J/MNRAS/480/5242 (non-)existence of five sparse open clusters (Kos+, 2018)
The GALAH survey and Gaia DR2:
(non-)existence of five sparse high-latitude open clusters.
Kos J., de Silva G., Buder S., Bland-Hawthorn J., Sharma S., Asplund M.,
D'Orazi V., Duong L., Freeman K., Lewis G.F., Lin J., Lind K.,
Martell S.L., Schlesinger K.J., Simpson J.D., Zucker D.B., Zwitter T.,
Bedding T.R., Cotar K., Horner J., Nordlander T., Stello D., Ting Y.-S.,
Traven G.
<Mon. Not. R. Astron. Soc., 480, 5242-5259 (2018)>
=2018MNRAS.480.5242K 2018MNRAS.480.5242K (SIMBAD/NED BibCode)
ADC_Keywords: Radial velocities ; Proper motions ; Surveys ; Clusters, open ;
Abundances ; Optical
Keywords: techniques: radial velocities - catalogues - surveys - parallaxes -
proper motions
Abstract:
Sparse open clusters can be found at high galactic latitudes where
loosely populated clusters are more easily detected against the lower
stellar background. Because most star formation takes place in the
thin disc, the observed population of clusters far from the Galactic
plane is hard to explain. We combined spectral parameters from the
GALAH survey with the Gaia DR2 catalogue to study the dynamics and
chemistry of five old sparse high-latitude clusters in more detail. We
find that four of them (NGC 1252, NGC 6994, NGC 7772, NGC 7826) -
originally classified in 1888 - are not clusters but are instead
chance projections on the sky. Member stars quoted in the literature
for these four clusters are unrelated in our multidimensional physical
parameter space; the quoted cluster properties in the literature are
therefore meaningless. We confirm the existence of visually similar
NGC 1901 for which we provide a probabilistic membership analysis. An
overdensity in three spatial dimensions proves to be enough to
reliably detect sparse clusters, but the whole six-dimensional space
must be used to identify members with high confidence, as demonstrated
in the case of NGC 1901.
Description:
Stars observed as a part of the GALAH survey are selected from the
2MASS catalogue (Skrutskie et al. 2006AJ....131.1163S 2006AJ....131.1163S, Cat. VII/233).
Depending on the observing mode, all the stars in a 1°radius
field are in a magnitude range 12<V<14 for regular fields and 9<V<12
for bright fields.
Most of the data used in this work comes from the Gaia DR2 (Gaia
Collaboration 2018A&A...616A...1G 2018A&A...616A...1G, Cat. I/345), which includes
positions, G magnitudes, proper motions and parallaxes for more than
1.3 billion stars. This part of the catalogue is essentially complete
for 12<G<17, which is the range where we expect to find most of the
cluster stars discussed in this paper. There are, however, a few
members of the four alleged clusters that are brighter than G=12 and
are not included in Gaia DR2, but do not impact the results of this
paper. We also disregarded all stars with the proper motion
error>0.5mas/yr or parallax error>10 per cent. Radial velocities in
Gaia DR2 are only given for 7.2 million stars down to G=13. Because
the precision of radial velocities is significantly higher in the
GALAH survey (Zwitter et al. 2018MNRAS.481..645Z 2018MNRAS.481..645Z) than the Gaia data
release, we use GALAH values wherever available. Because GALAH has a
more limited magnitude range than Gaia, there are many stars for which
Gaia DR2 radial velocities must be used. From the cluster stars used
in this work that have radial velocity measured in both Gaia DR2 and
GALAH we find no systematic differences larger than 0.2km/s between
the two surveys, so we can use whichever velocity is available.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 191 1 Final parameters for NGC 1901
tablea1.dat 66 39 *Coordinates, proper motions, parallax, and radial
velocity (where known) of NGC 1252 members from
the literature
tablea2.dat 66 11 *Coordinates, proper motions, parallax, and radial
velocity (where known) of NGC 6994 members from
the literature
tablea3.dat 66 21 *Coordinates, proper motions, parallax, and radial
velocity (where known) of NGC 7772 members from
