Symposium Proceedings

Life Cycles of Stars

The talks are in the same order as the Program Schedule.

A Detailed Study of the Pulsar Wind Nebula 3C 58

Patrick Slane (SAO)

Recent Chandra observations of the X-ray emission from young neutron stars have revolutionized our picture of everything from the structure of their cores to the composition of their energetic winds. Measurements of the thermal emission from their surfaces provide constraints on their cooling properties while high resolution images of the compact structure surrounding the stars reveal jets, toroidal features associated emission downstream of the wind termination shock, and complex structures both near the neutron stars and in their extended wind-powered nebulae. 3C 58 is a wind nebula powered by one of the youngest neutron stars in the Galaxy. I will summarize the results of Chandra observations, including a Large Project, that provide evidence for nonstandard cooling processes in the neutron star interior, complex structures that may be associated with magnetic loops torn from the termination shock by kink instabilities, and a shell of shock-heated ejecta into which the nebula is expanding.

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X-ray Eyes on the Brightest Explosions in the Universe: Probing the GRB Afterglow Emission Mechanism with Chandra

Nat Butler (UC Berkeley), George Ricker, Peter Ford, Roland Vanderspek, Herman Marshall (MIT), Kevin Hurley, Garrett Jernigan (UC Berkeley), Don Lamb (U Chicago)

Chandra ACIS is an established and vital link in the network of space and ground-based observatories chasing after Gamma-ray burst (GRB) afterglows. More than 35 afterglows fields-of-view of short and long duration GRBs and X-ray Flashes (XRFs) have been observed to date, with several of the observations beginning less than 1 day after the GRB. Imaging observations probe the density profile and constrain the jet-structure of the emitting region. The X-rays are uniquely penetrating, and Chandra observations have enabled the detection of several events not seen in the optical/IR. We discuss how these observations link GRBs to supernovae and constrain the popular fireball model for GRBs, and we highlight interesting departures from the model which suggest, e.g., continued energy from the GRB. Chandra has also provided the highest signal to noise gratings spectra of GRB afterglows. We discuss early claims of low to moderate significance X-ray lines. The lines are strong diagnostics on the geometry, ionization state, and chemical composition of the circumburst emitting region. However, they have not been detected in the three most recent Chandra spectra.

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Estimating the Rates of Electron Acceleration in SNR Shocks Using Chandra

Michael Stage (Univ. of Massachusetts, Amherst), Glenn Allen, John Houck, John Davis (MIT Kavli Institute)

Over the last six years, the Advanced CCD Imaging Spectrometer (ACIS) on Chandra has captured the highest resolution X-ray images of several supernova remnants, the most spectacular example the Cassiopeia A megasecond observation from cycle 5. The observations of thermally dominated, young supernova remnants such as Cassiopeia A, Kepler, and Tycho show complex morphology often featuring narrow, filamentary, continuum dominated emission at the outer shocks. Young supernova remnants are believed to be possibly a source of and the main accelerator of Galactic cosmic rays. The emission from the filaments is believed to be synchrotron radiation associated with the acceleration of cosmic-ray electrons to TeV energies, rather than thermal bremsstrahulung associated with the ejecta emission. Using a combination of CIAO tools and a suite of specialized software utilizing the S-Lang scripting capabilities of ISIS, we have been able to analyze these extended sources using the full spatial and spectral information available from the ACIS data. Specifically, for Cas A, we have been able to identify, isolate, extract, and fit the spectra of the emission at each of about ten thousand locations along the filaments with a synchrotron model. We present maps at 1 arcsecond scale of the critical frequency associated with the exponential cut-off of the synchrotron spectrum as well as of the ratio of the electron diffusion coefficient to the Bohm coefficient, calculated from the critical frequency and shock velocity. At several locations, our maps indicate diffusion rates comparable to the Bohm limit-that is, that electrons are being accelerated about as fast as possible.

