- ID:
- ivo://CDS.VizieR/J/ApJS/197/29
- Title:
- Chemical compositions of 11 RR Lyrae
- Short Name:
- J/ApJS/197/29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed abundance study of 11 RR Lyrae ab-type variables: AS Vir, BS Aps, CD Vel, DT Hya, RV Oct, TY Gru, UV Oct, V1645 Sgr, WY Ant, XZ Aps, and Z Mic. High-resolution and high signal-to-noise ratio echelle spectra of these variables were obtained with the 2.5m du Pont telescope at the Las Campanas Observatory. We obtained more than 2300 spectra, roughly 200 spectra per star, distributed more or less uniformly throughout the pulsational cycles. A new method has been developed to obtain the initial effective temperatures of our sample stars at a specific pulsational phase. We find that the abundance ratios are generally consistent with those of similar metallicity field stars in different evolutionary states and throughout the pulsational cycles for RR Lyrae stars. TY Gru remains the only n-capture enriched star among the RRab in our sample.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/463/265
- Title:
- Chemical compositions of 48 WR planetary nebulae
- Short Name:
- J/A+A/463/265
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Chemical compositions and other properties of planetary nebulae around central stars of spectral types [WC], [WO], and wels are compared with those of "normal" central stars, in order to clarify the evolutionary status of each type and their interrelation. We use plasma diagnostics to derive from optical spectra the plasma parameters and chemical compositions of 48 planetary nebulae. We also reanalyze the published spectra of a sample of 167 non-WR PN. The results as well as the observational data are compared in detail with those from other studies of the objects in common.
- ID:
- ivo://CDS.VizieR/III/58
- Title:
- Chemical elements in peculiar stellar spectra
- Short Name:
- III/58
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A systematic search of 27 journals, IAU Symposia, and Colloquia has yielded this catalogue of identifications of chemical species in peculiar spectra Ap, Bp and Am generally. Abundance surveys were only searched if they included element identification lists.
- ID:
- ivo://CDS.VizieR/J/ApJ/812/142
- Title:
- Chemical evolution in the LMC with a new model
- Short Name:
- J/ApJ/812/142
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using a new network and a new model, we have studied chemical complexity in cold portions of dense clouds of the Large Magellanic Cloud (LMC). We varied the hydrogen number density between 1x10^5^ and 5x10^5^/cm3 and, for each density, we ran models for A_V_=3, 5, and 10. Then, for each density and visual extinction we varied the grain temperature between 10 and 50K in small intervals, while keeping the gas temperature constant at 20K. We used a gas-to-dust mass ratio based on a variety of observations and analyses, and scaled the elemental abundances of the LMC so that they are representative of so-called "low" metallic abundances. We found that although the LMC is metal-poor, it still shows a rich chemistry; almost all the major observed species in the gas phase of our Galaxy should be detectable using present-day observational facilities. We compared our model results with observed gas-phase abundances in some cold and dense sources, and found reasonably good agreement for most species. We also found that some observed results, especially for methanol, are better matched if these regions currently possess lower temperatures, or possessed them in the past. Finally, we discussed our simulated abundances for H_2_O ice with respect to total hydrogen, and CO_2_, CO, CH_3_OH, and NH_3_ ices with respect to water ice, and compared our values with those for two observed ices --CO_2_ and CO-- detected in front of young stellar objects in the LMC.
- ID:
- ivo://CDS.VizieR/J/ApJ/822/105
- Title:
- Chemical evolution in the SMC
- Short Name:
- J/ApJ/822/105
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Large (LMC) and Small (SMC) Magellanic Clouds are irregular satellite galaxies of the Milky Way. Both are metal- and dust-poor, although the SMC is significantly poorer in both. We have recently simulated the chemistry in cold dense regions of the LMC and found that a rich chemistry exists in the gas-phase. In this paper, we report a companion study of the chemistry of dense regions of the SMC, confining our attention to cold regions of dense clouds with a variety of densities, visual extinctions, and grain temperatures, and a fixed gas-phase temperature. With a gas-to-dust ratio and elemental abundances based on observations and scaling, we found that for molecules like CO and N_2_, which are predominantly formed in the gas phase, their abundances are consistent with the reduced elemental abundances of their constituent elements above 25K; however, for species that are produced fully (e.g., CH_3_OH) or partially on the grain surface (e.g., H_2_CO, NH_3_), the dependence on metallicity can be complex. Most of the major gas-phase species observed in our Galaxy are produced in the SMC although in lower quantities. With our simulations, we are able to explain observed gas-phase abundances reasonably well in the dense sources N27 and LIRS 36. We have also compared our calculated abundances of selected ices with limited observations in dense regions in front of young stellar objects.
