Program Activities
-- Sweet Anne (Macalester College) - advisors: Bernadette Rodgers & Greg Doppmann "Near infrared spectra of Herbig Ae/Be double stars"
Herbig AeBe binary systems are good environments for the study of pre-main sequence stellar evolution in companion stars whose mass may be significantly lower than that of the primary. Measurements of the spectral type and surface gravity of the companion star in the system allow it to be placed on the H-R diagram, where theoretical evolutionary model tracks can then constrain its mass and age, and comparisons can be made between these low mass stars and those formed without the presence of a high mass star. Because of the extinction associated with objects in star forming regions, the near-infrared offers a less obscured wavelength region than the optical through which to study these objects. Medium (R= 1,700 & 6,000) and High Resolution (R=18,000) near-IR spectra was gathered for the analysis of these companion stars. We present two different ways to measure T_{eff} and estimate log g from the spectra of late type stars, depending on the spectral resolution. At high resolution, detailed model fits to the shapes of Na lines at 2.21 microns and the (2-0) CO bandhead at 2.29 microns provides an accurate way to measure effective temperature and surface gravity, in addition to allowing for values of vsini rotation, veiling, and radial velocity to be estimated. At medium resolution, the equivalent widths of 10 of the strongest absorption lines present in the K band spectrum were measured to determine T_{eff} at a lower accuracy. We present the results of these fitting techniques, in addition to a discussion of line strength versus temperature, in this work.
-- Widhalm Allison (University of Southern California) - advisor: Stella Kafka "WIYN Open Cluster Study long term monitoring: NGC 2141"
Old open clusters, located in the disk of the galaxy, are useful tools in understanding the variability of stars in a certain age range. In this paper, we study the old open cluster NGC 2141 which previous to this work has never been studied for variability. Long-term data for this project was taken at the 0.9m telescope at the Kitt Peak National Observatory from November 2004 through December 2005, as a part of the synoptic program. We present initial results of finding variable stars. Of the 100 candidate variables thus far, two have been confirmed to be Algol eclipsing binaries. Future work includes determining variability for the rest of the candidates.
-- Tucker Brad (Notre Dame) - advisors: Knut Olsen and Bob Blum "Do the LMC and Milky Way Globular Clusters Share a Common Origin?"
We took infrared spectroscopy in the wavelength of 1.5552 - 1.5600 microns, of six metal poor red giant stars in NGC 2019 with the Phoenix high-resolution spectrograph at the 8.1 Geminin South telescope. Previous measurements and calculations of NGC 2019 have metallicites differing by .6dex and ang within 1 Gyr of the oldest globular clusters in the Milky Way. We carried out detailed analysis on the six stars in order to determine accurate oxygen and iron abundances to see if a similarities exist between the LMC and the Milky Way globular clusters. We calculated, through different methods, the stellar parameters of effective temperature, bolometric correction, gravity, luminosity, and microturbulent velocity. We calculated these in order to accurately obtain stellar atmosphere models. The model atmosphere that we used, produced strong and dispersed [Si/Fe] and [Ti/Fe] due to the strong impact of the microturbulent velocity. We calculated a mean Oxygen to Iron ratio of .35, which is similar but not the same as that found in the Milky Way.
-- Newman Andrew (Washington University in Saint Lewis) - advisor: Armin Rest "A Difference Imaging Technique for Extracting Light Echo Fluxes with an Application to SN 1987A"
A new technique for extracting fluxes from light echoes is presented. Rather than relying on a single template image with no light echo flux, we contruct difference images from every pair of observations. From this, the NN2 method of Barris et al. (2005) is used to compute for each pixel the relative fluxes at each epoch. Statistical methods are presented to calculate the zero-flux level and thus the absolute flux, as well as to detect light echo regions in the resultant images. The technique is applied to the light echoes around SN 1987A, and the images obtained reveal remarkable new detail and structure. Basic geometric properties of the rings are calculated and found to be in agreement with the literature.
-- Klimek Matthew (Rutgers University) - advisors: Sean Points & Chris Smith "Multi-Wavelength Investigation of Newly Discovered SNRs in the LMC"
The Large Magellanic Cloud (LMC), with its low foreground absorption and proximity, offers the ideal site to study a large sample of supernova remnants (SNRs) in detail, both spatially and energetically. It is possible to obtain a relatively complete sample of SNRs in the LMC to examine both global properties and the subclasses of SNRs. Toward this goal, we have identified new SNRs using multi-wavelength data. The newly recognized SNRs are generally fainter than the known sample, and may represent a previously missed population.
