- ID:
- ivo://CDS.VizieR/J/AJ/126/2048
- Title:
- NStars project: the Northern Sample. I.
- Short Name:
- J/AJ/126/2048
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have embarked on a project, under the aegis of the Nearby Stars (NStars)/Space Interferometry Mission Preparatory Science Program, to obtain spectra, spectral types, and, where feasible, basic physical parameters for the 3600 dwarf and giant stars earlier than M0 within 40pc of the Sun. In this paper, we report on the results of this project for the first 664 stars in the northern hemisphere. These results include precise, homogeneous spectral types, basic physical parameters (including the effective temperature, surface gravity, and overall metallicity [M/H]), and measures of the chromospheric activity of our program stars.
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- ID:
- ivo://CDS.VizieR/J/AJ/132/161
- Title:
- NStars project: The southern sample. I.
- Short Name:
- J/AJ/132/161
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We are obtaining spectra, spectral types, and basic physical parameters for the nearly 3600 dwarf and giant stars earlier than M0 in the Hipparcos catalog within 40pc of the Sun. Here we report on results for 1676 stars in the southern hemisphere observed at Cerro Tololo Inter-American Observatory and Steward Observatory. These results include new, precise, homogeneous spectral types, basic physical parameters (including the effective temperature, surface gravity, and metallicity [M/H]), and measures of the chromospheric activity of our program stars. We include notes on astrophysically interesting stars in this sample, the metallicity distribution of the solar neighborhood, and a table of solar analogs. We also demonstrate that the bimodal nature of the distribution of the chromospheric activity parameter logR'_HK_ depends strongly on the metallicity, and we explore the nature of the "low-metallicity" chromospherically active.
- ID:
- ivo://CDS.VizieR/J/MNRAS/434/336
- Title:
- Nuclear activity in isolated galaxies
- Short Name:
- J/MNRAS/434/336
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a spectroscopic study of the incidence of active galactic nucleus (AGN) nuclear activity in two samples of isolated galaxies. Our results show that the incidence of non-thermal nuclear activity is about 43 and 31 percent for galaxies with emission lines and 40 and 27 percent for the total sample, respectively. For the first time we have a large number of bona fide isolated galaxies (513 objects), with statistically significant number of all morphological types. A large fraction (~70%) of elliptical galaxies or early-type spirals have an AGN and ~70% of them are low-ionization nuclear emission-line regions. We find a larger fraction of AGN in early morphological types, as also found in the general population of galaxies. Only 3% of the AGN show the presence of broad lines (not a single one can be classified as type 1 AGN). This is an important result which is at odds with the unified model even if we consider warped or clumpy tori. Finally, we interpret the large fraction of AGN in isolated galaxies as the result of secular accretion.
- ID:
- ivo://CDS.VizieR/J/ApJ/724/341
- Title:
- Nucleosynthesis of massive metal-free stars
- Short Name:
- J/ApJ/724/341
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The evolution and explosion of metal-free stars with masses 10-100M_{sun}_ are followed, and their nucleosynthetic yields, light curves, and remnant masses determined. Such stars would have been the first to form after the big bang and may have left a distinctive imprint on the composition of the early universe. When the supernova yields are integrated over a Salpeter initial mass function (IMF), the resulting elemental abundance pattern is qualitatively solar, but with marked deficiencies of odd-Z elements with 7<=Z<=13. Neglecting the contribution of the neutrino wind from the neutron stars that they form, no appreciable abundances are made for elements heavier than germanium. The computed pattern compares favorably with what has been observed in metal-deficient stars with [Z]<~-3. For the lower mass supernovae considered, the distribution of remnant masses clusters around typical modern neutron star masses, but above 20-30M-{sun}_, with the value depending on explosion energy, black holes are copiously formed by fallback, with a maximum hole mass of ~40M_{sun}_. A novel automated fitting algorithm is developed for determining optimal combinations of explosion energy, mixing, and IMF in the large model database to agree with specified data sets. The model is applied to the low-metallicity sample of Cayrel et al. (Cat. J/A+A/416/1117) and the two ultra-iron-poor stars HE0107-5240 and HE1327-2326. Best agreement with these very low metallicity stars is achieved with very little mixing, and none of the metal-deficient data sets considered show the need for a high-energy explosion component. In contrast, explosion energies somewhat less than 1.2B seem to be preferred in most cases.
