J/MNRAS/482/5302 GALAH co-orbiting stars and chemical tagging (Simpson+, 2019)
The GALAH survey: co-orbiting stars and chemical tagging.
Simpson J.D., Martell S.L., Da Costa G., Casey A.R., Freeman K.C.,
Horner J., Ting Y.-S., Nataf D.M., Lewis G.F., Ness M.K., Zucker D.B.,
Cottrell P.L., Cotar K., Asplund M., Bland-Hawthorn J., Buder S.,
D'Orazi V., De Silva G.M., Duong L., Kos J., Lin J., Lind K.,
Schlesinger K.J., Sharma S., Zwitter T., Kafle P.R., Nordlander T.
<Mon. Not. R. Astron. Soc., 482, 5302-5315 (2019)>
=2019MNRAS.482.5302S 2019MNRAS.482.5302S (SIMBAD/NED BibCode)
ADC_Keywords: Abundances ; Galactic plane ; Magnitudes ; Stars, fundamental
Keywords: stars: abundances, stars: formation, galaxy: disc
Abstract:
We present a study using the second data release of the GALAH survey
of stellar parameters and elemental abundances of 15 pairs of stars
identified by Oh et al. They identified these pairs as potentially
co-moving pairs using proper motions and parallaxes from Gaia DR1. We
find that 11 very wide (>1pc) pairs of stars do in fact have similar
Galactic orbits, while a further four claimed co-moving pairs are not
truly co-orbiting. Eight of the 11 co-orbiting pairs have reliable
stellar parameters and abundances, and we find that three of those are
quite similar in their abundance patterns, while five have significant
[Fe/H] differences. For the latter, this indicates that they could be
co-orbiting because of the general dynamical coldness of the thin
disc, or perhaps resonances induced by the Galaxy, rather than a
shared formation site. Stars such as these, wide binaries, debris of
past star formation episodes, and coincidental co-orbiters, are
crucial for exploring the limits of chemical tagging in the Milky Way.
Description:
We make use of an internally released catalogue of a similar size and
composition to the GALAH survey's second data release (GALAH DR2;
Buder et al. 2018MNRAS.478.4513B 2018MNRAS.478.4513B, Cat. J/MNRAS/478/4513) that
maximized the overlap between GALAH and Oh et al.
(2017AJ....153..257O 2017AJ....153..257O, Cat. J/AJ/153/257) (hereafter O17). It is based
upon spectra obtained between 2014 January and 2018 January using the
3.9-m Anglo-Australian Telescope with the HERMES spectrograph (Sheinis
et al. 2015JATIS...1c5002S 2015JATIS...1c5002S) and the Two-Degree Field (2dF) top-end
(Lewis et al. 2002MNRAS.333..279L 2002MNRAS.333..279L). The 2dF allows for the concurrent
acquisition of up to ∼360 science targets per exposure. HERMES
simultaneously acquires spectra using four independent cameras with
non-contiguous wavelength coverage totalling ∼1000Å at a spectral
resolving power of R∼28000.
Overall, the GALAH release used in this work contains a total of
365516 stars with up to 23 elemental abundances per star. For a
minority of stars, the label results from the cannon are not reliable:
The label result could be too far from the training set, the χ2
between the observed spectrum and the spectrum calculated by the
cannon could be too large, or the spectra could have been classified
by t-SNE (for details on the application of t-SNE to GALAH spectra see
Traven et al. 2017ApJS..228...24T 2017ApJS..228...24T, Cat. J/ApJS/228/24) as having
problems. In addition, the individual elemental abundance can be
flagged for similar reasons.
O17 identified 10606 stars to be in non-exclusive co-moving pairs or
groups.3 Unfortunately, only 117 of these stars are found in the GALAH
catalogue, and only 15 pairs had both stars observed (i.e. 30 stars).
