Evolutionary status of the spectral variable BD + 48°1220 = IRAS 05040+4820

Based on high-resolution observations (R = 60 000 and 75 000), we have studied the optical spectral variability of the star BD + 48°1220, identified with the IR source IRAS 05040+4820. We have measured the equivalent widths of numerous absorption lines of neutral atoms and ions at wavelengths from 4500 Å to 6760 Å, as well as the corresponding radial velocities. We use model atmospheres to determine the effective temperature T _eff = 7900 K, surface gravity log g = 0.0, microturbulence velocity ξ _t = 6.0, and the abundances for 16 elements. The star’s metallicity differs little from the solar value: [Fe/H] = ?0.10 dex. The main peculiarity of the chemical composition of the star is a large helium excess, derived from the Hel λ 5876 Å absorption, [He/H] = +1.04, and the equally large oxygen excess, [O/Fe] = +0.72 dex. The carbon excess is small, [C/Fe] = +0.09 dex, and the ratio [C/O] < 1. We obtained an altered relation for the light-metal abundances: [Na/Fe] = +0.87 dex with [Mg/Fe] = ?0.31 dex. The barium abundance is low, [Ba/Fe] = ?0.84 dex. It is concluded that the selective separation of elements onto dust grains of the envelope is probably efficient. The radial velocity of the star measured from photospheric absorption lines over three years of observations varies in the interval V _⊙ = ?(7–15) km/s. Time-variable differential line shifts have been revealed. The entire set of available data (the luminosity M _v ≈ ?5 ^m , velocity V _lsr ≈ ?20 km/s, metallicity [Fe/H] = ?0.10, and peculiarities of the optical spectrum and chemical composition) confirms the status of BD + 48°1220 as a post-AGB star with He and O excesses belonging to the Galactic disk.     

Observational constraints on potassium synthesis during the formation of stars of the Galactic disk

The non-LTE potassium abundances in the atmospheres of 33 Galactic-disk stars are derived and the parameters of the atmospheres of 23 of the stars are determined. Neglecting departures from LTE results in a systematic overestimation of the potassium abundances and an increase in their dispersion, even for differential analyses relative to the Sun. The non-LTE corrections are significant ((?0.2)–(?0.6) dex) and depend on the surface gravities and effective temperatures of the stars. The mean potassium abundance for a sample of ten stars with [Fe/H]～0.0 is in agreement with the solar and meteoritic abundances (log ? _⊙(K)=5.12). As the stellar metallicity increases from [Fe/H]=(?1.0) to (0.2) dex, the [K/Fe] ratio decreases systematically from 0.3 dex to ?0.1 dex. The derived dependence [K/Fe]-[Fe/H] is in agreement with the results of published model calculations of the chemical evolution of the Galaxy. This indicates the dominance of explosive oxygen burning in massive type II supernovae during the synthesis of potassium in the Galactic disk.     

Revised magnesium abundances in galactic halo and disk stars

A differential analysis of the magnesium abundances in 61 F-K dwarfs and subgiants with metallicities ?2.6<[Fe/H]<+0.2 is performed based on published observational data. Fundamental parameters for 36 stars are determined: T _eff from V-K and V-R; logg from HIPPARCOS parallaxes, and [Fe/H] and ξ_t from Fe II lines. The computations allow for non-LTE effects in the formation of the Mg I lines. For most of the stars, the standard errors in the Mg abundances do not exceed 0.07 dex. The metallicity dependence of [Mg/Fe] is analyzed. Magnesium shows a constant overabundance relative to Fe of 0.46±0.06 dex for metallicities ?2.6<[Fe/H] $\overline {[Mg/Fe]} = + 0.22 dex$ ) compared to the [Mg/Fe] values for other stars with similar [Fe/H].     

