Past Interns and Projects: Summer 2007
 
 SAO Summer Intern Program Projects, 2007


INTERN: Eric Baxter (Harvey Mudd College)

ADVISORS: Dr. Gus Covey, Dr. August Muench
PROJECT TITLE: The Distance to NGC 2264

Abstract:
Unavailable.


INTERN: Iara Cury (Yale University)

ADVISORS: Dr. Rosanne di Stefano, Dr. Pavlos Protopapas
PROJECT TITLE: Stellar Variability in the MACHO Data Set

Abstract:
Stellar variability is the key to understanding many stellar systems. Pulsations provide information about the state of a star; orbital effects can be used to measure stellar masses; star spots and even clouds in the atmospheres of low-mass dwarfs also cause variability. During recent years, the microlensing teams have monitored tens of millions of stars. Their data sets contain records of the variability of many types. Some of these observations have been exploited already; for example Cepheids and eclipsing binaries have been well studied. The more subtle types of variability have yet to be explored. We have carried out a preliminary analysis of the MACHO data set and find evidence of possible new types of stellar variability. The project we propose would involve a systematic examination of this variability using the techniques of wavelet analysis. On the scientific side, the results could have implications fore the study of stellar systems, since several percent of all stars in our sample show unusual variability. On the technical side, the results will be to provide a new tool for the study of variability, one which can be applied to a wide range of data sets. This will prepare us for the huge influx of data from the new surveys like Pan-STARRS and LSST. This work will be done in collaboration with the Initiative of Innovative Computing at Harvard University.


INTERN: Furqan Fazal (Amherst College)

ADVISORS: Dr. Sridharan Tirupati, Dr. Quizhou Zhang
PROJECT TITLE: Massive stars are the dominant ingradients of galaxies

Abstract:
Massive stars are the dominant ingradients of galaxies. Throughout their lives they inject enormous amounts of energy and momentum into the interstellar medium from which all stars form. Starting with powerful outflows and ending in supernovae which result in exotic object like neutron stars and pulsars their influence is far-reaching. However, the births of the massive stars are shrouded mystery. In studying their origins, we are primarily hampered by their small numbers, large distances, fast evolution and obscuration by dust. The SPITZER telescope, using its infrared detector, is able to peer through the dust and has produced a valuable resource called GLIMPSE, which is a systematic imaging survey of large portions of our Galaxy. In the proposed project, a summer student can use this image database to study the environments of a sample of high-mass proto-stellar objects (HMPOs) which contain massive stars in the earliest stages of their lives. We have studied this sample at other wavelengths and the summer student will get the first glimpse of their characteristics as imaged by SPITZER. Using images at multiple wavelengths, we will classify objects in the immediate vicinity of the luminous HMPOs, identify the most massive and youngest memebers and study their spatial distribution to understand the nature of star clusters in their earliest stages.


INTERN: Sarah Harrison (Massachusetts Institute of Technology)

ADVISORS: Dr. Dan Evans, Dr. Julia Lee
PROJECT TITLE:   Energetic processes in the environments of Active Galactic Nuclei

Abstract:
Active galactic nuclei (AGN) are among the most energetic astrophysical phenomena in the Universe. Powered by accretion onto a supermassive black hole, they are often observed to eject twin jets of particles at relativistic speeds out to very large distances from their centers. The Chandra X-ray Observatory has revolutionized our understanding of the energetic processes involved in AGN, through detailed studies of how jets interact with their hot-gas environments. In several cases, the energies of the X-ray gas environments exceed 1060 ergs, and giant cavities in the X-ray gas are often seen, believed to be the result of an jet expanding into its ambient medium.

This 10-week project will allow the REU student to (1) learn how to reduce Chandra data, (2) perform imaging and spectroscopy of the nucleus and thermal gas of several nearby AGN, and (3) combine these data with observations at radio and optical wavelengths to better understand the physical conditions present in active galaxies.

Clusters of galaxies are the most massive gravitationally bound objects in the universe. They formed relatively recently in the history of the universe, so we can try to measure their evolution directly. This project will focus on understanding the evolution of cluster and galaxy properties in a sample of clusters at moderate redshift. These clusters have been observed with Chandra, Spitzer, and ground-based optical telescopes. We will analyze infrared images of the clusters to identify likely cluster members and estimate the stellar masses of the galaxies and the clusters. If time allows, we will compare these properties to the X-ray and mid-infrared properties of the clusters. These detailed comparisons will be critical for using future cluster surveys to probe dark energy.

The abundance of clusters and groups in the nearby universe is a powerful constraint on cosmological parameters. In particular, the anisotropies seen in the microwave background should grow to form the clusters we see today. We have used the Sloan survey to measure the abundance of clusters in the nearby universe, but measuring the abundance of groups is more difficult. We have begun a survey of groups outside the Sloan survey region to measure the abundance of these lower-mass systems. The project will involve compiling the existing and new data to measure group masses and use these to measure cosmological parameters. The project may involve an observing run to Mt Hopkins to operate a telescope and collect some of the data for the survey.


