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. =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: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- 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 -------------------------------------------------------------------------------- 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 -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 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 6708{AA} 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 -------------------------------------------------------------------------------- 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). -------------------------------------------------------------------------------- Byte-by-byte Description of file: table2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 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 6708{AA} line (3) 66- 80 A15 --- Remarks Notes on binarity and rotation -------------------------------------------------------------------------------- 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). -------------------------------------------------------------------------------- Byte-by-byte Description of file: table3.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 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 {Delta}{mu} 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 -------------------------------------------------------------------------------- Byte-by-byte Description of file: table4.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 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 {Delta}{mu} 18- 21 F4.1 km/s DHRV Observed radial velocity residual {Delta}HRV 23- 25 F3.1 km/s Dv Observed total space motion residual {Delta}v 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) -------------------------------------------------------------------------------- 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 = H{alpha} in absorption but otherwise acceptable kinematic member Li = Lithium rich star with EWLi>100m{AA} Delta_v = Rejected as kinematic member with {Delta}_v_>5km/s -------------------------------------------------------------------------------- Byte-by-byte Description of file: table5.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 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? -------------------------------------------------------------------------------- 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). 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, Cat. J/ApJS/208/9). -------------------------------------------------------------------------------- Byte-by-byte Description of file: refs.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 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 -------------------------------------------------------------------------------- Acknowledgements: Simon J. Murphy, murphy(at)ari.uni-heidelberg.de ================================================================================ (End) Simon Murphy [ARI, Uni. Heidelberg], Patricia Vannier [CDS] 14-Jan-2015