X-ray and optical observations of 1RXS J154814.5-452845: a new intermediate polar with soft X-ray emission

We report the identification of the ROSAT all-sky survey source 1RXS J154814.5-452845as new intermediate polar and present the results from follow-up optical and X-ray observations. The source shows pulsations with a period of 693 s both in the optical and X-ray light curves and the detection of a synodic frequency strongly suggests that this is the rotation period of the white dwarf. Although the one day aliasing and the sparse optical data coverage does not allow to unambiguously identify the orbital period, the most likely values of 9.37 h and 6.72 h add 1RXS J154814.5-452845 to the intermediate polars with the longest orbital periods known. The optical spectrum displays features from the late type secondary and shows the presence of broad absorption lines at \Hbet and higher order Balmer lines which may be a signature of the white dwarf atmosphere, very similar to V 709 Cas. The average X-ray spectra as obtained by the EPIC instruments on board XMM-Newton show hard emission typical for this class of objects but also the presence of soft blackbody-like emission similar to that seen from soft intermediate polars and thought to arise from the white dwarf surface heated by the hard X-rays. The best fit model comprises thermal emission from multi-temperature plasma in collisional ionization equilibrium with a continuous temperature distribution up to a maximum of $\sim$60 keV, an Fe fluorescence line at 6.4 keV and with equivalent width of 260 eV and a blackbody component with kT of 86 eV. The hard X-ray emission is absorbed by matter covering 47% of the X-ray source with an equivalent hydrogen density of $\sim$\ohcm{23}. The remaining hard emission is absorbed by a much reduced column density of 1.5\hcm{21} as is the soft blackbody emission. (truncated)Comment: 14 pages, Latex, with 19 figures, accepted for publication in Astronomy and Astrophysic

Disk winds of B[e] supergiants

The class of B[e] supergiants is characterized by a two-component stellar wind consisting of a normal hot star wind in the polar zone and a slow and dense disk-like wind in the equatorial region. The properties of the disk wind are discussed using satellite UV spectra of stars seen edge-on, i.e. through the equatorial disk. These observations show that the disk winds are extremely slow, 50-90 km/s, i.e. a factor of about 10 slower than expected from the spectral types. Optical emission lines provide a further means to study the disk wind. This is discussed for line profiles of forbidden lines formed in the disk.Comment: 7 pages, LaTeX, 3 ps figures, uses lamuphys.sty from Springer-Verlag, to be published in the proceedings of IAU Coll. 169 "Variable and Non-spherical Stellar Winds in Luminous Hot Stars" held in Heidelberg 199

X-ray and optical observations of 1RXS J154814.5-452845: a new intermediate polar with soft X-ray emission

We report the identification of the ROSAT all-sky survey source 1RXS J154814.5-452845as new intermediate polar and present the results from follow-up optical and X-ray observations. The source shows pulsations with a period of 693 s both in the optical and X-ray light curves and the detection of a synodic frequency strongly suggests that this is the rotation period of the white dwarf. Although the one day aliasing and the sparse optical data coverage does not allow to unambiguously identify the orbital period, the most likely values of 9.37 h and 6.72 h add 1RXS J154814.5-452845 to the intermediate polars with the longest orbital periods known. The optical spectrum displays features from the late type secondary and shows the presence of broad absorption lines at \Hbet and higher order Balmer lines which may be a signature of the white dwarf atmosphere, very similar to V 709 Cas. The average X-ray spectra as obtained by the EPIC instruments on board XMM-Newton show hard emission typical for this class of objects but also the presence of soft blackbody-like emission similar to that seen from soft intermediate polars and thought to arise from the white dwarf surface heated by the hard X-rays. The best fit model comprises thermal emission from multi-temperature plasma in collisional ionization equilibrium with a continuous temperature distribution up to a maximum of $\sim$60 keV, an Fe fluorescence line at 6.4 keV and with equivalent width of 260 eV and a blackbody component with kT of 86 eV. The hard X-ray emission is absorbed by matter covering 47% of the X-ray source with an equivalent hydrogen density of $\sim$\ohcm{23}. The remaining hard emission is absorbed by a much reduced column density of 1.5\hcm{21} as is the soft blackbody emission. (truncated