INTERN: Colin Hill (Massachusetts Institute of Technology)

ADVISORS: Dr. Ken Rines
PROJECT TITLE: Understanding Cluster Evolution / Nearby Clusters and Cosmology Nuclei

Abstract:
Clusters of galaxies are the most massive gravitationally bound objects in the universe. They formed relatively recently in the history of the universe, so we can try to measure their evolution directly. This project will focus on understanding the evolution of cluster and galaxy properties in a sample of clusters at moderate redshift. These clusters have been observed with Chandra, Spitzer, and ground-based optical telescopes. We will analyze infrared images of the clusters to identify likely cluster members and estimate the stellar masses of the galaxies and the clusters. If time allows, we will compare these properties to the X-ray and mid-infrared properties of the clusters. These detailed comparisons will be critical for using future cluster surveys to probe dark energy.

The abundance of clusters and groups in the nearby universe is a powerful constraint on cosmological parameters. In particular, the anisotropies seen in the microwave background should grow to form the clusters we see today. We have used the Sloan survey to measure the abundance of clusters in the nearby universe, but measuring the abundance of groups is more difficult. We have begun a survey of groups outside the Sloan survey region to measure the abundance of these lower-mass systems. The project will involve compiling the existing and new data to measure group masses and use these to measure cosmological parameters. The project may involve an observing run to Mt Hopkins to operate a telescope and collect some of the data for the survey.


INTERN: Therese Jones (Penn State University)

ADVISORS: Dr. Kelly Korreck
PROJECT TITLE: Particle Acceleration from the Solar Corona to the Earth

Abstract:
We are examining the way particles are accelerated and heated as they propagate from the solar corona to the earth. The student would be exposed to data from XRT on Hinode, ACE, ULYSSES, and SOHO satellites. Specifically they would be responsible for fitting distribution of protons from the ACE, Ulysses and SOHO satellite. Then they would use the XRT data to compare the initial conditions of these energetic particles. By fitting the proton particle distributions and looking at timing, we can get a sense of the changes the plasma undergoes as it moves through theheliosphere and where it deposits the energy. The student would be responsible for fitting the data sets and then helping prepare the paper. The student will get an introduction to solar physics, some statistical mechanics, data analysis, plasma astrophysics, image processing, and stellar winds. The student would also have an opportunity to present the work either at an SSP seminar or at a monthly meeting of the New England Space Science Consortium.


INTERN: Kyle Penner (University of Texas at Austin)

ADVISORS: Dr. Silas Laycock, Dr. Maureen van den Berg
PROJECT TITLE: Optical and infrared identifications of ChaMPlane sources

Abstract:
The Chandra Multiwavelength Plane (ChaMPlane) survey is a large project to study the properties of the various classes of low-luminosity X-ray point sources in our Galaxy. These include binaries with compact objects like white dwarfs or neutron stars that accrete gas from a companion star, but also stars like the Sun, and close binaries where the tidal forces between the stars make them spin fast. The instruments on the Chandra X-ray Observatory have unique capabilities to expand our knowledge of these X-ray sources. The sensitivity of Chandra allows us to detect systems out to large distances; and thanks to Chandra's unprecedented spatial resolution the positions of these X-ray sources can be measured with a precision like never before, which is extremely important for follow-up studies and source classification. ChaMPlane makes use of archived Chandra images that were taken when Chandra was looking at objects that lie in directions close to the Galactic plane. Typically, the astronomers that have made these images are only interested in one object, but many more are detected. We process these images and try to classify all the sources, first by taking optical and near-infrared images to identify the objects that emit the X-rays, and finally by taking spectra to determine the source class. Currently, the ChaMPlane X-ray database includes almost 14000 point sources detected in about 120 discrete fields, that are covered by more than 200 Chandra observations. Deep optical images in three broad- and one narrow-band filter (V, R, I and Halpha) have been taken for all of them, and although far from complete, our spectral database is steadily growing with classification spectra being taken for more than 2700 candidate counterparts.

The REU summer internship will allow students to become familiar with several aspects of the ChaMPlane project. We suggest two possible projects from which the student can choose:

1) The goal of the first project is to characterize the properties of the brightest of the ChaMPlane sources. The first phase involves fitting X-ray spectra, from which we derive constraints on

a) the process that creates the X-ray emission (accretion versus magnetic activity), and

b) the amount of extinction (and consequently the distance) between us and the source. Currently there are between 50 and 75 such bright ChaMPlane sources (excluding sources close to the Galactic Center). In the second phase, a search for the optical counterparts will be done using the available optical/infrared data while taking into account the X-ray constraints on the source classes and distances.

