- ID:
- ivo://CDS.VizieR/J/ApJ/858/61
- Title:
- Carbon and Oxygen local interstellar spectra
- Short Name:
- J/ApJ/858/61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Local interstellar spectra (LIS) of primary cosmic ray (CR) nuclei, such as helium, oxygen, and mostly primary carbon are derived for the rigidity range from 10MV to ~200TV using the most recent experimental results combined with the state-of-the-art models for CR propagation in the Galaxy and in the heliosphere. Two propagation packages, GALPROP and HelMod, are combined into a single framework that is used to reproduce direct measurements of CR species at different modulation levels, and at both polarities of the solar magnetic field. The developed iterative maximum-likelihood method uses GALPROP- predicted LIS as input to HelMod, which provides the modulated spectra for specific time periods of the selected experiments for model-data comparison. The interstellar and heliospheric propagation parameters derived in this study are consistent with our prior analyses using the same methodology for propagation of CR protons, helium, antiprotons, and electrons. The resulting LIS accommodate a variety of measurements made in the local interstellar space (Voyager 1) and deep inside the heliosphere at low (ACE/CRIS, HEAO-3) and high energies (PAMELA, AMS-02).
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- ID:
- ivo://CDS.VizieR/J/A+A/620/A188
- Title:
- Carbon atom electron-impact double ionization
- Short Name:
- J/A+A/620/A188
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Electron-impact single- and double-ionization cross sections and Maxwellian rate coefficients are presented for the carbon atom. Scaling factors are introduced for the electron-impact excitation and ionization cross sections obtained in the distorted wave (DW) approximation. It is shown that the scaled DW cross sections provide good agreement with measurements for the single ionization of the C atom and C1+ ion. The direct double-ionization (DDI) process is studied using a multi-step approach. Ionization-ionization, excitation-ionization-ionization, and ionization-excitation-ionization branches are analyzed. It is demonstrated that the three-step processes contribute 40% of the total DDI cross sections for the case where one of the electrons takes all of the excess energy after the first ionization process.
- ID:
- ivo://CDS.VizieR/J/A+A/632/A32
- Title:
- Carbon depletion observed inside T Tauri inner rims
- Short Name:
- J/A+A/632/A32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The carbon content of protoplanetary disks is an important parameter to characterize planets formed at different disk radii. There is some evidence from far-infrared and submillimeter observations that gas in the outer disk is depleted in carbon, with a corresponding enhancement of carbon-rich ices at the disk midplane. Observations of the carbon content inside of the inner sublimation rim could confirm how much cpc on remains locked in kilometer size bodies in the disk. I aim to determine the density, temperature, and carbon abundance inside the disk dust sublimation rim in a set of T Tauri stars with full protoplanetary disks. Using medium-resolution, near-infrared (0.8 to 2.5um) spectra and the new GAIA DR2 distances, I self-consistently determine the stellar, extinction, veiling, and accretion properties of the 26 stars in my sample. From these values, and non-accreting T Tauri spectral templates, I extract the inner disk excess of the target stars from their observed spectra. Then I identify a series of C0 recombination lines in 18 of these disks and use the CHIANTI atomic line database with an optically thin slab model to constrain the average ne, Te, and nC for these lines in the five disks with a complete set of lines. By comparing these values with other slab models of the inner disk using the Cloudy photoionization code, I also constrain nH and the carbon abundance, XC, and hence the amount of carbon 'missing' from the slab. For one disk, DR Tau, I use relative abundances for the accretion stream from the literature to also determine XSi and XN . The inner disks modeled here are extremely dense (nH~10^16^cm^-3^), warm (Te~4500K), and moderately ionized (logXe~3.3). Three of the five modeled disks show robust carbon depletion up to a factor of 42 relative to the solar value. I discuss multiple ways in which the 'missing' carbon could be locked out of the accreting gas. Given the high-density inner disk gas, evidence for radial drift, and lack of obvious gaps in these three systems, their carbon depletion is most consistent with the 'missing' carbon being sequestered in kilometer size bodies. For DR Tau, nitrogen and silicon are also depleted by factors of 45 and 4, respectively, suggesting that the kilometer size bodies into which the grains are locked were formed beyond the N_2_ snowline. I explore briefly what improvements in the models and observations are needed to better address this topic in the future.
