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The observed abundance diversities among the CEMP stars can shed light on the formation and evolution of elements in the early Galaxy. In this work, we present results obtained from a detailed abundance analysis of a sample of seven extrinsic carbon stars. The analysis is based on high-resolution spectra obtained with HCT/HESP (R$\sim$60,000) and SUBARU/HDS (R$\sim$50,000). We present, for the first time, the elemental abundance results for the objects BD$-$19 132, BD$-$19 290, HE~1304$-$2111, HE~1354$-$2257, and BD+19 3109. Abundances of a few elements are available in literature for HE~1157$-$0518 and HD~202851, we present an update on the abundances of these elements along with new abundance estimates for several other elements. Our analysis confirms the object HD~202851 to be a CH star. While BD$-$19 132, HE~1354$-$2257, and BD+19 3109 are found to be CEMP-s stars, the objects BD$-$19 290, HE~1157$-$0518, and HE~1304$-$2111 are found to belong to CEMP-r/s group. The observed abundance patterns of the three CEMP-r/s stars are well reproduced with the i-process model predictions. While the objects BD+19 3109 and HD~202851 are confirmed binaries, the binary status of the remaining objects are not known. Analysis based on different elemental abundance ratios confirms low-mass former AGB companions for all the objects. Kinematic analysis shows that BD$-$19 290, HE~1157$-$0518, HE~1354$-$2257, and BD+19 3109 belong to the Galactic halo, whereas BD$-$19 132, HE~1304$-$2111, and HD~202851 are members of Galactic thin disk., Accepted for publication in the Astrophysical Journal (ApJ)

We present results from a study of 94 red giant stars in the globular cluster M53. We use low-resolution spectra to measure the strength of CN and CH features at ∼3800 and 4300 Å, respectively. The strengths of these features are used to classify stars into a CN-enhanced and CN-normal population and to measure C and N abundances in all 94 stars. We find the red giant branch stars to be evenly split between the two populations identified, and observe the presence of CN-enhanced stars on the asymptotic giant branch. In addition, we identify five CH star candidates based on the strength of their CN and CH band features, and the presence of a P-branch in their CH band. We compare our identification of multiple populations to those based on the Na–O anticorrelation and pseudo-color indices in Hubble Space Telescope UV photometry, and find general agreement between all three methods. Our large sample size also allows us to study the radial distribution of each population, and we find that the CN-enhanced population is more centrally concentrated. We use our C and N measurements to compare the evolutionary changes in these elements as a function of magnitude between the two populations, and show that both populations experience similar evolutionary changes to the surface abundances of C and N. Finally, we calculate C+N+O abundances for each population and compare them to similar measurements made in M10; we find that in both clusters, CN-enhanced stars have a slightly enhanced C+N+O (Δ(C+N+O) ∼ 0.2 dex).

The evolutionary status of the bright peculiar carbon giant TU Gemis fairly uncertain. The possibility that this is aCH star—aGalactic halo star with characteristic chemical-composition anomalies—is considered. Unfortunately, data on the atmospheric chemical composition of TUGem are relatively few and are ambiguous. The results of an analysis of a moderate-resolution optical and near-infrared spectrum of TU Gem obtained on the 2-m telescope of Terskol Peak Observatory (Northern Caucasus) is presented. The atmospheric parameters of TU Gem T eff = 3100 K, C/O = 1.10, and [N/Fe] = 0.0 for the derived metallicity [Fe/H] = 0.0 are taken from [1]. The abundances of Na, Mg, Ca, Ti, and Cr are estimated to be normal or slightly enhanced, and the lithium abundance is log N(Li) = +0.1. The abundances of s-process elements are substantially enhanced in the atmosphere of TU Gem, namely, [s/Fe] ≈ 2, for both light and heavy s-process elements. The range of uncertainty in [Fe/H] is 0.0−0.3, and the uncertainties in other estimates are Δ[M/Fe]≈ ±0.3 and Δ[s/Fe] = ±0.5. The results show that TU Gem is an anomalous carbon giant, but not a CH star.

The slow ($s$) and intermediate ($i$) neutron ($n$) capture processes occur both in asymptotic giant branch (AGB) stars, and in massive stars. To study the build-up of the $s$- and $i$-products at low metallicity, we investigate the abundances of Y, Ba, La, Nd, and Eu in 98 stars, at $-2.4+0.7$ is best fit with a model of a rapidly-rotating massive star, the second (likely CH star) with the $i$-process, while the third has no satisfactory fit. For a more general understanding of the build-up of the heavy elements, we calculate for the first time the cumulative contribution of the $s$- and $i$-processes to the chemical enrichment in Sculptor, and compare with theoretical predictions. By correcting for the $r$-process, we derive $\text{[Y/Ba]}_{s/i}=-0.85\pm0.16$, $\text{[La/Ba]}_{s/i}=-0.49\pm0.17$, and $\text{[Nd/Ba]}_{s/i}=-0.48\pm0.12$, in the overall $s$- and/or $i$-process in Sculptor. These abundance ratios are within the range of those of CEMP stars in the Milky Way, which have either $s$- or $i$-process signatures. The low $\text{[Y/Ba]}_{s/i}$ and $\text{[La/Ba]}_{s/i}$ that we measure in Sculptor are inconsistent with them arising from the $s$-process only, but are more compatible with models of the $i$-process. Thus we conclude that both the $s$- and $i$-processes were important for the build-up of $n$-capture elements in the Sculptor dwarf spheroidal galaxy., Comment: Accepted in A&A, 16 pages, 10 figures, Paper II in series

