A search for new members of the beta Pic, Tuc-Hor and epsilon Cha moving groups in the RAVE database
L.L. Kiss, A. Moor, T. Szalai, J. Kovacs, D. Bayliss, G.F. Gilmore, O. Bienayme, J. Binney, J. Bland-Hawthorn, R. Campbell, K.C. Freeman, J.P. Fulbright, B.K. Gibson, E.K. Grebel, A. Helmi, U. Munari, J.F. Navarro, Q.A. Parker, W. Reid, G.M. Seabroke, A. Siebert, A. Siviero, M. Steinmetz, F.G. Watson, M. Williams, R.F.G. Wyse, T. Zwitter
aa r X i v : . [ a s t r o - ph . S R ] S e p Mon. Not. R. Astron. Soc. , 1–7 (2010) Printed 29 October 2018 (MN L A TEX style file v2.2)
A search for new members of the β Pic, Tuc-Hor and ǫ Chamoving groups in the RAVE database
L. L. Kiss , ⋆ , A. Mo´or , T. Szalai , J. Kov´acs , D. Bayliss , G. F. Gilmore ,O. Bienaym´e , J. Binney , J. Bland-Hawthorn , R. Campbell , K. C. Freeman ,J.P. Fulbright , B. K. Gibson , E. K. Grebel , A. Helmi , U. Munari ,J. F. Navarro , Q. A. Parker , , W. Reid , G. M. Seabroke , A. Siebert ,A. Siviero , , M. Steinmetz , F. G. Watson , M. Williams , R. F. G. Wyse ,T. Zwitter , Konkoly Observatory of the Hungarian Academy of Sciences, PO Box 67, H-1525 Budapest, Hungary Sydney Institute for Astronomy, School of Physics, University of Sydney, NSW 2006, Australia Department of Optics and Quantum Electronics, University of Szeged, 6720 Szeged, D´om t´er 9., Hungary Gothard Astrophysical Observatory, ELTE University, 9707 Szombathely, Hungary Research School of Astronomy and Astrophysics, The Australian National University, Canberra, Australia Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK Observatoire de Strasbourg, 11 Rue de L‘Universit´e, 67000 Strasbourg, France Rudolf Pierls Center for Theoretical Physics, University of Oxford, 1 Keble Road, Oxford OX1 3NP, UK Western Kentucky University, Bowling Green, Kentucky, USA Johns Hopkins University, 3400 N Charles Street, Baltimore, MD 21218, USA Jeremiah Horrocks Institute for Astrophysics & Super-computing, University of Central Lancashire, Preston, UK Astronomisches Rechen-Institut, Zentrum f¨ur Astronomie der Universit¨at Heidelberg, D-69120 Heidelberg, Germany Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, Netherlands INAF Osservatorio Astronomico di Padova, Via dell‘Osservatorio 8, Asiago I-36012, Italy University of Victoria, P.O. Box 3055, Station CSC, Victoria, BC V8W 3P6, Canada Macquarie University, Sydney, NSW 2109, Australia Australian Astronomical Observatory, P.O. Box 296, Epping, NSW 1710, Australia Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, RH5 6NT, UK Astrophysikalisches Institut Potsdam, An der Sterwarte 16, D-14482 Potsdam, Germany Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, Ljubljana, Slovenia Center of excellence SPACE-SI, Ljubljana, Slovenia
Accepted ... Received ...; in original form ...
ABSTRACT
We report on the discovery of new members of nearby young moving groups, exploit-ing the full power of combining the RAVE survey with several stellar age diagnosticmethods and follow-up high-resolution optical spectroscopy. The results include theidentification of one new and five likely members of the β Pictoris moving group, rang-ing from spectral types F9 to M4 with the majority being M dwarfs, one K7 likelymember of the ǫ Cha group and two stars in the Tuc-Hor association. Based on thepositive identifications we foreshadow a great potential of the RAVE database in pro-gressing toward a full census of young moving groups in the solar neighbourhood.