- ID:
- ivo://CDS.VizieR/J/ApJ/833/20
- Title:
- Carbon-enhanced metal-poor (CEMP) star abundances
- Short Name:
- J/ApJ/833/20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate anew the distribution of absolute carbon abundance, A(C)=log{epsilon}(C), for carbon-enhanced metal-poor (CEMP) stars in the halo of the Milky Way, based on high-resolution spectroscopic data for a total sample of 305 CEMP stars. The sample includes 147 CEMP-s (and CEMP-r/s) stars, 127 CEMP-no stars, and 31 CEMP stars that are unclassified, based on the currently employed [Ba/Fe] criterion. We confirm previous claims that the distribution of A(C) for CEMP stars is (at least) bimodal, with newly determined peaks centered on A(C)=7.96 (the high-C region) and A(C)=6.28 (the low-C region). A very high fraction of CEMP-s (and CEMP-r/s) stars belongs to the high-C region, while the great majority of CEMP-no stars resides in the low-C region. However, there exists complexity in the morphology of the A(C)-[Fe/H] space for the CEMP-no stars, a first indication that more than one class of first-generation stellar progenitors may be required to account for their observed abundances. The two groups of CEMP-no stars we identify exhibit clearly different locations in the A(Na)-A(C) and A(Mg)-A(C) spaces, also suggesting multiple progenitors. The clear distinction in A(C) between the CEMP-s (and CEMP-r/s) stars and the CEMP-no stars appears to be as successful, and likely more astrophysically fundamental, for the separation of these sub-classes as the previously recommended criterion based on [Ba/Fe] (and [Ba/Eu]) abundance ratios. This result opens the window for its application to present and future large-scale low- and medium-resolution spectroscopic surveys.
- ID:
- ivo://CDS.VizieR/J/ApJ/824/L19
- Title:
- Carbon-enhanced metal-poor star BD+44493 EWs
- Short Name:
- J/ApJ/824/L19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The carbon-enhanced metal-poor star BD+44{deg}493 ([Fe/H]=-3.9) has been proposed as a candidate second-generation star enriched by metals from a single Pop III star. We report the first detections of P and S and the second detection of Zn in any extremely metal-poor carbon-enhanced star, using new spectra of BD+44493 collected by the Cosmic Origins Spectrograph on the Hubble Space Telescope. We derive [P/Fe]=-0.34+/-0.21, [S/Fe]=+0.07+/-0.41, and [Zn/Fe]=-0.10+/-0.24. We increase by 10-fold the number of SiI lines detected in BD+44493, yielding [Si/Fe]=+0.15+/-0.22. The [S/Fe] and [Zn/Fe] ratios exclude the hypothesis that the abundance pattern in BD+44493 results from depletion of refractory elements onto dust grains. Comparison with zero-metallicity supernova (SN) models suggests that the stellar progenitor that enriched BD+44493 was massive and ejected much less than 0.07M_{sun}_ of ^56^Ni, characteristic of a faint SN.
- ID:
- ivo://CDS.VizieR/J/ApJ/797/21
- Title:
- Carbon-enhanced metal-poor stars
- Short Name:
- J/ApJ/797/21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We revisit the observed frequencies of carbon-enhanced metal-poor (CEMP) stars as a function of the metallicity in the Galaxy, using data from the literature with available high-resolution spectroscopy. Our analysis excludes stars exhibiting clear overabundances of neutron-capture elements and takes into account the expected depletion of surface carbon abundance that occurs due to CN processing on the upper red giant branch. This allows for the recovery of the initial carbon abundance of these stars, and thus for an accurate assessment of the frequencies of carbon-enhanced stars. The correction procedure we develop is based on stellar-evolution models and depends on the surface gravity, log g, of a given star.