- ID:
- ivo://CDS.VizieR/J/ApJ/854/18
- Title:
- Nucleosynthesis of p nuclides
- Short Name:
- J/ApJ/854/18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The production of the heavy stable proton-rich isotopes between ^74^Se and ^196^Hg-the p nuclides-is due to the contribution from different nucleosynthesis processes, activated in different types of stars. Whereas these processes have been subject to various studies, their relative contributions to Galactic chemical evolution (GCE) are still a matter of debate. Here we investigate for the first time the nucleosynthesis of p nuclides in GCE by including metallicity and progenitor mass-dependent yields of core-collapse supernovae (ccSNe) into a chemical evolution model. We used a grid of metallicities and progenitor masses from two different sets of stellar yields and followed the contribution of ccSNe to the Galactic abundances as a function of time. In combination with previous studies on p-nucleus production in thermonuclear supernovae (SNIa), and using the same GCE description, this allows us to compare the respective roles of SNeIa and ccSNe in the production of p-nuclei in the Galaxy. The {gamma} process in ccSN is very efficient for a wide range of progenitor masses (13M_{sun}_-25M_{sun}_) at solar metallicity. Since it is a secondary process with its efficiency depending on the initial abundance of heavy elements, its contribution is strongly reduced below solar metallicity. This makes it challenging to explain the inventory of the p nuclides in the solar system by the contribution from ccSNe alone. In particular, we find that ccSNe contribute less than 10% of the solar p nuclide abundances, with only a few exceptions. Due to the uncertain contribution from other nucleosynthesis sites in ccSNe, such as neutrino winds or {alpha}-rich freeze out, we conclude that the light p-nuclides ^74^Se, ^78^Kr, ^84^Sr, and ^92^Mo may either still be completely or only partially produced in ccSNe. The {gamma}-process accounts for up to twice the relative solar abundances for ^74^Se in one set of stellar models and ^196^Hg in the other set. The solar abundance of the heaviest p nucleus ^196^Hg is reproduced within uncertainties in one set of our models due to photodisintegration of the Pb isotopes ^208,207,206^Pb. For all other p nuclides, abundances as low as 2% of the solar level were obtained.
- ID:
- ivo://CDS.VizieR/J/ApJ/769/99
- Title:
- Nucleosynthetic yields for stars >12M{sun}
- Short Name:
- J/ApJ/769/99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We explore the sensitivity of nucleosynthesis in massive stars to the truncation of supernova explosions above a certain mass. It is assumed that stars of all masses contribute to nucleosynthesis by their pre-explosive winds, but above a certain limiting main sequence mass, M_BH_, the presupernova star becomes a black hole and ejects nothing more. The solar abundances from oxygen to atomic mass 90 are fit quite well assuming no cutoff at all, i.e., by assuming all stars up to 120M_{sun}_ make successful supernovae. Little degradation in the fit occurs if M_BH_ is reduced to 25M_{sun}_. If this limit is reduced further however, the nucleosynthesis of the s-process declines precipitously and the production of species made in the winds, e.g., carbon, becomes unacceptably large compared with elements made in the explosion, e.g., silicon and oxygen. By varying uncertain physics, especially the mass loss rate for massive stars and the rate for the ^22^Ne({alpha},n)^25^Mg reaction rate, acceptable nucleosynthesis might still be achieved with a cutoff as low as 18M_{sun}_. This would require, however, a supernova frequency three times greater than the fiducial value obtained when all stars explode in order to produce the required ^16^O. The effects of varying M_BH_ on the nucleosynthesis of ^60^Fe and ^26^Al, the production of helium as measured by {Delta}Y/{Delta}Z, and the average masses of compact remnants are also examined.
