J/MNRAS/447/1267 Low-mass members of the Octans association (Murphy+, 2015)
New low-mass members of the Octans stellar association and an updated 30-40 Myr
lithium age.
Murphy S.J., Lawson W.A.
<Mon. Not. R. Astron. Soc. 447, 1267 (2015)>
=2015MNRAS.447.1267M 2015MNRAS.447.1267M
ADC_Keywords: Associations, stellar; Stars, pre-main sequence; Spectral types;
Radial velocities; Proper motions; Space velocities;
Stars, distances
Keywords: stars: kinematics and dynamics - stars: low-mass -
stars: pre- main sequence -
open clusters and associations: individual: Octans
Abstract:
The Octans association is one of several young stellar moving groups
recently discovered in the Solar neighbourhood and hence a valuable
laboratory for studies of stellar, circumstellar disc and planetary
evolution. However, a lack of low-mass members or any members with
trigonometric parallaxes means the age, distance and space motion of
the group are poorly constrained. To better determine its membership
and age, we present the first spectroscopic survey for new K- and
M-type Octans members, resulting in the discovery of 29 UV-bright
K5-M4 stars with kinematics, photometry and distances consistent with
existing members. Nine new members possess strong LiI 6708
absorption, which allow us to estimate a lithium age of 30-40Myr,
similar to that of the Tucana-Horologium association and bracketed by
the firm lithium depletion boundary ages of the beta Pictoris (20Myr)
and Argus/IC 2391 (50Myr) associations. Several stars also show hints
in our medium-resolution spectra of fast rotation or spectroscopic
binarity. More so than other nearby associations, Octans is much
larger than its age and internal velocity dispersion imply. It may be
the dispersing remnant of a sparse, extended structure which includes
some younger members of the foreground Octans-Near association
recently proposed by Zuckerman and collaborators.
Description:
Astrometric (positions, proper motions), photometric (V+K),
spectroscopic (spectral types, radial velocities, lithium, H-alpha)
and phase space (XYZUVW) measurements are presented for all proposed
members of Octans. The majority of the spectroscopic data were
obtained on the Australian National University 2.3-m telescope at
Siding Spring Observatory.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 88 60 Spectroscopy of Octans candidates
table2.dat 80 19 Previously proposed Octans members
table3.dat 74 48 New kinematic members of Octans
table4.dat 73 5 Provisional Octans members
table5.dat 70 12 Candidates observed by ROSAT
refs.dat 182 7 Membership and RV references
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See also:
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
IX/10 : ROSAT All-Sky Bright Source Catalogue (1RXS) (Voges+ 1999)
IX/29 : ROSAT All-Sky Survey Faint Source Catalog (Voges+ 2000)
IX/30 : Second ROSAT PSPC Catalog (ROSAT, 2000)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1 A1 --- More [*] indicates more data in tables 3, 4,
and/or 5
3- 4 I2 --- Name [1/61] Candidate identifier
5 A1 --- m_Name [AB] Multiplicity index on Name
7- 22 A16 --- 2MASS 2MASS designation (HHMMSSss+DDMMSSs)
24- 28 F5.2 mag Vmag ? Apparent V magnitude (1)
30- 34 F5.2 mag Kmag ? 2MASS Ks magnitude
36- 41 F6.2 mas/yr pmRA ? Proper motion RA component (2)
43- 48 F6.2 mas/yr pmDE ? Proper motion Dec component (2)
50- 53 A4 --- SpT MK spectral type
55- 59 F5.1 km/s HRV Heliocentric radial velocity
61- 63 I3 0.1pm EWLi [10/365]? Equivalent width of LiI 6708Å
65- 66 I2 0.1pm e_EWLi [10/20]? Error on Li equivalent width
68- 69 I2 0.1pm B_EWLi [30/50]? Upper limit on LiI detection
71- 74 F4.1 0.1nm EWHa [-9/1.4] Equivalent width of Halpha emission
76- 88 A13 --- Remarks Notes on binarity and CCF
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Note (1): All V magnitudes are from SPM4 (Cat. I/320) with the exception of
stars 3, 4, 12, 43AB, 47 and 61 (V from UCAC4, Cat. I/322).
Note (2): All proper motions are from SPM4 (Cat. I/320) with the exception of
stars 31, 61 (UCAC4, Cat. I/322), 25 and 42 (Hipparcos, Cat. I/311).
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- Name Name of proposed member
17- 19 A3 --- Ref Membership reference, in refs.dat file
21- 25 F5.2 mag Vmag Apparent V magnitude (1)
27- 30 F4.2 mag Ksmag 2MASS Ks magnitude
32- 36 F5.1 mas/yr pmRA Proper motion RA component (2)
38- 42 F5.1 mas/yr pmDE Proper motion Dec component (2)
44- 47 A4 --- SpT MK spectral type
49- 52 F4.1 km/s HRV Heliocentric radial velocity
54- 56 F3.1 km/s e_HRV ? Error on radial velocity
58- 60 A3 --- r_HRV Radial velocity reference, in refs.dat file
62- 64 I3 0.1pm EWLi ? Equivalent width of Li 6708Å line (3)
66- 80 A15 --- Remarks Notes on binarity and rotation
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Note (1): All V magnitudes are from SPM4 (Cat. I/320) with the exception of
CD-30 3394AB, CD-72 248 and TYC 7066-1037-1 (UCAC4, Cat. I/322).
