J/MNRAS/511/6179 Low-mass cool dwarfs of NYMGs from Gaia EDR3 (Lee+, 2022)
Low-mass members of nearby young stellar moving groups from Gaia EDR3.
Lee J., Song I., Murphy S.J.
<Mon. Not. R. Astron. Soc. 511, 6179-6192 (2022)>
=2022MNRAS.511.6179L 2022MNRAS.511.6179L (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Stars, nearby ; Stars, M-type ; Stars, L-type ;
Associations, stellar ; Stars, early-type ; Stars, dwarfs ;
Stars, brown dwarf ; Cross identifications ; Combined data ;
Positional data ; Proper motions ; Parallaxes, trigonometric ;
Radial velocities ; Optical ; Ultraviolet ; Infrared ;
Photometry ; Spectroscopy ; Spectral types ; Equivalent widths
Keywords: (stars:) brown dwarfs - stars: late-type - stars: low-mass -
(Galaxy:) open clusters and associations: general -
(Galaxy:) solar neighbourhood
Abstract:
Gaia EDR3 offers greatly improved kinematics for nearby objects,
including members of nearby young stellar moving groups (NYMGs). In
this study, we aim to identify low-mass NYMG members (spectral types
of M0 to mid-L) in Gaia EDR3. We calculated spatio-kinematic
membership probabilities by utilizing a Bayesian membership
probability calculation scheme developed in our previous study. We
evaluated stellar youth primarily based on colour-magnitude diagram
positions. Combining spatio-kinematic membership assessment and youth
evaluation, we identified ∼2900 low-mass NYMG candidate members,
including ∼700 previously claimed members. In the set of ∼2200 new
candidate members, ∼550 appear to be young based on NUV brightness.
Our pilot spectroscopic study with Wide Field Spectrograph (WiFeS) on
the ANU 2.3-m telescope observed 78 candidates, with 79 per cent
confirmed as members. Using our new member sample, we estimated an
isochronal age of the β Pictoris Moving Group. The mean age (∼10
Myr), which is around half the age of recent estimates, suggests
either a truly younger age of the β Pictoris Moving Group or
inaccuracies in contemporary isochrones. As the main results of this
study, we provide lists of newly confirmed and candidate low-mass NYMG
members.
Description:
Similar to the BANYAN method, we have developed a membership
probability calculation scheme, the Bayesian Analysis of Moving
Groups. BAMG offers several improvements over BANYAN, such as using a
more realistic field star model and less dependency on the initial
choice of members. The most recent version of the BAMG code updates
the groups based on the unsupervised machine learning analysis of nine
known NYMGs. Using 652 previously confirmed members of the nine NYMGs,
our unsupervised machine learning analysis recognized eight distinct
groups.
In this paper, we utilize the properties of the eight recognized
moving groups to identify previously unknown low-mass members included
in the Gaia EDR3 catalogue enables identification of very low-mass
NYMG members thanks to precise parallax measurements which can be also
used for the assessment of youth (≲ 150 Myr) from CMDs because
young stars and brown dwarfs are overluminous compared to their older
counterparts. Additionally, Gaia EDR3 includes RV measurements for
some stars down to early-M type stars, which makes a complete set of
astrometric parameters to calculate robust NYMG membership
probabilities. In this study, we present ∼2200 new low-mass (spectral
types of M0 to mid-L) NYMG candidate members identified by a combined
assessment of their spatio-kinematic membership and youth.
As explained in the result section 3.1.1 Cool dwarf members, NYMG
candidate selection combining Pkin and Youth(CMD). The
spatio-kinematic NYMG candidates and young candidates were
cross-matched, retaining 2611 stars, including 203 stars with RV
measurements. These 203 stars have full astrometric parameters and
confirmed youth based on a CMD, so we call them highly likely members.
