J/MNRAS/435/1325 Membership of the ε Cha association (Murphy+, 2013)
Re-examining the membership and origin of the ε Cha association.
Murphy S.J., Lawson W.A., Bessell M.S.
<Mon. Not. R. Astron. Soc. 435, 1325 (2013)>
=2013MNRAS.435.1325M 2013MNRAS.435.1325M
ADC_Keywords: Associations, stellar ; Stars, pre-main sequence ;
Radial velocities ; Stars, ages ; Equivalent widths
Keywords: stars: formation - stars: kinematics and dynamics - stars: low-mass -
stars: pre- main sequence -
open clusters and associations: individual: epsilon Chamaeleontis -
open clusters and associations: individual: eta Chamaeleontis
Abstract:
We present a comprehensive investigation of the ε Chamaeleontis
association, one of several young moving groups spread across the
southern sky. We re-assess the putative membership of ε Cha
using the best available proper motion and spectroscopic measurements,
including new ANU 2.3-m/Wide Field Spectrograph observations. After
applying a kinematic analysis, our final membership comprises 35-41
stars from B9 to mid-M spectral types. Theoretical evolutionary models
suggest ε Cha is 3-5Myr old, distinguishing it as the youngest
moving group in the solar neighbourhood. 15 members show 3-22um
spectral energy distributions attributable to circumstellar discs,
including 11 stars which appear to be actively accreting. ε
Cha's disc and accretion fractions are both consistent with a typical
3-5Myr old population. Multi-epoch spectroscopy reveals three M-type
members with broad and highly variable Ha emission as well as several
new spectroscopic binaries. We reject 11 stars proposed as members in
the literature and suggest they may belong to the background Cha I and
II clouds or other nearby young groups. Our analysis underscores the
importance of a holistic and conservative approach to assigning young
stars to kinematic groups, many of which have only subtly different
properties and ill-defined memberships. We conclude with a brief
discussion of ε Cha's connection to the young open cluster eta
Cha and the Scorpius- Centaurus OB association. Contrary to earlier
studies which assumed eta and ε Cha are coeval and were born in
the same location, we find the groups were separated by ∼30pc when
eta Cha formed 4-8Myr ago in the outskirts of Sco-Cen, 1-3Myr before
the majority of ε Cha members.
Description:
Astrometric (positions, proper motions), photometric (IJHKW1-W4,
E(B-V)) and spectroscopic (spectral types, radial velocities, lithium,
H-α) measurements are presented for all proposed members of
ε Cha. The majority of the spectroscopic data were obtained on
the Australian National University 2.3-m telescope at Siding Spring
Observatory. Ages, distances and heliocentric positions and velocities
are given for the 35 stars confirmed as members by our analysis, as
well as 6 provisional members requiring further observations.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table7.dat 103 35 Confirmed members of ε Cha
table8.dat 103 6 Provisional members of ε Cha
tableb1.dat 133 52 Spectroscopic and astrometric measurements for
all candidates
tableb2.dat 83 52 IJHK+WISE photometry for all candidates
refs.dat 176 31 References
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See also:
J/A+A/357/219 : ISOCAM observations in Cha I. (Persi+, 2000)
J/AJ/121/974 : JHK photometry in Cha I (Gomez+, 2001)
J/AJ/124/1001 : JHKs photometry of Cha I variables (Carpenter, 2002)
J/A+A/423/1029 : XMM-Newton obs, in Cha I South (Stelzer+, 2004)
J/ApJ/614/267 : Chandra sources in Cha I North (Feigelson+, 2004)
J/A+A/461/669 : XMM observations of Cha I dark cloud (Robrade+, 2007)
J/ApJ/675/1375 : IRAC/MIPS photometry in Cha I (Luhman+, 2008)
J/A+A/524/A97 : XMM observations of η Cha cluster (Lopez-Santiago+, 2011)
Byte-by-byte Description of file: table[78].dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- ID [1/40]? [FLG2003] eps Cha identifier (G1)
4- 26 A23 --- Name Star name
28- 32 A5 --- SpT MK spectral type
34- 36 I3 pc Dist Adopted distance
38 A1 --- f_Dist [H] Hipparcos flag (2)
40- 42 F3.1 km/s K ? Magnitude of velocity difference (3)
44- 48 F5.1 km/s U ? Heliocentric U velocity
50- 54 F5.1 km/s V ? Heliocentric V velocity
56- 60 F5.1 km/s W ? Heliocentric W velocity
62- 65 F4.1 pc X Heliocentric X coordinate
67- 72 F6.1 pc Y Heliocentric Y coordinate
74- 78 F5.1 pc Z Heliocentric Z coordinate
80- 85 F6.4 [K] logTe ? Logarithm of effective temperature
87- 93 F7.4 [Lsun] logLb ? Logarithm of bolometric luminosity
95- 98 F4.1 Myr Age1 ? Age measured from Dotter isochrones
100-103 F4.1 Myr Age2 ? Age measured from Siess isochrones
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Note (2): H = Hipparcos distance fixed in the analysis, otherwise the
best-fitting kinematic distance is given.
