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Physics

Photometry and Polarimetry on Broadband Energy AGNs

Maira Amezcua ('12); William Morrison ('12); Alma Zook

Blazars are active galactive nuclei (AGN) that emit over a wide range of the electromagnetic spectrum, peaking in the x-ray and infrared regions. Blazars are said to “go off,” when the intensity suddenly increases by factors up to 100 during the course of a few days. This summer’s goal was to observe a wide range of blazars through photometric measurements in gri filters and polarimetric measurements over a range of seven evenly-spaced polarimeter angles ranging from 0 to 90 degrees. The photometry monitors the changing intensity of the blazar while the polarimetry data can be fitted to find the polarization. The results collected this summer are a contribution to a world wide blazar project that continues to understand the location of the outbursts and broad band energy distribution.
Funding provided by: Pomona College SURP (MA, WM)

Sphagnum Moss: Exploding Capsules Genereate Vortex Rings for Increased Spore Range

Emily Chang ('12); Dwight Whitaker

Sphagnum moss, or common peat moss, ejects its spores in an explosive manner to propel them to a height sufficient to catch turbulent air currents. The round sporophyte contains the spores, and builds a pressure difference that causes the capsule to contract and air inside the capsule to be shot out with a stream of spores. Sphagnum spores can reach heights of up to 15 cm, however single spores shot out with the same initial velocity into still air would reach a distance of only 2-3 mm. High speed video analysis shows that the moss generates vortex rings from the launched air, allowing the spores to travel further than they would with regular ballistic motion. This is the first plant known to generate vortex rings. FLUENT, a computational fluid dynamics software, and Laser Doppler Velocimetry were used to analyze the efficiency and optimality of the vortex rings.
Funding provided by: Howard Hughes Medical Institute

Preparing the TMO Telescope for an Adaptive Optics System

Rachel Chin ('12); Oliver Hoidn ('11 HMC); Philip Choi

Atmospheric distortion has traditionally limited the clarity of imaging that ground-based telescopes can achieve. The development of adaptive optics (AO) systems has made it possible to correct that interference in real–time. In preparation for mounting an AO instrument on the Pomona College’s 1-meter telescope located at the JPL Table Mountain Facility, we have modeled the optical and opto-mechanical design of the telescope, its current instrumentation and the planned AO system. These models were then used to evaluate the performance of the current and planned systems and develop a new off-axis guiding system to improve telescope tracking. The guiding system has been fabricated and successfully tested on sky, resulting in a >10x improvement in guiding accuracy. The models will be used to finalize the optical and mechanical design of the planned AO instrument.
Funding provided by: Pomona College SURP (RC)

Molecular Structure and Nuclear Quadrupole Interaction of the Alkali Fluorides

Arolyn Conwill ('10); Zack Lasner ('12); Richard Mawhorter; Jens-Uwe Grabow*; Peter Schwerdtfeger**; Detlev Figgen**; Phil McCaffrey***; Derek Wann***
*Institute for Physical Chemistry, Leibniz University, Hannover, Germany; **University of Auckland, Auckland, NZ; ***University of Edinburgh, Edinburgh, Scotland

This project investigates diatomic and four-atom alkali halides in low vibrational energy states using high-precision Fourier transform microwave spectroscopy. Specifically, we are interested in the nuclear quadrupole coupling with the lower rotational energy states in alkali fluorides, including the several isotopologues 6,7LiF, 23NaF, 39,41KF, 85,87RbF, and 133CsF. With a resolution of 3 kHz, our measurements both extend the precision of previous XF monomer studies as well as determine new transition frequencies for both monomers and a new mixed dimer, Li2FCl.
Funding provided by: Pomona College SURP (AC, ZL); Pomona College Sontag Grant(RM)

Fluorescence Microscopy and Spectroscopy of Patterned Phospholipid Bilayer

Tewei Luo ('11); Alfred Kwok

Patterned 1-Palmitoyl,2-oleoyl-sn-Glycero-3-phosphocholine (POPC) bilayer was produced by UV photolithography with a photomask. Two types of pattern, namely squares and stripes were obtained. Fluorescence images and spectra of these patterned lipid bilayers were collected and the spatial resolution of the spectra was examined. The results showed that the spectrometer was able to resolve 10 µm features. Bilayers with smaller features were attempted but the patterns produced were not clearly defined, suggesting that new patterning techniques are required. The resolution of the system is important because Raman spectroscopy will be performed later on lipid rafts whose size is 1 to 200 microns.
Funding provided by: Howard Hughes Medical Institute

Blazar Observation: Data Reduction

Will Morrison ('12); Maira Amezcua ('12); Alma Zook

In order to calculate the magnitude of a photographed object, several sources of error inherent to the CCD camera and telescope optics must be compensated for. Three types of images are taken on the night of observation for this purpose, which are then combined and arithmetically applied to the night's other frames. This preprocessing stage was streamlined through the creation of an Awk script which automates the entire process when given several basic input parameters. Once corrected, the object and reference stars in each frame must be selected. The considerable monotony of effecting this by hand (30-70 frames/object; 6-12 objects/night) can be eliminated by first aligning all images for each object. Two methods were designed to deal with cases in which cumulative shifts are too large for the images to be aligned directly, both utilizing simple Awk scripts. These improvements cut reduction time drastically.
Funding provided by: Pomona College SURP (WM, MA)

Using Magic-Sized PBSE Nanocrystal Growth to Control Size and Photoluminescence in the Near-IR

Benjamin Pollard ('11); David Tanenbaum; Tobias Hanrath*
*Dept. of Chemical Engineering; Cornell University, Itaca, NY

Much work has been dedicated to the idea of using nanocrystals (NCs) as the active layer in solar cells due to their ability to absorb light and confine the resulting exciton. However, the NCs must be made small enough so that their band gap falls in a range near the peak energy of photons from the sun. Conventional wet-chemical synthesis procedures of PbSe NCs do not afford the size control needed to reliably create crystals in this range. By decreasing the reaction temperature to around 60C and adding an additional reducing agent, a synthesis procedure similar to work on magic-sized PbSe clusters can create monodisperse products of the size needed to build efficient nanocrystal solar cells.
Funding provided by: REU Program through National Science Foundation (Cornell University)

Measuring the Internal Kinematics of the Local Group Galaxy M32

Alexander Rudy ('11); Philip Choi

We used high-resolution spectroscopic observations taken with the Echellette Spectrograph and Imager (ESI) on the Keck ten-meter telescope to measure the internal kinematics of the nearby compact elliptical galaxy M32. Targeting approximately 50 red giant branch stars in the outer regions of the galaxy, we obtained individual stellar velocities for stars in the M31-M32 system. Data were obtained using a unique multiplexing technique that enabled an increase in observing efficiency by a factor of five, but that required the development of a special data reduction routine, which has now been completed and tested on our data. A preliminary velocity distribution based on the identification of the characteristic calcium triplet lines (found at 850, 854, 866 nm) is presented along with high confidence galaxy membership predictions. Refined velocities will be obtained in the future using a spectral template cross-correlation technique and eventually used to constrain various galaxy interaction models.
Funding provided by: Pomona College SURP

Research at Pomona