Thermal and hydrostatic structure of the protoplanetary nebula exposed to stellar radiation and stellar wind from the central star

High-resolution images in [O III] λ5007 of the hydrogen-poor knots of Abell 30 reveal comet-like structures which may be indicative of interaction with the stellar wind. In the near IR, new, higher-resolution, K-band images show an equatorial ring of hot dust that corresponds closely to optical knots 2 and 4 of Jacoby and Ford, while their polar knots 1 and 3 show no comparable IR emission. Both the thermal IR emission and the heavy internal extinction of the central star demands an extremely dusty ejecta. Greenstein showed that the UV extinction curve is fit by amorphous carbon. Our comprehensive dust models consider both the UV extinction and the IR emission from a population of carbon grains. The thermal emission from larger grains produces the far IR emission, while the stochastic heating of very small grains to high temperatures is essential to explain the near IR flux. We are able to reproduce the shape of the near IR spectrum with an a−3.0 distribution of grain radii which extends down to a minimum grain radius of 8 Å.

Download Full-text

Cosmic Pathways to Life: From Interstellar Molecules to the First Traces of Life

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319003120 ◽

2018 ◽

Vol 14 (S345) ◽

pp. 1-14

Author(s):

Manuel Güdel ◽

Bruce G. Elmegreen ◽

L. Viktor Tóth

Keyword(s):

Central Star ◽

Life Forms ◽

Disk Accretion ◽

Nearby Star ◽

Long Period ◽

Cosmic Evolution ◽

Stellar Radiation ◽

Solid Bodies ◽

Gaseous Envelope ◽

Central Stars

AbstractThe present-day Earth with its innumerable life forms is a product of cosmic evolution starting with the formation of our galaxy and the dense gas clouds within it, and proceeding through the contraction of one of those clouds about 4.6 Gyr ago, first into filaments and then one or more protostellar disks, planets, and central stars, one of which was our Sun. Radioactive debris from a massive nearby star was included. The planets themselves formed through coagulation, accretion, and fragmentation of solid bodies. Habitability depends on a delicate balance between disk accretion by gravity and dispersal by the central star, which determine the size of the planet and its gaseous envelope, combined with a long period of stellar radiation, which has to disperse this envelope but leave a hospitable secondary atmosphere. The final step toward life involves even more complexity as self-replicating bio-molecules form with ever increasing stability.

Download Full-text

Ablation and Wind Mass-Loading in the Born-Again Planetary Nebula A 30

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312011519 ◽

2011 ◽

Vol 7 (S283) ◽

pp. 378-379

Author(s):

Martín A. Guerrero ◽

You-Hua Chu ◽

Wolf-Rainer Hamann ◽

Lidia Oskinova ◽

Detlef Schönberner ◽

...

Keyword(s):

Stellar Wind ◽

Planetary Nebula ◽

Central Star ◽

Mass Loading ◽

Diffuse Emission ◽

X Ray ◽

Thermal Pulse ◽

Born Again

AbstractWe present XMM-Newton and Chandra observations of the born-again planetary nebula A 30. These X-ray observations reveal a bright unresolved source at the position of the central star whose X-ray luminosity exceeds by far the model expectations for photospheric emission and for shocks within the stellar wind. We suggest that a “born-again hot bubble” may be responsible for this X-ray emission. Diffuse X-ray emission associated with the petal-like features and one of the H-poor knots seen in the optical is also found. The weakened emission of carbon lines in the spectrum of the diffuse emission can be interpreted as the dilution of stellar wind by mass-loading or as the detection of material ejected during a very late thermal pulse.

Download Full-text

The Stellar Wind From the Central Star of NGC 7009

Proceedings of the International Astronomical Union ◽

10.1017/s1743921306004005 ◽

2006 ◽

Vol 2 (S234) ◽

pp. 513

Author(s):

G. Sonneborn ◽

R. C. Iping ◽

D. L. Massa ◽

Y-H Chu

Keyword(s):

Stellar Wind ◽

Central Star

Download Full-text

A Mechanism for Variability of Cometary Nebulae

Symposium - International Astronomical Union ◽

10.1017/s0074180900096091 ◽

1987 ◽

Vol 115 ◽

pp. 398-400

Author(s):

G. M. Rudnitskij

Keyword(s):

Tilt Angle ◽

Stellar Wind ◽

Large Scale ◽

Central Star ◽

Similar Model ◽

Conical Cavity ◽

Bipolar Outflow ◽

Circumstellar Gas ◽

Small Disc ◽

Optical Structure

A model is suggested to explain the variability of the optical structure and the integral brightness of cometary nebulae (CN) occurring at timescales of several years and tens of years (Gyulbudaghian et al. 1977, Cohen et al. 1977, 1981, Magakyan 1981, Gyulbudaghian 1982). A CN is assumed to be a reflection nebula; it is a wall of a conical cavity in the circumstellar gas-and-dust torus illuminated by the central star (Cohen 1974). I explain the CN's variability by the presence of small tilted circumstellar disc of gas-and-dust, located inside the internal channel of the large circumstellar torus (see Figure 1). A similar model was put forward by Ward-Thompson et al. (1985) to account for a tilt angle of about 30° between the direction of short optical jets (stellar wind, channelled by the small disc) and the large-scale bipolar outflow (focused by the large torus) in the CN NGC 6729 associated with the star R CrA. Tilt angles of about 30° between optical and radio structures exist in CN NGC 2261 (Cantó et al. 1981) and GM 1-29 (Levreault 1984).

