scholarly journals A Composition Gradient in the Galactic Disk

1977 ◽  
Vol 45 ◽  
pp. 173-175
Author(s):  
K. A. Janes
Keyword(s):  
Heavy Element ◽  
Galactic Disk ◽  
Theoretical Models ◽  
Galactic Evolution ◽  
Element Abundance ◽  
Composition Gradient ◽  
H Ii Regions ◽  
Galactic Disks ◽  
Stellar Ages ◽  
Gradient Variation

A number of recent investigations have demonstrated that the heavy element abundance in galactic disks decreases with increasing distance from the center. Although there is little question that the composition in the outermost parts of galactic disks differs from that in the inner regions, the precise nature of the presumed gradient in our own galaxy remains undetermined. At the present time, the most specific evidence for a gradient is based either on kinematics of stars in the solar vicinity (e.g., Janes, 1975 or Mayor, 1976) or on observations of distant H II regions (Hawley, 1977) and planetary nebulae (Peimbert, et al, 1977). Little is known about the variation of abundance ratios with position or the relation between stellar ages and the composition gradient. However, all three of these quantities (that is, the overall metallicity gradient, variation of abundance ratios and stellar age effects) can now be estimated from theoretical models of galactic evolution (for example, see Tinsley and Larson, 1977).

APOGEE: the Sloan Digital Sky Survey Apache Point Observatory Galactic Evolution Experiment. Insights into the Galactic Disk: A Review

2017 ◽  
Vol 13 (S334) ◽  
pp. 101-108
Author(s):  
Jon A. Holtzman ◽  
Sten Hasselquist ◽  
Keyword(s):  
Galactic Disk ◽  
Structural Parameters ◽  
Distribution Functions ◽  
Galactic Evolution ◽  
Sloan Digital Sky Survey ◽  
Element Abundance ◽  
Near Ir ◽  
Stellar Ages ◽  
Sky Survey ◽  
Evolution Experiment

AbstractThe SDSS Apache Point Observatory Galactic Evolution Experiment (APOGEE) has collected high resolution near-IR spectra for several hundred thousand stars throughout the Milky Way. We review some of the results related to chemistry of stars in the disk, where APOGEE has a particular advantage by virtue of being able to work in more obscured areas. The ability to measure carbon and nitrogen abundances in giants in the near-IR provides insight into stellar ages. We summarize results on the variation of mean metallicity, metallicity distribution functions, and the [α/Fe]–[Fe/H] relation across the Galactic disk, as well as results on the structural parameters in mono-abundance populations. Many of these results suggest that radial migration has played a significant role in the Galactic disk. It may be possible to disentangle radial mixing using multi-element abundance patterns.

scholarly journals Open cluster remnants in low-density Galactic fields

2009 ◽  
Vol 5 (S266) ◽  
pp. 487-490
Author(s):  
D. B. Pavani ◽  
L. O. Kerber ◽  
E. Bica ◽  
W. J. Maciel
Keyword(s):  
Galactic Disk ◽  
Information Source ◽  
Open Cluster ◽  
Dynamical Evolution ◽  
Theoretical Models ◽  
Open Clusters ◽  
Low Density ◽  
Statistical Tool ◽  
General Picture ◽  
Disk Evolution

AbstractOpen cluster remnants (OCRs) are fundamental objects to investigate open cluster dissolution processes (e.g., Bica et al. 2001; Carraro 2002; Pavani et al. 2003; Carraro et al. 2007; Pavani & Bica 2007). They are defined as poorly populated concentrations of stars, with enough members to show evolutionary sequences in colour–magnitude diagrams (CMDs) as a result of the dynamical evolution of an initially more massive physical system. An OCR is intrinsically poorly populated, which makes its differentiation from field-star fluctuations difficult. Among the possible approaches to establish the nature of OCRs, we adopted CMD analysis combined with a robust statistical tool applied to 2mass data. In addition, photometry is the main information source available for possible OCRs (POCRs). We developed a statistical diagnostic tool to analyse the CMDs of POCRs and verify them as physical systems, explore membership probabilityies taking into account field contamination and derive age, distance and reddening values in a self-consistent way. We present the results of our analysis of 88 POCRs that are part of a larger sample that is widely distributed across the sky, with a significant density contrast of bright stars compared to the Galactic field. The 88 objects are projected onto low-density Galactic fields, at relatively high latitudes (|b| > 15°). Studies of larger POCR samples will provide a better understanding of OCR properties and constraints for theoretical models, including new insights into the evolution of open clusters and their dissolution rates. The results of this ongoing survey will provide a general picture of these fossil stellar systems and their connection to Galactic-disk evolution.

scholarly journals A Spectroscopic Survey in the EUV of the “Coolest” Hot DA Stars

1996 ◽  
Vol 152 ◽  
pp. 217-222
Author(s):  
Jean Dupuis ◽  
Stéphane Vennes
Keyword(s):  
Effective Temperature ◽  
White Dwarfs ◽  
Heavy Element ◽  
Extreme Ultraviolet ◽  
Diffusion Theory ◽  
Hydrogen Atmosphere ◽  
Element Abundance ◽  
Pure Hydrogen ◽  
Element Abundances ◽  
The One

