2005 REU/PIA Projects

Photometry of Eta Carinae - Sonia Aggarwal

The Planetary Nebula NGC 6543 - Claire Bendersky

Herbig Ae/Be Stars - Ben Brandvig

Suspected SW Sextantis Stars - AJ Carver

Extinction Towards Planetary Nebulae - Betsy Mills

The Night Sky Brightness at CTIO - Dylan Semler

Red Quasars - Laura Pérez

The Energy Balance of LMC-1 - Omar Valdivia

Photometry of Eta Carinae
Sonia Aggarwal - Haverford College

Project Description:

During my time here at CTIO in La Serena, I have been working on the beginning of a long term uniform photometric baseline project for the monitoring of Eta Carinae using data taken by the SMARTS 1.3 meter telescope with ANDICAM. I have become comfortable using IRAF to reduce raw images in the visual and the infrared and then gone on to perform standard photometry on the reduced images. I have now completed the reduction of all the data associated with our project, which started in November of 2004.

Armed with standard photometry, I added more points to the historical V-band and H-band light curves and began to put points onto I-band and 10830 Å narrow-band curves. We chose V-band and I-band in the visual because R is dominated by the the H-alpha emission line so we choose to get color information for Eta Car using V and I instead. We chose H-band as an infrared wavelength, which ignores most of the atmospheric absorption. We chose a narrow-band (70 Å FWHM) 10830 Å to monitor excited line-emission but since we do not have a standard in that filter band, the photometry is only relative for now.

We have observed a significant amount of variation on the two week time scale after performing several sanity checks on this data to become more confident that the variation we are observing is real. These checks have included comparing photometry using various aperture sizes to minimize effects of cosmic rays and also plotting color differences over time to make sure that they remained relatively linear. All tests lead us to the conclusion that the variations we observe are real. We are working on getting more frequent observations of Eta Carinae based on the significance of the variations we have observed.

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The Planetary Nebula NGC 6543
Claire Bendersky - Mt. Holyoke College


Rings surrounding the core of planetary nebulae are a recent and unexpected discovery. Spectrapolarimetry was taken by ISIS, a double-armed, medium resolution spectrograph. The single to noise ratio was too low in all wavelengths, except in the [O III] (5007A) due to the nature of forbidden line emission. By plotting the angle and the degree of polarization vectors polarization from a central source becomes apparent, especially compared to the central source and halo which do not display polarization. Polarization in rings the imply they contain dust that scatters light from a central source. They are likely to be AGB remnants because their simple shape does not reflect the complex symmetry of the core.

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Herbig Ae/Be Stars
Ben Brandvig -University of Washington

Introduction and Goals

Herbig Ae/Be stars are young, fairly hot stars. They are of intermediate mass, meaning that they are about 2-10 times more massive than our Sun and they are pre-main-sequence stars, which means that they have not yet reached the stable, hydrogen-burning phase that our Sun is currently in. Another interesting fact is that they have been found (Leinert (1997), Testi (1997)) to often form in binary or mutiple groups. Their companion(s), to which they are gravitationally bound, are assumed to be of a similar age (if they are gravitationally bound, then they are close enough to have probably formed at the same time). T Tauri stars are about the same age as Herbig stars and are of lower mass (about the mass of our Sun) so the lower mass companions to Herbigs are assumed to be T Tauris. Both Herbig and T Tauri stars usually have circumstellar disks which cause NIR excess.
The goal of this project is to study the spectral energy distributions (SEDs) of the Herbig primaries and their (T Tauri?) companions. The Herbig stars in these systems have been fairly well studied and their spectral types are known. By comparing the SEDs of the system to SEDs of model stars we hope to gain some insight on the distance and extinction of the system, and more importantly, on the spectral type of the companion star. We will compare the SED results with spectroscopy for several systems and try to gauge the validity of the SED method.

