AGB Stars as Tracers of Star Formation Histories: Implications for GAIA Photometry and Spectroscopy (original) (raw)
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AGB Stars as Tracers of Star Formation Histories
2002
We argue that tracing star formation histories with GAIA using main sequence turn-off (MSTO) point dating will mainly be effective in cases of very mild interstellar extinction (E B−V < 0.5). For higher reddenings the MSTO approach will be severely limited both in terms of traceable ages (t < 0.5 Gyr at 8 kpc; E B−V = 1.0) and/or distances (d = 2 kpc if t ≤ 15 Gyr; E B−V = 1.0), since the MSTO will be located at magnitudes too faint for GAIA. AGB stars may alternatively provide precise population ages with GAIA for a wide range of ages and metallicities, with traceable distances of up to 250 kpc at E B−V = 0 (15 kpc if E B−V = 2.0). It is essential however that effective temperatures, metallicities, and reddenings of individual stars are derived with the precision of σ(log T eff) ∼ 0.01, σ([M/H]) ∼ 0.2, and σ(E B−V) ∼ 0.03, to obtain σ(log t) ∼ 0.15. This task is quite challenging for GAIA photometry and spectroscopy, though preliminary tests show that comparable precisions may be achieved with GAIA medium band photometry.
GAIA: AGB Stars as Tracers of Star Formation Histories in the Galaxy and Beyond
Astrophysics and Space Science Library, 2003
We discuss the tracing of star formation histories with ESA's space astrometry mission GAIA, emphasizing the advantages of AGB stars for this purpose. GAIA's microarcsecond-level astrometry, multi-band photometry and spectroscopy will provide individual distances, motions, T eff , log g and [M/H] for vast numbers of AGB stars in the Galaxy and beyond. Reliable ages of AGB stars can be determined to distances of ∼200 kpc in a wide range of ages and metallicities, allowing star formation histories to be studied in a diversity of astrophysical environments.
The promise of Gaia and how it will influence stellar ages
Proceedings of the International Astronomical Union, 2008
The Gaia space project, planned for launch in 2011, is one of the ESA cornerstone missions, and will provide astrometric, photometric and spectroscopic data of very high quality for about one billion stars brighter than V = 20. This will allow to reach an unprecedented level of information and knowledge on several of the most fundamental astrophysical issues, such as mapping of the Milky Way, stellar physics (classification and parameterization), Galactic kinematics and dynamics, study of the resolved stellar populations in the Local Group, distance scale and age of the Universe, dark matter distribution (potential tracers), reference frame (quasars, astrometry), planet detection, fundamental physics, Solar physics, Solar system science.I will present a description of the instrument and its main characteristics, and discuss a few specific science cases where Gaia data promise to contribute fundamental improvement within the scope of this Symposium.
Astronomy & Astrophysics
Context.Gaia’s third data release provides radial velocities for 33 million stars and spectroscopically derived atmospheric parameters for more than 5 million targets. When combined with the astrometric data, these allow us to derive orbital and stellar parameters that are key to understanding the stellar populations of the Milky Way and to perform Galactic archaeology. Aims. We used the calibrated atmospheric parameters, 2MASS and Gaia-EDR3 photometry, and parallax-based distances to compute the ages, initial stellar masses, and reddenings for the stars with spectroscopic parameters. We also derived the orbits for all of the stars with measured radial velocities and astrometry, adopting two sets of line-of-sight distances from the literature. Methods. Four different sets of ages, masses, and absolute magnitudes in different photometric bands are obtained through an isochrone fitting method, considering different combinations of input parameters. The reddenings are obtained by compa...
AGB stars as tracers of metallicity and mean age across M 33
Astronomy and Astrophysics, 2009
Context. Wide-field JHK s near-infrared observations covering an area of 1.8 • × 1.8 • centred on M 33 were obtained using WFCAM at UKIRT. These data show a large population of intermediate-age asymptotic giant branch (AGB) stars. Aims. We have used both C-type and M-type AGB stars to determine spatial variations in metallicity and mean age across the galaxy. Methods. We distinguished between C-type and M-type AGB stars from their location in the colour-magnitude diagram (J − K s , K s). The distribution of these stars is supported by a cross-identification between our sample and a catalogue of optically confirmed, long-period variable stars, as well as with the list of sources detected by Spitzer in the mid-infrared. We calculated the C/M ratio and the orientation of the galaxy in the sky, and compared the K s magnitude distribution with theoretical distributions spanning a range of metallicities and star formation rates (SFRs). Results. The C/M ratio surface map confirms a metallicity gradient in the galaxy corresponding to a spread in [Fe/H] = 0.6 dex with substructures in the inner and outer galaxy. Magnitude and colour variations suggest orientation and extinction effects on the galaxy disc. Maps showing the distribution of mean age and metallicity obtained from the K s method suggest that: the outer galaxy disc/halo is metal poorer than the nuclear region and metal-rich clumps in the inner galaxy change location with time. The average outer ring and nuclear stellar population is ∼6 Gyr old while central regions are a few Gyr younger.