Neutron-capture elements in halo,thick-disk,and thin-disk stars: Neodymium

We have derived the LTE neodymium abundances in 60 cool stars with metallicities [Fe/H] from 0.25 to ?1.71 by applying a synthetic-spectrum analysis to spectroscopic observations of NdII lines with a resolution of λ/Δλ?60 000 and signal-to-noise ratios of 100–200. We have improved the atomic parameters of NdII and blending lines by analyzing the corresponding line pro files in the solar spectrum. Neodymium is overabundant with respect to iron in halo stars, [Nd/Fe]=0.33±0.09, with the [Nd/Fe] ratio decreasing systematically with metallicity when [Fe/H]>?1. This reflects an onset of efficient iron production in type I supernovae during the formation of the thick disk. The [Nd/Ba] and [Nd/Eu] abundance ratios behave differently in halo, thick-disk, and thin-disk stars. The observed abundance ratios in halo stars, [Nd/Ba]=0.34±0.08 and [Nd/Eu]=?0.27±0.05, agree within the errors with the ratios of the elemental yields for the r-process. These results support the conclusion of other authors based on analyses of other elements that the r-process played the dominant role in the synthesis of heavy elements during the formation of the halo. The [Nd/Ba] and [Nd/Eu] ratios for thick-disk stars are almost independent of metallicity ([Nd/Ba]=0.28(±0.03)?0.01(±0.04) [Fe/H] and [Nd/Eu]=?0.13(±0.03)+0.05(±0.04) [Fe/H]) but are smaller in absolute value than the corresponding ratios for halo stars, suggesting that the synthesis of s-process nuclei started during the formation of the thick disk. The s-process is estimated to have contributed ?30% of the neodymium produced during this stage of the evolution of the Galaxy. The [Nd/Ba] ratio decreases abruptly by 0.17 dex in the transition from the thick to the thin disk. The systematic decrease of [Nd/Ba] and increase of [Nd/Eu] with increasing metallicity of thin-disk stars point toward a dominant role of the s-process in the synthesis of heavy elements during this epoch.     

Abundances of carbon,nitrogen, oxygen,and other elements in the atmospheres of the giants 25 Mon and HR 7389

An analysis of high-resolution CCD spectra of the giant 25 Mon, which shows signs of metallicity, and the normal giant HR 7389 is presented. The derived effective temperatures, gravitational accelerations, and microturbulence velocities are T_eff = 6700 K, log g = 3.24, and ξ _t = 3.1 km/s for 25 Mon and T_eff = 6630 K, log g = 3.71, and ξ _t = 2.6 km/s for HR 7389. The abundances (log ε) of nine elements are determined: carbon, nitrogen, oxygen, sodium, silicon, calcium, iron, nickel, and barium. The derived excess carbon abundances are 0.23 dex for 25 Mon and 0.16 dex for HR 7389. 25 Mon displays a modest (0.08 dex) oxygen excess, with the oxygen excess for HR 7389 being somewhat higher (0.15 dex). The nitrogen abundance is probably no lower than the solar value for both stars. The abundances of iron, sodium, calcium (for HR 7389), barium, and nickel exceed the solar values by 0.22–0.40 dex for both stars. The highest excess (0.62 dex) is exhibited by the calcium abundance for 25 Mon. Silicon displays a nearly solar abundance in both stars—small deficits of ?0.03 dex and ?0.07 dex for 25 Mon and HR 7389, respectively. No fundamental differences in the elemental abundances were found in the atmospheres of 25 Mon and HR 7389. Based on their T_eff and log g values, as well as theoretical calculations, A. Claret estimated the masses, radii, luminosities, and ages of 25 Mon (M/M_⊙ = 2.45, log(R/R_⊙) = 0.79, log(L/L_⊙) = 1.85, t = 5.3 × 10⁸ yr) and HR 7389 (M/M_⊙ = 2.36, log(R/R_⊙) = 0.50, log(L/L_⊙) = 1.24, t = 4.6 × 10⁸ yr), and also of the stars 20 Peg (M/M_⊙ = 2.36, log(R/R_⊙) = 0.73, log(L/L_⊙) = 1.79, t = 4.9 × 10⁸ yr) and 30 LMi (M/M_⊙ = 2.47, log(R/R_⊙) = 0.73, log(L/L_⊙) = 1.88, t = 4.8 × 10⁸ yr) studied by the author earlier.     

