J/A+A/699/A349 The bar/bulge traced by RRLs 6D (Prudil+, 2025)
The Galactic bulge exploration.
V. The secular spherical and X-shaped Milky Way bulge.
Prudil Z., Debattista V.P., Beraldo e Silva L., Anderson S.R.,
Gough-Kelly S., Kunder A., Rejkuba M., Gerhard O., Wyse R.F.G.,
Koch-Hansen A.J., Rich R.M., Savino A.
<Astron. Astrophys. 699, A349 (2025)>
=2025A&A...699A.349P 2025A&A...699A.349P (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable ; Radial velocities ; Optical
Keywords: stars: variables: RR Lyrae - Galaxy: bulge -
Galaxy: kinematics and dynamics - Galaxy: structure
Abstract:
In this work, we derive systemic velocities for 8456 RR Lyrae stars.
This is the largest dataset of these variables in the Galactic bulge
to date. In combination with Gaia proper motions, we computed their
orbits using an analytical gravitational potential similar to that of
the Milky Way (MW) and identified interlopers from other MW
structures, which amount to 22% of the total sample. Our analysis
revealed that most interlopers are associated with the halo, and the
remainder are linked to the Galactic disk. We confirm the previously
reported lag in the rotation curve of bulge RR Lyrae stars, regardless
of the removal of interlopers. The rotation patterns of metal-rich
RR Lyrae stars are consistent with the pattern of nonvariable
metal-rich giants, following the MW bar, while metal-poor stars rotate
more slowly. The analysis of the orbital parameter space was used to
distinguish bulge stars that in the bar reference frame have prograde
orbits from those on retrograde orbits. We classified the prograde
stars into orbital families and estimated the chaoticity (in the form
of the frequency drift, logΔΩ) of their orbits. RR Lyrae
stars with banana-like orbits have a bimodal distance distribution,
similar to the distance distribution seen in metal-rich red clump
stars. The fraction of stars with banana-like orbits decreases
linearly with metallicity, as does the fraction of stars on prograde
orbits (in the bar reference frame). The retrograde-moving stars (in
the bar reference frame) form a centrally concentrated nearly
spherical distribution. From analyzing an N-body+SPH simulation, we
found that some stellar particles in the central parts oscillate
between retrograde and prograde orbits and that only a minority stays
prograde over a long period of time. Based on the simulation, the
ratio of prograde and retrograde stellar particles seems to stabilize
within some gigayears after the bar formation. The nonchaoticity of
retrograde orbits and their high numbers can explain some of the
spatial and kinematical features of the MW bulge that have been often
associated with a classical bulge.
Description:
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 66 8456 Calculated systemic velocities of our
RR Lyrae dataset
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See also:
J/AcA/69/321 : OGLE RR Lyrae stars in Galactic bulge & disk (Soszynski+, 2019)
J/AcA/64/177 : VI light curves of Galactic Bulge RR Lyrae (Soszynski+, 2014)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 20 A20 --- ID OGLE-ID (OGLE-BLG-RRLYR-NNNNN)
22- 44 F23.18 km/s vsys Systemic velocity
46- 66 F21.17 km/s e_vsys Error on systemic velocity
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Acknowledgements:
Zdenek Prudil, zdenek.prudil(at)eso.org
(End) Zdenek Prudil [ARI, Germany], Patricia Vannier [CDS] 25-Jun-2025