QUEST Community Science Blog Author: Kyle S. Dawson

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Mountain-top telescopes and stars that don’t twinkle

May 5th, 2008 by Kyle S. Dawson

Infrared image of a zebra from the London Zoo.
Credit: Steve Lowe

Right now I am very excited about the possibility of working on a new small telescope in southern Utah. This telescope was funded by a private donation and will be run by the University of Utah. We even found a mountain top in the middle of nowhere that this telescope will call home.

Why this particular mountain? There are essentially three reasons:

It’s dark
It’s clear
It doesn’t make the stars twinkle

The first two reasons are so obvious that I am almost embarrassed. The last reason is not quite so intuitive. What makes a star twinkle and why do we care? This goes back to a post I made a few months ago.

The basic idea here is that the churning atmosphere blurs your astronomical image. Local geography and weather patterns can either mitigate or exaggerate this effect. It is difficult to predict and many measurements need to be done to determine what is actually happening. Cameras were placed all around southern Utah on various mountain tops to observe the North Star over the course of the year. The mountain top that produced the highest resolution image of the star won the competition. That was Frisco Peak.

The telescope that will be placed on Frisco Peak was built by a very specialized company. This is quite rare–more typical are either large custom-made telescopes or small amateur telescopes. This telescope falls in the middle. It is bought off the shelf but is far superior to the commercially made amateur telescopes.

We are now discussing plans for this telescope, like the type of cameras that should be used. There is a strong interest in building an infrared camera. This allows us to see through large clouds of dust and allows us to see very distant galaxies.

Like most people, I am much more experienced with cameras in the visible spectrum. I work on CCDs in Berkeley and have barely used anything in the infrared. CCDs are made of silicon which is sensitive to light that can be seen with the naked eye (plus a little more red than what can be seen).

However, there is a lot of information in the sky that is too red to be seen with the naked eye and too red to be detected with a silicon detector. New materials are required for detectors in this wavelength range. One of the major new materials for infrared detectors is a blend of mercury, cadmium and telluride, usually called Mer-Cad-Tell in the astro community. The wavelength range of the detector can be tuned by changing the amount of mercury in the blend.

Clearly, a lot of the legwork has been done for this new telescope. We have the funding, we have a vendor, and we have a location. Now all that’s left is to prioritize our science goals and to figure out how to get our hands on some mer-cad-tell.

Kyle S. Dawson is engaged in post-doctorate studies of distant supernovae and development of a proposed space-based telescope at Lawrence Berkeley National Laboratory.





Tags: cadmium, ccd, Frisco Peak, infrared camera, KQED, mer-cad-tell, mercury, Science, star twinkle, telescope, telluride, Utah



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Pixels are so 20th century - say hello to ’spaxels’

April 23rd, 2008 by Kyle S. Dawson

Making Every Photon Count

Last week I went to a talk given by the leader of the Supernova Factory collaboration at LBNL. What is SN factory? This is an ambitious project to study supernovae like never before. I mentioned this project briefly in a previous post , now that they are so close to releasing their results I want to discuss it a bit more.

The main idea of this project is to study several hundred nearby supernovae using an instrument known as the Supernova Integral Field Spectrograph, or SNIFS. This type of instrument is essentially a blend between a traditional imaging camera and a spectrograph.

The resolution in an integral field spectrograph is defined in spaxels instead of the pixels that have become all too familiar with the advent of digital cameras. A spaxel is quite similar to a pixel, there aren’t nearly as many and each one carries at least a 1000 times as much information.

In your digital camera, the light passes through the lens and directly onto the CCD. Each pixel on the CCD counts the number of photons in the red, the blue, and the green. Typically, there are millions of pixels, each counting photons from a slightly different region of the subject of your photograph.

Now imagine that instead of just counting red, green, and blue, that each pixel counts the entire rainbow of light from your subject. Now you have a spaxel. In an intregral field unit, the light passes through an array of microlenses and prisms before landing on the detector. We would call each set of microlenses and prisms a spaxel. The resulting image carries information about every wavelength of light from every region of your target.

