I/348 Orbital parameters in Milky-Way-like potentials (Mackereth+, 2018)
Fast estimation of orbital parameters in Milky-Way-like potentials
Mackereth J.T., Bovy J.
<Publ. Astron. Soc. Pac. 130, k4501 (2018)>
=2018PASP..130k4501M 2018PASP..130k4501M
=2018yCat.1348....0M 2018yCat.1348....0M
ADC_Keywords: Milky Way ; Populations, stellar ; Positional data ;
Space velocities ; Models
Keywords: galaxies: kinematics and dynamics - stars: kinematics and dynamics -
methods: data analysis - methods: numerical
Abstract:
Orbital parameters, such as eccentricity and maximum vertical
excursion, of stars in the Milky Way are an important tool for
understanding its dynamics and evolution, but calculation of such
parameters usually relies on computationally-expensive numerical orbit
integration. We present and test a fast method for estimating these
parameters using an application of the Sackel fudge, used previously
for the estimation of action-angle variables. We show that the method
is highly accurate, to a level of <1% in eccentricity, over a large
range of relevant orbits and in different Milky Way-like potentials,
and demonstrate its validity by estimating the eccentricity
distribution of the RAVE-TGAS data set and comparing it to that from
orbit integration. Using the method, the orbital characteristics of
the ∼7 million Gaia DR2 stars with radial velocity measurements are
computed with Monte Carlo sampled errors in ∼116 hours of parallelised
cpu time, at a speed that we estimate to be ∼3 to 4 orders of
magnitude faster than using numerical orbit integration. We
demonstrate using this catalogue that Gaia DR2 samples a large range
of orbits in the solar vicinity, down to those with rperi≲2.5kpc,
and out to rap≳13kpc. We also show that many of the features
present in orbital parameter space have a low mean zmax, suggesting
that they likely result from disk dynamical effects.
Description:
We have demonstrated a new application of the Binney
(2012MNRAS.426.1324B 2012MNRAS.426.1324B) Staeckel fudge for the rapid calculation of the
orbit parameters rperi, rap, zmax, and e, which does not depend
on orbit integration.
Using the method, the orbital characteristics of the ∼7 million Gaia
DR2 stars with radial velocity measurements are computed with Monte
Carlo sampled errors in ∼116 hours of parallelised cpu time, at a
speed that we estimate to be ∼3 to 4 orders of magnitude faster than
using numerical orbit integration.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
catalog.dat 1046 7224631 Catalog
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See also:
I/337 : Gaia DR1 (Gaia Collaboration, 2016)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
Byte-by-byte Description of file: catalog.dat
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Bytes Format Units Label Explanations
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1- 19 I19 --- Source Gaia DR2 source ID (source_id)
21- 44 F24.20 deg RAdeg Gaia barycentric right ascension
(ICRS) at Ep=2015.5 (ra)
46- 68 E23.18 deg DEdeg Gaia barycentric declination (ICRS)
at Ep=2015.5 (dec)
70- 90 F21.19 --- e ? Orbital eccentricity as defined in
Equation (10) (e)
92- 113 E22.17 --- e_e ? rms uncertainty on e (e_err)
115- 137 F23.19 kpc zmax ? maximum vertical excursion from the