the literature
tablea4.dat 66 11 *Coordinates, proper motions, parallax, and radial
velocity (where known) of NGC 7826 members from
the literature
tableb1.dat 113 71 List of most probable NGC 1901 members ordered
by probability
tablec1.dat 135 8 Effective temperature, gravity, and abundances
for 19 elements in eight NGC 1901 stars
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Note on tablea1.dat: Not a single pair of stars can be found with matching
parameters. Between all four sources the magnitudes of the stars extend
from V=6.62 to V=17.97
Note on tablea2.dat: Not a single pair of stars can be found with matching
parameters. The magnitudes of the stars extend from V=10.35 to V=19.53
Note on tablea3.dat: Not a single pair of stars can be found with matching
parameters. Between both sources the magnitudes of the stars extend
from V=11.08 to V=18.00
Note on tablea4.dat: Not a single pair of stars can be found with matching
parameters. The magnitudes of the stars extend from V=9.72 to V=16.67
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/MNRAS/478/4513 : GALAH Survey DR2 (Buder+, 2018)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 F6.3 deg RAdeg Right Ascension (ICRS) at Ep=2015.5 from
GAIA DR2 (1)
8- 12 F5.3 deg e_RAdeg Error on RAdeg (1)
14- 20 F7.3 deg DEdeg Declination (ICRS) at Ep=2015.5 from
GAIA DR2 (1)
22- 26 F5.3 deg e_DEdeg Error on DEdeg (1)
28- 34 F7.3 deg GLON Galactic longitude (1)
36- 40 F5.3 deg e_GLON Error on GLON (1)
42- 48 F7.3 deg GLAT Galactic latitude (1)
50- 54 F5.3 deg e_GLAT Error on GLAT (1)
56- 58 F3.1 arcsec r0 Core radius, where the radial density
profile falls sharply (2)
60- 62 F3.1 arcsec e_r0 Error on r0 (2)
64- 67 F4.1 arcsec r1 Radius at which the density stops
abruptly (2)
69- 71 F3.1 arcsec e_r1 Error on r1 (2)
73- 76 F4.1 arcsec r2 Radius at which the density becomes
indistinguishable from the density of the
surrounding field (2)
78- 81 F4.1 arcsec e_r2 Error on r2 (2)
83- 85 F3.1 arcsec rc Fitted King's core radius (3)
87- 89 F3.1 arcsec e_rc Error on rc (3)
91 A1 --- l_rt Lower limit of rt (3)
92- 93 I2 arcsec rt Fitted King's tidal radius (3)
95- 99 F5.3 mas/yr pmRA Proper motion in right ascension
(pmRAxcosDE) (4)
101-105 F5.3 mas/yr e_pmRA Error on pmRA (4)
107-112 F6.3 mas/yr pmDE Proper motion in declination (4)
114-118 F5.3 mas/yr e_pmDE Error on pmDE (4)
120-123 F4.2 km/s RV Radial velocity (5)
125-128 F4.2 km/s e_RV Error on RV (5)
130-134 F5.3 mas plx Parallax
136-140 F5.3 mas e_plx Error on plx
142-146 F5.1 pc Dist Distance inferred from plx (6)
148-150 F3.1 pc e_Dist Error on Dist (6)
152-155 F4.2 km/s sigRV Velocity dispersion (5)
157-160 F4.2 km/s e_sigRV Error on sigRV (5)
162-166 F5.2 --- [Fe/H] Iron abundance (7)
168-171 F4.2 --- e_[Fe/H] Error on [Fe/H] (7)
173-176 F4.2 --- [alpha/Fe] α-element to iron abundance ratio (7)
178-181 F4.2 --- e_[alpha/Fe] Error on [alpha/Fe] (7)
183-186 F4.2 [yr] logAge Age calculated by isochrone fitting
188-191 F4.2 [yr] e_logAge Error on logAge
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Note (1): RA, DE and GLON, GLAT give the cluster centre in celestial and
galactic coordinates, respectively
Note (2): Radii r0, r1, and r2 are estimated visually as described in
Kharchenko et al. (2012A&A...543A.156K 2012A&A...543A.156K, Cat. J/A+A/543/A156)
Note (3): King's (King 1962AJ.....67..471K 1962AJ.....67..471K) core radius (rc) and tidal radius
(rt) are fitted, although we were unable to measure the tidal radius
with any meaningful confidence
Note (4): Proper motions are the mean values for the cluster and the
uncertainties relate to the mean, not to the dispersion
Note (5): The radial velocity and the velocity dispersion are measured from a
combination of Gaia DR2 and GALAH radial velocities
Note (6): The distance is calculated from the parallaxes. A normal distribution
for the parallax of each star was sampled and the distance calculated
for every sample. The reported distance and its uncertainty are the
mean and standard deviation of all the samples for all members.
