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37-m Projects

The Haystack Observatory Undergraduate Education Initiative Project Book is an on line archive of recent projects carried out by students using the 37-meter radio telescope. New projects will be added during the observing season and users will be able to download the full text of each project in PDF or Postscript format by clicking on the highlighted links below each project description.

Questions about details of the project descriptions or additions to the project book should be directed to Dr. Preethi Pratap

Measuring Spectral Indices of Thermal and Non-Thermal Sources

Radio sources fall broadly into two main categories - thermal sources and non-thermal sources. The mechanism for creating the radio emission is different in these two categories. In the case of thermal sources one emission mechanism is the blackbody radiation from the source. If a source is at a particular temperature then its frequency spectrum is defined by the blackbody equation. By measuring the intensity of emission from the source at several frequencies the slope of the blackbody curve can be measured. Non-thermal emission mechanisms are usually from motions of electrons around magnetic field lines (cyclotron). If the motions are relativistic the phenomenon is called synchrotron. Synchrotron emission also has a characteristic frequency dependance. Most of the non-thermal emission from radio sources are due to synchrotron emission.

Spectral line emission from the rotation of molecules also causes radio emission. Most spectral line emission is thermal in nature although there are some types of emission such as maser emission that are non-thermal. We will discuss more of the spectral line radio emission in other projects. The project described here mainly deals with continuum emission. The spectral index defines the slope of the emission vs frequency curve. Knowing this slope can determine the nature of the emission mechanism for the particular source. The best thermal sources to observe are planets. Good strong non-thermal sources are supernova remnants or some quasars.

Download: PDF (89 kB), Postscript (179 kB)

Ammonia as a Temperature Probe in Star Forming Regions

Molecules in the interstellar medium have been used as probes of some of the physical and chemical conditions in the medium. The radio spectra of these molecules, which are typically caused by the rotation of the molecule and its collision with hydrogen molecules, are especially good tools for this purpose. The radio spectral region is also rich in spectral lines of more than 100 molecular species.

Ammonia (NH3) was the first polyatomic molecule discovered in interstellar space. This molecule has a rich rotation-inversion spectrum with a large number of transitions probing a wide range of excitation conditions. In molecular clouds these transitions are excited in collisions mainly with molecular hydrogen and their relative intensities reflect the kinetic temperature of the emitting medium. Ammonia is, thus, an invaluable tool in measuring the physical conditions in molecular clouds. Temperature determinations from NH3 have been used extensively in studies of star formation since ammonia emission has been found in regions of massive as well as low mass star formation. Such studies have proven useful in determining the conditions in molecular clouds that are necessary for star formation.

Download: PDF (119 kB), Postscript (249 kB)

Methanol (CH3OH) masers and Star formation

Maser emission from methanol has been detected toward many sources mostly associated with star formation. These masers have been divided into two main classes - I and II and the classification is dependent on the maser transition. Class II masers include maser emission from the 20 - 3-1E transition of methanol at 12 GHz. These masers are typically found to coincide with compact HII regions and sites of OH and H2O maser emission. Class II masers are thought to be associated with high mass star formation and appear to be radiatively pumped.

Class I masers, on the other hand, are not always associated with centers of star formation. The pumping mechanism appears to be collisional and they are sometimes found in regions where there is some outflow activity. They have also been detected offset from the star formation activity.

The questions that we would like to answer are as follows:

1. Are Class I methanol masers always associated with outflow activity? If so are they found at the interfaces between the outflows and the molecular material or in the disks around the young stars?

2. Are Class I masers a tracer of a very early stage of star formation? If so they could prove to be invaluable in detecting new star formation sites.
In trying to answer the above questions and other questions about these masers, there have been several surveys performed. At Haystack we propose a different kind of survey. While most surveys have been directed to previously identified sources of star formation, we propose to conduct unbiased searches toward molecular clouds. Such a survey does not depend on knowing where the stars are forming and can maybe result in new detections. The new detections can then be correlated with other signatures of star formation if they exist.

Based on this brief introduction we offer students an opportunity to participate in this discovery-based experiment. Students will select (or be assigned) a part or all of a molecular cloud. They will design the experiment within the survey guidelines and conduct the observations. These observations will be added to the database, and can be used by other students and scientists. In planning the experiment students will be required to follow the research process:

1. Do a background literature search on the masers and the particular molecular cloud that they will be studying.

2. Study the maser excitation mechanism and how their observations can be used to enhance the understanding of the process

3. Design the method of observing the masers paying close attention to the calibration of the data.

4. Correlate their data with other observations.

5. Write a research paper.

References for this subject can be found by searching the Astrophysics Data System and following the link to the Abstract service.


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