High Resolution X-ray Spectra of the Brightest OB Stars in the Cygnus OB2 Association

The Cygnus OB2 Association contains some of the most luminous OB stars in our Galaxy, the brightest of which are also among the most luminous in X-rays. We have obtained a Chandra High Energy Transmission Grating Spectrometer (HETGS) observation centered on Cyg OB2 No. 8a, the most luminous X-ray source in the Association. Although our analysis will focus on the X-ray properties of Cyg OB2 No. 8a, we also present limited analyses of three other OB stars (Cyg OB2 Nos. 5, 9, and 12). Applying standard diagnostic techniques as used in previous studies of early-type stars, we find that the X-ray properties of Cyg OB2 No. 8a are very similar to those of other OB stars that have been observed using high-resolution X-ray spectroscopy. From analyses of the He-like ion "fir" emission lines, we derive radial distances of the He-like line emission sources and find these fir-inferred radii are consistent with their corresponding X-ray continuum optical depth unity radii. Contrary to other O-star results, the emission lines of Cyg OB2 No. 8a show a large range in line centroid shifts (roughly -800 to +250 km/s). We discuss the implications of our results in light of the fact that Cyg OB2 No. 8a is a member of a rather tight stellar cluster, and shocks could arise at interfaces with the winds of these other stars.Comment: 36 pages (including 4 tables and 12 figures). LaTeX. Submitted to Ap

X-ray emitting young stars in the Orion Nebula

The Orion Nebula Cluster and the molecular cloud in its vicinity have been observed with the ACIS-I detector on board the Chandra X-ray Observatory with 23 hours exposure. We detect 1075 X-ray sources: 91% are spatially associated with known stellar members of the cluster, and 7% are newly identified deeply embedded cloud members. This provides the largest X-ray study of a pre-main sequence stellar population. We examine here the X-ray properties of Orion young stars as a function of mass. Results include: (a) the discovery of rapid variability in the O9.5 31 M_o star \theta^2A Ori, and several early B stars, inconsistent with the standard model of X-ray production in small wind shocks; (b) support for the hypothesis that intermediate-mass mid-B through A type stars do not themselves produce significant X-ray emission; (c) confirmation that low-mass G- through M-type T Tauri stars exhibit powerful flaring but typically at luminosities considerably below the `saturation' level; (d) confirmation that the presence or absence of a circumstellar disk has no discernable effect on X-ray emission; (e) evidence that T Tauri plasma temperatures are often very high with T >= 100 MK, even when luminosities are modest and flaring is not evident; and (f) detection of the largest sample of pre-main sequence very low mass objects showing high flaring levels and a decline in magnetic activity as they evolve into L- and T-type brown dwarfs.Comment: 82 pages, 16 figures, 6 tables. To appear in the Astrophysical Journal. For a version with high quality images and electronic tables, see ftp://ftp.astro.psu.edu/pub/edf/orion1

Collisionless Damping of Fast MHD Waves in Magneto-rotational Winds

We propose collisionless damping of fast MHD waves as an important mechanism for the heating and acceleration of winds from rotating stars. Stellar rotation causes magnetic field lines anchored at the surface to form a spiral pattern and magneto-rotational winds can be driven. If the structure is a magnetically dominated, fast MHD waves generated at the surface can propagate almost radially outward and cross the field lines. The propagating waves undergo collisionless damping owing to interactions with particles surfing on magnetic mirrors that are formed by the waves themselves. The damping is especially effective where the angle between the wave propagation and the field lines becomes moderately large ($\sim 20$ to $80^{\circ}$). The angle tends naturally to increase into this range because the field in magneto-rotational winds develops an increasingly large azimuthal component. The dissipation of the wave energy produces heating and acceleration of the outflow. We show using specified wind structures that this damping process can be important in both solar-type stars and massive stars that have moderately large rotation rates. This mechanism can play a role in coronae of young solar-type stars which are rapidly rotating and show X-ray luminosities much larger than the sun. The mechanism could also be important for producing the extended X-ray emitting regions inferred to exist in massive stars of spectral type middle B and later.Comment: 12 pages, including 7 figures, accepted for publication in Ap

Subjective response to and tolerability of long-term supraphysiological doses of levothyroxine in refractory mood disorders

NOTICE: this is the author’s version of a work that was accepted for publication in Journal of Affective Disorders. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Affective Disorders, [VOL 64, ISSUE 1, (2001)] DOI:10.1016/S0165-0327(00)00215-9

X-ray Point Sources in The Central Region of M31 as seen by Chandra

We report on \chandra observations of the central region of M31. By combining eight \chandra ACIS-I observations taken between 1999 and 2001, we have identified 204 X-ray sources within the central $\sim 17'\times17'$ region of M31, with a detection limit of $\sim 2\times10^{35}$\lum. Of these 204 sources, 22 are identified with globular clusters, 2 with supernova remnants, 9 with planetary nebula, and 9 as supersoft sources. By comparing individual images, about 50% of the sources are variable on time scales of months. We also found 13 transients, with light curves showing a variety of shapes. We also extracted the energy spectra of the 20 brightest sources; they can be well fit by a single power-law with a mean photon index of 1.8. The spectral shapes of 12 sources are shown to be variable, suggesting that they went through state changes. The luminosity function of all the point sources is consistent with previous observations (a broken power-law with a luminosity break at $1.7\times10^{37}$\lum). However, when the X-ray sources in different regions are considered separately, different luminosity functions are obtained. This indicates that the star-formation history might be different in different regions.Comment: 42 pages, 9 figures, ApJ, accepted, Higher-resolution figures available on reques