Key words: stars: kinematics – open clusters and associations: individual: β Pictorismoving group, Tucana-Horologium association, ǫ Cha association. ⋆ E-mail: [email protected]
In the last decade many young ( <
100 Myr) stars havebeen identified in the solar neighbourhood. Most of thembelong to different moving groups, in which stars share c (cid:13) L. L. Kiss et al. common age and motion through the Galaxy (for reviewsee Zuckerman & Song 2004). Up to now nine such kine-matic assemblages have been revealed within 150 pc of ourSolar System with ages ranging from 8 Myr to 70 Myr(Torres et al. 2008), most situated in the southern hemi-sphere far from known star forming regions. However, trac-ing back their space trajectories shows that the birth-place of some of them may have been close to the near-est sites of massive star formation, the Sco-Cen region(Fern´andez, Figueras & Torra 2008).Young moving groups are rich in debris discs, which im-plies very active planetesimal formation around these stars(Mo´or et al. 2006; Rebull et al. 2008). Since the epochs ofseveral key events in the early Solar System (e.g. formationof terrestrial planets, Apai 2009) overlap well with the age ofthese groups, discs around the members are favourable andso present nearby and well-dated sites for investigations ofplanet formation and evolution. The members are also idealtargets when one would like to detect sub-stellar objects viadirect imaging, since giant gas planets are thought to fadesignificantly during their evolution (e.g. Kasper et al. 2007).Most of the known young stellar kinematic groups oc-cupy a large area on the sky (up to thousands of squaredegrees), which makes the identification of members verydifficult. However, by combining astrometric data with ra-dial velocity information and by applying relevant age di-agnostic methods, one can search for additional members ofknown groups or reveal new kinematic assemblages. Usingthis approach, recent studies revealed more than 300 youngstars belonging to nine kinematic groups in the vicinity ofour Sun (Torres et al. 2008). It is clear, however, that thecensus of these groups is far from complete, because of thelack of necessary kinematic information – particularly theradial velocities and the trigonometric distances – for mostof the stars. For example, comparing the list of membersof the β Pic moving group with expectations based on thetypical stellar mass function, Shkolnik, Liu, & Reid (2009)estimated that about 60 M-type members remain undiscov-ered in our neighbourhood.The Radial Velocity Experiment (RAVE) is a large scalespectroscopic survey with the aim of measuring radial veloc-ities and atmospheric parameters for up to a several hundredthousand stars in the southern sky, using the UK Schmidttelescope of the Anglo-Australian Observatory equippedwith the 6dF multi-object spectrograph. The project hasalready resulted in two data releases (Steinmetz et al. 2006;Zwitter et al. 2008) and observed well over 300,000 starsaway from the plane of the Milky Way ( | b | > ◦ ) and withapparent magnitudes 9 < I DENIS <
13. Detailed compar-isons with external sets revealed that the velocities are accu-rate to 1-2 km s − , while the errors of the stellar parametersare in the order of 400 K in temperature, 0.5 dex in gravity,and 0.2 dex in metallicity, all errors changing significantlyacross the temperature range of the stars (Zwitter et al.2008). Proper motion data in the catalogue have been takenfrom Tycho-2 for the brighter stars, then UCAC2, USNO-Band PPMX for the non-Tycho stars.In order to capitalise on the potential of the RAVE sur-vey in the census of young moving groups we used the 2008 See also
August 30 internal release of the RAVE catalogue (withalmost 250,000 entries) to search for new members of threeyoung assemblages, the ǫ Cha association, the β Pic movinggroup and the Tucana-Horologium association. Each of theselected kinematic groups is younger than 40 Myr. From thelocation in the H-R diagram and from the lithium equivalentwidths of the members Zuckerman et al. (2001) derivedan age of 12 +8 − Myr for the β Pic moving group (BPMG).Estimates based on dynamical back-tracing models ofBPMG members, in good accordance with the previ-ous value, yielded an age of ∼
12 Myr (Ortega et al. 2002;Song, Zuckerman, & Bessell 2003). Recently, Mentuch et al.(2008) derived a somewhat higher age, 21 ± ǫ Cha association may bethe youngest among the three selected assemblages.Its age estimates range between 3 Myr and 15 Myr(Terranegra et al. 1999; Feigelson, Lawson, & Garmire2003; Jilinski, Ortega, & de la Reza 2005; Torres et al.2008), most cases below 7 Myr. We used strict criteriato select potential candidates and then the RAVE-basedlist was supplemented by some additional stars takenprimarily from the Hipparcos catalogue (Sect. 2). In orderto confirm the membership of our candidates we performedfollow-up high-resolution spectroscopy (Sect. 3). The finalassignments of the candidate stars are summarised inSect. 4, with concluding remarks in Sect. 5.
