New IR-Observations of Post AGB Stars and Proto-Planetary Nebulae

A sample was selected from the IRAS Point Source Catalogue based on the following selection criteria: very red (“cold”) IRAS-colours: roughly F25/F12 > 2.5 and F60/F25 < 1.2; and low IR-variability: VAR < 30. These non-variable IR-sources may be stars that have evolved beyond the AGB (Asymptotic Giant Branch); a large fraction (40%) is associated with known planetary nebulae (Van der Veen and Habing, 1987, Astron. Astrophys., in press). To determine the nature of the other 60% additional observations were made mainly in the infrared: 1–13 μm, during 4 observing runs: ESO (La Silla, Chile) in July 1986 and June 1987; UKIRT (Hawaii) in August 1986 and June 1987. A total number of 58 sources was observed. A summary of the observations: -IR broad band photometry at 1.2, 1.6, 2.2, 3.8 and 4,6 μm for all 58 sources. -IR broad band photometry at 8.4, 9.7 and 12.8 μm for 19 sources. -IR small band photometry for 4 sources in the ranges 2–2.5 μm and 3–3.5 μm. -IR spectroscopy for 10 sources in the ranges 2–2.5 μm and 3–3.5 μm, -V, R, I observations (0.55, 0.7 and 0.9 μm) for 5 sources associated with a star of visual magnitude 8–9. These observations were carried out by D. de Winter (Amsterdam) with the 0.5-m ESO telescope at La Silla (Chile). -Walraven photometry (0.32, 0.36, 0.38, 0.43 and 0.54 μm) for 21 stars brighter than V = 15 and within 10“ from the IRAS position. These observations were carried out by M. van Haarlem (Leiden) with the 0.9-m Dutch telescope at La Silla (Chile).

Download Full-text

Visual and Near-Infrared Photometry of Nearby Dwarf Spheroidals

Symposium - International Astronomical Union ◽

10.1017/s0074180900204506 ◽

1999 ◽

Vol 192 ◽

pp. 455-458 ◽

Cited By ~ 1

Author(s):

F. Kerschbaum ◽

W. Nowotny ◽

J. Hron ◽

M. Schultheis

Keyword(s):

Near Infrared ◽

Broad Band ◽

Feasibility Studies ◽

Asymptotic Giant Branch ◽

Agb Stars ◽

Faint Object ◽

Nearby Galaxies ◽

Dwarf Spheroidals ◽

Faint Object Spectrograph ◽

Infrared Survey

This paper is based on photometry from two different observational approaches. Both are of an explorative character and act as feasibility studies. For the future we plan to use these methods to study Asymptotic Giant Branch (AGB) stars in nearby galaxies.First, we present results on broad-band photometry in Bessell V and I, as well as narrow-band measurements in the Wing 778 nm and 812 nm filters of a galactic globular cluster using the new Austrian Oe-FOSC (Oesterreich Faint Object Spectrograph and Camera), a copy of the ESO Instrument EFOSC mounted on our 1.5 m-telescope.The second part of the contribution deals with the possibilities of using Gunn I, J and KS measurements originating from the DENIS (DEep Near Infrared Survey of the Southern Sky) project on similar objects. A few southern dwarf spheroidals already observed within DENIS (covering now some 40% of the southern hemisphere) are selected.

Download Full-text

Heavy elements in planetary nebulae: A theorist's gold mine

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312010824 ◽

2011 ◽

Vol 7 (S283) ◽

pp. 127-130

Author(s):

Amanda I. Karakas ◽

Maria Lugaro

Keyword(s):

Neutron Capture ◽

Planetary Nebulae ◽

Asymptotic Giant Branch ◽

Heavy Elements ◽

Gold Mine ◽

Agb Stars ◽

Capture Process ◽

Wide Range ◽

Model Predictions

AbstractObservations of planetary nebulae have revealed a wealth of information about the composition of heavy elements synthesized by the slow neutron capture process (the s process). In some of these nebulae the abundances of neutron-capture elements are enriched by factors of 10 to 30 times the solar value, indicating that these elements were produced in the progenitor star while it was on the asymptotic giant branch (AGB). In this proceedings we summarize results of our recent full s-process network predictions covering a wide range of progenitor masses and metallicities. We compare our model predictions to observations and show how this can provide important insights into nucleosynthesis processes occurring deep within AGB stars.

