scholarly journals A Molecular Line Survey of CRL 2688 at 1 mm and 3 mm Wavelengths

2012 ◽  
Vol 8 (S292) ◽  
pp. 68-68
Author(s):  
Yong Zhang ◽  
Sun Kwok ◽  
Jun-ichi Nakashima ◽  
Dinh-V Trung
Keyword(s):  
Time Scales ◽  
Active Sites ◽  
Planetary Nebulae ◽  
Asymptotic Giant Branch ◽  
Interstellar Space ◽  
Molecular Line ◽  
Chemical Enrichment ◽  
Evolved Stars ◽  
The Galaxy ◽  
Dynamical Time

AbstractIt is well established that circumstellar envelopes (CSEs) around evolved stars are active sites of molecular synthesis, and CSEs are one of the major sources of chemical enrichment in the interstellar space. The investigation of molecular compositions in CSEs is essential to understand the chemical evolution of the Galaxy. In order to study circumstellar chemistry in different environments, we have been systematically performing molecular line surveys of a sample of evolved stars from asymptotic giant branch (AGB) stars, proto-planetary nebulae (PPNs), to planetary nebulae (PNs). The dynamical time scales in different evolutionary stages can impose a time limit on the reaction time scales. Here we report our results for CRL 2688.

scholarly journals Historical overview of planetary nebulae research

2011 ◽  
Vol 7 (S283) ◽  
pp. 1-8
Author(s):  
Sun Kwok
Keyword(s):  
Planetary Nebulae ◽  
Central Star ◽  
Asymptotic Giant Branch ◽  
Evolutionary Status ◽  
Complex Molecules ◽  
Chemical Enrichment ◽  
Star Studies ◽  
The Galaxy ◽  
Underlying Causes

AbstractPlanetary nebulae (PNs) were first discovered over 200 years ago and our understanding of these objects has undergone significant evolution over the years. Developments in astronomical optical spectroscopy and atomic physics have shown that PNe are gaseous objects photoionized by UV radiation from a hot central star. Studies of the kinematics of the nebulae coupled with progress in theories of stellar evolution have led to the identification that PNe are evolved stars and progenitors of white dwarfs. Development of infrared and millimeter-wave technology in the 1970s made us realize that there is significant amount of neutral matter (molecules and dust) in PNe. The link of PNe to the stellar winds from their progenitor asymptotic giant branch (AGB) stars and subsequent dynamical interactions are now believed to be the underlying causes of the morphological structures of PNe. The role of PNe as prolific molecular factories producing complex molecules and organic solids has significant implications on the chemical enrichment of the Galaxy.In this paper, we discuss the misconceptions and errors that we have encountered in our journey of understanding the nature of PN. The various detours and dead ends that had happened during our quest to pin down the evolutionary status and causes of nebulae ejection will be discussed. As there are still many unsolved problems in PN research, these lessons of history have much to offer for future progress in this field.

scholarly journals Influence of Planets on Parent Stars: Angular Momentum

2004 ◽  
Vol 219 ◽  
pp. 323-332
Author(s):  
Noam Soker
Keyword(s):  
Angular Momentum ◽  
Globular Clusters ◽  
Hubble Space Telescope ◽  
Mass Loss Rate ◽  
Planetary Nebulae ◽  
Asymptotic Giant Branch ◽  
Tidal Interaction ◽  
Evolved Stars ◽  
The Galaxy ◽  
Red Giant

