scholarly journals Mapping the stellar age of the Milky Way bulge with the VVV

2019 ◽  
Vol 629 ◽  
pp. A1 ◽  
Author(s):  
F. Surot ◽  
E. Valenti ◽  
S. L. Hidalgo ◽  
M. Zoccali ◽  
O. A. Gonzalez ◽  
...  
Keyword(s):  
Surface Brightness ◽  
Main Sequence ◽  
Milky Way ◽  
Stellar Content ◽  
Star Count ◽  
Spread Function ◽  
The Galaxy ◽  
Photometric Measurements ◽  
Artificial Star ◽  
Different Levels

Context. The bulge represents the best compromise between old and massive Galactic components, and as such its study is a valuable opportunity to understand how the bulk of the Milky Way formed and evolved. In addition, being the only bulge in which we can individually resolve stars in all evolutionary sequences, the properties of its stellar content provide crucial insights into the formation of bulges. Aims. We are providing a detailed and comprehensive census of the Milky Way bulge stellar populations by producing deep and accurate photometric catalogs of the inner ∼300 deg2 of the Galaxy. Methods. We performed DAOPHOT/ALLFRAME point spread function (PSF) fitting photometry of multi-epochs J and Ks images provided by the VISTA Variables in the Vía Láctea (VVV) survey to obtain deep photometric catalogs. Artificial star experiments have been conducted on all images to properly assess the completeness and the accuracy of the photometric measurements. Results. We present a photometric database containing nearly 600 million stars across the bulge area surveyed by the VVV. Through the comparison of derived color-magnitude diagrams of selected fields representative of different levels of extinction and crowding, we show the quality, completeness and depth of the new catalogs. With the exception of the fields located along the plane, this new photometry samples stars down to ∼1–2 mag below the old main sequence turnoff with unprecedented accuracy. To demonstrate the tremendous potential inherent to this new dataset, we give a few examples of possible applications, including (i) star count studies through the dataset completeness map; (ii) surface brightness map; and (iii) cross-correlation with Gaia DR2. Conclusions. The database presented here represents an invaluable collection for the whole community, and we encourage its exploitation. The photometric catalogs including completeness information are publicly available through the ESO Science Archive as part of the MW-BULGE-PSPHOT release.

scholarly journals A quantitative spectral analysis of 14 hypervelocity stars from the MMT survey

2018 ◽  
Vol 615 ◽  
pp. L5 ◽  
Author(s):  
A. Irrgang ◽  
S. Kreuzer ◽  
U. Heber ◽  
W. Brown
Keyword(s):  
Main Sequence ◽  
Galactic Center ◽  
Radial Velocities ◽  
Stellar Ages ◽  
The Galaxy ◽  
Quantitative Spectral Analysis ◽  
Kinematic Studies ◽  
Ejection Mechanism ◽  
Photometric Measurements ◽  
Stellar Masses

Context. Hypervelocity stars (HVSs) travel so fast that they may leave the Galaxy. The tidal disruption of a binary system by the supermassive black hole in the Galactic center is widely assumed to be their ejection mechanism. Aims. To test the hypothesis of an origin in the Galactic center using kinematic investigations, the current space velocities of the HVSs need to be determined. With the advent of Gaia’s second data release, accurate radial velocities from spectroscopy are complemented by proper motion measurements of unprecedented quality. Based on a new spectroscopic analysis method, we provide revised distances and stellar ages, both of which are crucial to unravel the nature of the HVSs. Methods. We reanalyzed low-resolution optical spectra of 14 HVSs from the MMT HVS survey using a new grid of synthetic spectra, which account for deviations from local thermodynamic equilibrium, to derive effective temperatures, surface gravities, radial velocities, and projected rotational velocities. Stellar masses, radii, and ages were then determined by comparison with stellar evolutionary models that account for rotation. Finally, these results were combined with photometric measurements to obtain spectroscopic distances. Results. The resulting atmospheric parameters are consistent with those of main sequence stars with masses in the range 2.5–5.0 M⊙. The majority of the stars rotate at fast speeds, providing further evidence for their main sequence nature. Stellar ages range from 90 to 400 Myr and distances (with typical 1σ-uncertainties of about 10–15%) from 30 to 100 kpc. Except for one object (B 711), which we reclassify as A-type star, all stars are of spectral type B. Conclusions. The spectroscopic distances and stellar ages derived here are key ingredients for upcoming kinematic studies of HVSs based on Gaia proper motions.