Supernova 1987A at the Age of 18: An On-Going Life Story by Chandra

Sangwook Park (Penn State Univ.)

We present the morphological and spectral evolutions of SN/SNR 1987A from Chandra observations. We review the Chandra/ACIS observations of SNR 1987A performed since 1999, and report the latest results as of 2005 July. Brightening and expanding of the X-ray remnant as well as the softening of the X-ray spectrum continue. Remarkably, the latest soft X-ray flux increase rate turns up by significantly deviating from the model which successfully fits the earlier data covering over a decade. The high resolution X-ray spectrum observed with deep Chandra gratings observations reveals a disk-like structure and the kinematics of the X-ray emitting plasma.

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The Chandra Orion Ultradeep Project (COUP)

Giuseppina Micela (INAF - Oss. Astronomico. di Palermo), Eric Feigelson, COUP Collaboration (Penn State Univ.)

The 850 ksec Chandra observation of the Orion nebula region, obtained in January 2003, has provided an unprecedented dataset for the study of X-ray emission of very young stars. A wide range of studies involving a large international collaboration have been possible and others are in progress. Implications of the analysis and interpretation of data from COUP ( are very important for the study of the formation and evolution of stellar coronae, their interplay with stellar structure and for the investigation of the possible role of the accretion in producing and/or regulating X-ray emission from young stellar objects (YSOs). The X-ray emission properties of very young stars and the variety of circumstellar environment present in Orion, allow us also to explore the influence of YSO high energy radiation on the circumstellar material in the first phases of stellar life. We review some results we already obtained along these lines as well as new ongoing work on the subject.

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Neon and the Problem of the Sun and Stars, the Universe and Everything

Jeremy Drake (SAO), Paola Testa (MIT Kavli Institute for Astrophysics and Space Research)

The demure element Neon has gained great notoriety in recent months as attention has been focussed on its possible role in a serious new problem with understanding how the Sun works. Solar models including recent downward revisions of the Sun's metal content are now inconsistent with helioseismology. While Chandra X-ray spectra of nearby stars indicate that a higher neon abundance could be a possible way out of the solar quandry, this route might require some unsustainable ravaging of old-growth astrophysics and will draw objections from conservationists. We will attempt to describe this new role of Neon, the newcomer, in these problems of the Sun and Stars, the Universe and Everything.

Chandra and VLT Observations of Young Stellar Objects in the Eagle Nebula

Jeffrey L. Linsky (JILA/Univ. of Colorado and NIST), Marc Gagne, Anna Mytyk (West Chester Univ.), Mark J. McCaughrean (Exeter Univ.), Morten Andersen (Astro. Dept. Univ. Arizona)

We present the first X-ray images ever obtained of the Eagle Nebula star-forming region. On 2001 July 30 the Chandra X-ray Observatory obtained a 78-ks image of the Eagle nebula (M 16), that included the 2-Myr old star cluster NGC 6611 and the dark columns of dust and cold molecular gas known as the Pillars of Creation, the elephant trunks, or Columns. We find a total of 1103 X-ray sources in the 17 x 17 arcmin ACIS-I field of view. Most of the Chandra sources are associated with members of the 2-Myr old cluster NGC 6611 whose O stars ionize the nebula and are eroding the face of the adjacent molecular cloud. Only a small number of X-ray sources are associated with possibly younger stars just emerging from the molecular cloud. In particular, we detect no X-ray emission from the evaporating gaseous globules (EGGs) at the periphery of the Columns. We discuss the X-ray properties of two intermediate-mass YSOs at the heads of Columns 1 and 2, and of the bow shock of the Herbig-Haro object HH 216, and of some of the newly discovered YSOs. Comparing the X-ray luminosity function of NGC 6611 with the one in Orion, we estimate that NGC 6611 contains approximately 5300 cluster members. Although some stars appear to have formed in the last million years, the lion's share of star formation in M16 occurred some 2 Myr ago.

