J/AJ/168/206 Stars in Theia 456 from Gaia & MMT spectra (Tregoning+, 2024)
Theia 456: tidally shredding an open cluster.
Tregoning K.R., Andrews J.J., Agueros M.A., Cargile P.A., Chaname J.,
Curtis J.L., Schuler S.C.
<Astron. J., 168, 206 (2024)>
=2024AJ....168..206T 2024AJ....168..206T
ADC_Keywords: Clusters, open; Positional data; Radial velocities;
Spectra, optical; Rotational velocities; Abundances, [Fe/H];
Proper motions; Parallaxes, trigonometric; Stars, diameters;
Stars, ages; Stars, masses; Associations, stellar
Keywords: Star clusters ; Stellar dynamics ; Astrometry ; Galaxy tides ;
Stellar ages
Abstract:
The application of clustering algorithms to the Gaia astrometric
catalog has revolutionized our census of stellar populations in the
milky Way, including the discovery of many new dispersed structures.
We focus on one such structure, Theia 456 (COIN-Gaia-13), a loosely
bound collection of ∼320 stars spanning ∼120pc that has previously
been shown to exhibit kinematic, chemical, and gyrochronal coherency,
indicating a common origin. We obtain follow-up radial velocities and
supplement these with Gaia astrometry to perform an in-depth dynamical
analysis of Theia 456. By integrating stellar orbits through a Milky
Way potential, we find the currently dispersed structure coalesced
into a small cluster in the past. Via Bayesian modeling, we derive a
kinematic age of 245±3Myr (statistical), a half-mass-radius of
9±2pc, and an initial one-dimensional velocity dispersion of
0.14±0.02km/s. Our results are entirely independent of model
isochrones, details of stellar evolution, and internal cluster
dynamics, and the statistical precision in our age derivation rivals
that of the most precise age-dating techniques known today, though our
imperfect knowledge of the Milky Way potential and simple spherical
model for Theia 456 at birth add additional uncertainties. Using
posterior predictive checking, we confirm these results are robust
under reasonable variations to the Milky Way potential. Such
low-density structures that are disrupted by the Galactic tides before
virializing may be ubiquitous, signifying that Theia 456 is a valuable
benchmark for studying the dynamical history of stellar populations in
the Milky Way.
Description:
Data are obtained for members of Theia 456 with the Hectochelle
multiobject spectrograph on the Multiple Mirror Telescope (MMT) in
Arizona, USA. We use the RV31 filter setup, resulting in spectra with
a resolution of R∼32000 over a single wavelength range of 5150-5300Å.
We observe six fields along Theia 456, placing Hectochelle fibers on
kinematically selected cluster members. Each field was carefully
selected to simultaneously maximize the number of high-confidence,
bright cluster members (down to G∼18mag), while providing information
about stars across its extent.
In order to obtain a useful dynamical sample, we first refine the
catalog of Theia 456 members reported in Andrews+ 2022, J/AJ/163/275
in order to accurately determine Theia 456's median astrometric
quantities for comparison with the stars with Hectochelle radial
velocities. See Section 2.2.