I review some possible processes by which planets and brown dwarfs can influence the evolution of their parent evolved stars. As sunlike stars evolve on the red giant branch (RGB) and then on the asymptotic giant branch (AGB), they will interact with their close planets (if exist). The interaction starts with tidal interaction: this will lead the planets to deposit most of their angular momentum to the envelope of the giant, and then spiral-in to the envelope. (Too many papers dealing with close planets [less than about 3-6 AU] around evolved stars neglect tidal interaction, hence their results are questionable.) They may spin-up their parent stars by up to several orders of magnitude. The interaction of substellar objects with evolved star may enhance the mass loss rate, mainly in the equatorial plane. Possible outcomes are: (i) Planetary systems interacting with their parent AGB star may lead to the formation of moderate elliptical planetary nebulae. (ii) RGB stars which lose more mass turn to bluer horizontal branch (HB) stars. Therefore, planets may explain the formation of blue HB stars. This may explain the presence of many blue HB stars in many globular clusters (the planets be the second parameter), and some hot HB stars in the galaxy (sdB stars). (The 8.3 days use of the Hubble Space Telescope in search of planets in a globular clusters with no blue HB stars was a wrong move.) (iii) Most known stars with planets will not form planetary nebulae, because they will lose most of their envelope already on the RGB.

scholarly journals Recovering the Star Formation History of IC1613 Dwarf Galaxy Using Evolved Stars

2018 ◽  
Vol 14 (S344) ◽  
pp. 77-80
Author(s):  
Seyed Azim Hashemi ◽  
Atefeh Javadi ◽  
Jacco Th. van Loon
Keyword(s):  
Star Formation ◽  
Dwarf Galaxy ◽  
Stellar Populations ◽  
Asymptotic Giant Branch ◽  
Star Formation History ◽  
Evolved Stars ◽  
Formation History ◽  
The Galaxy ◽  
Red Supergiants ◽  
Period Variable

AbstractDetermining the star formation history (SFH) is key to understand the formation and evolution of dwarf galaxies. Recovering the SFH in resolved galaxies is mostly based on deep colour–magnitude diagrams (CMDs), which trace the signatures of multiple evolutionary stages of their stellar populations. In distant and unresolved galaxies, the integrated light of the galaxy can be decomposed, albeit made difficult by an age–metallicity degeneracy. Another solution to determine the SFH of resolved galaxies is based on evolved stars; these luminous stars are the most accessible tracers of the underlying stellar populations and can trace the entire SFH. Here we present a novel method based on long period variable (LPV) evolved asymptotic giant branch (AGB) stars and red supergiants (RSGs). We applied this method to reconstruct the SFH for IC1613, an irregular dwarf galaxy at a distance of 750 kpc. Our results provide an independent confirmation that no major episode of star formation occurred in IC1613 over the past 5 Gyr.

scholarly journals Chemical Peculiarities, Mass Loss, and Final Evolution of AGB Stars in the Magellanic Clouds

1988 ◽  
Vol 108 ◽  
pp. 31-37
Author(s):  
P.R. Wood
Keyword(s):  
Mass Loss ◽  
Great Majority ◽  
Magellanic Clouds ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Long Period ◽  
Evolved Stars ◽  
The Galaxy ◽  
Shed Light ◽  
Final Evolution

The Magellanic Clouds are sufficiently close that evolved stars which exhibit chemical peculiarities and the effects of mass loss can be readily observed. Such objects include carbon stars, S stars, long-period variables, OH/IR stars and planetary nebulae. Because of the relatively well-known distances of the Magellanic Clouds, the intrinsic luminosities of these objects can be accurately determined, in contrast to the situation in the Galaxy where the great majority of asymptotic giant branch (AGB) stars occur in the field population. In this review, observations of AGB stars in the Magellanic Clouds will be discussed with particular reference to those features which can shed light on mass loss and chemical peculiarities resulting from stellar evolution.

scholarly journals Spitzer observations of molecules and dust in evolved stars in nearby galaxies

2009 ◽  
Vol 5 (H15) ◽  
pp. 557-557
Author(s):  
Mikako Matsuura
Keyword(s):  
High Sensitivity ◽  
Gas Production ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Chemical Enrichment ◽  
Evolved Stars ◽  
Wide Range ◽  
Nearby Galaxies ◽  
The Impact ◽  
High Metallicity