Spectrum of the first SN observed with SNIFSThe advantage to an integral field spectrograph like SNIFS is that you gain a lot more information than either an imager or spectrograph alone. With an integral field spectrograph you can basically identify and organize every photon that reaches the telescope.

Specifically designed to observe supernovae, SNIFS is being operated at the 88-inch telescope on Mauna Kea. Spaxels are quite expensive - this particular instrument has only 225. However, this is more than enough to observe the entirety of a galaxy, a supernova, and the background.

The members of the SN Factory have now observed over 100 SNe using this new camera. Last Thursday, I saw the data from the first 25 well-calibrated supernovae and was very impressed. The data showed the evolution of each supernova and the properties of the host galaxy in great detail. I’m sure the supernova community will be equally impressed when they first see these new results.


Kyle S. Dawson is engaged in post-doctorate studies of distant supernovae and development of a proposed space-based telescope at Lawrence Berkeley National Laboratory.


Tags: Astronomy, camera, ccd, KQED, lbnl, mocrolenses, pixels, QUEST, Science, SNe, SNIFS, spaxel, spaxels, spectography, spectroscopy, supernova, telescope



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Supernova Legacy

April 8th, 2008 by Kyle S. Dawson

Last night we completed our observations for the Supernova Legacy Survey. This was a five year program to study supernovae using a 4-meter telescope in Hawaii in combination with several of the largest optical telescopes in the world.

The project was headed by a group at a university in Toronto and a group at a university in Paris. Canada and France sponsor the 4-meter telescope that is used to discover and observe the supernovae from the point of explosion to the final days when the supernova fades from view. We call this the imaging part of the program. This data constrains the apparent brightness and life cycle of the supernova, and eventually the absolute distance to the supernova.

Our contribution to the project was primarily through our affiliation with Keck Observatory. We were typically awarded four nights a year to observe recently discovered supernovae spectroscopically. The data is used to determine the redshift and the kind of supernova explosion.

The supernovae are used to study the rate of expansion of the universe. It was this type of experiment that was first used to discover that the universe is actually dominated by dark energy.

No one really suspected the presence of dark energy for almost the entirety of the 20^th century. Now, we not only know it exists but are actually trying to understand it in the same way we understand gravity, protons, and electrons. That is where projects like the Supernova Legacy Survey come in. With projects like this, we work to collect enormous samples of well-studied supernovae that can improve our understanding of dark energy.

We use a certain type of supernova as yardsticks to measure distances in the universe. We then model the affects of dark energy on the expansion history of the universe by comparing distances and rates of expansion. This comparison is typically represented in a Hubble Diagram.

The Supernova Legacy Survey has been very successful in its attempts thus far. On the right, I show the Hubble Diagram from the first year of data. This is less than 20% of the full sample. The dotted line outlines the expectations of the 1990’s cosmology crowd. The solid line shows the prediction from the more sophisticated cosmologists of the 21^st century. As you can see, the original expectations were pretty far off the mark - the supernovae just don’t lie on top of the dotted line.

Now that this program is finishing up, we should be seeing similar figures that are teeming with supernovae. Future programs should do an even better job of making these measurements. Someday we may actually understand this dark energy thing, it may turn out to be something else completely new and unexpected!

Kyle S. Dawson is engaged in post-doctorate studies of distant supernovae and development of a proposed space-based telescope at Lawrence Berkeley National Laboratory.


Tags: Astronomy, hubble, hubble space telescope, KQED, lbnl, QUEST, supernova, supernovae, telescope



37.8768, -122.251




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Excellent conditions for skiing and supernovae

March 24th, 2008 by Kyle S. Dawson

Julien Guy: supernova cosmologistI’m sitting in the airport right now, passing time as I wait for my flight back to SFO. Looking at the clock now, I see that my jet lag future does not bode well. I awoke at 5:00 AM here and nearly 11 hours later feel like the day is over, yet it is only 7:50 AM in CA.

