the filter wheel. The night operator removed the tape and we were running again. Other than that, our biggest enemy has been the moon. Our project involves shooting realtively deep wide-field (1 degree square) images to count the number of stars from one component of the Milky Way (the galaxy we reside in), the thick disk. By counting the number of thick disk stars that lie in certain directions on the sky, we hope to determine the origin of an asymmetry in the distribution of these stars seen in the sky. The moon is approaching full so each night we lose a bit more of the night, since when the moon is up we have to image each field for a lot longer in order to see faint objects. This combined with the seeing (1.5 to 2 arcseconds at this telescope, actually not horrid, but not pristine) has made it difficult to see the fainter stars in images shot when the moon is above the horizon. That is the life of an optical astronomer.

My collaborator, Dr. Roberta Humphreys, insisted I go outside for at least 10 minutes outside and let my eyes dark adjust. It may seem amazing, but when you are observing a program like ours, so much is going on that the longest stretches of time you can step away from the computer are only minutes in duration. Dr. Humphreys has spent many nights here at CTIO and insisted I had to see the night sky here with my eyes dark adapted. I was glad she pushed me, the sky outside was spectacular once the moon was down and I gave my eyes time to adjust. I thought previous night’s view had been spectacular when I stepped out for 5 minutes, but last night, after about 10 minutes, I was almost able to read by the light shining from the center of the Milky Way. I could even see the Small and Large Magellanic clouds, despite the fact that these small galaxies that orbit the Milky Way were very low on the horizon … they were faint, but clearly visible. The dust lanes of the Galaxy lept out at me. I have heard that the cultures down here had “dark constellations”, that is, they attached mythological figures not only to patterns in the stars, but patterns in the shapes of the areas without stars. Its going to be a bit of a disappointment to come back to the light polluted skies of central Minnesota after this. I hope my proposal for time in the fall goes through so that I can come back here.

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My First Night at CTIO

Thursday, April 6th, 2006 at 03:33 AM by Administrator

Well, my “night” started around 3:00 pm with my collaborator, Dr. Roberta Humphreys (U Minnesota), and I learning the ropes of running the Yale 1-m telescope. The first thing we learned is don’t trust the manuals that are online, since “tweaks” to those procedures seem to be par for the course. By 3:30 we were taking “dome flats” and learning about opening up and shutting down for the night. Running the telescope requires somewhat simultaneous monitoring of 4 seperate computers that talk to one another:

• Yale4k: This computer is running Windows Xp is basically controls the camera. All images froming from the CCD camera in observtory upstairs are routed down to this computer first. The images, by the way, are 16 megapixels. We have shot over 240 of them thus far, and we have about 2 and a half hours to go yet.
• PC-TCS: This is the telescope control computer, if you want to point the telescope at a new object or focus the telescope, you have to use this telescope.
• PCGuider: This controls a really cool autoguider to keep the telescope pointed. Simply select a star on this computer and the telscope will stay centered in the field by tracking that star.
• Yale1m: This computer runs Prospero, the observing program. From Prospero, we decide how many exposures to shoot, their duration, and the filter we will see through. It talks to Yale4k to clean up the output from the camera. It also is where we display the raw images using IRAF.

So far, our only issues tonight have been

• Focusing the images has proven to be a bit tricky, especially since the bluest filter we are using has a different focus than the blue, visible, and red filters we are using.
• Seeing that is a bit worse than we expected (about 1.2 to 1.4 arcseconds at this telescope, although the CTIO sky conditions tracker here is reporting only 0.6 arcseconds). Larger seeing means it is harder to see the really faint stars we are hoping to see, especially in the bluest filter.

We can’t really evaluate the images we have gotten tonight yet (I will have a summer student working on that problem for 2 months this summer), but this has already been very educational for me, since the only extensive observing I have done before tonight has been at radio wavelengths.

We don’t have a lot of free time (I am writing this blog entry in little 2 minute bursts during exposures), the longest stretch we have without touching the keyboard is ten minutes when we perform a sequence of 6 images on a field (before needing to re-focus). However, I have taken advantage of those short free moments to step outside. Since about 12:30 am, when the moon set, the sky outside has been amazing. Extremely dark, and within 30 seconds my eyes are dark adapted enough to see the Milky Way stretching over head. The Galactic Center is about 20 degrees from overhead and it is amazing. It bulges compared to the rest of the Milky Way, clearly indicating the galaxy is “thicker” in that direction. I was also able to see the whole of Scorpius high overhead, its tail dipping into the center of the galaxy (which lies in the constellation Sagatarius). Finally, since Dr. Humphreys is an expert on the high mass star Eta Carina, she pointed it out to me along with the Coalsack (a dark nebula). Everything in the skies here is crystal clear, it is amazing. You can’t miss the Milky Way and its dust lanes… they jump out at you and demand your attention. Amazing. Too bad we are moving toward full moon next week, because it means dark skies like this are going to get rarer as the week moves forward.

PS: I spoke too soon about things going smoothly. We had the Yale1m computer crash out of its GUI … we lost about 30 minutes … drat.

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