The RAVE sample was examined in the U, V, W, X, Y, Zspace, defined by the heliocentric space motion (U,V,W) andthe physical space coordinates centred on the Sun (X,Y,Z).The computation of these parameters for a star requiresknowledge of its coordinates, proper motion, radial veloc-ity and distance. While coordinates (right ascension, dec-lination), proper motion (in right ascension and in declina-tion) and radial velocity information could be taken from theRAVE catalogue, for most of the RAVE stars no trigonomet-ric distances were available. Therefore, the U,V,W,X,Y,Zvalues were calculated for a range of distances, between 5 pcand 120 pc with a resolution of 1 pc, to check whether anydistance resulted in a coordinate which coincided with theregion of a specific association in this 6-dimension space. Inthose cases where a RAVE star has a trigonometric paral-lax, measured by Hipparcos (van Leeuwen 2007), we usedthat value in the computations. The search was limited forthose stars whose proper motion measurement fullfils thefollowing criteria 1) µ = p µ α cos δ + µ δ >
20 mas yr − ;2) µ/σ µ > , V , W ) of thegroups were taken from Torres et al. (2008). We selectedthose objects from the RAVE catalogue, where min[(( U − U ) + ( V − V ) + ( W − W ) ) / ] < − . The chosenlimit corresponds to the internal dispersion of the known c (cid:13) , 1–7 ew members of young moving groups members of the groups, while the distance resulting theminimum value was adopted as the kinematic distance tothe object. For the β Pic moving group (hereafter BPMG),Torres et al. (2006) found a correlation between the U com-ponent of the Galactic space motion and the X space coor-dinate that was taken into account by calculating the U value as a function of X, using their Eq. 4. We searchedfor BPMG candidate members within 80 pc of the Sun. For ǫ Cha (ECA) and Tuc-Hor (THA) candidates the search waslimited to a region defined by the known members of thegroups (Torres et al. 2008). Using this method we compiledan initial list of stars, that includes 3 ECA, 803 BPMG and62 THA candidate members.The initial lists were further evaluated and filtered: 1)placing our candidates in the colour-magnitude diagramsof the specific kinematic groups; and 2) by searching forX-ray counterparts in the
ROSAT catalogues (Voges et al.1999, 2000). We selected only those targets whose fractionalX-ray luminosities (L x /L bol ) and position in the colour-magnitude diagram were consistent with the similar prop-erties of the known members (see Fig. 1a–d). Our pro-cedure finally resulted in 2, 9 and 7 candidate membersof the ǫ Cha, BPMG and THA groups, respectively. Bysearching the literature we revealed that ten of our can-didates (1 ǫ Cha, 4 BPMG and 5 THA stars) are alreadyknown members. Moreover, one of our THA candidate,J042110.3-243221 (HD 27679), has already assigned to theColumba moving group by Torres et al. (2008), while oneof the BPMG candidate (TYC 7558-655-1) has an ambigu-ous assignment in the literature. Torres et al. (2008) identi-fied TYC 7558-655-1 as a possible member of the Columbagroup, on the other hand Schlieder, L´epine, & Simon (2010)proposed that this star likely belongs to the BPMG. Weomitted these known/ambiguous members from the furtherobservations and analyis. Thus, we finally selected six RAVEcandidates (1 ǫ Cha, 4 BPMG and 1 THA stars) for furtherinvestigations. These RAVE-based candidate list was sup-plemented by one additional star, J19560294-3207186, thatis the comoving pair of one of new candidate object (TYC7443-1102-1).
