Chemical abundances in the Outer Disk Clusters Tombaugh 2, Melotte 71, and NGC 2112

1996 ◽  
Vol 112 ◽  
pp. 1551 ◽  
Author(s):  
Jeffery A. Brown ◽  
George Wallerstein ◽  
Doug Geisler ◽  
J. B. Oke
Keyword(s):  
Chemical Abundances ◽  
Outer Disk

scholarly journals Chemical Abundances of Planetary Nebulae in the Substructures of M31. II. The Extended Sample and a Comparison Study with the Outer-disk Group

2018 ◽  
Vol 853 (1) ◽  
pp. 50 ◽  
Author(s):  
Xuan Fang ◽  
Rubén García-Benito ◽  
Martín A. Guerrero ◽  
Yong Zhang ◽  
Xiaowei Liu ◽  
...  
Keyword(s):  
Planetary Nebulae ◽  
Comparison Study ◽  
Chemical Abundances ◽  
Outer Disk

scholarly journals Measuring Outer Disk Warps with Optical Spectroscopy

2008 ◽  
Vol 4 (S254) ◽  
pp. 283-288
Author(s):  
Daniel Christlein ◽  
Joss Bland-Hawthorn
Keyword(s):  
Star Formation ◽  
Optical Spectroscopy ◽  
Column Density ◽  
Rotational Velocity ◽  
Chemical Abundances ◽  
Circular Velocity ◽  
Outer Disk ◽  
The Galaxy ◽  
Galaxy Disk ◽  
Interesting Alternative

AbstractWarps in the outer gaseous disks of galaxies are a ubiquitous phenomenon, but it is still unclear what generates them. One theory is that warps are generated internally through spontaneous bending instabilities. Other theories suggest that they result from the interaction of the outer disk with accreting extragalactic material. In this case, we expect to find cases where the circular velocity of the warp gas is poorly correlated with the rotational velocity of the galaxy disk at the same radius. Optical spectroscopy presents itself as an interesting alternative to 21-cm observations for testing this prediction, because (i) separating the kinematics of the warp from those of the disk requires a spatial resolution that is higher than what is achieved at 21 cm at low HI column density; (ii) optical spectroscopy also provides important information on star formation rates, gas excitation, and chemical abundances, which provide clues to the origin of the gas in warps. We present here preliminary results of a study of the kinematics of gas in the outer-disk warps of seven edge-on galaxies, using multi-hour VLT/FORS2 spectroscopy.

Chemical Abundances for a Sample of Southern OB Stars. II. The Outer Disk

2004 ◽  
Vol 606 (1) ◽  
pp. 514-519 ◽  
Author(s):  
Simone Daflon ◽  
Katia Cunha ◽  
Keith Butler
Keyword(s):  
Chemical Abundances ◽  
Ob Stars ◽  
Outer Disk

The H [CSC]ii[/CSC] Regions of the Extreme Outer Disk of NGC 628

2000 ◽  
Vol 120 (3) ◽  
pp. 1306-1315 ◽  
Author(s):  
Mario Lelièvre ◽  
Jean-René Roy
Keyword(s):  
Outer Disk

Bidimensional Spectroscopic Mapping and Chemical Abundances of the Star‐forming Dwarf Galaxy I Zw 18

1998 ◽  
Vol 508 (1) ◽  
pp. 248-261 ◽  
Author(s):  
José M. Vílchez ◽  
Jorge Iglesias‐Páramo
Keyword(s):  
Dwarf Galaxy ◽  
Chemical Abundances ◽  
Star Forming

scholarly journals H2-Bearing Damped Lyman-α Systems as Tracers of Cosmological Chemical Evolution

2004 ◽  
Vol 217 ◽  
pp. 252-257
Author(s):  
M. T. Murphy ◽  
S. J. Curran ◽  
J. K. Webb
Keyword(s):  
Chemical Evolution ◽  
Selection Effects ◽  
Host Galaxies ◽  
Chemical Abundances ◽  
Physical Conditions ◽  
Observational Selection ◽  
Host Type ◽  
Molecular Fraction ◽  
Magnitude Variation

The chemical abundances in damped Lyman-α systems (DLAs) show more than 2 orders of magnitude variation at a given epoch, possibly because DLAs arise in a wide variety of host galaxies. This could significantly bias estimates of chemical evolution. We explore the possibility that DLAs in which H2 absorption is detected may trace cosmological chemical evolution more reliably since they may comprise a narrower set of physical conditions. The 9 known H2 absorption systems support this hypothesis: metallicity exhibits a faster, more well-defined evolution with redshift than in the general DLA population. The dust-depletion factor and, particularly, H2 molecular fraction also show rapid increases with decreasing redshift. We comment on possible observational selection effects which may bias this evolution. Larger samples of H2-bearing DLAs are clearly required and may constrain evolution of the UV background and DLA galaxy host type with redshift.