Inverse Compton Scattering as the Source of Diffuse EUV Emission in the Coma Cluster of Galaxies

We have examined the hypothesis that the majority of the diffuse EUV flux in the Coma cluster is due to inverse Compton scattering of low energy cosmic ray electrons (0.16 < epsilon < 0.31 GeV) against the 3K black-body background. We present data on the two-dimensional spatial distribution of the EUV flux and show that these data provide strong support for a non-thermal origin for the EUV flux. However, we show that this emission cannot be produced by an extrapolation to lower energies of the observed synchrotron radio emitting electrons and an additional component of low energy cosmic ray electrons is required.Comment: 11 pages, 5 figure

PET imaging of brain inflammation during early epileptogenesis in a rat model of temporal lobe epilepsy.

Background Recently, inflammatory cascades have been suggested as a target for epilepsy therapy. Positron emission tomography (PET) imaging offers the unique possibility to evaluate brain inflammation longitudinally in a non-invasive translational manner. This study investigated brain inflammation during early epileptogenesis in the post-kainic acid-induced status epilepticus (KASE) model with post-mortem histology and in vivo with [18F]-PBR111 PET. Methods Status epilepticus (SE) was induced (N = 13) by low-dose injections of KA, while controls (N = 9) received saline. Translocator protein (TSPO) expression and microglia activation were assessed with [125I]-CLINDE autoradiography and OX-42 immunohistochemistry, respectively, 7 days post-SE. In a subgroup of rats, [18F]-PBR111 PET imaging with metabolite-corrected input function was performed before post-mortem evaluation. [18F]-PBR111 volume of distribution (V t) in volume of interests (VOIs) was quantified by means of kinetic modelling and a VOI/metabolite-corrected plasma activity ratio. Results Animals with substantial SE showed huge overexpression of TSPO in vitro in relevant brain regions such as the hippocampus and amygdala (P < 0.001), while animals with mild symptoms displayed a smaller increase in TSPO in amygdala only (P < 0.001). TSPO expression was associated with OX-42 signal but without obvious cell loss. Similar in vivo [18F]-PBR111 increases in V t and the simplified ratio were found in key regions such as the hippocampus (P < 0.05) and amygdala (P < 0.01). Conclusion Both post-mortem and in vivo methods substantiate that the brain regions important in seizure generation display significant brain inflammation during epileptogenesis in the KASE model. This work enables future longitudinal investigation of the role of brain inflammation during epileptogenesis and evaluation of anti-inflammatory treatments. © 2012, Springer

A Chandra/ACIS Study of 30 Doradus II. X-ray Point Sources in the Massive Star Cluster R136 and Beyond

We have studied the X-ray point source population of the 30 Doradus star-forming complex in the Large Magellanic Cloud using high-spatial-resolution X-ray images and spatially-resolved spectra obtained with the Advanced CCD Imaging Spectrometer (ACIS) aboard the Chandra X-ray Observatory. Here we describe the X-ray sources in a 17' x 17' field centered on R136, the massive star cluster at the center of the main 30 Dor nebula. We detect 20 of the 32 Wolf-Rayet stars in the ACIS field. R136 is resolved at the subarcsecond level into almost 100 X-ray sources, including many typical O3--O5 stars as well as a few bright X-ray sources previously reported. Over two orders of magnitude of scatter in L_X is seen among R136 O stars, suggesting that X-ray emission in the most massive stars depends critically on the details of wind properties and binarity of each system, rather than reflecting the widely-reported characteristic value L_X/L_bol ~ 10^{-7}. Such a canonical ratio may exist for single massive stars in R136, but our data are too shallow to confirm this relationship. Through this and future X-ray studies of 30 Doradus, the complete life cycle of a massive stellar cluster can be revealed.Comment: 31 pages, 6 bitmapped figures, 5 tables; accepted to A

X-ray Observations of the New Pulsar--Supernova Remnant System PSR J1119-6127 and SNR G292.2-0.5

PSR J1119-6127 is a recently discovered 1700-year-old radio pulsar that has a very high inferred surface dipolar magnetic field. We present a detailed analysis of a pointed ASCA observation and archival ROSAT data of J1119-6127 and its surroundings. Both data sets reveal extended emission coincident with the newly-discovered radio supernova remnant G292.2-0.5, reported in a companion paper by Crawford et al. (astro-ph/0012287).. A hard point source, offset ~1.5' from the position of the radio pulsar, is seen with the ASCA GIS. No pulsations are detected at the radio period with a pulsed fraction upper limit of 61% (95% confidence). The limited statistics prevent a detailed spectral analysis, although a power-law model with photon index (Gamma=~1-2) describes the data well. Both the spectral model and derived X-ray luminosity are consistent with those measured for other young radio pulsars, although the spatial offset renders an identification of the source as the X-ray counterpart of the pulsar uncertain.Comment: Accepted by ApJ; 12 Pages in emulated ApJ format with embedded tables and color figure