REU Observing Project 2005

The GBT Scheduler has given us a block of 9.5 hours starting on Sunday, June 26 at 21:30 EDT. See the GBT Schedules Page for further information.

ALERT! NOTE: The GBT Observing Project is coupled to the CV Summer Student Trip to GB. ALERT!


Project Suggestions

HI Absorption Measurement from a Galactic Plane Pulsar

Submitted by ScottRansom. This project would examine a bright pulsar in the galactic plane and use its flux as a continuum source to measure the HI absorption from material in the foreground. Due to the pulsed nature of the pulsar's flux, off-source calibrations are not needed since we have on- and off-source measurements as a function of time, and hence the observations are very simple. Data analysis would include folding the data at the pulsar period, optimizing on- and off-pulse measurements of the pulsar as a function of observing frequency, calibrating the resultant spectrum with the off-pulse values, and comparing the resulting absorption spectrum with the galactic rotation model. The result would be a distance estimate for the pulsar (or at least distance limits). When combined with the known Dispersion Measure of the pulsar, we can constrain models of the galactic electron density. Measurements of this type have been made for only a small fraction of the known pulsars (~50 I think). The large gain of the GBT and the frequency resolution of the Spigot should allow us to choose an interesting pulsar (such as a millisecond pulsar or a young pulsar in a supernova remnant) that cannot be measured with Parkes.

ToDo Before the Pulsar Observing Run

  1. Determine what signal-to-noise you want to ultimately derive from your measurements and estimate what combination of integration time and bandwidth you will need given an assumed system temperature. HINT: Use the "radiometer equation".
  2. More...


Extragalactic HI

Submitted by JimBraatz. This experiment is to measure Neutral Hydrogen (HI) profiles for a variety of galaxies in the nearby universe. Neutral Hydrogen is the "bread and butter" of radio astronomy. Using HI measurements, one can: (1) measure the total hydrogen mass of the galaxy, (2) measure the redshift and distance to the galaxy, (3) get a measure of the rotation speed of the galaxy, (4) determine whether the gas in the galaxy is symmetrically distributed, and (5) more! The details of the experiment can be designed by the students. Some ideas might be:
  • Select a representative sample of galaxies with various Hubble types and compare the hydrogen content of those galaxies. (i.e. Do SA galaxies have more HI than SB of comparable luminosity? How about E galaxies?)
  • Measure the redshift of a sample of galaxies using the HI line, and compare to optical redshifts. Is there a difference? Which is more accurate? Does it matter if the galaxy is an AGN?
  • Select a sample of galaxies with a range of inclinations. How does the profile change with inclination, and why?
  • How does the HI profile compare between isolated large disk galaxies, and interacting large disk galaxies?

    There are many possibilities. The students will have an opportunity to measure and compare basic galaxy properties. The observing modes and data processing techniques are thoroughly tested and well defined, and are also standard and instructive to understanding basic position-switched spectroscopy.

ToDo Before the Extragalactic HI Observing Run

  1. Determine what signal-to-noise you want to ultimately derive from your measurements and estimate what combination of integration time and bandwidth you will need given an assumed system temperature. HINT: Use the "radiometer equation".
  2. More...


Formaldehyde (H2CO) Emission Studies of a Protostar

Submitted by JeffMangum. Note that this was the 2004 observing project. The project: Formaldehyde, H2CO, is a ubiquitous molecule in space as on Earth. Its structure provides it with a moderate dipole moment which in turn makes it a useful probe of moderately to highly dense regions. It also possesses lines at fairly low frequency, accessible with the GBT. Lines at 6cm and 2cm wavelength may be compared and used to estimate density, for example. However, owing again to the structure of the molecule and the specifics of interstellar conditions, the line is normally detected in absorption against the cosmic background radiation.

There are fewer than half dozen places in the Universe where the line has been detected in emission:
  • Wadiak et al. (1985) found one region of emission in Ophiuchus. Wadiak et al. (1985) mapped this line in the other region in Ophiuchus where it occurs in emission, the B1 core, and found two rotating elongated structures, which may represent evolutionary phases of a cloud core as it creates and nurtures the young stars.
  • Another emission region is in Orion A-BN/KL. This line was mapped in continuum mode in the VLA-D configuration by Barvainis and Wootten (1986), who sought to place limits upon the polarization in the line. Weak emission at 2 cm is known to extend over a wide range in the OMC1 cloud (Bastien et al. 1985, map from Effelsberg antenna). Johnston, Wadiak, Rood and Wilson have mapped the formaldehyde distribution in the region 3' north of the dense core. The emission in the Effelsberg map is quite intense, with main beam brightness temperatures ranging from 0.2 K at the compact southern extreme of the map to 2K at BN/KL.

The L1689S protostellar core has formed at least one star, and provides for us an opportunity to glimpse the next stage in the star formation process. If a disk is present, or a star of a solar mass or so, the gravitational velocity perturbations within 10" of the object should be as large as 1 km/s, easily detectable. If rotation is present, a dynamical mass estimate, which includes the central object, can be derived. The gas mass, from the line intensity, may be used to measure the gas in the rotating structure. In the mid-1980s, Mangum and Wootten used the 140ft telescope to discover 2cm H2CO emission near a dense portion of the Ophiuchus star-forming region. However, the large beam and low antenna efficiency of that telescope, coupled with the weakness of the emission conspired to prevent those estimable authors from figuring out exactly what the relation of the emission region was to any dense material and star formation in the vicinity.

The REU Mission: Using the better sensitivity and smaller beam of the GBT, discover the true location and extent of this rare region of 2cm formaldehyde emission and how it relates to star formation in the region.

ToDo Before the Protostar Observing Run

  1. Determine what signal-to-noise you want to ultimately derive from your measurements and estimate what combination of integration time and spectral resolution you will need given an assumed system temperature. HINT: Use the "radiometer equation".
  2. Which flavour of "switching" are you going to use? HINT: You want to choose an observing mode that is both efficient and allows you to make the measurements the way you want (i.e. lets you obtain the spectral resolution and bandwidth you desire).
  3. Are you going to want to map the source? You will need to map a source if it is larger than the primary beam of the antenna at your observing frequency. Look at the data from last year and decide if you need to map the source, and if so which positions need to be measured.


-- JeffMangum - 10 June 2005
Topic revision: r2 - 2006-03-29, JeffMangum
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