186 research outputs found

    The High-Velocity Outflow of PG1211+143 May Not be That Fast

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    We analyze the X-ray spectrum of the quasar PG1211+143 observed with the CCD and grating spectrometers on board XMM-Newton. Using an ion by ion fitting model we find an outflow component of about 3000 km/s that includes absorption lines of K-shell and L-shell ions of the astrophysically abundant elements. We also identify and include in our model broad (FWHM = 6000 km/s) emission lines from H-like ions of C, N, O, and Ne, and He-like ions of O, Ne, and Mg. The outflow velocity we find is an alternative interpretation of the data and is in contrast with the ultra high velocity of ~24000 km/s reported previously for this object. Nevertheless, we can not completely rule out the presence of a high velocity component due to the poor signal-to-noise ratio of the data.Comment: 7 pages, 2 figures, emulateapj, accepted for publication in The Astrophysical Journa

    Is The Fe M-shell Absorber Part of The Outflow in Active Galactic Nuclei?

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    The X-ray emission of many active galactic nuclei (AGNs) is absorbed between 15 and 17 Angstrom by means of unresolved (inner-shell) transition arrays (UTAs) of Fe M-shell ions. The outflow velocities implied by the Doppler shifts of the individual UTAs in the spectrum have never before been measured. Thus, the Fe-M absorber has been commonly assumed to be part of the ionized AGN outflow, whose velocities are readily obtained from more easily measured spectral lines. The best spectrum of Fe-M absorption is available from the integrated 900 ks Chandra HETGS observations of NGC 3783, in which some Fe-M ions are clearly resolved. We measure the velocities of the individual Fe-M ions in NGC 3783 for the first time. Surprisingly, we find that the Fe-M absorber, most noticeably Fe+8^{+8}, Fe+9^{+9}, and Fe+10^{+10}, is not outflowing at the same velocity as the previously known wind. In fact, it appears to be stationary and therefore not part of the outflow at all. It could, alternatively, be ascribed to the skin of the dusty torus. This reduces appreciably the mass loss rate estimated for the NGC 3783 outflow and perhaps for other similar sources as well, in which the various Fe-M ions are not resolved.Comment: To be published in Ap

    Coronae of Stars with Super Solar Elemental Abundances

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    Coronal elemental abundances are known to deviate from the photospheric values of their parent star, with the degree of deviation depending on the First Ionization Potential (FIP). This study focuses on the coronal composition of stars with super-solar photospheric abundances. We present the coronal abundances of six such stars: 11 LMi, ι\iota Hor, HR 7291, τ\tau Boo, and α\alpha Cen A and B. These stars all have high-statistics X-ray spectra, three of which are presented for the first time. The abundances measured in this paper are obtained using the line-resolved spectra of the Reflection Grating Spectrometer (RGS) in conjunction with the higher throughput EPIC-pn camera spectra on board the XMM-Newton observatory. A collisionally ionized plasma model with two or three temperature components is found to represent the spectra well. All elements are found to be consistently depleted in the coronae compared to their respective photospheres. For 11 LMi and τ\tau Boo no FIP effect is present, while ι\iota Hor, HR 7291, and α\alpha Cen A and B show a clear FIP trend. These conclusions hold whether the comparison is made with solar abundances or the individual stellar abundances. Unlike the solar corona where low FIP elements are enriched, in these stars the FIP effect is consistently due to a depletion of high FIP elements with respect to actual photospheric abundances. Comparing to solar abundances (instead of stellar) yields the same fractionation trend as on the Sun. In both cases a similar FIP bias is inferred, but different fractionation mechanisms need to be invoked.Comment: 11 pages, 7 figures, submitted to A&A. Comments are welcom

    X-Ray Emission from Planetary Nebulae Calculated by 1D Spherical Numerical Simulations

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    We calculate the X-ray emission from both constant and time evolving shocked fast winds blown by the central stars of planetary nebulae (PNs) and compare with observations. Using spherically symmetric numerical simulations with radiative cooling, we calculate the flow structure, and the X-ray temperature and luminosity of the hot bubble formed by the shocked fast wind. We find that a constant fast wind gives results that are very close to those obtained from the self-similar solution. We show that in order for a fast shocked wind to explain the observed X-ray properties of PNs, rapid evolution of the wind is essential. More specifically, the mass loss rate of the fast wind should be high early on when the speed is ~300-700 km/s, and then it needs to drop drastically by the time the PN age reaches ~1000 yr. This implies that the central star has a very short pre-PN (post-AGB) phase.Comment: accepted to MNRA
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