- 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.
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- 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/A+A/626/A127
- Title:
- Barium and related stars and WD companions
- Short Name:
- J/A+A/626/A127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper provides long-period and revised orbits for barium and S stars adding to previously published ones. The sample of barium stars with strong anomalies comprise all such stars present in the Lu et al. catalogue. We find orbital motion for all barium and extrinsic S stars monitored. We obtain the longest period known so far for a spectroscopic binary involving an S star, namely 57 Peg with a period of the order of 100-500yr. We present the mass distribution for the barium stars, which ranges from 1 to 3M_{sun}_, with a tail extending up to 5M_{sun}_ in the case of mild barium stars. This high-mass tail comprises mostly high-metallicity objects ([Fe/H]>=-0.1). Mass functions are compatible with WD companions and we derive their mass distribution which ranges from 0.5 to 1 Msun. Using the initial - final mass relationship established for field WDs, we derived the distribution of the mass ratio q'=M_AGB,ini_/M_Ba_ (where M_AGB,ini_ is the WD progenitor initial mass, i.e., the mass of the system former primary component) which is a proxy for the initial mass ratio. It appears that the distribution of q' is highly non uniform, and significantly different for mild and strong barium stars, the latter being characterized by values mostly in excess of 1.4, whereas mild barium stars occupy the range 1-1.4. We investigate as well the correlation between abundances, orbital periods, metallicities, and masses (barium star and WD companion). The 105 orbits of post-mass-transfer systems presented in this paper pave the way for a comparison with binary-evolution models.
- 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/321/L9
- Title:
- Barium stars in the HR diagram
- Short Name:
- J/A+A/321/L9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Table2 is an extension of Table 1 to 15 additional stars with slightly less accurate parallaxes (see text). The entries are the same in both tables.
- ID:
- ivo://CDS.VizieR/J/A+A/618/A34
- Title:
- Barlenses in the CALIFA survey
- Short Name:
- J/A+A/618/A34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It is theoretically predicted that, at low galaxy inclinations, boxy/peanut bar components have a barlens appearance of a round central component embedded in the narrow bar. We investigate barlenses in the Calar Alto Legacy Integral Field Area (CALIFA) survey galaxies, studying their morphologies, stellar populations, and metallicities. We show that, when present, barlenses account for a significant portion of light of photometric bulges, i.e., the excess light on top of the disks, which highlights the importance of bars in accumulating central galaxy mass concentrations in the cosmic timescale. We made multi-component decompositions for a sample of 46 barlens galaxies drawn from the CALIFA survey, where M_{star}_/M_{sun}_=10^9.7^-10^11.4^ and z=0.005-0.03. Unsharp masks of the Sloan Digital Sky Survey (SDSS) r'-band mosaics were used to identify the boxy/peanut or X-shaped features. Barlenses are identified in the images using our simulation snapshots as an additional guide. Our decompositions with GALFIT include bulges, disks, and bars as well as barlenses as a separate component. For 26 of the decomposed galaxies the CALIFA DR2 V500 grating data cubes were used to explore stellar ages and metallicities at the regions of various structure components. We find that 25+/-2% of the 1064 galaxies in the whole CALIFA sample show either X-shaped or barlens features. In the decomposed galaxies with barlenses, on average 13%+/-2% of the total galaxy light belongs to this component, leaving less than 10% for possible separate bulge components. Most importantly, bars and barlenses are found to have similar cumulative stellar age and metallicity distributions. The metallicities in barlenses are on average near solar, but exhibit a large range. In some of the galaxies barlenses and X-shaped features appear simultaneously, in which case the bar origin of the barlens is unambiguous. This is the first time that a combined morphological and stellar population analysis is used to study barlenses. We show that their stars are accumulated in a prolonged time period concurrently with the evolution of the narrow bar.