Download Full-text

Improved Neutron-Capture Element Abundances in Planetary Nebulae

Publications of the Astronomical Society of Australia ◽

10.1071/as08067 ◽

2009 ◽

Vol 26 (3) ◽

pp. 339-344 ◽

Cited By ~ 19

Author(s):

N. C. Sterling ◽

H. L. Dinerstein ◽

S. Hwang ◽

S. Redfield ◽

A. Aguilar ◽

...

Keyword(s):

Cross Sections ◽

Planetary Nebulae ◽

Asymptotic Giant Branch ◽

Rate Coefficients ◽

Atomic Data ◽

Agb Stars ◽

Iron Species ◽

Element Abundances ◽

Ionization Balance ◽

Initial Results

AbstractSpectroscopy of planetary nebulae (PNe) provides the means to investigate s-process enrichments of neutron(n)-capture elements that cannot be detected in Asymptotic Giant Branch (AGB) stars. However, accurate abundance determinations of these elements present a challenge. Corrections for unobserved ions can be large and uncertain, since in many PNe only one ion of a given n-capture element has been detected. Furthermore, the atomic data governing the ionization balance of these species are not well-determined, inhibiting the derivation of accurate ionization corrections. We present initial results of a program that addresses these challenges. Deep high-resolution optical spectroscopy of ∼20 PNe has been performed to detect emission lines from trans-iron species including Se, Br, Kr, Rb and Xe. The optical spectral region provides access to multiple ions of these elements, which reduces the magnitude and importance of uncertainties in the ionization corrections. In addition, experimental and theoretical efforts are providing determinations of the photoionization cross sections and recombination rate coefficients of Se, Kr and Xe ions. These new atomic data will make it possible to derive robust ionization corrections for these elements. Together, our observational and atomic data results will enable n-capture element abundances to be determined with unprecedented accuracy in ionized nebulae.

Download Full-text

Wind morphology around cool evolved stars in binaries

Astronomy and Astrophysics ◽

10.1051/0004-6361/202037492 ◽

2020 ◽

Vol 637 ◽

pp. A91 ◽

Cited By ~ 5

Author(s):

I. El Mellah ◽

J. Bolte ◽

L. Decin ◽

W. Homan ◽

R. Keppens

Keyword(s):

Mass Loss ◽

Adaptive Mesh Refinement ◽

Loss Rate ◽

Main Sequence ◽

Mass Loss Rate ◽

Large Fraction ◽

Orbital Plane ◽

Asymptotic Giant Branch ◽

Agb Stars ◽

Evolved Stars

Context. The late evolutionary phase of low- and intermediate-mass stars is strongly constrained by their mass-loss rate, which is orders of magnitude higher than during the main sequence. The wind surrounding these cool expanded stars frequently shows nonspherical symmetry, which is thought to be due to an unseen companion orbiting the donor star. The imprints left in the outflow carry information about the companion and also the launching mechanism of these dust-driven winds. Aims. We study the morphology of the circumbinary envelope and identify the conditions of formation of a wind-captured disk around the companion. Long-term orbital changes induced by mass loss and mass transfer to the secondary are also investigated. We pay particular attention to oxygen-rich, that is slowly accelerating, outflows in order to look for systematic differences between the dynamics of the wind around carbon and oxygen-rich asymptotic giant branch (AGB) stars. Methods. We present a model based on a parametrized wind acceleration and a reduced number of dimensionless parameters to connect the wind morphology to the properties of the underlying binary system. Thanks to the high performance code MPI-AMRVAC, we ran an extensive set of 72 three-dimensional hydrodynamics simulations of a progressively accelerating wind propagating in the Roche potential of a mass-losing evolved star in orbit with a main sequence companion. The highly adaptive mesh refinement that we used, enabled us to resolve the flow structure both in the immediate vicinity of the secondary, where bow shocks, outflows, and wind-captured disks form, and up to 40 orbital separations, where spiral arms, arcs, and equatorial density enhancements develop. Results. When the companion is deeply engulfed in the wind, the lower terminal wind speeds and more progressive wind acceleration around oxygen-rich AGB stars make them more prone than carbon-rich AGB stars to display more disturbed outflows, a disk-like structure around the companion, and a wind concentrated in the orbital plane. In these configurations, a large fraction of the wind is captured by the companion, which leads to a significant shrinking of the orbit over the mass-loss timescale, if the donor star is at least a few times more massive than its companion. In the other cases, an increase of the orbital separation is to be expected, though at a rate lower than the mass-loss rate of the donor star. Provided the companion has a mass of at least a tenth of the mass of the donor star, it can compress the wind in the orbital plane up to large distances. Conclusions. The grid of models that we computed covers a wide scope of configurations: We vary the terminal wind speed relative to the orbital speed, the extension of the dust condensation region around the cool evolved star relative to the orbital separation, and the mass ratio, and we consider a carbon-rich and an oxygen-rich donor star. It provides a convenient frame of reference to interpret high-resolution maps of the outflows surrounding cool evolved stars.

