Previous NRAO Summer Student Research Project Summaries

The symbol to the right indicates students who were supported under the National Science Foundation (NSF)'s Research Experiences for Undergraduates (REU) program. All other students were supported under the NRAO Summer Student Research Assistant Program. Follow this link for a list of all student programs at the NRAO. You can also view the student projects titles from 1991-present in tabular form.

For descriptions of the individual summer programs, including itineries, pictures, lectures, and joint student projects, see the previous Program Reports.

Select a date range, student program, and site below:

2005 Summer Students

Kelly Freed, of Metropolitan State College of Denver,
worked with Jeff Mangum on

The Star Formation Environment of the IRAM04191 Protostar

IRAM 04191+1523 has been identified by André, Motte, and Bacmann (1999) as a protostar on the basis of its outflow, stellar to circumstellar mass ratio, centimeter continuum emission, and low bolometric temperature. In these youngest Class 0 spectral energy distribution (SED) sources, the flattened molecular gas envelopes appear to show a ``rigid'' rotation, with the rotational velocity proportional to the radial distance from the embedded protostar, as measured through observations of HH111, HH212 and HH211. In these young objects, a centralized accretion disk is just beginning to form, and the highly collimated outflow provides the primary means for loss of core angular momentum, allowing the formation of the condensing star.

Observations of more mature protostars and T Tauri stars (e.g. Classes I, II, and III) have shown rotational velocities in the circumstellar gas which diverge at the center, with a Keplerian signature of V proportional to R^(-1/2) (e.g. Guilloteau & Dutrey 1998). Such a transition in rotation curves is to be expected if indeed stars form within massive gas envelopes which become more centrally condensed as more mass accretes onto the embedded protostar. For regions in which magnetic fields are important, their effects may be discerned in the rotation curve-slowing rotation in regions where magnetic fields are in control. Thus our observations provide evidence that the kinematics of gas envelopes around protostars indicate the maturity of the condensed embedded protostar.

IRAM 04191+1523 powers a highly collimated CO outflow and is associated with a weak VLA 3.6 cm radio continuum source (André, Motte, and Bacmann 1999). Molecular line observations show evidence of infall. But high resolution continuum measurements fail to detect evidence of significant dust concentrated at the center of the core, indicating that this source has not yet developed a large accretion disk.

Imaging of the interior 10000 AU in the ammonia (NH₃) lines (Wootten, Wiseman, and Fuller 2001, BAAS v33, 1394) revealed a 2100 AU region devoid of ammonia emission centered on the star. Recent imaging of the N₂H⁺ and H¹³CO⁺ J=1-0 transitions over similar spatial scales using the OVRO Millimeter Array indicates similar structure to that seen in NH₃.

Kelly accomplished the following during her research into this project:

Analyzed the correlation between the spatial and spectral structures measured in the NH₃, N₂H⁺, and C₂H (obtained from James DiFrancesco) images of IRAM04191. This correlation was compared to current chemical models which track the "early-time" evolution of these molecular species, which we hoped would lead to a scenario whereby the abundance drops in NH₃, N₂H⁺, and C₂H could be explained.
Tested various physical and chemical models to explain the NH₃, N₂H⁺, and C₂H distributions in IRAM04191.
Related the molecular gas structure observed in IRAM04191 to other protostellar regions. At this point, IRAM04191 appears to be unique, which likely represents our lack of understanding of the early physical and chemical phases of the star formation process.

Catherine Grier, of University of Illinois,
worked with Jim Braatz on

Statistical Study of H2O Megamaser Systems

The student conducted a statistical analysis of known H2O maser systems. Given the jump in the number of known H2O megamasers over the past few years, statistical comparisons between galaxies detected and undetected in H2O masers are warranted. We produced a catalog of galaxy parameters including morphological type, inclination, X-ray column density, and infrared fluxes and luminosities. The megamaser-detected population of galaxies were then compared to general populations of AGNs, especially nonmaser Seyfert 2 galaxies, using statistical comparisons including the K-S test. We are seeking trends that will provide an understanding into the underlying factors which lead to megamaser emission as well as practical aids to improve the efficiency of future surveys for masers in AGNs.

Amanda Heiderman, of Univ California- Berkeley,
worked with John Hibbard (NRAO) & Kelsey Johnson (UVa) on

A VLA HI and Spitzer mid-IR Study of Hickson Compact Group 7

Hickson Compact Groups (HCGs) provide a unique environment to study the mechanisms by which star formation occurs amid continuous gravitational encounters. These dense groups host a variety of modes of star formation, and they can provide insight into the role of gas in galaxy evolution. VLA archival HI data was reduced for HCG 7 and the integrated flux and mass of HI for each galaxy and the group was computed. The predicted mass of HI was compared to that measured to find the deficiency of HI (Def(HI)) for each galaxy and the group. The mass of HI in the group was found to be 5.2E9 Msun. The resulting HI Deficiency of 0.61 indicates that the group as a whole has 1/4 the amount of neutral gas as field galaxies of the same Hubble Types. Data from the Spitzer IRAC imaging detector at (3.6um, 4.5um, 5.8um, and 8.5um) was used to measure the infrared flux for each member in HCG 7. The Spectral Energy Distribution for each galaxy was compared to its individual HI Deficiency, and it was found that the more gas rich galaxies (lower HI Deficiency) are more likely to be forming stars. HCGs span three stages of a proposed evolutionary sequence: pre-interaction, shocked intergroup medium, and smooth intergalactic medium. HCG 7 was found to be in the pre- interaction phase due to the fact that most of its atomic hydrogen is contained in the galaxies, with no obvious signs of large scale disturbances. Further studies of other HCGs using data from the VLA, Spitzer IRAC and MIPS (24um, 70um) instruments, and 2MASS (1.25um, 1.65um, 2.17um) survey, will allow us to determine how in the dynamical state of these groups are linked the the level of star formation activity, and how the gas content evolves along the evolutionary sequence.