However, because of potential binary contamination, these stars still
need to be considered as candidate members until confirmed by
follow-up spectroscopic observations.Among these 2611 candidate
members, 609 have been claimed in the literature. The remaining 2002
stars are therefore new NYMG candidate members, and details of the
entire sample are provided in online tables. The 139 new highly likely
members having RVs are listed in the table4.dat. While the remaining
1863 new candidates without RVs are presented in the tableb1.dat.
Next, as explained in the result section 3.1.2 Ultracool dwarf
members, About two thousand ultracool dwarf candidates have
spatio-kinematic membership probabilities larger than 90 per cent
where from it we eliminate high-sigma astrometric-photometric, 817
objects were retained. Then the criteria for youth evaluation using
the three CMDs (i.e see section 2.2.2 Ultracool dwarfs were applied to
these objects. The numbers of objects assessed as young and probably
young are 180 and 107, respectively. Among these 287 candidate
members, 56 have been claimed in the literature. The 231 new ultracool
dwarf candidate members are listed in table6.dat.
Finally (i.e see section 3.2 Pilot spectroscopic observations), for
our results tables, spectroscopic follow-up observations are required
to obtain confirmation of youth (e.g. low surface gravity) for the
ultracool dwarf candidates and remove any remaining contaminants from
the sample. We obtained optical spectra for a subset of the candidates
with the WiFeS using the red grating which covers 5300-7060 Å. We
measured the RV of each spectrum ispec via cross-correlation against
the provided HARPS/SOPHIE line mask. In total 78 candidates fulfilling
the Pkin and Youth(CMD) selection criteria were observed with WiFeS.
Their newly obtained RVs were used in the re-calculation of their
Pkin, and 79 per cent (N = 62) still returned Pkin above the
threshold. Such a large hit rate proves the effectiveness of the BAMG
code in the NYMG member identification. Among these 62 members, 27
were claimed previously in the literature. Excluding these 27 members,
the newly confirmed NYMG members (N = 35) are listed in table7.dat.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
group.dat 27 7 NYMG groups in our sample
table4.dat 174 139 The new highly likely members of NYMGs
identified having Gaia EDR3 RVs
tableb1.dat 171 1863 The new highly likely members of NYMGs
identified without Gaia EDR3 RV measurements
table6.dat 175 231 The newly suggested ultracool dwarf candidate
members of NYMGs
table7.dat 159 35 Newly confirmed NYMG members after obtaining
WiFeS optical spectra
--------------------------------------------------------------------------------
See also:
J/MNRAS/489/2189 : Nearby young moving groups with machine learning
(Lee+, 2019)
J/ApJ/862/138 : BANYAN. XIII. Nearby young assoc. with Gaia DR2
(Gagne+, 2018)
J/ApJ/798/73 : BANYAN All-Sky Survey (BASS) catalog. V. Nearby YMGs
(Gagne+, 2015)
J/ApJ/788/81 : BANYAN III. RVel and rotation of low-mass stars
(Malo+, 2014)
J/ApJ/783/121 : BANYAN II. Nearby young assoc. candidate members
(Gagne+, 2014)
J/ApJ/762/88 : Young stellar kinematic group candidate members
(Malo+, 2013)
J/A+A/619/L8 : Ultra-cool dwarfs candidates in Gaia DR2 (Reyle, 2018)
J/MNRAS/411/2770 : Hot white dwarfs in GALEX-DR5 (Bianchi+, 2011)
I/350 : Gaia EDR3 (Gaia Collaboration, 2020)
