1,723,108 research outputs found
Analysis of sHB 6791
No full text"March 25, 1999."; Discusses sHB 6791, an Act Concerning the Transfer of the Department of Health Toxicology Lab to the Department of Public Safety Division of Scientific Services, eliminating the state police forensic science laboratory and the Department of Public Health (DPH) toxicology laboratory as separate organizational entities and creating a Division of Scientific Services within the Department of Public Safety to carry out the functions of the forensic laboratory and the forensic science functions of the toxicology laboratory
The old, massive, metal rich open cluster NGC 6791
No full textNGC~6791 is a rich open cluster that attracted a lot of attention in the last decade. Recent estimates indicate that the mass is even larger, around 5000\,. This is quite remarkable: the cluster is in fact 8\,Gyr old, while the typical dissolution time for Galactic open clusters is a few Myr only. This might imply that the cluster managed to survive so long either because its original mass was much larger, or because it moved along a preferential orbit. In any case, such combination of old age and large mass is unique among Galactic open clusters, especially for clusters located in the inner regions of the Galactic disk. This is not the only special property of NGC 6791. Its abundance in iron is [Fe/H] +0.40. again unique among Galactic star clusters of the same age range. Significant dispersions in various elements have been detected, that are not routinely found in Galactic open clusters. The combined UV flux of the few hot HB stars makes the cluster the closest proxy of an elliptical galaxy. This surprising result might indeed indicate that NGC 6791 was massive enough at origin to experience a strong burst of star formation and a fast enrichment.This pletora of unique properties renders NGC 6791 an extremely important object to study and understand.How and where could such a stellar system have formed? Is NGC 6791 just an open cluster? Did it form close to the bulge? How could have survived in the adverse, high-density, environment of the inner Galactic disk?These are difficult questions to answer to, of course. One of the still missing key observational evidence is whether the cluster suffered from tidal interaction, that could have significantly decreased its mass. We find such evidences, and use them as an argument to support a scenario in which the cluster formed as a massive object. We also estimate, using approximate analytic description based on available -body models, how much mass NGC~6791 lost, and which was its probable mass at formation.<!--EndFragment--
The chemical abundance of the very metal-rich old open clusters NGC 6253 and NGC 6791
No full textAims.In the framework of a project aiming at homogeneously deriving
the properties (age, distance, reddening, and detailed chemical
abundances) of a large sample of old open clusters, we present here
the metal abundance and the abundance ratios of light (C, N, O,
Na, Mg, Al, Si, Ca, Ti) and heavier (Cr, Mn, Ni, Ba, Eu) elements in
the galactic open clusters NGC 6253 and NGC 6791.
Methods.We performed spectrum synthesis of selected lines on
the high resolution spectra of
four red clump stars in NGC 6253, taken with the UVES and FEROS spectrographs.
We also
determined abundances of the same elements for four red clump stars in NGC 6791,
observed with SARG, for which we had derived the atmospheric parameters and the
iron, carbon and oxygen abundances in a previous paper (Gratton et al. 2006, ApJ, 462, 469).
Results.The average metallicity of NGC 6253 is [Fe/H] (rms = 0.03 dex,
systematic error = 0.08 dex),
obtained by extensive spectral synthesis of Fe lines. This intermediate age
cluster closely resembles the old open cluster NGC 6791, as far as the
chemical composition is concerned.
C, N, and O do not show any significant abundance scatter, and they are
underabundant with respect to the solar values both in NGC 6253 and
NGC 6791. We also
find no evident
star-to-star scatter in any of the elements measured in both clusters, with the
possible exception of Na in NGC 6791.