We present an analysis of the extreme ultraviolet (EUV) spectroscopy of a sample of 10 DA white dwarfs observed by the Extreme Ultraviolet Explorer (EUVE). We have selected white dwarfs cooler than about 50,000 K and with presumably low heavy element abundances. The goal of this study is to determine the fundamental atmospheric parameters, namely the effective temperature and chemical composition, of these stars by fitting their continua with synthetic spectra computed from pure hydrogen LTE/line-blanketed model atmospheres. The question of the presence (or absence) of trace elements is explored by comparing EUV-determined effective temperatures to the one obtained from a fit of hydrogen balmer lines. It is found that the majority of the DA in the sample are consistent with having a pure hydrogen atmosphere. One of the star, MCT0027-634, is another possible example of a HZ 43-type white dwarf, having an effective temperature above 50000 K and a low heavy element abundance, i.e., much lower than predicted by diffusion theory.

scholarly journals Supernova Abundance Generation

1991 ◽  
Vol 145 ◽  
pp. 21-38
Author(s):  
K. Nomoto ◽  
T. Shigeyama ◽  
T. Tsujimoto
Keyword(s):  
Heavy Element ◽  
Massive Stars ◽  
Theoretical Models ◽  
Light Curves ◽  
Maximum Brightness ◽  
Sn 1987A ◽  
New Models ◽  
Decline Rate ◽  
Type Ia ◽  
Supernova Explosions

Theoretical models of supernova explosions of various types are reviewed to obtain heavy element yields from supernovae. We focus on new models for SN 1987A, and Type Ia, Ib, and Ic supernovae. Maximum brightness and decline rate of their light curves suggest that 12–18 M⊙ stars produce larger amount of 56Ni than more massive stars. We discuss relative roles of various types of supernovae in the chemical evolution of galaxies.

scholarly journals Uncertainties in the Position of the β Cephei Instability Strip in the HR Diagram

1995 ◽  
Vol 155 ◽  
pp. 291-292
Author(s):  
A.A. Pamyatnykh ◽  
W.A. Dziembowski ◽  
P. Mikołaj
Keyword(s):  
Heavy Element ◽  
Element Abundance ◽  
Instability Strip ◽  
Metal Mixture ◽  
Hr Diagram

AbstractWe discuss the sensitivity of the theoretical B star instability domains to the heavy element abundance Z, the adopted metal mixture, the assumed overshooting from stellar convective cores and the choice of the opacity data.

scholarly journals Interstellar and Stellar Abundances Across the Galactic Disk

1977 ◽  
Vol 45 ◽  
pp. 149-159 ◽  
Author(s):  
Manuel Peimbert
Keyword(s):  
Chemical Composition ◽  
Density Distribution ◽  
Chemical Evolution ◽  
Galactic Disk ◽  
Theoretical Models ◽  
Observational Evidence ◽  
Stellar Abundances ◽  
Abundance Gradient ◽  
The Galaxy

Abstract.Observational evidence related to the chemical composition across the disk of the Galaxy is reviewed. The H2density distribution derived for the Galaxy is poorly known, consequently it is still not possible to compare theoretical models of the chemical evolution of the Galaxy with the gaseous density distribution. The H2density distribution is particularly sensitive to the fraction of carbon atoms embedded in CO molecules and to the possible presence of a C/H abundance gradient.

scholarly journals Element Abundances in Magellanic Cloud H II Regions from Carbon to Argon

1999 ◽  
Vol 190 ◽  
pp. 266-272 ◽  
Author(s):  
Donald R. Garnett
Keyword(s):  
Heavy Element ◽  
Hubble Space Telescope ◽  
Uv Spectroscopy ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
H Ii Regions ◽  
Ionized Gas ◽  
Mixing Processes ◽  
Element Abundances ◽  
C And N

I review measurements of heavy element abundances within H II regions in the Magellanic Clouds, highlighting in particular improved determinations of carbon abundances based on UV spectroscopy with Hubble Space Telescope. In general, the Magellanic Cloud H II regions show average underabundances in O, Ne, and S (relative to their Galactic counterparts) that are similar to those measured in Magellanic Cloud stars. However, comparison of stars and ionized gas shows discrepancies in C and N abundances that may be related to recently recognized mixing processes that may be operating in massive stars.

scholarly journals Element Abundance Analyses of Novae

1977 ◽  
Vol 42 ◽  
pp. 242-273 ◽  
Author(s):  
Robert E. Williams
Keyword(s):  
Temperature Distribution ◽  
Emission Line ◽  
Heavy Element ◽  
Element Abundance ◽  
Element Abundances ◽  
Maximum Light ◽  
Growth Studies ◽  
Nova Shells

AbstractThe different methods by which element abundances in novae have been determined are reviewed. Curve of growth studies of novae at maximum light have indicated CNO nuclei to be greatly enhanced with respect to hydrogen in certain objects. These results are questionable because they depend upon an assumed temperature distribution in the photosphere which is probably too steep to be realistic. Emission line analyses of novae, generally obtained in the period of early decline, also indicate possible heavy element enhancement, however these results are tentative because of uncertainties in the parameters of the emitting gas. It is suggested that useful abundance determinations of nova ejecta might be obtained from studies of old, extended nova shells.

Sign in / Sign up

Export Citation Format

Share Document