J/MNRAS/393/538 : Stellar association around gamma Vel (Jeffries+, 2009)
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
II/328 : AllWISE Data Release (Cutri+ 2013)
J/MNRAS/489/3625 : Applying Chronostar to β Pictoris group
(Crundall+, 2019)
J/AJ/153/95 : Catalog of Suspected Nearby Young Stars (Riedel+, 2017)
J/ApJ/758/56 : Young M dwarfs within 25pc. II. Kinematics
(Shkolnik+, 2012)
J/AJ/157/234 : ACRONYM. III. Candidate young low-mass stars
(Schneider+, 2019)
J/other/ARA+A/42.685 : Young stars near the Sun (Zuckerman+, 2004)
J/AJ/154/69 : ACRONYM II. The β Pictoris Moving Group
(Shkolnik+, 2017)
J/ApJ/833/96 : Hawaii infrared parallax program. II. Ultracool dwarfs
(Liu+, 2016)
J/A+A/590/A13 : New candidate members in young associations
(Elliott+, 2016)
Byte-by-byte Description of file: group.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- Group Nearby young stellar moving group NYMG (Group)
9- 10 I2 --- Ntab4 Relative number of group members in
the table4.dat
12- 15 I4 --- Ntabb1 Relative number of group members in
the tableb1.dat
17- 19 I3 --- Ntab6 Relative number of group members in
the table6.dat
21- 22 I2 --- Ntab7 Relative number of group members in
the table4.dat
24- 27 I4 --- Ntot Total number of group members
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- ID Identifier number (ID)
5- 23 I19 --- GaiaEDR3 Gaia EDR3 source identifier unique number
(GaiaEDR3source_id)
25- 31 A7 --- Group Nearby young stellar moving group NYMG
(Group)
33- 34 I2 h RAh Right Ascension (J2000)
36- 37 I2 min RAm Right Ascension (J2000)
39- 43 F5.2 s RAs Right Ascension (J2000)
45 A1 --- DE- Declination sign (J2000)
46- 47 I2 deg DEd Declination (J2000)
49- 50 I2 arcmin DEm Declination (J2000)
52- 55 F4.1 arcsec DEs [] Declination (J2000)
57- 64 F8.3 mas/yr pmRA Proper motion in right ascension pmRA*cosDE
of the source in ICRS at Ep=2016.0 (pmra)
66- 73 F8.3 mas/yr pmDE Proper motion in declination direction of
the source in ICRS at Ep=2016.0 (pmdec)
75- 81 F7.4 mas Plx Absolute stellar parallax of the source at
the Ep=2016.0 (plx)
83- 88 F6.2 km/s RV Gaia EDR3 radial velocity (rv)
90- 98 F9.6 mag Gmag G-band mean magnitude (Vega) (g)
100- 107 F8.6 mag BP-RP BP-RP colour (bp_rp)
109- 125 F17.14 % SPkin The sum of Pkin across multiple groups
denoted Σ Pkin (ΣPkin) (G1)
127- 144 F18.15 % Pkin The Pkin spatio-kinematic membership
probability for a single group is computed
with BAMG code (Pkin) (G2)
146- 163 F18.16 --- YouthCMD The Youth(CMD) parameter (YouthCMD) (G3)
165- 170 F6.3 mag NUVmag ? NUV magnitudes (AB mag) from GALEX DR5
Bianchi et al. 2011MNRAS.411.2770B 2011MNRAS.411.2770B,
Cat. J/MNRAS/411/2770 (NUV)
172- 174 F3.1 --- YouthNUV The Youth(NUV) parameter (YouthNUV) (1)
--------------------------------------------------------------------------------
Note (1): The Youth(NUV) parameter takes three values as follows:
0.0 = In the MNUV - GBPGRP plane figure 4, stars fainter than
the boundary line are likely old, 29 stars in our sample
1.0 = In the MNUV - GBPGRP plane figure 4, stars brighter than
the boundary line are evaluated as young, 59 stars in our
sample
2.0 = In the MNUV - GBPGRP plane figure 4, stars with youth
cannot be evaluated are indecisive of youth, 51 stars in our
sample
For youth evaluation young and old stars are distinguished around an
empirically determined boundary line as presented in the figure 4 of
the section 2.2.1 Cool dwarfs.