The Hipparcos catalogue was also searched for additionalcandidates members. Similarly to the RAVE sample, theHipparcos stars were also examined in the U, V, W, X,Y, Z space. Here the radial velocity data are lacking fora significant fraction of stars, therefore the U, V, W val-ues were calculated for a range of radial velocities (ra-dial velocity values were varied between −
50 km s − and+50 km s − with a resolution of 0.5 km s − ). For thosestars where radial velocity data were available in the lit-erature (Famaey et al. 2005; Mo´or et al. 2006; Gontcharov2006; Torres et al. 2006; Holmberg, Nordstr¨om, & Andersen2007; Kharchenko et al. 2007) we used the measured valuein the computation. The search was limited to stars withspectral type later than F8. In the selection of candidatestars we applied almost identical criteria as in the case ofRAVE objects. The only change in the method was relatedto those stars where all six parameters are available, thusU, V, W, X, Y, Z could be computed without any assump-tion, where we utilized a weaker criterion concerning to the X-ray luminosity of the object: we retained those candidatestoo where the upper limit of the X-ray luminosity was con-sistent with the similar property of the known members.Using this method in the BPMG we could recover – withthe exception of HIP 10679 – all known members that arequoted in Hipparcos (and has spectral type F8 or later).We note that HIP 10679 composes a binary system withHIP 10680 and the latter object has been successfully re-covered by our method. Moreover, HIP 10679 could be alsorecovered when we applied the more accurate trigonomet-ric parallax of HIP 10680 for this star as well. Three newcandidate stars, HD 37144, HD 160305 and HD 190102, havebeen revealed. For HD 37144 and HD 190102 radial velocitydata and lithium equivalent widths measured in the frame-work of the SACY survey (Torres et al. 2006) have alreadybeen available. Although the kinematic parameters fullfiledour criteria, the low values of the lithium equivalent widthsdid not confirm their membership. Based on similar consid-erations, da Silva et al. (2009) also rejected HD 190102 asa member of BPMG. For HD 160305 no radial velocity orlithium data were found in the literature, thus this objectwas added to the list of candidates. For THA and ECA werecovered all known members included in the Hipparcos cat-alogue. As a result of our search we revealed one new THAcandidate, HD 25402, for which radial velocity was avail-able in the catalogue of Holmberg, Nordstr¨om, & Andersen(2007). Since its computed kinematic parameters correspondwell to the characteristic values of THA we added this can-didate to our list. We have obtained new high-resolution optical spectroscopyfor all stars in Table 1 on six nights in July 2009 and threenights in August 2009, using the 2.3-m telescope and theEchelle spectrograph of the Australian National University.The total integration time per object ranged from 30 s to1800 s, depending on the target brightness. The spectra cov-ered the whole visual range in 27 echelle orders between3900 ˚A and 6720 ˚A with only small gaps between the threereddest orders. The nominal spectral resolution is λ/ ∆ λ ≈
23 000 at the H α line, with typical signal-to-noise ratios ofabout 100 (for the faintest red dwarf stars the blue parts ofthe spectra were much noisier).All data were reduced with standard IRAF tasks, in-cluding bias and flat-field corrections, cosmic ray removal,extraction of the 27 individual orders of the echelle spectra,wavelength calibration, and continuum normalization. ThArspectral lamp exposures were regularly taken before and af-ter every object spectrum to monitor the wavelength shiftsof the spectra on the CCD. We also obtained spectra for thetelluric standard HD 177724 and IAU radial velocity (RV)standards β Vir (sp. type F9V) and HD 223311 (K4III).The spectroscopic data analysis consisted of two mainsteps. First, we measured radial velocities (RVs) by cross-correlating the target spectra (using the IRAF task fxcor ) IRAF is distributed by the National Optical Astronomy Obser-vatories, which are operated by the Association of Universities forResearch in Astronomy, Inc., under cooperative agreement withthe National Science Foundation.c (cid:13) , 1–7
L. L. Kiss et al.
Table 1.
Properties of the candidate stars. References for spectral types: 1 - Riaz, Gizis, & Harvin (2006); 2 - Hipparcos catalogue;3 - L´epine & Simon (2009); 4 - this paper, based on V − K s . For HD 25402 and HD 160305, distances were taken from the Hipparcoscatalogue, otherwise we used kinematic distances (in parentheses). The typical uncertainty of the kinematic distances is estimated to be ∼ − . Source ID RA (2000) DEC (2000) SpT. V K s D v rad