1638. Barn 335 ALMA datacubes
- ID:
- ivo://CDS.VizieR/J/A+A/631/A64
- Title:
- Barn 335 ALMA datacubes
- Short Name:
- J/A+A/631/A64
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The relationship between outflow launching and the formation of accretion disks around young stellar objects is still not entirely understood, which is why spectrally and spatially resolved observations are needed. Recently, the Atacama Large Millimetre/ sub-millimetre Array (ALMA) carried out long-baseline observations towards a handful of young sources, revealing connections between outflows and the inner regions of disks. Here we aim to determine the small-scale kinematical and morphological properties of the outflow from the isolated protostar B335 for which no Keplerian disk has, so far, been observed on scales down to 10au. We used ALMA in its longest-baseline configuration to observe emission from CO isotopologues, SiO, SO_2_, and CH_3_OH. The proximity of B335 provides a resolution of ~3au (0.03"). We also combined our long-baseline data with archival observations to produce a high-fidelity image covering scales up to 700 au (7"). ^12^CO has an X-shaped morphology with arms ~50au in width that we associate with the walls of an outflow cavity, similar to what is observed on larger scales. Long-baseline continuum emission is confined to <7au from the protostar, while short- baseline continuum emission follows the ^12^CO outflow and cavity walls. Methanol is detected within ~30au of the protostar. SiO is also detected in the vicinity of the protostar, but extended along the outflow. The ^12^CO outflow does not show any clear signs of rotation at distances >=30au from the protostar. SiO traces the protostellar jet on small scales, but without obvious rotation. CH_3_OH and SO_2_ trace a region <16au in diameter, centred on the continuum peak, which is clearly rotating. Using episodic, high-velocity, ^12^CO features, we estimate the launching radius of the outflow to be<0.1au and dynamical timescales of the order of a few years.
- ID:
- ivo://CDS.VizieR/J/A+A/606/L3
- Title:
- Barnard 1b CO, NH_2_D and SO images
- Short Name:
- J/A+A/606/L3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The extremely young Class 0 object B1b-S and the first hydrostatic core (FSHC) candidate, B1b-N, provide a unique opportunity to study the chemical changes produced in the elusive transition from the prestellar core to the protostellar phase. We present 40"x70" images of Barnard 1b in the ^13^CO 1-0, C^18^O 1-0, NH_2_D 1(1,1)a-1(0,1)s, and SO 3(2)-2(1) lines obtained with the NOEMA interferometer. The observed chemical segregation allows us to unveil the physical structure of this young protostellar system down to scales of ~500au. The two protostellar objects are embedded in an elongated condensation, with a velocity gradient of ~0.2-0.4m/s/au in the east-west direction, reminiscent of an axial collapse. The NH_2_D data reveal cold and dense pseudo-disks (R~500-1000au) around each protostar. Moreover, we observe evidence of pseudo-disk rotation around B1b-S. We do not see any signature of the bipolar outflows associated with B1b-N and B1b-S, which were previously detected in H_2_CO and CH_3_OH, in any of the imaged species.The non-detection of SO constrains the SO/CH_3_OH abundance ratio in the high-velocity gas.
- ID:
- ivo://CDS.VizieR/J/A+A/606/A35
- Title:
- Barnard 1b-N and 1b-S 350GHz images
- Short Name:
- J/A+A/606/A35
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The formation epoch of protostellar disks is debated because of the competing roles of rotation, turbulence, and magnetic fields in the early stages of low-mass star formation. Magnetohydrodynamics simulations of collapsing cores predict that rotationally supported disks may form in strongly magnetized cores through ambipolar diffusion or misalignment between the rotation axis and the magnetic field orientation. Detailed studies of individual sources are needed to cross check the theoretical predictions. We present 0.06-0.1arcsec resolution images at 350GHz toward B1b-N and B1b-S, which are young class 0 protostars, possibly first hydrostatic cores. The images have been obtained with ALMA, and we compare these data with magnetohydrodynamics simulations of a collapsing turbulent and magnetized core. The submillimeter continuum emission is spatially resolved by ALMA. Compact structures with optically thick 350GHz emission are detected toward both B1b-N and B1b-S, with 0.2 and 0.35arcsec radii (46 and 80au at the Perseus distance of 230pc), within a more extended envelope. The flux ratio between the compact structure and the envelope is lower in B1b-N than in B1b-S, in agreement with its earlier evolutionary status. The size and orientation of the compact structure are consistent with 0.2arcsec resolution 32GHz observations obtained with the Very Large Array as a part of the VANDAM survey, suggesting that grains have grown through coagulation. The morphology, temperature, and densities of the compact structures are consistent with those of disks formed in numerical simulations of collapsing cores. Moreover, the properties of B1b-N are consistent with those of a very young protostar, possibly a first hydrostatic core. These observations provide support for the early formation of disks around low-mass protostars.