Molecules and dust are formed in and around the asymptotic giant branch (AGB) stars and supernovae (SNe), and are ejected into the interstellar medium (ISM) through the stellar wind. The dust and gas contain elements newly synthesised in stars, thus, dying stars play an important role in the chemical enrichment of the ISM of galaxies. However, quantitative analysis of molecules and dust in these stars had been difficult beyond our Galaxy. The high sensitivity instruments on-board the Spitzer Space Telescope (SST; Werner et al. 2004) have enabled us to study dust and molecules in these stars in nearby galaxies. Nearby galaxies have a wide range in metallicity, thus the impact of the metallicity on dust and gas production can be studied. This study will be useful for chemical evolution of galaxies from low to high metallicity.

scholarly journals Abundances in Local Group Planetary Nebulae

1995 ◽  
Vol 10 ◽  
pp. 480-482
Author(s):  
James B. Kaler
Keyword(s):  
Local Group ◽  
Initial Conditions ◽  
Planetary Nebulae ◽  
Magellanic Clouds ◽  
Chemical Compositions ◽  
Core Mass ◽  
Know How ◽  
Chemical Enrichment ◽  
Clear Link ◽  
The Galaxy

We are able to measure the chemical compositions of hundreds of planetary nebulae in our own Galaxy and in the Magellanic Clouds. Why, therefore, do we need to expend the effort to observe much more difficult targets in other Local Group galaxies? A severe lack of distances does not allow us to place Galactic planetary nuclei on the log L-log T plane with any degree of accuracy, so we cannot properly examine composition differences relative to core mass and state of evolution. We can perform such tasks for Magellanic Cloud objects, but do not know how the Clouds’ low-metallicities affect the results, and thus do not know how this sample of planetaries relates to the nebulae in our own system. We know, for example, that in the Clouds, nitrogen enrichment begins above a core mass of about 0.68 M⊙ (Kaler and Jacoby 1990), but other than a clear link between core mass and chemical enrichment in the Galaxy, do not know at what point it becomes important. To study such relationships, we therefore have to go to other galaxies with a variety of initial conditions for which distances are secure, namely those of the Local Group.

scholarly journals Molecular Evolution from AGB Stars to Planetary Nebulae

2011 ◽  
Vol 7 (S280) ◽  
pp. 203-215 ◽  
Author(s):  
Sun Kwok
Keyword(s):  
Chemical Synthesis ◽  
Stellar Evolution ◽  
Planetary Nebulae ◽  
Active Phase ◽  
Molecular Ions ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
The Galaxy ◽  
Short Time ◽  
Late Stages

AbstractThe late stages of stellar evolution from the Asymptotic Giant Branch (AGB) to planetary nebulae represent the most active phase of molecular synthesis in a star's life. Over 60 molecular species, including inorganics, organics, radicals, chains, rings, and molecular ions have been detected in the circumstellar envelopes of evolved stars. Most interestingly, complex organic compounds of aromatic and aliphatic structures are synthesized over very short time intervals after the end of the AGB. Also appeared during the post-AGB evolution are the unidentified 21 and 30 μm emission features, which are believed to originate from carbonaceous compounds.The circumstellar environment is an ideal laboratory for the testing of theories of chemical synthesis. The distinct spectral behavior among AGB stars, proto-planetary nebulae (PPN), and planetary nebulae (PN) and the short evolutionary time scales that separate these stages pose severe constraints on models. In this paper, we will present an observational summary of the chemical synthesis in the late stages of stellar evolution, discuss chemical and physical processes at work, and speculate on the possible effects these chemical products have on the Galaxy and the Solar System.

scholarly journals Observational Evidence Points at AGB Stars as Possible Progenitors of CEMP-s and CEMP-r/s Stars*

2021 ◽  
Vol 922 (1) ◽  
pp. 28
Author(s):  
Meenakshi Purandardas ◽  
Aruna Goswami
Keyword(s):  
Asymptotic Giant Branch ◽  
Chemical Compositions ◽  
Agb Stars ◽  
Surface Chemical ◽  
Chemical Enrichment ◽  
Group I ◽  
Internal Mixing ◽  
The Galaxy ◽  
Halo Population ◽  
First Time