2) Some parts of the Galaxy are heavily obscured by clouds of dust and gas that prevent us from seeing what is behind them when we use optical images. The effects of extinction are less severe in the near-infrared. The ChaMPlane near-infrared images serve to look for counterparts of obscured X-ray sources, but a lot more can be learned from them. For example, candidate star clusters, previously identified by other groups in lower-resolution images, can be studied with a "sharper view" and a search for more candidate clusters can be done. Potentially associated X-ray sources can then be used to learn more about both the clusters and X-ray sources, like their distances and when/how they were formed. Close examination of the infrared images can lead to other interesting discoveries (and possible X-ray counterparts), like planetary nebulae that are formed when a low-mass star expels its outer layers at the end of its life (in an initial examination we have already found one new planetary nebula).

The colors of a star are sensitive to the amount of gas and dust through which we see it. Another application of this infrared project is to derive a relation between the infrared and X-ray colors of ChaMPlane sources, which can then be used to constrain an X-ray source's distance even when no obvious counterpart is found; information on distances is crucial to study the distribution of X-ray sources in the Galaxy.

Both projects are suitable for a poster presentation at the January 2008 AAS meeting. Throughout the 10-week period, the student will have the opportunity to interact with different ChaMPlane group members, and experience what it is like to be part of a research group. For more details on ChaMPlane, visit http://hea-www.harvard.edu/ChaMPlane.


INTERN: Megan Reiter (University of California Berkeley)

ADVISOR: Dr. Massimo Marengo
PROJECT TITLE: An IRAC view of Galactic Asymptotic Giant Branch Stars

Abstract:
The Sun, towards the end of its life, will become an Asymptotic Giant Branch (AGB) Star. Once exhausted its primary Hydrogen nuclear fuel, it will ultimately become 10,000 more luminous than today, and swell beyond the orbit of our planet, that will be engulfed and vaporized. This act of destruction, however, will also be an act of creation: it is in the nuclear furnaces of AGB stars that most of the carbon, the basic element of life, available in the Galaxy is synthesized. This carbon, together with other heavy elements, is slowly released to the circumstellar environment in the form of a dusty wind, that gradually surrounds the star with a thick opaque cocoon. Like a butterfly from the chrysalis, the cocoon will ultimately burst to give rise to a Planetary Nebula, one of the most beautiful and ephemeral objects in the sky, leaving behind a white dwarf. The carbon and the other elements released in the AGB wind will merge with the interstellar medium, ready for a new cycle of stellar and planetary formation: the carbon atoms in our body have likely been produced in an AGB stars billion of years ago.


INTERN: Blake Sherwin (Cambridge University)

ADVISOR: Dr. Avi Loeb
PROJECT TITLE: Hypervelocity Stars from the Andromeda Galaxy

Abstract:
Unavailable.


INTERN: Johanna Teske (American University)

ADVISOR: Dr. Andreas Zezas
PROJECT TITLE: A combined Chandra/Spitzer study of galaxy mergers

Abstract:
We have embarked on a multiwavelength program to study the relation between galaxy interactions and the level and type of activity they induce. The main element of this program is Spitzer multiband imaging and spectroscopic observations of a large sample of nearby interacting galaxies. These data provide a view of the evolution of star-formation and AGN activity as a function of the stage and the parameters of the interaction. An independent picture of the activity in a subset of these galaxies, is given by X-ray observations, which provide diagnostics for the presence of AGNs and they allow us to study the evolution of X-ray binaries and hot gas in the different stages of galaxy interactions.In total 18 systems from the Spitzer sample have been observed with Chandra. These systems span the full range of interaction stages from weak interactions to coalescing galaxies. In particular the Chandra data will allow us to investigate: (a) how the discrete source and diffuse X-ray emission components evolve in the different stages of the interaction; (b) address the connection of Ultra-luminous X-ray sources with enhanced star-formation; (c) study the X-ray emission from the nuclei and search for the presence of AGNs. We will measure as a function of the merger stage: the relative contribution of the diffuse emission and the discrete sources in the overall X-ray emission of the systems; their relation with IR, optical and radio emission; the spectral parameters of the diffuse emission and the luminosity distribution of the discrete sources. Comparison with the already analyzed Spitzer data will identify emission components related with on-going star-formation. A student who will work on this project will learn how to analyze X-ray data using existing and previously tested software (CIAO, Sherpa), and perform comparisons between the X-ray, infrared and optical data. There are ready made scripts and tasks to do parts of this analysis which will be used by the student (after of course the required training). They will also analyze Spitzer data (as needed) again using existing and previously tested software. Since the overall sample is too large to be analyzed in such a short period of time, the student will focus on a subset of 10 objects with good quality Chandra data, spanning the full range of interaction parameters (the actual size of the sample can be adjusted depending on the progress of the student). The main focus will be on the analysis of the Chandra data and the comparison with data in other wavebands. This way the student will be exposed to the interpretation of scientific data and learn about galaxy interactions, star-formation and sources of X-ray emission in galaxies. They will be introduced to the physical mechanisms of emission in different wavebands and the different diagnostics we use in order to distinguish between them. Finally they will learn how to do background literature research on a specific topic.

 
 

Clay Fellow Warren Brown