scholarly journals Energy Distribution of Planetary Nebulae (UV to Radio)

1993 ◽  
Vol 155 ◽  
pp. 99-108
Author(s):  
C.Y. Zhang
Keyword(s):  
Energy Distribution ◽  
Planetary Nebula ◽  
Spectral Energy Distribution ◽  
Planetary Nebulae ◽  
Central Star ◽  
Spectral Energy ◽  
Significant Progress ◽  
Dust Shell ◽  
The Past ◽  
Entire Wavelength Range

The past decade has seen significant progress in our understanding of spectral energy distribution of planetary nebulae over the entire wavelength range from UV to radio. In this review we show the detailed breakdown of the energy budget for a planetary nebula as a system of the three components, i.e., the central star, the gaseous nebula and the dust shell. This picture of the energy distribution is further discussed in the context of planetary nebula evolution.

scholarly journals Bi-Abundance Ionisation Structure of the Wolf–Rayet Planetary Nebula PB 8

2018 ◽  
Vol 35 ◽  
Author(s):  
A. Danehkar
Keyword(s):  
Planetary Nebula ◽  
Spectral Energy Distribution ◽  
Homogeneous Model ◽  
Planetary Nebulae ◽  
Central Star ◽  
Model Atmosphere ◽  
Stellar Model ◽  
Spectral Energy ◽  
Mean Values ◽  
Infrared Observations

AbstractThe planetary nebula PB 8 around a [WN/WC]-hybrid central star is one of planetary nebulae with moderate abundance discrepancy factors (ADFs ~ 2–3), which could be an indication of a tiny fraction of metal-rich inclusions embedded in the nebula (bi-abundance). In this work, we have constructed photoionisation models to reproduce the optical and infrared observations of the planetary nebula PB 8 using a non-LTE stellar model atmosphere ionising source. A chemically homogeneous model initially used cannot predict the optical recombination lines. However, a bi-abundance model provides a better fit to most of the observed optical recombination lines from N and O ions. The metal-rich inclusions in the bi-abundance model occupy 5.6% of the total volume of the nebula, and are roughly 1.7 times cooler and denser than the mean values of the surrounding nebula. The N/H and O/H abundance ratios in the metal-rich inclusions are ~1.0 and 1.7 dex larger than the diffuse warm nebula, respectively. To reproduce the Spitzer spectral energy distribution of PB 8, dust grains with a dust-to-gas ratio of 0.01 (by mass) were also included. It is found that the presence of metal-rich inclusions can explain the heavy element optical recombination lines, while a dual-dust chemistry with different grain species and discrete grain sizes likely produces the infrared continuum of this planetary nebula. This study demonstrates that the bi-abundance hypothesis, which was examined in a few planetary nebulae with large abundance discrepancies (ADFs > 10), could also be applied to those typical planetary nebulae with moderate abundance discrepancies.

scholarly journals Diffraction-Limited Speckle Interferometry and Modeling of the Circumstellar Envelope of R CrB at Maximum and Minimum Light

2003 ◽  
Vol 209 ◽  
pp. 88-88
Author(s):  
K. Ohnaka ◽  
T. Blöcker ◽  
K.-H. Hofmann ◽  
N. R. Ikhsanov ◽  
G. Weigelt ◽  
...  
Keyword(s):  
Energy Distribution ◽  
Thermal Emission ◽  
Spectral Energy Distribution ◽  
Dust Cloud ◽  
Special Astrophysical Observatory ◽  
Spectral Energy ◽  
Circumstellar Envelope ◽  
Dust Shell ◽  
Maximum Light ◽  
Minimum Light

We present the first speckle interferometric observations of R CrB, the prototype of a class of peculiar stars which undergo irregular declines in their visible light curves. The observations were carried out with the 6 m telescope at the Special Astrophysical Observatory near maximum light (V = 7, 1996 Oct. 1) and at minimum light (V = 10.61, 1999 Sep. 28). A spatial resolution of 75 mas was achieved in the K-band. The dust shell around R CrB is partially resolved, and the visibility is approximately 0.8 at a spatial frequency of 10 cycles/arcsec. The two-dimensional power spectra obtained at both epochs do not show any significant deviation from circular symmetry. The visibility function and spectral energy distribution obtained near maximum light can be simultaneously fitted with a model consisting of the central star and an optically thin dust shell with density proportional to r−2 and amorphous carbon as its constituent. The inner boundary of the shell is found to be 82 R* (19 mas) with a temperature of 920 K near maximum light. However, this simple model fails to simultaneously reproduce the visibility and spectral energy distribution obtained at minimum light. We show that this discrepancy can be attributed to thermal emission from a newly formed optically thick dust cloud. Simultaneous fits of the observed SED and visibility with models including a thermally emitting dust cloud suggest the presence of a newly formed dust cloud as hot as 1200 K with a radius of 4 – 5R*, in addition to an optically thin dust shell whose inner boundary is ~ 170 R* with a temperature of ~ 690 K. Alternatively the discrepancy can be attributed to an unusual extinction curve of dust grains in the obscuring cloud which was present in front of the star at minimum light. The details of the observations and modeling are described in Ohnaka et al. (2001, A&A 380, 212).

