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1) Deborah L. Freedman's project abstract
PROJECT TITLE: X-Ray Observation of Groups of Galaxies with Chandra and XMM
ADVISOR: Jan Vrtilek
INTERN: Deborah L. Freedman
Galaxy clusters are judged to be the smallest segments of the Universe that are large enough to be representative in the sense of fairly sampling its composition. With the advent of the Chandra X-ray Observatory, we now have the means to examine clusters with a vastly-improved combination of spatial and spectral analysis, which is revealing important physical features of the intergalactic medium never before observable. By the summer of 2000 we will have nearly a year's worth of Chandra data in hand, and a correspondingly large variety of investigations will be possible.
We are conducting a program of X-ray observations of groups of galaxies with Chandra and XMM. The sparseness of groups and their relatively simple dynamical history allow the properties of the IGM to be more directly related to galaxy evolution than may be possible in clusters, and their lower gas temperatures produce strong lines from a broader range of elements than is the case in hotter clusters. Our observations exploit the high X-ray brightness of some groups and the angular resolution of Chandra to determine accurately the abundances of heavy elements as a function of position in the group, to test whether abundance variations are associated with individual galaxies, to trace the origin of the enrichment, and to examine the central cooling flow.
The intern will learn about and be directly involved in the most current research in clusters of galaxies. This research bears closely on our understanding of some core topics of modern extragalactic astronomy and cosmology: the formation and evolution of structure in the Universe, the nature and distribution of dark matter, and the interactions between galaxies and their environments. In addition, the intern will learn about and use the software tools needed for contemporary data analysis in X-ray astrophysics.
2) Mark Kramer's project abstract
PROJECT TITLE: Mapping Molecular Outflows Toward High_Mass Star Formation Regions
ADVISOR: Qizhou Zhang
INTERN: Mark Kramer
Molecular outflows in dark molecular clouds were first discovered in the early 1980s (Snell et al. 1980, Rodriguez et al. 1981). Although unexpected theoretically prior to the discovery, the phenomenon is found to be prevalent during the course of star formation. Both theoretical and observational studies now show that the formation of a low-mass star involves a disk which accretes material from the cloud core and at the same time drives the material into the outflow.
Over 300 molecular outflows have been cataloged so far. The majority of them, however, are associated with low to intermediate mass stars (< 8 Msun). Since high-mass stars (> 8 Msun) are formed only in cluster environments, it's not clear if disks and/or outflows are present in those regions.
With this question, we carried out a survey of 70 odd high-mass star forming regions in the CO J=1-0 line with the National Radio Astronomy Observatory 12m radio telescope. The number of new outflows revealed in the preliminary analysis doubled the outflows known to date. In this project, we will calibrate the data in details and obtain outflow maps. The calibration and the analysis will be performed in CLASS, a user friendly astronomical software package. We will analyze the outflow maps and compute the mass, momentum, and energy in the outflow. The project can be done in less than three months and lead to a publication in an astronomical journal.
3) Julia M. Kregenow's project abstract
PROJECT TITLE: Analysis of Chandra Data of Centaurus A
ADVISOR: Ralph Kraft
INTERN: Julia M. Kregenow
We are searching for an undergraduate intern to assist us in the analysis of Chandra X-ray Observatory observations of the nearby radio galaxy Centaurus A. There are a variety of projects related to these observations that an intern could become involved with such as studying the X-ray emission from the hot ISM or characterizing the population of bright discrete X-ray sources within the galaxy. The intern will be expected to learn to use the software tools commonly employed for X-ray data analysis, and in particular those tools related to X-ray spectral analysis and spectral fitting.
4) Emily M. Laubacher's project abstract
PROJECT TITLE: Develop New Instruments for High REsolution Spectroscopy
ADVISOR: Eric Silver
INTERN: Emily M. Laubacher
As a complement to high spatial resolution images, high energy resolution spectroscopy enables astronomers to use the relative strengths of spectral lines to measure the elemental composition as well as the density and temperature of the emitting plasma. The wavelength of the lines can determine the object's velocity or redshift. We are currently developing new instruments to carry out high resolution spectroscopy and carrying out a program to better measure the spectral line features.