A study of the shell of Nova V2659 Cyg

Results of a study of the shell of Nova V2659 Cyg based on spectrophotometric observations carried out over a year and a half after its eruption are presented. The physical conditions in the nova shell have been studied. The electron temperature (9000 K) and density (5 × 10⁶ cm^?3) in the nebular stage have been estimated, together with the abundances of helium, oxygen, nitrogen, neon, argon, and iron. The abundances of nitrogen, oxygen, neon, and argon are enhanced relative to the solar values. The relative abundances are [N/H] = 2.26 ± 0.25 dex, [O/H] = 1.66 ± 0.35 dex, [Ne/H] = 0.78 ± 0.25 dex, and [Ar/H] = 0.32 ± 0.38 dex. The estimated mass of oxygen and total mass of the emitting shell are ≈1 × 10^?4M_⊙ and ≈3 × 10^?4M_⊙, respectively. In the period of chaotic brightness oscillations, the maximum velocity of the shell expansion derived from the radial velocities of the absorption components of the HI and FeII line profiles increased by ≈400 km/s 41 days after the maximum, and by ≈200 km/s 101 days after the maximum, reaching 1600 km/s in both cases.     

Chemical composition of stars in the galactic halo

The chemical compositions of the atmospheres of six metal-poor stars are analyzed. Spectra with signal-to-noise ratios of no less than 100 and a resolution of R≈17 000 were obtained using the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. The abundances of Li, O, α-process elements (Mg, Si, Ca, Ti), Na, K, Sc, iron-peak elements (Cr, Mn, Fe, Ni, Cu, Zn), and s-process elements (Y, Ba) are derived. The star G251-54 ([Fe/H]=?1.55, T _eff=5541 K, logg=3.58) is deficient in some elements compared to both stars with similar metallicities and the Sun. The atmosphere of G251-54 has the following elemental abundances relative to iron: [O/Fe]=+0.47, [α/Fe]≈?0.3, [Na/Fe]=?0.60, [Sc/Fe]=?0.57, [Cr, Ni, Fe]≈0, [Zn/Fe]=+0.16, [Cu/Fe]=?0.66, [Y/Fe]=?0.70, and [Ba/Fe]=?1.35. The remaining five stars have metallicities in the range ?1.6<[Fe/H]相似文献   

Analysis of the spectral energy distributions of four cool R CrB stars near the brightness maximum

The effective temperatures T _eff and carbon and nitrogen abundances in the atmospheres of the cool R CrB stars ES Aql, SV Sge, Z UMi, and NSV 11154 have been determined by modeling their spectral energy distributions in the optical and near-infrared. The hydrogen-deficient model atmospheres were computed using the SAM12 code in the classical approximation, taking into account sources of opacity characteristic of the atmospheres of R CrB stars. The influence of the hydrogen deficiency on theoretical stellar spectra is analyzed. The resulting effective-temperature estimates for ES Aql, SV Sge, Z UMi, and NSV 11154 are in the range T _eff = 4600–5200 K. The carbon abundances log n(C) in the atmospheres of ES Aql, SV Sge, and Z UMi are 8.9–10.1, corresponding to [C/Fe] values typical of the atmospheres of R CrB stars. The nitrogen abundances are lower than those determined in other studies, and differ considerably from star to star. The mean [N/Fe] value for these three stars is ≈1.5 dex lowthan the mean [N/Fe] for known warm R CrB stars. Abnormally high estimates were obtained for the atmosphere of NSV 11154: log n(C) = 10.8 and log n(N) = 10.0. The approximate log g estimates agree with the conclusion from photometric observations that cool R CrB stars have lower luminosities than hotter R CrB stars.     

Detection of spectral variability of the optical component of the IR source IRAS 20508+2011

Our high-resolution spectral observations have revealed variability of the optical spectrum of the cool star identified with the IR source IRAS 20508+2011. We measured the equivalent widths of numerous absorption lines of neutral atoms and ions at wavelengths 4300–7930 Å, along with the corresponding radial velocities. Over the four years of our observations, the radial velocity derived from photospheric absorption lines varied in the interval V _r⊙ = 15–30 km/s. In the same period, the Hα profile varied from being an intense bell-shaped emission line with a small amount of core absorption to displaying two-peaked emission with a central absorption feature below the continuum level. At all but one epoch, the positions of the metallic photospheric lines were systematically shifted relative to the Hα emission: ΔV _r = V _r(met) ? V _r(Hα, emis) ≈ ?23 km/s. The Na D doublet displayed a complex profile with broad (half-width ≈ 120 km/s) emission and photospheric absorption, as well as an interstellar component. We used model atmospheres to determine the physical parameters and chemical composition of the star’s atmosphere: T _eff = 4800 K, log g = 1.5, ξ_t = 4.0 km/s. The metallicity of the star differs little from the solar value: [Fe/H]_⊙ = ?0.36. We detected overabundances of oxygen [O/Fe]_⊙ = +1.79 (with the ratio [C/O] ≈ ?0.9), and α-process elements, as well as a deficit of heavy metals. The entire set of the star’s parameters suggests that the optical component of IRAS 20508+2011 is an “O-rich” AGB star with luminosity M _v ≈ ?3^m that is close to its evolutionary transition to the post-AGB stage.     