I spent the last week at a conference in the Italian Alps with about 200 skier/cosmologists. Mornings were spent in the conference hall watching 15 or 25 minute presentations. Afternoons were for the slopes. Evenings were back in the conference hall.

The conference started with supernova talks - I was fourth on the list. Being in the field, I had heard most of the results that were presented in the other talks. Ditto the other attendees’ perspectives on my talk. However, there were some new and very promising results from the Supernova Factory.

The supernova factory is a LBNL-based research group that focuses on “nearby supernovae”. By nearby, I mean only a few hundred million light years away. These supernovae occur in galaxies that are distant enough to be free of the gravity of the Milky Way and our neighboring galaxies but close enough to observe with smaller telescopes.

The supernovae observed by the SN factory are very bright compared to the supernovae I observe with the Hubble Space Telescope. The supernovae are bright enough to make very precise measurements at each wavelength of the supernova spectrum. Just like my earlier post on spectroscopy, the supernova light is imaged after passing through a prism. These images provide very detailed information about the molecules and atoms that are present in the supernova explosion.

The spectroscopic observations also tell us how one supernova may differ from another. The small variations in type Ia supernovae have been a mystery for quite some time. If we can learn the causes of these variations, these supernovae could be come even more useful for measuring distances in space.

There are several models and theories to explain the differences, but none has been extensively tested. A large number of bright nearby supernovae is required to test these models. Hopefully, a project like the supernova factory will provide that sample. In this conference, they only showed a handful of supernovae. All but one of these supernovae was well-behaved, fitting our current models. The last one differed enormously from the others, but the detailed spectroscopic observations lent evidence as to why this may be the case. The data is still being examined, but I am encouraged by the progress necessary if supernovae are to be used to explain the cosmology of our universe.

The presentations over the next five days covered a very large range of topics. Some conference attendees presented ideas that had never occurred to me. One that I found very interesting was an experiment to model the orbital paths of stars around the black hole at the center of the Milky Way. For those patient enough to watch these stars for 15 years, it should be possible to measure the properties of gravity and the black hole itself by looking for deviations in the stars orbits from our current models.

While the talks were very interesting and well-attended, I can’t help but comment on the other important side of this conference. That would of course be the skiing. The Europeans really have it right - they chose the site and the schedule with the perfect balance for leisure time. We were only ten miles from the tallest mountain in Europe, within site of the Matterhorn, had perfect snow all week, and had just enough time to enjoy it. I even had a chance to practice my amateur photography on the slopes. Now the next challenge will be to organize a conference in Tahiti!

Kyle S. Dawson is engaged in post-doctorate studies of distant supernovae and development of a proposed space-based telescope at Lawrence Berkeley National Laboratory.




Tags: galaxies, KQED, kqedquest, lbnl, matterhorn, pbs, skiing, spectroscopy, supernova, supernovae, telescopes



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H-R: Not just for “Human Resources” Anymore

March 10th, 2008 by Kyle S. Dawson

H-R diagram of 47 Tucanae

I started off my last post talking about the well-known properties of globular clusters, but I chose not to dive into the details of the stars inside the clusters. The stars really deserve an article all to themselves. Now is the time for that article.

Basically all of the stars in a globular cluster have the same age and formed under the same conditions. Observations of a globular cluster are a snapshot of one point along the evolutionary track of all these stars. Each star will have well defined properties depending on its mass and the age of the cluster. In the early 1900’s, Ejnar Herstzprung and Henry Norris Russell made the first observations of this age and mass relation, thus earning the honor of having the model named after them. Not to be confused with more common corporate acronym, we now refer to the model describing the brightness and color of stars as the Hertzsprung-Russell diagram, or H-R diagram.

The H-R diagram shows the relationship between the brightness of a star and its color. In the figure at the top of this page, the y-axis shows the brightness of the stars in the cluster. The brightest stars are represented by the dots at the top of the figure. The faintest stars are near the bottom. The x-axis shows the color of these stars – red stars are on the right and blue stars are on the left.

