CN Band Strengths Research Articles

Variations in C-12/C-13 as an explanation for the 3883 A CN-bimodality among 47 Tucanae subgiants

view Abstract Citations (21) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Variations in 12C/ 13C as an Explanation for the 3883 Angstrom CN-Bimodality among 47 Tucanae Subgiants Briley, Michael M. ; Bell, Roger A. ; Smith, Graeme H. ; Hesser, James E. Abstract Spectroscopic observations of subgiants in the metal-rich globular cluster 47 Tucanae are used to measure the strengths of the CN bands located at 3883 A and 4215 A. A bimodal distribution is clearly seen in the 3883 A CN band strengths, but not in the 4215 A bands. Synthetic spectrum calculations are used to probe the effect on both CN bands of varying the C-12/C-13 ratio. The sensitivity of the 3883 A CN feature to C-13 relative abundance is found to be considerably higher than that of the 4215 A band for the stars observed. Thus, spectroscopic indices derived from these features are observable probes of atmospheric C-13/C-12 enhancements. It is suggested that the bimodality observed in the 3883 A CN band may be due largely to a difference in the C-12/C-13 ratios of the two groups. Publication: The Astrophysical Journal Pub Date: June 1989 DOI: 10.1086/167537 Bibcode: 1989ApJ...341..800B Keywords: Abundance; Astronomical Spectroscopy; Cn Emission; Globular Clusters; Subgiant Stars; Carbon 12; Carbon 13; Metallicity; Stellar Spectra; Stellar Structure; Astrophysics; CLUSTERS: GLOBULAR; STARS: ABUNDANCES full text sources ADS | data products SIMBAD (2)

Spectroscopy of metal-rich M31 globular clusters

Integrated CCD spectra with a wavelength resolution of ~2.1 A covering the wavelength region λλ 3850 to 4200 A have been obtained for nine metal-rich ([Fe/H >= -1) globular clusters in M31. The spectra have been analyzed using the quantitative, reddening-free spectral-classification system developed by Rose ( 1984) that compares the strengths of neighboring absorption features. The data have been combined with similar data for nine metal-rich Galactic globular clusters previously discussed by Rose and Tripicco (1986). Spectra of 72 stars with well-determined atmospheric parameters have also been obtained, with most having been observed on several nights over the different observing runs. These spectra provide fiducial sequences in the various diagnostic diagrams, monitor the stability of the instrumental system, and provide a large database of multiple observations which are used to assess the reproducibility of the spectral indices. The following results have been found: (1) The 4000 A light from the metal-rich M31 globulars is dominated by dwarfs, which typically contribute four times as much light as do giants. This has been determined from a diagram that is based on the ratio of the Sr II λ 4077 and Fe I λ 4045, λ 4063 lines and is sensitive to the integrated surface gravity of a stellar system independent of metal abundance. In contrast, the light from the mean of the metal-rich Galactic globulars is contributed equally by giants and dwarfs, in good agreement with theoretical and observed cluster luminosity function data. (2) The contribution of early-type stars to the 4000 A light from the M31 clusters is constrained to be less than 5% in most cases by an index that compares the central intensities of the Ca II H + Hɛ and Ca II K lines. The index increases sharply with spectral type in stars of types AO through mid-F and remains constant thereafter, enabling the prediction of its value in the integrated spectrum of an old metal-rich system. Even a small contribution from stars of types earlier than mid-F will cause the index to clearly deviate from the prediction. This constraint rules out the presence of hot-star populations (e.g., blue horizontal branches), which have previously been proposed to explain the anomalously strong Balmer-line absorption reported for these clusters. (3) The λ 3883 and λ 4216 CN bands are exceptionally strong in the M31 globular clusters for their integrated spectral types. The band strengths are such that no combination of CN-normal solar-metallicity stars can reproduce them, requiring giants and dwarfs having roughly order-of-magnitude CN excesses. This observation of anomalous strength in both CN bands extends the results of Burstein et al. (1984), who discovered the enhancement of the λ 4215 CN band in metal-rich M31 clusters. The most plausible and consistent explanation for the combination of dwarf domination, Balmer-line enhancement, and hot-star constraints may be that the metal-rich M31 globular clusters are substantially younger than Galactic metal-rich clusters like 47 Tuc or M71. However, this interpretation does not explain the excess CN band strengths in the integrated spectra of the M31 globulars.

