scholarly journals Star formation history and metallicity in the Galactic inner bulge revealed by the red giant branch bump

2018 ◽  
Vol 620 ◽  
pp. A83 ◽  
Author(s):  
F. Nogueras-Lara ◽  
R. Schödel ◽  
H. Dong ◽  
F. Najarro ◽  
A. T. Gallego-Calvente ◽  
...  
Keyword(s):  
Stellar Population ◽  
Milky Way ◽  
Angular Resolution ◽  
Interstellar Extinction ◽  
Star Formation History ◽  
Galactic Centre ◽  
Luminosity Functions ◽  
Formation History ◽  
Red Giant ◽  
The One

Context. The study of the inner region of the Milky Way bulge is hampered by high interstellar extinction and extreme source crowding. Sensitive high angular resolution near-infrared imaging is needed to study stellar populations and their characteristics in such a dense and complex environment. Aims. We aim at investigating the stellar population in the innermost Galactic bulge, to study the star formation history in this region of the Galaxy. Methods. We used the 0.2″ angular resolution JHKs data from the GALACTICNUCLEUS survey to study the stellar population within two 8.0′×3.4′ fields, about 0.6° and 0.4° to the Galactic north of the Milky Way centre and to compare it with the one in the immediate surroundings of Sagittarius A*. We also characterise the absolute extinction and the extinction curve of the two fields. Results. The average interstellar extinction to the outer and the inner field is AKs ∼ 1.20 ± 0.08 mag and ∼1.48 ± 0.10 mag, respectively. We present Ks luminosity functions that are complete down to at least two magnitudes below the red clump (RC). We detect a feature in the luminosity functions that is fainter than the RC by 0.80 ± 0.03 and 0.79 ± 0.02 mag, respectively, in the Ks band. It runs parallel to the reddening vector. We identify the feature as the red giant branch bump. Fitting α-enhanced BaSTI luminosity functions to our data, we find that a single old stellar population of ∼12.8 ± 0.6 Gyr and Z = 0.040 ± 0.003 provides the best fit. Our findings thus show that the stellar population in the innermost bulge is old, similar to the one at larger distances from the Galactic plane, and that its metallicity is about twice solar at distances as short as about 60 pc from the centre of the Milky Way, similar to what is observed at about 500 pc from the Galactic Centre. Comparing the obtained metallicity with previous known values at larger latitudes (|b| > 2°), our results favour a flattening of the gradient at |b| < 2°. As a secondary result we obtain that the extinction index in the studied regions agrees within the uncertainties with our previous value of α = 2.30 ± 0.08 that was derived for the very Galactic centre.

scholarly journals The Massive stellar Population at the Galactic Center

2016 ◽  
Vol 12 (S329) ◽  
pp. 287-291
Author(s):  
Francisco Najarro ◽  
Diego de la Fuente ◽  
Tom R. Geballe ◽  
Don F. Figer ◽  
D. John Hillier
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Stellar Population ◽  
Milky Way ◽  
Local Group ◽  
Galactic Center ◽  
Spectroscopic Studies ◽  
Star Formation History ◽  
Stellar Content ◽  
Formation History

AbstractWe present results from our ongoing infrared spectroscopic studies of the massive stellar content at the Center of the Milky Way. This region hosts a large number of apparently isolated massive stars as well as three of the most massive resolved young clusters in the Local Group. Our survey seeks to infer the presence of a possible top-heavy recent star formation history and to test massive star formation channels: clusters vs isolation.

scholarly journals GALACTICNUCLEUS: A high angular-resolution JHKs imaging survey of the Galactic centre

2020 ◽  
Vol 641 ◽  
pp. A141
Author(s):  
F. Nogueras-Lara ◽  
R. Schödel ◽  
N. Neumayer ◽  
E. Gallego-Cano ◽  
B. Shahzamanian ◽  
...  
Keyword(s):  
Stellar Population ◽  
Near Infrared ◽  
Angular Resolution ◽  
Interstellar Extinction ◽  
Extinction Curve ◽  
Line Of Sight ◽  
Galactic Centre ◽  
High Angular Resolution ◽  
The Galaxy ◽  
Red Clump