U,V,W EW Li EW H α log L x L bol [mag] [mag] [pc] [km s − ] [km s − ] [˚A] [˚A] [dex]candidate ǫ Cha group membersJ12210499-7116493 12 21 05.00 -71 16 49.3 K7 ± ± ± β Pic moving group membersJ01071194-1935359 01 07 11.94 -19 35 36.0 M1 ± ± ± ± ± ± ± ± ± ± < ± ± ± ± < -3.47J20013718-3313139 20 01 37.18 -33 13 14.0 M1 ± < ± ± < ± ± ± ± < -4.02 with that of the RV standard that matched the spectral typeof the target – β Vir was used for the early-type targets (A–F–mid-G), HD 223311 for the late-type ones (late-G–K–M).Each spectral order was treated separately and the resultingvelocities and the estimated uncertainties were calculated asthe means and the standard deviations of the velocities fromthe individual orders. For most of the targets, the two IAUstandards yielded RVs within 0.1–0.5 km s − , which is an in-dependent measure of the absolute uncertainties. Using thenew, more accurate RV data we recomputed the U, V, W,X, Y, Z values for each candidate star, as described earlier.The equivalent width of the 6708˚A Li and the H α lines weremeasured with the IRAF task splot . Though stars in a specific group can be widely scatteredacross the sky, their common properties offer an oppor-tunity to identify other members in the field by prescrib-ing that a candidate must have similar space motion, aswell as age, to the known members. The age criterionis essential because there may be a non-negligible frac-tion of old field stars which have similar space motionto the young group members (Zuckerman & Song 2004;L´opez-Santiago, Micela, & Montes 2009).Using the new RV data we recomputed the U, V, W val-ues for each candidate star and compared the values with thecharacteristic space motion (U , V , W ) of the correspond-ing kinematic groups. Apart from HD 25402 and HD 160305,we used kinematic distances and the proper motion datawere taken from the UCAC3 catalogue (Zacharias et al.2010) for all of our targets. For HD 25402 and HD 160305,distances and proper motions were taken from the Hippar-cos catalogue. For J19560294-3207186, we adopted the kine-matic distance and U, V, W values of its companion (TYC7443-1102-1). We required [(( U − U ) + ( V − V ) + ( W − W ) ) / ] < − for the group membership. This cri-terion was fulfilled for all candidate stars, i.e. none of therefined RV data resulted in a deprived candidacy.We used three different age diagnostic methods to eval-uate whether the candidates are approximately coeval with the corresponding kinematic groups. In all age indicators wecompared the specific properties of the candidates stars tothe corresponding properties of the known members withsimilar colour indices.Figure 1 a,b,c show the colour-magnitude diagrams(M Ks vs. V − K s ) of the ECA, BPMG and THA groups. Thelists of known group members are from Torres et al. (2008),which have then been queried in the Hipparcos and 2MASSdatabases to produce Fig. 1 a,b,c. Candidate members areplotted with different symbols in the corresponding panels,showing that they indeed occupy a distinct region in theCMD. Since in these young groups a significant fraction ofthe stars are in pre-main sequence evolutionary stage, thecharacteristic loci of the members in the CMD deviate fromthe position of the main-sequence stars, which helps filterout spurious (old) candidates. The younger the associationthe higher the deviation, because more and more massivestars are still in pre-main sequence stage.Young stars are also known to have enhanced coro-nal activity with strong X-ray emission making the lat-ter property a good indicator of youth. We have cross-correlated the list of the candidates and known membersof the three groups with the ROSAT All-Sky Survey cat-alogues (Voges et al. 1999, 2000). We selected only thoseobjects where the match between the optical and X-ray po-sitions was within 40 ′′ . In all of the positive matches wechecked the DSS images to evaluate whether there are anyother nearby sources of X-ray emission within the ROSATpositional uncertainties. The X-ray fluxes of the sources werecomputed using the count rate to-energy flux conversion for-mula by Schmitt et al. (1995). For those two objects whereno X-ray counterparts were found we utilized the ROSATAll-Sky survey images to derive an upper limit in the X-rayflux. Figure 1d displays the fractional X-ray luminosities vs.V − K s for the group members and the candidate stars. TheROSAT X-ray hardness ratios (HR1 and HR2) of the X-raycounterparts were also plotted in an inset of Fig.1d. Ana-lyzing the ROSAT hardness ratio values (HR1 and HR2)for T Tauri stars, young moving group members and for oldfield stars, Kastner et al. (2003) demonstrated that the X-ray spectra of F through M stars soften with age. They ar- c (cid:13) , 1–7 ew members of young moving groups s M K s a J12210499-7116493
ECA s b J01071194-1935359J16430128-1754274HD 160305J19560294-3207186T7443 01102 1J20013718-3313139
BPMG s HD 25402J01521830-5950168 c THA s -7-6-5-4-3 L x / L b o l d s E W L i [ m A ] e -0.5 0.0 0.5 1.0HR1-0.6-0.4-0.2-0.00.20.40.6 H R MP Mus
Figure 1.