We identify 233 X-ray sources, of which 95 are new, in a 222 ks exposure of Omega Centauri with the Chandra X-ray Observatory's ACIS-I detector. The limiting unabsorbed flux in the core is $f_x$ (0.5$-$6.0 keV) $\simeq$ 3 $\times$ 10$^{-16}$ erg s$^{-1}$ cm$^{-2}$ ($L_X$ $\simeq$ 1 $\times$ 10$^{30}$ erg s$^{-1}$ at 5.2 kpc). We estimate that ~$60\pm 20$ of these are cluster members, of which ~30 lie within the core ($r_c$ $=$ 155 arcsec), and another ~30 between 1$-$2 core radii. We identify four new optical counterparts, for a total of 45 likely identifications. Probable cluster members include 18 cataclysmic variables (CVs) and CV candidates, one quiescent low-mass X-ray binary, four variable stars, and five stars that are either associated with w Cen's anomalous red giant branch, or are sub-subgiants. We estimate that the cluster contains $40\pm 10$ CVs with $L_X$ $>$ 10$^{31}$ erg s$^{-1}$, confirming that CVs are underabundant in w Cen relative to the field. Intrinsic absorption is required to fit X-ray spectra of six of the nine brightest CVs, suggesting magnetic CVs, or high-inclination systems. Though no radio millisecond pulsars (MSPs) are currently known in w Cen, more than 30 unidentified sources have luminosities and X-ray colours like those of MSPs found in other globular clusters; these could be responsible for the Fermi-detected gamma-ray emission from the cluster. Finally, we identify a CH star as the counterpart to the second-brightest X-ray source in the cluster and argue that it is a symbiotic star. This is the first such giant/white dwarf binary to be identified in a globular cluster.

The TU Gem star has long been known as a peculiar carbon giant of the Galaxy halo, but its classification as a CH star is still debated. We estimated the TU Gem atmosphere parameters through modeling its spectrum and comparision one with the spectra of the star observed in two wide spectral ranges (λλ 400–720 nm and λλ 900–2440 nm). The low-dispersion optical TU Gem spectrum obtained by Barnbaum et al. (2006) (R ∼ 600) and the infrared spectrum presented by Tanaka et al. (2007) (R ∼ 2600) were used in the analysis. The model atmospheres were calculated using the SAM12 software (Pavlenko, 2003). Since the metallicity ([Fe/H]) value could not be determined conclusively based on our spectral data, only the TU Gem effective temperature T eff (that depends weakly on metallicity) was defined with certainty (T eff = 3000 ± 100 K). We determined the C/O, [C/Fe], and [N/Fe] values for the −2.0 ≤ [Fe/H] ≤ 0.0 range with a step of Δ[Fe/H] = 0.5. Our estimate of [C/Fe] (0.63–0.67 at [Fe/H] = −1.0) is higher than the corresponding estimate ([C/Fe] = 0.21 at [Fe/H] = −1.1) given in (Kipper et al., 1996), while the estimates for [N/Fe] at the stated metallicities agree with each other: [N/Fe] = +1.0. This brings TU Gem closer to CH stars, but a detailed analysis of the chemical composition of the TU Gem atmosphere is required to reach a definite conclusion.

We present a comprehensive chemical abundance analysis of five red giants and two horizontal branch (HB) stars towards the southern Galactic bulge, at (l,b)$\sim$(0$^{\rm o}$,-11$^{\rm o}$). Based on high-resolution spectroscopy obtained with the Magellan/MIKE spectrograph, we derived up to 23 chemical element abundances and identify a mixed bag of stars, representing various populations in the central regions of the Galaxy. Although cosmological simulations predict that the inner Galaxy was host to the first stars in the Universe, we see no chemical evidence of the ensuing massive supernova explosions: all of our targets exhibit halo-like, solar [Sc/Fe] ratios, which is in contrast to the low values predicted from Population III nucleosynthesis. One of the targets is a CEMP-s star at [Fe/H]=-2.52 dex, and another one is a moderately metal-poor ([Fe/H]=-1.53 dex) CH star with strong enrichment in s-process elements (e.g., [Ba/Fe]=1.35). These individuals provide the first contenders of these classes of stars towards the bulge. Four of the carbon-normal stars exhibit abundance patterns reminiscent of halo star across a metallicity range spanning -2.0 to -2.6 dex, i.e., enhanced $\alpha$-elements and solar Fe-peak and n-capture elements, and the remaining one is a regular metal-rich bulge giant. The position, distance, and radial velocity of one of the metal-poor HB stars coincides with the old trailing arm of the disrupted Sagittarius dwarf galaxy. While their uncertain proper motions prohibit a clear kinematic separation, the stars' abundances and distances suggest that these metal-poor candidates, albeit located towards the bulge, are not of the bulge, but rather inner halo stars on orbits that make them pass through the central regions. Thus, we caution similar claims of detections of metal-poor stars as true habitants of the bulge. (Abridged), Comment: 15 pages, 11 figures, accepted for publication in Astronomy & Astrophysics

