| 1. |
- Casali, G., et al.
(författare)
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The Gaia-ESO survey : the non-universality of the age-chemical-clocks-metallicity relations in the Galactic disc
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 639
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Tidskriftsartikel (refereegranskat)abstract
- Context. In the era of large spectroscopic surveys, massive databases of high-quality spectra coupled with the products of the Gaia satellite provide tools to outline a new picture of our Galaxy. In this framework, an important piece of information is provided by our ability to infer stellar ages, and consequently to sketch a Galactic timeline.Aims. We aim to provide empirical relations between stellar ages and abundance ratios for a sample of stars with very similar stellar parameters to those of the Sun, namely the so-called solar-like stars. We investigate the dependence on metallicity, and we apply our relations to independent samples, that is, the Gaia-ESO samples of open clusters and of field stars.Methods. We analyse high-resolution and high-signal-to-noise-ratio HARPS spectra of a sample of solar-like stars to obtain precise determinations of their atmospheric parameters and abundances for 25 elements and/or ions belonging to the main nucleosynthesis channels through differential spectral analysis, and of their ages through isochrone fitting.Results. We investigate the relations between stellar ages and several abundance ratios. For the abundance ratios with a steeper dependence on age, we perform multivariate linear regressions, in which we include the dependence on metallicity, [Fe/H]. We apply our best relations to a sample of open clusters located from the inner to the outer regions of the Galactic disc. Using our relations, we are able to recover the literature ages only for clusters located at R-GC > 7 kpc. The values that we obtain for the ages of the inner-disc clusters are much greater than the literature ones. In these clusters, the content of neutron capture elements, such as Y and Zr, is indeed lower than expected from chemical evolution models, and consequently their [Y/Mg] and [Y/Al] are lower than in clusters of the same age located in the solar neighbourhood. With our chemical evolution model and a set of empirical yields, we suggest that a strong dependence on the star formation history and metallicity-dependent stellar yields of s-process elements can substantially modify the slope of the [s/alpha]-[Fe/H]-age relation in different regions of the Galaxy.Conclusions. Our results point towards a non-universal relation [s/alpha]-[Fe/H]-age, indicating the existence of relations with different slopes and intercepts at different Galactocentric distances or for different star formation histories. Therefore, relations between ages and abundance ratios obtained from samples of stars located in a limited region of the Galaxy cannot be translated into general relations valid for the whole disc. A better understanding of the s-process at high metallicity is necessary to fully understand the origin of these variations.
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| 2. |
- Baratella, M., et al.
(författare)
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The Gaia-ESO Survey : a new approach to chemically characterising young open clusters I. Stellar parameters, and iron-peak, alpha-, and proton-capture elements
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP SCIENCES S A. - 0004-6361 .- 1432-0746. ; 634
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Tidskriftsartikel (refereegranskat)abstract
- Context: Open clusters are recognised as excellent tracers of Galactic thin-disc properties. At variance with intermediate-age and old open clusters, for which a significant number of studies is now available, clusters younger than less than or similar to 150 Myr have been mostly overlooked in terms of their chemical composition until recently (with few exceptions). On the other hand, previous investigations seem to indicate an anomalous behaviour of young clusters, which includes (but is not limited to) slightly sub-solar iron (Fe) abundances and extreme, unexpectedly high barium (Ba) enhancements.Aims: In a series of papers, we plan to expand our understanding of this topic and investigate whether these chemical peculiarities are instead related to abundance analysis techniques.Methods: We present a new determination of the atmospheric parameters for 23 dwarf stars observed by the Gaia-ESO survey in five young open clusters (tau < 150 Myr) and one star-forming region (NGC 2264). We exploit a new method based on titanium (Ti) lines to derive the spectroscopic surface gravity, and most importantly, the microturbulence parameter. A combination of Ti and Fe lines is used to obtain effective temperatures. We also infer the abundances of Fe I, Fe II, Tit, Tin,Na I, Mg I, Al I,Sit, Ca I, Cr I, and Ni I.Results: Our findings are in fair agreement with Gaia-ESO iDR5 results for effective temperatures and surface gravities, but suggest that for very young stars, the microturbulence parameter is over-estimated when Fe lines are employed. This affects the derived chemical composition and causes the metal content of very young clusters to be under-estimated.Conclusions: Our clusters display a metallicity [Fe/H] between +0.04 +/- 0.01 and +0.12 +/- 0.02; they are not more metal poor than the Sun. Although based on a relatively small sample size, our explorative study suggests that we may not need to call for ad hoc explanations to reconcile the chemical composition of young open clusters with Galactic chemical evolution models.
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| 3. |
- Bonito, R., et al.