Distance uncertainty might be underestimated, if the parallaxes of
individual stars have correlated errors
Note (7): Iron and α abundances are calculated by SME
(Valenti & Piskunov 1996A&AS..118..595V 1996A&AS..118..595V;
Piskunov & Valenti 2017A&A...597A..16P 2017A&A...597A..16P) from the GALAH spectra in the
same manner as in Buder et al. (2018MNRAS.478.4513B 2018MNRAS.478.4513B,
Cat. J/MNRAS/478/4513) and are based on eight members only
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Byte-by-byte Description of file: tablea*
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 F8.4 deg RAdeg Right ascension (ICRS) at Ep=2015.5 from
GAIA DR2
10- 17 F8.4 deg DEdeg Declination (ICRS) at Ep=2015.5 from GAIA DR2
19- 24 F6.2 mas/yr pmRA Proper motion in right ascension
(pmRAxcosDE)
26- 29 F4.2 mas/yr e_pmRA Error on pmRA
31- 36 F6.2 mas/yr pmDE Proper motion on declination
38- 41 F4.2 mas/yr e_pmDE Error on pmDE
43- 47 F5.2 mas plx Parallax
49- 52 F4.2 mas e_plx Error on plx
54- 58 F5.1 km/s RV ? Radial velocity
60- 62 F3.1 km/s e_RV ? Error on RV
64 A1 --- r_RV ? Reference of the values of RV (1)
66 A1 --- MembRef Member reference (2)
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Note (1): References as follows:
a = Radial velocity from Gaia DR2 (2018A&A...616A...1G 2018A&A...616A...1G, Cat. I/345)
b = Radial velocity from GALAH (2018MNRAS.478.4513B 2018MNRAS.478.4513B, Cat. J/MNRAS/478/4513)
Note (2): Member reference as follows:
a = Members in Kharchenko et al. (2013A&A...558A..53K 2013A&A...558A..53K, Cat. J/A+A/558/A53)
with probability>0.8
b = Members in de la Fuente Marcos et al. (2013MNRAS.434..194D 2013MNRAS.434..194D,
Cat. J/MNRAS/434/194)
c = Members in Pavani et al. (2001A&A...374..554P 2001A&A...374..554P)
d = Members in Bouchet & The (1983PASP...95..474B 1983PASP...95..474B)
e = Members in Bassino et al. (2000A&A...355..138B 2000A&A...355..138B, Cat. J/A+A/355/138)
f = Members in Carraro (2002A&A...385..471C 2002A&A...385..471C, Cat. J/A+A/385/471)
g = Members in Dias et al. (2002A&A...389..871D 2002A&A...389..871D, Cat. B/ocl)
with probability>0.9
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Byte-by-byte Description of file: tableb1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 I19 --- GaiaDR2 Gaia DR2 source ID
21- 27 F7.4 deg RAdeg Right ascension (ICRS) at Ep=2015.5 from
GAIA DR2
29- 36 F8.4 deg DEdeg Declination (ICRS) at Ep=2015.5 from GAIA DR2
38- 42 F5.3 deg r Distance from the cluster center
44- 48 F5.3 mas/yr pmRA Proper motion in right ascension
(pmRAxcosDE)
50- 54 F5.3 mas/yr e_pmRA Error on pmRA
56- 61 F6.3 mas/yr pmDE Proper motion on declination
63- 67 F5.3 mas/yr e_pmDE Error on pmDE
69- 73 F5.3 mas plx Parallax
75- 79 F5.3 mas e_plx Error on plx
81- 85 F5.2 mag Gmag Gaia G-band magnitude
87- 92 F6.2 km/s RV ? Radial velocity
94- 97 F4.2 km/s e_RV ? Error on RV
99 A1 --- r_RV [*] Reference of RV (1)
101-105 F5.3 --- P5D Probability of being a member without taking
into account the radial velocity of the star
107-111 F5.3 --- P6D ? Probability of being a member with radial
velocity taken into account
113 A1 --- Binary ? Possible binary marked as 'y' (2)
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Note (1): * = Radial velocity taken from GALAH (2018MNRAS.478.4513B 2018MNRAS.478.4513B,
Cat. J/MNRAS/478/4513)
Note (2): Possible binaries have been identified from the GALAH spectra for
stars with GALAH radial velocity only
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Byte-by-byte Description of file: tablec1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 I19 --- GaiaDR2 Gaia DR2 source ID
21- 24 I4 K Teff Effective temperature
26- 29 F4.2 [cm/s2] logg Surface gravity
31- 34 F4.2 --- [Li/Fe] ? Lithium to iron abundance ratio
36- 39 F4.2 --- [C/Fe] ? Carbon to iron abundance ratio
41- 45 F5.2 --- [O/Fe] Oxygen to iron abundance ratio
47- 51 F5.2 --- [Na/Fe] Sodium to iron abundance ratio
53- 57 F5.2 --- [Mg/Fe] Magnesium to iron abundance ratio
59- 63 F5.2 --- [Al/Fe] ? Aluminum to iron abundance ratio
65- 68 F4.2 --- [Si/Fe] ? Silicon to iron abundance ratio
70- 73 F4.2 --- [K/Fe] Potassium to iron abundance ratio
75- 79 F5.2 --- [Ca/Fe] ? Calcium to iron abundance ratio
81- 84 F4.2 --- [Sc/Fe] ? Scandium to iron abundance ratio
86- 90 F5.2 --- [Ti/Fe] ? Titanium to iron abundance ratio
92- 96 F5.2 --- [Cr/Fe] ? Chromium to iron abundance ratio
98-102 F5.2 --- [Mn/Fe] ? Manganese to iron abundance ratio
104-108 F5.2 --- [Fe/H] Iron abundance
110-113 F4.2 --- [Ni/Fe] ? Nickel to iron abundance ratio
115-119 F5.2 --- [Cu/Fe] ? Copper to iron abundance ratio
121-125 F5.2 --- [Zn/Fe] ? Zinc to iron abundance ratio
127-130 F4.2 --- [Y/Fe] ? Yttrium to iron abundance ratio
132-135 F4.2 --- [Ba/Fe] Barium to iron abundance ratio
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(End) Ana Fiallos [CDS] 01-Jun-2022