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Articles 1 - 7 of 7
Full-Text Articles in Physical Sciences and Mathematics
On The Importance Of The Interclump Medium For Superionization: O Vi Formation In The Wind Of Zeta Puppis, J. Zsargó, D. J. Hillier, J.-C. Bouret, T. Lanz, M. A. Leutenegger, David H. Cohen
On The Importance Of The Interclump Medium For Superionization: O Vi Formation In The Wind Of Zeta Puppis, J. Zsargó, D. J. Hillier, J.-C. Bouret, T. Lanz, M. A. Leutenegger, David H. Cohen
Physics & Astronomy Faculty Works
We have studied superionization and X-ray line formation in the spectra of zeta Pup using our new stellar atmosphere code (XCMFGEN) that can be used to simultaneously analyze optical, UV, and X-ray observations. Here, we present results on the formation of the O VI lambda lambda 1032, 1038 doublet. Our simulations, supported by simple theoretical calculations, show that clumped wind models that assume void in the interclump space cannot reproduce the observed O vi profiles. However, enough O vi can be produced if the voids are filled by a low-density gas. The recombination of O vi is very efficient in …
High-Resolution Chandra X-Ray Imaging And Spectroscopy Of The Sigma Orionis Cluster, S. L. Skinner, K. R. Sokal, David H. Cohen, M. Gagné, S. P. Owocki, R. H.D. Townsend
High-Resolution Chandra X-Ray Imaging And Spectroscopy Of The Sigma Orionis Cluster, S. L. Skinner, K. R. Sokal, David H. Cohen, M. Gagné, S. P. Owocki, R. H.D. Townsend
Physics & Astronomy Faculty Works
We present results of a 90 ks Chandra X-ray observation of the young sigma Orionis cluster ( age similar to 3 Myr) obtained with the HETGS. We use the high-resolution grating spectrum and moderate-resolution CCD spectrum of the massive central star sigma Ori AB (O9.5 V + B0.5 V) to test wind shock theories of X-ray emission and also analyze the high spatial resolution zero-order ACIS-S image of the central cluster region. Chandra detected 42 X-ray sources on the primary CCD (ACIS-S3). All but five have near-IR or optical counterparts and about one-fourth are variable. Notable high-mass stellar detections are …
Chandra Spectroscopy Of The Hot Star Β Crucis And The Discovery Of A Pre-Main-Sequence Companion, David H. Cohen, Michael Ascher Kuhn , '07, M. Gagné, Eric L.N. Jensen, N. A. Miller
Chandra Spectroscopy Of The Hot Star Β Crucis And The Discovery Of A Pre-Main-Sequence Companion, David H. Cohen, Michael Ascher Kuhn , '07, M. Gagné, Eric L.N. Jensen, N. A. Miller
Physics & Astronomy Faculty Works
In order to test the O star wind-shock scenario for X-ray production in less luminous stars with weaker winds, we made a pointed 74-ks observation of the nearby early B giant, beta Crucis (beta Cru; B0.5 III), with the Chandra High Energy Transmission Grating Spectrometer. We find that the X-ray spectrum is quite soft, with a dominant thermal component near 3 million K, and that the emission lines are resolved but quite narrow, with half widths of 150 km s(-1). The forbidden-to-intercombination line ratios of Ne IX and Mg XI indicate that the hot plasma is distributed in the wind, …
Flow Dynamics And Plasma Heating Of Spheromaks In Ssx, Michael R. Brown, C. D. Cothran, David H. Cohen, Jason Alexander Horwitz , '07, Vernon Hampden Chaplin , '07
Flow Dynamics And Plasma Heating Of Spheromaks In Ssx, Michael R. Brown, C. D. Cothran, David H. Cohen, Jason Alexander Horwitz , '07, Vernon Hampden Chaplin , '07
Physics & Astronomy Faculty Works
We report several new experimental results related to flow dynamics and heating from single dipole-trapped spheromaks and spheromak merging studies at SSX. Single spheromaks (stabilized with a pair of external coils, see Brown, Phys. Plasmas 13 102503 (2006)) and merged FRC-like configurations (see Brown, Phys. Plasmas 13, 056503 (2006)) are trapped in our prolate (R = 0.2 m, L = 0.6 m) copper flux conserver. Local spheromak flow is studied with two Mach probes (r(1) = rho(i) ) calibrated by time-of-flight with a fast set of magnetic probes at the edge of the device. Both Mach probes feature six ion …
The Evolution Of Circumstellar Disks In Ophiuchus Binaries, J. Patience, R. L. Akeson, Eric L.N. Jensen
The Evolution Of Circumstellar Disks In Ophiuchus Binaries, J. Patience, R. L. Akeson, Eric L.N. Jensen
Physics & Astronomy Faculty Works
Four Ophiuchus binaries, two Class I systems and two Class II systems, with separations of similar to 450-1100 AU, were observed with the Owens Valley Radio Observatory (OVRO) millimeter interferometer. In each system, the 3 mm continuum maps show dust emission at the location of the primary star, but no emission at the position of the secondary. This result is different from observations of less evolved Class 0 binaries, in which dust emission is detected from both sources. The nondetection of secondary disks is, however, similar to the dust distribution seen in wide Class II Taurus binaries. The combined OVRO …
Resonance Scattering In The X-Ray Emission Lines Profiles Of Ζ Puppis, M. A. Leutenegger, David H. Cohen, S. M. Kahn, S. P. Owocki, F. B.S. Paerels
Resonance Scattering In The X-Ray Emission Lines Profiles Of Ζ Puppis, M. A. Leutenegger, David H. Cohen, S. M. Kahn, S. P. Owocki, F. B.S. Paerels
Physics & Astronomy Faculty Works
We present XMM-Newton Reflection Grating Spectrometer observations of pairs of X-ray emission line profiles from the O star ζ Pup that originate from the same He-like ion. The two profiles in each pair have different shapes and cannot both be consistently fit by models assuming the same wind parameters. We show that the differences in profile shape can be accounted for in a model including the effects of resonance scattering, which affects the resonance line in the pair but not the intercombination line. This implies that resonance scattering is also important in single resonance lines, where its effect is difficult …
Quantitative Analysis Of Resolved X-Ray Emission Line Profiles Of O Stars, David H. Cohen, M. A. Leutenegger, R. H.D. Townsend
Quantitative Analysis Of Resolved X-Ray Emission Line Profiles Of O Stars, David H. Cohen, M. A. Leutenegger, R. H.D. Townsend
Physics & Astronomy Faculty Works
By quantitatively fitting simple emission line profile models that include both atomic opacity and porosity to the Chandra X-ray spectrum of ζ Pup, we are able to explore the trade-offs between reduced mass-loss rates and wind porosity. We find that reducing the mass-loss rate of ζ Pup by roughly a factor of four, to 1.5 \times 10^{-6} M_sun/yr, enables simple non-porous wind models to provide good fits to the data. If, on the other hand, we take the literature mass-loss rate of 6 \times 10^{-6} M_sun/yr, then to produce X-ray line profiles that fit the data, extreme porosity lengths -- …