J/A+A/695/A211 Galactic bar/bulge traced by RRLs (Prudil+, 2025)
The Galactic Bulge exploration. IV. RR Lyrae stars as traces of the Galactic
bar: 3D and 5D analysis, extinction variation.
Prudil Z., Kunder A., Beraldo e Silva L., Gough-Kelly S., Rejkuba M.,
Anderson S.R., Debattista V.P., Gerhard O., Rich R.M., Nataf D.M.,
Koch-Hansen A.J., Savino A., Dekany I.
<Astron. Astrophys. 695, A211 (2025)>
=2025A&A...695A.211P 2025A&A...695A.211P (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Stars, variable ; Photometry ; Magnitudes, absolute ;
Stars, distances
Keywords: stars: variables: RR Lyrae - Galaxy: bulge -
Galaxy: kinematics and dynamics - Galaxy: structure
Abstract:
RR Lyrae stars towards the Galactic bulge are used to investigate
whether this old stellar population traces the Galactic bar. Although
the bar is known to dominate the mass in the inner Galaxy, there is no
consensus on whether the RR Lyrae star population, which constitutes
some of the most ancient stars in the bulge and thus traces the
earliest epochs of star formation, contributes to the barred bulge. We
create new reddening maps and derive new extinction laws from visual
to near-infrared passbands using improved RR Lyrae period- absolute
magnitude-metallicity relations, thus enabling distance estimates for
individual bulge RR∼Lyrae variables. The extinction law is most
uniform in RIKs and RJKs and the distances to individual RR Lyrae
based on these colors are determined with an accuracy six and four
percent, respectively. Using only the near-infrared passbands for
distance estimation we inferred the distance to the Galactic center
equal to dJKscen=8217±1((stat)±528(sys)pc after geometrical
correction. We show that variations in the extinction law toward the
Galactic bulge can mimic a barred spatial distribution in the bulge RR
Lyrae star population in visual passbands. This arises from a gradient
in extinction differences along Galactic longitudes and latitudes,
which can create the perception of the Galactic bar, particularly when
using visual passband-based distances. A barred angle in the RR∼Lyrae
spatial distribution disappears when near- infrared passband-based
distances are used, as well as when reddening law variations are
incorporated in visual passband-based distances. The prominence of the
bar, as traced by RR∼Lyrae stars, depends on their metallicity, with
metal-poor RR∼Lyrae stars ([Fe/H]←1.0dex) showing little to no tilt
with respect to the bar. Metal-rich ([Fe/H]>-1.0dex) RR∼Lyrae stars do
show a barred/bulge signature in spatial properties derived using
near-infrared distances, with an angle ι=18±5deg, consistent
with previous bar measurements from the literature. This also hints at
a younger age for this RR∼Lyrae subgroup. The 5D kinematic analysis,
primarily based on transverse velocities, indicates a rotational lag
in RR Lyrae stars compared to red clump giants. Despite variations in
the extinction law, our kinematic conclusions are robust across
different distance estimation methods.
Description:
In this study, we have analyzed the spatial and transverse velocity
distribution of RR Lyrae stars toward the Galactic bulge. We utilized
data from OGLE-IV, Gaia, VVV, and VHS surveys to create reddening
maps, derive reddening laws, and estimate distances tailored to each
given RR Lyrae variable identified in the Galactic bulge (covering
approximately 20<l←15deg and -15<b<15 deg area).
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablec1.dat 595 72165 The bar/bulge traced by RRLs
--------------------------------------------------------------------------------
See also:
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
J/AcA/69/321 : OGLE RR Lyrae stars in Galactic bulge & disk (Soszynski+, 2019)
Byte-by-byte Description of file: tablec1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 20 A20 --- OGLEIV OGLE-IV survey ID
22- 39 F18.14 deg RAdeg Right ascension (J2000)
41- 59 F19.15 deg DEdeg Declination (J2000)
61- 79 I19 --- GaiaDR3 Gaia source ID
81-103 F23.19 [-] [Fe/H] Photometric metallicity
105-126 F22.18 [-] e_[Fe/H] Uncertainty on photometric metallicity
128-150 E23.17 mag KsMAG Absolute magnitude in Ks band
152-172 F21.17 mag e_KsMAG Uncertainty on absolute magnitude in Ks band
174-197 E24.17 mag JMAG Absolute magnitude in J band
199-219 F21.17 mag e_JMAG Uncertainty on absolute magnitude in Ks band
221-243 E23.17 mag IMAG Absolute magnitude in I band
245-265 F21.17 mag e_IMAG Uncertainty on absolute magnitude in Ks band
267-289 F23.19 mag VMAG Absolute magnitude in V band
291-311 F21.17 mag e_VMAG Uncertainty on absolute magnitude in Ks band
313-336 E24.17 mag GMAG Absolute magnitude in Gbp band
338-358 F21.17 mag e_GMAG Uncertainty on absolute magnitude in Ks band
360-383 E24.17 mag E(J-K) ? Color excess in J and Ks bands
385-407 F23.17 mag e_E(J-K) ? Uncertainty on color excess in J and Ks bands
409-431 E23.16 mag E(I-K) ? Color excess in I and Ks bands
433-454 F22.17 mag e_E(I-K) ? Uncertainty on color excess in I and Ks bands
456-480 F25.20 mag E(V-I) ? Color excess in V and I bands
482-503 F22.17 mag e_E(V-I) ? Uncertainty on color excess in V and I bands
505-528 F24.19 mag E(B-I) ? Color excess in Gbp and I bands
530-551 F22.17 mag e_E(B-I) ? Uncertainty on color excess in Gbp and I bands
553-572 F20.16 kpc Dist Distance
574-595 F22.18 kpc e_Dist ?=-9.99 Uncertainty on distance
--------------------------------------------------------------------------------
Acknowledgements:
Zdenek Prudil, zdenek.prudil(at)eso.org
(End) Zdenek Prudil [ESO, Germany], Patricia Vannier [CDS] 26-Feb-2025