scholarly journals ISO's View of the Molecular Content of Evolved Stars

2000 ◽  
Vol 197 ◽  
pp. 375-390
Author(s):  
J. Cernicharo
Keyword(s):  
Systematic Study ◽  
Molecular Species ◽  
Planetary Nebulae ◽  
Far Infrared ◽  
Agb Stars ◽  
Circumstellar Envelopes ◽  
Mid Infrared ◽  
Evolved Stars ◽  
Vibrational Bands

The recent results of the ISO satellite in the field of molecular spectrocopy of AGB stars are reviewed. For the fist time, the two spectrometers onboard ISO have provided the opportunity to observe the pure rotational lines of several molecules in the far infrared and the ro-vibrational bands of the most abundant molecular species in the near and mid-infrared. These data allow to carry out a systematic study of the circumstellar envelopes of AGB stars and Planetary Nebulae. I analyze in this paper the role of resonant scatterring in the pumping of the ro-vibrational molecular levels in CSEs.

scholarly journals Polyynes and Polycyclic Aromatic Molecules in C-rich Circumstellar Envelopes

1994 ◽  
Vol 146 ◽  
pp. 134-148 ◽  
Author(s):  
Alain Omont
Keyword(s):  
Planetary Nebulae ◽  
Agb Stars ◽  
Circumstellar Envelopes ◽  
Aromatic Molecules ◽  
Evolved Stars ◽  
Ngc 7027 ◽  
Polycyclic Aromatic ◽  
Circumstellar Shells ◽  
Evolution Stage ◽  
Circumstellar Environment

The aim of this review is to discuss our knowledge on molecules in the circumstellar environment of evolved stars. In particular the presence and the behaviour of various kinds of molecules with several or many carbon atoms, in relation to C-rich dust, is considered.Such objects include mainly: (i) circumstellar shells of AGB carbon stars, either visible (such as Y CVn) or infrared (such as IRC+10216 (CW Leo)); (ii) planetary nebulae (PNe, e.g. NGC 7027); (iii) pre-planetary nebulae (PPNe, also called post-AGB stars, such as CRL 2688 or the Red Rectangle), probably in an intermediate evolution stage between the two former classes. I will not discuss more peculiar classes, such as R CrB stars and novae, for which very little is known about the presence of such molecular species.

scholarly journals Dust Production around Carbon-Rich Stars: The Role of Metallicity

Universe ◽  
2021 ◽  
Vol 7 (7) ◽  
pp. 233
Author(s):  
Ambra Nanni ◽  
Sergio Cristallo ◽  
Jacco Th. van Loon ◽  
Martin A. T. Groenewegen
Keyword(s):  
Wind Speed ◽  
Galactic Halo ◽  
Magellanic Clouds ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Circumstellar Envelopes ◽  
Chemical Enrichment ◽  
Wide Range ◽  
The Universe

Background: Most of the stars in the Universe will end their evolution by losing their envelope during the thermally pulsing asymptotic giant branch (TP-AGB) phase, enriching the interstellar medium of galaxies with heavy elements, partially condensed into dust grains formed in their extended circumstellar envelopes. Among these stars, carbon-rich TP-AGB stars (C-stars) are particularly relevant for the chemical enrichment of galaxies. We here investigated the role of the metallicity in the dust formation process from a theoretical viewpoint. Methods: We coupled an up-to-date description of dust growth and dust-driven wind, which included the time-averaged effect of shocks, with FRUITY stellar evolutionary tracks. We compared our predictions with observations of C-stars in our Galaxy, in the Magellanic Clouds (LMC and SMC) and in the Galactic Halo, characterised by metallicity between solar and 1/10 of solar. Results: Our models explained the variation of the gas and dust content around C-stars derived from the IRS Spitzer spectra. The wind speed of the C-stars at varying metallicity was well reproduced by our description. We predicted the wind speed at metallicity down to 1/10 of solar in a wide range of mass-loss rates.

scholarly journals Thermal Pulses and Planetary Nebula Ejection

1993 ◽  
Vol 155 ◽  
pp. 291-298 ◽  
Author(s):  
P.R. Wood ◽  
E. Vassiliadis
Keyword(s):  
Mass Loss ◽  
Planetary Nebula ◽  
Planetary Nebulae ◽  
Stellar Surface ◽  
Agb Stars ◽  
Theoretical Evolution ◽  
Thermal Pulses

