- ID:
- ivo://CDS.VizieR/J/MNRAS/437/2106
- Title:
- Barium abundance in Galactic Cepheids
- Short Name:
- J/MNRAS/437/2106
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using an Non-Local Thermodynamic Equilibrium (NLTE) analysis and a homogenous spectral data base, we have determined Ba abundances in a sample of 210 Galactic Cepheids and related objects. We confirm the previous result reported in Andrievsky et al. that the barium distribution in the range of Galactocentric distances from 5 to 18kpc shows very small gradient value. The value determined here - d[Ba/H]/dR~-0.01dex/kpc - is smaller than that for other s-process elements, such as La, Pr, Nd and Sm (Luck & Lambert, 2011AJ....142..136L, Cat. J/AJ/142/136), that typically show gradients of -0.03dex/kpc.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/428/3252
- Title:
- Barium abundances in Cepheids
- Short Name:
- J/MNRAS/428/3252
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derived the barium atmospheric abundances for a large sample of Cepheids, comprising 270 stars. The sample covers a large range of Galactocentric distances, from about 4 to 15kpc, so it is appropriate to investigate the existence of radial barium abundance gradients in the Galactic disc. In fact, this is the first time that such a comprehensive analysis of the distribution of barium abundances in the Galactic disc has been carried out. As a result, we conclude that the Ba abundance distribution can be characterized by a zero gradient. This result is compared with derived gradients for other elements, and some reasons are briefly discussed for the independence of the barium abundances from Galactocentric distances.
- ID:
- ivo://CDS.VizieR/J/ApJ/869/50
- Title:
- Barium abundances of red giant branch stars
- Short Name:
- J/ApJ/869/50
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- There are many candidate sites of the r-process: core-collapse supernovae (CCSNe; including rare magnetorotational core-collapse supernovae), neutron star mergers (NSMs), and neutron star/black hole mergers. The chemical enrichment of galaxies --specifically dwarf galaxies-- helps distinguish between these sources based on the continual build-up of r-process elements. This technique can distinguish between the r-process candidate sites by the clearest observational difference --how quickly these events occur after the stars are created. The existence of several nearby dwarf galaxies allows us to measure robust chemical abundances for galaxies with different star formation histories. Dwarf galaxies are especially useful because simple chemical evolution models can be used to determine the sources of r-process material. We have measured the r-process element barium with Keck/DEIMOS medium-resolution spectroscopy. We present the largest sample of barium abundances (almost 250 stars) in dwarf galaxies ever assembled. We measure [Ba/Fe] as a function of [Fe/H] in this sample and compare with existing [{alpha}/Fe] measurements. We have found that a large contribution of barium needs to occur at more delayed timescales than CCSNe in order to explain our observed abundances, namely the significantly more positive trend of the r-process component of [Ba/Fe] versus [Fe/H] seen for [Fe/H]<~-1.6 when compared to the [Mg/Fe] versus [Fe/H] trend. We conclude that NSMs are the most likely source of r-process enrichment in dwarf galaxies at early times.
- ID:
- ivo://CDS.VizieR/J/MNRAS/474/2129
- Title:
- Barium dwarfs with white dwarf companions
- Short Name:
- J/MNRAS/474/2129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report three new barium (Ba) dwarfs lying in Sirius-like systems. They provide direct evidence that Ba dwarfs are companions to white dwarfs (WDs). Atmospheric parameters, stellar masses and the chemical abundances of 25 elements, including light, {alpha}, Fe-peak and s-process elements, are derived from high-resolution and high S/N spectra. The enhancement of s-process elements with [s/Fe] ratios between 0.4 and 0.6 confirm them as mild barium stars. The estimated metallicities (-0.31, -0.06 and 0.13) of BD+68 1027, RE J0702+129 and BD+80 670 are in the range of known Ba dwarfs and giants. As expected, the observed indices [hs/ls], [s/Fe] and [C/Fe] show an anti-correlation with metallicity. Asymptotic giant branch (AGB) progenitor masses are estimated for the WD companions of RE J0702+129 (1.47M_{sun}_) and BD+80 670 (3.59M_{sun}_). These confirm the predicted range of progenitor AGB masses (1.5-4M_{sun}_) for unseen WDs around Ba dwarfs. The surface abundances of s-process elements in RE J0702+129 and BD+80 670 are compared with AGB models and they are in close agreement, within the predicted accretion efficiencies and pollution factors for Ba stars. These results support that the origin of s-process overabundances in Ba dwarfs is similar to those of Ba giants via the McClure hypothesis in which Ba stars accumulate s-process elements through mass transfer from their host companions during the AGB phase.
