- ID:
- ivo://CDS.VizieR/J/A+AS/113/539
- Title:
- A survey of carbon stars in the SMC
- Short Name:
- J/A+AS/113/539
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A survey of carbon stars in the outer parts of the Small Magellanic Cloud has been completed; the candidate objects were identified by inspecting UK Schmidt Telescope objective-prism plates which cover a total area of ~220 sq deg on the sky, including the inter-Cloud region. Co-ordinates are given for 1185 newly identified carbon stars.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/586/A158
- Title:
- Binary properties of CH and CEMP stars
- Short Name:
- J/A+A/586/A158
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The HERMES spectrograph installed on the 1.2-m Mercator telescope has been used to monitor the radial velocity of 13 low-metallicity carbon stars, among which seven carbon-enhanced metal-poor (CEMP) stars and six CH stars. All stars but one show clear evidence for binarity. New orbits are obtained for eight systems. The sample covers an extended range in orbital periods, extending from 3.4d (for the dwarf carbon star HE 0024-2523) to about 54yr (for the CH star HD 26, the longest known among barium, CH, and extrinsic S stars). The period - eccentricity diagram for the 40 low-metallicity carbon stars with orbits now available shows no difference between CH and CEMP-s stars (the latter corresponding to those CEMP stars enriched in s-process elements, as are CH stars). We suggest that they must be considered as one and the same family and that their different names only stem from historical reasons. Indeed, these two families have as well very similar mass-function distributions, corresponding to companions with masses in the range 0.5-0.7M_{sun}_, indicative of white-dwarf companions, adopting 0.8-0.9M_{sun}_ for the primary component. This result confirms that CH and CEMP-s stars obey the same mass-transfer scenario as their higher-metallicity analogues, barium stars. The P-e diagrams of barium, CH, and CEMP-s stars are indeed very similar. They reveal two different groups of systems: one with short orbital periods (P<1000d) and mostly circular or almost circular orbits, and another with longer period and eccentric (e>0.1) orbits. These two groups either trace different evolutionary channels during the mass-transfer episode responsible for the chemical peculiarities of the Ba/CH/CEMP-s stars, or result from the operation of tidal circularisation in a more recent past, when the current giant star was ascending the first giant branch.
- ID:
- ivo://CDS.VizieR/J/ApJ/652/1585
- Title:
- Bright metal-poor stars from HES survey
- Short Name:
- J/ApJ/652/1585
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a sample of 1777 bright (9<B<14) metal-poor candidates selected from the Hamburg/ESO Survey (HES). Despite saturation effects present in the red portion of the HES objective-prism spectra, the data were recoverable and quantitative selection criteria could be applied to select the sample. Analyses of medium-resolution (~2{AA}) follow-up spectroscopy of the entire sample, obtained with several 24m class telescopes, yielded 145 new metal-poor stars with metallicity [Fe/H]<-2.0, of which 79 have [Fe/H]<-2.5 and 17 have [Fe/H]<-3.0. We also obtained C/Fe estimates for all of these stars.
- ID:
- ivo://CDS.VizieR/J/A+A/344/263
- Title:
- B-V colour excess of Miras
- Short Name:
- J/A+A/344/263
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A study of 73 carbon-rich Miras (see Subsec. 6.1) with suitable solution for 56 stars at one or several phase of their variations. In the second part, preliminary and incomplete results are reported for 17 additional Miras observed at only one phase. Table 5 contains our HC-CV-classification (see text) for the stars and their colour excess E(B-V) as determined by the method described in Subsec. 2.2.
- ID:
- ivo://CDS.VizieR/J/ApJ/791/58
- Title:
- C and O abundances across the Hertzsprung gap
- Short Name:
- J/ApJ/791/58
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derived atmospheric parameters and spectroscopic abundances for C and O for a large sample of stars located in the Hertzsprung gap in the Hertzsprung-Russell diagram in order to detect chemical peculiarities and get a comprehensive overview of the population of stars in this evolutionary state. We have observed and analyzed high-resolution spectra (R = 60,000) of 188 stars in the mass range 2-5 M_{sun}_ with the 2.7 m Harlan J. Smith Telescope at the McDonald Observatory including 28 stars previously identified as Am/Ap stars. We find that the C and O abundances of the majority of stars in the Hertzsprung gap are in accordance with abundances derived for local lower-mass dwarfs but detect expected peculiarities for the Am/Ap stars. The C and O abundances of stars with T_eff_< 6500 K are slightly lower than for the hotter objects but the C/O ratio is constant in the analyzed temperature domain. No indication of an alteration of the C and O abundances of the stars by mixing during the evolution across the Hertzsprung gap could be found before the homogenization of their atmospheres by the first dredge-up.
- ID:
- ivo://CDS.VizieR/J/AJ/130/2804
- Title:
- Carbon abundances in metal-poor stars
- Short Name:
- J/AJ/130/2804
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We develop and test a method for the estimation of metallicities ([Fe/H]) and carbon abundance ratios ([C/Fe]) for carbon-enhanced metal-poor (CEMP) stars based on the application of artificial neural networks, regressions, and synthesis models to medium-resolution (1-2{AA}) spectra and J-K colors. We calibrate this method by comparison with metallicities and carbon abundance determinations for 118 stars with available high-resolution analyses reported in the recent literature.
- 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/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.