Thermal pulses in AGB stars cause large luminosity variations at the stellar surface. The role of these luminosity variations in the production of planetary nebulae is discussed. Results of theoretical evolution calculations which include mass loss modulated by thermal pulses are presented.

scholarly journals OH mainline maser polarisation properties of post-AGB stars

2012 ◽  
Vol 8 (S287) ◽  
pp. 250-251
Author(s):  
Jessica M. Chapman ◽  
Ioannis Gonidakis ◽  
Rachel M. Deacon ◽  
Anne Green
Keyword(s):  
Far Infrared ◽  
Agb Stars ◽  
Evolved Stars

AbstractThe Parkes 64-m telescope was used to study the OH mainline polarisation properties at 1665 and 1667 MHz for a sample of 36 evolved stars, identified by their far-infrared and OH 1612 MHz maser properties as likely post-AGB stars.

Millimetre Observations of Evolved Stars

1996 ◽  
Vol 13 (2) ◽  
pp. 185-186
Author(s):  
Jessica M. Chapman
Keyword(s):  
Mass Loss ◽  
Stellar Atmosphere ◽  
Asymptotic Giant Branch ◽  
High Mass ◽  
Circumstellar Envelope ◽  
Agb Stars ◽  
Circumstellar Envelopes ◽  
Evolved Stars ◽  
High Mass Loss ◽  
Transfer Momentum

Radio emission at centimetre and millimetre wavelengths provides a powerful tool for studying the circumstellar envelopes of evolved stars. These include stars on the asymptotic giant branch (AGB), post-AGB stars and a small number of massive M-type supergiant stars. The AGB stars and M-type supergiants are characterised by extremely high mass-loss rates. The mass loss in such an evolved star is driven by radiation pressure acting on grains which form in the outer stellar atmosphere. The grains are accelerated outwards and transfer momentum to the gas through grain–gas collisions. The outflowing dust and gas thus form an expanding circumstellar envelope through which matter flows from the star to the interstellar medium, at a typical velocity of 15 km s−1. For a recent review of circumstellar mass loss see Chapman, Habing & Killeen (1995).

scholarly journals Far-Infrared Atomic Lines: PDRs or Shocks?

2003 ◽  
Vol 209 ◽  
pp. 349-352
Author(s):  
Margaret Meixner ◽  
David Fong ◽  
Edmund C. Sutton ◽  
Arancha Castro-Carrizo ◽  
Valentín Bujarrabal ◽  
...  
Keyword(s):  
Radiation Field ◽  
Chemical Change ◽  
Far Infrared ◽  
Relative Role ◽  
Evolved Stars ◽  
Stellar Radiation ◽  
Atomic Gas ◽  
Atomic Lines ◽  
Spectroscopy Studies

The relative role of the stellar radiation field, the stellar outflows and the interstellar radiation field (ISRF) in transforming the molecular ejecta into atomic gas was the subject of our ISO LWS and SWS spectroscopy study of 24 evolved stars which span the range from AGB stars to proto-planetary nebulae (PPNs) and PNs. The far-infrared (FIR) atomic fine-structure lines are powerful probes of the warm atomic gas in photodissociation regions (PDRs) and shocks. This paper summarizes and compares the ISO spectroscopy studies of carbon-rich (C-rich) and oxygen-rich (O-rich) evolved stars, published by Fong et al. (2001) and Castro-Carrizo et al. (2001), respectively. We find that photodissociation, not shocks, is responsible for the chemical change from molecular to atomic gas.

scholarly journals Rings and arcs around evolved stars – II. The Carbon Star AFGL 3068 and the Planetary Nebulae NGC 6543, NGC 7009, and NGC 7027

2020 ◽  
Vol 495 (2) ◽  
pp. 2234-2246 ◽  
Author(s):  
M A Guerrero ◽  
G Ramos-Larios ◽  
J A Toalá ◽  
B Balick ◽  
L Sabin
Keyword(s):  
Proper Motion ◽  
Planetary Nebulae ◽  
Carbon Star ◽  
Agb Stars ◽  
Spiral Pattern ◽  
High Quality ◽  
Hydrodynamic Simulations ◽  
Evolved Stars ◽  
Ngc 7027 ◽  
Regular Patterns