Context. The characterisation of the extinction curve in the near-infrared (NIR) is fundamental to analysing the structure and stellar population of the Galactic centre (GC), whose analysis is hampered by the extreme interstellar extinction (AV ~ 30 mag) that varies on arc-second scales. Recent studies indicate that the behaviour of the extinction curve might be more complex than previously assumed, pointing towards a variation of the extinction curve as a function of wavelength. Aims. We aim to analyse the variations of the extinction index, α, with wavelength, line-of-sight, and absolute extinction, extending previous analyses to a larger area of the innermost regions of the Galaxy. Methods. We analysed the whole GALACTICNUCLEUS survey, a high-angular resolution (~0.2″) JHKs NIR survey specially designed to observe the GC in unprecedented detail. It covers a region of ~6000 pc2, comprising fields in the nuclear stellar disc, the inner bulge, and the transition region between them. We applied two independent methods based on red clump (RC) stars to constrain the extinction curve and analysed its variation superseding previous studies. Results. We used more than 165 000 RC stars and increased the size of the regions analysed significantly to confirm that the extinction curve varies with the wavelength. We estimated a difference Δα = 0.21 ± 0.07 between the obtained extinction indices, αJH = 2.44 ± 0.05 and αHKs = 2.23 ± 0.05. We also concluded that there is no significant variation of the extinction curve with wavelength, with the line-of-sight or the absolute extinction. Finally, we computed the ratios between extinctions, AJ∕AH = 1.87 ± 0.03 and AH/AKs = 1.84 ± 0.03, consistent with all the regions of the GALACTICNUCLEUS catalogue.

Evidence for discrete star formation events in the Small Magellanic Cloud based on 6.5m Magellan Telescope observations

2018 ◽  
Vol 14 (S344) ◽  
pp. 143-146
Author(s):  
A. Strantzalis ◽  
D. Hatzidimitriou ◽  
A. Zezas ◽  
V. Antoniou
Keyword(s):  
Star Formation ◽  
Spatial Resolution ◽  
Milky Way ◽  
Magellanic Cloud ◽  
Star Formation History ◽  
Main Body ◽  
Small Magellanic Cloud ◽  
Environmental Processes ◽  
Luminosity Functions ◽  
Formation History

AbstractThe Small Magellanic Cloud (SMC) presents us with a unique opportunity to study in detail the effect of environmental processes (interaction with the LMC and the Milky Way) on its star formation history. With the 6.5m Magellan Telescope at the Las Campanas Observatory in Chile we have acquired deep B and I images in four 0.44 degree fields covering a large part of the main body of the SMC, yielding accurate photometry for 1,068,893 stars down to ~24th magnitude, with a spatial resolution of 0.201 arcsec/pixel. Colour-magnitude diagrams and luminosity functions (corrected for completeness) have been constructed, yielding significant new results that indicate at least two discrete star formation events around 2.7 and 4-5 Gyr ago.

scholarly journals GALACTICNUCLEUS: A high-angular-resolution JHKs imaging survey of the Galactic centre

2019 ◽  
Vol 631 ◽  
pp. A20 ◽  
Author(s):  
F. Nogueras-Lara ◽  
R. Schödel ◽  
A. T. Gallego-Calvente ◽  
H. Dong ◽  
E. Gallego-Cano ◽  
...  
Keyword(s):  
Stellar Population ◽  
Near Infrared ◽  
Milky Way ◽  
Angular Resolution ◽  
State Of The Art ◽  
Zero Point ◽  
Uncertainty Estimation ◽  
Galactic Centre ◽  
High Angular Resolution ◽  
Central Regions