Table 1 lists the O17 group ID, the GALAH sobject_id, stellar
parameters, photometry, and orbital parameters for the 15 pairs.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 1008 30 The stellar parameters and orbital
characteristics of the 15 pairs
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See also:
J/MNRAS/478/4513 : GALAH Survey DR2 (Buder+, 2018)
J/AJ/153/257 : Comoving stars in Gaia DR1 (Oh+, 2017)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 21 A21 --- Name GALAH Name (GALAH NNNNNNNNNNNNNNN)
23- 36 A14 --- GName Group Name ([OPH2017] NNNN)
38- 41 F4.2 --- e Eccentricity
43- 46 F4.2 --- e_e Error on e
48- 50 I3 pc zmax Maximum distance above Galactic plane
52- 53 I2 pc e_zmax Error on zmax
55- 58 F4.2 kpc Rperi Perigalactic distance of the Galactic orbit
60- 63 F4.2 kpc e_Rperi Error on Rperi
65- 68 F4.2 kpc Rapo Apogalactic distance of the Galactic orbit
70- 73 F4.2 kpc e_Rapo Error on Rapo
75- 93 I19 --- GaiaDR2 Gaia DR2 identifier
95-104 F10.7 mag Gmag Gaia DR2 G-band magnitude
106-115 F10.8 mag BP-RP Gaia DR2 BP-RP color index
117-129 F13.9 km/s RVsynt Barycentric radial velocity from
cross-correlation against synthetic
spectra
131-142 F12.10 km/s e_RVsynt Error on RVsynt
144 I1 --- flagcannon Flags for spectrum information in a bitmask
format (1)
146-156 F11.6 K Teff Effective temperature
158-168 F11.8 K e_Teff Error on Teff
170-180 F11.9 [cm/s2] logg Surface gravity
182-194 F13.11 [cm/s2] e_logg Error on logg
196-209 F14.11 --- [Fe/H] Iron abundance
211-223 F13.11 --- e_[Fe/H] Error on [Fe/H]
225-236 F12.10 km/s vmic Microturbulence velocity
238-250 F13.11 km/s e_vmic Error on vmic
252-263 F12.9 km/s vsini Line of sight rotational velocity
265-276 F12.10 km/s e_vsini Error on vsini
278-292 F15.12 --- [alpha/Fe] ? α enhancement, determined as an
error-weighted combination of
Mg, Si, Ca, Ti abundances
294-306 F13.11 --- e_[alpha/Fe] ? Error on [alpha/Fe]
308-322 F15.12 --- [Li/Fe] Lithium to iron abundance ratio
324-336 F13.11 --- e_[Li/Fe] Error on [Li/Fe]
338 I1 --- f_[Li/Fe] Flag on [Li/Fe] (2)
340-353 F14.11 --- [C/Fe] Carbon to iron abundance ratio
355-367 F13.11 --- e_[C/Fe] Error on [C/Fe]
369 I1 --- f_[C/Fe] Flag on [C/Fe] (2)
371-384 F14.11 --- [O/Fe] Oxygen to iron abundance ratio
386-398 F13.11 --- e_[O/Fe] Error on [O/Fe]
400 I1 --- f_[O/Fe] Flag on [O/Fe] (2)
402-416 F15.12 --- [Na/Fe] Sodium to iron abundance ratio
418-430 F13.11 --- e_[Na/Fe] Error on [Na/Fe]
432 I1 --- f_[Na/Fe] Flag on [Na/Fe] (2)
434-448 F15.12 --- [Mg/Fe] ? Magnesium to iron abundance ratio
450-462 F13.11 --- e_[Mg/Fe] ? Error on [Mg/Fe]
464-465 I2 --- f_[Mg/Fe] Flag on [Mg/Fe] (2)
467-481 F15.12 --- [Al/Fe] Aluminum to iron abundance ratio
483-495 F13.11 --- e_[Al/Fe] Error on [Al/Fe]
497 I1 --- f_[Al/Fe] Flag on [Al/Fe] (2)
499-513 F15.12 --- [Si/Fe] ? Silicon to iron abundance ratio
515-527 F13.11 --- e_[Si/Fe] ? Error on [Si/Fe]
529-530 I2 --- f_[Si/Fe] Flag on [Si/Fe] (2)
532-546 F15.12 --- [K/Fe] Potassium to iron abundance ratio
548-560 F13.11 --- e_[K/Fe] Error on [K_Fe]
