Open Access. Powered by Scholars. Published by Universities.®
Physical Sciences and Mathematics Commons™
Open Access. Powered by Scholars. Published by Universities.®
Articles 1 - 9 of 9
Full-Text Articles in Physical Sciences and Mathematics
Helium-Like X-Ray Line Complexes Show That The Hottest Plasma On The O Supergiant Ζ Puppis Is In Its Wind, David H. Cohen, Ariel M. Overdorff, M. A. Leutenegger, M. Gagné, V. Petit, A. David-Uraz
Helium-Like X-Ray Line Complexes Show That The Hottest Plasma On The O Supergiant Ζ Puppis Is In Its Wind, David H. Cohen, Ariel M. Overdorff, M. A. Leutenegger, M. Gagné, V. Petit, A. David-Uraz
Physics & Astronomy Faculty Works
We present an analysis of Chandra grating spectra of key helium-like line complexes to put constraints on the location with respect to the photosphere of the hottest (T ≳ 6 × 10⁶ K) plasma in the wind of the O supergiant ζ Pup and to explore changes in the 18 yr between two sets of observations of this star. We fit two models—one empirical and one wind-shock-based—to the S XV, Si XIII, and Mg XI line complexes and show that an origin in the wind flow, above r ≈ 1.5 R∗, is strongly favoured over an origin less than 0.3 …
Chandra Grating Spectroscopy Of Embedded Wind Shock X-Ray Emission From O Stars Shows Low Plasma Temperatures And Significant Wind Absorption, David H. Cohen, V. Vaughn Parts, Graham M. Doskoch , '20, Jiaming Wang , '22, V. Petit, M. A. Leutenegger, M. Gagné
Chandra Grating Spectroscopy Of Embedded Wind Shock X-Ray Emission From O Stars Shows Low Plasma Temperatures And Significant Wind Absorption, David H. Cohen, V. Vaughn Parts, Graham M. Doskoch , '20, Jiaming Wang , '22, V. Petit, M. A. Leutenegger, M. Gagné
Physics & Astronomy Faculty Works
We present a uniform analysis of six examples of embedded wind shock (EWS) O star X-ray sources observed at high resolution with the Chandra grating spectrometers. By modelling both the hot plasma emission and the continuum absorption of the soft X-rays by the cool, partially ionized bulk of the wind we derive the temperature distribution of the shock-heated plasma and the wind mass-loss rate of each star. We find a similar temperature distribution for each star’s hot wind plasma, consistent with a power-law differential emission measure, dlogEMdlogT, with a slope a little steeper than −2, up to temperatures of only …
Chandra Spectral Measurements Of The O Supergiant Ζ Puppis Indicate A Surprising Increase In The Wind Mass-Loss Rate Over 18 Yr, David H. Cohen, Jiaming Wang , '22, V. Petit, M. A. Leutenegger, L. Dakir, C. Mayhue , '23, A. David-Uraz
Chandra Spectral Measurements Of The O Supergiant Ζ Puppis Indicate A Surprising Increase In The Wind Mass-Loss Rate Over 18 Yr, David H. Cohen, Jiaming Wang , '22, V. Petit, M. A. Leutenegger, L. Dakir, C. Mayhue , '23, A. David-Uraz
Physics & Astronomy Faculty Works
New long Chandra grating observations of the O supergiant ζ Pup show not only a brightening of the X-ray emission line flux of 13 per cent in the 18 yr since Chandra’s first observing cycle, but also clear evidence – at more than 4σ significance – of increased wind absorption signatures in its Doppler-broadened line profiles. We demonstrate this with non-parametric analysis of the profiles as well as Gaussian fitting and then use line-profile model fitting to derive a mass-loss rate of 2.47 ± 0.09 × 10−6[Math Processing Error], which is a 40 per cent increase over the value obtained …