Note (2): All proper motions are from SPM4 (Cat. I/320) with the exception of
CD-30 3394AB (UCAC4, Cat. I/322), TYC 7066-1037-1 (Tycho 2,
Cat. I/259/tyc2), TYC 9300-0529-1 and TYC 9300-0891-1 (PPXML, Cat. I/317).
Note (3): All equivalent width measurements are from Torres et al., (2006,
Cat. J/A+A/460/695) except for RX J1123.2-7924 (Murphy et al, 2013,
Cat. J/MNRAS/435/1325) and BD-20 1111 (C. Torres, private communication).
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- Name Name or ID of member
17- 19 I3 pc dkin Best kinematic distance
21- 25 F5.2 mag VMAG Absolute V at kinematic distance
27- 29 F3.1 mas/yr Dmu Observed total proper motion residual Δµ
31- 34 F4.1 km/s DHRV Observed radial velocity residual
36- 38 F3.1 km/s Dv Observed total space motion residual
40- 44 F5.1 km/s U Heliocentric U velocity component
46- 49 F4.1 km/s V Heliocentric V velocity component
51- 55 F5.1 km/s W Heliocentric W velocity component
57- 61 F5.1 pc X Heliocentric X coordinate
63- 68 F6.1 pc Y Heliocentric Y coordinate
70- 74 F5.1 pc Z Heliocentric Z coordinate
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Name ID of provisional member
3 A1 --- m_Name [AB] Multiplicity index on Name
5- 7 I3 pc dkin Best kinematic distance
9- 12 F4.2 mag VMAG Absolute V at kinematic distance (1)
14- 16 F3.1 mas/yr Dmu Observed total proper motion residual Δµ
18- 21 F4.1 km/s DHRV Observed radial velocity residual ΔHRV
23- 25 F3.1 km/s Dv Observed total space motion residual Δv
27- 31 F5.1 km/s U Heliocentric U velocity component
33- 36 F4.1 km/s V Heliocentric V velocity component
38- 42 F5.1 km/s W Heliocentric W velocity component
44- 48 F5.1 pc X Heliocentric X coordinate
50- 55 F6.1 pc Y Heliocentric Y coordinate
57- 61 F5.1 pc Z Heliocentric Z coordinate
63- 73 A11 --- Remarks Reason for provisional membership (2)
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Note (1): Absolute magnitudes for the components of binary 32 assume an equal
mass system with combined brightness VMAG=5.77mag.
Note (2): Remarks are;
Halpha = Hα in absorption but otherwise acceptable kinematic member
Li = Lithium rich star with EWLi>100mÅ
Delta_v = Rejected as kinematic member with Δv>5km/s
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Name ID of candidate
4- 6 A3 --- Survey ROSAT Bright or Faint Source Catalog
8- 28 A21 --- 1RXS ROSAT identifier
30- 31 I2 arcsec offset Offset from optical position
33- 34 I2 arcsec PosErr ROSAT positional uncertainty
36- 40 F5.3 ct/s CR 0.1-2.4keV count rate
42- 46 F5.3 ct/s e_CR Error on count rate
48- 52 F5.2 --- HR1 [-1/1] ROSAT HR1 hardness ratio
54- 57 F4.2 --- e_HR1 [0.1/0.5] Error on hardness ratio
59- 62 F4.1 [10-7W] logLx log X-ray luminosity (1)
64- 68 F5.2 [-] log(Lx/bol) log X-ray to bolometric luminosity ratio (2)
70 A1 --- Member [Y] Octans kinematic member?
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Note (1): X-ray luminosities (in erg/s) calculated from the kinematic distance,
count rate and hardness ratio using the conversion factor of Fleming
(1995ApJ...450..401F 1995ApJ...450..401F).
Note (2): X-ray to bolometric luminosity ratio calculated from the V-K colour,
apparent V magnitude and the bolometric corrections tabled by Pecaut &
Mamajek (2013ApJS..208....9P 2013ApJS..208....9P, Cat. J/ApJS/208/9).
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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- 3 A3 --- Ref Reference code from Table 2
5- 23 A19 --- BibCode Bibcode
25- 38 A14 --- Aut Author's name
40-182 A143 --- Com Comments
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Acknowledgements:
Simon J. Murphy, murphy(at)ari.uni-heidelberg.de
(End) Simon Murphy [ARI, Uni. Heidelberg], Patricia Vannier [CDS] 14-Jan-2015