5) Nicholas Pearson's project abstract
PROJECT TITLE: Effects of Stellar Magnetic Activity on High Resolution Line Profiles
ADVISOR: Steve Saar
INTERN: Nicholas Pearson
Detection of sub-Jupiter mass extra-solar planets by radial velocities is currently limited by sources of velocity noise intrinsic to the stars themselves. These noise sources arise largely due to stellar magnetic activity (spots and non-uniform convection). We will study the effects of stellar magnetic activity on high resolution line profiles with an aim towards devising methods to correct the resulting velocity perturbations and recover information on lower mass planets currently hidden in the "magnetic noise".
6) Jennifer Posson-Brown's project abstract
PROJECT TITLE: A Search for Brown Dwarfs and Extr-Solar Planets
ADVISOR: David Latham
INTERN: Jennifer Posson-Brown
This research project would involve working with stellar observations. The primary goals would be the search for brown dwarfs and extrasolar planets, the determination of the orbits of binaries and their mass determinations, and the selection of SETI targets.
7) Brant Robertson's project abstract
PROJECT TITLE: Analyses of Galaxy Clusters Using Chandra Data
ADVISOR: Larry David
INTERN: Brant Robertson
Observations of clusters of galaxies by the Chandra X-ray Observatory provide astonomers with the first opportunity to study clusters of galaxies in the X-ray band with the same spatial resolution as ground based optical telescopes. I would like to supervise a summer intern with the analysis of Chandra data on several clusters of galaxies. The primary goals of the project will be to determine the distribution of hot gas, dark matter, and heavy elements within the central regions of rich clusters. These observations will be used to help advance our understanding of the dynamic and chemical evolution of clusters of galaxies, and the cosmological implications concerning abundance and distribution of baryons in these systems.
8) Shanna Shaked's project abstract
PROJECT TITLE: X-rays from the galaxy M33
ADVISOR: Jonathan McDowell
INTERN: Shanna Shaked
This project involves analysing X-ray observations of the nearby spiral galaxy M33. The scientific goal is to understand the nature of the X-ray sources in M33, and to identify the mysterious luminous source X-8 in the nucleus. We'll use mostly archival data from the ROSAT and ASCA satellites, but we have some Chandra data on X-8 and we expect to get some better data during the summer which may be available for the student to work on towards the end of the project. The main goal for the student will be to extract positions and spectral information to make an up to date and uniform catalog of X-ray sources in the galaxy and correlate them with known optical sources in the galaxy.
The student would gain experience in X-ray data analysis and the phenomenology of black holes, neutron stars and accretion processes. A student wishing to work on this project should have some background in astronomy and math, and ideally would be familiar with Unix systems.
9) Daniel Joseph Sherman's project abstract
PROJECT TITLE: Variable Stars in the Globular Clusters of the Fornax Dwarf Galaxy
ADVISORS: David Bersier and Kris Stanek
INTERN: Daniel Joseph Sherman
The technique known as "Image Difference Analysis" allows one to detect variable stars in very crowded fields, where the density of stars is so large that other techniques (such as standard PSF-fitting programs like DoPHOT and DAOPHOT) fail. We have data on the Fornax dwarf galaxy, containing several globular clusters. Variable stars have been searched for in the field of the galaxy, using standard techniques (PSF-fitting photometry).
The proposed work is to use the image subtraction technique to look for variable stars in and around the globular clusters of the Fornax galaxy. This should result in a catalogue of variables, periods and light curves. The next step is to compare the detection efficiency of variable stars using both techniques.
10) Sabrina Zoe Siloti's project abstract
PROJECT TITLE: Photometric and Sprctroscopic Observations of a Type II Supernova
ADVISOR: Eric M. Schlegel
INTERN: Sabrina Zoe Siloti
Type II supernovae show hydrogen in their spectra. The light curve declines over a period of ~1 year; the spectra show emission lines of hydrogen at the time of the outburst.
Over the course of about a year, the emission lines evolve, gradually becoming weaker in strength and increasingly narrow. The lines are broad in the early days of the supernova because of the large velocity gradients present in the expanding debris. As the debris thins, the emission arises from material with a decreasing gradient.