(författare)
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The Gaia-ESO Survey : A new diagnostic for accretion and outflow activity in the young cluster NGC 2264
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 642
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Tidskriftsartikel (refereegranskat)abstract
- Context. NGC 2264 is a young cluster whose accretion properties can be investigated in detail by taking advantage of the FLAMES data in the context of the Gaia-ESO Survey. In fact, the analysis of the Hα emission line profile can provide us with information about the accretion and ejection activity of young stars. However, a strong nebular emission that contributes to the Hα emission can alter the profiles, with consequences for their physical interpretation. Aims. Our study is aimed at investigating the accretion and ejection properties of NGC 2264 by applying a proper treatment of the sky contribution to the Hα and forbidden emission lines (FELs; [SII] and [NII] doublets). Methods. We developed a tool, the OHαNA-method, to handle the strong nebular contribution and spectra with spurious profiles of the Hα and FELs, namely altered Hα profiles or absorption features artificially created where emission lines (FELs) are expected. We derived the quantitative measurements of relevant parameters to describe the accretion and ejection processes in young members of NGC 2264, focusing on reliable quantities derived from the width of the lines, which is relatively unaffected by the nebular emission, unlike the intensity peak, which can be altered significantly. Results. We derive the quantitative measurements related to the Hα emission line and discuss the comparison between the original and sky-subtracted spectra. We thus reveal possible profile alterations with consequences for their physical interpretation. Furthermore, we show the analysis of the variability for multi-epoch observations, also deriving the velocity of the infalling and outflowing plasma from the wings of the broad Hα emission line (in accreting stars). We also explore the mass accretion rate versus full width at zero intensity of the Hα line, namely M versus FWZI(Hα), a correlation based on the width of the emission line, which is expected to be more robust with respect to any measurement derived from the peak (e.g., Hα10%) and possibly altered by the nebular contribution. Conclusions. We are able to ascertain that more than 20% of the confirmed accretors, which have already been identified in NGC 2264, are affected by the alteration of their line profiles due to the contribution of the nebular emission. Therefore, this is an important issue to consider when investigating accretion and ejection processes in young stellar clusters. While a small fraction of spectra can be unequivocally classified as either unaffected by nebular emission or dominated by nebular emission, the majority (> 90%) represent intermediate cases whose spectral features have to be investigated in detail to derive reliable measurements of the relevant parameters and their physical implications.
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| 4. |
- Isaksson, Johan, et al.
(författare)
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Risky sexual behaviour among Russian adolescents : association with internalizing and externalizing symptoms
- 2021
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Ingår i: Child and Adolescent Psychiatry and Mental Health. - : BioMed Central. - 1753-2000. ; 15
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Tidskriftsartikel (refereegranskat)abstract
- Background: Risky sexual behaviour (RSB) is regarded as a major health problem during adolescence. Russia has one of the highest rates of teenage pregnancy, abortion and newly diagnosed HIV infections in the world, but research on RSB in Russian youth has been limited. To address this deficit, this study examined the role of several factors, including internalizing and externalizing symptoms, in RSB among Russian adolescents. Methods: Self-reported data were collected from 2573 Russian adolescents aged 13–17 years old (59.4 % girls; Mean age = 14.89) regarding RSB (unprotected sex, early pregnancy, multiple sexual partners and substance use during sexual encounters). Information was also obtained on externalizing (conduct problems and delinquent behaviour) and internalizing (depression, anxiety and posttraumatic stress) symptoms, as well as interpersonal risk and protective factors (affiliation with delinquent peers, parental involvement and teacher support). Hierarchical multiple binary logistic regression analysis was used to examine the associations between these variables and RSB. Results: Boys reported engaging in more RSB than girls. Externalizing symptoms and affiliation with delinquent peers were most strongly associated with RSB, whereas symptoms of anxiety were negatively associated with RSB. There was an interaction effect for sex and affiliation with delinquent peers on RSB with boys reporting RSB when having more delinquent peers. Neither parental involvement nor teacher support were protective against RSB. Conclusions: Early detection of and interventions for RSB and associated externalizing symptoms may be important for adolescent physical and mental wellbeing. Affiliation with delinquent peers should, especially among boys, be regarded as a risk marker for RSB.
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| 5. |
- Stickley, Andrew, et al.
(författare)
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Attention-Deficit/Hyperactivity Disorder Symptoms and Community Violence Exposure in Russian Adolescents
- 2021
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Ingår i: Journal of Interpersonal Violence. - : Sage Publications. - 0886-2605 .- 1552-6518. ; 36:17-18, s. NP9738-NP9756
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Tidskriftsartikel (refereegranskat)abstract
- A large body of research has shown that exposure to community violence is common for many children across the world. However, less is known about exposure in particular subgroups such as those children with developmental disorders. To address this research gap, the aim of this study was to examine community violence exposure (CVE) in adolescents with attention-deficit/hyperactivity disorder (ADHD) symptoms and the role of gender in this association. Data were analyzed from 2,782 adolescents aged 13 to 17 years from Arkhangelsk, Russia that were collected during the Social and Health Assessment (SAHA). ADHD status was assessed with the hyperactivity/inattention scale of the Strengths and Difficulties Questionnaire (SDQ). Information was obtained on past-year witnessing and violence victimization in the community. Results showed that CVE was more prevalent in children with ADHD symptoms. Specifically, 75.1% of children with ADHD symptoms had been exposed to any violence versus 62.3% in the non-ADHD group (χ2 = 18.65, p <.001). Multivariate analyses of covariance (MANCOVAs) revealed that CVE was significantly higher for adolescents with ADHD symptoms for both witnessing and victimization, while exposure was significantly higher for ADHD boys compared with girls. The findings of this study suggest that CVE may be elevated in adolescents with higher ADHD symptoms. Given that CVE has been associated with a variety of negative social and psychological outcomes in typically developing children, an important task for future research is to determine what factors are associated with CVE in adolescents with ADHD symptoms including those relating to such phenomena as comorbid psychopathology, the family, and peer relations, so that interventions can be designed and implemented to reduce CVE and its detrimental effects in this population.
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