mountain profile Institute for Astronomy University of Hawaii

2009 REU Students' AAS Abstracts

Maintained by LG

AAS meeting, January 2010, Washington, DC
The Stellar Mass-Exoplanet Correlation
Kimberly Aller (University of California, Berkeley & IfA), J. Johnson (Caltech)

We have derived an empirical relation between stellar mass and planet occurrence by measuring the occurrence rate of planets from Doppler surveys spanning a wide range of stellar masses. We used Bayesian parameter estimation to fit a parametric model to the sample of detections and non-detections in our data set, while simultaneously correcting for the effects of metallicity. Remarkably, we find no correlation between stellar metallicity and planet occurrence for stars with masses greater than 1.5 Msun. We see a slow increase in the measured planet occurrence for stars with masses less than 1.5 Msun which rises steeply thereafter. There is a much higher chance of finding a gas giant planet around an A-type star, regardless of its metallicity, than around either an M-dwarf or Sun-like star.

DPS meeting, October 2009, Ithaca, NY
Detectability of Low-Mass Trojans in Transiting Systems Using Transit Timing Variations
Stephanie Capen (Eastern Nazarene College), N. Haghighipour (IfA & NASA astrobiology Institute, University of Hawai), S. Kirste (IfA & NASA astrobiology Institute, University of Hawai)

We present the results of a study of the feasibility of detecting small, terrestrial-sized planets in a transiting system consisting of a Jupiter-like planet and an M-dwarf using the variations in the transit timing of the larger body. Specifically, we studied the case where the two planets are in 1:1 mean-motion resonance. To determine the detectability of such Trojan planets, a number of systems with different masses, eccentricities, and periods were numerically integrated and the amplitudes of their TTV signals were calculated. Results indicate that Trojan planets in 3 to 10 day orbits and with eccentricities ranging from 0 to 0.15 have a high probability for detection. We present the results of our study and discuss the applicability of our analysis to the probability of the detection of such planets with the recently launched Kepler space telescope. Support for S.C. through the NSF funded REU program at the Institute for Astronomy, University of Hawaii is acknowledged.

AAS meeting, January 2010, Washington, DC
Color Analysis of Local (U)LIRGs
Michele Dufault (Yale University & IfA), D. Sanders (IfA), V. U (IfA & Harvard-Smithsonian Center for Astrophysics)

Luminous and ultra-luminous galaxies, galaxies with LIR > 1011Lsol and 1012Lsol respectively, are critical in understanding galaxy interaction and evolution; however, the local population (z < 0.088) as a class has been understudied. We present a color analysis of a subset of 22 local (U)LIRGs from the Great Observatory All-sky LIRG Survey (GOALS) sample. We examine the g - r color distribution for both global and localized regions within each system in order to understand what physical mechanisms give rise to the appearance and color of these sources. The 2 kpc regions surrounding the K-band centroid of each object are redder and optically fainter than the corresponding hosts, which are aligned with the luminous end of the blue cloud. We compare the total photometry colors with pipeline data from the SDSS archives and find the database color distribution to differ significantly. Finally, two color profiles of the ULIRGs Mrk 231, host of a known QSO, and Arp 220, host of a heavily obscured AGN, show that despite their differences, their host colors are very similar. This result suggests that the vast difference between the two objects might be dominated by the amount of dust obscuration in the central regions. This work was conducted by a Research Experience for Undergraduates (REU) position at the University of Hawai'i's Institute for Astronomy and funded by the NSF.

AAS meeting, January 2010, Washington, DC
Evidence for a Composite Starburst-AGN Class of Infrared Galaxies
F
rancesca Fornasini (College of William and Mary), L. J. Kewley (IfA)

In order to determine whether composite starburst-AGN galaxies demonstrate any radio properties distinct from starbursts and AGNs, we studied 156 infrared objects for which spectroscopic and VLBI or LBA radio data was available. We found that 19 of 28 (68%) optically classified AGN had a compact radio core, 16 of 55 (29%) optically classified starburst had a compact radio core, and only 8 of 52 (15%) optically classified composites had a compact radio core. Thus, there appears to be a depletion of compact radio cores among composites, an unexpected result considering that in previous classification schemes, composites were often classified as LINERs. We calculate that there is <1% chance that such an uneven distribution of compact radio cores would randomly occur if composites were AGNs, and that there is a 7% chance that this distribution would occur if composites were starbursts. The latter is a small but significant percentage, and it is probably a lower bound, considering that some of the optically classified starbursts with compact radio cores may actually be obscured AGN. In addition, we find that the compact radio core luminosity of composites tends to be in between that of starbursts and AGNs, supporting the hypothesis that composites may possess a mixture of starburst and AGN phenomena. Thus, these results, though not enough to decisively confirm the existence of composites as a distinct class, certainly lend support to such a conclusion, and suggest that composite galaxies may be an interesting area of future research. This research was undertaken at the Institute for Astronomy at the University of Hawaii as part of a Research Experience for Undergraduates (REU) program funded by the National Science Foundation.

American Geophysical Union, Fall Meeting 2009, San Francisco, California
Determining CME Azimuthal Properties from Stereoscopic Heliospheric Observations
N. Lugaz (IfA), J. N. Hernandez (Universidad de los Andes, Bogota, Colombia), I. I. Roussev (IfA), A. Vourlidas (Naval Research Laboratory, Washington, DC)

We discuss how remote-sensing observations by multiple white-light imagers can provide some information about the azimuthal deflection and azimuthal expansion of Coronal Mass Ejections (CMEs) as they propagate in the heliosphere. Our analysis focuses on one CME which was well observed by the SECCHI/HIs onboard STEREO-A and B on April 26-28, 2008. By considering two simple models of CME geometry and using simultaneous observations from the two different viewpoints, we show that the observations can be best understood by modeling the CME as a propagating sphere of expanding radius on a fixed radial trajectory. Preliminary analysis shows that the CME expansion is self-similar from 0.2 AU until 0.5 AU and slows down afterwards. An alternative explanation of the observations is a deflection towards the east of a bubble CME. While observational effects may play a role, the results from these two models are corroborated by the non-detection of the CME at L1, where a CME hit was expected based on its initial width and direction.

 

AAS meeting, May 2010, Miami, Florida
Double Lobed Radio Sources in Cl1604 at z~.9
Stephen Sirisky (Rutgers University), R. Gal (Institute for Astronomy)
                 

We present findings from the Observations of Redshift Evolution in Large-Scale Environments (ORELSE) super cluster survey. The super cluster Cl1604 residing at z ~ 9 is one of only a few such large scale structures discovered at high redshift. The structure has been imaged in a variety of wavelengths, including radio, optical, infrared, and x-ray, and spectroscopic measurements have been taken using DEIMOS and LRIS on Keck. Using the 1.4 GHz VLA maps and HST optical imaging of Cl 1604 to visually inspect for double radio sources with associated optical host galaxies, we have confirmed three double lobed radio sources within the large scale structure. From the observations of these sources, we calculate radio luminosities and lobe separations using data from previously discovered double lobes at similar redshifts in the VVDS and FIRST surveys. Furthermore, we examine the host galaxy properties, including optical colors, morphologies, spectra, and each of their specific locations within the constituent cluster and the broader super cluster. Although the low number of sources limits statistical analysis, we find that the double lobes only appear in the large scale structure, and within the large scale structure only in areas of high galactic density.