- ID:
- ivo://CDS.VizieR/J/A+A/509/A93
- Title:
- Carbon-enhanced metal-poor stars
- Short Name:
- J/A+A/509/A93
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Carbon-enhanced metal-poor (CEMP) stars are known to have properties that reflect the nucleosynthesis of the first low- and intermediate- mass stars, because most have been polluted by a now-extinct AGB star. By considering abundances in the various CEMP subclasses separately, we try to derive parameters (such as metallicity, mass, temperature, and neutron source) characterising AGB nucleosynthesis from the specific signatures imprinted on the abundances, and separate them from the impact of thermohaline mixing, first dredge-up, and dilution associated with the mass transfer from the companion. To place CEMP stars in a broader context, we collect abundances for about 180 stars of various metallicities (from solar to [Fe/H]=-4), luminosity classes (dwarfs and giants), and abundance patterns (e.g. C-rich and poor, Ba-rich and poor), from both our own sample and the literature.
- ID:
- ivo://CDS.VizieR/J/AJ/139/1051
- Title:
- Carbon-enhanced metal-poor stars in the Galaxy
- Short Name:
- J/AJ/139/1051
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have developed a new procedure to search for carbon-enhanced metal-poor (CEMP) stars from the Hamburg/ESO (HES) prism-survey plates. This method employs an extended line index for the CH G band, which we demonstrate to have superior performance when compared to the narrower G-band index formerly employed to estimate G-band strengths for these spectra.
- ID:
- ivo://CDS.VizieR/J/A+A/614/A68
- Title:
- Carbon-enhanced metal-poor stars sample
- Short Name:
- J/A+A/614/A68
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Carbon-enhanced metal-poor (CEMP) stars represent a sizeable fraction of all known metal-poor stars in the Galaxy. Their formation and composition remains a significant topic of investigation within the stellar astrophysics community. We analysed a sample of low-resolution spectra of 30 dwarf stars, obtained using the the visual and near UV FOcal Reducer and low dispersion Spectrograph for the Very Large Telescope (FORS/VLT) of the European Southern Observatory (ESO) and the Gemini Multi-Object Spectrographs (GMOS) at the GEMINI telescope, to derive their metallicity and carbon abundance. We derived C and Ca from all spectra, and Fe and Ba from the majority of the stars. Conclusions. We have extended the population statistics of CEMP stars and have confirmed that in general, stars with a high C abundance belonging to the high C band show a high Ba-content (CEMP-s or -r/s), while stars with a normal C-abundance or that are C-rich, but belong to the low C band, are normal in Ba (CEMP-no).
- ID:
- ivo://CDS.VizieR/J/ApJ/801/125
- Title:
- Carbon in red giants in GCs and dSph galaxies
- Short Name:
- J/ApJ/801/125
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present carbon abundances of red giants in Milky Way (MW) globular clusters and dwarf spheroidal galaxies (dSphs). Our sample includes measurements of carbon abundances for 154 giants in the clusters NGC2419, M68, and M15 and 398 giants in the dSphs Sculptor, Fornax, Ursa Minor, and Draco. This sample doubles the number of dSph stars with measurements of [C/Fe]. The [C/Fe] ratio in the clusters decreases with increasing luminosity above (L/L_{sun}_)~=1.6, which can be explained by deep mixing in evolved giants. The same decrease is observed in dSphs, but the initial [C/Fe] of the dSph giants is not uniform. Stars in dSphs at lower metallicities have larger [C/Fe] ratios. We hypothesize that [C/Fe] (corrected to the initial carbon abundance) declines with increasing [Fe/H] due to the metallicity dependence of the carbon yield of asymptotic giant branch stars and due to the increasing importance of SNe Ia at higher metallicities. We also identified 11 very carbon-rich giants (eight previously known) in three dSphs. However, our selection biases preclude a detailed comparison to the carbon-enhanced fraction of the MW stellar halo. Nonetheless, the stars with [C/Fe]<+1 in dSphs follow a different [C/Fe] track with [Fe/H] than the halo stars. Specifically, [C/Fe] in dSphs begins to decline at lower [Fe/H] than in the halo. The difference in the metallicity of the [C/Fe] "knee" adds to the evidence from [{alpha}/Fe] distributions that the progenitors of the halo had a shorter timescale for chemical enrichment than the surviving dSphs.
