Modelling the Galactic Bar using Red Clump Stars

AbstractThe color-magnitude diagrams of ~ 1 × 106 stars obtained for 19 fields towards the Galactic bulge with the OGLE project reveal a well-defined population of bulge red clump stars. We found that the distributions of the extinction-adjusted apparent magnitudes of red clump stars in fields lying at ι = ±5° in galactic longitude differ by ∼ 0.4 mag. A plausible explanation of this observed difference in the luminosity distribution is that the Galactic bulge is a triaxial structure, or a bar, which is inclined to the line of sight by no more than 45°. The part of the bar at the positive galactic longitude is closer to us. Work is now under way to model the Galactic bar by fitting the observed luminosity functions in the red clump region for various fields. Preliminary results indicate that the angle of the inclination of the bar to the line of sight can be as small as ∼ 20°. Gravitational microlensing can provide us with additional constraints on the structure of the Galactic bar.

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New VIRAC proper motion maps show signature of galactic boxy/peanut bulge

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319008779 ◽

2019 ◽

Vol 14 (S353) ◽

pp. 29-30

Author(s):

Jonathan P. Clarke ◽

Christopher Wegg ◽

Ortwin Gerhard ◽

Leigh C. Smith ◽

Phil W. Lucas ◽

...

Keyword(s):

Proper Motion ◽

Dynamical Model ◽

Line Of Sight ◽

Selection Function ◽

Kinematic Structure ◽

Proper Motions ◽

Galactic Bulge ◽

Bulge Region ◽

Pattern Speed ◽

Red Clump

AbstractWe have derived absolute proper motions of stars in the Galactic bulge region combining the VVV InfraRed Astrometric Catalogue (VIRAC) and Gaia. We use the proper motions to study the kinematic structure of the bulge both integrated along the line-of-sight and in magnitude intervals using red clump stars as standard candles. In parallel we compare to a made-to-measure barred dynamical model, folding in the VIRAC selection function, to understand and interpret the structures that we observe. The barred dynamical model, which contains a boxy/peanut bulge, and has a pattern speed of 37.5 kms−1 kpc−1, is able to reproduce all structures impressively well.

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Evidence for the Galactic Bar from the Two Color Photometry of the Bulge Red Clump Stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900229574 ◽

1996 ◽

Vol 169 ◽

pp. 103-109

Author(s):

K. Z. Stanek ◽

M. Mateo ◽

A. Udalski ◽

M. Szymański ◽

J. Kałużny ◽

...

Keyword(s):

Data Base ◽

Gravitational Lensing ◽

Galactic Bulge ◽

Gravitational Microlensing ◽

Huge Data ◽

Red Clump

The Optical Gravitational Lensing Experiment (OGLE, Udalski et al. 1994a; Paczynski et al. 1994b – these proceedings; and references therein) is an extensive photometric search for the rare cases of gravitational microlensing of Galactic bulge stars by foreground objects. It provides a huge data base (Szymański & Udalski 1993), from which color-magnitude diagrams have been compiled (Udalski et al. 1993, 1994b). Here we discuss the use a of well-defined population of bulge red clump stars to investigate the presence of the bar in our Galaxy. The results of our earlier studies are described by Stanek et al. (1994).

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Distribution of red clump stars does not support the X-shaped Galactic bulge

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935571 ◽

2019 ◽

Vol 627 ◽

pp. A3 ◽

Cited By ~ 2

Author(s):

M. López-Corredoira ◽

Y.-W. Lee ◽

F. Garzón ◽

D. Lim

Keyword(s):

Density Distribution ◽

Near Infrared ◽

Absolute Magnitude ◽

Line Of Sight ◽

Galactic Bulge ◽

Double Peak ◽

The Absolute ◽

The Difference ◽

Red Clump ◽

Two Peaks

Context. Claims of an X-shaped Galactic bulge were based on the assumption of red clump stars as standard candles in some lines of sight crossing the off-plane bulge. However, some doubts have been cast on whether the two peaks in star counts along the line of sight really represent a double peak in the density distribution, or whether there is something wrong with the assumption of a unique constant absolute magnitude for all of these stars. Aims. With the advent of Gaia-DR2 parallaxes in combination with near-infrared VISTA-VVV data, we are able to check which of the hypotheses is correct. Methods. We calculated the median absolute magnitude MK corresponding to both peaks of putative red clumps in seven lines of sight with the lowest extinction in the interesting coordinates’ range. Results. The difference between the absolute magnitude of the bright and the faint peak is ΔMK ≈ 0.4. The selected stars in both peaks cannot be represented by the same red clump giants with constant MK ≈ −1.6. Conclusions. The hypothesis that the bulge contains an X-shape is based on the assumption that the faint and bright peaks of the density distribution towards the bulge are dominated by standard red clump stars. However, we show that both the faint and bright peaks cannot be dominated by standard red clump stars simultaneously.

