J/A+A/701/A136 RR Lyrae stars trace the Milky Way warp (Cabrera-Gadea+, 2025)
RR Lyrae stars trace the Milky Way warp.
Cabrera-Gadea M., Mateu C., Ramos P.
<Astron. Astrophys. 701, A136 (2025)>
=2025A&A...701A.136C 2025A&A...701A.136C (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Stars, variable ; Stars, distances ;
Abundances, [Fe/H] ; Optical
Keywords: stars, variables: RR Lyrae - Galaxy: disk -
Galaxy: kinematics and dynamics - Galaxy: structure
Abstract:
The outskirts of the Milky Way disc have been known to be warped since
the late 1950s. Although various stellar populations
have shown an underlying warped distribution, the relation between the
age of the population and the warp they trace remains an open
question. Understanding this relation may shed light on the origin of
the warp which remains a puzzle to be solved.
Our goal in this work is to detect the presence of the warp in the RR
Lyrae (RRL) population of the Milky Way disc.
We use a compilation of the three largest public catalogues of RRL
stars, precise photometric distances (∼5%) and Gaia DR3 proper
motions to kinematically select a sample of thin disc RRL in the
Galactic anticentre, where the tangential velocity best approximates
the azimuthal velocity to differentiate between those that rotate
(disc) and those that do not (halo). For those disc-like RRL we
analyse their mean vertical height and mean vertical velocity.
We show, for the first time, that RRL stars with thin disc-like
kinematics trace the warp. In the anticentre direction, the RRL
population reaches a minimum in mean vertical height of ∼0.4kpc, with
a trend systematically lower than the one found with Classical
Cepheids. The kinematical signal of the RRL warp starts at R∼10kpc
and, rather than resembling the Cepheid's, shows a similar trend to
the Red Clump population from previous works, reaching a maximum value
of ∼7km/s in vertical velocity. We also obtain an estimation of the
pattern speed of the RRL warp with a prograde rotation of
∼13±2km/s/kpc, compatible with results obtained from Classical
Cepheids. Finally, we also obtain a vertical velocity dispersion
∼17km/s, inconsistent with the kinematics of a canonical old age
(>10Gyr) disc population and, instead, favouring a population
dominated by intermediate-age (3-4Gyr).
Our results indicate that the thin disc RRL stars are a dynamical
intermediate-age tracer of the warp, opening a new window to study the
dependency of the warp with stellar age in the Milky Way.
Description:
In this work, we used a catalogue containing 309998 stars,
compiled by combining the three largest public RRL surveys: Gaia DR3
Specific Objects Study (SOS, Clementini et al., 2023A&A...674A..18C 2023A&A...674A..18C,
Cat. J/A+A/674/A18), ASAS-SN-II (Jayasinghe et al.,
2019MNRAS.485..961J 2019MNRAS.485..961J, see Cat. II/366) and PanSTARRS1 (PS1, Sesar et
al., 2017AJ....153..204S 2017AJ....153..204S, Cat. J/AJ/153/204).
The file contains the sample of RR Lyrae from the thin disc in the
anticentre (table1.dat) and the results from this sample (table2.dat).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 201 321 Catalog of RR Lyrae stars
table2.dat 68 7 Results from RR Lyrae sample
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See also:
II/366 : ASAS-SN catalog of variable stars (Jayasinghe+, 2018-2020)
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
J/AJ/153/204 : RR Lyrae stars from the PS1 3π survey (Sesar+, 2017)
J/A+A/674/A18 : Gaia DR3. The RR Lyrae sample (Clementini+, 2023)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 19 I19 --- GaiaDR3 Gaia DR3 source ID
21- 38 F18.16 kpc Dist Heliocentric distance
40- 59 F20.18 kpc e_Dist Distance error
60- 77 F18.14 deg GLON Galactic longitude
79- 99 F21.17 deg GLAT Galactic latitude
100-119 F20.16 mas/yr pmGLON Proper motion in GLON
121-140 F20.16 mas/yr pmGLAT Proper motion in GLAT
142-160 F19.16 [-] [Fe/H] Metallicity used for distance calculation
162-179 F18.16 d Per Period of the RR Lyrae star
182-199 F18.16 mag AmpV V-band amplitude of the RR Lyrae
201 I1 --- f_[Fe/H] [0/1] Metallicity flag:
1=photometric, 0=assigned
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 5 F5.2 kpc R Mean Galactocentric radius
7- 11 F5.2 kpc Z Mean vertical height
13- 16 F4.2 kpc s_Z Standard deviation of Z (bootstrap)
18- 22 F5.2 km/s Vz Mean vertical velocity
24- 27 F4.2 km/s s_Vz Standard deviation of Vz (bootstrap)
29- 33 F5.2 km/s stdVz Standard deviation of vertical velocity
35- 38 F4.2 km/s s_stdVz Standard deviation of stdVz (bootstrap)
40- 44 F5.2 km/s/kpc medianOmega Median pattern speed
46- 50 F5.2 km/s/kpc b_medianOmega 15% percentile of omega distribution
52- 56 F5.2 km/s/kpc B_medianOmega 85% percentile of omega distribution
58- 63 F6.2 km/s meanVphi Mean azimuthal velocity
65- 68 F4.2 km/s e_meanVphi Standard deviation of Vphi (bootstrap)
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Acknowledgements:
Mauro Cabrera-Gadea, mauro.cabrera(at)pedeciba.edu.uy
(End) Cabrera-Gadea Mauro [Udelar], Patricia Vannier [CDS] 29-Jul-2025