JHK PHOTOMETRY OF POPULATION I CN-RICH FIELD GIANTS

ABSTRACT IR JHK photometry has been obtained for a sample of CN-rich field red giants. It is found that these giants segregate according to metallicity or CN band strength in the (J-H), (H-K) two-color diagram. A delta (H-K) color-excess index is presented, which correlates with the strength of the 4215 wavelength CN band as measured by the delta Cm index of the DDO photometric system (McClure, 1970). The sensitivity of delta (H-K) as a metal abundance indicator is shown to be relatively small. It is suggested that the CN-rich field giants have colors comparable to many of the metal-rich giants in the Galactic bulge studied by Whitford and Rich (1983), although a few of the bulge giants appear to have higher abundances.

BIMODAL CYANOGEN DISTRIBUTIONS IN MODERATELY METAL-POOR GLOBULAR CLUSTERS. I. CARBON AND NITROGEN ABUNDANCES FOR SIX M5 GIANTS.

ABSTRACT In order to determine carbon and nitrogen abundances for three CN-strong and three CN-weak red giants in the globular cluster M5, spectrum-synthesis techniques are used. It is shown that all six stars have approximately the same luminosity and surface temperature and are, presumably, in the same stage of evolution. CN-strong and CN-weak stars that sit side by side on the C-M diagram are found to have significantly different carbon and nitrogen abundances, but there is no evidence for a difference in the total (C+N) abundance. The CN band strengths indicate that the carbon abundances should be shifted to higher values by about 0.2 dex while the nitrogen abundances should be shifted by about 0.2 dex to lower values. The observed abundances are interpreted by a simple mixing scenario in which C-N processing proceeds at different rates in apparently similar stars.

BIMODAL CYANOGEN DISTRIBUTIONS IN MODERATELY METAL-POOR GLOBULAR CLUSTERS. II. EVIDENCE FOR "MIXING" AND "SATURATION".

ABSTRACT Recent work indicates that both the observed carbon and nitrogen abundances and the bimodal 3883 A cyanogen distributions that are often observed in moderately metal-poor globular clusters fit easily into a simple mixing scenario in which C-N nucleosynthesis proceeds at different rates in otherwise similar stars. It is shown that there is no evidence for a difference in (C+N)/Fe between CN-strong and CN-weak stars in moderately metal-poor globular clusters. Carbon and nitrogen are approximately equally abundant in CN-strong stars in M3, M13, and M5; carbon is more abundant than nitrogoen in otherwise similar CN-weak giants and less abundant in CN-weak AGB stars. The observed carbon and nitrogen abundances imply that the product of C and N is only 1.3 to 2 times larger in a typical CN-strong giant than in a comparable CN-weak giant. The distribution of 3883 A CN band strengths appears to be bimodal because the band saturates for values of C x N near its maximum. There is no evidence for a bimodal distribution in the strengths of the weaker violet CN bands. The observed values of C/Fe and N/Fe can account, at least approximately, for the strengths of the observed bimodal 3883 A cyanogen bands in moderately metal-poor stars. The 3883 A cyanogen band strengths observed in M3, M13, and M5 suggest shifts of approximately +0.2 dex and -0.2 dex in the zero points of the Lick carbon and nitrogen abundance scales.