All stars start on the main sequence, regardless of their mass. A star on the main sequence is burning hydrogen in its core. The more massive main sequence stars burn much more hydrogen, making them hotter, bluer, and brighter than the lower mass stars. The main sequence stars can be seen as the dots below the objects labeled “subgiant branch” in the H-R diagram at the top of the page. You should be able to see the bluer-brighter relationship that describes the main sequence stars.

The massive stars also consume all of the hydrogen in their cores very quickly, causing them to evolve off the main sequence much sooner than the lower mass stars. The stars that have just evolved off the main sequence are the “subgiant branch”. These stars still burn hydrogen but only in regions away from the core. They mark the turn-off from the main sequence and are used to determine the age of a globular cluster.

The more massive a star is, the further it has evolved from the main sequence in an old cluster. The more massive stars can be seen as the red giant branch, the horizontal branch (burning helium in the core), and the asymptotic giant branch. These stars are all still burning their material through fusion, but appear much different in color, size, and brightness than stars on the main sequence.

Finally, there are some stars that have made a huge jump from the top right hand corner of the H-R diagram to the bottom left. These are the white dwarf stars, seen as the faintest and bluest objects in globular clusters. These stars have burned the last of their available fuel and change from big, cool, and red to very small, hot, and blue very quickly when they purge their outer layers. They no longer burn any material in their cores and are simply radiating the last of their energy left from a lifetime of fusion into space.

I found many good examples of the H-R diagram on the web and you’ll need to run Java on your computer to see my favorite. This is a really cool program that allows you to simulate the evolution of stars. Just give it a mass and watch it go. You can see how it changes brightness, color, and size as it grows old. Check it out!

Kyle S. Dawson is engaged in post-doctorate studies of distant supernovae and development of a proposed space-based telescope at Lawrence Berkeley National Laboratory.




latitude: 37.8769, longitude: -122.247


Tags: Astronomy, cluster, h-r diagram, KQED, kqedquest, lawrence berkeley national lab, QUEST, Science, white dwarf



37.8768, -122.251




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Star Clusters in the Milky Way

February 25th, 2008 by Kyle S. Dawson

47 Tucunae

My research group has temporarily stepped away from the distant universe to focus on the stars that are actually inside our galaxy. We’re looking at these stars because they are so bright and so well understood that we can use them to test the calibration of the telescopes we use to study the most distant supernovae. The other day my co-worker showed the results of the analysis and my jaw dropped. I had forgotten how amazing certain observations of nearby stars can be.

We are looking at stars in a very specific environment known as a globular cluster. For those of you lucky enough to find yourself in Chile or Australia, this particular globular cluster is visible to the naked eye. It is known as 47 Tucanae. The stars in this and all globular clusters formed at roughly the same time and under the same conditions. All the known globular clusters in our galaxy are more than 10 billion years old, almost as old as the galaxy and the Universe.

Pleiades

Similar to globular clusters are groups of stars known as open clusters. Probably the best known open cluster is the Pleiades. The Pleiades are extremely close–the brightest stars are discernible to the naked eye and inspired the logo of the Subaru motor company. These stars are so bright because they are blue, massive, and most importantly–young. Pleiades was giving birth to its first stars just as our Earthling dinosaurs were bracing themselves for the killer asteroid!

There are several differences between globular clusters and open clusters, but the most important is the difference in density and mass. Globular clusters form in much denser environments and remain gravitationally bound. It is very rare for a star to escape from a globular cluster. Open clusters are not nearly as dense and are not gravitationally bound. Stars escape much more quickly from open clusters than they do from globular clusters.

Because globular clusters and open clusters are so spectacular and bright, they are some of the best targets for viewing with smaller telescopes available to the public. If you are interested in seeing a few for yourself, you should ping my fellow QUEST astronomy blogger, Ben Burress. I’m sure he or another astronomer can point the Chabot telescope at some of the best looking clusters in the Bay Area sky.

