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Warum Deutschland und was ist CDMS?

A (Ful)bright Future

Warum Deutschland und was ist CDMS?

Olivia Wilkins

When I began working at the Harvard Smithsonian Center for Astrophysics (CfA) in June 2015, I had just returned from a semester abroad in Norwich, U.K. Just a month before, Alex and I had taken a two-week trip through several European countries that he had been planned around visiting the second- and third-largest fully-steerable Radioteleskope in the world (if that isn't true love, then I don't know what is). Die teleskope that we visited were the Lovell Telescope in Jodrell Bank near Manchester, U.K., and the Radioteleskop Effelsberg in mountains of the Eifel near Bad Münstereifel, Germany.

In the map above, the 100 meter dish of the Radioteleskop Effelsberg can be seen as the white circle to the Northeast of the village of Effelsberg (pinned).

During my stay in the Eifel, I fell in love with Germany. Bad Münstereifel is a beautiful bath town nestled in the mountains populated by half-timbered houses and friendly shopkeepers. A kind woman working at the small train station ordered us—despite limited communications between my lack of Deutsch and her broken Englisch—a Taxibus (a van that works like a taxi, but can only be ordered at certain times from a scheduled route) to take us to the Radioteleskop. After a 1.5 kilometer (nearly 1 mile) walk down a winding dirt and stone path from das Dorf into a valley, we came upon the Radioteleskop Effelsberg.

The Radioteleskop Effelsberg, nabbed from Wikipedia. (I left my own pictures on an external hard drive in storage back in the States....)

While the GBT (the first-largest fully-steerable radio telescope in the world) at the NRAO in Green Bank, WV, is—and probably always will be—my Lieblingsradioteleskop of all time, the Effelsberg scope was breathtaking and made me fall in love with radio astronomy efforts in Germany on the spot. Despite my instant infatuation with the Radioteleskop Effelsberg, I was not yet considering during research in Deutschland.

This is where working at the CfA comes in.

At the CfA, I studied spectra of young stellar objects called protostars. If you do some basic word breakdown, you find that a protostar is simply a gas cloud that is collapsing and condensing such that it will eventually become a star. In these protostars is some pretty cool chemistry. These clouds are full of all sorts of molecules including complex organic molecules (COMs) and long carbon chains (many of which don't even exist on Earth). Each of these molecules has a signature that is picked up by a radio telescope, in this case the IRAM 30 meter in Granada, Spain. Just like your fingers have a unique set of lines that make up your fingerprints, every molecule has a unique set of spectral lines that makes it identifiable.

To identify the owner of a set of fingerprints, the prints are scanned into a computer and cross-referenced with databases from police departments and government bureaus. Once the computer finds a suitable match in the database, the prints' owner can be identified. Interstellar molecules, like the ones I was studying in the protostars, are no different. The molecules we are searching for aren't criminals, so FBI databases are of no help in cross-referencing their fingerprints. Instead, astrochemists and radio astronomers use databases such as the Cologne Database for Molecular Spectroscopy (CDMS), JPL's line list, or data from other research institutions. I was advised to use CDMS because it is not only among the most reliable databases, but also the most complete.

During my summer at the CfA, I used the CDMS to identify COMs and long carbon chains, as well as to study the compositions of these species. From information compiled in the CDMS, I was able to determine characteristics such as rotational temperature, energy levels, and abundances. About halfway through my project, I became interested in what happens on the other side of the database; what went into making the CDMS?

Between my love of the Germany I encountered in Bad Münstereifel and my fascination with the inner workings of the CDMS, a Fulbright to Germany to work at the Universität zu Köln was the perfect opportunity to experience what makes the CDMS possible.

My mortarboard from my graduation from Dickinson. A nod to Germany with a German-flag-inspired sunset behind a mountainous backdrop for the Effelsberg Telescope.

In couple of months that I've been working with the CDMS thus far, I have gotten a grasp on what makes the CDMS possible:

  1. Find a molecule for which there is very limited information available but is also likely to be found in interstellar space.
  2. Order this molecule, or—if not available from chemical distributors—have it synthesized (high purity is a must!).
  3. Take the molecule's spectra, a weeklong undertaking for a range of about 70 GHz. For me, this ended up being a month-long endeavor because:
    1. I was working with a rather large molecule, so its rotational signature is not as strong, especially at lower frequencies (i.e. less than 100 GHz), and
    2. we had problems with our detector, so the experiment had surprisingly low signal-to-noise. Basically, our instruments were giving off a lot of static and it was difficult to see our molecule. There was a lot of trouble shooting and trying to improve the experiment that kept putting off actual measurements.
  4. Make the data look nice. Subtract out backgrounds ("standing waves") that make the data look distorted or wavy rather than linear.
  5. Come up with line predictions using computational chemistry software.
  6. Assign lines.
  7. Assign lines again, but this time include more predictions.
  8. Assign lines again, with even more predictions.
  9. Assign more lines. At this point, you are seeing a whole lot of nothing.
  10. Assign some more lines, watch as your data turns funky. Delete a lot of the work you just did because it must have been wrong.
  11. ...
    ∞. Check with current telescope data to see if your molecule has unknowingly been discovered in space. If so, publish! If not, publish and hope someone finds it soon!

At times, the process from having merely the name of a molecule to having an elaborate physical and chemical fingerprint profile is tedious (see steps 6 through 10+ above). However, the work is rewarding because not only have I have experienced the power of the CDMS myself but I am contributing to unlocking the secrets of the invisible universe. And that is pretty stellar.