Variations in the strength of spectral features in spheroidal galactic systems. I - The method and CN band variation

view Abstract Citations (5) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Variations in the strength of spectral features in spheroidal galacticsystems. I. The method and CN band variation. Wirth, A. Abstract Moderate-resolution, high signal-to-noise spectra of elliptical galaxies are used to study the relation of the strength of the CN bands to other properties of the Galaxy. A new technique for the measurement of the strength of spectral features is described. Galaxy spectra are divided, pixel by pixel, to reveal subtle differences without loss in spectral resolution. Large intergalaxy CN variations are seen. Further, the CN band strength is shown to be not well correlated with either the strength of other spectral features or with the total luminosity. Two tentative explanations for this effect are proposed. Publication: The Astrophysical Journal Pub Date: January 1985 DOI: 10.1086/162770 Bibcode: 1985ApJ...288..132W Keywords: Astronomical Spectroscopy; Cn Emission; Elliptical Galaxies; Galactic Radiation; Milky Way Galaxy; Absorption Spectra; Bandwidth; Signal To Noise Ratios; Spheroids; Visible Spectrum; Wavelengths; Astrophysics full text sources ADS | data products NED (13) SIMBAD (12)

The giant branch of the old open cluster M67

view Abstract Citations (108) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The giant branch of the old open cluster M 67. Janes, K. A. ; Smith, G. H. Abstract DDO and UBV photometry of 36 red giants in M67 and spectroscopy of a small sample of giants in the cluster shows that with the exception of a few (i.e., two or possibly three) stars, the giant branch stars are extremely homogeneous in composition. These few anomalous stars have enhanced CN-band strengths, probably caused by a modest (0.2 dex) enhancement of nitrogen relative to the abundance in other cluster stars. Two of the four stars lying near, but not on, the giant branch are almost certainly binaries, while the remaining two stars may be binaries, asymptotic giant branch stars, or nonmembers. When the extensive published photometry is combined with the present data for the giants (including outlying proper motion members of the cluster), the color-magnitude diagram for the cluster becomes exceedingly well defined. Finally, the DDO photometry indicates that the cluster is virtually identical in composition to the Sun. Publication: The Astronomical Journal Pub Date: April 1984 DOI: 10.1086/113539 Bibcode: 1984AJ.....89..487J Keywords: Abundance; Giant Stars; Open Clusters; Stellar Spectrophotometry; Ubv Spectra; Astronomical Catalogs; Asymptotic Giant Branch Stars; Binary Stars; Chemical Composition; Color-Magnitude Diagram; Cyanogen; Mass To Light Ratios; Astronomy full text sources ADS | data products SIMBAD (57) GCPD (1)

Abundance indicators from vidicon spectra in six globular clusters

Spectroscopic scans with the CTIO vidicon systems are described for a total of 63 stars in six globular clusters, including 47 Tuc, NGC 288, NGC 362, M15, M2, and Pal 12. Several abundance-sensitive features (calcium lines, iron lines, G band, CN bands) are synthesized from the spectra and used to determine the relative compositions of the clusters. The principal results are: (a) 47 Tuc is clearly the most metal rich system in our sample, followed in order of decreasing (Fe/H) by NGC 362, Pal 12, NGC 288, M2, and M15. Except for CN, the rankings given by the individual parameters tend to be closely consistent; (b) NGC 288, NGC 362, and Pal 12 all have nearly similar metallicities (at (Fe/H)approx.-1.2 if 47 Tuc is at -0.8 and M2 at -1.5) but strongly different average ultraviolet CN strengths. Their observed spectroscopic differences are not well correlated with their equally strong color-magnitude differences: (c) the giants in both 47 Tuc and NGC 362 have similar average CN (lambda3883) band strengths and also variable star-to-star CN strengths, at all levels along the giant branch. The more metal poor clusters show smaller CN variations.