Note (3): Magnitude of the vector difference between the star's space
motion and the average space motion of ε Cha members.
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Byte-by-byte Description of file: tableb1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- ID [1/40]? [FLG2003] eps Cha identifier (G1)
4- 26 A23 --- Name Star name
28- 37 F10.6 deg RAdeg Right Ascension (J2000.0 degrees)
39- 48 F10.6 deg DEdeg Declination (J2000.0 degrees)
50- 54 A5 --- SpT MK Spectral type
56- 59 A4 --- r_SpT ? Reference for spectral type (1)
61- 64 F4.2 mag E(B-V) ? E(B-V) extinction
66- 69 F4.1 km/s HRV ? Heliocentric radial velocity
71- 73 F3.1 km/s e_HRV ? Radial velocity uncertainty
75- 78 A4 --- r_HRV ? Reference for radial velocity (1)
80- 82 I3 0.1pm EWLi ? LiI 6708Å equivalent width (mÅ)
84- 85 I2 0.1pm e_EWLi ? LiI EW uncertainty (mÅ)
87- 90 A4 --- r_EWLi ? Reference for LiI EW (1)
92- 97 F6.1 0.1nm EWHa ? H-α equivalent width (Å)
99-103 F5.1 0.1nm B_EWHa ? Maximum H-α width if variable
105-107 A3 --- r_EWHa ? Reference for H-alpha EW (1)
109-113 F5.1 mas/yr pmRA ? Proper motion in Right Ascension pmRA*cosDE
115-117 F3.1 mas/yr e_pmRA ? Uncertainty in pmRA
119-123 F5.1 mas/yr pmDE ? Proper motion in Declination
125-127 F3.1 mas/yr e_pmDE ? Uncertainty in pmDE
129-133 A5 --- r_pmDE Reference for proper motion (1)
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Note (1): Unless otherwise stated, all measurements are from this work.
References to other works are given in the file refs.dat.
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Byte-by-byte Description of file: tableb2.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- ID [1/40]? [FLG2003] eps Cha identifier (G1)
4- 26 A23 --- Name Star name
28- 32 F5.2 mag Imag ? I magnitude
34- 37 A4 --- r_Imag Reference for I magnitude (2)
39- 43 F5.2 mag Jmag J magnitude
45- 49 F5.2 mag Hmag H magnitude
51- 55 F5.2 mag Kmag K magnitude
57- 59 A3 --- r_Kmag Reference for JHK magnitudes (3)
61- 65 F5.2 mag W1mag ? WISE W1 magnitude (3.4um) (4)
67- 71 F5.2 mag W2mag ? WISE W2 magnitude (4.6um) (4)
73- 77 F5.2 mag W3mag ? WISE W3 magnitude (12um) (4)
79- 83 F5.2 mag W4mag ? WISE W4 magnitude (22um) (4)
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Note (2): P = photometry of binary corrected to that of the primary component.
Unless otherwise stated, Imag are from DENIS (Cat. B/denis/)
References to other works are given in the file refs.dat.
Note (3): Unless otherwise stated, JHK photometry is from 2MASS
(2006, Cat. II/246)
Note (4): Photometry from WISE All Sky Release (Cat. II/311).
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Byte-by-byte Description of file: refs.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- Ref Reference code
7- 25 A19 --- Bibcode Bibcode
27- 49 A23 --- Aut Author's name
51-176 A126 --- Com Comments
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Global Notes:
Note (G1): Identified as <[FLG2003] EPS CHA {ID}> in Simbad.
ID values above 21 are newly assigned in this work.
Acknowledgements:
Simon J. Murphy, murphy(at)ari.uni-heidelberg.de
(End) Simon Murphy [ARI, Uni. Heidelberg], Patricia Vannier [CDS] 25-Sep-2013