The Structure of the Homunculus. III. Forming a Disk and Bipolar Lobes in a Rotating Surface Explosion

We present a semi-analytic model for shaping the nebula around eta Carinae that accounts for the simultaneous production of bipolar lobes and an equatorial disk through a rotating surface explosion. Material is launched normal to the surface of an oblate rotating star with an initial kick velocity that scales approximately with the local escape speed. Thereafter, ejecta follow ballistic orbital trajectories, feeling only a central force corresponding to a radiatively reduced gravity. Our model is conceptually similar to the wind-compressed disk model of Bjorkman & Cassinelli, but we modify it to an explosion instead of a steady line-driven wind, we include a rotationally-distorted star, and we treat the dynamics somewhat differently. Continuum-driving avoids the disk inhibition that normally operates in line-driven winds. Our model provides a simple method by which rotating hot stars can simultaneously produce intrinsically bipolar and equatorial mass ejections, without an aspherical environment or magnetic fields. Although motivated by eta Carinae, the model may have generic application to other LBVs, B[e] stars, or SN1987A's nebula. When near-Eddington radiative driving is less influential, our model generalizes to produce bipolar morphologies without disks, as seen in many PNe.Comment: ApJ accepted, 9 page

Kinematical structure of the circumstellar environments of galactic B[e]-type stars

High resolution line profiles are presented for selected forbidden and permitted emission lines of a sample of galactic B[e]-type stars. The spectral resolution corresponds to 5-7 km/s with the exception of some line profiles which were observed with a resolution of 9-13 km/s. All Ha profiles are characterized by a narrow split or single emission component with a width of about 150-250 km/s (FWHM) and broad wings with a full width of ~1000-2000 km/s. The Ha profiles can be classified into three groups: double-peaked profiles representing the majority, single-peaked emission-line profiles, and normal P Cygni-type profiles. The forbidden lines exhibit in most cases double-peaked profiles. The split forbidden line profiles have peak separations of as little as 10 km/s. The ratio of violet to red emission peak intensities, V/R, is predominantly smaller or equal to 1. Theoretical profiles were calculated for the optically thin case. A latitude-dependent stellar wind with a radial expansion and a velocity decreasing from the pole to the equator was adopted. In addition an equatorial dust ring with various optical depths was assumed. This model can explain split lines and line asymmetries observed in some stars. Moreover, the V/R ratios can be understood in terms of this model. The comparison of the observed line profiles with the models thus confirms the assumption of disk-like line-formation regions as commonly adopted for B[e]-type stars.Comment: Astronomy & Astrophysics, in pres

And in the Darkness Bind Them: Equatorial Rings, B[e] Supergiants, and the Waists of Bipolar Nebulae

We report the discovery of two new circumstellar ring nebulae in the western Carina Nebula. The brighter object, SBW1, resembles a lidless staring eye and encircles a B1.5 Iab supergiant. Its size is identical to the inner ring around SN1987A, but SBW1's low N abundance indicates that the star didn't pass through a RSG phase. The fainter object, SBW2, is a more distorted ring, is N-rich, and has a central star that seems to be invisible. We discuss these two new nebulae in context with rings around SN1987A, Sher25, HD168625, RY Scuti, WeBo1, SuWt2, and others. The ring bearers fall into two groups: Five rings surround hot supergiants, and all except for the one known binary are carbon copies of the ring around SN1987A. We propose a link between these rings and B[e] supergiants, where the rings derive from the same material in an earlier B[e] phase. The remaining four rings surround evolved intermediate-mass stars; all members of this ring fellowship are close binaries, hinting that binary interactions govern the forging of such rings. We estimate that there may be several thousand more dark rings in the Galaxy, but we are scarcely aware of their existence due to selection effects. The lower-mass objects might be the equatorial density enhancements often invoked to bind the waists of bipolar PNe.Comment: AJ accepted, 27 page