scholarly journals Non-parametric density reconstruction of the Galactic bulge area using red clump stars in the VVV survey

2020 ◽  
Vol 499 (2) ◽  
pp. 1937-1947
Author(s):  
Dylan Paterson ◽  
Brendan Coleman ◽  
Chris Gordon
Keyword(s):  
Parametric Method ◽  
Major Axis ◽  
Galactic Bulge ◽  
Buckling Instability ◽  
Giant Stars ◽  
Red Clump ◽  
Red Giant ◽  
High Resolution Reconstruction ◽  
Spiral Arm ◽  
Non Parametric

ABSTRACT Studies of the red clump giant population in the inner Milky Way suggest the Galactic bulge/bar has a boxy/peanut/X-shaped structure as predicted by its formation via a disc buckling instability. We used a non-parametric method of estimating the Galactic bulge morphology that is based on maximum entropy regularization. This enabled us to extract the 3D distribution of the red giant stars in the bulge from deep photometric catalogues of the VISTA Variables in the Via Lactea survey. Our high-resolution reconstruction confirms the well-known boxy/peanut/X-shaped structure of the bulge. We also find spiral arm structures that extend to around 3 kpc in front of and behind the bulge and are on different sides of the bulge major axis. We show that the detection of these structures is robust to the uncertainties in the luminosity function.

scholarly journals Mapping the Galactic disc with the LAMOST and Gaia red clump sample: II. 3D asymmetrical kinematics of mono-age populations in the disc between 6–14  kpc

2019 ◽  
Vol 491 (2) ◽  
pp. 2104-2118 ◽  
Author(s):  
H-F Wang ◽  
M López-Corredoira ◽  
Y Huang ◽  
J L Carlin ◽  
B-Q Chen ◽  
...  
Keyword(s):  
Milky Way ◽  
Galactic Disc ◽  
Giant Stars ◽  
Bending Mode ◽  
Red Clump ◽  
Minor Mergers ◽  
Gaia Dr2 ◽  
South Asymmetry ◽  
Spiral Arm ◽  
Fast Rotating

ABSTRACT We perform analysis of the 3D kinematics of Milky Way disc stars in mono-age populations. We focus on stars between Galactocentric distances of R = 6 and 14  kpc, selected from the combined LAMOST Data Release 4 (DR4) red clump giant stars and Gaia DR2 proper motion catalogue. We confirm the 3D asymmetrical motions of recent works and provide time tagging of the Galactic outer disc asymmetrical motions near the anticentre direction out to Galactocentric distances of 14 kpc. Radial Galactocentric motions reach values up to 10 km s−1, depending on the age of the population, and present a north–south asymmetry in the region corresponding to density and velocity substructures that were sensitive to the perturbations in the early 6  Gyr. After that time, the disc stars in this asymmetrical structure have become kinematically hotter, and are thus not sensitive to perturbations, and we find the structure is a relatively younger population. With quantitative analysis, we find stars both above and below the plane at R ≳ 9 kpc that exhibit bending mode motions of which the sensitive duration is around 8  Gyr. We speculate that the in-plane asymmetries might not be mainly caused by a fast rotating bar, intrinsically elliptical outer disc, secular expansion of the disc, or streams. Spiral arm dynamics, out-of-equilibrium models, minor mergers or others are important contributors. Vertical motions might be dominated by bending and breathing modes induced by complicated inner or external perturbers. It is likely that many of these mechanisms are coupled together.

scholarly journals Chemical similarities between Galactic bulge and local thick disk red giant stars

2008 ◽  
Vol 484 (3) ◽  
pp. L21-L25 ◽  
Author(s):  
J. Meléndez ◽  
M. Asplund ◽  
A. Alves-Brito ◽  
K. Cunha ◽  
B. Barbuy ◽  
...  
Keyword(s):  
Thick Disk ◽  
Galactic Bulge ◽  
Giant Stars ◽  
Red Giant Stars ◽  
Red Giant

scholarly journals The K2 Galactic Caps Project – going beyond the Kepler field and ageing the Galactic disc

2019 ◽  
Vol 490 (4) ◽  
pp. 4465-4480 ◽  
Author(s):  
B M Rendle ◽  
A Miglio ◽  
C Chiappini ◽  
M Valentini ◽  
G R Davies ◽  
...  
Keyword(s):  
Galactic Plane ◽  
Age Distribution ◽  
High Resolution Spectroscopy ◽  
Giant Stars ◽  
Red Clump ◽  
Red Giant ◽  
Stellar Masses ◽  
Two Peaks ◽  
Global Population ◽  
Selection Of

ABSTRACT Analyses of data from spectroscopic and astrometric surveys have led to conflicting results concerning the vertical characteristics of the Milky Way. Ages are often used to provide clarity, but typical uncertainties of >40 per cent from photometry restrict the validity of the inferences made. Using the Kepler APOKASC sample for context, we explore the global population trends of two K2 campaign fields (3 and 6), which extend further vertically out of the Galactic plane than APOKASC. We analyse the properties of red giant stars utilizing three asteroseismic data analysis methods to cross-check and validate detections. The Bayesian inference tool PARAM is used to determine the stellar masses, radii, and ages. Evidence of a pronounced red giant branch bump and an [α/Fe] dependence on the position of the red clump is observed from the K2 fields radius distribution. Two peaks in the age distribution centred at ∼5 and ∼12 Gyr are found using a sample with σage < 35 per cent. In comparison with Kepler, we find the older peak to be more prominent for K2. This age bimodality is also observed based on a chemical selection of low-[α/Fe] (≤0.1) and high-[α/Fe] (>0.1) stars. As a function of vertical distance from the Galactic mid-plane (|Z|), the age distribution shows a transition from a young to old stellar population with increasing |Z| for the K2 fields. Further coverage of campaign targets with high-resolution spectroscopy is required to increase the yield of precise ages achievable with asteroseismology.

