Near-infrared Speckle Interferometry Research Articles

A new spectroscopic and interferometric study of the young stellar object V645 Cygni

Aims. We present the results of high-resolution optical spectroscopy, low-resolution near-IR spectroscopy and near-infrared speckle interferometry of the massive young stellar object candidate V645 Cyg that were taken in order to refine its fundamental parameters and properties of its circumstellar envelope. Methods. Speckle interferometry in the H- and K-bands and an optical spectrum in the range 5200-6680 A with a spectral resolving power of R = 60000 were obtained at the 6 m telescope of the Russian Academy of Sciences. Another optical spectrum in the range 4300-10500 A with R = 79000 was obtained at the 3.6m CFHT. A low-resolution spectrum in the ranges 0.46-1.4 and 1.4-2.5 microns with a R approx. 800 and approx. 700, respectively, were obtained at the 3m Shain telescope of the Lick Observatory. Results. Using a new kinematic method based on non-linear modeling of the neutral hydrogen density profile in the direction toward the object, we suggest a new a distance D = 4.2+/-0.2 kpc. We also suggest a new estimate for the star's effective temperature, T(sub eff) approx. 25000 K. We have resolved the object in both H- and K-bands. Using a two-component ring fit, we derived a compact component size of 18 mas and 15 mas in the H- and K-band, respectively, which correspond to 37 and 33 AU at the new distance. Analysis of our and previously published data shows a approx. 2 mag drop of the near-infrared brightness of V645 Cyg in the beginning of the 1980 s. At the same time, the cometary nebular condensation N1 seems to fade in this wavelength range with respect to the N0 object, which represent the star with a nearly pole-on optically-thick disk and an optically-thin envelope. Conclusions. We conclude that V645 Cyg is a young massive main-sequence star, which recently emerged from its cocoon. and already passed the protostellar accretion stage. The presence of accretion is not necessary to account for the high observed luminosity of (2.6) x 10(exp 4) Solar Mass/yr. The receding part of a strong, mostly uniform outflow with a terminal velocity of approx.800 km/s is only blocked from view far from the star, where forbidden lines form. The near-infrared size of the source is consistent with the dust sublimation distance near this hot and luminous star and is the largest among young stellar objects observed interferometrically to-date.

Near-infrared speckle interferometry and radiative transfer modelling of the carbon star LP Andromedae

We present the near-infrared speckle interferometry for LP And in the H and $K^{\prime}$ bands with diffraction-limited resolutions of 56 and 72 mas, new $\it JHKLM$ photometry, and the results of our radiative transfer modelling of this carbon star. The reconstructed visibility reveals a spherically-symmetric envelope surrounding the central star. To determine the physical parameters of the latter and the properties of its dusty envelope, we performed extensive radiative transfer calculations. The well-defined spectral energy distribution of LP And in the entire range from the near-IR to millimeter wavelengths (including the absorption feature visible in the stellar continuum at 3 ${\mu}$m and the shapes of the dust emission bands at 11 and 27 ${\mu}$m), together with our H -band visibility can be reproduced by a spherical dust envelope with parameters that are very similar to those of CW Leo (IRC +10 216), the best studied carbon star. For the newly estimated pulsation period $P = 617 \pm 6$ days and distance $D = 740 \pm 100$ pc, our model of LP And changes its luminosity $L_{\star}$ between 16 200 and 2900 $L_{\odot}$, its effective temperature $T_{\star}$ between 3550 and 2100 K, and its radius $R_{\star}$ between 340 and 410 $R_{\odot}$. The model estimates the star's mass-loss rate $\dot{M} \approx 1.9 \times 10^{-5}$ $M_{\odot}$ yr - 1 , assuming a constant outflow velocity $v = 14$ km s -1 . If the latter also applied to the innermost parts of the dusty envelope, then presently the star would be losing mass at a rate $\dot{M} \approx 6.0 \times 10^{-5}$ $M_{\odot}$ yr -1 . However, we believe that the inner wind velocity must actually be closer to $v \approx 4$ km s -1 instead, as wind acceleration is expected in the dust-formation zone. The dusty envelope of LP And extends from $R_1 \approx 2$ $R_{\star}$ to distances of $R_2 \approx 3$ pc from the star. The total mass of the envelope lost by the central star is $M = 3.2$ $M_{\odot}$ assuming a dust-to-gas mass ratio of $\rho_{\rm d}/\rho$ = 0.0039. The circumstellar optical depth towards the star is $\tau_{V} = 25$ in the visual. The dust model contains small silicon carbide grains, inhomogeneous grains made of a mixture of SiC and incompletely amorphous carbon, and thin mantles made of iron-magnesium sulfides. This dust mixture perfectly fits the infrared continuum and both the 11.3 ${\mu}$m and 27 ${\mu}$m emission bands. We find that our $K^{\prime}$-band visibility could not be fitted by our spherical model, so we discuss possible reasons for this interesting result. More observations are required in order to determine what causes this effect. If slight deviations from spherical geometry in its envelope are the reason, then the object's evolutionary stage would be even more similar to that of CW Leo. It appears that LP And is a highly-evolved intermediate-mass star (initial mass $M^0_{\star}$ ≈ 4 $M_{\odot}$) at the end of its AGB phase.