Kyle S. Dawson is engaged in post-doctorate studies of distant supernovae and development of a proposed space-based telescope at Lawrence Berkeley National Laboratory.




latitude: 37.8769, longitude: -122.247


Tags: Astronomy, KQED, kqedquest, pleiades, QUEST, Science



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Where in the web?

February 11th, 2008 by Kyle S. Dawson

Saturn’s moon Epimetheus from the Cassini spacecraft.
Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA
and APOD.

On the bus in Denali National Park a few years ago, I found myself sitting next a couple from the East Bay. If you’ve ever been on the Denali bus, you know that it’s a long ride and it was just a matter of time before we struck up a conversation. As often happens, we wound up talking about work and then about astronomy research. Both of them were very interested in the field but were unsure of where to find good information on the web. At the time, I hadn’t really thought about that and wasn’t much help.

Now that I’m writing for QUEST, I am much better suited to answer them. I spend a lot of time surfing the web for images and links to websites to provide the full details for readers who want to follow up on my posts. Over the course of a year or so, I’ve discovered quite a few resources and have settled on a few favorites. Of course, being a Berkeley and Cornell grad, I have a few biases…

First of all, it is common for a university astronomy department to organize a public outreach campaign. I won’t bother with the obvious disclaimers and instead will just say that two of my favorites are “Ask an Astronomer” at Cornell University and the Berkeley Center for Cosmological Physics.

These two sites are quite different. As the name implies, the Cornell site encourages questions and suggestions from readers. The content of the site is therefore governed by the public, covering a wide variety of topics in fairly brief, straightforward language. The Berkeley site is much more structured. They cover the history of cosmology and outline the history of our universe with all the appropriate links (scroll down to see the links). This provides a very detailed and organized explanation of a specific field of astronomy.

In addition to universities, there are quite a few NASA missions that maintain excellent public relations. Almost everyone knows the Hubble Space Telescope and Mars Rovers. Both sites are updated almost daily with galleries, discoveries, and recent news. NASA also has several other large missions at other wavelengths that are probably not as well known. Three examples are the Chandra X-ray observatory, the WMAP mission, and the Spitzer infrared observatory. Like the Hubble and Rover sites, these space-based observatories perform ground-breaking science and do an excellent job explaining their discoveries to the public.

Besides QUEST, there are also quite a few other excellent blogs out there. Each site has a different approach and finds its own balance between astronomy coverage, opinion, and discussion of general science. One of the most popular is the Bad Astro site–we even have a link on the right hand side of the QUEST blog web page. You can also check out About.com’s top ten space and astronomy blogs.

Of course, one obvious place to learn about astronomy is from journalists. Two websites that do a very good job of covering the field are Space.com and New Scientist (some content requires subscription).

Finally, if you enjoy beautiful images of the sky, a great place to look is the “Astronomy Picture of the Day.” This is where I got my image for today. If you look tomorrow you’re guaranteed to find something just as exciting!

Kyle S. Dawson is engaged in post-doctorate studies of distant supernovae and development of a proposed space-based telescope at Lawrence Berkeley National Laboratory.




latitude: 37.8768, longitude: -122.251


Tags: astronomer, Astronomy, Chandra X-Ray Observatory, denali, hubble space telescope, JPL, KQED, kqedquest, QUEST, Science, Spitzer, WMAP



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Posted in Astronomy, KQED, Partners, Physics | 2 Comments

Converting the Comets Back into Stars

January 29th, 2008 by Kyle S. Dawson

Star or Comet?Yesterday was a very long day at work. I was stuck in meetings with our collaborators for over 6 hours! To make it worse, we spent the entire time discussing a single topic. I even wrote my last paper on it. What could possibly be so captivating, you ask?

Remember the solar wind I wrote about a few weeks ago? This stream of protons does more than create comet tails and aurora, it also destroys all of those fancy electronics we work so hard to put into orbit.