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 (including HIP 53522, a new member of the family, as revealed by a detailed abundance study). 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 3.4 d (for the dwarf carbon star HE 0024-2523) to about 54 yr (for the CH star HD 26, the longest known among barium, CH, and extrinsic S stars). Three systems exhibit low-amplitude velocity variations with periods close to 1 yr superimposed on a long-term trend. In the absence of an accurate photometric monitoring of these systems, it is not clear yet whether these variations are the signature of a very low-mass companion or of regular envelope pulsations. The period-eccentricity (P-e) 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 0.5-0.7 M⊙, indicative of white-dwarf companions, adopting 0.8-0.9 M⊙ 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< 1000 d) 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., SCOPUS: ar.j, info:eu-repo/semantics/published

We report on the serendipitous discovery of a carbon star near the centre of the low-metallicity globular cluster NGC 6426. We determined its membership and chemical properties using medium-resolution spectra. The radial velocity of −159 km s−1 makes it a member of the cluster. We used photometric data from the literature and the COMARCS stellar atmospheric models to derive its luminosity, effective temperature, surface gravity, metallicity, and approximate C, N and O abundance ratios. According to these properties, we suggest that this star is a genuine carbon-rich low-metallicity asymptotic giant branch star.

Aims. We determined the atmospheric parameters and abundance pattern of two chemically peculiar metal-poor stars: HD 10613 and BD+04 ◦ 2466 in order to better understand their evolutionary state and the nature of the s-element enhancement of these stars. Methods. We used high resolution optical spectroscopy. Atmospheric parameters and abundances were determined in the localthermodynamic-equilibrium model atmospheres of Kurucz using the spectral analysis code MOOG. Results. We conclude that HD 10613 is another metal-poor barium star with C/O = 0.52 and [Fe/H] = −0.82, while BD+04 ◦ 2466 is a CH star with C/O = 3.6 and [Fe/H] = −1.92 rather than a metal-deficient barium star as it was previously classified. BD+04 ◦ 2466 appears to be enriched in lead with [Pb/Ce] =+ 0.85 and [Pb/La] =+ 0.72. For BD+04 ◦ 2466 the abundance of lead is in agreement with predictions from AGB models. Due to the low luminosity of these two stars, their observed s-process overabundance is better explained by mass-transfer in the past from an AGB star.

We present carbon abundances of red giants in Milky Way globular clusters and dwarf spheroidal galaxies (dSphs). Our sample includes measurements of carbon abundances for 154 giants in the clusters NGC 2419, 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 log(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 Type Ia supernovae at higher metallicities. We also identified 11 very carbon-rich giants (8 previously known) in three dSphs. However, our selection biases preclude a detailed comparison to the carbon-enhanced fraction of the Milky Way 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., accepted to ApJ; 20 pages, 11 figures, 2 machine-readable tables

We present results of an analysis of high-resolution spectra obtained with the Subaru Telescope High Dispersion Spectrograph, of two Carbon-Enhanced Metal-Poor stars, HE 1305+0007 and HE 1152-0355, and of the classical CH star HD 5223. All of these stars have relatively low effective temperatures (4000-4750 K) and high carbon abundances. The stellar atmospheric parameters indicate that they all have surface gravities consistent with a present location on the red-giant branch, and metallicities of [Fe/H] = -2.0 (HE 1305+0007, HD 5223) and [Fe/H]= -1.3 (HE 1152-0355). In addition to their large enhancements of carbon all three stars exhibit strong enhancements of the s-process elements relative to iron. HE 1305+0007 exhibits a large enhancement of the 3rd-peak s-process element lead, with [Pb/Fe] = +2.37, as well as a high abundance of the r-process element europium, [Eu/Fe] = +1.97. Thus, HE 1305+0007 joins the growing class of the so-called ``Lead Stars'', and also the class of objects that exhibit the presence of both r-process and s-process elements, the CEMP-r/s stars. The large enhancement of n-capture elements exhibited by HE 1152-0355 and HD 5223 are more consistent with the abundance patterns generally noticed in CH stars. The elemental abundance distributions observed in these stars are discussed in the light of existing theories of CH star formation, as well as the suggested formation scenarios of the CEMP-r/s group., Comment: 19 pages, 11 figures, MNRAS format, accepted for publication in MNRAS

We report results of a photometric survey with the WIYN telescope for carbon stars in the M 31 dwarf spheroidal (dSph) companions And III, And V, And VI, and And VII, as well as in the relatively isolated Local Group dSph Cetus. We find three carbon-star candidates in And VII and one carbon star in each And VI and Cetus. Comparing the carbon star content with other Local Group dwarf galaxies, we argue against the presence of substantial intermediate-age stellar populations in the all of the galaxies surveyed with the exception of And VII. We discuss these results in the context of the origin of the Andromeda dSphs and conclude that these are ancient galaxies, most of which ceased star formation long before the main merger events in M31. The M31 dSphs therefore show less diversity in star formation histories than the Galactic dSph companions, or the M31 dE companions, as illustrated by NGC147 which was surveyed as a calibration object. All of our dSph targets except And V have candidate carbon stars below the tip of the RGB, which resemble CH stars found in globular clusters. We estimate that 0.3% of stars in the dSphs are CH stars, presumably as a result of C pollution from a binary companion. Comparisons with CH star frequencies in globular clusters could constrain the impact of dense environments on the frequency of this form of binary star evolution., accepted for publication in AJ

