The Spectra of Main Sequence Stars in Galactic Globular Clusters II. CH and CN Bands in M71

Spectra with a high signal-to-noise ratio of 79 stars which are just below the main sequence turnoff of M71 are presented. They yield indices for the strength of the G band of CH and the ultraviolet CN band at 3885 \AA. These indices are each to first order bimodal and they are anti-correlated. There are approximately equal numbers of CN weak/CH strong and CN strong/CH weak main sequence stars in M71. It is not yet clear whether these star-to-star variations arise from primordial variations or from mixing within a fraction of individual stars as they evolve.Comment: Accepted for publication in the AJ to appear back to back with paper I. 14 pages with 5 figure

The link between chemical anomalies along the red giant branch and the horizontal branch extension in globular clusters

We find a strong correlation between the extension of the Na-O anticorrelation observed in red giant branch (RGB) stars and the high temperature extension of the horizontal branch (HB) blue tails of Galactic globular clusters (GCs). The longer is the O-depleted tail of the Na-O anticorrelation observed in the RGB stars, the higher is the maximum temperature reached by the bluest HB stars in the GC. This result provides a clear, empirical evidence of a link between the extension of the HB and the presence of star-to-star abundance variations of proton-capture elements in GC stars. We discuss the possible interpretation of this correlation.Comment: Comments: 6 pages, 1 figure, uses emulateapj.cls; accepted for publication in the Astrophysical Journal Letter

Краудсорсинг и платформенные решения на транспорте: возможности для развития «Цифрового метро» в России

An increase in importance of quality and quantity of services provided, the rapidly growing amount of data required to manage an enterprise and strengthen its competitive position in the market, require rethinking of management models. The article is devoted to development of digital metro in the context of global automation and digitalization of business models of organizations in order to improve quality of services and optimize business processes.The objective of the research is to study the world and Russian experience in the use of digital and crowd platforms in transport and to develop an own model of metro management in modern conditions. To achieve the objective of the research, comparative and content analysis methods, benchmarking of successful foreign practices of using crowd and digital platforms in the transport industry, the method of generalization and conceptual and methodological modeling have been used.The authors have analyzed global trends in development and use of digital technologies in the transport industry, conducted a comparative analysis of world and Russian practices of using platform and crowd solutions in transport, and revealed the advantages of integrating digital technologies for development of metro in Russia. Based on the results of the research, the authors proposed an «e-Platform», accumulating, analyzing and sorting data from the external environment for its subsequent transmission to the business metro control blocks and optimizing the process of generating and making operational decisions, and also developed a target model for moving from «analogue» data management in metro to a digital one based on integration of digital technologies on a virtual platform for managing business processes and a crowdbased platform for collecting ideas and proposals to develop metro. Увеличение значимости качества и количества предоставляемых услуг, быстрорастущий объём данных, необходимых для управления предприятием и укрепления конкурентных позиций на рынке, требуют пересмотра моделей управления. Статья посвящена развитию цифрового метро в условиях глобальной автоматизации и цифровизации бизнес-моделей организаций с целью повышения качества предоставляемых услуг и оптимизации бизнес- процессов.Целью исследования является изучение мирового и российского опыта применения цифровых и крауд- платформ на транспорте и разработка авторской модели управления метрополитеном в современных условиях. Для достижения поставленной цели исследования применялись методы сравнительного и контент- анализа, бенчмаркинг успешных зарубежных практик использования крауд- и цифровых платформ в транспортной отрасли, метод обобщения и концептуальнометодологического моделирования.Авторы проанализировали мировые тренды в области развития и использования цифровых технологий в транспортной отрасли, провели сравнительный анализ мировой и российской практики применения платформенных и краудрешений на транспорте, раскрыли преимущества интеграции цифровых технологий для развития метрополитена в России. На основе полученных результатов исследования авторы предложили «е-Платформу», аккумулирующую, анализирующую и сортирующую данные, поступающие из внешней среды для последующей её передачи в бизнес-блоки управления метрополитеном и оптимизации процесса выработки и принятия оперативных решений, а также разработали целевую модель перехода от «аналогового» управления данными в метрополитене к цифровому на основе интеграции цифровых технологий на базе виртуальной платформы управления бизнеспроцессами и крауд-платформы сбора идей и предложений по развитию метрополитена