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An Episodic Heating Model for Stellar Coronae: Spectral Diagnostics of Non-Equilibrium Ionization

Nancy Brickhouse, Priya Desai, Andrea Dupree, Richard Edgar, Ronnie Hoogerwerf, John Raymond (Harvard-Smithsonian Center for Astrophysics), Randall Smith (NASA/GSFC)

Standard emission measure distribution analysis of Capella shows a strongly pronounced peak near 6 MK (Dupree et al. 1993; Canizares et al 2000), near the formation temperature of Fe XVIII and XIX; similar structures are observed on many active stars. Recently, the Chandra grating observations have revealed that the line ratios from these two ions are inconsistent, in the sense that the X-ray (11 to 17 A) lines are observed to be stronger than predicted by their EUV (90 to 120 A) counterparts (Desai et al. 2005). The discrepancies for the strongest lines are larger than expected from errors in the atomic data and calibration, and thus we consider an astrophysical explanation.

We construct a simple time-dependent heating model for active stellar coronae, following Sturrock et al. (1990), who suggested that the solar corona is heated by a distribution of short heating bursts, followed by radiative cooling. The Capella X-ray/EUV line ratios indicate temperatures above 10 MK, suggesting the presence of non-equilibrium ionization conditions. Thus, as in Raymond (1990) we follow the time-dependent ionization state of the gas and predict its EUV and X-ray spectrum. Parameters of the model are the maximum temperature, the heating time, and the electron density. We discuss the predicted iron line ratios, density, and charge state distribution in view of the observations.

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High Resolution X-ray Spectra of Classical T Tauri Stars

Jürgen Schmitt (Hamburger Sternwarte)

With the advent of Chandra and XMM-Newton high resolution spectroscopy of all classes of stars has become possible. I will present the available X-ray spectra of classical T Tauri stars and discuss the physical implications of these data. I will argue that all available spectra support an scenario where mass accretion is responsbile for soft X-ray emission. Mass accretion rates can be determined from the data. However, accretion alone cannot account for all the observed high energy phenomena.

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Chandra Monitoring of Nova V4743 Sgr

Joachim Krautter (Landessternwarte, Heidelberg), Jan-Uwe Ness (Dept. of Theoretical Physics, Oxford), Sumner Starrfield (ASU, Tempe), Alexander Petz, Peter Hauschildt (Hamburger Sternwarte), Jeremy Drake (Harvard-Smithsonian Center for Astrophysics)

The classical nova V4743 Sgr was observed five times with Chandra covering a time span of 16 months. Both lightcurve and spectra show strong temporal variations. An analysis of the lightcurve shows a stable period of about 1300 sec in all observations, but no stable amplitude. Also harmonic overtones were detected. During one epoch the X-ray countrate dropped to essentially zero over more than 5 ksec. Here only emission lines were observed while on all other occasions the spectra were dominated by a strong soft continuum with absorption lines. The cause of the pulsations, the decrease of the X-ray flux and the spectral properties will be discussed.

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X-Ray Jets from White Dwarfs - Detection of the Collimated Outflow from CH Cygni with Chandra

Jeno Sokoloski (Harvard-Smithsonian Center for Astrophysics), Duncan Galloway (Univ. of Melbourne)

Most symbiotic stars consist of a white dwarf accreting material from the wind of a red giant. A growing number of these objects have been found to produce jets. Analysis of archival Chandra data of the symbiotic system CH Cygni reveals faint extended X-ray emission to the south, aligned with the optical and radio jets seen in earlier HST and VLA observations. CH Cygni thus contains only the second known white dwarf with an X-ray jet, after R Aquarii. The jet was produced when CH Cygni transitioned from an optical low state to an optical high state - a behavior reminiscent of X-ray binaries, which can produce discrete ejections in association with X-ray state changes. We briefly compare the X-ray jets from symbiotic stars to the non-relativistic X-ray jets seen in several Herbig-Haro objects and the collimated outflows from the central stars or binaries in planetary nebulae.