Searching for the first stars with the Gaia mission
Astronomy & Astrophysics, 2012
We construct a theoretical model to predict the number of orphan afterglows (OA) from gamma-ray bursts (GRBs) triggered by primordial metal-free (Pop III) stars expected to be observed by the Gaia mission. In particular, we consider primordial metal-free stars that were affected by radiation from other stars (Pop III.2) as a possible target. Methods. We use a semi-analytical approach that includes all relevant feedback effects to construct cosmic star formation history and its connection with the cumulative number of GRBs. The OA events are generated using the Monte Carlo method, and realistic simulations of Gaia's scanning law are performed to derive the observation probability expectation. Results. We show that Gaia can observe up to 2.28 ± 0.88 off-axis afterglows and 2.78 ± 1.41 on-axis during the five-year nominal mission. This implies that a nonnegligible percentage of afterglows that may be observed by Gaia (∼ 10%) could have Pop III stars as progenitors.
arXiv (Cornell University), 2021
Post-AGB stars are exquisite probes of AGB nucleosynthesis. However, the previous lack of accurate distances jeopardised comparison with theoretical AGB models. The Gaia Early Data Release 3 (Gaia EDR3) has now allowed for a breakthrough in this research landscape. In this study, we focus on a sample of single Galactic post-AGBs for which chemical abundance studies were completed. We combined photometry with geometric distances to carry out a spectral energy distribution (SED) analysis and derive accurate luminosities. We subsequently determined their positions on the HRdiagram and compared this with theoretical post-AGB evolutionary tracks. While most objects are in the post-AGB phase of evolution, we found a subset of low-luminosity objects that are likely to be in the post-horizontal branch phase of evolution, similar to AGB-manqué objects found in globular clusters. Additionally, we also investigated the observed bi-modality in the s-process enrichment of Galactic post-AGB single stars of similar T eff and metallicities. This bi-modality was expected to be a direct consequence of luminosity with the s-process rich objects having evolved further on the AGB. However, we find that the two populations: the s-process enriched and non-enriched, have similar luminosities (and hence initial masses), revealing an intriguing chemical diversity. For a given initial mass and metallicity, AGB nucleosynthesis appears inhomogeneous and sensitive to other factors which could be mass-loss, along with convective and non-convective mixing mechanisms. Modelling individual objects in detail will be needed to investigate which parameters and processes dominate the photospheric chemical enrichment in these stars.
Studying the evolution of AGB stars in theGaiaepoch
Monthly Notices of the Royal Astronomical Society, 2016
We present asymptotic giant branch (AGB) models of solar metallicity, to allow the interpretation of observations of Galactic AGB stars, whose distances should be soon available after the first release of the Gaia catalogue. We find an abrupt change in the AGB physical and chemical properties, occurring at the threshold mass to ignite hot bottom burning, i.e. 3.5 M. Stars with mass below 3.5 M reach the C-star stage and eject into the interstellar medium gas enriched in carbon, nitrogen and 17 O. The higher mass counterparts evolve at large luminosities, between 3 × 10 4 and 10 5 L. The mass expelled from the massive AGB stars shows the imprinting of proton-capture nucleosynthesis, with considerable production of nitrogen and sodium and destruction of 12 C and 18 O. The comparison with the most recent results from other research groups is discussed, to evaluate the robustness of the present findings. Finally, we compare the models with recent observations of galactic AGB stars, outlining the possibility offered by Gaia to shed new light on the evolution properties of this class of objects.
Probing stellar evolution with S stars and Gaia
Proceedings of the International Astronomical Union, 2018
S-type stars are late-type giants enhanced with s-process elements originating either from nucleosynthesis during the Asymptotic Giant Branch (AGB) or from a pollution by a binary companion. The former are called intrinsic S stars, and the latter extrinsic S stars. The intrinsic S stars are on the AGB and have undergone third dredge-up events. The atmospheric parameters of S stars are more numerous than those of M-type giants (C/O ratio and s-process abundances affect the thermal structure and spectral synthesis), and hence they are more difficult to derive. These atmospheric parameters are also entangled within each other. Nevertheless, high-resolution spectroscopic data of S stars combined with the Gaia Data Release 2 (GDR2) parallaxes and with the MARCS model atmospheres for S-type stars were used to derive effective temperatures, surface gravities, and luminosities. These parameters not only allow to locate the intrinsic and extrinsic S stars in the Hertzsprung-Russell (HR) diag...
Nucleosynthesis in AGB stars traced by oxygen isotopic ratios
Astronomy & Astrophysics, 2017
Aims. We seek to investigate the 17 O/ 18 O ratio for a sample of AGB stars containing M-, Sand nd C-type stars. These ratios are evaluated in relation to fundamental stellar evolution parameters: the stellar initial mass and pulsation period. Methods. Circumstellar 13 C 16 O, 12 C 17 O, and 12 C 18 O line observations were obtained for a sample of nine stars with various singledish long-wavelength facilities. Line intensity ratios are shown to relate directly to the surface 17 O/ 18 O abundance ratio. Results. Stellar evolution models predict the 17 O/ 18 O ratio to be a sensitive function of initial mass and to remain constant throughout the entire TP-AGB phase for stars initially less massive than 5 M. This makes the measured ratio a probe of the initial stellar mass. Conclusions. Observed 17 O/ 18 O ratios are found to be well in the range predicted by stellar evolution models that do not consider convective overshooting. From this, accurate initial mass estimates are calculated for seven sources. For the remaining two sources, there are two mass solutions, although there is a larger probability that the low-mass solution is correct. Finally, we present hints at a possible separation between M/S-and C-type stars when comparing the 17 O/ 18 O ratio to the stellar pulsation period.