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We report detailed X-ray observations of the unique binary system $\epsilon$ Lupi, the only known short-period binary consisting of two magnetic early-type stars. The components have comparably strong, but anti-aligned magnetic fields. The orbital and magnetic properties of the system imply that the magnetospheres overlap at all orbital phases, suggesting the possibility of variable inter-star magnetospheric interaction due to the non-negligible eccentricity of the orbit. To investigate this effect, we observed the X-ray emission from $\epsilon$ Lupi both near and away from periastron passage, using the Neutron Star Interior Composition Explorer mission (NICER) X-ray Telescope. We find that the system produces excess X-ray emission at the periastron phase, suggesting the presence of variable inter-star magnetospheric interaction. We also discover that the enhancement at periastron is confined to a very narrow orbital phase range ($\approx 5\%$ of the orbital period), but the X-ray properties close to periastron phase are similar to those observed away from periastron. From these observations, we infer that the underlying cause is magnetic reconnection heating the stellar wind plasma, rather than shocks produced by wind-wind collision. Finally, by comparing the behavior of $\epsilon$ Lupi with that observed for cooler magnetic binary systems, we propose that elevated X-ray flux at periastron phase is likely a general characteristic of interacting magnetospheres irrespective of the spectral types of the constituent stars., Comment: Accepted for publication in MNRAS (20 pages, 17 figures)

We quantify the rapid variations in X-ray brightness ("flares") from the extremely massive colliding wind binary Eta Carinae seen during the past three orbital cycles by RXTE. The observed flares tend to be shorter in duration and more frequent as periastron is approached, although the largest ones tend to be roughly constant in strength at all phases. Plausible scenarios include (1) the largest of multi-scale stochastic wind clumps from the LBV component entering and compressing the hard X-ray emitting wind-wind collision (WWC) zone, (2) large-scale corotating interacting regions in the LBV wind sweeping across the WWC zone, or (3) instabilities intrinsic to the WWC zone. The first one appears to be most consistent with the observations, requiring homologously expanding clumps as they propagate outward in the LBV wind and a turbulence-like power-law distribution of clumps, decreasing in number towards larger sizes, as seen in Wolf-Rayet winds.

In the 1840s, Eta Carinae, a massive binary near the end of its hydrogen burning cycle, ejected at least ten solar masses of material rich in nitrogen at the expense of carbon and oxygen. The resultant chemistry has led to a most peculiar mix of metals, molecules and dust. We identify thousands of nebular absorption lines of ions including Fe, Ni, V, Sr, Sc and molecules including H2, CH, OH, but no CO. Today we see a wind-enshrouded massive binary in the center of an expanding neutral hourglass and skirt. A similar ionized internal structure is associated with a lesser ejection of the 1890s. Both systems respond to the 5.54-year modulation of X-ray and ultraviolet radiation as the less massive, hotter companion plunges through the extended wind of the more massive, cooler primary. Observations and models are being brought together to understand the properties of the wind-enshrouded central binary. In turn we are learning much atomic spectroscopy, what molecules form in oxygen-and carbon-deprived environments and potentially about a dust that is quite different from the interstellar dust. As the next periastron occurs in January 2009, a number of observing teams are preparing to test these models with new observations.

We discuss the history of X-ray observations of the η Car system, concentrating on the periodic variability discovered in the 1990s. We discuss the interpretation of these variations, concentrating on a model of the system as a “colliding-wind” binary. This interpretation allows the physical and orbital parameters of η Car and its companion star to be constrained.

We report on variations in important X-ray emission lines in a series of Chandra grating spectra of the supermassive colliding wind binary star Eta Carinae, including key phases around the X-ray minimum/periastron passage in 2003.5. The X-rays arise from the collision of the slow, dense wind of Eta Car with the fast, low-density wind of an otherwise hidden companion star. The X-ray emission lines provide the only direct measure of the flow dynamics of the companion's wind along the wind-wind collision zone. We concentrate here on the silicon and sulfur lines, which are the strongest and best resolved lines in the X-ray spectra. Most of the line profiles can be adequately fit with symmetric Gaussians with little significant skewness. Both the silicon and sulfur lines show significant velocity shifts and correlated increases in line widths through the observations. The R = forbidden-to-intercombination ratio from the Si XIII and S XV triplets is near or above the low-density limit in all observations, suggesting that the line-forming region is >1.6 stellar radii from the companion star. We show that simple geometrical models cannot simultaneously fit both the observed centroid variations and changes in line width as a function of phase. We show that the observed profiles can be fitted with synthetic profiles with a reasonable model of the emissivity along the wind-wind collision boundary. We use this analysis to help constrain the line formation region as a function of orbital phase, and the orbital geometry., 23 pages, 24 figures. Accepted for publication in the Astrophysical Journal. New layout for Figure 21; corrected typo in Table 7; corrected x-axis label in Figure 23

We report X-ray measurements of nearly all known galactic Wolf-Rayet stars from the ROSAT all-sky survey and derive 0.2-2.4 keV luminosties.

New ROSAT PSPC and HRI observations of the Carina Nebula region are used to examine the X‐ray emission from the discrete sources as well as the diffuse hot gas in the Carina Nebula near Eta Carina. The spectral and spatial response of the PSPC allow analysis of the 0.1–2.4 keV spectra of all the bright point sources in the region and an examination of the spectral variation of the diffuse X‐rays. Analysis of the diffuse emission shows that most of the emission comes from gas at a temperature of a few million degrees, but also indicates the presence of hot (4E7 K) diffuse gas in an 11 pc region around Eta Car. Eta Car shows a 3 component spectrum with temperatures of 1E6 and 4E7 K. A 0.1×0.2 pc shell of X‐ray emitting gas around Eta Car has been resolved by the HRI, and comparison of the Einstein HRI and ROSAT HRI images supports the suggestion that the soft components originate in the shell (which is unresolved by the PSPC) while the hottest gas is produced less than an arcsec from the optical star. Spect...