We present a detailed abundance analysis, including spectral syntheses, of a very metal-poor ([Fe/H]= -2.7), peculiar main sequence star, HE0024-2523 detected during the course of the Keck Pilot Program. Radial velocities of this star were obtained during four different observing runs over a time span of 1.1 years, and demonstrate that it is clearly a short period spectroscopic binary. An orbital solution was obtained, and orbital parameters were determined with high precision. The rotational velocity was also measured (vsin i=9.7$\pm$1.5 kms); rotation appears likely to be synchronous with the orbit. The abundance analysis and spectral syntheses indicate that the object is a CH star characterized by extreme s-process enrichment, likely due to mass accretion from an evolved companion which has now probably become a white dwarf. The lead (Pb) abundance of HE0024-2523 is very high, the same as that of the recently discovered lead-rich metal-poor star CS 29526-110, [Pb/Fe]=+3.3. The abundance ratio of the heavy-s to light-s elements, as characterized by Pb and Ba, [Pb/Ba]=+1.9, is the highest yet found for any metal-poor star, and is about 0.7 dex higher than that of CS29526-110. On the basis of the measured isotopic ratio of carbon (12C/13C about 6) we argue that the mass donor must have had an original mass of at least 3 Msun. The unusually short period of this CH star suggests that it underwent a past common-envelope phase with its evolved companion. Our results are compared to the latest available models for AGB yields and s-process nucleosynthesis. We also discuss the possible connection between HE0024-2523 the lithium depletion of halo stars, and halo blue straggler formation., Comment: 55 pages, 17 color figures included; Accepted for publication in the February 2003 issue of the Astronomical Journal

We report the abundances of neutron-capture elements in eight carbon-rich, metal-poor (-2.7=

We present Magellan/MIKE and Keck/HIRES high-resolution spectra of six red giant stars in the dwarf galaxy Segue 1. Including one additional Segue 1 star observed by Norris et al. (2010), high-resolution spectra have now been obtained for every red giant in Segue 1. Remarkably, three of these seven stars have metallicities below [Fe/H] = -3.5, suggesting that Segue 1 is the least chemically evolved galaxy known. We confirm previous medium-resolution analyses demonstrating that Segue 1 stars span a metallicity range of more than 2 dex, from [Fe/H] = -1.4 to [Fe/H] = -3.8. All of the Segue 1 stars are alpha-enhanced, with [alpha/Fe] ~ 0.5. High alpha-element abundances are typical for metal-poor stars, but in every previously studied galaxy [alpha/Fe] declines for more metal-rich stars, which is typically interpreted as iron enrichment from supernova Ia. The absence of this signature in Segue 1 indicates that it was enriched exclusively by massive stars. Other light element abundance ratios in Segue 1, including carbon-enhancement in the three most metal-poor stars, closely resemble those of metal-poor halo stars. Finally, we classify the most metal-rich star as a CH star given its large overabundances of carbon and s-process elements. The other six stars show remarkably low neutron-capture element abundances of [Sr/H] < -4.9 and [Ba/H] < -4.2, which are comparable to the lowest levels ever detected in halo stars. This suggests minimal neutron-capture enrichment, perhaps limited to a single r-process or weak s-process synthesizing event. Altogether, the chemical abundances of Segue 1 indicate no substantial chemical evolution, supporting the idea that it may be a surviving first galaxy that experienced only one burst of star formation., ApJ, accepted, 20 pages (emulateapj), 9 figures

We have monitored the radial velocities of seven very metal-poor stars with abnormally strong CH G bands. On the basis of their colors four are giants (gCH) and three are subgiants (sgCH). Three of the gCH stars are definite spectroscopic binaries with long periods, 505 days < P < 3125 days. Two of these possess s-process overabundances, while the third does not. The binary status of the fourth, the r-process–rich giant CS 22892-052, is uncertain. The three sgCH stars possess marked s-process overabundances, but contrary to the expectations of the asymptotic giant branch mass transfer paradigm, their radial velocities have remained constant with σ ±0.4 km s-1 for the past eight years. Comparison of the standard deviations of our radial velocities with those of McClure's sgCH binaries indicates that the probability that our three stars belong to the population of sgCH binary stars is very small. The dereddened colors and effective temperatures of these stars are similar to those of LP 706-7, which has similar composition and also no measurable velocity variation. The carbon overabundances and the heavy-to-light s-process ratios of all four stars exceed those of disk sgCH stars by an order of magnitude. We return to Bond's 1974 suggestion that these are post–He flash stars that have mixed some envelope material into their cores according to a scheme proposed by Rood.