- ID:
- ivo://CDS.VizieR/J/A+A/642/A176
- Title:
- Chemical evolution of dSph galaxy Sextans
- Short Name:
- J/A+A/642/A176
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present our analysis of the FLAMES dataset targeting the central 25' region of the Sextans dwarf spheroidal galaxy (dSph). This dataset is the third major part of the high-resolution spectroscopic section of the ESO large program 171.B-0588(A) obtained by the Dwarf galaxy Abundances and Radial-velocities Team (DART). Our sample is composed of red giant branch stars down to V~20.5mag, the level of the horizontal branch in Sextans, and allows users to address questions related to both stellar nucleosynthesis and galaxy evolution. We provide metallicities for 81 stars, which cover the wide [Fe/H]=-3.2 to -1.5dex range. The abundances of ten other elements are derived: Mg, Ca, Ti, Sc, Cr, Mn, Co, Ni, Ba, and Eu. Despite its small mass, Sextans is a chemically evolved system, showing evidence of a contribution from core-collapse and Type Ia supernovae as well as low-metallicity asymptotic giant branch stars (AGBs). This new FLAMES sample offers a sufficiently large number of stars with chemical abundances derived with high accuracy to firmly establish the existence of a plateau in [alpha/Fe] at ~0.4dex followed by a decrease above [Fe/H]~-2dex. These features reveal a close similarity with the Fornax and Sculptor dSphs despite their very different masses and star formation histories, suggesting that these three galaxies had very similar star formation efficiencies in their early formation phases, probably driven by the early accretion of smaller galactic fragments, until the UV-background heating impacted them in different ways. The parallel between the Sculptor and Sextans dSph is also striking when considering Ba and Eu. The same chemical trends can be seen in the metallicity region common to both galaxies, implying similar fractions of SNeIa and low-metallicity AGBs. Finally, as to the iron-peak elements, the decline of [Co/Fe] and [Ni/Fe] above [Fe/H]~-2 implies that the production yields of Ni and Co in SNeIa are lower than that of Fe. The decrease in [Ni/Fe] favours models of SNeIa based on the explosion of double-degenerate sub-Chandrasekhar mass white dwarfs.
- ID:
- ivo://CDS.VizieR/J/A+A/637/A58
- Title:
- Chemical evolution of galaxy clusters
- Short Name:
- J/A+A/637/A58
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the chemical evolution of galaxy clusters by measuring the iron mass in the ICM after dissecting the abundance profiles into different components. We used Chandra archival observations of 186 morphologically regular clusters in the redshift range of [0.04, 1.07]. For each cluster, we computed the azimuthally averaged iron abundance and gas density profiles. In particular, our aim is to identify a central peak in the iron distribution, which is associated with the central galaxy, and an approximately constant plateau reaching the largest observed radii, which is possibly associated with early enrichment that occurred before or shortly after achieving virialization within the cluster. We were able to firmly identify two components in the iron distribution in a significant fraction of the sample simply by relying on the fit of the iron abundance profile. From the abundance and ICM density profiles, we computed the iron mass included in the iron peak and iron plateau, and the gas mass-weighted iron abundance of the ICM out to an extraction radius of 0.4r_500_ and to r_500_ by extending the abundance profile as a constant. We find that the iron plateau shows no evolution with redshift. On the other hand, we find a marginal (<2{sigma} c.l.) decrease with redshift in the iron mass included in the iron peak rescaled by the gas mass. We measure that the fraction of iron peak mass is typically a few percent (~1%) of the total iron mass within r_500_. Therefore, since the total iron mass budget is dominated by the plateau, we find consistently that the global gas mass-weighted iron abundance does not evolve significantly across our sample. We were also able to reproduce past claims of evolution in the global iron abundance, which turn out to be due to the use of cluster samples with different selection methods combined with the use of emission-weighted, instead of gas mass-weighted, abundance values. Finally, while the intrinsic scatter in the iron plateau mass is consistent with zero, the iron peak mass exhibits a large scatter, in line with the fact that the peak is produced after the virialization of the halo and depends on the formation history of the hosting cool core and the strength of the associated feedback processes. We conclude that only a spatially resolved approach can resolve the issue of iron abundance evolution in the ICM, reconciling the contradictory results obtained in the last ten years. Evolutionary effects below z~1 are marginally measurable with present-day data, while at z>1 the constraints are severely limited by poor knowledge of the high-z cluster population. The path towards a full and comprehensive chemical history of the ICM requires the application of high angular resolution X-ray bolometers and a dramatic increase in the number of faint, extended X-ray sources.
- ID:
- ivo://CDS.VizieR/J/A+A/472/101
- Title:
- Chemical evolution of SMC planetary nebulae
- Short Name:
- J/A+A/472/101
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the chemical evolution of the Small Magellanic Cloud (SMC) based on abundance data of planetary nebulae (PNe). The main goal is to investigate the time evolution of the oxygen abundance in this galaxy by deriving an age-metallicity relation. Such a relation is of fundamental importance as an observational constraint for chemical evolution models of the SMC. We have used high quality PNe data to derive the properties of the progenitor stars, so that the stellar ages could be estimated. We collected a large number of measured spectral fluxes for each nebula and derived accurate physical parameters and nebular abundances. New spectral data for a sample of SMC PNe obtained between 1999 and 2002 are also presented. These data are used with data available in the literature to improve the accuracy of the fluxes for each spectral line.
- ID:
- ivo://CDS.VizieR/J/A+A/275/101
- Title:
- Chemical evolution of the galactic disk I.
- Short Name:
- J/A+A/275/101
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- From high resolution, high S/N spectroscopic observations of carefully selected northern and southern stars, abundances of O, Na, Mg, Al, Si, Ca, Ti, Fe, Ni, Y, Zr, Ba and Nd, as well as photometric ages, are derived for 189 nearby field F and G stars.
- ID:
- ivo://CDS.VizieR/J/A+AS/102/603
- Title:
- Chemical evolution of the galactic disk II.
- Short Name:
- J/A+AS/102/603
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Equivalent widths of programme stars used in Paper I (1993A&A...275..101E, see catalog <J/A+A/275/101>) from observations at ESO and McDonald observatories are compared.
