scholarly journals Diffraction-limited 76 mas speckle-masking interferometry of the carbon star IRC+10 216 and related AGB objects with the SAO 6 m telescope

1999 ◽  
Vol 191 ◽  
pp. 273-278
Author(s):  
G. Weigelt ◽  
T. Blöcker ◽  
K.-H. Hofmann ◽  
R. Osterbart ◽  
Y.Y. Balega ◽  
...  
Keyword(s):  
High Resolution ◽  
Radiative Transfer ◽  
Carbon Star ◽  
Central Star ◽  
Dust Shell ◽  
Bipolar Structure ◽  
The Core ◽  
Transfer Modelling ◽  
Projected Distance ◽  
K Band

We present high-resolution J–, H–, and K–band observations of the carbon star IRC+10 216. The images were reconstructed from 6 m telescope speckle interferograms using the speckle masking bispectrum method. The H image has the unprecedented resolution of 70 mas. The H and K images consist of at least five dominant components within a 0.21 arcsec radius and a fainter asymmetric nebula. The J-, H-, and K—band images seem to have an X-shaped bipolar structure. A comparison of our images from 1995, 1996, 1997, and 1998 shows that the separation of the two brightest components A and B increased from ∼ 193 mas in 1995 to ∼ 246 mas in 1998.The cometary shapes of component A in the H and J images and the 0.79 μm and 1.06 μm HST images suggest that the core of A is not the central star, but the southern (nearer) lobe of the bipolar structure. The position of the central star is probably at or near the position of component B, where the H—K color has its largest value of H—K = 4.2.If the star is located at or near B, then the components A, C, and D are located close to the inner boundary of the dust shell at separations of ∼200 mas ∼30 AU (projected distance) ∼6 stellar radii for a distance of ∼ 150 pc, in agreement with our 2-dimensional radiative transfer modelling.In addition to IRC+ 10 216 we studied the stellar disks and the dust shells of several related objects. Angular resolutions of 24 mas at 700 nm or 57 mas 1.6 μm were achieved.

scholarly journals Core-halo structures in the 12CO emission of CIT 6, AFGL 618 and IRAS 21282+5050

1997 ◽  
Vol 180 ◽  
pp. 359-359
Author(s):  
M. Meixner ◽  
M.T. Campbell ◽  
W. J. Welch ◽  
L. Likkel ◽  
M. Tafalla
Keyword(s):  
Mass Loss ◽  
Spatial Resolution ◽  
Planetary Nebula ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Line Emission ◽  
Carbon Star ◽  
The Core ◽  
Evolved Stars ◽  
Transfer Modelling

We present full synthesis 12CO J= 1–0 line emission images of three carbon rich evolved stars: CIT 6, AFGL 618 and IRAS 21282+5050. Each of these objects represents a different stage of evolution: CIT 6 is a carbon star still on the AGB, AFGL 618 is a transition object, and IRAS 21282+5050 is a young planetary nebula. Common to all three sources, we find what appears to be two mass loss components: a bright “core” located at the center of the source and a fainter “halo” surrounding the core (see Table below for observed characteristics). We speculate that the bright core was created by a more recent and higher mass loss rate wind than the fainter surrounding halo. However, concrete support for this idea awaits radiative transfer modelling of the 12CO that we are currently pursuing. Our full synthesis data are combined from millimeter interferometry using the Berkeley–Illinois–Maryland millimeter array (BIMA) and single dish maps using the NRAO 12m. We find that full-synthesis imaging, which combines the sensitivity of single dish and the spatial resolution of interferometry, is the only means to reveal such core-halo structures.

scholarly journals Circumstellar H2O in M-type AGB stars

2008 ◽  
Vol 4 (S251) ◽  
pp. 163-164
Author(s):  
Matthias Maercker ◽  
Fredrik L. Schöier ◽  
Hans Olofsson
Keyword(s):  
Radiative Transfer ◽  
Radiation Field ◽  
Central Star ◽  
Thermal Excitation ◽  
Circumstellar Envelope ◽  
Agb Stars ◽  
Dust Grains ◽  
Transfer Modelling

AbstractSurprisingly high amounts of H2O have recently been reported in the circumstellar envelope around the M-type AGB star W Hya. However, substantial uncertainties remain, as the required radiative transfer modelling is difficult due to high optical depths, sub-thermal excitation and the sensitivity to the combined radiation field from the central star and dust grains.