We have obtained X-ray images and spectra of three of these recently identified SNRs using the xmm observatory. These data, in conjunction with pre-existing optical emission-line images and spectra and radio continuum data, are used to determine the physical conditions of the warm (wim) ionized gas and the hot (him) ionized gas. We compare the morphologies of the SNRs in the different waveband. The physical properties of the warm ionized shell are determined from the Ha surface brightness and the SNR expansion velocity. The X-ray spectra were fit with a Raymond-Smith thermal plasma model and the physical conditions of the hot gas are derived from the model fits. We find that the pressure of the hot gas is greater than that in the warm shell by about an order of magnitude, implying that these remnants are in the pressure-driven expansion stage. We also discuss the ages and classifications of the remnants.
-- Rudie Gwen (Darmouth College) - advisor: Bryan Miller "The Formation of a dE Nucleus Caught in the Act"
We present the preliminary findings of a kinematic study of the low luminosity elliptical galaxy IC225. This object is of considerable interest as it contains two bright nuclei which could give cadence to the theory of Dwarf Elliptical (dE) formation through merger scenario. We present Integral Field Unit (IFU) data of the dE from the Gemini-North Multi Object Spectrograph (GMOS) Integral Field Unit (IFU) taken December of 2005. This paper consists largely of technical information about the reduction process; and we present a new comprehensive reduction plan for data of this sort. From the reduced IFU data, we present several 2D maps of the region including higher order Balmer lines and the [OIII] couplet atlambd 4959, 5007. From these images we conclude that within IC 225, the off-center nucleus is almost certainly assocaited with a large cloud of gas. Preliminary kinematic evidence of net rotation within the gas of the galaxy is also presented along with evidence of some stellar movement.
-- Cordero María José (Pontificia Universidad Católica de Chile) - advisors: Nicole van der Bliek & Sandrine Thomas "Searching for Herbig Ae/Be multiples"
We present the analysis of high-resolution near-infrared (NIR) adaptive optics images of a sample of 42 Herbig Ae/Be stars (HAEBE). HAEBE stars are pre-main sequence stars which have spectral type from B through F and show emission lines and NIR excess associated to a circumstellar disk. They are intermediate mass stars with masses between 2-8 M_{sun} and HAEBE stars are useful to try to understand the formation as function of the mass. They are in between the low and high mass stars. It is important for the formation models to know multiplicity of young stars as a function of mass.
Using NIRI/Altair system it is possible to detect companions as close as 0.1 and about 5 magnitudes fainter in the best conditions. In this stellar study there are 42 stars, 17 binaries were found with typical detection limits rho > 0.087 for small dK and dK < 9.7 for larger rho. Objects as faint as dK = 5 could be detected at rho > 0.3.
-- Mateluna Renée (Universidad de Concepción) - advisors: Hugo Schwarz & Joey Richards "Properties of Planetary Nebulae"
We present, for the planetary nebula NGC 2022, the results of spectral-line flux mapping extracted from long-slit spectra taken with the 2.56 m Nordic Optical Telescope, in the Observatorio del Roque de los Muchachos, Spain. Two-dimensional emission-line images for the entire nebula are created using data from only half of the nebula, and are used to derive fluxes for 19 lines. We also create the Halpha/Hbeta extinction map, the [SII] and [Ar IV] line ratio density maps, and the [OIII] temperature map of the nebula. The total Hbeta flux is compared with values obtained by other authors. With these results we are ready to begin modelling the nebula with a 3-D photoionization code, which will allow us to determine the distance to NGC 2022.
-- Damke Guillermo (Universidad de La Serena) - advisor: Armin Rest "Probing the Dust Structures in the LMC with Light Echoes"
Light echoes provide us one of the best ways to map the dust structures in the ISM. A preliminary study in infrared an HI of three light echoes regions in the LMC associated to ancient supernovae (Rest et al. 2005) is presented. Infrared images are used to identify dust structures where light echoes have been detected and they are used to improve the measurements of relative distances to dust structures up to 1 kpc in the foreground of one of the SNR. HI data is used to measure the velocities of the dust structures. We find out different correlations between relative distances and HI-velocities and they allow us to recognize different dust structures for the light echoes regions.