Extreme Resonance Line Profile Variations In The Ultraviolet Spectra Of Ngc 1624-2: Probing The Giant Magnetosphere Of The Most Strongly Magnetized Known O-Type Star, A. David-Uraz, C. Erba, V. Petit, A. W. Fullerton, F. Martins, N. R. Walborn, R. Macinnis, R. H. Barbá, David H. Cohen, J. Maíz Apellániz, Y. Nazé, S. P. Owocki, J. O. Sundqvist, A Ud-Doula, G. A. Wade
Extreme Resonance Line Profile Variations In The Ultraviolet Spectra Of Ngc 1624-2: Probing The Giant Magnetosphere Of The Most Strongly Magnetized Known O-Type Star, A. David-Uraz, C. Erba, V. Petit, A. W. Fullerton, F. Martins, N. R. Walborn, R. Macinnis, R. H. Barbá, David H. Cohen, J. Maíz Apellániz, Y. Nazé, S. P. Owocki, J. O. Sundqvist, A Ud-Doula, G. A. Wade
Physics & Astronomy Faculty Works
In this paper, we present high-resolution HST/COS observations of the extreme magnetic O star NGC 1624-2. These represent the first ultraviolet spectra of this archetypal object. We examine the variability of its wind-sensitive resonance lines, comparing it to that of other known magnetic O stars. In particular, the observed variations in the profiles of the C iv and Si iv doublets between low state and high state are the largest observed in any magnetic O-type star, consistent with the expected properties of NGC 1624-2’s magnetosphere. We also observe a redshifted absorption component in the low state, a feature not seen …
An ‘Analytic Dynamical Magnetosphere’ Formalism For X-Ray And Optical Emission From Slowly Rotating Magnetic Massive Stars, S. P. Owocki, A. Ud-Doula, J. O. Sundqvist, V. Petit, David H. Cohen, R. H. D. Townsend
An ‘Analytic Dynamical Magnetosphere’ Formalism For X-Ray And Optical Emission From Slowly Rotating Magnetic Massive Stars, S. P. Owocki, A. Ud-Doula, J. O. Sundqvist, V. Petit, David H. Cohen, R. H. D. Townsend
Physics & Astronomy Faculty Works
Slowly rotating magnetic massive stars develop ‘dynamical magnetospheres’ (DMs), characterized by trapping of stellar wind outflow in closed magnetic loops, shock heating from collision of the upflow from opposite loop footpoints, and subsequent gravitational infall of radiatively cooled material. In 2D and 3D magnetohydrodynamic (MHD) simulations, the interplay among these three components is spatially complex and temporally variable, making it difficult to derive observational signatures and discern their overall scaling trends. Within a simplified, steady-state analysis based on overall conservation principles, we present here an ‘analytic dynamical magnetosphere’ (ADM) model that provides explicit formulae for density, temperature, and flow speed …
X-Ray Emission From The Giant Magnetosphere Of The Magnetic O-Type Star Ngc 1624-2, V. Petit, David H. Cohen, G. A. Wade, Y. Nazé, S. P. Owocki, J. O. Sundqvist, A. Ud-Doula, A. Fullerton, M. Leutenegger, M. Gagné
X-Ray Emission From The Giant Magnetosphere Of The Magnetic O-Type Star Ngc 1624-2, V. Petit, David H. Cohen, G. A. Wade, Y. Nazé, S. P. Owocki, J. O. Sundqvist, A. Ud-Doula, A. Fullerton, M. Leutenegger, M. Gagné
Physics & Astronomy Faculty Works
We observed NGC 1624-2, the O-type star with the largest known magnetic field (Bp ∼ 20 kG), in X-rays with the Advanced CCD Imaging Spectrometer (ACIS-S) camera on-board the Chandra X-ray Observatory. Our two observations were obtained at the minimum and maximum of the periodic Hα emission cycle, corresponding to the rotational phases where the magnetic field is the closest to equator-on and pole-on, respectively. With these observations, we aim to characterize the star's magnetosphere via the X-ray emission produced by magnetically confined wind shocks. Our main findings are as follows. (i) The observed spectrum of NGC 1624-2 is hard, …
