Galactic stellar populations with APOGEE andKepler

2016 ◽  
Vol 337 (8-9) ◽  
pp. 917-921 ◽  
Author(s):  
J. A. Johnson ◽  
APOKASC collaboration
Keyword(s):  
Stellar Populations ◽  
Galactic Stellar Populations

scholarly journals The Metallicity Distribution of Late Type Dwarfs

1998 ◽  
Vol 11 (1) ◽  
pp. 571-571
Author(s):  
M. Haywood ◽  
J. Palasi ◽  
A. Gómez ◽  
L. Meillon Dasgal
Keyword(s):  
Star Formation Rate ◽  
Formation Rate ◽  
Angular Separation ◽  
Stellar Populations ◽  
Late Type ◽  
Limited Sample ◽  
Hipparcos Catalogue ◽  
Galactic Stellar Populations ◽  
Metallicity Distribution ◽  
Hr Diagram

The Hipparcos catalogue provides an accurate and extensive sampling of the solar neighbourhood HR diagram. The morphology of this diagram depends on selection criteria of the catalogue such as the limiting magnitude, angular separation and on the characteristics of the stellar populations near the sun (space density, metallicity, star formation rate, etc). Since the Hipparcos data are so accurate, one needs to model precisely the different selection bias and, at the same time, parametrize models of the galactic stellar populations with sufficient flexibility that as much information as possible can be grasped from the catalogue. Comparisons between our model and the Hipparcos catalogue will be presented elsewhere. Since the quantity of information contained in the Hipparcoscatalogue is so important, models ought to be complex, and external contraints, obtained prior to any general comparison with the model, are welcome. A major factor that influences the distribution of the stars in the HR diagram is the metallicity. For the late type stars, the metallicity distribution can be best studied by re-analysing a volume-limited sample of stars from the catalogue.

scholarly journals Deep Multi-Colour Starcounts

1994 ◽  
Vol 161 ◽  
pp. 423-424
Author(s):  
I.N. Reid ◽  
S.R. Majewski
Keyword(s):  
Standard Model ◽  
Stellar Population ◽  
Stellar Populations ◽  
The North ◽  
Halo Stars ◽  
The Standard Model ◽  
The Galaxy ◽  
Best Fitting ◽  
Galactic Stellar Populations ◽  
North Galactic

Starcounts remain one of the most effective methods of probing the structure of the Galactic stellar populations. However, studies of the distribution at large distances above the Plane demand accurate photometry extending to faint magnitudes (V > 20), and such datasets are still rare. We (Reid & Majewski 1993) have analyzed data from one field — Majewski's (1992) UJF observations of SA57, the North Galactic Pole field. Our results revealed significant discrepancies with the standard model of the Galaxy (see refs. in Reid & Majewski), notably a paucity in the number of halo stars by a factor of two and the presence of a factor of two more disk stars than predicted — sufficient stars that the disk is the majority stellar population, outnumbering halo stars 2:1 even at V = 21. Majewski et al. (1993) has obtained UJFN photographic data for several other fields, and Fig. 1 shows a preliminary comparison of these observations with the predictions of the best-fitting SA57 model. Given that none of the parameters have been modified, the agreement is surprisingly good.

scholarly journals Milky Way demographics with the VVV survey

2018 ◽  
Vol 619 ◽  
pp. A4 ◽  
Author(s):  
Javier Alonso-García ◽  
Roberto K. Saito ◽  
Maren Hempel ◽  
Dante Minniti ◽  
Joyce Pullen ◽  
...  
Keyword(s):  
Near Infrared ◽  
Milky Way ◽  
Stellar Populations ◽  
Wide Field ◽  
Public Survey ◽  
Wide Field Of View ◽  
Spread Function ◽  
The Galaxy ◽  
Infrared Wavelengths ◽  
Galactic Stellar Populations

Context. The inner regions of the Galaxy are severely affected by extinction, which limits our capability to study the stellar populations present there. The Vista Variables in the Vía Láctea (VVV) ESO Public Survey has observed this zone at near-infrared wavelengths where reddening is highly diminished. Aims. By exploiting the high resolution and wide field-of-view of the VVV images we aim to produce a deep, homogeneous, and highly complete database of sources that cover the innermost regions of our Galaxy. Methods. To better deal with the high crowding in the surveyed areas, we have used point spread function (PSF)-fitting techniques to obtain a new photometry of the VVV images, in the ZY JHKs near-infrared filters available. Results. Our final catalogs contain close to one billion sources, with precise photometry in up to five near-infrared filters, and they are already being used to provide an unprecedented view of the inner Galactic stellar populations. We make these catalogs publicly available to the community. Our catalogs allow us to build the VVV giga-CMD, a series of color-magnitude diagrams of the inner regions of the Milky Way presented as supplementary videos. We provide a qualitative analysis of some representative CMDs of the inner regions of the Galaxy, and briefly mention some of the studies we have developed with this new dataset so far.