Stars that are either faint in NUV or near the Galactic plane
(|b| < 15°) are not in the GALEX DR5 catalogue. We considered an
upper limit for them, taking the sensitivity limit of GALEX
(NUV = 25.3 mag). As presented in the figure 4, we established an
empirical boundary based on a visual inspection that separates young
stars from old stars.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: tableb1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- ID Identifier number (ID)
6- 24 I19 --- GaiaEDR3 Gaia EDR3 source identifier unique number
(GaiaEDR3source_id)
26- 32 A7 --- Group Nearby young stellar moving group NYMG
(Group)
34- 35 I2 h RAh Right Ascension (J2000)
37- 38 I2 min RAm Right Ascension (J2000)
40- 44 F5.2 s RAs Right Ascension (J2000)
46 A1 --- DE- Declination sign (J2000)
47- 48 I2 deg DEd Declination (J2000)
50- 51 I2 arcmin DEm Declination (J2000)
53- 56 F4.1 arcsec DEs [] Declination (J2000)
58- 65 F8.3 mas/yr pmRA Proper motion in right ascension pmRA*cosDE
of the source in ICRS at Ep=2016.0 (pmra)
67- 74 F8.3 mas/yr pmDE Proper motion in declination direction of
the source in ICRS at Ep=2016.0 (pmdec)
76- 83 F8.4 mas Plx Absolute stellar parallax of the source at
the Ep=2016.0 (plx)
85- 93 F9.6 mag Gmag G-band mean magnitude (Vega) (g)
95- 102 F8.6 mag BP-RP BP-RP colour (bp_rp)
104- 121 F18.14 % SPkin The sum of Pkin across multiple groups
denoted Σ Pkin (ΣPkin) (G1)
123- 141 F19.15 % Pkin The Pkin spatio-kinematic membership
probability for a single group is computed
with BAMG code (Pkin) (G2)
143- 160 F18.16 --- YouthCMD The Youth(CMD) parameter (YouthCMD) (G3)
162- 167 F6.3 mag NUVmag ? NUV magnitudes (AB mag) from GALEX DR5
Bianchi et al. 2011MNRAS.411.2770B 2011MNRAS.411.2770B,
Cat. J/MNRAS/411/2770 (NUV)
169- 171 F3.1 --- YouthNUV The Youth(NUV) parameter (YouthNUV) (1)
--------------------------------------------------------------------------------
Note (1): The Youth(NUV) parameter takes three values as follows:
0.0 = In the MNUV - GBPGRP plane figure 4, stars fainter than
the boundary line are likely old, 379 stars in our sample
1.0 = In the MNUV - GBPGRP plane figure 4, stars brighter than
the boundary line are evaluated as young, 463 stars in our
sample
2.0 = In the MNUV - GBPGRP plane figure 4, stars with youth
cannot be evaluated are indecisive of youth, 1021 stars in our
sample
Stars that are either faint in NUV or near the Galactic plane
(|b| < 15°) are not in the GALEX DR5 catalogue. We considered an
upper limit for them, taking the sensitivity limit of GALEX
(NUV = 25.3 mag). As presented in the figure 4, we established an
empirical boundary based on a visual inspection that separates young
stars from old stars.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table6.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- ID Identifier number (ID)
5- 23 I19 --- GaiaEDR3 Gaia EDR3 source identifier unique number
(GaiaEDR3source_id)
25- 31 A7 --- Group Nearby young stellar moving group NYMG
(Group)
33- 34 I2 h RAh Right Ascension (J2000)
36- 37 I2 min RAm Right Ascension (J2000)
39- 43 F5.2 s RAs Right Ascension (J2000)
45 A1 --- DE- Declination sign (J2000)
46- 47 I2 deg DEd Declination (J2000)
49- 50 I2 arcmin DEm Declination (J2000)
52- 55 F4.1 arcsec DEs [] Declination (J2000)
57- 64 F8.3 mas/yr pmRA Proper motion in right ascension pmRA*cosDE
of the source in ICRS at Ep=2016.0 (pmra)
66- 73 F8.3 mas/yr pmDE Proper motion in declination direction of
the source in ICRS at Ep=2016.0 (pmdec)
75- 82 F8.4 mas Plx Absolute stellar parallax of the source at
the Ep=2016.0 (plx)
84- 92 F9.6 mag Gmag G-band mean magnitude (Vega) (g)
94- 99 F6.3 mag Jmag J-band at 1.25 µm apparent magnitude
(Vega) from the 2MASS catalogue Cutri et al.
