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Curriculum Vitae





John Feldmeier's Astronomical Research

Here's a brief summary of the different astronomy fields that I work on. For more details, you can see my list of publications

What's intracluster light anyway?
What's a planetary nebula?

Searching for intracluster light through deep imaging

Using both the KPNO 2.1 meter telescope and the Case Burrell Schmidt telescope, we are conducting a deep imaging survey of clusters and groups of galaxies, to detect and quantify the structure of the diffuse intracluster starlight as a function of cluster and group properties.

Collaborators: Chris Mihos, Heather Morrison, Paul Harding

Intracluster Planetaries
Searching for intracluster light using planetary nebulae

Planetary nebulae are excellent tracers of the intracluster light in nearby galaxy clusters because they allow for both spatial and kinematical studies. We have conducted multiple narrow-band imaging surveys of nearby galaxy clusters to find intracluster planetaries, and have obtained follow-up spectroscopy for some of them to obtain radial velocities.

Primary Collaborators: Robin Ciardullo, George Jacoby, Patrick Durrell, Kelly Holley-Bockelmann, Chris Mihos
Secondary Collaborators: Magda Arnaboldi, Ken Freeman, Ortwin Gerhard, Holland Ford, Aaron Romanowsky

Intracluster Red Giant Stars
Searching for intracluster light using red giant stars

Another way to learn about intracluster stars is through imaging intracluster red giant stars with the Hubble Space Telescope. This allows us to learn detailed properties of the stellar population of the intracluster stars.

Primary Collaborators: Robin Ciardullo, George Jacoby, Patrick Durrell, Ben Williams, Steinn Sigurdsson
Secondary Collaborators: Magda Arnaboldi, Harry Ferguson, Ken Freeman, Ortwin Gerhard, Ted von Hippel, Nial Tanvir,

M101 Planetary image
Finding the distances to galaxies using planetary nebulae

Using the [O III] 5007 emission line, and the empirical planetary nebula luminosity function (PNLF) distance indicator, the distances to nearby galaxies can be found to high precision, comparable to that of Cepheids. Our recent focus has been only applying the PNLF method to spiral galaxies, and to better calibrate the absolute magnitudes of supernovae Type Ia

Collaborators: Robin Ciardullo, George Jacoby, Mark Phillips

Understanding stellar populations in galaxies using planetary nebulae

Since planetary nebulae are one of the normal end phases of stellar evolution, by measuring the number of planetary nebulae in a distant galaxy, we can probe the mechanices of stellar evolution. We have been surveying planetary nebulae in both spiral and elliptical galaxies and comparing them to the overall stellar distribution.

Collaborators: Robin Ciardullo, George Jacoby, Kim Herrmann

M86 image
Emission-line studies of nearby galaxies

Studying the ionized gas of nearby galaxies can be useful for many topics in astrophysics. Currently, I'm involved in groups studying the giant elliptical galaxy M86 (seen here in Hydrogen-alpha emission), and also in a search for Gamma-Ray burst remnants.

Collaborators: George Jacoby, Jeffrey Kenney, Tomer Tal, Hugh Crowl, James Rhoads, Rosalba Perna, Jochen Grenier, S.G. Bhargavi

Lyman-alpha galaxies
Studying high-redshift emission-line galaxies

Searches for extragalactic planetary nebulae turn out to be also good ways to find Lyman-alpha galaxies, particularly those around a redshift of z = 3.1. We have compiled a large sample of these galaxies, and are studying their properties. On the left are some examples of Lyman-alpha galaxy candidates. Notice that the object is present in the left-most frame, but almost disappears in the middle frame. The right frame is the two images subtracted by each other, which shows the candidate clearly.

Collaborators: Robin Ciardullo, Caryl Gronwall, Eric Gawiser and the MUSYC collaboration

High-Precision Stellar Variability Observations

Using careful observing, reduction, and analysis techniques, we can perform relative photometry as accurate as a few milli-magnitudes using 1-meter class telescopes, such as the Burrell Schmidt. We intend to use these capabilities to carry out some long-term studies of variable stars, and to possibly search for extra-solar planetary transits. On the left is a light curve of the RR Lyrae star CL Boo.

Collaborators: Steve Howell, Mark Everett, Chris Mihos, Paul Harding, Bill Sherry, Kaspar von Braun

The Thinker
Applying Astronomy Education Research to the Classroom

We are using the new astronomy education tools developed by the Center for Astronomy Education (CAE) at the University of Arizona's Steward Observatory and the Cognition in Astronomy, Physics and Earth sciences Research (CAPER) Team at the University of Wyoming. Our goal is to refine and fine-tune these tools to aid student learning, and to better apply them to our classrooms.

Collaborators: Ed Prather, Gina Brissenden, Timothy Slater, Patrick Durrell

What is intracluster light?

Intracluster light (ICL) is optical light that is emitted between the galaxies in a galaxy cluster or group. This light, sometimes called the diffuse light, mostly comes from intracluster stars, which are stars between the galaxies. It is generally thought that most of the stars were actually formed within galaxies, but were then were later ejected from them, usually due to interactions between galaxies, or with the gravitational force of an entire cluster themself.

Below here is an image of the center region of the Virgo Cluster of galaxies. You can see many images of this region in the sky in astronomy books of all kinds:

Image of Virgo Cluster

Now, look at the image below. Notice that the space betwen the galaxies is filled with light in complicated structures:

Image of Virgo Cluster

(see here for a press release about these images)

Some high quality computer animations that show the creation of intracluster light can be found with my collaborators, Chris Mihos and John Dubinski. The animations can be found here and here.

So, if intracluster light is so interesting, why is it not well known? Well, the original idea of intracluster light was first proposed by the scientist Fritz Zwicky in 1951. So the concept has been around for over fifty years, and three generations of scientists have looked for the intracluster light. Actually observing the intracluster light is very difficult because the light is spread out over a large area.

A simple example will explain this better. Suppose we have a small container of food coloring:

Image of food coloring

We can see the colors clearly with our eyes. Now, drop some food coloring into a swimming pool:

Image of swimming pol

For maybe a minute or two, we can still see the food coloring dye, but it will quickly spread out through the pool. The atoms that make up the food coloring however, are still there, just difficult to see. Likewise, there can be a lot of light between the galaxies, but if it is spread out over a large area it becomes hard to observe. We observe the intracluster light two different ways. First, we directly image the intracluster light, using special techniques, and specialized telescopes to pull out the faint emission. Second, we search for bright individual intracluster stars in nearby clusters, and use those observations to understand the global properties of the intracluster light.

A nice article by the famed science writer Dennis Overbye about intracluster light in the Virgo cluster can be found at the New York Times website here.

What is a planetary nebulae?

A planetary nebulae is an ending phase of a star's life that most stars between 0.8 times the mass of the Sun and 8 times the mass of the sun go through. A planetary nebulae consists of 1) the remaining hot stellar core of the star (that will eventually become a white dwarf star), and 2) an expanding shell of gas that is being ionized by the hot core. Planetary nebulae exist for very short lifetimes, as far as stars go, only 25,000 years.

There are many beautiful pictures of planetary nebulae. Here is a famous example, the Ring Nebula:

HST Image of Ring Nebula

There is a very complete Wikipedia article on planetary nebulae here