J/MNRAS/530/2972 Mira variable cand. in Milky Way NSD region (Sanders+, 2024)
The epoch of the Milky Way's bar formation:
dynamical modelling of Mira variables in the nuclear stellar disc.
Sanders J.L., Kawata D., Matsunaga N., Sormani M.C., Smith L.C., Minniti D.,
Gerhard O.
<Mon. Not. R. Astron. Soc. 530, 2972-2993 (2024)>
=2024MNRAS.530.2972S 2024MNRAS.530.2972S (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Stars, variable ; Photometry, infrared ;
Binaries, orbits
Keywords: stars: AGB - stars: variables: general - Galaxy: evolution -
Galaxy: formation - Galaxy: kinematics and dynamics - Galaxy: nucleus
Abstract:
A key event in the history of the Milky Way is the formation of the
bar. This event affects the subsequent structural and dynamical
evolution of the entire Galaxy. When the bar formed, gas was likely
rapidly funnelled to the centre of the Galaxy settling in a
star-forming nuclear disc. The Milky Way bar formation can then be
dated by considering the age distribution of the oldest stars in the
formed nuclear stellar disc. In this highly obscured and crowded
region, reliable age tracers are limited, but bright, high-amplitude
Mira variables make useful age indicators as they follow a period--age
relation. We fit dynamical models to the proper motions of a sample of
Mira variables in the Milky Way's nuclear stellar disc region. Weak
evidence for inside-out growth and both radial and vertical dynamical
heating with time of the nuclear stellar disc is presented suggesting
the nuclear stellar disc is dynamically well-mixed. Furthermore, for
Mira variables around a ∼350 day period, there is a clear transition
from nuclear stellar disc-dominated kinematics to background
bar-bulge-dominated kinematics. Using a Mira variable period--age
relation calibrated in the solar neighbourhood, this suggests the
nuclear stellar disc formed in a significant burst in star formation
(8±1)Gyr ago, although the data are also weakly consistent with a
more gradual formation of the nuclear stellar disc at even earlier
epochs. This implies a relatively early formation time for the Milky
Way bar (≳8Gyr), which has implications for the growth and state of
the young Milky Way and its subsequent history.
Description:
A catalogue of Mira variable candidates extracted from the VIRAC2
reduction of the VVV survey (see Sanders et al., 2022MNRAS.517..257S 2022MNRAS.517..257S,
for details). VIRAC2 provides photometry and astrometry (proper
motions) as used in the analysis of the paper. For consistency with
the corresponding publications, the provided photometry corresponds to
an intermediate version of VIRAC2 that was used to discover the Mira
variable candidates whilst the astrometry is from the version of
VIRAC2 that will be public.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
catalog.dat 891 1782 Mira variable data set
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Byte-by-byte Description of file: catalog.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- VIRAC2Mira [0/1823] Unique VIRAC2 Mira source ID
(viracmiraid)
6- 17 F12.8 deg RAdeg VIRAC-2 right ascension (ICRS)
at Ep=2014.0 (ra)
19- 30 F12.8 deg DEdeg VIRAC-2 declination (ICRS)
at Ep=2014.0 (dec)
32- 43 F12.8 deg GLON VIRAC-2 Galactic longitude at epoch
2014.0 if proper motion computed (l)
45- 56 F12.8 deg GLAT VIRAC-2 Galactic latitude at epoch
2014.0 if proper motion computed (b)
58- 61 I4 --- M09Id ? ID from Matsunaga et al.
(2009MNRAS.399.1709M 2009MNRAS.399.1709M,
Cat. J/MNRAS/399/1709) (M09_id)
63 I1 --- unreliable [0/1] Binary flag if Mira variable
classification is unreliable (=1)
based on a visual classification of
the light curve (unreliable)
65- 67 I3 --- KsEpochs Number of VIRAC-2 Ks epochs used in the
light curve processing for
classification as a Mira variable
(Ks_nepochs)
69- 78 F10.6 d Per Recommended period - either from multi-
band or single band depending on
reliability from visual inspection
(period)
80- 93 F14.9 d e_Per ? Uncertainty in recommended period
(period_error)
95-105 F11.9 mag Amp Ks amplitude (95th-5th Ks percentile)
averaged over a period around each
data point (amplitude)
107-117 F11.8 mag TAmp ? Ks amplitude (95th-5th Ks percentile)
across the total timespan of the data
(total_amplitude)
119-128 F10.6 d PerS Period from the Ks single band fit.