scholarly journals Chemical similarities between the Galactic bulge and local thick disk red giant stars: analysis from optical data

2009 ◽  
Vol 5 (S265) ◽  
pp. 342-343
Author(s):  
Alan Alves-Brito ◽  
Jorge Meléndez ◽  
Martin Asplund
Keyword(s):  
High Resolution ◽  
Thick Disk ◽  
Elemental Abundance ◽  
Optical Data ◽  
Galactic Bulge ◽  
Open Problems ◽  
Chemical Enrichment ◽  
Giant Stars ◽  
Red Giant Stars ◽  
Red Giant

AbstractThe Galactic structure and composition remain as one of the greatest open problems in modern astrophysics. We show here that there are chemical similarities between the Galactic bulge and local thick disk red giant stars. This finding puts strong constraints on the IMF, SFR and chemical enrichment timescale of the bulge and thick disk. Our results are based upon a detailed elemental abundance analysis of 80 high S/N and high resolution optical spectra of giant stars, in the range −1.5 < [Fe/H] < +0.5.

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°).

Isolating Red Giant Stars in M31's Elusive Outer Spheroid

1998 ◽  
Vol 116 (2) ◽  
pp. 707-722 ◽  
Author(s):  
David B. Reitzel ◽  
Puragra Guhathakurta ◽  
Andrew Gould
Keyword(s):  
Giant Stars ◽  
Red Giant Stars ◽  
Red Giant

scholarly journals Circulant Singular Spectrum Analysis to Monitor the State of the Economy in Real Time

Mathematics ◽  
2021 ◽  
Vol 9 (11) ◽  
pp. 1169
Author(s):  
Juan Bógalo ◽  
Pilar Poncela ◽  
Eva Senra
Keyword(s):  
Business Cycles ◽  
Real Time ◽  
Parametric Method ◽  
Singular Spectrum Analysis ◽  
The State ◽  
Signal Extraction ◽  
Alternative Procedure ◽  
State Of The Economy ◽  
Regular Patterns ◽  
Non Parametric

Real-time monitoring of the economy is based on activity indicators that show regular patterns such as trends, seasonality and business cycles. However, parametric and non-parametric methods for signal extraction produce revisions at the end of the sample, and the arrival of new data makes it difficult to assess the state of the economy. In this paper, we compare two signal extraction procedures: Circulant Singular Spectral Analysis, CiSSA, a non-parametric technique in which we can extract components associated with desired frequencies, and a parametric method based on ARIMA modelling. Through a set of simulations, we show that the magnitude of the revisions produced by CiSSA converges to zero quicker, and it is smaller than that of the alternative procedure.

scholarly journals Modeling Post-Liberalized European Gas Market Concentration—A Game Theory Perspective

Forecasting ◽  
2020 ◽  
Vol 3 (1) ◽  
pp. 1-16
Author(s):  
Hassan Hamie ◽  
Anis Hoayek ◽  
Hans Auer
Keyword(s):  
Game Theory ◽  
Statistical Tests ◽  
Parametric Method ◽  
Linear Complementarity Problems ◽  
Market Concentration ◽  
Cournot Equilibrium ◽  
Gas Markets ◽  
Gas Market ◽  
Equilibrium Test ◽  
Non Parametric

The question of whether the liberalization of the gas industry has led to less concentrated markets has attracted much interest among the scientific community. Classical mathematical regression tools, statistical tests, and optimization equilibrium problems, more precisely non-linear complementarity problems, were used to model European gas markets and their effect on prices. In this research, the parametric and nonparametric game theory methods are employed to study the effect of the market concentration on gas prices. The parametric method takes into account the classical Cournot equilibrium test, with assumptions on cost and demand functions. However, the non-parametric method does not make any prior assumptions, a factor that allows greater freedom in modeling. The results of the parametric method demonstrate that the gas suppliers’ behavior in Austria and The Netherlands gas markets follows the Nash–Cournot equilibrium, where companies act rationally to maximize their payoffs. The non-parametric approach validates the fact that suppliers in both markets follow the same behavior even though one market is more liquid than the other. Interestingly, our findings also suggest that some of the gas suppliers maximize their ‘utility function’ not by only relying on profit, but also on some type of non-profit objective, and possibly collusive behavior.

Ellipsoidal Variability and Long Secondary Periods in MACHO Red Giant Stars

2006 ◽  
Vol 650 (1) ◽  
pp. L55-L58 ◽  
Author(s):  
A. Derekas ◽  
L. L. Kiss ◽  
T. R. Bedding ◽  
H. Kjeldsen ◽  
P. Lah ◽  
...  
Keyword(s):  
Giant Stars ◽  
Red Giant Stars ◽  
Red Giant
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