midplane (zmax)
138 A1 --- n_zmax [iI] i for -inf I for inf
139- 160 E22.17 kpc e_zmax ? rms uncertainty on zmax (zmax_err)
162- 187 F26.18 kpc rperi ? 3D pericenter radius (rperi)
188 A1 --- n_rperi [iI] i for -inf I for inf
189- 210 E22.17 kpc e_rperi ? rms uncertainty on rperi (rperi_err)
212- 231 F20.16 kpc rap ? 3D apocenter radius (rap)
232 A1 --- n_rap [iI] i for -inf I for inf
233- 254 E22.17 kpc e_rap ? rms uncertainty on rap (rap_err)
256- 278 E23.18 --- ezmaxCor ? Correlation between e and zmax
(ezmaxcorr) (1)
280- 302 E23.18 --- erperiCor ? Correlation between e and rperi
(erpericorr) (1)
304- 326 E23.18 --- erapCor ? Correlation between e and rap
(erapcorr) (1)
328- 350 E23.18 --- zmaxrperiCor ? Correlation between zmax and rperi
(zmaxrpericorr) (1)
352- 374 E23.18 --- zmaxrapCor ? Correlation between zmax and rap
(zmaxrapcorr) (1)
376- 398 E23.18 --- rperirapCor ? Correlation between rperi and rap
(rperirapcorr) (1)
400- 427 F28.19 kpc.km/s JR ? Radial action (jr)
429- 450 E22.17 kpc.km/s e_JR ? rms uncertainty on JR (jr_err)
452- 474 E23.18 kpc.km/s Lz ? Azimuthal action (equivalent to
vertical component of angular
momentum) (Lz)
476- 497 E22.17 kpc.km/s e_Lz ? rms uncertainty on Lz (Lz_err)
499- 520 E22.17 kpc.km/s JZ ? Vertical action (jz)
522- 543 E22.17 kpc.km/s e_JZ ? rms uncertainty on JZ (jz_err)
545- 567 E23.18 --- JRLZCor ? Correlation between JR and LZ
(jrLzcorr) (1)
569- 591 E23.18 --- JRJZCor ? Correlation between JR and JZ
(jrjzcorr) (1)
593- 615 E23.18 --- LZJZCor ? Correlation between LZ and JZ
(lzjzcorr) (1)
617- 640 F24.16 Gyr-1 omegaR ? Radial frequency (omega_r)
641 A1 --- n_omegaR [i] i for infinity
642- 663 E22.17 Gyr-1 e_omegaR ? rms uncertainty on omegaR
(omegarerr)
665- 690 F26.19 Gyr-1 omegaphi ? Azimuthal frequency (omega_phi)
692- 713 E22.17 Gyr-1 e_omegaphi ? rms uncertainty on omegaphi
(omegaphierr)
715- 738 F24.16 Gyr-1 omegaz ? Vertical frequency (omega_z)
739 A1 --- n_omegaz [i] i for infinity
740- 761 E22.17 Gyr-1 e_omegaz ? rms uncertainty on omegaz
(omegazerr)
763- 786 F24.19 rad thetaR ? Radial angle (theta_r)
788- 809 E22.17 rad e_thetaR ? rms uncertainty on thetaR
(thetarerr)
811- 836 F26.20 rad thetaphi ? Azimuthal angle (theta_phi)
838- 859 E22.17 rad e_thetaphi ? rms uncertainty on thetaphi
(thetaphierr)
861- 884 F24.19 rad thetaz ? Vertical angle (theta_z)
886- 907 E22.17 rad e_thetaz ? rms uncertainty on thetaz
(thetazerr)
909- 930 E22.17 kpc Rguide ? Radius of a circular orbit at the
same Lz (rl)
932- 953 E22.17 kpc e_Rguide ? rms uncertainty on Rguide (rl_err)
955- 977 E23.18 km+2/s+2 E ? Orbital energy (E)
979-1000 E22.17 km+2/s+2 e_E ? rms uncertainty on E (E_err)
1002-1023 E22.17 km+2/s+2 E-Ec ? Difference between orbit energy and
energy of a circular orbit of the
same Lz (EminusEc)
1025-1046 E22.17 km+2/s+2 e_E-Ec ? rms uncertainty on E-Ec
(EminusEc_err)
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Note (1): Correlation coefficients are only computed for the orbital parameters
and actions, and are computed separately for each set of quantities.
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Acknowledgements:
Ted Mackereth, J.E.Mackereth(at)2011.ljmu.ac.uk
(End) Patricia Vannier [CDS] 27-Sep-2018