Infrared photometry of red giants in the globular cluster 47 Tucanae

view Abstract Citations (220) References (73) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Infrared photometry of red giants in the globular cluster 47 Tucanae. Frogel, J. A. ; Persson, S. E. ; Cohen, J. G. Abstract Infrared broad-band JHK and intermediate-band CO and R2O photometry is presented for 64 stars in the globular cluster 47 Tucanae including the long period variables (LPV) V1-4. These data are combined with optical photometric data and compared with evolutionary tracks for giant branch (GB) stars, with models for asymptotic giant branch (AGB) stars, and with determinations of CN band strengths. The main results of this paper are as follows: 1. At a fixed luminosity, the 47 Tuc giants show negligible scatter in V-K or, equivalently, effective temperature. Except for the upper half-magnitude, the slope of the GB is similar to theoretical giant branch slopes of the appropriate metallicity. These two results set an upper limit of 0.2 Msun to the mass lost by stars as they evolve from the level of the horizontal branch to within 0.5 mag of the GB tip. 2. Comparison of theoretical GB tracks with the observed giant branches of M92, Ml3, 47 Tuc, M7 1, and M67 show that shifts in Teff are required to bring theory and observation into agreement. These shifts seem to be a function of [Fe/H] and are in the sense that the observed tracks lie progressively cooler than the theoretical tracks for higher metal abundance. This suggests that the ratio of the mixing length to the pressure scale height in the convective envelope may be a function of metallicity and/or stellar mass. 3. While an independent estimate of the metallicity of 47 Tuc cannot be made from the IR data alone, the close similarity in all observed parameters of the 47 Tuc stars and the M7 1 giants studied previously implies that the two clusters must have essentially the same metallicity. 4. At a given effective temperature, the CO absorption strengths of the 47 Tuc giants have a significant scatter. This scatter can be accounted for by an anticorrelation between the CO strengths and the CN strengths measured by Norris and Freeman. The origin of this anticorrelation is likely to be the effect of CN-blanketing in one of the filter band passes used to measure the CO strengths. 5. At mean light the four LPVs lie sufficiently above the tip of the giant branch that they must be AGB stars. Their luminosities, temperatures, and periods are in qualitative agreement with model predictions for such stars. The periodic behavior of these variables is similar to that of Galactic LPVs. 6. Stellar H2O absorption in the band passes of the H and K filters is a strong influence on the J-H and H-K colors of some of the stars studied. Furthermore, the H2O strengths observed in the four LPVs are greater than those in the non-LPV variables which, in turn, are greater than those in the nonvariables. Again, this is similar to the situation for cool Galactic variable and nonvariable giants. Publication: The Astrophysical Journal Pub Date: June 1981 DOI: 10.1086/158979 Bibcode: 1981ApJ...246..842F Keywords: Globular Clusters; Infrared Astronomy; Infrared Photometry; Late Stars; Red Giant Stars; Stellar Spectrophotometry; Variable Stars; Bolometers; Hertzsprung-Russell Diagram; Stellar Luminosity; Stellar Models; Astronomy full text sources ADS | data products SIMBAD (59) GCPD (1)

Carbon and nitrogen abundances on the first giant branch of NGC 6752

Spectrum synthesis techniques have been used to derive quantitative carbon and nitrogen abundances for two stars with M/sub v/approx. =0.0 in the globular cluster NGC 6752. The stars CL 25 and CL 166 have similar effective temperature and gravity but different lambda3883 CN band strength. The abundance ratios derived, relative to the other elements for which (A/H)=-1.5, are ((C/A),(N/A))+0.1, -0.2for CL 25 and (-0.2, +0.6) for CL 166. The abundance ratios for CL 166, and presumably those of the other CN-strong stars in this cluster, can be explained by the mixing of processed material into the atmosphere of the star.

Stellar CN Band Strengths and the Abundance of Nitrogen

Violet and ultra-violet CN band strength parameters observed photo-electrically and photographically, respectively, are related by a semi-empirical method to horizontal curve-of-growth shifts predicted from model atmospheres with known basic parameters |$\theta_\text {eff},\enspace g, [\text {Fe/H}]$| , assuming that [C/Fe] = [O/Fe] = [N/Fe] = 0. Population I stars generally fit the standard relations, implying little variation in the abundances of C, N, O relative to metals, except in certain special cases in which either such variations occur or the basic parameters are in doubt (e.g. μ Leo, |$\epsilon$| And). Stars with halo kinematics, on the other hand, quite often have weaker CN bands than predicted, most probably because [N/Fe] < 0, although HD 25329 and a CH star deviate in the opposite direction. Most of the halo stars may fit the relation [N/Fe] ≃ [Fe/H], which is not unexpected on the basis of current ideas on explosive nucleosynthesis, but the weakness of their CN bands leads to ambiguous results except in a few cases.