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Spectral Synthesis of the Integrated Spectrum of the Galactic Bulge

Symposium - International Astronomical Union ◽

10.1017/s0074180900232804 ◽

1996 ◽

Vol 171 ◽

pp. 361-361

Author(s):

Sonya Delisle ◽

Eduardo Hardy

Keyword(s):

Globular Cluster ◽

Spectral Synthesis ◽

Line Of Sight ◽

Population Synthesis ◽

Galactic Bulge ◽

Stellar Spectra ◽

Optimization Program ◽

Preliminary Results ◽

Solar Metallicity

We present preliminary results of the population synthesis of the Galactic Bulge using different techniques. The observations, taken with CTIO's 4m CS, cover the range 3600Å to 10000Å. The integrated spectrum includes light from stars in the line-of-sight. For the synthesis, we used first a program that we developed (Couture & Hardy (1993), and Hardy et al. (1994)) along with three libraries, one of composite population spectra, (Jablonka et al. (1990) and Bica (1988)), one of stellar spectra (Pickles (1985)), and one of equivalent widths measured on the integrated spectra of coeval populations (Bica and Alloin (1986a), (1986b) and (1987)). Results obtained with the spectra were inconclusive. With the equivalent widths, we found indication of the presence of a young and rich population (1 Myr and [Z/Z⊙]=+0.3), but no old population or poor globular cluster-like population. Further tests are needed to evaluate the extent of the contamination from disk giants and its impact on the synthesis results. We also used Bica and Alloin's optimization program (Bica (1988)) with their library of equivalent witdhs. The contributions are spread over many groups but mainly intermediate-age, above-solar metallicity groups and old and poor groups. In all cases, no old metal-rich population was detected.

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Unveiling the Secrets of the Galactic bulge through stellar abundances in the near-IR: a VLT/Crires project

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308027543 ◽

2008 ◽

Vol 4 (S254) ◽

pp. 159-164

Author(s):

Nils Ryde

Keyword(s):

Milky Way ◽

Line Of Sight ◽

Galactic Bulge ◽

Stellar Abundances ◽

Preliminary Results ◽

Elemental Abundances ◽

Near Ir ◽

Visual Extinction ◽

Formation And Evolution

AbstractThe formation and evolution of the Milky Way bulge can be constrained by studying elemental abundances of bulge stars. Due to the large and variable visual extinction in the line-of-sight towards the bulge, an analysis in the near-IR is preferred. Here, I will present some preliminary results of an on-going project in which elemental abundances, especially those of the C, N, and O elements, of bulge stars are investigated by analysing CRIRES spectra observed with the VLT.

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Variation of the amount of hydrogen along the galactic ridge

Symposium - International Astronomical Union ◽

10.1017/s0074180900100889 ◽

1967 ◽

Vol 31 ◽

pp. 171-172

Author(s):

Th. Schmidt-Kaler

Keyword(s):

Surface Brightness ◽

Milky Way ◽

Neutral Hydrogen ◽

Line Of Sight ◽

Optical Surface ◽

Hydrogen Density ◽

Continuous Radiation ◽

Galactic Longitude

The integralNHof neutral-hydrogen density along the line of sight is determined from the Kootwijk and Sydney surveys. The run ofNHwith galactic longitude agrees well with that of thermal continuous radiation and that of the optical surface brightness of the Milky Way.

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The surface mass density in the solar neighbourhood using red clumps stars in TGASxRAVE

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317006524 ◽

2017 ◽

Vol 13 (S334) ◽

pp. 304-305

Author(s):

Jorrit H. J. Hagen ◽

Amina Helmi

Keyword(s):

Vertical Velocity ◽

Velocity Dispersion ◽

Mass Density ◽

Solar Neighbourhood ◽

Local Distribution ◽

Surface Mass ◽

Preliminary Results ◽

Combining Data ◽

Surface Mass Density ◽

Red Clump

AbstractWe investigate the kinematics of red clump stars in the Solar neighbourhood by combining data from the RAVE survey with the TGAS dataset presented in Gaia DR1. Our goal is to put new constraints on the (local) distribution of mass using the Jeans Equations. Here we show the variation of the vertical velocity dispersion as function of height above the mid-plane for both a thin and a thick disk tracer sample and present preliminary results.

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

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2834 ◽

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.

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