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

2006 ◽  
Vol 448 (1) ◽  
pp. 271-281 ◽  
Author(s):  
A. B. Men'shchikov ◽  
Y. Y. Balega ◽  
M. Berger ◽  
T. Driebe ◽  
K.-H. Hofmann ◽  
...  
Keyword(s):  
Radiative Transfer ◽  
Near Infrared ◽  
Carbon Star ◽  
Speckle Interferometry ◽  
Transfer Modelling

scholarly journals Planetary Nebula Evolution Traced by Distance-Independent Parameters

1993 ◽  
Vol 155 ◽  
pp. 480-480
Author(s):  
C.Y. Zhang ◽  
S. Kwok
Keyword(s):  
Physical Properties ◽  
Mass Distribution ◽  
Planetary Nebula ◽  
Strong Support ◽  
Planetary Nebulae ◽  
Central Star ◽  
Evolution Model ◽  
The Core ◽  
Independent Parameters ◽  
Central Stars

Making use of the results from recent infrared and radio surveys of planetary nebulae, we have selected 431 nebulae to form a sample where a number of distance-independent parameters (e.g., Tb, Td, I60μm and IRE) can be constructed. In addition, we also made use of other distance-independent parameters ne and T∗ where recent measurements are available. We have investigated the relationships among these parameters in the context of a coupled evolution model of the nebula and the central star. We find that most of the observed data in fact lie within the area covered by the model tracks, therefore lending strong support to the correctness of the model. Most interestingly, we find that the evolutionary tracks for nebulae with central stars of different core masses can be separated in a Tb-T∗ plane. This implies that the core masses and ages of the central stars can be determined completely independent of distance assumptions. The core masses and ages have been obtained for 302 central stars with previously determined central-star temperatures. We find that the mass distribution of the central stars strongly peaks at 0.6 M⊙, with 66% of the sample having masses <0.64 MM⊙. The luminosities of the central stars are then derived from their positions in the HR diagram according to their core masses and central star temperatures. If this method of mass (and luminosity) determination turns out to be accurate, we can bypass the extremely unreliable estimates for distances, and will be able to derive other physical properties of planetary nebulae.

scholarly journals Chemical Enrichment and Central Star Properties

1993 ◽  
Vol 155 ◽  
pp. 572-572
Author(s):  
C.Y. Zhang
Keyword(s):  
Planetary Nebulae ◽  
Central Star ◽  
Agb Stars ◽  
Physical Processes ◽  
Chemical Abundances ◽  
Core Mass ◽  
Chemical Enrichment ◽  
The Core ◽  
Stellar Temperature ◽  
Independent Parameters

We have selected a sample of planetary nebulae, for which the core masses are determined using distance-independent parameters (Zhang and Kwok 1992). The chemical abundances of He, N, O, and C are taken from the literature for them. Relationships of the ratios of He/H, N/O, and C/O with various stellar parameters of planetary nebulae (PN), such as the core mass, the mass of the core plus the ionized nebular gas, the stellar age and temperature, are examined. It is found that the N/O increases with increasing mass, while the C/O first increases and then decreases with the core mass. No strong correlation seems to exist between the He/H and the core mass. A correlation of the N/O and He/H with the stellar temperature exists. The current dredge-up theory for the progenitor AGB stars cannot satisfactorily account for these patterns of chemical enrichment in PN. Furthermore, the correlations of the N/O and He/H with the stellar age and temperature indicate that besides the dredge-ups in the RG and AGB stages, physical processes that happen in the planetary nebula stage may also play a role in forming the observed patterns of chemical enrichment in the planetary nebulae.

Sign in / Sign up

Export Citation Format

Share Document