The copper and zinc abundances in stars of galactic sub-structures

We have determined abundances of copper, zinc, sodium, and aluminum in the atmospheres of 172 F, G, and K dwarf stars (−1.0 < [Fe/H] < 0.3) belonging to the Galaxy’s thin and thick disks and to the Hercules moving group. Our observations were performed with the ELODIE échelle spectrometer on the 1.93-m telescope of the Haute Provence Observatory, with a resolving power of R = 42 000 and signal-to-noise ratio S/N > 100. The Na, Al, Cu, and Zn abundances were derived in an LTE approximation; the synthetic spectrum for the copper lines was calculated taking into account super-fine structure of the lines. We analyzed the abundances of these elements as a function of metallicity [Fe/H] for stars of the thin and thick disks of the Galaxy and the Hercules moving group. The Cu abundances and their trends with metallicity are essentially the same in the three studied sub-structures. The mean Al and Zn abundances for stars of the thin and thick disks differ significantly.     

IR photometry and models for the dust envelopes of two carbon stars

The results of JHKLM photometry of two carbon stars are presented: the irregular variable NQ Cas and the Mira star BD Vul. Data on the mean fluxes supplemented with mid-IR observations with the IRAS, AKARI, andWISE satellites are used to compute spherically symmetrical model dust envelopes for the stars, consisting of particles of amorphous carbon and silicon carbide. The optical depth in the visible for the comparatively cool dust envelope of BD Vul, with a dust temperature at its inner boundary T₁ = 610 K, is fairly low: τ_V = 0.13. The dust envelope of NQ Cas is appreciably hotter (T₁ = 1550 K), and has τ_V = 0.32. The estimated mass-loss rates are 1.5 × 10^?7M_⊙/yr for NQ Cas and 5.9 × 10^?7M_⊙/yr for BD Vul.     

Modeling and analysis of the spectrum of the globular cluster NGC 2419

The properties of the stellar population of the unusual object NGC 2419 are studied; this is the most distant high-mass globular cluster of the Galaxy’s outer halo, and a spectrum taken with the 1.93-m telescope of the Haute Provence Observatory displays elemental abundance anomalies. Since traditional high-resolution spectroscopicmethods are applicable to bright stars only, spectroscopic information for the cluster’s stellar population as a whole, integrated along the spectrograph slit placed in various positions, is used. Population synthesis is carried out for the spectrum of NGC 2419 using synthetic spectra calculated from a grid of stellar model atmospheres, based on the theoretical isochrone from the literature that best fits the color-magnitude diagram of the cluster. The derived age (12.6 billion years), metallicity ([Fe/H] = ?2.25 dex), and abundances of helium (Y = 0.26) and other chemical elements (a total of 14) are in a good qualitative agreement with estimates from the literature made from high-resolution spectra of eight red giants in the cluster. The influence on the spectrum of deviations from local thermodynamic equilibrium is considered for several elements. The derived abundance of α-elements ([α/Fe] = 0.13 dex, as the mean of [O/Fe], [Mg/Fe], and [Ca/Fe]) differs from the mean value in the literature ([α/Fe] = 0.4 for the eight brightest red giants) and may be explained by recently discovered in NGC2419 large [a/Fe] dispersion. Further studies of the integrated properties of the stellar population in NGC 2419 using higher-resolution spectrographs in various wavelength ranges should help improve our understanding of the cluster’s chemical anomalies.     

The effects of deviations from LTE in sulphur lines for late-type stars

We analyze the formation of lines of neutral sulfur in the spectra of F-K stars taking into account the effects of deviations from local thermodynamical equilibrium (LTE). Our calculations were carried out for Kurucz model atmospheres with T _eff = 5000–6500 K, log g = 2?4 and [Fe/H] = ?4?0, using a 65-level model of the SI atom. Deviations from LTE affect lines of different multiplets of the sulfur atom differently. Non-LTE corrections, which are relatively small (to ?0.10 dex) for the 6543–6557 Å lines, increase to ?0.26 dex for the 8694 Å line, and reach ?1.1 dex for the 9212–9237 Å IR triplet. The model of the atom was verified by modeling the sulfur lines of the studied multiplets in the spectra of the Sun, two main sequence stars, and two supergiants. Good consistency with the observed line profiles was obtained. Failure to take into account strong non-LTE-effects may explain the large sulfur excesses detected in stars with very low metal abundances.     