Objects:
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RA (2000) DE Designation(s)
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05 32 44.63 +42 05 13.2 Theia 456 = [CKS2019] COIN-Gaia 13
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 336 321 Theia 456 catalog, phase-space and astrometry
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See also:
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
V/164 : LAMOST DR5 catalogs (Luo+, 2019)
J/ApJ/799/136 : IN-SYNC. II. Cand. young stars in NGC 1333 (Foster+, 2015)
J/A+A/618/A93 : Gaia DR2 open clusters in the MW (Cantat-Gaudin+, 2018)
J/MNRAS/473/849 : Mass segregation in Galactic stellar clusters (Dib+, 2018)
J/A+A/624/A126 : New open clusters in Perseus direction (Cantat-Gaudin+, 2019)
J/AJ/158/122 : Local structure & star formation hist. of MW (Kounkel+, 2019)
J/ApJ/870/32 : Kinematics in young star clusters & assoc. (Kuhn+, 2019)
J/A+A/633/A99 : GaiaDR2 open clusters in Milky Way. II (Cantat-Gaudin+, 2020)
J/ApJ/904/140 : Ruprecht 147 members & rot. data: 5 other cl. (Curtis+, 2020)
J/AJ/160/279 : Untangling the Gal. II. Within 3kpc (Kounkel+, 2020)
J/AJ/160/44 : Upper Scorpius spectroscopy and photometry (Luhman+, 2020)
J/ApJ/904/196 : Stellar parameters of a Young Stellar Snake (Tian, 2020)
J/AJ/159/166 : Membership & data of moving groups: Gaia (Ujjwal+, 2020)
J/MNRAS/495/663 : Gaia DR2 OB associations (Ward+, 2020)
J/A+A/646/A104 : Improving the open cluster census. I. (Hunt+, 2021)
J/ApJ/917/23 : SPYGLASS. I. Mapping young stellar structures (Kerr+, 2021)
J/A+A/645/A84 : Coronae of nearby star clusters (Meingast+, 2021)
J/MNRAS/505/5978 : Gaia EDR3 view on Gal. globular clusters (Vasiliev+, 2021)
J/AJ/163/275 : Theia 456; a stellar stream in MW disk (Andrews+, 2022)
J/A+A/661/A118 : 628 new open clusters found: OCfinder (Castro-Ginard+, 2022)
J/A+A/660/A4 : Gaia EDR3 new Galactic open clusters (Hao+, 2022)
J/ApJS/262/7 : 886 nearby star clusters (He+, 2022)
J/ApJS/266/36 : Open star clusters within 5kpc in Gaia DR3 (Chi+, 2023)
J/A+A/673/A114 : Improving the open cluster census. II. (Hunt+, 2023)
J/A+A/686/A42 : Improving the open cluster census. III. (Hunt+, 2024)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 19 I19 --- ID Gaia DR3 identifier
21- 25 F5.2 deg RAdeg [65/88] Gaia DR3 Right Ascension (J2000)
27- 30 F4.2 deg e_RAdeg [0.01/0.2] Error in RAdeg
32- 36 F5.2 deg DEdeg [37/56] Gaia DR3 Declination (J2000)
38- 41 F4.2 deg e_DEdeg [0.01/0.1] Error in DEdeg
43- 46 F4.2 mas plx [1.7/2.3] Gaia DR3 Parallax
48- 51 F4.2 mas e_plx [0.01/0.2] Error in plx
53- 57 F5.2 mas/yr pmRA [-5.4/-3.2] Gaia DR3 Proper Motion in
RA*cos(Declination), pmRA*cos (DEdeg)
59- 62 F4.2 mas/yr e_pmRA [0.01/0.3] Error in pmRA
64- 68 F5.2 mas/yr pmDE [-2.1/-0.5] Gaia DR3 Proper Motion in
Declination
70- 73 F4.2 mas/yr e_pmDE [0.01/0.2] Error in pmDE
75- 81 F7.3 km/s RVel [-35/14]? Gaia DR3 Radial Velocity
83- 88 F6.3 km/s e_RVel [0.01/19]? Error in RVel
90- 94 A5 --- sp Flag for stars with MMT-Hectochelle spectra
and derived stellar parameters via
MINESweeper (True = 43 occurrences) (2)
96- 101 F6.2 --- SNR [0.5/174]? SNR of MMT-Hectochelle spectra
103- 108 F6.2 km/s Vrad [-17/-11]? Radial Velocity derived via
MINESweeper (1)
110- 113 F4.2 km/s e_Vrad [0.01/5.4]? Lower Quartile Error (16%) on
Vrad (1)
115- 118 F4.2 km/s E_Vrad [0.01/5.3]? Upper Quartile Error (84%) on
Vrad (1)
120- 127 F8.5 km/s Vrot [6e-5/50]? Rotational Velocity derived via
MINESweeper (1)