- ID:
- ivo://CDS.VizieR/J/A+A/576/A89
- Title:
- O abundances from HARPS in F-G stars
- Short Name:
- J/A+A/576/A89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed and uniform study of oxygen abundance from two different oxygen lines at 6158{AA} and 6300{AA} in a large sample of solar-type stars. The results are used to check the behaviour of these spectral lines as oxygen abundance indicators and to study the evolution of oxygen in thick and thin disk populations of the Galaxy. Equivalent width measurements were carried out for the [OI]6158 and [OI]6300 lines. LTE abundances were obtained from these two lines in 610 and 535 stars, respectively. Careful error analysis has been performed.
- ID:
- ivo://CDS.VizieR/J/MNRAS/453/2682
- Title:
- Observation & modelling for radio-loud AGN
- Short Name:
- J/MNRAS/453/2682
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The interactions between radio-loud AGN and their environments play an important role in galaxy and cluster evolution. Recent work has demonstrated fundamental differences between high- and low-excitation radio galaxies (HERGs and LERGs), and shown that they may have different relationships with their environments. In the Chandra Large Project ERA (Environments of Radio-loud AGN), we made the first systematic X-ray environmental study of the cluster environments of radio galaxies at a single epoch (z~0.5), and found tentative evidence for a correlation between radio luminosity and cluster X-ray luminosity. We also found that this relationship appeared to be driven by the LERG subpopulation. We have now repeated the analysis with a low-redshift sample (z~0.1), and found strong correlations between radio luminosity and environment richness and between radio luminosity and central density for the LERGs but not for the HERGs. These results are consistent with models in which the HERGs are fuelled from accretion discs maintained from local reservoirs of gas, while LERGs are fuelled more directly by gas ingested from the intracluster medium. Comparing the samples, we found that although the maximum environment richness of the HERG environments is similar in both samples, there are poorer HERG environments in the z~0.1 sample than in the z~0.5 sample. We have therefore tentative evidence of evolution of the HERG environments. We found no differences between the LERG subsamples for the two epochs, as would be expected if radio and cluster luminosities are related.
- ID:
- ivo://CDS.VizieR/J/AJ/159/199
- Title:
- OCCAM. IV. Open cluster abundances using APOGEE DR16
- Short Name:
- J/AJ/159/199
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Open Cluster Chemical Abundances and Mapping (OCCAM) survey aims to constrain key Galactic dynamical and chemical evolution parameters by the construction of a large, comprehensive, uniform, infrared-based spectroscopic data set of hundreds of open clusters. This fourth contribution from the OCCAM survey presents analysis using Sloan Digital Sky Survey/APOGEE DR16 of a sample of 128 open clusters, 71 of which we designate to be "high quality" based on the appearance of their color-magnitude diagram. We find the APOGEE DR16 derived [Fe/H] abundances to be in good agreement with previous high-resolution spectroscopic open cluster abundance studies. Using the high-quality sample, we measure Galactic abundance gradients in 16 elements, and find evolution of some of the [X/Fe] gradients as a function of age. We find an overall Galactic [Fe/H] versus Rgc gradient of -0.068{+-}0.001dex/kpc over the range of 6<Rgc<13.9kpc; however, we note that this result is sensitive to the distance catalog used, varying as much as 15%. We formally derive the location of a break in the [Fe/H] abundance gradient as a free parameter in the gradient fit for the first time. We also measure significant Galactic gradients in O, Mg, S, Ca, Mn, Cr, Cu, Na, Al, and K, some of which are measured for the first time. Our large sample allows us to examine four well-populated age bins in order to explore the time evolution of gradients for a large number of elements and comment on possible implications for Galactic chemical evolution and radial migration.
- ID:
- ivo://CDS.VizieR/J/PASJ/58/389
- Title:
- O/Fe abundances of 15 RR Lyrae
- Short Name:
- J/PASJ/58/389
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In order to study how the conventional spectroscopic method based on the equivalent widths of the Fe I and Fe II lines effectively applies to determining the atmospheric parameters (Teff, logg, v_t_, [Fe/H]) of RR Lyrae variables and how accurately the abundances can be established from such constructed model atmospheres, we analyzed 15 high-dispersion spectrograms of RR Lyr, DX Del, DH Peg, and VY Ser taken at several different phases by using the HDS spectrograph of the Subaru Telescope, and examined the consistency of the resulting phase-to-phase abundances.
