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Full-Text Articles in Astrophysics and Astronomy

New Challenges For Wind Shock Models: The Chandra Spectrum Of The Hot Star Delta Orionis, N. A. Miller, J. P. Cassinelli, W. L. Waldron, J. J. Macfarlane, David H. Cohen Oct 2002

New Challenges For Wind Shock Models: The Chandra Spectrum Of The Hot Star Delta Orionis, N. A. Miller, J. P. Cassinelli, W. L. Waldron, J. J. Macfarlane, David H. Cohen

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The Chandra spectrum of delta Ori A shows emission lines from hydrogen- and helium-like states of Si, Mg, Ne, and O, along with N VII Lyalpha and lines from ions in the range Fe XVII-Fe XXI In contrast to the broad lines seen in zeta Pup and zeta Ori (850 +/- 40 and 1000 +/- 240 km s(-1) half-width at half-maximum [HWHM], respectively), these lines are broadened to only 430 +/- 60 km s(-1) HWHM. This is much lower than the measured wind terminal velocity of 2000 km s(-1). The forbidden, intercombination, and resonance (fir) lines from He-like ions indicate …

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Radiation Science Using Z-Pinch X-Rays, J. E. Bailey, G. A. Chandler, David H. Cohen, M. E. Cuneo, M. E. Foord, R. F. Heeter, D. Jobe, P. W. Lake, J. J. Macfarlane, T. J. Nash, D. S. Nielson, R. Smelser, J. Torres May 2002

Radiation Science Using Z-Pinch X-Rays, J. E. Bailey, G. A. Chandler, David H. Cohen, M. E. Cuneo, M. E. Foord, R. F. Heeter, D. Jobe, P. W. Lake, J. J. Macfarlane, T. J. Nash, D. S. Nielson, R. Smelser, J. Torres

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Present-day Z-pinch experiments generate 200 TW peak power, 5–10 ns duration x-ray bursts that provide new possibilities to advance radiation science. The experiments support both the underlying atomic and plasma physics, as well as inertial confinement fusion and astrophysics applications. A typical configuration consists of a sample located 1–10 cm away from the pinch, where it is heated to 10–100 eV temperatures by the pinch radiation. The spectrally-resolved sample-plasma absorption is measured by aiming x-ray spectrographs through the sample at the pinch. The pinch plasma thus both heats the sample and serves as a backlighter. Opacitymeasurements with this source are …

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Mass-Loss And Magnetospheres: X-Rays From Hot Stars And Young Stellar Objects, M. Gagné, David H. Cohen, S. P. Owocki, A. Ud-Doula Jan 2002

Mass-Loss And Magnetospheres: X-Rays From Hot Stars And Young Stellar Objects, M. Gagné, David H. Cohen, S. P. Owocki, A. Ud-Doula

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High-resolution X-ray spectra of high-mass stars and low-mass T-Tauri stars obtained during the first year of the Chandra mission are providing important clues about the mechanisms which produce X-rays on very young stars. For zeta Puppis (O4 If) and zeta Ori (O9.5 I), the broad, blue-shifted line profiles, line ratios, and derived temperature distribution suggest that the X-rays are produced throughout the wind via instability-driven wind shocks. For some less luminous OB stars, like theta^1 Ori C (O7 V) and tau Sco (B0 V), the line profiles are symmetric and narrower. The presence of time-variable emission and very high-temperature lines …

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A Robotic Wide-Angle Hα Survey Of The Southern Sky, John E. Gaustad, P. R. Mccullough, W. Rosing, D. Van Buren Nov 2001

A Robotic Wide-Angle Hα Survey Of The Southern Sky, John E. Gaustad, P. R. Mccullough, W. Rosing, D. Van Buren

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We have completed a robotic wide-angle imaging survey of the southern sky (delta = +15 degrees to -90 degrees) at 656.3 nm wavelength, the H alpha emission line of hydrogen. Each image of the resulting Southern H alpha Sky Survey Atlas (SHASSA) covers an area of the sky 13 degrees square at an angular resolution of approximately 0.'8 and reaches a sensitivity level of 2 R (1.2 x 10(-17) ergs cm(-2) s(-1) arcsec(-2)) pixel(-1), corresponding to an emission measure of 4 cm(-6) pc and to a brightness temperature for microwave free-free emission of 12 muK at 30 GHz. Smoothing over …

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X-Ray Line Profiles From Parameterized Emission Within An Accelerating Stellar Wind, S. P. Owocki, David H. Cohen Oct 2001

X-Ray Line Profiles From Parameterized Emission Within An Accelerating Stellar Wind, S. P. Owocki, David H. Cohen

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Motivated by recent detections by the XMM and Chandra satellites of X-ray line emission from hot, luminous stars, we present synthetic line profiles for X-rays emitted within parameterized models of a hot-star wind. The X-ray line emission is taken to occur at a sharply defined comoving-frame resonance wavelength, which is Doppler-shifted by a stellar wind outflow parameterized by a "beta" velocity law, nu (r) = nu (infinity)(1-R-*/r)(beta). Above some initial onset radius for R-o X-ray emission, the radial variation of the emission filling factor is assumed to decline as a power law in radius, f (r) similar tor(-q). The computed …