Sodium abundances in stellar atmospheres with differing metallicities

The non-LTE sodium abundances of 100 stars with metallicities ?3<[Fe/H]<0.3 are determined using high-dispersion spectra with high signal-to-noise ratios. The sodium abundances [Na/Fe] obtained are close to the solar abundance and display a smaller scatter than values published previously. Giants (logg<3.8) with [Fe/H]g>3.8) with metallicities ?2<[Fe/H]相似文献   

Peculiarities of the abundances of neutron-capture elements in Galactic open clusters

The properties of the relative abundances of rapid and slow neutron-capture elements are studied using a catalog containing spectroscopic abundance determinations for 14 elements produced in various nuclear-synthesis processes for 90 open clusters. The catalog also contains the positions, ages, velocities, and elements of the Galactic orbits of the clusters. The relative abundances of both r-elements (Eu) and s-elements (Y, Ba, La, and Ce) in clusters with high, elongated orbits and in field stars of the Galactic thin disk display different dependences on metallicity, age, Galactocentric distance, and the elements of the Galactic orbits, supporting the view that these objects have different natures. In young clusters, not only barium, but also the three other studied s-elements display significantly higher relative abundances than field stars of the same metallicity. The relative abundances of Eu are lower in highmetallicity clusters ([Fe/H] > -0.1) with high, elongated orbits than in field giants, on average, while the [Eu/Fe] ratios in lower-metallicity clusters are the same as those in field stars, on average, although with a large scatter. The metallicity dependence of the [O, Mg/Eu] ratios in clusters with high, elongated orbits and in field stars are substantially different. These and other described properties of the Eu abundances, together with the properties of the abundances of primary a-elements, can be understood in a natural way if clusters with high, elongated orbits with different metallicities formed as a result of interactions of two types of high-velocity clouds with the interstellar medium of the Galactic disk: low-metallicity highvelocity clouds that formed from “primordial” gas, and high-metallicity clouds with intermediate velocities that formed in “Galactic fountains.”     

Peculiarities of α-element abundances in Galactic open clusters

A catalog compiling the parameters of 346 open clusters, including their metallicities, positions, ages, and velocities has been composed. The elements of the Galactic orbits for 272 of the clusters have been calculated. Spectroscopic determinations of the relative abundances, [el/Fe], for 14 elements synthesized in various nuclear processes averaged over data from 109 publications are presented for 90 clusters. The compiled data indicate that the relative abundances of primary α elements (oxygen and magnesium) exhibit different dependences on metallicity, age, Galactocentric distance, and the elements of the Galactic orbits in clusters with high, elongated orbits satisfying the criterion (Z_max² + 4e²)^1/2 > 0.40 and in field stars of the Galactic thin disk (Z_max is the maximum distance of the orbit from the Galactic plane in kiloparsec and e is the eccentricity of the Galactic orbit). Since no systematic effects distorting the relative abundances of the studied elements in these clusters have been found, these difference suggest real differences between clusters with high, elongated orbits and field stars. In particular, this supports the earlier conclusion, based on an analysis of the elements of the Galactic orbits, that some clusters formed as a result of interactions between high-velocity,metal-poor clouds and the interstellar mediumof theGalactic thin disk. On average, clusters with high, elongated orbits and metallicities [Fe/H] < -0.1 display lower relative abundances of the primary a elements than do field stars. The low [O, Mg/Fe] ratios of these clusters can be understood if the high-velocity clouds that gave rise to them were formed of interstellar material from regions where the star-formation rate and/or the masses of Type II supernovae were lower than near the Galactic plane. It is also shown that, on average, the relative abundances of the primary a elements are higher in relatively metal-rich clusters with high, elongated orbits than in field stars. This can be understood if clusters with [Fe/H] > -0.1 formed as a result of interactions between metal-rich clouds with intermediate velocities and the interstellar medium of the Galactic disk; such clouds could form from returning gas in a so-called “Galactic fountain.”     