The Abundance Evolution of Oxygen, Sodium and Magnesium in Extremely Metal-Poor Intermediate Mass Stars: Implications for the Self-Polution Scenario in Globular Clusters

We present full stellar evolution and parametric models of the surface abundance evolution of O16, Ne22, Na23 and the magnesium isotopes in an extremely metal-poor intermediate mass star M_ZAMS=5M_sun, Z=0.0001. O16 and Ne22 are injected into the envelope by the third dredge-up following thermal pulses on the asymptotic giant branch. These species and the initially present Mg24 are depleted by hot bottom burning (HBB) during the interpulse phase. As a result, Na23, Mg25 and Mg26 are enhanced. If the HBB temperatures are sufficiently high for this process to deplete oxygen efficiently, Na23 is first produced and then depleted during the interpulse phase. Although the simultaneous depletion of O16 and enhancement of Na23 is possible, the required fine tuning of the dredge-up and HBB casts some doubt on the robustness of this process as the origin of the O-Na anti-correlation observed in globular cluster stars. However, a very robust prediction of our models are low Mg24/Mg25 and Mg24/Mg26 ratios whenever significant O16 depletion can be achieved. This seems to be in stark contrast with recent observations of the magnesium isotopic ratios in the globular cluster NGC6752.Comment: ApJ Letters, in pres

Star-to-star Na and O abundance variations along the red giant branch in NGC 2808

We report for the first time Na and O abundances from high-resolution, high S/N echelle spectra of 20 red giants in NGC 2808, taken as part of the Science Verification program of the FLAMES multi-object spectrograph at the ESO VLT. In these stars, spanning about 3 mag from the red giant branch (RGB) tip, large variations are detected in the abundances of oxygen and sodium, anticorrelated with each other; this is a well known evidence of proton-capture reactions at high temperatures in the ON and NeNa cycles. One star appears super O-poor; if the extension of the Na-O anticorrelation is confirmed, NGC 2808 might reach O depletion levels as large as those of M 13. This result confirms our previous findings based on lower resolution spectra (Carretta et al. 2003) of a large star-to-star scatter in proton capture elements at all positions along the RGB in NGC 2808, with no significant evolutionary contribution. Finally, the average metallicity for NGC 2808 is [Fe/H]= -1.14 +/- 0.01 dex (rms=0.06) from 19 stars.Comment: 12 pages, 3 figures, accepted for publication in ApJ Letter

Abundances in red giant stars of NGC 2808 and correlations between chemical anomalies and global parameters in globular clusters

We present the abundance analysis of stars from the tip of the red giant branch (RGB) to below the RGB-bump in the globular cluster NGC 2808, based on high resolution echelle spectra. We derived abundances of Al, alpha-process elements (Si I, Ca I, Ti I and Ti II) and Fe-group elements (Sc II, V I, Cr I, Cr II, Mn I, Co I, Ni I). Apart from Mg being somewhat reduced, likely because it has been depleted at the expense of Al in the MgAl cycle, the other alpha-element ratios show the overabundance typical of halo stars of similar metallicity. Mn is underabundant, whereas Fe-group elements have typical abundance ratios near the solar value. We detect star-to-star differences in Al abundances from the RGB tip down to the faintest star below the RGB-bump, correlated with Na abundances at all luminosities. The slope of the Na-Al correlation is similar to the one found in M 13 by Sneden et al. (2004), but it is different from those in other globular clusters of similar metallicity. We find that the amount of chemical inhomogeneities along the Na-O and Mg-Al anticorrelations in globular cluster red giants is correlated with the present day cluster mass and ellipticity. Moreover, we find for the first time a correlation between the spread in proton-capture elements and orbital parameters of clusters. The chemical anomalies are more extended in clusters having large-sized orbits and longer periods, and in clusters with larger inclination angles of the orbit with respect to the Galactic plane.Comment: 25 pages, 6 tables and 16 figures, accepted for publication on A

