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Register a new userConstraining the Physical Parameters of the Circumstellar Disk of chi Ophiuchi
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We present a numerical model describing a circularly symmetric gaseous disk around the Be star chi Ophiuchi. The model is constrained by long-baseline interferometric observations that are sensitive to the H-alpha Balmer line emission from the disk. For the first time our interferometric observations spatially resolve the inner region of the circumstellar disk around chi Ophiuchi and we use these results to place a constraint on the physical extent of the H-alpha-emitting region. We demonstrate how this in turn results in very specific constraints on the parameters that describe the variation of the gas density as a function of radial distance from the central star.
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We present the first observations of the circumstellar (CS) disk system 51 Ophiuchi with the Far Ultraviolet Spectroscopic Explorer. We detect several absorption lines arising from the unusual metastable atomic species NI (2D), NI (2P), and SII (2D). These levels lie 1.8 - 3.6 eV above the ground level and have radiative decay lifetimes of 2 days or less, indicating that the lines arise from warm CS gas. The high S/N FUSE spectra, obtained six days apart, also show time-variable absorption features arising from NI, NII, OI (1D), and FeIII, which are redshifted with respect to the stellar velocity. The resolved redshifted absorption extends over many tens of km/s (40 for NI, 100 for NII, 65 for OI, and 84 for FeIII). We calculate column densities for all the variable infalling CS gasses, using the apparent optical depth method. The FeIII and NII infalling gasses must be produced through collisional ionization, and the ionization fraction of nitrogen suggests a gas temperature between 20000 and 34000 K. The infalling gas shows a peculiar, non-solar composition, with nitrogen and iron more abundant than carbon. We also set upper limits on the line-of-sight column densities of molecular hydrogen and carbon monoxide. These observations strengthen the connection between 51 Oph and the older debris-disk system Beta Pictoris, and indicate that there may be infalling planetesimals in the 51 Oph system.
Interferometric observations of two well-known Be stars, gamma Cas and phi Per, were collected and analyzed to determine the spatial characteristics of their circumstellar regions. The observations were obtained using the Navy Prototype Optical Interferometer equipped with custom-made narrowband filters. The filters isolate the H-alpha emission line from the nearby continuum radiation, which results in an increased contrast between the interferometric signature due to the H-alpha-emitting circumstellar region and the central star. Because the narrowband filters do not significantly attenuate the continuum radiation at wavelengths 50 nm or more away from the line, the interferometric signal in the H-alpha channel is calibrated with respect to the continuum channels. The observations used in this study represent the highest spatial resolution measurements of the H-alpha-emitting regions of Be stars obtained to date. These observations allow us to demonstrate for the first time that the intensity distribution in the circumstellar region of a Be star cannot be represented by uniform disk or ring-like structures, whereas a Gaussian intensity distribution appears to be fully consistent with our observations.
We report the results of a long-term spectroscopic monitoring of the A-type supergiant with the B[e] phenomenon 3 Pup = HD 62623. We confirm earlier findings that it is a binary system. The orbital parameters were derived using cross-correlation of the spectra in a range of 4460-4632 A, which contains over 30 absorption lines. The orbit was found circular with a period of $137.4pm0.1$ days, radial velocity semi-amplitude $K_{1} = 5.0pm0.8$ km s$^{-1}$, systemic radial velocity $gamma = +26.4pm2.0$ km s$^{-1}$, and the mass function $f(m) = (1.81^{+0.97}_{-0.76})times10^{-3}$ M$_{odot}$. The object may have evolved from a pair with initial masses of $sim$6.0 M$_{odot}$ and $sim$3.6 M$_{odot}$ with an initial orbital period of $sim$5 days. Based on the fundamental parameters of the A-supergiant (luminosity $log$ L/L$_{odot} = 4.1pm$0.1 and effective temperature T$_{rm eff} = 8500pm$500 K) and evolutionary tracks of mass-transferring binaries, we found current masses of the gainer M$_{2} = 8.8pm$0.5 M$_{odot}$ and donor M$_{1} = 0.75pm0.25$ M$_{odot}$. We also modeled the objects IR-excess and derived a dust mass of $sim 5,times10^{-5}$ M$_{odot}$ in the optically-thin dusty disk. The orbital parameters and properties of the H$alpha$ line profile suggest that the circumstellar gaseous disk is predominantly circumbinary. The relatively low mass of the gainer led us to a suggestion that 3 Pup should be excluded from the B[e] supergiant group and moved to the FS CMa group. Overall these results further support our original suggestion that FS CMa objects are binary systems, where an earlier mass-transfer caused formation of the circumstellar envelope.
We present high spatial resolution (< 0.3 = 40$ AU) Submillimeter Array observations of the 865 micron continuum emission from the circumstellar disk around the young star DoAr 25. Despite its bright millimeter emission, this source exhibits only a comparatively small infrared excess and low accretion rate, suggesting that the material and structural properties of the inner disk may be in an advanced state of evolution. A simple model of the physical conditions in the disk is derived from the submillimeter visibilities and the complete spectral energy distribution using a Monte Carlo radiative transfer code. For the standard assumption of a homogeneous grain size distribution at all disk radii, the results indicate a shallow surface density profile, $Sigma propto r^{-p}$ with p = 0.34, significantly less steep than a steady-state accretion disk (p = 1) or the often adopted minimum mass solar nebula (p = 1.5). Even though the total mass of material is large (M_d = 0.10 M_sun), the densities inferred in the inner disk for such a model may be too low to facilitate any mode of planet formation. However, alternative models with steeper density gradients (p = 1) can explain the observations equally well if substantial grain growth in the planet formation region (r < 40 AU) has occurred. We discuss these data in the context of such models with dust properties that vary with radius and highlight their implications for understanding disk evolution and the early stages of planet formation.
We report the discovery in NIR with SofI at the NTT of a resolved circumstellar dust disk around a 2MASS source at the periphery of the rho Ophiuchi dark cloud. We present follow-up observations in J, H, and Ks-band obtained with ISAAC at the VLT, under 0.4-seeing conditions, which unveil a dark dust lane oriented East-West between two characteristic northern and southern reflection nebulae. This new circumstellar dust disk has a radius of 2.15 (300 AU at 140 pc), and a width of 1.2 (170 AU at 140 pc). Thanks to its location at the periphery of the dense cores, it suffers small foreground visual extinction (Av=2.1pm2.6 mag). Although this disk is seen close to edge-on, the two reflection nebulae display very different colors. We introduce a new NIR data visualization called ``Pixel NIR Color Mapping, which allows to visualize directly the NIR colors of the nebula pixels. Thanks to this method we identify a ridge, 0.3 (40 AU at 140 pc) to the north of the dark lane and parallel to it, which displays a NIR color excess. This ridge corresponds to an unusual increase of brightness from J to Ks, which is also visible in the NTT observation obtained 130 days before the VLT one. We also find that the northern nebula shows ~3 mag more extinction than the southern nebula. We compute axisymmetric disk models to reproduce the VLT scattered light images and the spectral energy distribution from optical to NIR. Our best model, with a disk inclination i=86pm1 deg, correctly reproduces the extension of the southern reflection nebula, but it is not able to reproduce either the observed NIR color excess in the northern nebula or the extinction difference between the two reflection nebulae. We discuss the possible origin of the peculiar asymmetrical NIR color properties of this object.
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