scholarly journals NLTE modelling of integrated light spectra

2019 ◽  
Vol 627 ◽  
pp. A40 ◽  
Author(s):  
P. Eitner ◽  
M. Bergemann ◽  
S. Larsen
Keyword(s):  
Globular Cluster ◽  
Stellar Populations ◽  
Spectral Lines ◽  
Reference Object ◽  
Individual Stars ◽  
Light Spectra ◽  
All Optical ◽  
Non Local ◽  
The Individual ◽  
Galactic Stellar Populations

Aims.We study the effects of non-local thermodynamic equilibrium (NLTE) on the abundance analysis of barium, magnesium, and manganese from integrated light spectroscopy, as typically applied to the analysis of extra-galactic star clusters and galaxies. In this paper, our reference object is a synthetic simple stellar population (SSP) representing a mono-metallicα-enhanced globular cluster with the metallicity [Fe/H] = −2.0 and the age of 11 Gyr.Methods.We used the MULTI2.3 program to compute LTE and NLTE equivalent widths of spectral lines of Mg I, Mn I, and Ba II ions, which are commonly used in abundance analyses of extra-galactic stellar populations. We used ATLAS12 model atmospheres for stellar parameters sampled from a model isochrone to represent individual stars in the model SSP. The NLTE and LTE equivalent widths calculated for the individual stars were combined to calculate the SSP NLTE corrections.Results.We find that the NLTE abundance corrections for the integrated light spectra of the metal-poor globular cluster are significant in many cases, and often exceed 0.1 dex. In particular, LTE abundances of Mn are consistently under-estimated by 0.3 dex for all optical lines of Mn I studied in this work. On the other hand, Ba II, and Mg I lines show a strong differential effect: the NLTE abundance corrections for the individual stars and integrated light spectra are close to zero for the low-excitation lines, but they amount to − 0.15 dex for the strong high-excitation lines. Our results emphasise the need to take NLTE effects into account in the analysis of spectra of individual stars and integrated light spectra of stellar populations.

scholarly journals The Evolution of Old Stellar Populations in Our Galaxy

2002 ◽  
Vol 187 ◽  
pp. 185-193
Author(s):  
Steven R. Majewski
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Star Clusters ◽  
Stellar Populations ◽  
Large Scatter ◽  
Chemical Abundance ◽  
The Galaxy ◽  
Satellite Galaxies ◽  
Galactic Stellar Populations

I would like to focus on one aspect regarding the evolution of Galactic stellar populations that is particularly relevant to discussions at this symposium: Where were the sites of early star formation in the Galaxy? The large scatter in abundance ratios for metal poor stars suggests multiple early settings of star formation in the Milky Way. In this and other ways, interpretation of detailed stellar chemical abundance analyses are converging with those of spatial-kinematical analyses of field stars, star clusters and satellite galaxies.

scholarly journals Planetary mass–radius relations across the galaxy

2020 ◽  
Vol 639 ◽  
pp. A66 ◽  
Author(s):  
A. Michel ◽  
J. Haldemann ◽  
C. Mordasini ◽  
Y. Alibert
Keyword(s):  
Bulk Composition ◽  
Chemical Species ◽  
Stellar Populations ◽  
Chemical Abundance ◽  
Thick Disc ◽  
Thin Disc ◽  
Planetary Mass ◽  
The Galaxy ◽  
Galactic Stellar Populations ◽  
Internal Structure Models

Context. Planet formation theory suggests that planet bulk compositions are likely to reflect the chemical abundance ratios of their host star’s photosphere. Variations in the abundance of particular chemical species in stellar photospheres between different galactic stellar populations demonstrate that there are differences among the expected solid planet bulk compositions. Aims. We aim to present planetary mass-radius relations of solid planets for kinematically differentiated stellar populations, namely, the thin disc, thick disc, and halo. Methods. Using two separate internal structure models, we generated synthetic planets using bulk composition inputs derived from stellar abundances. We explored two scenarios, specifically iron-silicate planets at 0.1 AU and silicate-iron-water planets at 4 AU. Results. We show that there is a persistent statistical difference in the expected mass-radius relations of solid planets among the different galactic stellar populations. At 0.1 AU for silicate-iron planets, there is a 1.51–2.04% mean planetary radius difference between the thick and thin disc stellar populations, whilst for silicate-iron-water planets past the ice line at 4 AU, we calculate a 2.93–3.26% difference depending on the models. Between the halo and thick disc, we retrieve at 0.1 AU a 0.53–0.69% mean planetary radius difference, and at 4 AU we find a 1.24–1.49% difference depending on the model. Conclusions. Future telescopes (such as PLATO) will be able to precisely characterize solid exoplanets and demonstrate the possible existence of planetary mass-radius relationship variability between galactic stellar populations.

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