Abstract The origin of enhanced abundance of heavy elements observed in the surface chemical composition of carbon-enhanced metal-poor (CEMP) stars still remains poorly understood. Here, we present detailed abundance analysis of seven CEMP stars based on high-resolution (R ∼ 50,000) spectra that reveal enough evidence of asymptotic giant branch (AGB) stars being possible progenitors for these objects. For the objects HE 0110−0406, HE 1425−2052, and HE 1428−1950, we present for the first time a detailed abundance analysis. Our sample is found to consist of one metal-poor ([Fe/H] < −1.0) and six very metal-poor ([Fe/H] < −2.0) stars with enhanced carbon and neutron-capture elements. We have critically analyzed the observed abundance ratios of [O/Fe], [Sr/Ba], and [hs/ls] and examined the possibility of AGB stars being possible progenitors. The abundance of oxygen estimated in the program stars is characteristic of AGB progenitors except for HE 1429−0551 and HE 1447+0102. The estimated values of [Sr/Ba] and [hs/ls] ratios also support AGB stars as possible progenitors. The locations of the program stars in the absolute carbon abundance A(C) versus [Fe/H] diagram, along with the Group I objects, hint at the binary nature of the object. We have studied the chemical enrichment histories of the program stars based on abundance ratios [Mg/C], [Sc/Mn], and [C/Cr]. Using [C/N] and 12C/13C ratios, we have examined whether any internal mixing had modified their surface chemical compositions. Kinematic analysis shows that the objects HE 0110−0406 and HE 1447+0102 are thick-disk objects and the remaining five objects belong to the halo population of the Galaxy.

Evolutionary versus dynamical time scales for the evolution of the central stars of planetary nebulae

1990 ◽  
Vol 351 ◽  
pp. 230 ◽  
Author(s):  
J. K. McCarthy ◽  
J. R. Mould ◽  
R. H. Mendez ◽  
R. P. Kudritzki ◽  
D. Husfeld ◽  
...  
Keyword(s):  
Time Scales ◽  
Planetary Nebulae ◽  
Dynamical Time ◽  
Central Stars

scholarly journals The timescales of chemical enrichment in the Galaxy

2008 ◽  
Vol 4 (S258) ◽  
pp. 39-50
Author(s):  
Antonio Pipino ◽  
Francesca Matteucci
Keyword(s):  
Star Formation ◽  
Time Delay ◽  
Time Scales ◽  
Galaxy Formation ◽  
Star Formation History ◽  
Delay Model ◽  
Galactocentric Distance ◽  
Chemical Enrichment ◽  
The Galaxy ◽  
Hubble Time

AbstractThe time-scales of chemical enrichment are fundamental to understand the evolution of abundances and abundance ratios in galaxies. In particular, the time-scales for the enrichment by SNe II and SNe Ia are crucial in interpreting the evolution of abundance ratios such as [α/Fe]. In fact, the α-elements are produced mainly by SNe II on time-scales of the order of 3 to 30 Myr, whereas the Fe is mainly produced by SNe Ia on a larger range of time-scales, going from 30 Myr to a Hubble time. This produces differences in the [α/Fe] ratios at high and low redshift and it is known as “time-delay” model. In this talk we review the most common progenitor models for SNe Ia and the derived rates together with the effect of the star formation history on the [α/Fe] versus [Fe/H] diagram in the Galaxy. From these diagrams we can derive the timescale for the formation of the inner halo (roughly 2 Gyr), the timescale for the formation of the local disk (roughly 7-8 Gyr) as well the time-scales for the formation of the whole disk. These are functions of the galactocentric distance and vary from 2-3 Gyr in the inner disk up to a Hubble time in the outer disk (inside-out formation). Finally, the timescale for the formation of the bulge is found to be no longer than 0.3 Gyr, similar to the timescale for the formation of larger spheroids such as elliptical galaxies. We show the time-delay model applied to galaxies of different morphological type, identified by different star formation histories, and how it constrains differing galaxy formation models.

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