We present new K-band long-baseline interferometer observations of three young stellar objects of the FU Orionis class, namely, V1057 Cyg, V1515 Cyg, and Z CMa-SE, obtained at the Keck Interferometer ...during its commissioning science period. The interferometer clearly resolves the source of near-infrared emission in all three objects. Using simple geometric models, we derive size scales (0.5-4.5 AU) for this emission. All three objects appear significantly more resolved than expected from simple models of accretion disks tuned to fit the broadband optical and infrared spectrophotometry. We explore variations in the key parameters that are able to lower the predicted visibility amplitudes to the measured levels and conclude that accretion disks alone do not reproduce the spectral energy distributions and K-band visibilities simultaneously. We conclude that either disk models are inadequate to describe the near-infrared emission or additional source components are needed. We hypothesize that large-scale emission (tens of AU) in the interferometer field of view is responsible for the surprisingly low visibilities. This emission may arise in scattering by large envelopes believed to surround these objects.
High angular resolution images of IRC +10216 taken at various bandpasses within the near-infrared H, K, and L bands are presented. The maps have the highest angular resolution yet recovered and were ...reconstructed from interferometric measurements obtained at the Keck I telescope in 1997 December and 1998 April, forming a subset of a seven-epoch monitoring program presented earlier by Tuthill and coworkers in Paper I. Systematic changes with observing wavelength are found and discussed in the context of present geometrical models for the circumstellar envelope. With these new high-resolution, multiwavelength data and contemporaneous photometry, we also revisit the hypothesis that the bright compact core of the nebula (component "A") marks the location of the central carbon star. We find that directly measured properties of the core (angular size, flux density, color temperature) are consistent with a reddened carbon star photosphere (line-of-sight tau sub(2.2) = 5.3).
We have detected asymmetry in the symbiotic star CH Cyg through the measurement of precision closure phase with the Integrated Optics Near-Infrared Camera (IONIC) beam combiner, at the infrared ...optical telescope array interferometer. The position of the asymmetry changes with time and is correlated with the phase of the 2.1-year period found in the radial velocity measurements for this star. We can model the time-dependent asymmetry either as the orbit of a low-mass companion around the M giant or as an asymmetric, 20 per cent change in brightness across the M giant. We do not detect a change in the size of the star during a 3-year monitoring period neither with respect to time nor with respect to wavelength. We find a spherical dust shell with an emission size of 2.2 ± 0.1 D* full width at half-maximum around the M giant star. The star to dust flux ratio is estimated to be 11.63 ± 0.3. While the most likely explanation for the 20 per cent change in brightness is non-radial pulsation, we argue that a low-mass companion in close orbit could be the physical cause of the pulsation. The combined effect of pulsation and low-mass companion could explain the behaviour revealed by the radial velocity curves and the time-dependent asymmetry detected in the closure-phase data. If CH Cyg is a typical long secondary period variable then these variations could be explained by the effect of an orbiting low-mass companion on the primary star.
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We have used the Sydney University Stellar Interferometer to measure the angular diameter of α Cir. This is the first detailed interferometric study of a rapidly oscillating A (roAp) star, α Cir ...being the brightest member of its class. We used the new and more accurate Hipparcos parallax to determine the radius to be 1.967 ± 0.066 R⊙. We have constrained the bolometric flux from calibrated spectra to determine an effective temperature of 7420 ± 170 K. This is the first direct determination of the temperature of an roAp star. Our temperature is at the low end of previous estimates, which span over 1000 K and were based on either photometric indices or spectroscopic methods. In addition, we have analysed two high-quality spectra of α Cir, obtained at different rotational phases and we find evidence for the presence of spots. In both spectra we find nearly solar abundances of C, O, Si, Ca and Fe, high abundance of Cr and Mn, while Co, Y, Nd and Eu are overabundant by about 1 dex. The results reported here provide important observational constraints for future studies of the atmospheric structure and pulsation of α Cir.
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Observations of the southern Cepheid ℓ Car to yield the mean angular diameter and angular pulsation amplitude have been made with the Sydney University Stellar Interferometer at a wavelength of 696 ...nm. The resulting mean limb-darkened angular diameter is 2.990 ± 0.017 mas (i.e. ± 0.6 per cent) with a maximum-to-minimum amplitude of 0.560 ± 0.018 mas corresponding to 18.7 ± 0.6 per cent in the mean stellar diameter. Careful attention has been paid to uncertainties, including those in measurements, in the adopted calibrator angular diameters, in the projected values of visibility squared at zero baseline, and to systematic effects. No evidence was found for a circumstellar envelope at 696 nm. The interferometric results have been combined with radial displacements of the stellar atmosphere derived from selected radial velocity data taken from the literature to determine the distance and mean diameter of ℓ Car. The distance is determined to be 525 ± 26 pc and the mean radius 169 ± 8 R⊙. Comparison with published values for the distance and mean radius shows excellent agreement, particularly when a common scaling factor from observed radial velocity to pulsation velocity of the stellar atmosphere (the p-factor) is used.