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 Metallicity Mapping with gri Photometry: The Virgo Overdensity and the Halos of the Galaxy

2009 ◽  
Vol 5 (S262) ◽  
pp. 127-130
Author(s):  
Timothy C. Beers ◽  
Deokkeun An ◽  
Jennifer A. Johnson ◽  
Marc H. Pinsonneault ◽  
Donald M. Terndrup ◽  
...  
Keyword(s):  
Main Sequence ◽  
Main Sequence Stars ◽  
Abundance Estimates ◽  
The Galaxy ◽  
Metal Abundance ◽  
Nearby Stars ◽  
Metal Abundances ◽  
Photometric Measurements ◽  
Halo Population ◽  
Recent Interpretation

AbstractWe describe the methodology required for estimation of photometric estimates of metallicity based on the SDSS gri passbands, which can be used to probe the properties of main-sequence stars beyond ~10 kpc, complementing studies of nearby stars from more metallicity-sensitive color indices that involve the u passband. As a first application of this approach, we determine photometric metal abundance estimates for individual main-sequence stars in the Virgo Overdensity, which covers almost 1000 deg2 on the sky, based on a calibration of the metallicity sensitivity of stellar isochrones in the gri filter passbands using field stars with well-determined spectroscopic metal abundances. Despite the low precision of the method for individual stars, internal errors of σ[Fe/H]~0.1 dex can be achieved for bulk stellar populations. The global metal abundance of the Virgo Overdensity determined in this way is 〈[Fe/H]〉 = −2.0±0.1 (internal) ±0.5 (systematic), from photometric measurements of 0.7 million stars with heliocentric distances from ~10 kpc to ~20 kpc. A preliminary metallicity map, based on results for 2.9 million stars in the northern SDSS DR-7 footprint, exhibits a shift to lower metallicities as one proceeds from the inner- to the outer-halo population, consistent with recent interpretation of the kinematics of local samples of stars with spectroscopically available metallicity estimates and full space motions.

scholarly journals The stellar content of NGC 3603

1999 ◽  
Vol 193 ◽  
pp. 403-411
Author(s):  
Laurent Drissen
Keyword(s):  
Main Sequence ◽  
Stellar Content ◽  
The Galaxy ◽  
H Ii Region ◽  
Low Mass

At the heart of the galactic giant H II region NGC 3603, low-mass (1–4 M⊙) stars slowly contract toward the main sequence, while peacefully cohabiting with the three most luminous, hydrogen-rich Wolf-Rayet stars in the Galaxy, a dozen hot O3–4 stars and their more modest but numerous O and B companions. This is the story of a very young and dense starburst cluster …

scholarly journals Stellar populations in the outskirts of M31: the mid-infrared view

2016 ◽  
Vol 11 (S321) ◽  
pp. 19-21
Author(s):  
P. Barmby ◽  
M. Rafiei Ravandi
Keyword(s):  
Point Source ◽  
Surface Brightness ◽  
Cross Correlation ◽  
Stellar Populations ◽  
Low Mass Stars ◽  
Mid Infrared ◽  
Star Count ◽  
The Galaxy ◽  
Low Mass ◽  
Point Source Catalog

AbstractThe mid-infrared provides a unique view of galaxy stellar populations, sensitive to both the integrated light of old, low-mass stars and to individual dusty mass-losing stars. We present results from an extended Spitzer/IRAC survey of M31 with total lengths of 6.6 and 4.4 degrees along the major and minor axes, respectively. The integrated surface brightness profile proves to be surprisingly difficult to trace in the outskirts of the galaxy, but we can also investigate the disk/halo transition via a star count profile, with careful correction for foreground and background contamination. Our point-source catalog allows us to report on mid-infrared properties of individual objects in the outskirts of M31, via cross-correlation with PAndAS, WISE, and other catalogs.

What do RR Lyrae tell us about the formation of the Milky Way and M31 haloes?

2017 ◽  
Vol 13 (S334) ◽  
pp. 290-291
Author(s):  
C. Gallart ◽  
G. Fiorentino ◽  
M. Monelli ◽  
C. Martínez-Vázquez ◽  
E. J. Bernard ◽  
...  
Keyword(s):  
Star Formation ◽  
Structure Formation ◽  
Milky Way ◽  
Building Blocks ◽  
Assembly Process ◽  
Stellar Content ◽  
Rr Lyrae ◽  
The Galaxy ◽  
Star Formation In Galaxies ◽  
Galaxy Assembly

RR Lyrae variables are old (>10 Gyr) stars and, as such, they are useful probes of the earliest events of star formation in galaxies (Bernard et al. 2008, Martínez-Vázquez et al. 2016) as well as of the galaxy assembly process predicted by ΛCDM simulations of structure formation. In fact, the nature of the building-blocks of galaxies such as the Milky Way, and in particular, those of their stellar haloes, has been a matter of a substantial debate (Venn et al. 2004). Unlike other stellar tracers, RR Lyrae offer a snapshot of the stellar content present at the epoch when most of the merging action is predicted to have taken place, and thus they are ideal witnesses of this process.

scholarly journals The building blocks of the Milky Way halo using APOGEE and Gaia or Is the Galaxy a typical galaxy?