For the last 40 entries, this duplicates
the M09 result (period_single)
130-143 F14.9 d e_PerS ? Uncertainty in period_single
(perioderrorsingle)
145-155 F11.8 mag AmpS ? Ks amplitude (95th-5th Ks percentile)
from the single band fit averaged over
a period around each data point
(amplitude_single)
157-167 F11.8 mag TAmpS ? Ks amplitude (95th-5th Ks percentile)
from the single band fit across the
total timespan of the data
(totalamplitudesingle)
169-180 F12.6 d PerM Period from the multi-band fit
(period_multi)
182-201 F20.9 d e_PerM ? Uncertainty in period_multi
(perioderrormulti)
203-212 F10.4 mag AmpM Ks amplitude (95th-5th Ks percentile)
from the multi-band fit averaged over a
period around each data point
(amplitude_multi)
214-223 F10.4 mag TAmpM Ks amplitude (95th-5th Ks percentile)
from the multi-band fit across the
total timespan of the data
(totalamplitudemulti)
225-234 F10.6 mag Zmag ? Mean Z magnitude from VIRAC2
(Zmeandata)
236-245 F10.6 mag Ymag ? Mean Y magnitude from VIRAC2
(Ymeandata)
247-257 F11.7 mag Jmag ? Mean J magnitude from VIRAC2
(Jmeandata)
259-269 F11.7 mag Hmag ? Mean H magnitude from VIRAC2
(Hmeandata)
271-281 F11.7 mag Ksmag ? Mean Ks magnitude from VIRAC2
(Ksmeandata)
283-293 F11.7 mag KsmagModS ? Mean Ks magnitude from single-band VVV
model fit (Ksmeanmodel_single)
295-307 F13.10 mag e_KsmagModS ? Uncertainty in mean Ks magnitude from
single- band VVV model fit
(Kserrormodel_single)
309-318 F10.6 mag ZmagMod ? Mean Z magnitude from multiband model
(Zmeanmodel)
320-330 F11.7 mag YmagMod ? Mean Y magnitude from multiband model
(Ymeanmodel)
332-342 F11.7 mag JmagMod ? Mean J magnitude from multiband model
(Jmeanmodel)
344-354 F11.7 mag HmagMod ? Mean H magnitude from multiband model
(Hmeanmodel)
356-365 F10.7 mag KsmagMod Mean Ks magnitude from multiband model
(Ksmeanmodel)
367-377 F11.7 mag W1magMod ? Mean W1 magnitude from multiband model
(W1meanmodel)
379-389 F11.7 mag W2magMod ? Mean W2 magnitude from multiband model
(W2meanmodel)
391-402 F12.9 mag e_ZmagMod ? Uncertainty in mean Z magnitude from
multiband model (Zerrormodel)
404-416 F13.10 mag e_YmagMod ? Uncertainty in mean Y magnitude from
multiband model (Yerrormodel)
418-430 F13.10 mag e_JmagMod ? Uncertainty in mean J magnitude from
multiband model (Jerrormodel)
432-444 F13.10 mag e_HmagMod ? Uncertainty in mean H magnitude from
multiband model (Herrormodel)
446-457 F12.10 mag e_KsmagMod Uncertainty in mean Ks magnitude from
multiband model (Kserrormodel)
459-471 F13.10 mag e_W1magMod ? Uncertainty in mean W1 magnitude from
multiband model (W1errormodel)
473-485 F13.10 mag e_W2magMod ? Uncertainty in mean W2 magnitude from
multiband model (W2errormodel)
487-497 F11.8 --- AmpZ/Ks ? Ratio of Z amplitude to Ks amplitude
from multi-band fit
(ZKsamplitude_ratio)