Download Full-text

New models for the evolution of central stars of planetary nebulae: Faster and Brighter

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317001533 ◽

2016 ◽

Vol 12 (S323) ◽

pp. 179-183

Author(s):

Marcelo M. Miller Bertolami

Keyword(s):

Planetary Nebulae ◽

Asymptotic Giant Branch ◽

Agb Stars ◽

Intermediate Mass ◽

Short Article ◽

Intermediate Mass Stars ◽

New Models ◽

Central Stars

AbstractThe post-asymptotic giant branch (AGB) phase is arguably one of the least understood phases of the evolution of low- and intermediate- mass stars. The recent post-AGB evolutionary sequences computed by Miller Bertolami (2016) are at least three to ten times faster than those previously published by Vassiliadis & Wood (1994) and Blöcker (1995) which have been used in a large number of studies. This is true for the whole mass and metallicity range. The new models are also ~0.1–0.3 dex brighter than the previous models with similar remnant masses. In this short article we comment on the main reasons behind these differences, and discuss possible implications for other studies of post-AGB stars or planetary nebulae.

Download Full-text

Silicon Carbide as the Carrier of the 21μm Feature

Symposium - International Astronomical Union ◽

10.1017/s0074180900208899 ◽

2003 ◽

Vol 209 ◽

pp. 315-315

Author(s):

A. K. Speck ◽

A. M. Hofmeister

Keyword(s):

Silicon Carbide ◽

Solid State ◽

Ir Spectra ◽

Planetary Nebulae ◽

Asymptotic Giant Branch ◽

Agb Stars ◽

Transient Species ◽

Physical Conditions ◽

Show Evidence ◽

Central Stars

Some proto-planetary nebulae (PPNe) exhibit an enigmatic feature in their infrared (IR) spectra at ~21 μm. PPNe which display this feature are all C-rich and all show evidence for s-process enhancements in their photospheres, indicative of efficient dredge-up during the ascent of the asymptotic giant branch (AGB). Furthermore, this 21 μm feature is not seen in the spectra of either the precursors to PPNe, the AGB stars, or the successors of PPNe, planetary nebulae (PNe). However the 21 μm feature has been seen in the spectra of PNe with Wolf-Rayet central stars. Therefore the carrier of this feature is unlikely to be a transient species that only exists in the PPNe phase. It is more likely that the physical conditions in the AGB stars and PNe conspire against the observation of an IR feature at 21 μm. This feature has been attributed to various molecular and solid state species, none of which satisfy all constraints, although TiC and PAHs have seemed the most viable.

Download Full-text

On the Origin of the 21 Micron Feature in Post-AGB Stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900203203 ◽

1999 ◽

Vol 191 ◽

pp. 297-302 ◽

Cited By ~ 6

Author(s):

Sun Kwok ◽

Kevin Volk ◽

Bruce J. Hrivnak

Keyword(s):

Planetary Nebulae ◽

Emission Feature ◽

Asymptotic Giant Branch ◽

Agb Stars

The unidentified emission feature at 21 μm is now observed in 12 sources, all being objects in transition between the asymptotic giant branch and planetary nebulae phases. The relations between the 21 μm and other emission features, such as the PAH features and the broad 30 μm feature, and the possible origins of the 21 μm feature are discussed.