The data to be reduced and analyzed include CCD photometry and spectroscopy. To obtain photometric measurements from the CCD images, aperture photometry will be used. The steps to reduce the CCD spectroscopy are similar to the CCD photometry at the start. Once the spectra have been extracted, the additional steps to reduce the data include the calibration of the spectra onto flux and wavelength scales.
The target object will be either the Type IIP supernova 1999em in NGC 1637 or the Type IIn supernova 1998S in NGC 3877. The designation ``IIP'' indicates a very normal Type II supernova with a Plateau on the decline from maximum. The designation ``IIn'' indicates a supernova with very narrow emission lines from the earliest observations.
11) Fernando Angel Torres' project abstract
PROJECT TITLE: Optical and X-ray Analyses of Galaxy Clusters
ADVISOR: R. Hank Donnelly
INTERN: Fernando Angel Torres
The student will perform optical and X-ray analyses of galaxy clusters and their component parts. This will include characterizing the performance of various metric diameters used in optical photometry, generating and analysing maps of the temperature distribution of the hot intra-cluster medium, from both ASCA and CHANDRA data.
1) Deborah L. Freedman
Princeton University, Department of Astrophysical Sciences, Princeton, NJ 08544,
An Analysis of Point Sources in Two Chandra Deep Fields
We study the discrete point sources in two deep Chandra observations
in order to determine their distribution and spectral properties. In
one observation of 120 ksec, identified by the inclusion of the
cluster MS1137.5+6625, we detected 130 point sources. In a combined
190 ksec observation of the field that includes the cluster
CL0848.6+4453 we found 135 point sources. Plots of log N - log S for
both fields showed a gradual flattening of the slope toward fainter
fluxes, indicating that the number of sources per square degree with
smaller fluxes is increasing less rapidly than at higher fluxes. In
addition, we determined the average spectra for point sources as a
function of the point source flux. The photon index of the spectra
decreased as the fluxes of the sources in the group decreased, i.e.,
source spectra hardened at fainter fluxes.
D.L.F. gratefully acknowledges support from the NSF-REU program and
from the SAO.
Advisor: Jan Vrtilek
Molecular Outflows and Massive Stars
Molecular outflows from young stellar objects provide insight into the star
formation process. Using the 12m telescope and 1mm SIS Array Receiver at the
NRAO in Kit Peak, Arizona, we have mapped the CO(J = 1 → 2)
rotational transition in 67 high mass, M > 8Modot, protostellar
candidates. Of the 20 sources we have completely analyzed, 12 have outflows,
5 do not have outflows, and 3 remain unknown. We have determined the mass,
energy, momentum and dynamic time scale of the outflows and compared these
properties with a simple driving mechanism.
Advisor: Qizhou Zhang
Chandra Observations of the Point Sources in Centaurus A
We present the results from a study of the X-ray point source population in two Chandra X-ray Observatory observations of the nearby radio galaxy Centaurus A (NGC 5128). Using a wavelet decomposition detection algorithm, we detect 246 individual point sources above a limiting flux of 1.34 times 10-15erg / cm2s, which corresponds to a luminosity of 1.96 times 1036 erg/s. Of the 246 sources detected, 82 are detected in both data sets where the fields of view overlap. We positively identify 8 foreground stars in our observations, and estimate approximately 15% to 20% of the sources to be background AGN not associated with Centaurus A. The remaining ∼200 sources, likely associated with the galaxy, are probably X-ray binaries and supernova remnants. We identify 11 with known globular clusters, and 41 as possible transient or variable sources. We find that the population of X-ray point sources in Centaurus A, a merged elliptical and spiral galaxy with an active nucleus, is not significantly different than that of M31 in both spatial distribution and luminosity range. We also detect in one observation a possible super-Eddington X-ray transient previously detected by ROSAT.
This project was supported by NASA contract NAS8-38248, and the observations were made as part of the HRC GTO program. The research was conducted, in part, through the Harvard-Smithsonian CfA Undergraduate Summer Intern Program.