2003, Cat. II/246 (j)
101- 106 F6.3 mag Hmag H-band at 1.65 µm apparent magnitude
(Vega) from the 2MASS catalogue Cutri et al.
2003, Cat. II/246 (h)
108- 113 F6.3 mag Kmag Ks-band at 1.85 µm apparent magnitude
(Vega) from the 2MASS catalogue Cutri et al.
2003, Cat. II/246 (k)
115- 120 F6.3 mag W1mag W1-band at 3.35 µm apparent magnitude
(Vega) from the ALLWISE catalogue Cutri et
al. 2014, Cat. II/328 (w1)
122- 127 F6.3 mag W2mag W2-band at 4.6 µm apparent magnitude
(Vega) from the ALLWISE catalogue Cutri et
al. 2014, Cat. II/328 (w2)
129- 145 F17.14 % SPkin The sum of Pkin across multiple groups
denoted Σ Pkin (ΣPkin) (G1)
147- 164 F18.15 % Pkin The Pkin spatio-kinematic membership
probability for a single group is computed
with BAMG code (Pkin) (G2)
166- 171 F6.3 mag NUVmag ? NUV magnitudes (AB mag) from GALEX DR5
Bianchi et al. 2011MNRAS.411.2770B 2011MNRAS.411.2770B, Cat.
J/MNRAS/411/2770 (NUV)
173- 175 F3.1 --- YouthNUV The Youth(NUV) parameter (YouthNUV) (1)
--------------------------------------------------------------------------------
Note (1): The Youth(NUV) parameter takes three values as follows:
0.0 = Assigned as old stars, 58 objects in our sample
1.0 = Assigned as young stars, 33 objects in our sample
2.0 = Indecisive of youth assessment, 140 objects in our sample
For youth evaluation young and old stars distinguished with CMD
procedure explained in the section 2.2.2 Ultracool dwarfs UCDs.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table7.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 I19 --- GaiaEDR3 Gaia EDR3 source identifier unique number
(GaiaEDR3source_id)
21- 27 A7 --- Group Nearby young stellar moving group NYMG
(Group)
29- 32 A4 --- SpType Spectral type from observations detailed in
the section 3.2 Pilot spectroscopic
observations (SpT)
34- 35 I2 h RAh Right Ascension (J2000)
37- 38 I2 min RAm Right Ascension (J2000)
40- 44 F5.2 s RAs Right Ascension (J2000)
46 A1 --- DE- Declination sign (J2000)
47- 48 I2 deg DEd Declination (J2000)
50- 51 I2 arcmin DEm Declination (J2000)
53- 56 F4.1 arcsec DEs [] Declination (J2000)
58- 64 F7.2 mas/yr pmRA Proper motion in right ascension pmRA*cosDE
of the source in ICRS at Ep=2016.0 (pmra)
66- 72 F7.2 mas/yr pmDE Proper motion in declination direction of
the source in ICRS at Ep=2016.0 (pmdec)
74- 78 F5.2 mas Plx Absolute stellar parallax of the source at
the Ep=2016.0 (plx)
80- 85 F6.2 km/s RV Newly obtained measured RV (RV) (2)
87- 90 F4.2 km/s e_RV Uncertainty of RV measurements (errRV)
92- 96 F5.2 mag Gmag G-band mean magnitude (Vega) (g)
98- 102 F5.2 mag BPmag Integrated BP mean magnitude (Vega) (BPmag)
104- 108 F5.2 mag RPmag Integrated RP mean magnitude (Vega) (RPmag)
110- 114 F5.2 mag NUVmag ? NUV magnitudes (AB mag) from GALEX DR5
Bianchi et al. 2011MNRAS.411.2770B 2011MNRAS.411.2770B, Cat.