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ABSTRACT
We have used optical interferometry to obtain multiwavelength visibility curves for eight red giants over the wavelength range 650–1000 nm. The observations consist of wavelength‐dispersed ...fringes recorded with MAPPIT (Masked Aperture‐Plane Interference Telescope) at the 3.9‐m Anglo‐Australian Telescope. We present results for four Miras (R Car, o Cet, R Hya and R Leo) and four semiregular variables (R Dor, W Hya, L2 Pup and γ Cru). All stars except γ Cru show strong variations of angular size with wavelength. A uniform‐disc model was found to be a poor fit in most cases, with Gaussian (or other more tapered) profiles preferred. This, together with the fact that most stars showed a systematic increase in apparent size towards the blue and a larger‐than‐expected linear size, even in the red, all point towards significant scattering by dust in the inner circumstellar environment. Some stars showed evidence for asymmetric brightness profiles, while L2 Pup required a two‐component model, indicating an asymmetrical circumstellar dust shell.
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Pinwheel Nebula around WR 98a Monnier, J. D; Tuthill, P. G; Danchi, W. C
The Astrophysical journal,
11/1999, Volume:
525, Issue:
2
Journal Article
Peer reviewed
We present the first near-infrared images of the dusty Wolf-Rayet star WR 98a. Aperture-masking interferometry has been utilized to recover images at the diffraction limit of the Keck I telescope, ...less, similar50 mas at 2.2 µm. Multiepoch observations spanning about 1 yr have resolved the dust shell into a "pinwheel" nebula, the second example of a new class of dust shell first discovered around WR 104 by Tuthill, Monnier, & Danchi. Interpreting the collimated dust outflow in terms of an interacting winds model, the binary orbital parameters and apparent wind speed are derived: a period of 565+/-50 days, a viewing angle of 35 +/-6 degrees from the pole, and a wind speed of 99+/-23 mas yr-1. This period is consistent with a possible approximately 588 day periodicity in the infrared light curve, linking the photometric variation to the binary orbit. Important implications for binary stellar evolution are discussed by identifying WR 104 and WR 98a as members of a class of massive, short-period binaries whose orbits were circularized during a previous red supergiant phase. The current component separation in each system is similar to the diameter of a red supergiant, which indicates that the supergiant phase was likely terminated by Roche lobe overflow, leading to the present Wolf-Rayet stage.
The binary star δ Sco (HD143275) underwent remarkable brightening in the visible in 2000, and continues to be irregularly variable. The system was observed with the Sydney University Stellar ...Interferometer (SUSI) in 1999, 2000, 2001, 2006 and 2007. The 1999 observations were consistent with predictions based on the previously published orbital elements. The subsequent observations can only be explained by assuming that an optically bright emission region with an angular size of ≳2 ± 1 mas formed around the primary in 2000. By 2006/2007 the size of this region grew to an estimated ≳4 mas. We have determined a consistent set of orbital elements by simultaneously fitting all the published interferometric and spectroscopic data as well as the SUSI data reported here. The resulting elements and the brightness ratio for the system measured prior to the outburst in 2000 have been used to estimate the masses of the components. We find MA= 15 ± 7 M⊙ and MB= 8.0 ± 3.6 M⊙. The dynamical parallax is estimated to be 7.03 ± 0.15 mas, which is in good agreement with the revised Hipparcos parallax.
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New diffraction-limited speckle images of the Red Rectangle in the wavelength range 2.1–3.3 with angular resolutions of 44–68 mas (Tuthill et al. CITE) and previous speckle images at 0.7–2.2 ...(Osterbart et al. CITE; Men'shchikov et al. CITE) revealed well-resolved bright bipolar outflow lobes and long X-shaped spikes originating deep inside the outflow cavities. This set of high-resolution images stimulated us to reanalyze all infrared observations of the Red Rectangle using our two-dimensional radiative transfer code. The high-resolution images imply a geometrically and optically thick torus-like density distribution with bipolar conical cavities and are inconsistent with the flat disk geometry frequently used to visualize bipolar nebulae. The new detailed modeling, together with estimates of the interstellar extinction in the direction of the Red Rectangle enabled us to more accurately determine one of the key parameters, the distance $D \approx 710$ pc with model uncertainties of 70 pc, which is twice as far as the commonly used estimate of 330 pc. The central binary is surrounded by a compact, massive ($M \approx 1.2$ ), very dense dusty torus with hydrogen densities reaching $n_{\rm H} \approx 2.5 \times 10^{12}$ cm-3 (dust-to-gas mass ratio ${\hbox{$\rho_{\rm d}/\rho$}} \approx 0.01$). The model implies that most of the dust mass in the dense torus is in very large particles and, on scales of more than an arcsecond, the polar outflow regions are denser than the surrounding medium. The bright component of the spectroscopic binary HD 44179 is a post-AGB star with mass ${\hbox{$M_{\star}$}} \approx 0.57$ , luminosity ${\hbox{$L_{\star}$}} \approx 6000$ , and effective temperature ${\hbox{$T_{\star}$}} \approx 7750$ K. Based on the orbital elements of the binary, we identify its invisible component with a helium white dwarf with MWD , LWD , and TWD K. The hot white dwarf ionizes the low-density bipolar outflow cavities inside the dense torus, producing a small H II region observed at radio wavelengths. We propose an evolutionary scenario for the formation of the Red Rectangle nebula, in which the binary initially had 2.3 and 1.9 components at a separation of ~130 . The nebula was formed in the ejection of a common envelope after Roche lobe overflow by the present post-AGB star.
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