Abundances of carbon,nitrogen, oxygen,and other elements in the atmospheres of the giants 15 ori and 22 <Emphasis Type="Italic">ɛ</Emphasis> sex

We have used high-resolution spectra to study the giants 15 Ori and 22 ? Sex. The effective temperature T _eff = 7060 K, gravity log g = 3.16, and microturbulence velocity ξ _t = 3.5 km/s were determined for 15 Ori, with T _eff = 7350 K and log g = 3.90 for 22 ? Sex (the microturbulence velocity for 22 ? Sex was assumed to be ξ _t = 2.7 km/s). We estimated the abundances of C, N, O, Na, Si, Ca, Fe, and Ba (N and Ba, for 15 Ori only). The abundances of carbon, iron, and oxygen in 22 ? Sex are higher than the solar values by +0.31 dex, +0.33 dex, and +0.18 dex, respectively, while the calcium abundance is ?0.19 dex below the solar level. For 15 Ori, we find a slight carbon excess (+0.19 dex), a slight nitrogen deficiency (?0.13 dex), and a considerable deficiency of silicon (?0.42 dex). The abundances of the remaining elements in both stars are near-solar. We find no substantial differences between the abundances derived for 15 Ori and 22 ? Sex and the results of earlier studies of giants by both ourselves and Erspamer and North. A comparison of the atmospheric elemental abundances of giants and δ Scuti stars indicates that the abundances of some lighter elements (oxygen, sodium, silicon, and possibly nitrogen) are somewhat lower for δ Scuti stars than for A-F giants. We determined the masses, radii, luminosities, and ages for 15 Ori and 22 ? Sex.     

Masses of RR Lyrae Stars with Different Chemical Abundances in the Galactic Field

The surface gravities and effective temperatures have been added to a compilative catalog published earlier, which includes the relative abundances of several chemical elements for 100 field RR Lyrae stars. These atmoshperic parameters and evolutionary tracks from the Dartmouth database are used to determine the masses of the stars and perform a comparative analysis of the properties of RR Lyrae stars with different chemical compositions. The masses of metal-rich ([Fe/H] > −0.5) RR Lyrae stars with thin disk kinematics are in the range (0.51−0.60)M_⊙. Only stars with initial masses exceeding 1M_⊙ can reach the horizontal branch during the lifetime of this subsystem. To become an RR Lyrae variable, a star must have lost approximately half of its mass during the red-giant phase. The appearance of such young, metal-rich RR Lyrae stars is possibly due to high initial helium abundances of their progenitors. According to the Dartmouth evolutionary tracks for Y = 0.4, a star with an initial mass as low as 0.8 M_⊙ could evolve to become an RR Lyrae variable during this time. Such stars should have lost (0.2−0.3)M_⊙ in the red-giant phase, which seems quite realistic. Populations of red giants and RR Lyrae stars with such high helium abundances have already been discovered in the bulge; some of these could easily be transported to the solar neighborhood as a consequence of perturbations due to inhomogeneities of the Galaxy’s gravitational potential.

     

Atmospheric chemical composition of the peculiar carbon giant TU Gem

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 chemical composition of HR 1512, a peculiar helium-weak star

We have used high-resolution spectra to study the chemical composition of HR 1512, a star with effective temperature T _eff = 15 200 K, atmospheric gravity log g = 3.52, microturbulence parameter V _t = 1.5 km/s, and rotation rate v sin i = 17 km s^?1. We confirm the presence of a helium deficiency (?0.6 dex), indicating that HR 1512 is a helium-weak star. Its considerable phosphorus excess (1.6 dex) testifies that the star belongs to the PGa subtype. We suggest that the He and P abundances increase with height; i.e., that there is stratification of He and P in the star’s atmosphere. Among the CNO elements, nitrogen demonstrates an underabundance of ?0.4 dex, while the abundances of carbon and oxygen are solar. Deficits of about ?0.5 or ?0.6 dex were also found for Mg, Si, and S. A neon excess of 0.4 dex was derived from our non-LTE analysis of NeI lines. The largest excess among the iron-peak elements (Cr, Mn, Fe, and Ni) is 0.6 dex, for manganese; the abundances of chromium and nickel display excesses of 0.5 and 0.3 dex, respectively, while the iron abundance is almost normal. The chemical anomalies of HR 1512 generally agree with those for mercury-manganese stars. This supports the hypothesis that PGa stars represent an extension of HgMn stars to higher temperatures.