We present calibrations of the effective temperatures of giant stars versus [Fe/H] and colours , , , , , , , , , , and . These calibrations are based on a large sample of field and globular cluster stars which roughly cover spectral types from F0 to K5. Their effective temperatures, scaled to direct determinations via reliable angular diameter measurements, were derived by applying the infrared flux method. The empirical relations have been fitted to polynomials of the form by using the least squares method. The precision of the fits ranges from 40 K for to 170 K for . We tabulate intrinsic colours of giant stars in the ranges: 3500 K 8000 K; -3.0 . We also present the calibration of BC(V) as a function of log and metallicity. Finally, we compare the resulting scale of temperatures with previous works.

The strengths of the CN, NH, and CH bands in the spectra of Population II red giants are discussed based on observations of a sample of both globular cluster and field giants. We confirm an anticorrelation between the oxygen abundance and the CN indices and a correlation between the 3883 A CN band and the 3360 A NH band strengths among giants in the globular clusters M15 and M13. We find one M15 star (IV-38) with a strong 3883 A CN band and detectable 4215 A CN and 3360 A NH bands. Abundance analysis of M15 IV-38 reveals a comparable carbon abundance to a comparison star that has much weaker CN bands. One possible reason for this may be that IV-38 is an insipid CH star that has also undergone some deep mixing. Alternatively, the atmosphere of IV-38 may have been extensively processed through the O→N cycle of hydrogen burning such that carbon has been affected by O→C conversion. By combining our data set with material from the literature and high-quality B–V photometry, we find that the CN band strength differences among the M5 red giants do not appear to broaden the giant branch of that cluster within the photometric errors. Using the CN, CH, and NH bands, we are able to confirm that the metal-poor field giant HD 135148 is a CH-strong star and has not undergone deep mixing.

New, improved, barium abundances for 33 extremely metal-poor halo stars from the 1995 sample of McWilliam et al. have been computed. The mean [Ba/Eu] ratio for stars with [Fe/H] ≤ -2.4 is -0.69 ± 0.06 dex, consistent with pure r-process nucleosynthesis within the measurement uncertainties. Although the [Sr/Fe] and [Ba/Fe] abundance ratios span a range of 2.6 dex, the mean values are approximately constant with [Fe/H]. This is consistent with a model of chemical evolution in which the parent clouds were enriched by small numbers of supernova events. In this model, the decreasing heavy-element dispersion with increasing [Fe/H] is simply due to the averaging of element yields from many supernovae at higher [Fe/H]; however, it is necessary to increase the number of extremely metal-poor stars known in order to confirm this picture. In addition to the random Sr component from the r-process, the [Sr/Ba] ratios indicate that there is a second, also random, source of Sr from an as yet unidentified nucleosynthesis site.

Abundances relative to iron for carbon, nitrogen, strontium and barium are presented for 33 stars on the red giant branch of the globular cluster omega Centauri. They are based on intermediate-resolution spectroscopic data covering the blue spectral region analyzed using spectrum synthesis techniques. The data reveal the existence of a broad range in the abundances of these elements, and a comparison with similar data for main sequence stars enables insight into the evolutionary history of the cluster. The majority of the red giant branch stars were found to be depleted in carbon, i.e. [C/Fe], 20 pages, 13 figures, Accepted to ApJ

Infrared JHK photometry is given for all the proposed LMC CH stars in the list (43 stars) of Hartwick & Cowley (1985, A. J., 334). Their luminosities range up to M(bol) ∼ −6 or brighter, making them the most massive carbon stars in the LMC. However, the kinematic discussion of Hartwick & Cowley suggests an age of a few Gyr for them. They may thus be the products of binary mergers, i.e. evolutionary products of blue stragglers of an intermediate-age population. Some analogous stars in the halo of our Galaxy may have evolved from globular cluster type blue stragglers

CH stars form a distinct class of objects with characteristic properties like iron deficiency, enrichment of carbon and overabundance in heavy elements. These properties can provide strong observational constraints for theoretical computation of nucleosynthesis at low-metallicity. An important question is the relative surface density of CH stars which can provide valuable inputs to our understanding on the role of low to intermediate-mass stars in the early Galactic chemical evolution. Spectroscopic characterization provides an effective way of identifying CH stars. The present analysis is aimed at a quantitative assessment of the fraction of CH stars in a sample of stars using a set of spectral classification criteria. The sample consists of 92 objects selected from a collection of candidate Faint High Latitude Carbon stars from the Hamburg/ESO survey. Medium resolution (R ~ 1300) spectra for these objects were obtained using OMR at VBO, Kavalur and HFOSC at HCT, IAO, Hanle, during 2007 - 2009 spanning a wavelength range 3800 - 6800 A. Spectral analysis shows 36 of the 92 objects to be potential CH stars; combined with our earlier studies (Goswami 2005, Goswami et al. 2007) this implies ~ 37% (of 243) objects as the CH fraction. We present spectral descriptions of the newly identified CH star candidates. Estimated effective temperatures, 12C/13C isotopic ratios and their locations on the two colour J-H vs H-K plot are used to support their identification., 18 pages, 8 figures,Accepted for publication in MNRAS

