J/MNRAS/493/5195 Milky Way halo stars ages and kinematics (Das+, 2020)
Ages and kinematics of chemically selected, accreted Milky Way halo stars.
Das P., Hawkins K., Jofre P.
<Mon. Not. R. Astron. Soc., 493, 5195-5207 (2020)>
=2020MNRAS.493.5195D 2020MNRAS.493.5195D (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Stars, halo ; Abundances ; Stars, ages
Keywords: Galaxy: halo - Galaxy: abundances - Galaxy: evolution
Abstract:
We exploit the [Mg/Mn]-[Al/Fe] chemical abundance plane to help
identify nearby halo stars in the 14th data release from the APOGEE
survey that have been accreted on to the Milky Way. Applying a
Gaussian Mixture Model, we find a 'blob' of 856 likely accreted
stars, with a low disc contamination rate of about 7 percent.
Cross-matching the sample with the second data release from Gaia gives
us access to parallaxes and apparent magnitudes, which place
constraints on distances and intrinsic luminosities. Using a Bayesian
isochrone pipeline, this enables us to estimate new ages for the
accreted stars, with typical uncertainties of 20 percent. Our new
catalogue is further supplemented with estimates of orbital
parameters.
The blob stars span a metallicities between -0.5 to -2.5, and [Mg/Fe]
between -0.1 to 0.5. They constitute 30 percent of the metal-poor
([Fe/H]←0.8) halo at metallicities of -1.4. Our new ages are mainly
range between 8 to 13Gyr, with the oldest stars the metal-poorest,
and with the highest [Mg/Fe] abundance. If the blob stars are assumed
to belong to a single progenitor, the ages imply that the system
merged with our Milky Way around 8 Gyr ago and that star formation
proceeded for 5Gyr. Dynamical arguments suggest that such a single
progenitor would have a total mass of 1011M☉, similar to that
found by other authors using chemical evolution models and
simulations. Comparing the scatter in the [Mg/Fe]-[Fe/H] plane of the
blob stars to that measured for stars belonging to the Large
Magellanic Cloud suggests that the blob does indeed contain stars from
only one progenitor.
Description:
A table including the APOGEE information along with the computed ages,
actions/orbital parameters and positions for the full sample of blob
stars. This table is referenced in footnote 2 in the paper.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
blob.dat 615 856 Catalogue of the spectroscopic, age, and
kinematic properties of the blob stars
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Byte-by-byte Description of file: blob.dat
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Bytes Format Units Label Explanations
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1- 18 A18 --- APOGEE APOGEE name, 2MHHMMSSss+DDMMSSs (apogee_id)
20- 23 I4 --- Loc APOGEE location ID (apogeelocationid)
25- 30 F6.3 mag Jmag 2MASS J magnitude (J)
32- 37 F6.3 mag Hmag 2MASS H magnitude (H)
39- 44 F6.3 mag Kmag 2MASS K magnitude (K)
46- 50 F5.3 mag e_Jmag rms uncertainty on Jmag (J_ERR)
52- 56 F5.3 mag e_Hmag rms uncertainty on Hmag (H_ERR)
58- 62 F5.3 mag e_Kmag rms uncertainty on Kmag (K_ERR)
64- 77 F14.10 deg RAdeg Right ascension (J2000) (RA)
79- 92 F14.10 deg DEdeg Declination (J2000) (DEC)
94-104 F11.6 km/s HV Average heliocentric velocity
(apogeevhelioavg)
106-115 F10.8 km/s e_HV rms uncertainty on HV (apogee_verr)
117-126 F10.8 [cm2/s] logg Syrface gravity (apogee_logg)
128-138 F11.9 [cm2/s] e_logg rms uncertainty on loog (apogeeloggerr)
140-148 F9.4 K Teff Effective temperature (apogee_teff
150-159 F10.6 K e_Teff rms uncertainty on Teff (apogeetefferr)
161-171 F11.8 [-] [M/H] Metallicity (apogeemh)
173-183 F11.9 [-] e_[M/H] rms uncertainty on [M/H] (apogeemh_err)
185-197 F13.10 [-] [alpha/M] Alpha-element enhancement (apogeeam_)
199-210 F12.10 [-] e_[alpha/M] rms uncertainty on [alpha/M]
(apogeeam_err)
212-224 F13.10 [-] [C/Fe] Abundance [C/Fe] (apogeecfe)
226-236 F11.9 [-] e_[C/Fe] rms uncertainty on [C/Fe] (apogeecfe_err)
238-250 E13.10 [-] [N/Fe] Abundance [N/Fe] (apogeenfe)
252-262 F11.9 [-] e_[N/Fe] rms uncertainty on [N/Fe] (apogeenfe_err)
264-279 E16.10 [-] [O/Fe] ?=-9999 Abundance [O/Fe] (apogeeofe)
281-295 F15.9 [-] e_[O/Fe] ?=-9999 rms uncertainty on [O/Fe]
(apogeeofe_err)
297-311 F15.9 [-] [Na/Fe] ?=-9999 Abundance [Na/Fe] (apogeenafe)
313-327 F15.9 [-] e_[Na/Fe] ?=-9999 rms uncertainty on [Na/Fe]
(apogeenafe_err)
329-341 E13.10 [-] [Mg/Fe] Abundance [Mg/Fe] (apogeemgfe)
343-353 F11.9 [-] e_[Mg/Fe] rms uncertainty on [Mg/Fe]
(apogeemgfe_err)
355-366 F12.9 [-] [Al/Fe] Abundance [Al/Fe] (apogeealfe)
368-378 F11.9 [-] e_[Al/Fe] rms uncertainty on [Al/Fe]
(apogeealfe_err)
380-391 F12.9 [-] [Mn/Fe] Abundance [Mn/Fe] (apogeemnfe)
393-403 F11.9 [-] e_[Mn/Fe] rms uncertainty on [Mn/Fe]
(apogeemnfe_err)
405-417 E13.10 [-] [Ni/Fe] Abundance [Ni/Fe] (apogeenife)
419-429 F11.9 [-] e_[Ni/Fe] rms uncertainty on [Ni/Fe]
(apogeenife_err)
431-435 I5 [-] [Y/Fe] ?=-9999 Abundance [Y/Fe] (apogeeyfe)
437-441 I5 [-] e_[Y/Fe] ?=-9999 rms uncertainty on [Y/Fe]
(apogeeyfe_err)
443-461 I19 --- GaiaDR2 Gaia DR2 identifier (gaiasourceid)
463-474 F12.10 [Gyr] logAge New age (log10agenew)
476-495 E20.14 [Gyr] e_logAge rms uncertainty on Age (log10ageerr_new)
497-509 F13.10 --- MOD New distance modulus (dm_new)
511-522 F12.10 --- e_MOD rms uncertainty on MOD (dmerrnew)
524-539 F16.10 kpc.km/s JR New radial action (JR_new)
541-555 F15.10 kpc.km/s Jz New vertical action (Jz_new)
557-572 F16.10 kpc.km/s Lz New z component of angular momentum
(Lz_new)
574-586 F13.10 kpc s New Galactocentric azimuth angle distance
(s_new)
588-600 F13.10 kpc R New Galactocentric radius distance (R_new)
602-615 F14.10 kpc z New height above Galactocentric plane
distance (z_new)
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Acknowledgements:
Keith Hawkins, keithhawkins(at)utexas.edu
(End) Patricia Vannier [CDS] 30-Jul-2020