Download Full-text

Spectrophotometry and Multicolour Imagery of the Planetary Nebula Around the P Cygni Star AG Carinae

Symposium - International Astronomical Union ◽

10.1017/s0074180900170792 ◽

1993 ◽

Vol 155 ◽

pp. 217-217

Author(s):

C. Rossi ◽

A. Altamore ◽

R.D.D. Costa ◽

A. Damineli Neto ◽

J.A. De Freitas Pacheco ◽

...

Keyword(s):

Stellar Wind ◽

Planetary Nebula ◽

Central Star ◽

Interesting Case ◽

Circumstellar Dust ◽

High Luminosity ◽

Peak Separation ◽

Dust Temperature ◽

Ring Nebula ◽

H Ii Region

Some of the high luminosity stars in our Galaxy are surrounded by planetary-like nebulae formed by material ejected from the central star. The most interesting case is that of the ring nebula PK 289-0° 1 around the P Cygni star AG Car. Long slit spectroscopy shows that nitrogen is overabundant and oxygen underabundant in the nebula. The Hα/[NII] ratio is lower in the nebula with respect to the surrounding H II region, possibly as a result of the N overabundance in the stellar wind. The emission line peak separation confirms a model of a distorted spherical shell expanding at 66 km s−1. The scattered star's spectrum is observable near the star, suggesting the presence of circumstellar dust grains. A nebular mass of at least 2.7 M⊙ is derived. While the nebula in the Hα imagery reveals the ring-like shape with many structures, in the blue it is much fainter and smoother. No nebular emission was detected in the JHK bands, suggesting a low dust temperature.

Download Full-text

A Hydrodynamic Modelling of Atmospheric Escape and Absorption Line of WASP-12b

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319001480 ◽

2018 ◽

Vol 14 (S345) ◽

pp. 301-303

Author(s):

N. K. Dwivedi ◽

M. L. Khodachenko ◽

I. F. Shaikhislamov ◽

A. G. Berezutsky ◽

I. B. Miroshnichenko ◽

...

Keyword(s):

Mass Loss ◽

Stellar Wind ◽

Energy Input ◽

Gravitational Interaction ◽

Radiation Energy ◽

Tidal Force ◽

Atmospheric Escape ◽

Planetary Mass ◽

Stellar Radiation ◽

Self Consistent

AbstractSelf-Consistent 2D modelling of stellar wind interaction with the upper atmosphere of WASP-12b has been performed. The two case-scenarios of the planetary material escape and interaction with the stellar wind, namely the ‘blown by the wind’ (without the inclusion of tidal force) and ‘captured by the star’ (with the tidal force) have been modelled under different stellar XUV radiations and stellar wind parameters. In the first scenario, a shock is formed around the planet, and the planetary mass loss is controlled completely by the stellar radiation energy input. In the second scenario, the mass loss is mainly due to the gravitational interaction effects. The dynamics of MGII and related absorption were modelled with three sets of different stellar wind parameters and XUV flux values.

Download Full-text

Dust Rings in the Circumstellar Gas Disks

Symposium - International Astronomical Union ◽

10.1017/s0074180900218305 ◽

2004 ◽

Vol 202 ◽

pp. 375-377

Author(s):

Taku Takeuchi ◽

Pawel Artymowicz

Keyword(s):

Drag Force ◽

Radiation Pressure ◽

Brown Dwarfs ◽

Central Star ◽

Outer Edge ◽

Dust Grains ◽

Stellar Radiation ◽

Circumstellar Gas ◽

Gas Drag ◽

Dust Ring

In optically thin gas disks around young Vega-type stars, dust grains are exposed to the stellar radiation pressure and gas drag force. The combination of these forces pushes the grains away from the central star. Typically, 10–100 μm grains migrate outward to become concentrated at the outer edge of the gas disk. A dust ring naturally forms without the help of clearing bodies, such as planets or brown dwarfs.

Download Full-text

Photoionization Models

Symposium - International Astronomical Union ◽

10.1017/s0074180900137738 ◽

1989 ◽

Vol 131 ◽

pp. 157-166

Author(s):

J. Patrick Harrington

Keyword(s):

Radiative Transfer ◽

Ionizing Radiation ◽

Density Distribution ◽

Stellar Wind ◽

Model Atmosphere ◽

Axially Symmetric ◽

Molecular Component ◽

Substantial Agreement ◽

Stellar Radiation ◽

Future Work

A recent comparison of the photoionization models generated by five independent codes run with the same density and stellar radiation shows substantial agreement. Problems are more likely to arise with the defining parameters: the density distribution should be based on observed images, and the ionizing radiation should be from model atmosphere calculations, which, however, are inadequate for stars with winds. Models can be improved by including dust and by incorporating, self-consistently, radiative transfer in optically thick lines. Future work may extend modeling to axially-symmetric objects, to the interface with the hot, shocked, stellar wind, and to the molecular component present around many nebulae.

Download Full-text