The CH star CS 31062-050 ([Fe/H]=-2.42) is one of the most useful stars yet discovered for evaluating the s-process in metal-poor stars. It is very abundant in heavy elements (e.g., [La/Fe]=2.2), and its relatively cool temperature and low gravity mean that there are many lines of interesting elements present in the spectrum. We measured the abundances of 22 elements with Z>29, including the rarely measured Lu and Pd. We derive an upper limit on the Th abundance as well. The abundances in CS 31062-050 show a similar pattern to many other metal-poor CH stars: high [Pb/Fe] and [Pb/La] ratios, low [Y/La] ratios and high [Eu/La] values compared to the solar system s-process. However, the Th limit, with additional assumptions, is not consistent with the idea that the excess Eu in CS 31062-050 is contributed by the r-process. In addition, the observed [Eu/Tb] cannot be explained by any ratio of solar-system s-process and r-process abundances. We therefore argue that the abundance pattern in CS 31062-050 is most likely the result of the s-process, and we discuss possible modifications that could explain the non-solar-system pattern observed., to be published in ApJ

We present a sample of 403 faint high latitude carbon (FHLC) stars selected from the digitized objective prism plates of the Hamburg/ESO Survey (HES). Because of the ~15 Angstroem spectral resolution and high signal-to-noise ratio of the HES prism spectra, our automated procedure based on the detection of C_2 and CN molecular bands permits high-confidence identification of carbon stars without the need for follow-up spectroscopy. From a set of 329 plates (87% of the survey), covering 6400 square degrees to a magnitude limit of V~16.5, we analyze the selection efficiency and effective surface area of the HES FHLC survey to date. The surface density of FHLC stars that we detect (0.072 +/- 0.005 square degrees) is 2-4 times higher than that of previous objective prism and CCD surveys at high galactic latitude, even though those surveys claimed a limiting magnitude up to 1.5 magnitudes fainter. This attests to the highest selection sensitivity yet achieved for these types of stars., 8 pages, 6 figures; A&A in press

We report the discovery of a probable CH star in the core of the Galactic globular cluster M14, identified from an integrated-light spectrum of the cluster obtained with the MOS spectrograph on the CFHT. From a high- resolution echelle spectrum of the same star obtained with the Hydra fiber positioner and bench spectrograph on the WIYN telescope, we measure a radial velocity of $-53.0\pm1.2$ km s$^{-1}$. Although this velocity is inconsistent with published estimates of the systemic radial velocity of M14 (eg, ${\bar {v_r}} \approx -123$ km s$^{-1}$), we use high-precision Hydra velocities for 20 stars in the central 2.6 arcminutes of M14 to calculate improved values for the cluster mean velocity and one-dimensional velocity dispersion: $-59.5\pm1.9$ km s$^{-1}$ and $8.2\pm1.4$ km s$^{-1}$, respectively. Both the star's location near the tip of the red giant branch in the cluster color magnitude diagram and its radial velocity therefore argue for membership in M14. Since the intermediate-resolution MOS spectrum shows not only enhanced CH absorption but also strong Swan bands of C$_2$, M14 joins Omega Cen as the only globular clusters known to contain classical CH stars. Although evidence for its duplicity must await additional radial velocity measurements, the CH star in M14 is probably, like all field CH stars, a spectroscopic binary with a degenerate (white dwarf) secondary. The candidate and confirmed CH stars in M14 and Omega Cen, and in a number of Galactic dSph galaxies, may then owe their existence to the long timescales for the shrinking and coalescence of hard binaries in low-concentration environments., Accepted to the Astrophysical Journal Letters. 13 pages, AAS LaTeX and three postscript figures (numbers 2,3,4). Entire paper (including Figure 1) available at http://www.hia.nrc.ca/DAO/SCIENCE/science.html

High-velocity halo stars provide important information about the properties of the extreme Galactic halo. The study of unbound and bound Population II stars permits us to better estimate the mass of the halo.} {We carried out a detailed spectroscopic and kinematic study and have significantly refined the distance and the evolutionary state of the star. Its atmospheric parameters, chemical abundances and kinematical properties were determined using high-resolution optical spectroscopy and employing the local-thermodynamic-equilibrium model atmospheres of Kurucz and the spectral analysis code {\sc moog}. We found that CD-62$\degr$1346 is a metal-poor ([Fe/H]=$-$1.7) evolved giant star with $T_{\rm eff}=5300$ K and $\log g=1.7$. The star exhibits high carbon and s-element abundances typical of CH stars. It is also a lead star. Our kinematic analysis of its 3D space motions shows that this star has a highly eccentric ($e=0.91$) retrograde orbit with an apogalactic distance of $\sim 100$ kpc, exceeding by a factor of three the distance to the Magellanic Clouds. The star travels with very high velocity relative to the Galactocentric reference frame ($V_{\rm GRF}=570$ km\,s$^{-1}$). CD-62$\degr$1346 is an evolved giant star and not a subgiant star, as was considered earlier. Whether it is bound or unbound to the Galaxy depends on the assumed mass and on the adopted Galactic potential. We also show that the star HD 5223 is another example of a high-velocity CH star that exceeds the Galactic escape velocity. Possible origins of these two high-velocity stars are briefly discussed. CD-62$\degr$1346 and HD 5223 are the first red giant stars to join the restricted group of hypervelocity stars.