Context. The high extinction and extreme source crowding of the central regions of the Milky Way are serious obstacles to the study of the structure and stellar population of the Galactic centre (GC). Existing surveys that cover the GC region (2MASS, UKIDSS, VVV, SIRIUS) do not have the necessary high angular resolution. Therefore, a high-angular-resolution survey in the near infrared is crucial to improve the state of the art. Aims. Here, we present the GALACTICNUCLEUS catalogue, a near infrared JHKs high-angular-resolution (0.2″) survey of the nuclear bulge of the Milky Way. Methods. We explain in detail the data reduction, data analysis, calibration, and uncertainty estimation of the GALACTICNUCLEUS survey. We assess the data quality comparing our results with previous surveys. Results. We obtained accurate JHKs photometry for ∼3.3 × 106 stars in the GC detecting around 20% in J, 65% in H, and 90% in Ks. The survey covers a total area of ∼0.3 deg2, which corresponds to ∼6000 pc2. The GALACTICNUCLEUS survey reaches 5σ detections for J ∼ 22 mag, H ∼ 21 mag, and Ks ∼ 21 mag. The uncertainties are below 0.05 mag at J ∼ 21 mag, H ∼ 19 mag, and Ks ∼ 18 mag. The zero point systematic uncertainty is ≲0.04 mag in all three bands. We present colour–magnitude diagrams for the different regions covered by the survey.

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

2020 ◽  
Vol 644 ◽  
pp. A140 ◽  
Author(s):  
F. Surot ◽  
E. Valenti ◽  
O. A. Gonzalez ◽  
M. Zoccali ◽  
E. Sökmen ◽  
...  
Keyword(s):  
Galactic Plane ◽  
Interstellar Extinction ◽  
Star Formation History ◽  
Galactic Bulge ◽  
Formation History ◽  
Color Excess ◽  
Infrared Surveys ◽  
Red Clump ◽  
Red Giant ◽  
Giant Branch Stars

Context. A detailed study of the Galactic bulge stellar population necessarily requires an accurate representation of the interstellar extinction, particularly toward the Galactic plane and center, where severe and differential reddening is expected to vary on sub-arcmin scales. Although recent infrared surveys have addressed this problem by providing extinction maps across the whole Galactic bulge area, dereddened color-magnitude diagrams near the plane and center appear systematically undercorrected, prompting the need for higher resolution. These undercorrections affect any stellar study sensitive to color (e.g., star formation history analyses via color-magnitude diagram fitting), either making them inaccurate or limiting them to small and relatively stable extinction windows where this value is low and better constrained. Aims. This study is aimed at providing a high-resolution (2 arcmin to ∼10 arcsec) color excess map for the VVV bulge area in J − Ks color. Methods. We used the MW-BULGE-PSFPHOT catalogs, sampling ∼300 deg2 across the Galactic bulge (|l| < 10° and −10° < b <  5°) to isolate a sample of red clump and red giant branch stars, for which we calculated the average J − Ks color in a fine spatial grid in (l, b) space. Results. We obtained an E(J − Ks) map spanning the VVV bulge area of roughly 300 deg2, with the equivalent of a resolution between ∼1 arcmin for bulge outskirts (l <  6°) to below 20 arcsec within the central |l| < 1°, and below 10 arcsec for the innermost area (|l| < 1° and |b| < 3°).

scholarly journals FEDReD

2020 ◽  
Vol 641 ◽  
pp. A79
Author(s):  
C. Hottier ◽  
C. Babusiaux ◽  
F. Arenou
Keyword(s):  
Near Infrared ◽  
Milky Way ◽  
Interstellar Extinction ◽  
Galactic Centre ◽  
Infrared Photometry ◽  
Galactic Disc ◽  
Thin Disc ◽  
The One ◽  
Distance Relation ◽  
Hr Diagram

Aims. We aim to map the 3D distribution of the interstellar extinction of the Milky Way disc up to distances larger than those probed with the Gaia parallax alone. Methods. We applied the FEDReD (Field Extinction-Distance Relation Deconvolver) algorithm to the 2MASS near-infrared photometry together with the Gaia DR2 astrometry and photometry. This algorithm uses a Bayesian deconvolution approach, based on an empirical HR-diagram representative of the local thin disc, in order to map the extinction as a function of distance of various fields of view. Results. We analysed more than 5.6 million stars to obtain an extinction map of the entire Galactic disc within |b| < 0.24°. This map provides information up to 5 kpc in the direction of the Galactic centre and more than 7 kpc in the direction of the anticentre. This map reveals the complete shape of structures that are known locally, such as the Vela complex and the split of the local arm. Furthermore, our extinction map shows many large “clean bubbles”, especially the one in the Sagittarius-Carina complex, and four others, which define a structure that we nickname the butterfly.