ABSTRACT We present a detailed comparative study of the arcs and fragmented ring-like features in the haloes of the planetary nebulae (PNe) NGC 6543, NGC 7009, and NGC 7027 and the spiral pattern around the carbon star AFGL 3068 using high-quality multi-epoch HST images. This comparison allows us to investigate the connection and possible evolution between the regular patterns surrounding AGB stars and the irregular concentric patterns around PNe. The radial proper motion of these features, ≃15 km s−1, are found to be consistent with the AGB wind and their linear sizes and interlapse times (500–1900 yr) also agree with those found around AGB stars, suggesting a common origin. We find evidence using radiative-hydrodynamic simulations that regular patterns produced at the end of the AGB phase become highly distorted by their interactions with the expanding PN and the anisotropic illumination and ionization patterns caused by shadow instabilities. These processes will disrupt the regular (mostly spiral) patterns around AGB stars, plausibly becoming the arcs and fragmented rings observed in the haloes of PNe.

OH/IR stars versus YSOs in infrared photometric surveys

2018 ◽  
Vol 14 (S343) ◽  
pp. 454-455
Author(s):  
Cécile Loup ◽  
Mark Allen ◽  
Ariane Lançon ◽  
Anais Oberto
Keyword(s):  
Selection Criteria ◽  
Far Infrared ◽  
High Mass ◽  
Agb Stars ◽  
Infrared Photometry ◽  
Mid Infrared ◽  
Ir Stars ◽  
High Mass Loss ◽  
Infrared Surveys ◽  
Methanol Masers

AbstractAGB stars play a major role in the chemical evolution of the galaxies. It thus is important to establish reliable photometric selection criteria to count them, especially AGB stars at the last stages of AGB evolution like OH/IR stars. Here, we have identified about 1500 OH/IR stars and 500 YSOs with methanol masers, in all major mid– and far–infrared surveys (IRAS, MSX, AKARI, WISE, GLIMPSE, and Hi–Gal). We show that AGB stars with high mass-loss rates cannot be disentagled from YSOs with only mid–infrared photometry; far–infrared photometry is essential. In the region observed by GLIMPSE, we show that the proportion of AGB stars has been severely underestimated in previous works: about 70% of “intrinsically” red objects in GLIMPSE are AGB stars rather than YSOs.

scholarly journals Molecular studies of Planetary Nebulae

2016 ◽  
Vol 12 (S323) ◽  
pp. 141-149 ◽  
Author(s):  
Yong Zhang
Keyword(s):  
Molecular Species ◽  
Active Site ◽  
Planetary Nebula ◽  
Central Star ◽  
Asymptotic Giant Branch ◽  
Circumstellar Envelopes ◽  
Evolved Stars ◽  
Diffuse Interstellar Bands ◽  
Diffuse Clouds ◽  
Complex Organic

AbstractCircumstellar envelopes (CEs) around evolved stars are an active site for the production of molecules. After evolving through the Asymptotic Giant Branch (AGB), proto-planetary nebula (PPN), to planetary nebula (PN) phases, CEs ultimately merge with the interstellar medium (ISM). The study of molecules in PNe, therefore, is essential to understanding the transition from stellar to interstellar materials. So far, over 20 molecular species have been discovered in PNe. The molecular composition of PNe is rather different from those of AGB and PPNe, suggesting that the molecules synthesized in PN progenitors have been heavily processed by strong ultraviolet radiation from the central star. Intriguingly, fullerenes and complex organic compounds having aromatic and aliphatic structures can be rapidly formed and largely survive during the PPN/PN evolution. The similar molecular compositions in PNe and diffuse clouds as well as the detection of C60+ in the ISM reinforce the view that the mass-loss from PNe can significantly enrich the ISM with molecular species, some of which may be responsible for the diffuse interstellar bands. In this contribution, I briefly summarize some recent observations of molecules in PNe, with emphasis on their implications on circumstellar chemistry.

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