High-resolution near-infrared speckle interferometry and radiative transfer modeling of the OH/IR star OH 104.9+2.4

We present near-infrared speckle interferometry of the OH/IR star OH 104.9+2.4 in the K' band obtained with the 6m telescope of the Special Astrophysical Observatory (SAO). At a wavelength of lambda = 2.12 micron the diffraction-limited resolution of 74 mas was attained. The reconstructed visibility reveals a spherically symmetric, circumstellar dust shell (CDS) surrounding the central star. The visibility function shows that the stellar contribution to the total flux at lambda = 2.12 micron is less than ~50%, indicating a rather large optical depth of the CDS. The azimuthally averaged 1-dimensional Gaussian visibility fit yields a diameter of 47 +/- 3mas (FHWM), which corresponds to 112 +/- 13 AU for an adopted distance of D = 2.38 +/- 0.24 kpc. To determine the structure and the properties of the CDS of OH 104.9+2.4, radiative transfer calculations using the code DUSTY were performed to simultaneously model its visibility and the spectral energy distribution (SED). We found that both the ISO spectrum and the visibility of OH 104.9+2.4 can be well reproduced by a radiative transfer model with an effective temperature T_eff = 2500 +/- 500 K of the central source, a dust temperature T_in = 1000 +/- 200 K at the inner shell boundary R_in = 9.1 R_star = 25.4 AU, an optical depth tau = 6.5 +/- 0.3 at 2.2 micron, and dust grain radii ranging from a_min = 0.005 +/- 0.003 micron to a_max = 0.2 +/- 0.02 micron with a power law with index -3.5. It was found that even minor changes in a_max have a major impact on both the slope and the curvature of the visibility function, while the SED shows only minor changes. Our detailed analysis demonstrates the potential of dust shell modeling constrained by both the SED and visibilities.

Visual orbit for the low-mass binary Gliese 22 AC from speckle interferometry

Based on 14 data points obtained with near-infrared speckle interferometry and covering an almost entire revolution, we present a first visual orbit for the low-mass binary system Gliese 22 AC. The quality of the orbit is largely improved with respect to previous astrometric solutions. The dynamical system mass is $0.592\pm 0.065\,M_{\odot}$, where the largest part of the error is due to the Hipparcos parallax. A comparison of this dynamical mass with mass-luminosity relations on the lower main sequence and theoretical evolutionary models for low-mass objects shows that both probably underestimate the masses of M dwarfs. A mass estimate for the companion Gliese 22 C indicates that this object is a very low-mass star with a mass close to the hydrogen burning mass limit.

Mass ratios of the components in T Tauri binary systems and implications for multiple star formation

Using near-infrared speckle interferometry we have obtained resolved JHK-photometry for the components of 58 young binary systems. From these measurements, combined with other data taken from literature, we derive masses and particularly mass ratios of the components. We use the J-magnitude as an indicator for the stellar luminosity and assign the optical spectral type of the system to the primary. On the assumption that the components within a binary are coeval we can then also place the secondaries into the HRD and derive masses and mass ratios for both components by comparison with different sets of current theoretical pre-main sequence evolutionary tracks. The resulting distribution of mass ratios is comparatively flat for , but depends on assumed evolutionary tracks. The mass ratio is neither correlated with the primary's mass or the components' separation. These findings are in line with the assumption that for most multiple systems in T associations the components' masses are principally determined by fragmentation during formation and not by the following accretion processes. Only very few unusually red objects were newly found among the detected companions.This finding shows that the observed overabundance of binaries in the Taurus-Auriga association compared to nearby main sequence stars should be real and not the outcome of observational biases related to infrared observing.