Upper panels:
Absolute K s magnitude versus V − K s colour diagrams for the known and candidates members of ECA ( panela ), BPMG ( panel b ) and THA ( panel c ) kinematic groups. Following L´epine & Simon (2009), the loci of the known members of thespecific groups were fitted by a line, the ± panel d: Fractional X-ray luminosities as a function of V − K s for the known and candidates members of the three kinematic groups.The inset shows the X-ray hardness ratio HR1 vs. hardness ratio HR2 for the same objects. Large purple and blue diamonds show thecharacteristic hardness values for T Tauri stars and old K- and M-type main-sequence field stars, respectively. The characteristic valueswere taken from Kastner et al. (2003). The inset does not cover any symbol of the large panel. panel e: Equivalent width of Li λ − K s . In all panels known members of BPMG, THA and ECA are plotted as black circles, black plus signs and blacktriangles, respectively. Squares denote those known close binaries where no photometric data are available separately for the individualcomponents. Upper limits are displayed with down arrows. gued that the distributions of hardness ratios for BPMG,THA and TW Hya association members are tightly clus-tered and very similar to one another. Thus these ratios canalso be used to discriminate between young and old stars.Lithium is burned at low temperatures (2.5 × K) instellar interiors. Since lithium is destroyed and never cre-ated in nuclear reactions, primordial lithium depletes mono-tonically with time in stars with a convective layer. Itmakes lithium one of the best age indicators for young stars(Zuckerman & Song 2004). The measured lithium equiva-lent widths of the candidates (from Table 1), as well asthe known group members are plotted in Figure 1e as afunction of V − K s . For known group members the lithiumdata were taken from different surveys (Torres et al. 2006;da Silva et al. 2009).In tight binaries the tidal interactions can induce strongactivity indicating a spurious young age even if the sys-tem is old otherwise. Thus in these cases the usage ofX-ray luminosity as a diagnostic of youth could be erro-neous. The confusion between single and binary stars can also lead to the estimates of spurious stellar parameters.Our high-resolution spectra allowed us to search for double-and multilined binaries by cross-correlating with the IAURV standards. We found no double-lined binaries amongour sample stars. Apart from HD 160305 – where no pre-vious RV data were available – velocities measured by usall agree well with those in the RAVE data or published byHolmberg, Nordstr¨om, & Andersen (2007). Thus currentlythere is no evidence to suggest that any of our candidatesreside in a tight multiple system. Unfortunately, we have parallax information only for two ofour candidates (HD 25402 and HD 160305). The lack of reli-able trigonometric distances for RAVE stars makes the iden-tification of new members ambiguous, even in those caseswhere the age diagnostic methods confirm the youth of theobjects, because we cannot completely exclude the possibil-ity that we observe a young star whose kinematic properties c (cid:13) , 1–7 L. L. Kiss et al. deviate from those of the moving group because its real dis-tance deviate from the one we predicted using our method.Thus the RAVE-based candidates – in accordance withthe nomenclature proposed by Schlieder, L´epine, & Simon(2010) – are classified as likely new members even in thosecases when all of the prescribed membership criteria are ful-filled.
J12210499-7116493:
Its position coincides well withthe known members of ECA in all age diagnostic figures(Fig. 1 a,d,e). The star has a somewhat larger HR1 ra-tio than most of the young group members, similar tothe classical T Tauri star MP Mus recently assigned toECA by Torres et al. (2008). Kastner et al. (2003) pro-posed that for T Tauri stars the presence of star-disc in-teraction and especially accretion can explain the strongerX-ray hardness ratios. Using the empirical criterion pro-posed by Barrado y Navascu´es & Mart´ın (2003) to distin-guish between stars with chromospheric activity and ob-jects with accretion we conclude that the weak H α emis-sion of J12210499-7116493 (see Table 1) may be of chro-mospheric origin. Based on photometric data from ASAS3,Bernhard, Bernhard, & Bernhard (2009) found J12210499-7116493 to be a probable BY Dra type variable star witha period of 6.855 days. Since the properties of J12210499-7116493 fulfilled all of our criteria we propose it is a likelynew member of ECA. J01071194-1935359 and J16430128-1754274:
All threeage determination methods confirm that these stars arelikely to be coeval with the BPMG. Although their spatiallocation somewhat deviate from the location of the knownmembers, we classify both stars as likely new members ofthe BPMG.
HD 160305:
This star is located quite close tothree other BPMG stars (GSC 8350-1924, CD-54 7336,HD 161460), all within a sphere of 14 pc across. The posi-tion of the star in the age diagnostic diagrams is in goodaccordance with the known members of BPMG, hence weidentify HD 160305 as a new member of the BPMG.