DDO Photometry of M71: Carbon and Nitrogen Patterns Among Evolving Giants

We present V, B-V, and DDO C(41-42) and C(42-45) photometry for a sample of 75 red giants down to M_V = +2 in the relatively metal-rich Galactic globular cluster M71. The C(41-42) colors reveal a bimodal distribution of CN band strengths generally anticorrelated with CH band strength as measured by the C(42-45) color. Both DDO colors agree well with those found in 47 Tucanae -- a nearby globular cluster of similar metallicity -- and suggest nearly identical C and N abundance patterns among the giants of both clusters. A comparison with synthetic DDO colors demonstrates that little change in surface C or N abundance is required to match the colors of the M71 giants over the entire luminosity range observed. Apparently like 47 Tuc (a cluster of much greater mass and central concentration), M71 exhibits an abundance pattern which cannot be solely the result of internal mixing.Comment: To appear in the Astronomical Journal, November 2001. 17 Pages, 5 Figure

Fluorine Abundance Variations as a Signature of Enhanced Extra Mixing in Red Giants of the Globular Cluster M4

We show that enhanced extra mixing in low-mass red giants can result in a fluorine abundance that is correlated with abundance variations of other elements participating in H burning, such as C, N, O and Na. This finding is used to explain the fluorine abundance variations recently found in bright red giants of the globular cluster M4.Comment: 17 pages, 6 figures, submitted to Ap

A Double Main Sequence in the Globular Cluster NGC 6397

High-precision multi-band HST photometry reveals that the main sequence (MS) of the globular cluster NGC 6397 splits into two components, containing ~30% and ~70% of the stars. This double sequence is consistent with the idea that the cluster hosts two stellar populations: (i) a primordial population that has a composition similar to field stars, and containing ~30% of the stars, and (ii) a second generation with enhanced sodium and nitrogen, depleted carbon and oxygen, and a slightly enhanced helium abundance (Delta Y~0.01). We examine the color difference between the two sequences across a variety of color baselines and find that the second sequence is anomalously faint in m_F336W. Theoretical isochrones indicate that this could be due to NH depletion.Comment: 19 pages, 11 figures, accepted for pubblication in Ap

Abundances in Stars from the Red Giant Branch Tip to Near the Main Sequence Turn Off in M71: III. Abundance Ratios

We present abundance ratios for 23 elements with respect to Fe in a sample of stars with a wide range in luminosity, from luminous giants to stars near the turnoff, in the globular cluster M71. The analyzed spectra, obtained with HIRES at the Keck Observatory, are of high dispersion (R=35,000). We find that the neutron capture, the iron peak and the alpha-element abundance ratios show no trend with Teff, and low scatter around the mean between the top of the RGB and near the main sequence turnoff. The alpha-elements Mg, Ca, Si and Ti are overabundant relative to Fe. The anti-correlation between O and Na abundances, observed in other metal poor globular clusters, is detected in our sample and extends to the main sequence. A statistically significant correlation between Al and Na abundances is observed among the M71 stars in our sample, extending to Mv = +1.8, fainter than the luminosity of the RGB bump in M5. Lithium is varying, as expected, and Zr may be varying from star to star as well. M71 appears to have abundance ratios very similar to M5 whose bright giants were studied by Ivans et al. (2001), but seems to have a smaller amplitude of star-to-star variations at a given luminosity, as might be expected from its higher metallicity. The results of our abundance analysis of 25 stars in M71 provide sufficient evidence of abundance variations at unexpectedly low luminosities to rule out the mixing scenario. Either alone or, even more powerfully, combined with other recent studies of C and N abundances in M71 stars, the existence of such abundance variations cannot be reproduced within the context of our current understanding of stellar evolution.Comment: AJ, in press (June 2002), 18 figure