On the day prior to the Symposium, we held a special session to review the current status of the XMEGA observations, to discuss upcoming observations, and to plan for future observing programs

We present the X-ray lightcurve of the canonical colliding-wind binary WR 140 from the time of the last periastron through late 1997. Variations in column density, and intrinsic and absorbed X-ray flux agree well with the expectations of colliding wind theory in which the winds from the stars are spherically symmetric.

The system parameters for the massive X-ray binary 4U 1700 - 37 are reexamined in the light of modern spectroscopic theory and new UV and X-ray data. The system is composed of HD 153919, an O6f star having a stronger wind, and an accreting neutron star. Revised parameters for the Of component are derived which are in accord with the parameters of single Of stars, which resolves the problem that 'the O star is undermassive by a factor of 2' formulated by Conti (1978). The ratio of the terminal velocity of the wind to the photospheric escape velocity agrees with those of O stars. The discrepancy between the values of the wind acceleration parameter, derived from X-ray and UV data, is resolved. The acceleration of the wind is similar to that of single OB star winds. It is suggested that the supernova explosion producing the neutron star in 4U 1700 - 37 occurred over a million years ago when HD 153919 was still on the main sequence.

An analysis is presented of previously unpublished intermediate and narrow band H-beta light curves of the short period eclipsing binary V1010 Oph. The temperature of the primary is determined directly by comparing the UV continuum with Kurucz model atmospheres and solve the broadband lightcurve using the Wilson-Devinney program. The present solution has the primary filling its Roche lobe while the secondary is detached from its lobe. An asymmetry in the light curve in which first quadrature (0.25 P) is brighter than the second quadrature (0.75 P) may be the result of local heating of the inner surface of the secondary by mass transfer from the primary. The present semidetached solution indicates that the system is probably evolved.

The origins of visible-band linear polarimetry of Algols and objects related to them are reviewed. It is pointed out, not for the first time, that the polarization signals of these systems can vary sporadically by significant amounts. The difficulty of evaluating the interstellar component of the observed polarization is discussed and these components are evaluated anew for each object studied in this paper. With one possible exception, the polarization signals intrinsic to these binaries derive from electron scattering. A well-defined model is applied to the constant and variable (but phase-locked) polarization signals. Limits to the mass associated with a scattering disk in each binary are derived. Within broad limits, concentrations of scattering mass within and above or below the orbital plane are also developed as are the centroid longitudes of these concentrations within the system. It is pointed out that very few measures of visible-band, circular polarization have been made but that cm-wavelength measures of Algol itself have been very informative.

Observations of the nova-like variable V Sge are discussed, and the ground-based light curve is analyzed, compensating for the component interaction effect. Low-dispersion IUE spectra indicate that interstellar reddening is smaller than suggested from visible-band observations. The UV and visible continuum are modeled by a He-rich model and by a simple accretion disk, and the UV spectrum emission lines are used to determine ionization temperatures and a lower N(e) limit. The present data are consistent with the picture of the companion to the He star being embedded in an accretion disk, with the disk being large (of dimension comparable to that of the embedding Roche lobe as a result of vigorous mass transfer) at the time of the ground-based data, and with the disk having been diminished to a radius of the order of 200 times of the neutron star, at the time of the IUE spectra.

During its first 2 years of operation, the gamma-ray AGILE satellite accumulated an extensive dataset for the Galactic plane. The data have been monitored for transient sources and several gamma-ray sources were detected. Their variability and possible association were studied. In this talk we will focus on the results of extensive observations of the Carina Region during the time period 2007 July - 2009 January, for a total livetime of ~130 days. The region is extremely complex, hosting massive star formation, with the remarkable colliding wind binary Eta Carinae, massive star clusters and HII regions (e.g. NGC 3324, RCW49, Westerlund II) and a giant molecular cloud extending over 150 pc (between l=284.7 and l=289). The Carina Nebula itself is the largest and IR highest surface brightness nebula of the Southern emisphere. We monitored several gamma ray sources in the Carina Region. In particular we detect a gamma ray source (1AGL J1043-5931) consistent with the position of Eta Carinae and report a remarkable 2-days gamma-ray flaring episode from this source on 2008 Oct 11-13. If 1AGL J1043-5931 is associated with the Eta Car system, our data provides the long sought first detection above 100 MeV of a colliding wind binary., 5 pages, 5 figures, proceedings of RICAP 2009

We present the results of extensive observations by the gamma-ray AGILE satellite of the Galactic region hosting the Carina nebula and the remarkable colliding wind binary Eta Carinae (Eta Car) during the period 2007 July to 2009 January. We detect a gamma-ray source (1AGL J1043-5931) consistent with the position of Eta Car. If 1AGL J1043-5931 is associated with the Eta Car system our data provide the long sought first detection above 100 MeV of a colliding wind binary. The average gamma-ray flux above 100 MeV and integrated over the pre-periastron period 2007 July to 2008 October is F = (37 +/- 5) x 10-8 ph cm-2 s-1 corresponding to an average gamma-ray luminosity of L = 3.4 x 10^34 erg s-1 for a distance of 2.3 kpc. We also report a 2-day gamma-ray flaring episode of 1AGL J1043-5931 on 2008 Oct. 11-13 possibly related to a transient acceleration and radiation episode of the strongly variable shock in the system., Comment: 5 pages, 4 figure, accepted for publication in ApJ Letters