Deborah Freedman
Princeton University, Department of Astrophysical Sciences, Princeton, NJ 08544,
We study the discrete point sources in two Chandra deep field observations in order to determine their distribution and spectral properties. In one Chandra 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 steepening of the slope toward higher fluxes, indicating that the number of sources per square degree with large fluxes decreased rapidly. We determined the spectra for groups of point sources, where the point sources are grouped according to their number of counts. The photon index of the spectra increased as the fluxes of the sources in the group increased: sources with fluxes of 3.17 times 10-16 - 6.34 times10-16 ergs cm-2 s-1 fit an index of 1.21, and sources with fluxes greater than 8.24 times 10-15 ergs cm-2 s-1 fit an index of 1.68.
================================================================================= Molecular Outflows and Massive Stars
Mark Kramer
Oberlin College, Department of Physics, Oberlin, Ohio 44074,
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. ================================================================================= Chandra Observations of the Point Sources in Centaurus A
J. M. Kregenow
Department of Physics, Wittenberg University, Springfield, OH 45501,
We present an analysis of the X-ray point source population in the galaxy Centaurus A (NGC 5128) from two observations with Advanced CCD Imaging Spectrometer on the Chandra X-ray Observatory. Using a wavelet deconvolution detection algorithm, we detect 246 individual point sources above a limiting luminosity of 1.96 times 1036 erg/s, 82 of which are detected in both data sets where the fields of view overlap. We identify 2 possible foreground stars in our observations, and estimate 49 sources in our field of view to be contaminating background sources (e.g., AGN). The 197 sources likely associated with the galaxy are most likely a population of X-ray binaries, of which 14 were seen by the ROSAT satellite. The remaining 183 galactic sources are identified in X-ray wavelengths for the first time in this paper. We identify 8 with known globular clusters and 31 as possible transient or variable sources. The population of X-ray points sources in Centaurus A, a merged elliptical and spiral galaxy, appears to be different than that of the Milky Way and M31 in both luminosity range and spatial distribution. We detect at least 19 sources with a luminosity greater than 1038 erg/s in Centaurus A, while the Milky Way and M31 combined have at most one or two such luminous sources. Also, the brightest sources are distributed more loosely throughout the central part of the galaxy in Centaurus A, rather then clustered tightly around the nucleus as in the spiral galaxies previously studied. We also find a strange clumping of bright X-ray sources in a region SW of the nucleus.
================================================================================= X-Ray Performance of the Engineering Prototype of the Polarimeter for Low Energy X-Ray Astrophysical Sources
Emily M. Laubacher
The University of Dayton
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 procedure and design of the PLEXAS prototype are presented and the results are evaluated. ================================================================================= Effects of Stellar Magnetic Activity on High Resolution Line Profiles and Radial Velocity Measurements
N. S. Pearson
Bowling Green State University, Bowling Green, OH 43403,
We study the spectra of five G to early K type stars (β Com, ε Eri, 61 UMa, 59 Vir, and xi Boo A) and construct bisectors for many Iron 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 bisectors, and average them over the subgroups. We plot these statistical measures against various properties of the stars, such as activity and v sin i as well as against properties of the bisectors and find several interesting correlations. Also, we investigate how the bisectors change over time with relation to stellar properties in an effort to find trends between the bisector properties and surface features of the star caused by magnetic activity. Such correlations would allow for the correction of some of the error in measurements of the radial velocity (vr) and thus would allow for the detection of sub-jovian exoplanets. ================================================================================= Spectroscopic Follow-Up Observations of Ten Planetary Transit Candidates
Jennifer Posson-Brown
Smith College, Northampton, MA 01063,
We analyze spectroscopic data obtained for ten planetary transit candidates for which we have been given photometric data, with the intent of characterizing the primary stars and explaining the light curves, which all show a periodic dimming on the order of a few percent. In characterizing the primaries, we are most concerned with getting accurate estimates for the masses and radii, as these figures are needed to analyze the transit depth and duration from the light curves. We find that, for three of the candidates, the dimming seen in the light curve is due to a grazing eclipse by a stellar companion. For two more of the candidates, we conclude that the dimming in the light curve is unlikely to be due to a planetary transit, as these candidates are most likely giants, and therefore too large for a planetary transit to be detectable. Three or more of our candidates are very hot and/or rapidly rotating, making high-precision spectroscopic observation difficult. The remaining two candidates may be giants, and so could not have detectable planetary transits, but as we are not as certain of their correct luminosity types, they may warrant further study. In all cases of further study, we believe that it is critical that more photometric observation be made to confirm the light curves before follow-up high-precision spectroscopy is undertaken. ================================================================================= A Comparison of Chandra observations of Clusters of Galaxies with Dark Matter Models
Brant E. Robertson
University of Washington, Astronomy Department, Seatle, WA 98195-1580
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 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 virial mass M200 and virial radius rs, 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. ================================================================================= X-ray Observations of ARP 220
Shanna Shaked
University of Arizona, Department of Astronomy, Tucson, AZ 85718,
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. ================================================================================= Image-Subtraction Photometry of variable Stars in the Fornax Dwarf Galaxy
Daniel J. Sherman
University of Pennsylvania, Department of Physics, Philadelphia, PA 19104
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. ================================================================================= Photometric and Spectroscopic Analysis of the Type IIn Supernova 1999E
S. Zoe Siloti
University of Oklahoma, Department of Physics & Astronomy, University of Oklahoma, Norman, OK 73069,
and High Energy Astrophysics Division, Smithsonian Astrophysical Observatory, Cambridge, MA 02138
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. ================================================================================= The Effects of Simulated Seeing Profiles on the Photometric Parameters of Elliptical Galaxies
Fernando A. Torres
Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA,
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.