J/MNRAS/411/2770 (NUV)
116- 120 F5.2 0.1nm EWHa Equivalent width of Hα emission line
are measured with the splot task in IRAF
(EWHα)
122- 125 F4.2 0.1nm e_EWHa EWHa uncertainties are calculated using
equation 6 of Cayrel 1988IAUS..132..345C 1988IAUS..132..345C
(errEWHα)
127 A1 --- l_EWLi Upper limit flag of EWLi values in the case
of non-detection, upper limits are provided
129- 131 I3 10-4nm EWLi Equivalent width of Li 6708 Å emission
line measured with the splot task in IRAF
(EWLi)
133- 135 I3 10-4nm e_EWLi ? EWLi uncertainties are calculated using
equation 6 of Cayrel 1988IAUS..132..345C 1988IAUS..132..345C
(errEWLi)
137- 139 I3 % Pkin Recomputed Pkin with the RV new values
and applying procedure explicited in the
section 2 Method (Pkin)
141 A1 --- f_Pkin Flag indicating with Pkin of a single
group is less than 90 per cent and
ΣPkin => 90 per cent (G2)
143- 146 F4.2 --- YouthCMD The Youth(CMD) parameter (YouthCMD) (G3)
148 I1 --- YouthNUV [] The Youth(NUV) parameter (YouthNUV) (1)
150- 159 A10 "Y:M:D" Obs Observation date WiFeS spectrograph
(Obs.date)
--------------------------------------------------------------------------------
Note (1): The Youth(NUV) parameter takes three values as follows:
0 = Assigned as old stars, 5 objects in our sample
1 = Assigned as young stars, 27 objects in our sample
2 = Indecisive of youth assessment, 3 objects in our sample
For youth evaluation young and old stars distinguished with CMD
procedure explained in the section 2.2.2 Ultracool dwarfs UCDs and in
the section 2.2.1 Cool dwarfs.
Note (2): Obtained with the red R7000 grating of the WiFeS which covers
5300-7060 Å, each RV is computed with ISPEC via cross-correlation
against the provided HARPS/SOPHIE line mask taken from Blanco-Cuaresma
et al. 2014A&A...569A.111B 2014A&A...569A.111B, 2019MNRAS.486.2075B 2019MNRAS.486.2075B.
--------------------------------------------------------------------------------
Global notes:
Note (G1): SPkin computed with each spatio-kinematic membership probability
calculation using a candidate's six astrometric parameters are
required (RA,Dec,pmRA,pmDE,Dist,RV).
Note (G2): As mentionned in the section 2.1 Spatio-kinematic membership
assessment, to be considered as potential candidate members, we adopt
a threshold of Pkin => 90 per cent, as was used in Paper II. If the
source has Pkin => 90 per cent in any of the eight NYMGs considered
in this paper, then the source is retained as a candidate member.
Sources having a marginal Pkin value (< 90 per cent) for a group
but the sum of Pkin across multiple groups over the threshold
(ΣPkin => 90) are retained, they are considered to have
ambiguous membership status for a single group. For more details on
the BAMG algorithm and the definition of these moving groups, we
refer the reader to Papers I, II, and III.
Spatio-kinematic membership is assessed using the Bayesian Analysis
of Moving Groups code BAMG from Lee & Song :
2018MNRAS.475.2955L 2018MNRAS.475.2955L Paper I,
2019MNRAS.486.3434L 2019MNRAS.486.3434L Paper II,
2019MNRAS.489.2189L 2019MNRAS.489.2189L Paper III, Cat. J/MNRAS/489/2189.
Note (G3): Quantifying how close a star's position on the CMD is to that of
young stars, value ranges from 0.0 to 1.0 which corresponds to the
CMD position of old and young stars respectively.
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History:
From electronic version of the journal
(End) Luc Trabelsi [CDS] 07-Feb-2025