Halos around Herbig Ae/Be stars -more common than for the less massive T Tauri stars

We present sub-arcsec observations of a sample of 31 Herbig Ae/Be and related stars obtained with the technique of near-infrared speckle interferometry. In 18 of the 31 stars we nd evidence for circumstellar halos. These halos have a typical size of 1.1 00 , corresponding to1000 AU at the distances of the objects. Most of the halos have blue colours, hence are seen in scattered light. The incidence of observable circumstellar matter is signicantly higher than in a larger sample of T Tauri stars observed with the same technique (Leinert et al. 1993a). We suggest that this dierence results as a consequence of a faster initial evolution of the more massive Herbig Ae/Be stars. The near-infrared halos found in our study appear to correspond to the \envelopes invoked to model the strong mid-infrared excesses of Herbig Ae/Be stars.

Broken symmetry: The structure of the dust envelope of IRC +10216

view Abstract Citations (56) References (40) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Broken Symmetry: The Structure of the Dust Envelope of IRC +10216 Kastner, Joel H. ; Weintraub, David A. Abstract We present polarimetric, coronagraphic near-infrared images of the reflection nebula surrounding the carbon star IRC +10216. These images demonstrate convincingly that the dust envelope is not spherically symmetric. In unocculted images at J (1.25 micrometers) and in occulted images at H (1.65 micrometers) and K (2.2 micrometers), the nebula appears elongated, with major axis lying at position angle approximately 20 deg. The position angle of elongation is the same as that previously determined from near-infrared speckle interferometry for the inner approximately 1 sec of the envelope. The elliptical symmetry of the J polarimetric map offers additional evidence of the axial symmetry of the envelope and indicates that the equatorial plane of IRC +10216 lies perpendicular to the major axis of the nebula. The polarization map also indicates that the source of illumination -- presumably the stellar photosphere or hot dust located very near the photosphere -- is directly detected at wavelengths as short as approximately 1 micrometers. We find that the density distribution of grains in the polar regions is roughly n varies as r-2 and estimate that the scattering dust mass within 12 sec in radius of the central star is approximately 5 x 10-6 solar masses. These results support a model in which the envelope of IRC +10216 is weakly bipolar and is viewed at an intermediate inclination angle such that we have a direct line of sight to the central star. The axisymmetric near-infrared intensity and polarization morphologies are best understood in terms of enhanced mass loss in the equatorial plane. An examination of previous near-infrared and millimeter-wave mapping observations supports this hypothesis. These observations make clear that axisymmetric structure can be well established before an intermediate-mass star leaves the asymptotic giant branch. It is possible that the dust envelope of IRC +10216 presents an early manifestation of the more profound bipolar structure that characterizes highly evolved preplanetary nebulae. Publication: The Astrophysical Journal Pub Date: October 1994 DOI: 10.1086/174774 Bibcode: 1994ApJ...434..719K Keywords: Broken Symmetry; Carbon Stars; Cosmic Dust; Density Distribution; Infrared Astronomy; Optical Polarization; Reflection Nebulae; Stellar Envelopes; Astronomical Interferometry; Astronomical Polarimetry; Coronagraphs; Infrared Imagery; Stellar Evolution; Astronomy; ISM: DUST; EXTINCTION; ISM: STRUCTURE; POLARIZATION; ISM: REFLECTION NEBULAE; STARS: CARBON; STARS: INDIVIDUAL ALPHANUMERIC: IRC; 10216 full text sources ADS | data products SIMBAD (6)

Near-infrared speckle interferometry of evolved stars and bipolar nebulae

view Abstract Citations (116) References (46) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Near-infrared speckle interferometry of evolved stars and bipolar nebulae. Dyck, H. M. ; Zuckerman, B. ; Leinert, Ch. ; Beckwith, S. Abstract Near-infrared visibility functions are presented for 16 late-type giants and supergiants and bipolar nebulae. The observational sample consists primarily of OH/IR stars and carbon stars with millimeter wave CO emission. The results are discussed in terms of currently available circumstellar envelope models and in relationship to radio observations. It is found that many infrared-bright stars with dense circumstellar dust envelopes are at least partially resolvable from the ground by speckle interferometry. If the near-infrared diameters are interpreted as the inner boundary for dust in the envelope, this boundary has a radius of order 10 to the 15th cm. The envelope diameters show a systematic increase with wavelength, carbon stars appearing to have a shallower increase than oxygen stars. There is a systematic increase of the apparent angular diameter of the dust envelope with increasing mass loss rate. Publication: The Astrophysical Journal Pub Date: December 1984 DOI: 10.1086/162739 Bibcode: 1984ApJ...287..801D Keywords: Infrared Stars; Interferometry; Late Stars; Near Infrared Radiation; Nebulae; Stellar Evolution; Giant Stars; Infrared Interferometers; Speckle Patterns; Spectral Resolution; Stellar Mass Ejection; Supergiant Stars; Visibility; Astrophysics full text sources ADS | data products SIMBAD (11)