129- 135 F7.5 km/s e_Vrot [0/7.6]? Lower Quartile Error (16%) on Vrot
(1)
137- 143 F7.5 km/s E_Vrot [0/6.1]? Upper Quartile Error (84%) on Vrot
(1)
145- 149 F5.1 pc Dist [434/598]? Distance derived via MINESweeper
(1)
151- 154 F4.1 pc e_Dist [0.1/17]? Lower Quartile Error (16%) on Dist
(1)
156- 159 F4.1 pc E_Dist [0.2/21]? Upper Quartile Error (84%) on Dist
(1)
161- 164 F4.2 mag Av [0.01/1.5]? V Band Extinction derived via
MINESweeper (1)
166- 169 F4.2 mag e_Av [0/0.2]? Lower Quartile Error (16%) on Av (1)
171- 174 F4.2 mag E_Av [0/0.2]? Upper Quartile Error (84%) on V Av
(1)
176- 179 I4 K Teff [3616/7760]? Effective Temperature derived
via MINESweeper (1)
181- 182 I2 K e_Teff [2/65]? Lower Quartile Error (16%) on Teff (1)
184- 185 I2 K E_Teff [2/72]? Upper Quartile Error (84%) on Teff (1)
187- 191 F5.3 [cm/s2] logg [4.2/4.8]? Log of Surface Gravity derived via
MINESweeper (1)
193- 197 F5.3 [cm/s2] e_logg [1e-3/0.04]? Lower Quartile Error (16%) on
logg (1)
199- 203 F5.3 [cm/s2] E_logg [2e-3/0.04]? Upper Quartile Error (84%) on
logg (1)
205- 210 F6.3 [Rsun] logRs [-0.3/0.3]? Log of Stellar Radius derived via
MINESweeper (1)
212- 216 F5.3 [Rsun] e_logRs [2e-3/0.02]? Lower Quartile Error (16%) on
logRs (1)
218- 222 F5.3 [Rsun] E_logRs [1e-3/0.02]? Upper Quartile Error (84%) on
logRs (1)
224- 229 F6.3 [Sun] Fe/H [-0.4/0.2]? Iron Abundance relative to Sun
derived via MINESweeper (1)
231- 235 F5.3 [Sun] e_Fe/H [3e-3/0.4]? Lower Quartile Error (16%) on
Fe/H (1)
237- 241 F5.3 [Sun] E_Fe/H [4e-3/0.2]? Upper Quartile Error (84%) on
Fe/H (1)
243- 248 F6.3 [Sun] a/Fe [-0.2/0.3]? Alpha Process Elemental Abundance
relative to Sun derived via MINESweeper (1)
250- 254 F5.3 [Sun] e_a/Fe [0/0.07]? Lower Quartile Error (16%) on a/Fe
(1)
256- 260 F5.3 [Sun] E_a/Fe [1e-3/0.2]? Upper Quartile Error (84%) on
a/Fe (1)
262- 266 F5.3 [yr] logAge [7/9]? Log of Stellar Age derived via
MINESweeper (1)
268- 272 F5.3 [yr] e_logAge [1e-3/0.7]? Lower Quartile Error (16%) on
logAge (1)
274- 278 F5.3 [yr] E_logAge [2e-3/0.7]? Upper Quartile Error (84%) on
logAge (1)
280- 284 F5.3 Msun Mstar [0.5/1.5]? Stellar Mass derived via
MINESweeper (1)
286- 290 F5.3 Msun e_Mstar [4e-3/0.04]? Lower Quartile Error (16%) on
Mstar (1)
292- 296 F5.3 Msun E_Mstar [2e-3/0.02]? Upper Quartile Error (84%) on
Mstar (1)
298- 303 F6.3 [Lsun] logLs [-1.4/0.9]? Log of Stellar Luminosity derived
via MINESweeper (1)
305- 309 F5.3 [Lsun] e_logLs [5e-3/0.05]? Lower Quartile Error (16%) on
LogLs (1)
311- 315 F5.3 [Lsun] E_logLs [3e-3/0.05]? Upper Quartile Error (84%) on
logLs (1)
317- 322 F6.4 mas plx2 [1.6/2.4]? Parallax derived via MINESweeper
(1)
324- 329 F6.4 mas e_plx2 [1e-3/0.1]? Lower Quartile Error (16%) on
plx2 (1)
331- 336 F6.4 mas E_plx2 [6e-4/0.1]? Upper Quartile Error (84%) on
plx2 (1)
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Note (1): For information on the derivation of stellar parameters via
MINESweeper, see Cargile+ 2020ApJ...900...28C 2020ApJ...900...28C
Note (2): Note that three stars (Gaia IDs 194628676403051392,
194563427259442176, 272689569568329216) have 'sp' = False, but
these stars do have RVs and stellar parameters - just with large
uncertainties so we do not use those parameters in our analysis.
For information on the derivation of stellar parameters via
MINESweeper, see Cargile+ 2020ApJ...900...28C 2020ApJ...900...28C
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History:
From electronic version of the journal
(End) Prepared by [AAS], Robin Leichtnam [CDS] 23-Jun-2025