Variations in Star Formation History and the Red Giant Branch Tip

2004 ◽  
Vol 606 (2) ◽  
pp. 869-893 ◽  
Author(s):  
Michael K. Barker ◽  
Ata Sarajedini ◽  
Jason Harris
Keyword(s):  
Star Formation ◽  
Star Formation History ◽  
Formation History ◽  
Red Giant

Calibrating TP-AGB stellar models and chemical yields through resolved stellar populations in the Small Magellanic Cloud

2018 ◽  
Vol 14 (S343) ◽  
pp. 269-272
Author(s):  
Giada Pastorelli ◽  
Paola Marigo ◽  
Léo Girardi ◽  
Keyword(s):  
Mass Loss ◽  
Magellanic Cloud ◽  
Star Formation History ◽  
Agb Stars ◽  
Population Synthesis ◽  
Small Magellanic Cloud ◽  
Luminosity Functions ◽  
Formation History ◽  
Best Fitting ◽  
The Impact

AbstractMost of the physical processes driving the TP-AGB evolution are not yet fully understood and they need to be modelled with parameterised descriptions. We present the results of the on-going calibration of the TP-AGB phase based on a complete sample of AGB stars in the Small Magellanic Cloud (SAGE-SMC survey). We computed large grids of TP-AGB models with several combinations of third dredge-up and mass-loss prescriptions with the COLIBRI code. The SMC AGB population is modelled with the population synthesis code TRILEGAL according to the space-resolved star formation history derived with the deep photometry from the VISTA survey of the Magellanic Clouds. We put quantitative constraints on the efficiencies of the third dredge-up and mass loss by requiring the models to reproduce the star counts and the luminosity functions of the observed Oxygen-, Carbon-rich and extreme-AGB stars and we investigate the impact of the best-fitting prescriptions on the chemical yields.

scholarly journals High-speed stars: Galactic hitchhikers

2020 ◽  
Vol 638 ◽  
pp. A122 ◽  
Author(s):  
E. Caffau ◽  
L. Monaco ◽  
P. Bonifacio ◽  
L. Sbordone ◽  
M. Haywood ◽  
...  
Keyword(s):  
Star Formation ◽  
High Speed ◽  
Milky Way ◽  
Star Formation History ◽  
Proper Motions ◽  
Orbital Parameters ◽  
Blue Stragglers ◽  
Formation History ◽  
Cool Stars ◽  
Age Estimates

Context. The search for stars born in the very early stages of the Milky Way star formation history is of paramount importance in the study of the early Universe since their chemistry carries irreplaceable information on the conditions in which early star formation and galaxy buildup took place. The search for these objects has generally taken the form of expensive surveys for faint extremely metal-poor stars, the most obvious but not the only candidates to a very early formation. Aims. Thanks to Gaia DR2 radial velocities and proper motions, we identified 72 bright cool stars displaying heliocentric transverse velocities in excess of 500 km s−1. These objects are most likely members of extreme outer-halo populations, either formed in the early Milky Way build-up or accreted from since-destroyed self-gravitating stellar systems. Methods. We analysed low-resolution FORS spectra of the 72 stars in the sample and derived the abundances of a few elements. Despite the large uncertainties on the radial velocity determination, we derived reliable orbital parameters for these objects. Results. The stars analysed are mainly slightly metal poor, with a few very metal-poor stars. Their chemical composition is much more homogeneous than expected. All the stars have very eccentric halo orbits, some extending well beyond the expected dimension of the Milky Way. Conclusions. These stars can be the result of a disrupted small galaxy or they could have been globular cluster members. Age estimates suggest that some of them are evolved blue stragglers, now on the subgiant or asymptotic giant branches.

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