Advisor: Ralph Kraft
X-Ray Performance of the Engineering Prototype of the Polarimeter for Low Energy X-Ray Astrophysical Sources
An engineering prototype of the Polarimeter for Low Energy X-Ray Astrophysical Sources (PLEXAS) has been built and tested. A Ni/C multilayer crystal was used as the X-Ray polarimeter of the PLEXAS instrument. 100% polarized bremstrahlung X-rays were used to measure the response of the instrument at ∼0.18 keV. The experimental concept and design of the PLEXAS prototype will be presented and the test results evaluated. A discussion of the most recent measurements will be presented.
PLEXAS is designed for a University Explorer Mission.
D.L.F. gratefully acknowledges support from the NSF-REU program and from the SAO.
Advisor: Eric Silver
Effects of Stellar Magnetic Activity on High Resolution Line Profiles and Radial Velocity Measurements
We study very high resolution (λ / Δ λ ≅200,000), high S/N (350 - 550) echelle spectra of five G to early K type stars (β Com, ε Eri, 61 UMa, 59 Vir, and ξ Boo A) and construct bisectors for ∼30 unblended Fe I absorption lines in each. We collate the bisectors into subgroups based upon absorption line depth and excitation potential, calculate many statistical measures of the bisector position and shape, and average these measurements over the subgroups. We then search for relationships between the averaged bisector properties and various stellar properties, such as temperature, activity and v sin i; several significant trends are found. We investigate how the bisectors change over time with relation to stellar properties in an effort to find trends between the bisector properties, stellar magnetic surface features, and apparent radial velocity (vr).
Such correlations would allow for the correction of some of the scatter in measurements of the vr, permitting easier detection of sub-jovian exoplanets. We find changes in certain bisector measures to be well correlated with vr changes.
This work was supported by National Science Foundation grant AST-9731652.
Advisor: Steve Saar
Spectroscopic Follow-Up Observations of Ten Planetary Transit Candidates Identified by Project Vulcan
The discovery of close-in extrasolar giant planets raised the possibility that planetary transits might be observable using ground-based photometry. This was confirmed by the detection of transits for HD 209458. We analyze echelle spectra for ten planetary transit candidates identified by the photometric project Vulcan, all of which show periodic dimming of a few percent, and periods of up to a few days. Our goal is to look for orbital motion and to derive estimates for the astrophysical characteristics of the parent stars, especially the radius and mass, to see if the light curves can be explained by stellar rather than planetary companions. Five of the transit candidates are spectroscopic binaries with stellar companions. In three cases the orbits have the same period as the light curve, so the dimming is due to a grazing eclipse by a stellar companion. The periods for the other two are longer than a year, so the stellar companions are not responsible for the dimming. However, for both of these systems, we conclude that dimming due to a planetary companion is unlikely, because the primary stars appear to be giants, and are therefore too large for a planetary transit to be detected by Vulcan. Three more of the candidates are very hot and/or rapidly rotating, making it difficult to determine precise radial velocities. The two remaining candidates may be giants, but we are unsure of their luminosity classification. They may warrant further study, such as highly precise velocity measurements and dedicated photometric observations designed to produce better light curves.
Part of this work was done as a Research Experience for Undergraduates at the Harvard-Smithsonian Center for Astrophysics, funded by the National Science Foundation. Funding for the Vulcan photometric search for extrasolar planets was provided by the NASA Origins and Astrobiology Programs.
Advisor: David Latham
A Comparison of Chandra observations of Clusters of Galaxies with Dark Matter Models
We present Chandra X-ray Observatory data for several clusters of galaxies over a range of temperatures and redshifts. X-ray surface brightness profiles are produced for each cluster. Mass profiles are calculated for the inner 300 kpc of each cluster and compared with cold dark matter profiles from the literature. We find that the profile presented in Moore et. al. (1999) produces a reasonable fit to the cluster mass distributions while maintaining best fit parameters consistent with cosmological and structure formation constraints (e.g., the epoch of cluster formation). The Navarro, Frenk, and White (1996) profile is found to reproduce the behavior of observed cluster mass distributions but fails to maintain best fit parameters consistent with cosmological constraints. When normalized to the dark matter profile virial mass equivalent M200, the measured mass distributions are found to be self-similar. Each cluster is also compared with the King approximation to an isothermal sphere, and all are found to be highly inconsistent with a flat density core.
