1,721,176 research outputs found
The Contribution of Asymptotic Giant Branch Stars to the Infrared Luminosities of Galaxies
Full text linkUsing resolved stellar photometry in Hubble Space Telescope WFC3 images of 22 nearby galaxies, we measure the fraction of near-infrared (NIR) luminosity produced by short-lived asymptotic giant branch (AGB) stars. While AGB stars represent a negligible number fraction of stars in a given galaxy, they can contribute as much as 30% of the total NIR flux, even though local galaxies have large populations of red giant branch stars. In the early Universe, the AGB contribution to the total IR luminosity could be as high as 80%. For younger metal-rich galaxies, the AGB models used in this study tend to under-predict the contribution of the AGB to the galaxy's luminosity (at NIR wavelengths). The same models tend to over-predict the AGB for old metal-poor systems
Semi-regular red giants as distance indicators
Full text linkContext. Semi-regular variables (SRVs) are similar to Miras in brightness, and they also follow one or more period–luminosity relations (PLRs), though not necessarily the same one as Miras. As potential standard candles they are more challenging than Miras because of their smaller variability amplitudes and less regular light curves, but they are substantially more numerous and especially promising for probing old stellar populations.
Aims. We aim to characterise the variability of SRVs, specifically focusing on their connection with Miras, in order to prepare the ground for investigating their potential as distance indicators.
Methods. We examine SRVs and Miras in the Magellanic Clouds from OGLE-III observations, with data from Gaia and 2MASS. After cleaning the sample of variability periods unrelated to pulsation, we classify each source by chemical type and combination of pulsation modes. We examine the results in terms of global photometric and pulsation properties.
Results. We identify four SRV groups that fit the general evolutionary scenario predicted by theory. SRVs dominated by fundamental-mode pulsation are very similar to Miras, especially if mono-periodic. They further split into two subgroups, one of which follows the same sequence as Miras in the period–luminosity and period–amplitude diagrams, without discontinuity.
Conclusions. The similarities between Miras and SRVs suggest that the latter can be adopted as distance indicators in a way that is complementary to the use of the former, thereby at least doubling the available number of long-period variables (LPVs) suitable for use as distance indicators. The traditional amplitude-based separation between Miras and SRVs is not necessarily appropriate, and a more physically sound criterion should also involve pulsation periods. While this would require comparatively longer time-series, they are expected to become accessible in the coming years even for weak sources thanks to current and future large-scale surveys. The table of reclassified LPVs is made public
Modelling Long-Period Variables in the Gaia Era
Full text linkLuminous red giant stars exhibit variability due to stellar pulsation, that is interconnected with uncertain processes (convection, mass loss and dust formation) and results in observable features that are strongly related to stellar properties. These so-called long-period variables (LPVs) provide us with a powerful tool to infer global stellar parameters and constrain the physics of late evolutionary phases in intermediate- and old-age stellar populations. Moreover, their period-luminosity relations represent a highly promising distance indicator. Large-scale optical microlensing surveys carried out during the last few decades made ideal laboratories out of the Magellanic Clouds to investigate the ensemble properties of LPVs with low impact from distance and interstellar extinction. Building on those results, the second data release (DR2) from the Gaia mission is providing new insight on these objects and novel methods to exploit them in the study of the evolution of stars and stellar populations. These results, together with related developments, are summarized here...
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Li abundnces along the RGB: FLAMES_GIRAFFE Spectra of a large sample of low-mass bulge stars
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Low-mass lithium-rich AGB stars in the Galactic bulge: evidence for cool bottom processing?
No full textA new method to identify subclasses among AGB stars using Gaia and 2MASS photometry
Full text linkAims. We explore the wealth of high-quality photometric data provided by data release 2 (DR2) of the Gaia mission for long-period variables (LPVs) in the Large Magellanic Cloud (LMC). Our goal is to identify stars of various types and masses along the asymptotic giant branch. Methods. For this endeavour, we developed a new multi-band approach combining Wesenheit functions WRP,BP−RP and WKs,J−Ks in the Gaia BP, RP, and 2MASS J, Ks spectral ranges, respectively, and use a new diagram, (WRP,BP−RP − WKs,J−Ks) versus Ks, to distinguish between different kinds of stars in our sample of LPVs. We used stellar population synthesis models to validate our approach. Results. We demonstrate the ability of the new diagram to discriminate between O- and C-rich objects, and to identify low-mass, intermediate-mass, and massive O-rich red giants, as well as extreme C-rich stars. Stellar evolution and population synthesis models guide the interpretation of the results, highlighting the diagnostic power of the new tool to discriminate between stellar initial masses, chemical properties, and evolutionary stages
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