Anatoly S. Miroshnichenko

Dust Emission from Herbig AE/BE Stars: Evidence for Disks and Envelopes

Infrared and millimeter-wave emission from Herbig Ae/Be stars has produced conflicting conclusions regarding the dust geometry in these objects. We show that the compact dimensions of the millimeter-wave-emitting regions are a decisive indication for disks. But a disk cannot explain the spectral energy distribution unless it is embedded in an extended envelope that (1) dominates the IR emission and (2) provides additional disk heating on top of the direct stellar radiation. Detailed radiative transfer calculations based on the simplest model for envelope-embedded disks successfully fit the data from UV to millimeter wavelengths and show that the disks have central holes. This model also resolves naturally some puzzling results of IR imaging.

VLTI/AMBER spectro-interferometry of the Herbig Be star MWC 297 with spectral resolution 12 000

Context. Circumstellar disks and outflows play a fundamental role in star formation. Infrared spectro-interferometry allows the inner accretion-ejection region to be resolved. Aims. We study the disk and Br-emitting region of MWC 297 with high spatial and spectral resolution and compare our observations with disk-wind models. Methods. We measured interferometric visibilities, wavelength-differential phases, and closure phases of MWC 297 with a spectral resolution of 12000. To interpret our MWC 297 observations, we employed disk-wind models. Results. The measured continuum visibilities confirm previous results that the continuum-emitting region of MWC 297 is remarkably compact. We derive a continuum ring-fit radius of �2.2 mas (�0.56 AU at a distance of 250 pc), which is �5.4 times smaller than the 3 AU dust sublimation radius expected for silicate grains (in the absence of radiation-shielding material). The strongly wavelength-dependent and asymmetric Br-emitting region is more extended (�2.7times) than the continuum-emitting region. At the center of the Br line, we derive a Gaussian fit radius of �6.3 mas HWHM (�1.6 AU). To interpret the observations, we employ a magneto-centrifugally driven disk-wind model consisting of an accretion disk, which emits the observed continuum radiation, and a disk wind, which emits the Br line. The calculated wavelength-dependent model intensity distributions and Br line profiles are compared with the observations (i.e., K-band spectrum, visibilities, differential phases, and closure phases). The closest fitting model predicts a continuumemitting disk with an inner radius of �0.3 AU and a disk wind ejection region with an inner radius of �0.5 AU (�17.5 stellar radii). We obtain a disk-wind half-opening angle (the angle between the rotation axis and the innermost streamline of the disk wind) of �80 � , which is larger than in T Tau models, and a disk inclination angle of �20 � (i.e., almost pole-on). Conclusions. Our observations with a spectral resolution of 12000 allow us to study the AU-scale environment of MWC 297 in �10 different spectral channels across the Br emission line. We show that the K-band flux, visibilities, and remarkably strong phases can be explained by the employed magneto-centrifugally driven disk wind model.

Spectroscopic observations of the δ Scorpii binary during its recent periastron passage

The bright star Delta Sco has been considered a typical B0-type object for many years. Spectra of the star published prior to 1990 showed no evidence of emission, but only of short-term line profile variations attributed to nonradial pulsations. Speckle interferometric observations show that Delta Sco is a binary system with a highly-eccentric orbit and a period of ~10.6 years. Weak emission in the Ha line was detected in its spectrum for the first time during a periastron passage in 1990. Shortly before the next periastron passage in the summer of 2000, the binary entered a strong Ha emission and enhanced mass-loss phase. We monitored the spectroscopic development of the Be outburst from July 2000 through March 2001. In this paper we present results from our spectroscopy, refine elements of the binary orbit, and discuss possible mechanisms for the mass loss.