Blue spectra of a sample of 24 bright M55 (NGC 6809 = GC 1936-310) red giants within the magnitude range of 11.8

A detailed abundance analysis of seven red-giant CH stars has been conducted. Using high resolution echelle and coude spectrographic data and modern analysis techniques involving model stellar atmospheres and computer codes which model LTE radiative transfer, the abundances of carbon, nitrogen and oxygen, the carbon isotope ratios and the abundances of the s-process elements have been determined. The red-giant CH stars are a class of metal-poor giants with equivalent spectral types of G and K which show enhanced abundances of s-process elements. Studies of their kinematics indicate that the red-giant CH stars are members of the halo of our galaxy (Hartwick & Cowley 1985). Therefore, the CH stars provide valuable information about the early chemical evolution of our galaxy. In addition, it is known that the red-giant CH stars are members of binary systems like the barium stars (McClure 1984), so they are also valuable in the study of mass transfer. The carbon isotope ratios are found to break the red-giant CH stars into two groups--those with 12C 13C >/= 20 and those with 12C 13C ~4 (a value associated with equilibrium burning of the CN cycle) and carbon and nitrogen abundances are found to be greatly enhanced, [C+N/Fe] ~+1.0. In addition, it is found that the red-giant CH stars show large enhancements of the s-process elements with the enhancements of the heavy s-process peak elements (Ba through Sm) being larger than the light s-process peak elements (Sr, Y and Zr) by a factor of approximately six. Taken with the orbital data available for the red-giant CH stars, the carbon, nitrogen and oxygen abundances and the carbon isotope ratios are consistent with a picture in which carbon and s-process elements were dumped onto the incipient red-giant CH star from an AGB star. The accreted material is mixed deep enough into the star's interior to be subjected to CN burning. In addition, the greatly enhanced s-process abundances stars strongly suggest that the 13C (alpha ,n)16O reaction is the source of neutrons for the s-process. In addition, the abundance patterns in the globular-cluster CH star, M22 III-106, have been analyzed. It is found to have an abnormally large carbon abundance, but the C/O ratio is much less than unity and the star shows no evidence for enhanced abundances of the s-process elements. Therefore, M22 III-106 is most likely not a CH star in the sense that term is applied to galactic CH stars. The most probable explanation for the carbon overabundance in M22 III-106 is that CN processing has not been as complete in this star as in other giants of similar composition in M22.

An analysis of the CNO and s-process abundances in the M22 star III-106 has been completed. This star has been identified on the basis of DDO photometry by Hesser, Hartwick, and McClure, and on the basis of a low-resolution spectrum by McClure and Norris as a CH star. We find the star to have C = 7.1, N = 7.65,.

Using the 1-0 C 2 Swan Band at 4737 A and the CN red system 2-0 band near 8000 A, the ratio of stable carbon isotopes, 12 C/ 13 C, has been determined for eight CH giants. For a majority of the sample stars, we find that 12 C/ 13 C∼3 near the equilibrium value of the CN cycle, though there seems to be a second population of CH stars with high isotope ratios ( 12 C/ 13 C≥25). This range of ratios is the same as found for the Population II giants and globular cluster giant stars

We report on spectroscopic observations for 1044 stars, located primarily in the southern Galactic hemisphere, chosen from a list of candidate metal-deficient stars discovered in the HK objective-prism survey. Metal abundances for the program stars, on the [Fe/H] scale, are obtained from a previously published calibration of the variation in the equivalent width of the Ca II K absorption line (λ3933 A) as a function of broadband (B-V) 0 color. Broadband UBV photometry is available for roughly one-third of the present sample

Though model-atmosphere analyses of high-resolution photographic echelle spectrograms, chemical abundances in 15 subgiant CH stars, five barium stars, and four objects classified as metal-deficient barium stars have been determined. The stars in each of these groups show enhanced surface abundances of carbon and the very heavy elements produced by s-process neutron-capture reactions. The atmospheric parameters of subgiant CH stars are found to be typical of F- and G-type main-sequence stars and subgiants. Barium stars are more luminous G- and K-type stars.

This paper examines the properties of the LMC halo through the kinematics of its CH stars, which are known to be excellent halo tracers in the Galaxy. Velocities have been measured for 40 CH stars lying in the direction of LMC. These supplement 41 previously determined values. The main result of this investigation is that the distribution of CH-star velocities is asymmetrical, possessing a relatively sharp cutoff at the high-velocity end with an extended low-velocity tail. It is speculated that the asymmetry arises from two discrete groups of CH stars, one associated with the old globular cluster population and a second with the LMC disk. 11 refs.

Results are presented from a 10-year program to monitor the velocity variations of Ba II and CH stars, showing that all Ba II and CH stars are binaries. Radial-velocity observations for Ba II and CH binaries are given. Also, the results of orbit calculations and orbital element determinations are analyzed. It is shown that the eccentricities of Ba II star orbits are significantly lower than the eccentricities for a sample of normal G and K giants. In addition, the eccentricities of CH star orbits are significantly lower than those of Ba II stars, suggesting dissipation due to mass exchange, probably from a previous AGB star. The mass functions for Ba II and CH stars indicate that the stars come from samples of binary systems with a small dispersion in mass ratios. If the Ba II and CH stars are assumed to have masses of 1.5 and 0.8 solar mass, respectively, then their companions would have masses near 0.6 solar mass, similar to the values expected for white dwarfs. 45 refs.