Comprehensive Panchromatic Data Analyses and Photoionization Modeling of NGC 6781

2018 ◽  
Vol 14 (S343) ◽  
pp. 514-515
Author(s):  
Toshiya Ueta ◽  
Masaaki Otsuka ◽  
Keyword(s):  
Planetary Nebula ◽  
Milky Way ◽  
Spectral Energy Distribution ◽  
Central Star ◽  
Spectral Energy ◽  
Molecular Gas ◽  
Material Recycling ◽  
Data Analyses ◽  
Dust Component ◽  
Data Points

AbstractWe characterized the dusty circumstellar nebula and central star of the C-rich bipolar planetary nebula (PN) NGC 6781 using our own Herschel data augmented with the archival data from UV to radio and constructed one of the most comprehensive photoionization PN models ever produced consisting of the ionized, atomic and molecular gas components as well as the dust component. We reproduced the observed spectral energy distribution (SED), constrained by 136 observational data points. The total nebula mass was estimated to be 0.41 M⊙, with a significant fraction (about 70 %) of it existing in the photo-dissociation region (PDR) surrounding the ionized nebula. This finding demonstrates the critical importance of the PDR in PNe, which are typically recognized as the hallmark of ionized/H+ region. It is therefore essential to characterize the PDR of the circumstellar nebula to understand material recycling in the Milky Way and other galaxies.

scholarly journals Determination of Planetary Nebulae angular diameters from radio continuum spectral energy distribution modelling

2021 ◽  
Vol 503 (2) ◽  
pp. 2887-2898
Author(s):  
I S Bojičić ◽  
M D Filipović ◽  
D Urošević ◽  
Q A Parker ◽  
T J Galvin
Keyword(s):  
Energy Distribution ◽  
Spectral Energy Distribution ◽  
Angular Size ◽  
Planetary Nebulae ◽  
High Sensitivity ◽  
Radio Continuum ◽  
Spectral Energy ◽  
Wide Field ◽  
Distribution Fitting ◽  
New Radio

ABSTRACT Powerful new, high-resolution, high-sensitivity, multifrequency, wide-field radio surveys such as the Australian Square Kilometre Array Pathfinder (ASKAP) Evolutionary Map of the Universe are emerging. They will offer fresh opportunities to undertake new determinations of useful parameters for various kinds of extended astrophysical phenomena. Here, we consider specific application to angular-size determinations of Planetary Nebulae (PNe) via a new radio continuum spectral energy distribution fitting technique. We show that robust determinations of angular size can be obtained, comparable to the best optical and radio observations but with the potential for consistent application across the population. This includes unresolved and/or heavily obscured PNe that are extremely faint or even non-detectable in the optical.

scholarly journals Herschel Planetary Nebula Survey (HerPLaNS): Construction of a Detailed Dusty Photoionization Model of NGC6781

2016 ◽  
Vol 12 (S323) ◽  
pp. 348-349
Author(s):  
Masaaki Otsuka ◽  
Toshiya Ueta ◽  
You-Hua Chu ◽  
Kentaro Asano ◽  
Keyword(s):  
Planetary Nebula ◽  
Spectral Energy Distribution ◽  
Image Data ◽  
Central Star ◽  
Spectral Energy ◽  
Molecular Line ◽  
The Rich ◽  
Cold Dust ◽  
Photoionization Model

AbstractAs one of the follow-up studies of Herschel Planetary Nebula Survey (HerPlaNS; Ueta et al. 2014), we focus on a bipolar planetary nebula (PN) NGC6781 to characterize the dusty nebula and the central star based on our own Herschel data and the rich archival spectroscopic/photometric image data in the wavelengths from UV to far-IR. With CLOUDY, we constructed a comprehensive photoionization model of NGC6781 ever made including data from UV to radio. We succeeded to reproduce the observed spectral energy distribution (SED) and the atomic gas, H2, CO, and OH molecular line fluxes. We found that about 40% of the total dust mass would be from warm-cold dust components.