Advisor: Larry David
Chandra Observations of ARP 220
We analyze recent Chandra data of the ultraluminous infrared galaxy Arp 220 and compare it to previously acquired ROSAT data. Chandra's high resolution allows us to see that a concentrated source of hard X-ray emission is concentrated within 2′′ (< 1 kpc) of the radio/infrared nuclei. We extract an emission-line rich spectrum from this hard emission, implying that most of the nuclear X-rays are probably emitted from thermal sources. By fitting this spectrum and calculating a flux, we put an upper limit of ∼1040 ergs s-1 on the AGN luminosity. By comparing our Chandra data to Hα data, we find that the extended X-ray nebula coincides with the Hα morphology thus supporting the double-bubble ``superwind'' theory of Heckman et al. 1996. Finally, we find that the southern cluster seen in the ROSAT image is resolved into point-like sources, the positions of which coincide with bright optical galaxies.
Funding was provided by the NSF REU program.
Advisor: Jonathan McDowell
Image-Subtraction Photometry of variable Stars in the Fornax Dwarf Galaxy
Analysis of variable stars in nearby galaxies and globular clusters is an effective technique for gaining insight into the creation, evolution, and population of such structures. However, current standards in detection software are unable to properly reslove faint variables in dense fields. Using the new technique of ``Image Difference Analysis'', we have attained reasonable estimates of the relative abundances of and fluctuations in several variable stars, opening the possiblity for an improved catalog of variables, particularly in and near these clusters. We compare the accuracy of this method with that to DoPHOT, both in detection of variables and in extracting light curves. Example curves for several variables in all regions of Fornax are provided.
This project was funded by the National Science Foundation's Research Experience for Undergraduates Program.
Advisors: David Bersier and Kris Stanek
Photometric and Spectroscopic Analysis of the Type IIn Supernova 1999E
SN 1999E is an unusually luminous type IIn supernova that may have been associated with GRB 980910. Its spectrum most closely resembles those of the hypernovae SN IIn 1997cy and SN Ic 1998bw. These characteristics make it a possible hypernova. In this article we examine photometric and spectroscopic data obtained for SN99E in an effort to determine how it compares and contrasts with other SNe IIn. SN99E's light curve did not have an evolution as slow as some other SNe IIn, having decay rates estimated at 7.9 millimag day-1 in the B-band, 6.9 millimag day-1 in the V-band, and 7.7 millimag day-1 in the R-band. The spectra showed the characteristic dominating narrow (FWHM ∼ 5 - 10) Hα emission line. There was also a weak flux from an Hβ line. Both H lines had broad (FWHM ∼ 100 - 200 during the first four months) components. Narrow emission lines of NII and possibly [OII] were also identified. SN99E's spectra are very peculiar, having several extremely broad features overlapping each other making it difficult to even determine whether the features are emission or absorption lines. A spectrum taken over a year after discovery shows a flat, near-zero flux with the more prominent narrow emission lines of H, NII, and [OII] still present, though at much lower fluxes than earlier spectra. This suggests the presence of an HII region, although whether it is interacting with the SN or is completely separate from the SN and only contaminating the spectra is not known.
This research was supported by the National Science Foundation's REU program.
Advisor: Eric M. Schlegel
The Effects of Simulated Seeing Profiles on the Photometric Parameters of Elliptical Galaxies
The effects of different simulated seeing profiles on the photometric parameters of elliptical galaxies is studied. The seeing profiles were simulated using Gaussian, Moffat, and the modified Saglia et al. (1993) point spread functions (PSFs). We used a set of previously generated synthetic galaxy images and convolved them with the PSFs . We compared the differences of the photometric parameters of the convolved galaxies using the Moffat and Saglia PSFs to those using the Gaussian PSF. The photometric parameters studied are : re, (Dn), rc, rs, D26.5, rη, and D25. We found that at z ≥0.075 and FWHM ≥1.25, the modified Saglia et al. (1993) and Moffat, differentiated substantially to the photometric results from the galaxies convolved with the Gaussian PSF.
Advisor: R. Hank Donnelly