Abundances in intermediate-mass AGB stars undergoing third dredge-up and hot-bottom burning

Abstract

High dispersion near-infrared spectra have been taken of seven highly-evolved, variable, intermediate-mass (4-6 Msun) AGB stars in the LMC and SMC in order to look for C, N and O variations that are expected to arise from third dredge-up and hot-bottom burning. The pulsation of the objects has been modelled, yielding stellar masses, and spectral synthesis calculations have been performed in order to derive abundances from the observed spectra. For two stars, abundances of C, N, O, Na, Al, Ti, Sc and Fe were derived and compared with the abundances predicted by detailed AGB models. Both stars show very large N enhancements and C deficiencies. These results provide the first observational confirmation of the long-predicted production of primary nitrogen by the combination of third dredge-up and hot-bottom burning in intermediate-mass AGB stars. It was not possible to derive abundances for the remaining five stars: three were too cool to model, while another two had strong shocks in their atmospheres which caused strong emission to fill the line cores and made abundance determination impossible. The latter occurrence allows us to predict the pulsation phase interval during which observations should be made if successful abundance analysis is to be possible.

Accepted for publication in MNRAS

References in corpus (10)

• Improved Color-Temperature Relations and Bolometric Corrections for Cool Stars
• Bump Cepheids in the Magellanic Clouds: Metallicities, the Distances to the LMC and SMC, and the Pulsation-Evolution Mass Discrepancy
• Abundances in Spiral Galaxies: Evidence for Primary Nitrogen Production
• Synthetic Spectra and Color-Temperature Relations of M Giants
• Chemical Abundances in Twelve Red Giants of the Large Magellanic Cloud from High-Resolution Infrared Spectroscopy
• Oxygen Abundances in Metal-Poor Stars (-2.2 < [Fe/H] < -1.2) from Infrared OH lines
• The luminosity function of the Large Magellanic Cloud globular cluster NGC 1866
• Pulsation of M-type Mira variables with moderately different mass: search for observable mass effects
• Observable Effects of Dust Formation in Dynamic Atmospheres of M-type Mira Variables
• Lithium during the AGB evolution in young open clusters of the Large Magellanic cloud

Cited by in corpus (40)

• The Dawes Review 2: Nucleosynthesis and stellar yields of low and intermediate-mass single stars
• Evolution, nucleosynthesis and yields of AGB stars at different metallicities (III): intermediate mass models, revised low mass models and the ph-FRUITY interface
• What is a globular cluster? An observational perspective
• Low-temperature gas opacity - AESOPUS: a versatile and quick computational tool
• Super and Massive AGB Stars: II - Nucleosynthesis and Yields - Z=0.02, 0.008 and 0.004
• Super and massive AGB stars - III. Nucleosynthesis in metal-poor and very metal-poor stars - Z=0.001 and 0.0001
• Heavy-element yields and abundances of Asymptotic Giant Branch models with a Small Magellanic Cloud metallicity
• A Spitzer Space Telescope far-infrared spectral atlas of compact sources in the Magellanic Clouds. I. The Large Magellanic Cloud
• The ASAS-SN Catalog of Variable Stars IX: The Spectroscopic Properties of Galactic Variable Stars
• NGC 1866: a milestone for understanding the chemical evolution of stellar populations in the LMC
• Carbon and oxygen isotopic ratios for nearby miras
• A Spitzer Space Telescope far-infrared spectral atlas of compact sources in the Magellanic Clouds. II. The Small Magellanic Cloud
• New light on Galactic post-asymptotic giant branch stars. I. First distance catalogue
• Suzaku Observations of the North Polar Spur: Evidence for Nitrogen Enhancement
• The Large Magellanic Cloud as a laboratory for Hot Bottom Burning in massive Asymptotic Giant Branch stars
• Short-lived radioactivity in the early Solar System: the Super-AGB star hypothesis
• Confronting uncertainties in stellar physics II. exploring differences in main-sequence stellar evolution tracks
• The evolutionary state of Miras with changing pulsation periods
• On the alumina dust production in the winds of O-rich Asymptotic Giant Branch stars
• Properties of carbon stars in the Solar neighbourhood based on Gaia DR2 astrometry
• The Hamburg/ESO R-process Enhanced Star survey (HERES) VIII. The r+s star HE 1405 0822
• On the necessity of composition-dependent low-temperature opacity in metal-poor AGB stars
• On the internal pollution mechanisms in the globular cluster NGC 6121 (M4): heavy-element abundances and AGB models
• From the CMD of Omega Centauri and (super-)AGB stellar models to a Galactic plane passage gas purging chemical evolution scenario
• Evolution and nucleosynthesis of helium-rich asymptotic giant branch models
• The puzzling dredge-up pattern in NGC 1978
• Period-luminosity diagram of long period variables in the Magellanic Clouds. New aspects revealed from Gaia Data Release 2
• Abundance analysis for long-period variables II. RGB and AGB stars in the globular cluster 47\,Tuc
• New Post-AGB star models as tools to understand AGB evolution and nucleosynthesis
• Understanding AGB evolution in Galactic bulge stars from high-resolution infrared spectroscopy
• Analysis of the infrared spectra of the peculiar post-AGB stars EPLyr and HD52961
• Rubidium and zirconium abundances in massive Galactic asymptotic giant branch stars revisited
• Carbon stars with increased oxygen and nitrogen abundances: hydrostatic dust-free model atmospheres
• First detection of CO lines in a water fountain star
• Supernova 1604, Kepler's supernova, and its remnant
• Testing the AGB Scenario as the Origin of the Extreme-Helium Population in omega Centauri
• Abundance analysis for long period variables. Velocity effects studied with O-rich dynamic model atmospheres
• Spectroscopic study of four metal-poor carbon stars from the Hamburg/ESO Survey: On confirming the low-mass nature of their companions
• Exploring circumstellar effects on the lithium and calcium abundances in massive Galactic O-rich AGB stars
• Prospects of Stellar Abundance Studies from Near-IR Spectra Observed with the E-ELT