RR Tel: Determination of Dust Properties During Minimum Obscuration

2012 ◽  
Vol 21 (1-2) ◽  
Author(s):  
T. Jurkić ◽  
D. Kotnik-Karuza
Keyword(s):  
Energy Distribution ◽  
Thermal Emission ◽  
Mass Loss Rate ◽  
Spectral Energy Distribution ◽  
Dust Emission ◽  
Circumstellar Dust ◽  
Spectral Energy ◽  
Dust Shell

Abstractthe ISO infrared spectra and the SAAO long-term JHKL photometry of RR Tel in the epochs during minimum obscuration are studied in order to construct a circumstellar dust model. the spectral energy distribution in the near- and the mid-IR spectral range (1–15 μm) was obtained for an epoch without the pronounced dust obscuration. the DUSTY code was used to solve the radiative transfer through the dust and to determine the circumstellar dust properties of the inner dust regions around the Mira component. Dust temperature, maximum grain size, dust density distribution, mass-loss rate, terminal wind velocity and optical depth are determined. the spectral energy distribution and the long-term JHKL photometry during an epoch of minimum obscuration show almost unattenuated stellar source and strong dust emission which cannot be explained by a single dust shell model. We propose a two-component model consisting of an optically thin circmustellar dust shell and optically thick dust outside the line of sight in some kind of a flattened geometry, which is responsible for most of the observed dust thermal emission.

scholarly journals 2-D Radiation Transfer Model of Non-Spherically Symmetric Dust Shell in Proto-Planetary Nebulae

2003 ◽  
Vol 209 ◽  
pp. 139-140
Author(s):  
Kate Y. L. Su ◽  
Kevin Volk ◽  
Sun Kwok
Keyword(s):  
Radiation Transfer ◽  
Spectral Energy Distribution ◽  
Planetary Nebulae ◽  
Asymptotic Giant Branch ◽  
Radiative Transfer Model ◽  
Spectral Energy ◽  
Transfer Model ◽  
Agb Stars ◽  
Dust Shell ◽  
Radiation Transfer Model

Resent high-resolution optical imaging has directly revealed reflection nebulosity around proto-planetary nebulae (PPNs), the transition objects between asymptotic giant branch (AGB) stars and planetary nebulae (Sahai et al. 1998, Su et al. 1998, Ueta et al. 2000, Su et al. 2001). The existence of bipolar nebulae observed in the PPN phase suggests the presence of asymmetry in the AGB circumstellar dust shell. In order to model these objects, a self-consistent radiation transfer model is necessary. As a first attempt, we construct an approximate two-dimensional dust radiative transfer model to simultaneously fit the spectral energy distribution (SED) and images of a centrally-heated dust envelope.

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 The Remarkable Evolution of the Post-Agb Star FG SGE

1998 ◽  
Vol 11 (1) ◽  
pp. 363-363
Author(s):  
Johanna Jurcsik ◽  
Benjamin Montesinos
Keyword(s):  
Time Scales ◽  
Effective Temperature ◽  
Planetary Nebula ◽  
Planetary Nebulae ◽  
Central Star ◽  
Evolutionary Models ◽  
Single Star ◽  
Line Intensities ◽  
Evolutionary Changes ◽  
Evolutionary Studies

FG Sagittae is one of the most important key objects of post-AGB stellar evolutionary studies. As a consequence of a final helium shell flash, this unique variable has shown real evolutionary changes on human time scales during this century. The observational history was reviewed in comparison with predictions from evolutionary models. The central star of the old planetary nebula (Hel-5) evolved from left to right in the HR diagram, going in just hundred years from the hot region of exciting sources of planetary nebulae to the cool red supergiant domain just before our eyes becoming a newly-born post-AGB star. The effective temperature of the star was around 50,000 K at the beginning of this century, and the last estimates in the late 1980s give 5,000-6,500 K. Recent spectroscopic observations obtained by Ingemar Lundström show definite changes in the nebular line intensities. This fact undoubtedly rules out the possibility that, instead of FG Sge, a hidden hot object would be the true central star of the nebula. Consequently, the observed evolutionary changes are connected with the evolution of a single star.

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