The protons streaming from the sun carry a lot of energy, and they leave a lot of this energy behind as they pass through satellites and astronauts that don’t have the Earth’s atmosphere to protect them. The energy released wrecks havoc on the system, throwing electrons and atoms around like a game of ping-pong. This is one form of radiation damage.

Definitely a comet!
This radiation damage is harmless over short periods of time, much like an occasional X-ray at the dentist. However the solar wind becomes a problem for something like the Hubble Space Telescope or our proposed satellite SNAP which are exposed for many years.

To understand how a telescope degrades from exposure to radiation, let me give an extremely quick explanation of how we gather astronomical images. A telescope is very similar to a camera you buy in the store. The large mirror is equivalent to the lens on your camera. The part that suffers the most radiation damage is the Charge Coupled Device, also known as a CCD.

The CCD is essentially the same as the 8-megapixel chip in your digital camera. This serves as an electronic version of film, recording the image through the photoelectric effect rather than through a chemical reaction. If you can still remember how photography was in the days of film, I’m sure you can appreciate the relief of going digital. Astronomers realized this early on and were pioneers in the use of CCDs.

The photons from the subject of the photograph collide with electrons in the silicon of a CCD, knocking them free from their parent atom. The free electrons are then collected in a well near the site of the collision. Once the exposure is complete, charge is moved one well (or pixel) at a time toward a transistor which then reports the number of electrons found. This process is usually described through the analogy of a bucket brigade passing buckets of water from a reservoir to a fire.

When the CCD is brand new, the bucket brigade performs almost perfectly. If I want to observe a star, the image comes out crystal clear. However, after enough time in space and in the solar wind, the CCD begins to show its wear. The bucket brigade gets sloppy at work and has to contend with an increasingly difficult obstacle course, spilling a little bit of water (or electrons) during each transfer. That same star now leaves a trail of charge behind and begins to look more like a comet.

Now, if I am observing a star, I want my image to look like a star, not like a comet. Is that really too much to ask? Unfortunately, the CCD will inevitably deteriorate in space and astronomers have to find ways to predict and correct for this deterioration. This is what we spent yesterday discussing. We passed around some pretty good ideas but still have a bit of work to do before we can prove a new method for correcting the images. I just hope we it figured out before our satellite launches in 2015!

Kyle S. Dawson is engaged in post-doctorate studies of distant supernovae and development of a proposed space-based telescope at Lawrence Berkeley National Laboratory.




latitude: 37.8768, longitude: -122.251


Tags: Astronomy, camera, ccd, charge coupled device, electrons, exposure, hubble space telescope, KQED, kqedquest, pbs, photoelectric effect, photons, radiation damage, satellite, Science, SNAP, x ray



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Centers of the universe

January 14th, 2008 by Kyle S. Dawson

Cosmic microwave background and the infant universe.
From the WMAP science team.It was on the UC Berkeley astronomy website this morning that I was reminded of something I had wanted to post for QUEST. About a month ago, Cal publicly announced the Berkeley Center for Cosmological Physics. This was quite a big deal for the Physics and Astronomy departments at Berkeley.

The center was founded by George Smoot, who won the Nobel Prize in 2006 and was the focus of a QUEST TV segment. As described in our press release, George donated the bulk of his prize money to the founding of this new center. His donation seeded the center which now has an endowment exceeding $8 million in little more than a year of fund-raising. After watching my girlfriend raise funds for non-profits around SF, I can say that is quite impressive.

The center and endowment ensure that Berkeley remains competitive for years to come in the field of cosmology research. It helps Cal recruit excellent researchers by providing funds for postdoctoral researchers and students. The people supported by the Center can choose any project in the department, projects that I have covered in several of my QUEST articles. It also gives new post-docs the freedom to explore the department before starting on a specific project. This differs from the usual postdoctoral researcher who is recruited by a specific faculty member for a specific project.

The center will also sponsor researchers’ visits to Berkeley from other institutions, educational outreach to K-12 science teachers and several collaborative international workshops on cosmology each year.