scholarly journals Chemical Abundances of Early Type Stars

1998 ◽  
Vol 188 ◽  
pp. 224-225
Author(s):  
S. Tanaka ◽  
S. Kitamoto ◽  
T. Suzuki ◽  
K. Torii ◽  
M.F. Corcoran ◽  
...  
Keyword(s):  
Surface Layer ◽  
Stellar Wind ◽  
Nuclear Reactions ◽  
X Rays ◽  
Early Type ◽  
Chemical Abundances ◽  
X Ray ◽  
Low Metallicity ◽  
Early Type Stars

X-rays from early-type stars are emitted by the corona or the stellar wind. The materials in the surface layer of early-type stars are not contaminated by nuclear reactions in the stellar inside. Therefore, abundance study of the early-type stars provides us an information of the abundances of the original gas. However, the X-ray observations indicate low-metallicity, which is about 0.3 times of cosmic abundances. This fact raises the problem on the cosmic abundances.

scholarly journals Chemical Enrichment and Central Star Properties

1993 ◽  
Vol 155 ◽  
pp. 572-572
Author(s):  
C.Y. Zhang
Keyword(s):  
Planetary Nebulae ◽  
Central Star ◽  
Agb Stars ◽  
Physical Processes ◽  
Chemical Abundances ◽  
Core Mass ◽  
Chemical Enrichment ◽  
The Core ◽  
Stellar Temperature ◽  
Independent Parameters

We have selected a sample of planetary nebulae, for which the core masses are determined using distance-independent parameters (Zhang and Kwok 1992). The chemical abundances of He, N, O, and C are taken from the literature for them. Relationships of the ratios of He/H, N/O, and C/O with various stellar parameters of planetary nebulae (PN), such as the core mass, the mass of the core plus the ionized nebular gas, the stellar age and temperature, are examined. It is found that the N/O increases with increasing mass, while the C/O first increases and then decreases with the core mass. No strong correlation seems to exist between the He/H and the core mass. A correlation of the N/O and He/H with the stellar temperature exists. The current dredge-up theory for the progenitor AGB stars cannot satisfactorily account for these patterns of chemical enrichment in PN. Furthermore, the correlations of the N/O and He/H with the stellar age and temperature indicate that besides the dredge-ups in the RG and AGB stages, physical processes that happen in the planetary nebula stage may also play a role in forming the observed patterns of chemical enrichment in the planetary nebulae.

scholarly journals Are “realistic” model atmospheres realistic enough?

2009 ◽  
Vol 5 (S265) ◽  
pp. 187-196 ◽  
Author(s):  
Bengt Gustafsson
Keyword(s):  
Realistic Model ◽  
Considerable Progress ◽  
Observational Methods ◽  
Construction Technology ◽  
Mixing Length ◽  
Late Type ◽  
Chemical Abundances ◽  
Stellar Spectra ◽  
Analysis Methods ◽  
Major Break

AbstractDuring the latest decades the number of papers on stellar chemical abundances has increased dramatically. This is basically reflecting the very great achievements in telescope- and spectrometer-construction technology. The analysis of the resulting stellar spectra, however, is still not up to the standard that is offered by the observational methods. Recent significant advances in the analysis methods (i.e., in constructing model atmospheres and model spectra to compare with the observed ones) is reviewed with the emphasis on the application to abundance analysis of late-type stars. It is found that the very considerable progress that have been made beyond mixing-length convection and LTE is a major break-through for physically consistent modeling. Still, however, further steps must be taken, in particular for the cooler stars, before the situation is fully satisifactory.

scholarly journals Structure and dynamics of the Milky Way disk as revealed from the radial velocity distributions of APOGEE red clump stars

2016 ◽  
Vol 11 (S321) ◽  
pp. 50-50
Author(s):  
Daisuke Toyouchi ◽  
Masashi Chiba
Keyword(s):  
Near Infrared ◽  
Milky Way ◽  
Radial Velocities ◽  
Galactocentric Distance ◽  
Chemical Abundances ◽  
Structure And Dynamics ◽  
Evolution Experiment ◽  
Dynamical Properties ◽  
Red Clump ◽  
Independent Work

AbstractWe investigate the structure and dynamics of the Milky Way (MW) disk stars based on the analysis of the Apache Point Observatory Galactic Evolution Experiment (APOGEE) data, to infer the past evolution histories of the MW disk component(s) possibly affected by radial migration and/or satellite accretions. APOGEE is the first near-infrared spectroscopic survey for a large number of the MW disk stars, providing their radial velocities and chemical abundances without significant dust extinction effects. We here adopt red-clump (RC) stars (Bovy et al. 2014), for which the distances from the Sun are determined precisely, and analyze their radial velocities and chemical abundances in the MW disk regions covering from the Galactocentric distance, R, of 5 kpc to 14 kpc. We investigate their dynamical properties, such as mean rotational velocities, 〈Vφ〉 and velocity dispersions, as a function of R, based on the MCMC Bayesian method. We find that at all radii, the dynamics of alpha-poor stars, which are candidates of young disk stars, is much different from that of alpha-rich stars, which are candidates of old disk stars. We find that our Jeans analysis for our sample stars reveals characteristic spatial and dynamical properties of the MW disk, which are generally in agreement with the recent independent work by Bovy et al. (2015) but with a different method from ours.

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