- ID:
- ivo://CDS.VizieR/J/MNRAS/459/4299
- Title:
- Barium stars abundances and kinematics
- Short Name:
- J/MNRAS/459/4299
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we present an homogeneous analysis of photospheric abundances based on high-resolution spectroscopy of a sample of 182 barium stars and candidates. We determined atmospheric parameters, spectroscopic distances, stellar masses, ages, luminosities and scaleheight, radial velocities, abundances of the Na, Al, {alpha}-elements, iron-peak elements, and s-process elements Y, Zr, La, Ce, and Nd. We employed the local thermodynamic equilibrium model atmospheres of Kurucz and the spectral analysis code MOOG. We found that the metallicities, the temperatures and the surface gravities for barium stars cannot be represented by a single Gaussian distribution. The abundances of {alpha}-elements and iron peak elements are similar to those of field giants with the same metallicity. Sodium presents some degree of enrichment in more evolved stars that could be attributed to the NeNa cycle. As expected, the barium stars show overabundance of the elements created by the s-process. By measuring the mean heavy-element abundance pattern as given by the ratio [s/Fe], we found that the barium stars present several degrees of enrichment. We also obtained the [hs/ls] ratio by measuring the photospheric abundances of the Ba-peak and the Zr-peak elements. Our results indicated that the [s/Fe] and the [hs/ls] ratios are strongly anticorrelated with the metallicity. Our kinematical analysis showed that 90 per cent of the barium stars belong to the thin disc population. Based on their luminosities, none of the barium stars are luminous enough to be an asymptotic giant branch star, nor to become self-enriched in the s-process elements. Finally, we determined that the barium stars also follow an age-metallicity relation.
- ID:
- ivo://CDS.VizieR/J/A+A/584/A88
- Title:
- Barred & unbarred galaxies N, O abundance ratio
- Short Name:
- J/A+A/584/A88
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Bar-induced gas inflows towards galaxy centres are recognised as a key agent for the secular evolution of galaxies. One immediate consequence of this inflow is the accumulation of gas in the centre of galaxies where it can form stars and alter the chemical and physical properties. Our aim is to study whether the properties of the ionised gas in the central parts of barred galaxies are altered by the presence of a bar and whether the change in central properties is related to bar and/or parent galaxy properties. We use a sample of nearby face-on disc galaxies with available SDSS spectra, morphological decomposition, and information on the stellar population of their bulges, to measure the internal Balmer extinction from the H{alpha} to H{beta} line ratio, star formation rate, and relevant line ratios to diagnose chemical abundances and gas density.
- ID:
- ivo://CDS.VizieR/J/AJ/121/2159
- Title:
- Basic parameters for 372 A, F & G stars
- Short Name:
- J/AJ/121/2159
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Paper I (Cat. <J/AJ/121/2148>) of this series presented precise MK spectral types for 372 late A-, F-, and early G-type stars with the aim of understanding the nature of luminosity classification on the MK spectral classification system for this range of spectral types. In this paper, a multidimensional downhill simplex technique is introduced to determine the basic parameters of the program stars from fits of synthetic spectra and fluxes with observed spectra and fluxes from Strvmgren uvby photometry. This exercise yields useful calibrations of the MK spectral classification system but, most importantly, gives insight into the physical nature of luminosity classification on the MK spectral classification system. In particular, we find that in this range of spectral types, microturbulence appears to be at least as important as gravity in determining the MK luminosity type.