499-509 F11.8 --- AmpY/Ks ? Ratio of Y amplitude to Ks amplitude
from multi-band fit
(YKsamplitude_ratio)
511-521 F11.8 --- AmpJ/Ks ? Ratio of J amplitude to Ks amplitude
from multi-band fit
(JKsamplitude_ratio)
523-533 F11.8 --- AmpH/Ks ? Ratio of H amplitude to Ks amplitude
from multi-band fit
(HKsamplitude_ratio)
535-546 F12.9 --- AmpW1/Ks ? Ratio of W1 amplitude to Ks amplitude
from multi-band fit
(W1Ksamplitude_ratio)
548-559 F12.9 --- AmpW2/Ks ? Ratio of W2 amplitude to Ks amplitude
from multi-band fit
(W2Ksamplitude_ratio)
561-571 F11.8 --- e_AmpZ/Ks ? Uncertainty in ratio of Z amplitude to
Ks amplitude from multi-band fit
(ZKsamplituderatioerror)
573-584 F12.9 --- e_AmpY/Ks ? Uncertainty in ratio of Y amplitude to
Ks amplitude from multi-band fit
(YKsamplituderatioerror)
586-598 F13.10 --- e_AmpJ/Ks ? Uncertainty in ratio of J amplitude to
Ks amplitude from multi-band fit
(JKsamplituderatioerror)
600-613 F14.10 --- e_AmpH/Ks ? Uncertainty in ratio of H amplitude to
Ks amplitude from multi-band fit
(HKsamplituderatioerror)
615-628 F14.10 --- e_AmpW1/Ks ? Uncertainty in ratio of W1 amplitude
to Ks amplitude from multi-band fit
(W1Ksamplituderatioerror)
630-642 F13.10 --- e_AmpW2/Ks ? Uncertainty in ratio of W2 amplitude
to Ks amplitude from multi-band fit
(W2Ksamplituderatioerror)
644-656 F13.10 --- tau10um Optical depth at 10 microns from
radiatively- driven wind model
(opticaldepth10micron)
658-667 F10.7 km/s Vexp Expansion velocity from
radiatively-driven wind model
(expansion_velocity)
669-680 F12.8 10-6Msun/yr dM/dt Mass loss rate from radiatively-driven
wind model (masslossrate)
682-699 F18.16 mas e_RAdeg VIRAC-2 right ascension uncertainty,
RA*cos(DE) (ra_error)
701-719 F19.16 mas e_DEdeg VIRAC-2 declination uncertainty
(dec_error)
721-740 F20.16 mas/yr pmRA VIRAC-2 right ascension proper motion
with cos(DE) factor (pmRA*cosDE) (pmra)
742-761 F20.16 mas/yr pmDE VIRAC-2 declination proper motion
(pmdec)
763-780 F18.16 mas/yr e_pmRA Uncertainty in VIRAC-2 right ascension
proper motion with cos (dec) factor
(pmra_error)
782-799 F18.16 mas/yr e_pmDE Uncertainty in VIRAC-2 declination
proper motion (pmdec_error)
801-812 F12.8 --- pmRApmDEcor VIRAC-2 correlation coefficient between
pmRA and pmDE (pmrapmdeccorr)
814-834 F21.16 mas plx VIRAC-2 parallax (parallax)
836-854 F19.16 mas e_plx VIRAC-2 parallax uncertainty
(parallax_error)
856-867 F12.8 --- plxpmRAcor VIRAC-2 correlation coefficient between
parallax and pmRA (parallaxpmracorr)
869-880 F12.8 --- plxpmDEcor VIRAC-2 correlation coefficient between
parallax and pmDE (parallaxpmdeccorr)
882-891 F10.8 --- astfituwe VIRAC-2 astrometric fit unit weight
error (chisq per degree of freedom)
(astfit_uwe)
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Acknowledgements:
Jason Sanders, jason.sanders(at)ucl.ac.uk
(End) Patricia Vannier [CDS] 14-May-2024