Download Full-text

Luminosities and mass-loss rates of Local Group AGB stars and red supergiants

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731089 ◽

2018 ◽

Vol 609 ◽

pp. A114 ◽

Cited By ~ 24

Author(s):

M. A. T. Groenewegen ◽

G. C. Sloan

Keyword(s):

Radiative Transfer ◽

Mass Loss ◽

Local Group ◽

Mass Loss Rate ◽

Large Fraction ◽

Large Magellanic Cloud ◽

Asymptotic Giant Branch ◽

Spectral Energy ◽

Agb Stars ◽

Evolved Stars

Context. Mass loss is one of the fundamental properties of asymptotic giant branch (AGB) stars, and through the enrichment of the interstellar medium, AGB stars are key players in the life cycle of dust and gas in the universe. However, a quantitative understanding of the mass-loss process is still largely lacking. Aims. We aim to investigate mass loss and luminosity in a large sample of evolved stars in several Local Group galaxies with a variety of metalliticies and star-formation histories: the Small and Large Magellanic Cloud, and the Fornax, Carina, and Sculptor dwarf spheroidal galaxies (dSphs). Methods. Dust radiative transfer models are presented for 225 carbon stars and 171 oxygen-rich evolved stars in several Local Group galaxies for which spectra from the Infrared Spectrograph on Spitzer are available. The spectra are complemented with available optical and infrared photometry to construct spectral energy distributions. A minimization procedure was used to determine luminosity and mass-loss rate (MLR). Pulsation periods were derived for a large fraction of the sample based on a re-analysis of existing data. Results. New deep K-band photometry from the VMC survey and multi-epoch data from IRAC (at 4.5 μm) and AllWISE and NEOWISE have allowed us to derive pulsation periods longer than 1000 days for some of the most heavily obscured and reddened objects. We derive (dust) MLRs and luminosities for the entire sample. The estimated MLRs can differ significantly from estimates for the same objects in the literature due to differences in adopted optical constants (up to factors of several) and details in the radiative transfer modelling. Updated parameters for the super-AGB candidate MSX SMC 055 (IRAS 00483−7347) are presented. Its current mass is estimated to be 8.5 ± 1.6 M⊙, suggesting an initial mass well above 8 M⊙ in agreement with estimates based on its large Rubidium abundance. Using synthetic photometry, we present and discuss colour-colour and colour-magnitude diagrams which can be expected from the James Webb Space Telescope.

Download Full-text

Molecular Evolution from AGB Stars to Planetary Nebulae

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311024987 ◽

2011 ◽

Vol 7 (S280) ◽

pp. 203-215 ◽

Cited By ~ 2

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.

Download Full-text

Long-period variable AGB stars in a field towards the Galactic Bulge

Symposium - International Astronomical Union ◽

10.1017/s0074180900123307 ◽

1993 ◽

Vol 153 ◽

pp. 291-292

Author(s):

J.A.D.L. Blommaert ◽

A.G.A. Brown ◽

H.J. Habing ◽

W.E.C.J. van der Veen ◽

Y.K. Ng

Keyword(s):

Mass Loss ◽

Large Fraction ◽

Asymptotic Giant Branch ◽

Agb Stars ◽

Galactic Bulge ◽

Long Period ◽

Infrared Measurements ◽

Period Variable ◽

Optically Detected ◽

Late Stages

We study two different samples of long-period variable Asymptotic Giant Branch (AGB) stars in a field of low and homogeneous extinction towards the Galactic bulge, the Palomar-Groningen field Nr. 3. The samples were selected to study the evolution of the late phases on the AGB. One sample consists of 486 variables (mostly Miras) optically detected and studied by Plaut (1971) and by Wesselink (1987). The other sample is selected from the IRAS Point Source Catalogue and consists of 239 sources. We made additional infrared measurements between 1.2 and 13 μm for a large fraction of both samples. This information was used to identify the IRAS sources and derive the apparent bolometric magnitudes. The samples of Miras and variable IRAS sources have a similar apparent bolometric magnitude distributions, but are displaced by an amount significantly less than expected from the Mira period-luminosity relation (Feast et al. 1989; 0.3 magnitudes as opposed to 0.6 magnitudes). The surface density distribution along the minor axis of the bulge is the same for both samples. We conclude that both samples have evolved from the same parent population and that they represent different evolutionary stages on the AGB. The IRAS sources with the longer periods (on average 450 days (Whitelock et al. 1991) versus on average 250 days for the optical sample) are the further evolved objects. As the IRAS sources have higher mass loss rates we conclude that mass loss increases during the late stages of the evolution. However, we find indications that in some stars the mass loss process has been interrupted for some time; mass loss could be an intermittent process although its overall rate increases in time.

Download Full-text