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Suspected SW Sextantis Stars
AJ Carver - University of Wisconsin-Madson


The 2005 CTIO REU program observed two catalsmyic variables, AH Men and V393 Hya, using the 0.9m Cassegrain telescope on Cerro Tololo. 936 images of AH men were taken over two nights. 386 images of V393 Hya were taken over three nights. Aperture photometry was done using IRAF to produce light curves. Superhumps were not observed in V393 Hya. Evidence for superhumps was observed in AH Men, however we discovered that superhumps had already been observed in AH Men by Joseph Patterson (Patterson 1995) under the name H 0551-819. Power spectra plots of AH Men qualitatively agree with Patterson.

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Extinction Towards Planetary Nebulae
Betsy Mills - Indiana University


In general planetary nebula distances are not well known. There are a few planetary nebulae for which special means can be employed to find an accurate distance, but until recently there has not been a generally applicable method which has yielded accurate results. Most methods require assumptions that are likely incorrect such as constant mass for all the nebulae that lead to systematic over or under-estimations of distance. It is important to have some way to measure distances to a large number of planetary nebulae accurately, and without having to assume anything about the nebula itself.

We present progress in a survey of planetary nebulae distances determined by the extinction method. This method measures the extinction, or the amount of dust and gas, between us and a nebula, and compares it to that measured for surrounding stars of known distances to determine a distance for the nebula. No assumptions about the nebula are made to measure these quantities, and thus this method should yield a set of accurate distances.

We have measured nebular extinctions for long-slit spectra of 50 nebulae. By measuring the Balmer decrement and comparing it to theoretical values in the absence of extinction we have measured exactly how much each nebula has been reddened, and thus how much extinction is between us and the nebula. These values will help us progress toward our ultimate goal of finding accurate distances to these nebulae.

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The Night Sky Brightness at CTIO
Dylan Semler - Macalester College


The goal is to measure accurately the sky brightness. On a given night, there are many parameters that may artificially add too or subtract from the brightness of the sky. In determining the long-term trend of sky-brightness, these artificial factors must be identified and accounted for. I present here examples demonstrating the effects of some of the currently identified parameters so as to help determine the extent to which they alter the sky-brightness level.

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Red Quasars
Laura Pérez - Universidad de Chile


With data obtained using ISPI (Infrared Side Port Imager) in the 4.0 Meter Blanco Telescope at CTIO, we are trying to find "Red Quasars", i.e. those with 10 times more X-ray flux than r flux. We have 8 ChaMP fields (Chandra Multiwavelenght Project) like the one in the picture, observed in two filters: J and Ks band, and this fields have been previously observed in X-ray and g', r' and i' filters using CHANDRA Satellite and NOAO/MOSAIC imaging respectively.

Because X-ray emission is an very efficient way to select AGNs (Active Galactic Nuclei) no matter their obscuration and redshift, we are looking for red objects in those fields in order to find their counterparts for the X-ray sources already found by CHANDRA.

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The Energy Balance of LMC-1
Omar Valdivia - Universidad de Concepción

Project: Star Formation History in The Supergiant shell LMC-1

Supergiant shells are the largest interstellar structures in galaxies and play an important role in the global structure and evolution of the interstellar medium. It is believed that supergiant shells are formed collectively by fast stellar winds and supernova explosions from a large number of massive stars. Much work has been done to investigate the massive stellar content and star formation histories of supergiant shells in galaxies. These investigations conclude that the past massive stellar content of several of the largest supergiant shells could not have formed and powered the supergiant shells. This conclusion, however, is based upon integrated photometry of clusters, not observations of individual stars. My mentors have obtained spectroscopic and X-ray images of the supergiant shell LMC-1 which enable us to measure the kinematic and thermal energy contained by the supergiant shell, respectively. My work is try to obtain UBV photometry of individual stars toward LMC-1. This photometric data can be used to derive the amount of energy which the massive stellar content of LMC-1 has deposited into the ISM. Thus, it is possible to determine if the underlying stellar population of LMC-1 has been able to provide the energy to power the supergiant shell. If the massive stellar content has been able to provide the required energy input, we will also be able to determine the efficiency of stellar energy feedback into the ISM on scales of ~1kpc.

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