• BL Lac 1997 Flare
• Asteroid Light Curves
• Cataclysmic Variable Star Monitoring
• Timing Observations of Close Binary Stars
• Supernova Search
• Variable Star Search
• Publications

Observations of BL Lac

We observed a large optical outburst in the blazar BL Lac in 1997. The observations consist of 50-second exposures in each of the two filters (photometric R and I) during the observing period for August 5 and 7, 1997 UT. In the light curves found below, BL Lac is plotted along with the check star C, with star B used as the calibrator (see finding chart). Also, a check star with comparable magnitude to BL Lac was plotted. More light curves will be posted as we collect new data.

• Finding Chart - From Smith et al., AJ, vol 90, pp 1184-1187, (plates pp 1385-1386). GIF image courtesy of Thomas Balonek at Colgate University.
• Image - For comparison. 7 Aug 1997, 06:09:47 UT, 50-second I filter.
• 7 August 1997 UT
  • R Band Light Curve
  • I Band Light Curve
• 5 August 1997 UT
  • R Band Light Curve
  • I Band Light Curve

Additional information about these observations and optical monitoring of AGN can be found at the following websites:

• A Serendipitous Multi-wavelength study of BL Lac in the Summer of 1997
• Colgate University Optical Quasar Page
  

Student Researcher: Grant Denn

Asteroid Light Curves

As asteroids travel around the sun in their orbits, they turn on their axes. Because the asteroids are neither spherical nor smooth, they reflect a varying amount of sunlight back towards the Earth as they turn. Imagine rotating a potato and observing the surface which faces you to get an idea of how this works. A plot of the light received from the asteroid versus time will show periodic behavior. Of the more than 5,500 cataloged asteroids, only a few hundred have known periods. The asteroid light curve research group's primary focus is to determine the periods of several dozen asteroids which have no previously measured period. An accurate knowledge of the rotation periods of many asteroids may help to define the distribution of angular momentum in the Solar System. Some asteroid light curves are shown here: 67 Asia (V=12.0, P=15.9h), 40 Harmonia (V=10.1, P=9.1h), 264 Libussa (V=12.0, uncatalogued period) 76 Freia (V=12.6, uncatalogued period)

Student Researchers: Carrie McGivern, Bill Peterson

Cataclysmic Variable Star Monitoring

Cataclysmic variable stars (also known as eruptive variables) generally consist of a contact binary system in which mass is being transferred from a cool M-type star to a white dwarf. These systems have short periods, and can provide information about the late stages of stellar evolution. Accretion phenomena and accretion disk properties may also be investigated by studying these stars. Cataclysmic variables will often brighten by several orders of magnitude during outburst. The AAVSO often enlists the aid of helpful astronomers to monitor stars in outburst. We are currently monitoring SS Cygnus in its outburst period.

Researchers: Carrie McGivern, Bill Peterson

Timing Observations of Close Binary Stars

Binary star systems periodically undergo variations in their light curves due to the motion of the stars in their orbit. As the stars pass in front of one another, the light from the background star is obscured, causing a temporary and often dramatic decrease in the amount of light received from these stars. The goal of this project is to acurately determine the times of the minima of these systems. From the times and depths of the minima, it is possible to extract information about the system, such as the masses and luminosities of the two stars, and information about the distance between them.

Researcher: Naysunee Buckner

Supernova Search

One of the first challenges encountered in the study of supernovae is finding them. This project is designed to expedite the process. The basis of the supernova search is the archive, which contains images of over 1000 nearby galaxies (mainly from the Thompson and Bryan and Alavarez lists). A number of these galaxies are observed approximately once per week, weather permitting. The search itself is done automatically, with a program checking new images against the images in the archive. The program flags all images with sources which appear in the new image, but not in the archive image. These images are checked manually using finding charts.

A recent example is SN1999cl, discovered in galaxy M88 (NGC4501, Hubble type Sc) by the KAIT supernovae search group on 29 May 1999. The Iowa Robotic Observatory observing list includes M88 on its late-type spiral observing list. Unfortunately, the nearest observation of this galaxy was June 3, four days after the discovery image from KAIT. Here are IRO images of the galaxy taken on March 23, 1999 (pre-discovery) and June 3, when the unfiltered apparent magnitude was 14.6.

    

Researcher:Allen Rogel

Search for Variable Stars

This project seeks to find previously unknown variable stars and confirm suspected variable stars. Using field images from other projects such as the supernova search project, we are observing the same region of sky repeatedly over a few months time. We then run a program that views each image in a particular field and labels each star. It then organizes each star according to the probability of it being variable. Next we analyze the graphs of these sky fields and using statistics determine whether or not the star appears to be variable.

According to The American Association of Variable Star Observers (AAVSO) variable stars are stars that change in brightness. These brightness changes can range from a few hundredths to as much as twenty magnitudes over periods of a fraction of a second to years,depending on the type of variable star. Stars change in brightness when they are very young, or when they are very old or dying.

There are now over 28,000 stars known to be variable, and 14,000 more that are suspected to be changing in brightness in our galaxy, the Milky Way. Variables are divided into four main classes: pulsating and eruptive, where the variability is due to physical changes in the star or star system, and eclipsing binary and rotating stars, where the variability is due to an eclipse of one star by another, or the effect of stellar rotation.

This light curve was done on the rx andromeda field and came up with the known variable as variable. This substantiates our findings because we found a known variable to be variable using our methods.

Links to Variable Star Pages:

• www.aavso.org: This sight is the home of the AAVSO. It offers a searchable database on variable star related topics.
• VSNET: A mailing list on variable stars. It has information on current variables of interest and a number of light curves mapping certain variables.

Researcher:Chris Anson

Publications

Postscript versions of published papers are available for downloading:

Supernova light curves:

Sauerbrei, P. and Mutel, R.L. , Multicolor Photometry of SN1993J, I.A.P.P.P. 53, 34, 1993.

Determining Extinction Coefficients:

Simon, L. M. and Mutel, R.L., Measuring Filter Response and Extinction Coefficients using CCD Observations of Photometric Standard Stars, I.A.P.P.P., 57, 48, 1994.

Binary Stars:

Benbow, W. and Mutel, R.L., Eclipse Observations of EQ-TAU, Commissions 27 and 42 of the IAU circular on variable stars, #4187. Also available as HTML.

Fortney, B. and Mutel, R.L., Determining the Ephemerides of Short Period Eclipsing Binaries: V566 Ophiuchi, I.A.P.P.P., 56, 6, 1994.

Asteroid Rotation Curves:

Armstrong, J. C., Nellermoe, B. L., and Reitzler, L. E., Measuring Rotation Periods of Asteroids Using Differential CCD Photometry, I.A.P.P.P. 63, 59, 1996. Also available as HTML.