Confirming Hd 23478 As A New Magnetic B Star Hosting An Hα-Bright Centrifugal Magnetosphere, J. Sikora, G. A. Wade, D. A. Bohlender, C. Neiner, M. E. Oksala, M. Shultz, David H. Cohen, A. Ud-Doula, J. Grunhut, D. Monin, S. Owocki, V. Petit, T. Rivinus, R. H. D. Townsend
Confirming Hd 23478 As A New Magnetic B Star Hosting An Hα-Bright Centrifugal Magnetosphere, J. Sikora, G. A. Wade, D. A. Bohlender, C. Neiner, M. E. Oksala, M. Shultz, David H. Cohen, A. Ud-Doula, J. Grunhut, D. Monin, S. Owocki, V. Petit, T. Rivinus, R. H. D. Townsend
Physics & Astronomy Faculty Works
In this paper, we report 23 magnetic field measurements of the B3IV star HD 23478: 12 obtained from high-resolution Stokes V spectra using the ESPaDOnS (Canada–France–Hawaii Telescope) and Narval (Télescope Bernard Lyot) spectropolarimeters, and 11 from medium-resolution Stokes V spectra obtained with the DimaPol spectropolarimeter (Dominion Astronomical Observatory). HD 23478 was one of two rapidly rotating stars identified as potential ‘centrifugal magnetosphere’ hosts based on IR observations from the Apache Point Observatory Galactic Evolution Experiment survey. We derive basic physical properties of this star including its mass (M=6.1+0.8−0.7M⊙), effective temperature (Teff = 20 ± 2 kK), radius (R=2.7+1.6−0.9R⊙), and age …
Measuring The Shock-Heating Rate In The Winds Of O Stars Using X-Ray Line Spectra, David H. Cohen, Zequn Li , '16, K. G. Gayley, S. P. Owocki, J. O. Sundqvist, V. Petit, M. A. Leutenegger
Measuring The Shock-Heating Rate In The Winds Of O Stars Using X-Ray Line Spectra, David H. Cohen, Zequn Li , '16, K. G. Gayley, S. P. Owocki, J. O. Sundqvist, V. Petit, M. A. Leutenegger
Physics & Astronomy Faculty Works
We present a new method for using measured X-ray emission line fluxes from O stars to determine the shock-heating rate due to instabilities in their radiation-driven winds. The high densities of these winds means that their embedded shocks quickly cool by local radiative emission, while cooling by expansion should be negligible. Ignoring for simplicity any non-radiative mixing or conductive cooling, the method presented here exploits the idea that the cooling post-shock plasma systematically passes through the temperature characteristic of distinct emission lines in the X-ray spectrum. In this way, the observed flux distribution among these X-ray lines can be used …
Measuring Mass-Loss Rates And Constraining Shock Physics Using X-Ray Line Profiles Of O Stars From The Chandra Archive, David H. Cohen, Emma E. Wollman , '09, M. A. Leutenegger, J. O. Sundqvist, A. W. Fullerton, J. Zsargó, S. P. Owocki
Measuring Mass-Loss Rates And Constraining Shock Physics Using X-Ray Line Profiles Of O Stars From The Chandra Archive, David H. Cohen, Emma E. Wollman , '09, M. A. Leutenegger, J. O. Sundqvist, A. W. Fullerton, J. Zsargó, S. P. Owocki
Physics & Astronomy Faculty Works
We quantitatively investigate the extent of wind absorption signatures in the X-ray grating spectra of all non-magnetic, effectively single O stars in the Chandra archive via line profile fitting. Under the usual assumption of a spherically symmetric wind with embedded shocks, we confirm previous claims that some objects show little or no wind absorption. However, many other objects do show asymmetric and blueshifted line profiles, indicative of wind absorption. For these stars, we are able to derive wind mass-loss rates from the ensemble of line profiles, and find values lower by an average factor of 3 than those predicted by …