TOWARD UNDERSTANDING THE B(e) PHENOMENON. I. DEFINITION OF THE GALACTIC FS CMa STARS

The B[e] phenomenon is defined as the simultaneous presence of low-excitation forbidden line emission and strong infrared excess in the spectra of early-type stars. It was discovered in our Galaxy 30 years ago in the course of the early exploration of the infrared sky and initially identified in 65 Galactic objects, of which nearly half remained unclassified. The phenomenon is associated with objects at different evolutionary stages, ranging from the preYmainsequence to the planetary nebula stage. We review the studies of both the original 65 and subsequently identified Galactic stars with the B[e] phenomenon. A new classification is proposed for stars with the B[e] phenomenon based on the time of dust formation in their environments. Properties of the unclassified Galactic B[e] stars are analyzed. We propose that these objects are binary systems that are currently undergoing or have recently undergone a phase of rapid mass exchange, associated with a strong mass loss and dust formation. A new name, FS CMa stars, and classification criteria are proposed for the unclassified B[e] stars. Subject headingg circumstellar matter — stars: early-type — stars: emission-line, Be

Properties of the δ Scorpii Circumstellar Disk from Continuum Modeling

We present optical W BV R and infrared JHKL photometric observations of the Be binary system d Sco, obtained in 2000–2005, mid-infrared (10 and 18 µm) photometry and optical (?? 3200–10500 ^A) spectropolarimetry obtained in 2001. Our optical photometry confirms the results of much more frequent visual monitoring of d Sco. In 2005, we detected a significant decrease in the object’s brightness, both in optical and near-infrared brightness, which is associated with a continuous rise in the hydrogen line strenghts. We discuss possible causes for this phenomenon, which is difficult to explain in view of current models of Be star disks. The 2001 spectral energy distribution and polarization are successfully modeled with a three-dimensional non-LTE Monte Carlo code which produces a self-consistent determination of the hydrogen level populations, electron temperature, and gas density for hot star disks. Our disk model is hydrostatically supported in the vertical direction and radially controlled by viscosity. Such a disk model has, essentially, only two free parameters, viz., the equatorial mass loss rate and the disk outer radius. We find that the primary companion is surrounded by a small (7 R?), geometrically-thin disk, which is highly nonisothermal and fully ionized. Our model requires an average equatorial mass loss rate of 1.5 × 10-9M? yr-1.

On Protostellar Disks in Herbig Ae/Be Stars

The spectral shape of IR emission from Herbig Ae/Be stars has been invoked as evidence for accretion disks around high-mass protostars. Instead, we present here models based on spherical envelopes with r -1.5 dust density profile that successfully explain the observed spectral shapes. The spectral energy distributions (SEDs) of eight primary candidates for protostellar disks are fitted in detail for all wavelengths available, from visual to far IR. The only envelope property adjusted in individual sources is the overall visual optical depth, and it ranges from 0.3 to 3. In each case, our models properly reproduce the data for both IR excess, visual extinction and reddening. The success of our models shows that accretion disks cannot make a significant contribution to the radiation observed in these pre-main sequence stars.

Discs and haloes in pre-main-sequence stars

A B S T R A C T We study the infrared (IR) emission from flared discs with and without additional optically thin haloes. Flux calculations of a flared disc in vacuum can be considered a special case of the more general family of models in which the disc is imbedded in an optically thin halo. In the absence of such a halo, flux measurements can never rule out its existence because the disc flaring surface defines a mathematically equivalent halo that produces the exact same flux at all IR wavelengths. When a flared disc with height H at its outer radius R is imbedded in a halo whose optical depth at visual wavelengths is τhalo, the system IR flux is dominated by the halo whenever τhalo > (1/4)H/R. Even when its optical depth is much smaller, the halo can still have a significant effect on the disc temperature profile. Imaging is the only way to rule out the existence of a potential halo, and we identify a decisive test that extracts a signature unique to flared discs from imaging observations.

VLTI/AMBER and VLTI/MIDI spectro-interferometric observations of the B(e) supergiant CPD¡57 - 2874 ? Size and geometry of the circumstellar envelope in the near- and mid-IR

We present the first high spatial and spectral observations of the circumstellar envelope (CSE) of a B[e] supergiant (CPD

A Study of π Aquarii during a Quasi-normal Star Phase: Refined Fundamental Parameters and Evidence for Binarity

-57 2874

SPECTROSCOPIC AND SPECTROPOLARIMETRIC OBSERVATIONS OF V838 MONOCEROTIS

), performed with the Very Large Telescope Interferometer (VLTI). Spectra, visibilities, and closure phase, were obtained using the beam-combiner instruments AMBER (near-IR interferometry with three 8.3 m Unit Telescopes or UTs) and MIDI (mid-IR interferometry with two UTs). The interferometric observations of the CSE are well fitted by an elliptical Gaussian model with FWHM diameters varying linearly with wavelength. Typical diameters measured are