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Chandra Detection Of Doppler-Shifted X-Ray Line Profiles From The Wind Of Zeta Puppis (O4f), J. P. Cassinelli, N. A. Miller, W. L. Waldron, J. J. Macfarlane, David H. Cohen Jun 2001

Chandra Detection Of Doppler-Shifted X-Ray Line Profiles From The Wind Of Zeta Puppis (O4f), J. P. Cassinelli, N. A. Miller, W. L. Waldron, J. J. Macfarlane, David H. Cohen

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We report on a 67 ks High-Energy Transmission Grating observation of the optically brightest early O star zeta Puppis (O4 f). Many resolved X-ray lines are seen in the spectra over a wavelength range of 5-25 Angstrom. Chnndra has sufficient spectral resolution to study the velocity structure of isolated X-ray line profiles and to distinguish the individual forbidden, intercombination, and resonance (fir) emission lines in several He-like ions, even where the individual components are strongly Doppler-broadened. In contrast to X-ray line profiles in other hot stars, zeta Pup shows blueshifted and skewed line profiles, providing the dearest and most direct …

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Can Post T Tauri Stars Be Found? Yes!, Eric L.N. Jensen Jan 2001

Can Post T Tauri Stars Be Found? Yes!, Eric L.N. Jensen

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I review the observational challenges of finding post T Tauri stars (PTTS), defined here as low-mass, pre-main-sequence stars with ages of 10(7)-10(8) yr. Such stars are difficult to find because they are less active than younger T Tauri stars, and they may not be associated with molecular gas. They are useful for studying the evolution of circumstellar disks and stellar activity between the 10(6)-yr ages of nearby star-forming regions and the main sequence. However, care must be taken in the search process so that the selection criteria used to locate such stars do not bias the sample used for subsequent …

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Disk Clearing In The Young Binary Ak Sco, Eric L.N. Jensen Jan 2001

Disk Clearing In The Young Binary Ak Sco, Eric L.N. Jensen

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The pre-main-sequence spectroscopic binary AK Sco is surrounded by a circumbinary disk. Yet while this disk must be somewhat disturbed by the binary at its center, there is no evidence from current data that it has a cleared central hole like those seen in some young binaries, nor that accretion from the outer disk has been cut off. Indeed, most of its spectral and photometric diagnostics are indistinguishable from those of young single stars. Why doesn't this system show any evidence of disturbance of its disk? It may be that the center of the disk is indeed largely cleared, but …

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Disks In Young Binary Systems: Unresolved Millimeter-Wave Observations, Eric L.N. Jensen Jan 2001

Disks In Young Binary Systems: Unresolved Millimeter-Wave Observations, Eric L.N. Jensen

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Observations at millimeter and submillimeter wavelengths are sensitive to the total mass of circumstellar and circumbinary dust in a multiple system, and in some cases single-dish observations can help constrain the location of disk material in spite of their lack of spatial resolution. Young binary stars show a great diversity of disk properties, with a large part of the variation accounted for by binary separation. Many of the closest binaries (those with separations a less than a few AU) harbor massive circumbinary disks. Binaries with a greater than or equal to 100 AU tend to have massive circumstellar disks. In …

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A Single Circumbinary Disk In The Hd 98800 Quadruple System, D. W. Koerner, Eric L.N. Jensen, K. L. Cruz, T. B. Guild, K. Gultekin Apr 2000

A Single Circumbinary Disk In The Hd 98800 Quadruple System, D. W. Koerner, Eric L.N. Jensen, K. L. Cruz, T. B. Guild, K. Gultekin

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We present subarcsecond thermal infrared imaging of HD 98800, a young quadruple system composed of a pair of low-mass spectroscopic binaries separated by 0".8 (38 AU), each with a K-dwarf primary. Images at wavelengths ranging from 5 to 24.5 mu m show unequivocally that the optically fainter binary, HD 98800B, is the sole source of a comparatively large infrared excess on which a silicate emission feature is superposed. The excess is detected only at wavelengths of 7.9 mu m and longer, peaks at 25 mu m, and has a best-fit blackbody temperature of 150 K, indicating that most of the …

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The Three-Dimensional Structure Of The Infrared Cirrus, John E. Gaustad Jan 1994

The Three-Dimensional Structure Of The Infrared Cirrus, John E. Gaustad

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This project was carried out over a period of four years, beginning 6/15/89 and continuing through 9/15/93. Intermediate results have been reported as poster papers at several meetings of the American Astronomical Society. A brief summary was presented in April 1993 at a symposium on the infrared cirrus. The final results were published in late 1993. The measurements have been deposited in NASA's Astronomical Data Center. Briefly, the results are as follows: Using the IRAS data base, we surveyed the 1808 06-B9.5 stars in the Bright Star Catalog for extended excess emission at 60 micrometers, indicating the presence of heated …

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