2019 ◽  
Vol 14 (S351) ◽  
pp. 170-173 ◽  
Author(s):  
Ricardo P. Schiavon ◽  
J. Ted Mackereth ◽  
Joel Pfeffer ◽  
Rob A. Crain ◽  
Jo Bovy
Keyword(s):  
Numerical Simulations ◽  
Globular Clusters ◽  
Milky Way ◽  
Galactic Halo ◽  
Dwarf Galaxies ◽  
Stellar Populations ◽  
Building Blocks ◽  
Stellar Content ◽  
The Galaxy ◽  
Milky Way Halo

AbstractWe summarise recent results from analysis of APOGEE/Gaia data for stellar populations in the Galactic halo, disk, and bulge, leading to constraints on the contribution of dwarf galaxies and globular clusters to the stellar content of the Milky Way halo. Intepretation of the extant data in light of cosmological numerical simulations suggests that the Milky Way has been subject to an unusually intense accretion history at z ≳ 1.5.

scholarly journals A Canis Major Overdensity Imaging Survey. I. Stellar Content and Star-Count Maps: A Distinctly Elongated Body of Main-Sequence Stars

2007 ◽  
Vol 133 (5) ◽  
pp. 2274-2290 ◽  
Author(s):  
D. J. Butler ◽  
D. Martínez-Delgado ◽  
H-W. Rix ◽  
J. Peñarrubia ◽  
J. T. A. de Jong
Keyword(s):  
Main Sequence ◽  
Stellar Content ◽  
Main Sequence Stars ◽  
Star Count

scholarly journals Optical and H-Alpha Emission from Unresolved Red Dwarf Stars in the Galaxy

1990 ◽  
Vol 139 ◽  
pp. 107-109
Author(s):  
G. Szécsényi-Nagy
Keyword(s):  
Main Sequence ◽  
Stellar Content ◽  
Main Sequence Stars ◽  
M Dwarfs ◽  
Dwarf Stars ◽  
Alpha Emission ◽  
Cool Stars ◽  
Red Dwarfs ◽  
The Galaxy ◽  
Red Dwarf Stars

Although many of the nearest dim and cool stars (the red dwarfs) were catalogued in the early sixties, the majority of the astronomers did not realize that these objects provide almost nine tenths of all the stars in our Galaxy. In fact 90-95% of the stars in the solar vicinity (r ≤ 25 pc) are main sequence stars, and at least 80% of them are M dwarfs. Outside the main sequence (MS) one can find a few subdwarfs and somewhat more white dwarfs, but the contribution of this latter type is not known precisely. Estimates range between 4% and 8%. The relative frequency of giants and supergiants can not be determined from the census of the local star population because they are not represented in a statistically meaningful number. But investigations of much greater cosmic volumes demonstrate that luminosity classes Ia, Ib, II, III, and IV altogether contribute fewer than 1% of the stellar content of the Galaxy.

Assembly of the Galactic Halo System Based on Carbon-Enhanced Metal-Poor Stars

2017 ◽  
Vol 13 (S334) ◽  
pp. 327-328
Author(s):  
Young Sun Lee ◽  
Timothy C. Beers ◽  
Jinmi Yoon ◽  
Young Kwang Kim ◽  
Jaehun Jeong
Keyword(s):  
Neutron Capture ◽  
Main Sequence ◽  
Milky Way ◽  
Galactic Halo ◽  
Sloan Digital Sky Survey ◽  
Sky Survey ◽  
History Of ◽  
Process Elements ◽  
Critical Constraints ◽  
Different Levels

AbstractThere is growing evidence that, among the various subclasses of carbon-enhanced metal-poor (CEMP) stars, the outer halo of the Milky Way exhibits a higher frequency of CEMP-no stars (those having no over-abundances of heavy neutron-capture elements) compared with the CEMP-s stars (those with over-enhancements of the s-process elements), while the inner halo shows a higher frequency of CEMP-s stars. We map out fractions of CEMP-no and CEMP-s stars in the inner- and outer-halo populations, separated by their spatial distribution of carbonicity ([C/Fe]), a so-called “carbonicity map”, based on a sample of over 100,000 main-sequence turnoff stars with available spectroscopy from the Sloan Digital Sky Survey. The CEMP-no and CEMP-s objects are classified by different levels of absolute carbon abundances for our sample, A(C). We also present kinematic and orbital characteristics of these subclasses for each population. The contrast appearing in these characteristics provides critical constraints on the assembly history of the two primary stellar components of the Galactic halo.

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