Berkeley is actually both one of the first and one of the latest institutions to establish a center for cosmology research. In the ’90s, we had the Center for Particle Astrophysics, which was funded for 10 years by NSF. I think this was one of the first of its kind.

In the last few years, a philanthropist named Fred Kavli has funded quite a few cosmology centers all around the world. I just learned that the Kavli foundation also funds centers in other fields, like nanoscience research at my alma mater. The foundation funds 15 centers in all, including ones at Caltech, UC San Diego, Stanford, and UC Santa Barbara in California.

If you’re a big fan of MASH or Alan Alda, you’ll be a big fan of Kavli foundation. I just looked at their web page and see that they have made him the narrator for their astrophysics, neuroscience, and nanoscience initiatives. Maybe we can recruit Donald Sutherland to promote the movie version of the Berkeley Center for Cosmological Physics.

Kyle S. Dawson is engaged in post-doctorate studies of distant supernovae and development of a proposed space-based telescope at Lawrence Berkeley National Laboratory.




latitude: 37.8768, longitude: -122.251


Tags: Berkeley, George Smoot, Kavli Foundation, KQED, kqedquest, QUEST, Science



37.763553, -122.457913




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Catching rainbows from distant galaxies

January 9th, 2008 by Kyle S. Dawson

A single email on Sunday afternoon brought my weekend to a screeching halt. Some collaborators made a very exciting discovery and needed to confirm if it was real. This would be the last time we’d have for almost another year on the 10 meter Keck Telescope so I jumped at the chance and scheduled it into our observing run Monday night.

I spent the rest of Sunday studying similar projects and forming my observing strategy. Early Monday morning, with only two hours before the final deadline, I finally got the images I needed from the collaborators. I quickly examined these images and identified the interesting galaxies for our observations.

I chose the galaxies which looked to be the most distant. We were hoping to find a cluster of galaxies some 10-12 billion light years away. Confirming so many distant galaxies is only possible with a large telescope like Keck.

For the first two hours of the night we observed these galaxies using spectroscopy. This technique is essentially inspired by the rainbows at the end of a thunderstorm. Just like the raindrops that create a rainbow, the spectrograph has a prism that separates light into its fundamental colors. The difference in my observations is the light comes from distant galaxies instead of the sun.

Because there are so many galaxies and stars in the sky, the important galaxies have to be singled out and shielded from the not-so-important galaxies–sometimes I wonder if some astronomer in the Andromeda galaxy is flagging our Milky Way as one of those not-so-important galaxies.

All of the distractions on the sky are blocked from view with a slitmask. A long and narrow slit is milled into a sheet of aluminum for each object you are studying. The slitmask is aligned to match the positions of the objects that are being targeted. If you were to peek at the sky through the slitmask and telescope, you would only see the handful of galaxies that were hand-selected. Everything else would be blocked by the mask.

In spectroscopy, the light from a galaxy passes through the slit, then through the prism and into the camera. In an observation of a sun-like star using color film, the resulting image would look a lot like a rainbow. In this case I was not observing a star and I was not using color film. The image loses the fancy colors but still carries the same amount of information.

Believe it or not, a rainbow can be just as beautiful in black and white as it is in color. The black and white rainbow tells you how much light is at every wavelength. From this information you can infer the properties and the redshift of the galaxy.

So what happened in last night’s observations? We haven’t finished the analysis, but I did take a quick look at the data before calling it a night. Skimming through the spectra of all the galaxies in the slitmask, I didn’t find the features I was hoping for. I’ll look more carefully at the final processed data, but I have a bad feeling that we didn’t confirm this new discovery. Maybe we’ll have better luck next year.

Kyle S. Dawson is engaged in post-doctorate studies of distant supernovae and development of a proposed space-based telescope at Lawrence Berkeley National Laboratory.




latitude: 19.5228, longitude: -155.152


Tags: galaxies, Keck, KQED, kqedquest, QUEST, rainbow, Science, slitmask



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