The two clusters show very similar abundances, except for Mg,
overabundant in NGC 6791 and not in NGC 6253. Both have solar-scaled
α-elements abundances. We compared our abundance
ratios with the literature values for disk giants and dwarfs and bulge giants,
finding generally good agreement with the run of elemental ratios with [Fe/H]
of disk objects
New insights in the origin and evolution of the old, metal-rich open cluster NGC 6791
No full textNGC 6791 is one of the most studied open clusters, it is massive (∼5000 M⊙), located at the solar circle, old (∼8 Gyr) and yet the most metal-rich cluster ([Fe/H] ≃ 0.4) known in the Milky Way. By performing an orbital analysis within a Galactic model including spiral arms and a bar, we found that it is plausible that NGC 6791 formed in the inner thin disc or in the bulge, and later displaced by radial migration to its current orbit. We apply different tools to simulate NGC 6791, including direct N-body summation in time-varying potentials, to test its survivability when going through different Galactic environments. In order to survive the 8 Gyr journey moving on a migrating orbit, NGC 6791 must have been more massive, M0 ≥ 5 × 104M⊙, when formed. We find independent confirmation of this initial mass in the stellar mass function, which is observed to be flat; this can only be explained if the average tidal field strength experienced by the cluster is stronger than what it is at its current orbit. Therefore, the birth place and journeys of NGC 6791 are imprinted in its chemical composition, in its mass loss, and in its flat stellar mass function, supporting its origin in the inner thin disc or in the bulge
A study of variable stars in star clusters NGC 2808 and NGC 6791
No full textStudying the variable stars in star clusters gives us an insight into the early universe that we might not otherwise have. NGC 2808 has features that set it apart from the majority of other globular clusters. Understanding why it is different will help us understand the mechanics of globular cluster formation and evolution. Likewise, NGC 6791 is an unusual open cluster that may be able to provide insight into stellar evolution. This thesis presents the results from a study of globular cluster NGC 2808 and open cluster NGC 6791 with a focus on finding new variable stars. Images were obtained in the R band using SARA consortium telescopes. For NGC 2808 the SARA 0.6 meter telescope at CTIO in Cerro Tololo, Chile was used, and for NGC 6791 the SARA 1.0 meter telescope at ORM in La Palma, Spain was used. NGC 2808 was observed for five nights, from March 2017 to March 2018 while NGC 6791 was observed for four nights, between April 2017 and October 2017. In NGC 2808, 51 variable stars were detected. Of these, 32 had been previously found by Kunder et al (2013), while 19 had not. In NGC 6791, 37 variables were detected of which 8 had been previously found by de Marchi et al (2007) and 29 had not, including 2 exoplanet candidates.Thesis (M.S.)Department of Physics and Astronom
STELLAR LIFETIME AND ULTRAVIOLET PROPERTIES OF THE OLD METAL-RICH GALACTIC OPEN CLUSTER NGC 6791: A PATHWAY TO UNDERSTAND THE ULTRAVIOLET UPTURN OF ELLIPTICAL GALAXIES∗
No full textThe evolutionary properties of the old metal-rich Galactic open cluster NGC 6791 are assessed based on deep UB photometry and Two Micron All Sky Survey JK data. For the 4739 stars in the cluster, bolometric luminosity and effective temperature have been derived from theoretical (U − B) and (J − K) color fitting. The derived H-R diagram has been matched with the Uvblue grid of synthetic stellar spectra to obtain the integrated spectral energy distribution (SED) of the system, together with a full set of UV (Fanelli) and optical (Lick) narrowband indices. The total bolometric magnitude of NGC 6791 is M ᵇ°ˡ₆₇₉₁= −6.29, with a color (B − V ) ₆₇₉₁= 0.97. The cluster appears to be a fairly good proxy of standard elliptical galaxies, although with significantly bluer infrared colors, a shallower 4000Å Balmer break, and a lower Mg2 index. The confirmed presence of a dozen hot stars along their extreme horizontal-branch evolution leads the cluster SED to consistently match the properties of the most active UV-upturn galaxies, with 1.7% ± 0.4% of the total bolometric luminosity emitted shortward of 2500 Å. The cluster helium abundance results in Y₆₇₉₁ = 0.30 ± 0.04, while the post-main-sequence (PMS) implied stellar lifetime from star number counts fairly agrees with the theoretical expectations from both the Padova and Basti stellar tracks. A PMS fuel consumption of 0.43 ± 0.01Mꙩ is found for NGC 6791 stars, in close agreement with the estimated mass of cluster He-rich white dwarfs. Such a tight figure may lead one to suspect that a fraction of the cluster stellar population does not actually reach the minimum mass required to effectively ignite He in the stellar core
New insights in the origin and evolution of the old, metal-rich open cluster NGC 6791
No full textNGC 6791 is one of the most studied open clusters, it is massive (∼5000 M⊙), located at the solar circle, old (∼8 Gyr) and yet the most metal-rich cluster ([Fe/H] ≃ 0.4) known in the Milky Way. By performing an orbital analysis within a Galactic model including spiral arms and a bar, we found that it is plausible that NGC 6791 formed in the inner thin disc or in the bulge, and later displaced by radial migration to its current orbit. We apply different tools to simulate NGC 6791, including direct N-body summation in time-varying potentials, to test its survivability when going through different Galactic environments. In order to survive the 8 Gyr journey moving on a migrating orbit, NGC 6791 must have been more massive, M0 ≥ 5 × 104M⊙, when formed. We find independent confirmation of this initial mass in the stellar mass function, which is observed to be flat; this can only be explained if the average tidal field strength experienced by the cluster is stronger than what it is at its current orbit. Therefore, the birth place and journeys of NGC 6791 are imprinted in its chemical composition, in its mass loss, and in its flat stellar mass function, supporting its origin in the inner thin disc or in the bulge
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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