The Swan bands in the spectra of the omega Cen CH stars RGO 55 and RGO 70 have been analyzed, using synthetic spectra calculations, and yield C/sup 12// C/sup 13/ approximates 10 and STAO/H! approximates -0.8, the latter abundance being obtained under the assumption that STAO/H! = -- 1.3. The nitrogen abundance, STAN/H!, obtained from bands of the blue and red CN systems, is approximately solar for both of the stars. The UBV colours of the CH star models show ultraviolet excesses of approximates 0.3 mag when compared with normal giant models, in agreement with photometry of the cluster stars. The models also show that the fact that the CH stars are grouped with the red variables in the cluster c--m diagram is caused by the reddening effects of the carbon features on B-- V. The weak appearance of the Ca I 4226 line in CH star spectra is shown to be caused to a large extent by the great strength of the CH and CN features. (auth)

Results from high-resolution spectral analyses of a selected sample of CH stars are presented. Detailed chemical composition studies of these objects, which could reveal abundance patterns that in turn provide information regarding nucleosynthesis and evolutionary status, are scarce in the literature. We conducted detailed chemical composition studies for these objects based on high resolution (R ~ 42000) spectra. The spectra were taken from the ELODIE archive and cover the wavelength range from 3900 to 6800 A, in the wavelength range. We estimated the stellar atmospheric parameters, the effective temperature Teff, the surface gravity log g, and metallicity [Fe/H] from Local thermodynamic equilibrium analyses using model atmospheres. Estimated temperatures of these objects cover a wide range from 4550 K to 6030 K, the surface gravity from 1.8 to 3.8 and metallicity from -0.18 to -1.4. We report updates on elemental abundances for several heavy elements and present estimates of abundance ratios of Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu and Dy with respect to Fe. For the object HD 188650 we present the first abundance analyses results based on a high resolution spectrum. Enhancements of heavy elements relative to Fe, that are characteristic of CH stars are evident from our analyses for most of the objects. A parametric model based study is performed to understand the relative contributions from the s- and r-processes to the abundances of the heavy elements., 18 pages, 14 figures, published in MNRAS

A photograph of $omega$ Centauri made with a transmission-grating slitless spectrograph has revealed a new CH star near the center of this globular cluster. The star's radial velocity is found to be consistent with cluster membership, and a visual absolute magnitude M/subv/=-1.8 is derived. The total number of carbon stars now known in globular clusters is three, all of which are in $omega$ Cen. (AIP)

Subgiant CH stars are late F to early G stars showing enhanced CH and Sr ii features on low-dispersion spectrograms. In this paper we report abundance analyses of seven relatively bright subgiant CH stars and the red-giant CH star HD 26, based on Palomar and Mount Wilson photographic coude spectrograms in the blue spectral region and on Mount Wilson coude scans in the red region.

ROA No. 577 is found to have the spectroscopic characteristics of the Population II carbon stars known as CH stars. Its radial velocity and proper motion show it to be a cluster member, although it is fainter than the previously identified cool CH stars in ω Cen.

Carbon isotope ratios for stars in four globular clusters are derived by means of spectrum synthesis analysis of CN features in high-resolution spectra around 8000 A. In the strong-CN stars in the clusters M4, M22, Omega Cen, and 47 Tuc, the isotope ratios are generally quite low, approaching the equilibrium value in the CN cycle, namely 3-8; this includes a barium star and an S star in Omega Cen and a CH star in M22. (C-13)N is not detected in weak-CN stars, but the limits on the (C-12)/(C-13) ratios in these stars are not significant. Ratios as low as 3-8 are not predicted by standard evolution models of low-mass metal-poor stars. 37 refs.

Spectra from 2.1-2.5 microns and broad-band observations from 1.2-3.5 microns are presented for the CH star III-106 in the globular cluster M22. The visual to infrared color implies an effective temperature of about 4600 K. The CO index is 0.11, significantly greater than for other cluster giants of this temperature and metallicity. The strength of the CO can be understood if the carbon abundance in III-106 has been enriched by nucleosynthesis. A carbon enhancement of at least a factor of 4 appears to be required.

On presente des observations de vitesses radiales qui indiquent que de nombreuses etoiles CH sont des systemes binaires

Lick Observatory spectrophotometry is presented for three recognized 4670-A stars (G47-18, G99-37, and G257-38) and the DC star L1363-3. New C I features are reported for G47-18; G257-38 has no C I but definite C2; weak bands are also noted in L1363-3, which is a Wolf 219 group member. The magnetic CH star G99-37 is examined in greater detail. Model-atmosphere calculations show that it must have a helium-dominated atmosphere, since stringent upper limits on H-alpha and H-beta central Zeeman components are found. The CH 'G' band profile is compared with the theoretical calculations of Angel and Landstreet (1974). Other upper limits for atomic lines are discussed.

Rotational lines of the (0, 0) and (1, 1) bands of the C2(-) ion are shown to be coincident with absorption features in the CH star HD 201626 (C1, 1). Of the 72 lines of the (0, 0) band studied, the coincidences are within 0.04 A in all but two cases. These two lines are obviously blends, but of unknown origin. The identification of C2(-) must still be considered uncertain because the spectrum of HD 201626 is complex and many of the coincident lines are blended.