Background Reading:

Paul Hickson's Compact Group webpage (through 1998)
Compact Groups of Galaxies, Hickson, 1997, ARAA, 35, 357
"Where is the Neutral Gas in Compact Groups?", Verdes-Montenegro et al. 2001, A&A, 377, 812 (excellent study; proposed evolutionary sequence)
"The evolution of HCG 31: Optical and high-resolution HI study" Verdes-Montenegro et al. 2005, A&A, 430, 443 (good example of detailed study of individual object)
Lourdes Verdes Montenegro's website of Compact Groups
An HI Rogues Gallery, see esp. Figs. 154-162.

John Kelly, of University of Virginia,
worked with Ken Kellermann on

Radio Observations of the Chandra Deep Field South

This summer John completed data reduction of approximately 50 hours of VLA 20 cm observations of the Chandra Deep Field South, which includes the new Hubble Ultra Deep Field, taken February and March 2004. The elevation of the CDFS field at the VLA is very low, compounding problems with ground pickup and interference, as well as limiting the observable time to only six hours per day. To obtain the highest fidelity image possible, John broke the data into small time segments and cleaned each of these separately before combining them in the image plane. This removed time variable effects and allowed much improved images to be made. The deepest image made using the 2004 data had a noise of ~15 uJy in the center of the field, somewhat higher than the theoretical, likely due to dynamic range effects from the bright sources. This was combined with a previous set of observations to produce an image with a noise ~7 uJy. John also began preliminary work on optical and X-ray comparisons with data from Hubble, Chandra and the VLT. The Chandra data contained about 50 obvious X-ray counterparts to radio sources, as well as a systematic offset in both RA and DEC which must be accounted for in future analysis

Michael McCarty, of Morehead State University,
worked with Scott Ransom on

GBT Pulsar Observations

There are several projects available in the field of pulsars. In particular, several deep observations from the Green Bank Telescope are available that need to be searched for exotic binary millisecond pulsars, one or more of which will likely be uncovered by the student. In addition many observations are available from X-ray satellites (XMM-Newton and RXTE) and radio telescopes (Parkes, Arecibo, and the GBT) with pulsar data for high-precision timing of millisecond pulsars, eclipse measurements of the original "Black Widow" pulsar, and timing observations of the very young pulsar in the supernova remnant 3C58. Each of the projects will demand some programming (C and Python preferably) and computationally intensive data analysis on a dedicated computer cluster.

Vinayak Nagpal, of Chalmers University of Technology,
worked with Rich Bradley on

Development of an Adaptive RFI Mitigation System for the GBT

Vinayak participated in the development of real-time, adaptive interference canceling algorithm suitable for implementation in Field-Programmable Gate Array (FPGA) technology. Several permutations of the LMS and RLS algorithms were evaluated on a PC-based signal processing system using data from the Green Bank RFI monitoring station and synthesized data. The results underscore the need for a high quality reference for each interfering signal. In addition, we are beginning to understand how these algorithms breakdown in the presence of multiple interference signals within the filter's passband and explored the use of multi-channel feedback to combat this problem.

Oluleye Olorode, of Benedict College,
worked with Eric Bryerton on

Optimization of a THz Heterodyne Test Receiver

The student made significant improvements to a 600-720 GHz test receivers for HEB mixers. He designed and built a beamsplitter to replace the Martin-Puplett LO diplexer. This improved the overall receiver noise performance from 900K to 500K at 660 GHz. The student also made significant improvements to the mechanical test apparatus by designing stands and brackets for the test dewar and LO source. These improvements allowed the student to efficiently test and compare different HEB mixer designs. This work addresses the THz technology gap, helping to exploit many new and exciting applications in this under-utilized frequency range, including but not limited to radio astronomy.

Julia Sandell, of Barnard College/Colmubia University,
worked with John Hibbard on

HI and GALEX Observations of Interacting Galaxies

One of the fascinating results of the Galaxy Evolution Explorer (GALEX) far- and near-UV imaging mission was the detection of UV-bright regions outside the optical disks of galaxies. For several of these systems, neutral hydrogen (HI) maps from the VLA were available (many from the HI Rogues Gallery). In these cases, the extra-disk star forming regions were found to be contained within HI extensions. Together with Jacqueline van Gorkom and David Schiminovich (both at Columbia University) and others, we have targeted other systems from the Rogues Gallery with GALEX to look for similar sites of extra-disk star formation. For this project, the student will reduce archival VLA HI data on several of these systems and compare the GALEX FUV and NUV images with the HI maps. Questions to be addressed: is there a correlation between star formation and HI column density similar to that found within normal disks? Is there any relationship to the underlying gas kinematics?

Background Reading:

Hibbard et al. 2005 ApJ, 619, L87 (HI & GALEX of "The Antennae")
Kennicutt 1989. ApJ, 344, 685 (SF Threshold)
Martin et al. 2005 ApJ, 619, L1 (GALEX)
Neff et al. 2005 ApJ, 619, L91 (HI & GALEX of 4 more interacting)
Thilker et al. 2005 ApJ, 619, L79 (HI & GALEX of M83)