562 I1 --- f_[K/Fe] Flag on [K_Fe] (2)
564-578 F15.12 --- [Ca/Fe] Calcuim to iron abundance ratio
580-592 F13.11 --- e_[Ca/Fe] Error on [Ca/Fe]
594 I1 --- f_[Ca/Fe] Flag on [Ca/Fe] (2)
596-610 F15.12 --- [Sc/Fe] Scandium to iron abundance ratio
612-624 F13.11 --- e_[Sc/Fe] Error on [Sc/Fe]
626 I1 --- f_[Sc/Fe] Flag on [Sc/Fe] (2)
628-642 F15.12 --- [Ti/Fe] ? Titanium to iron abundance ratio
644-656 F13.11 --- e_[Ti/Fe] ? Error on [Ti/Fe]
658-659 I2 --- f_[Ti/Fe] Flag on [Ti/Fe] (2)
661-675 F15.12 --- [V/Fe] Vanadium to iron abundance ratio
677-689 F13.11 --- e_[V/Fe] Error on [V/Fe]
691 I1 --- f_[V/Fe] Flag on [V/Fe] (2)
693-707 F15.12 --- [Cr/Fe] Chromium to iron abundance ratio
709-721 F13.11 --- e_[Cr/Fe] Error on [Cr/Fe]
723 I1 --- f_[Cr/Fe] Flag on [Cr/Fe] (2)
725-739 F15.12 --- [Mn/Fe] Manganese to iron abundance ratio
741-753 F13.11 --- e_[Mn/Fe] Error on [Mn/Fe]
755 I1 --- f_[Mn/Fe] Flag on [Mn/Fe] (2)
757-771 F15.12 --- [Co/Fe] Cobalt to iron abundance ratio
773-785 F13.11 --- e_[Co/Fe] Error on [Co/Fe]
787 I1 --- f_[Co/Fe] Flag on [Co/Fe] (2)
789-803 F15.12 --- [Ni/Fe] Nickel to iron abundance ratio
805-817 F13.11 --- e_[Ni/Fe] Error on [Ni/Fe]
819 I1 --- f_[Ni/Fe] Flag on [Ni/Fe] (2)
821-834 F14.11 --- [Cu/Fe] Copper to iron abundance ratio
836-848 F13.11 --- e_[Cu/Fe] Error on [Cu/Fe]
850 I1 --- f_[Cu/Fe] Flag on [Cu/Fe] (2)
852-866 F15.12 --- [Zn/Fe] Zinc to iron abundance ratio
868-880 F13.11 --- e_[Zn/Fe] Error on [Zn/Fe]
882 I1 --- f_[Zn/Fe] Flag on [Zn/Fe] (2)
884-897 F14.11 --- [Y/Fe] Yttrium to iron abundance ratio
899-911 F13.11 --- e_[Y/Fe] Error on [Y/Fe]
913 I1 --- f_[Y/Fe] Flag on [Y/Fe] (2)
915-928 F14.11 --- [Ba/Fe] Barium to iron abundance ratio
930-942 F13.11 --- e_[Ba/Fe] Error on [Ba/Fe]
944 I1 --- f_[Ba/Fe] Flag on [Ba/Fe] (2)
946-960 F15.12 --- [La/Fe] Lanthanum to iron abundance ratio
962-974 F13.11 --- e_[La/Fe] Error on [La/Fe]
976 I1 --- f_[La/Fe] Flag on [La/Fe] (2)
978-992 F15.12 --- [Eu/Fe] Europium to iron abundance ratio
994-1006 F13.11 --- e_[Eu/Fe] Error on [Eu/Fe]
1008 I1 --- f_[Eu/Fe] Flag on [Eu/Fe] (2)
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Note (1): flagcannon as follows:
0 = No flag recommended
+1 (1st bit raised) = The Cannon starts to extrapolate.
For some stars the values could be incorrect
+2 (2nd bit raised) = The chi2 of the best fitting model spectrum is
significantly higher or lower
+4 (3rd bit raised) = Reduction flag raised
+8 (4th bit raised) = Binary star
+16 (5th bit raised) = Negative flux
+32 (6th bit raised) = Oscillating continuum
+64 (7th bit raised) = General reduction issues
+128 (8th bit raised) = Emission lines
Note (2): Abundance flag as follows:
0 = No flag recommended
+1 (1st bit raised) = Line strength below 2-sigma upper limit
+2 (2nd bit raised) = The Cannon starts to extrapolate.
For some stars the values could be incorrect
+4 (3rd bit raised) = The chi2 of the best fitting model spectrum is
significantly higher or lower
+8 (4th bit raised) = flagcannon is not 0
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 04-Jul-2022