- ID:
- ivo://CDS.VizieR/J/A+A/506/213
- Title:
- B6-B9.5 stars abundance analysis
- Short Name:
- J/A+A/506/213
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The CoRoT satellite is collecting precise time-resolved photometry for tens of asteroseismology targets. To ensure a correct interpretation of the CoRoT data, the atmospheric parameters, chemical compositions, and rotational velocities of the stars must be determined. The main goal of the ground-based seismology support program for the CoRoT mission was to obtain photometric and spectroscopic data for stars in the fields monitored by the satellite. These ground-based observations were collected in the GAUDI archive. High-resolution spectra of more than 200 B-type stars are available in this database, and about 45% of them is analysed here. To derive the effective temperature of the stars, we used photometric indices. Surface gravities were obtained by comparing observed and theoretical Balmer line profiles. To determine the chemical abundances and rotational velocities, we used a spectrum synthesis method, which consisted of comparing the observed spectrum with theoretical ones based on the assumption of LTE. Atmospheric parameters, chemical abundances, and rotational velocities were determined for 89 late-B stars. The dominant species in their spectra are iron-peak elements. The average Fe abundance is 7.24+/-0.45dex. The average rotational velocity is 126km/s, but there are 13 and 20 stars with low and moderate Vsini values, respectively. The analysis of this sample of 89 late B-type stars reveals many chemically peculiar (CP) stars. Some of them were previously known, but at least 9 new CP candidates, among which at least two HgMn stars, are identified in our study. These CP stars as a group exhibit Vsini values lower than the stars with normal surface chemical composition.
- ID:
- ivo://CDS.VizieR/J/A+A/319/593
- Title:
- [Be] abundances in low-metallicity stars
- Short Name:
- J/A+A/319/593
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present observations of the Be II 313.0nm resonance doublet in 14 halo and old disk stars with metallicities ranging from [Fe/H]=-0.4 to =~-3.0 obtained with the CASPEC spectrograph of the ESO 3.6m telescope at a FWHM=~8.6km/s resolution. Abundances are derived by means of the synthetic spectra technique employing Kurucz (1993, CD-ROM 13 and CD-ROM 18) atmospheric models, with enhanced {alpha}-elements and no overshooting.
- ID:
- ivo://CDS.VizieR/J/ApJ/763/L33
- Title:
- Be-B concentrations in rare CB/CH chondrite
- Short Name:
- J/ApJ/763/L33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A search for short-lived ^10^Be in 21 calcium-aluminum-rich inclusions (CAIs) from Isheyevo, a rare CB/CH chondrite, showed that only 5 CAIs had ^10^B/^11^B ratios higher than chondritic correlating with the elemental ratio ^9^Be/^11^B, suggestive of in situ decay of this key short-lived radionuclide. The initial (^10^Be/^9^Be)_0_ ratios vary between ~10^-3^ and ~10^-2^ for CAI 411. The initial ratio of CAI 411 is one order of magnitude higher than the highest ratio found in CV3 CAIs, suggesting that the more likely origin of CAI 411 ^10^Be is early solar system irradiation. The low (^26^Al/^27^Al)_0_ [<=8.9x10^-7^] with which CAI 411 formed indicates that it was exposed to gradual flares with a proton fluence of a few 10^19^protons/cm2, during the earliest phases of the solar system, possibly the infrared class 0. The irradiation conditions for other CAIs are less well constrained, with calculated fluences ranging between a few 10^19^ and 10^20^protons/cm2. The variable and extreme value of the initial ^10^Be/^9^Be ratios in carbonaceous chondrite CAIs is the reflection of the variable and extreme magnetic activity in young stars observed in the X-ray domain.