J19560294-3207186, TYC 7443-1102-1 and J20013718-3313139:
L´epine & Simon (2009) proposed that TYC 7443-1102-1 and J19560294-3207186, forming a common propermotion pair, belong to the BPMG. Our observations showedthat the radial velocities of the two stars are also ingood agreement within the uncertainty of the measure-ments. J20013718-3313139, one of our candidates, is lo-cated at an angular distance of 1.6 ◦ from TYC 7443-1102-1/J19560294-3207186. Both the proper motions ( µ α cos δ =27 . ± . µ δ = − . ± . v rad = − . ± . − ) of J20013718-3313139are in good agreement with the corresponding astrometricproperties of TYC 7443-1102-1 ( µ α cos δ = 30 . ± . µ δ = − . ± . v rad = − . ± . − ). The derivedkinematic distance of J19560294-3207186 is also close to thatof TYC 7443-1102-1. We note that all three stars overlapwell with the space distribution of previously known BPMGmembers. Even if J20013718-3313139 and TYC 7443-1102-1/J19560294-3207186 do not form a bound system, the starsare likely to be co-eval, therefore we can combine the resultsof different age diagnostic methods for the three objects. Theabsolute magnitudes and the X-ray fractional luminosities(only an upper limit for TYC 7443-1102-1) overlap well withthe locus of known BPMG members in the CMD (Fig 1 b) and in X-ray related diagrams (Fig 1 d). On the other hand,the Li equivalent width of TYC 7443-1102-1 and J20013718-3313139 (the latter is only an upper limit) are somewhatlower than that of the known members with similar V − K s colour. We classified these three stars as likely new BPMGmembers. J01521830-5950168:
For stars with V − K s > ∼
30 Myr). Thus, this age diagnostic methodcannot be used to support or reject the youth of J01521830-5950168. Since both the X-ray properties and the positionof the star in the CMD coincide well with the known THAmembers, we list this object as a likely new member of THA.
HD 25402:
Both the K s absolute magnitude and themeasured lithium equivalent width of HD 25402 are con-sistent with the similar properties of early G-type stars ofthe THA. The star was not detected in the ROSAT sur-vey. HD 25402 is identified as a wide binary system in theCCDM catalogue (Dommanget & Nys 2002). However, ac-cording to the UCAC3 catalogue (Zacharias et al. 2010), theproper motion of the proposed companion (CCDM J04005-4145B, µ α cos δ = 60 . ± . µ δ = − . ± . µ α cos δ =70 . ± . µ δ = +2 . ± . We searched for new members of three young kine-matic assemblages ( β Pic moving group, ǫ Cha and Tucana-Horologium associations) by combining radial velocity datafrom the RAVE survey with other astrometric information.We used strict selection criteria to filter out false candi-dates by requiring consistency with the colour-magnituderelationship and X-ray properties of the known members.In addition to recovering 10 known members of the threegroups, we identified seven late-type (K,M) new candidates.This list was supplemented by two additional member can-didates, HD 25402 and HD 160305, that were selected fromthe Hipparcos catalogue.Utilizing our new high-resolution spectroscopic observa-tions we found further pieces of evidence for the membershipof our targets. As a result, we identified two new members(1 BPMG, 1 THA) and seven likely members ( 1 ECA, 5BPMG, 1 THA) of the groups. All stars, except TYC 7443-1102-1 and J19560294-3207186, two likely BPMG membersidentified by L´epine & Simon (2009), are new discoveries.These results demonstrate the potential of the RAVE sur-vey in improving the census of young moving groups. Usingthe same methods the searches can be extended for othermoving groups as well. Moreover, the final version of theRAVE catalogue will contain data for approximately threetimes more stars, offering a great opportunity for furthersteps towards a full census of young kinematic groups in theGalactic neighbourhood. c (cid:13) , 1–7 ew members of young moving groups ACKNOWLEDGMENTS
REFERENCES
Apai D., 2009, EM&P, 105, 311Barrado y Navascu´es D., Mart´ın E. L., 2003, AJ, 126, 2997Bernhard K., Bernhard C., Bernhard M., 2009, OEJV, 98,1da Silva L., et al., 2009, A&A, 508, 833Dommanget, J. & Nys, O. 2002, Observations et Travaux54, 5Famaey B., Jorissen A., Luri X., Mayor M., Udry S., De-jonghe H., Turon C., 2005, A&A, 430, 165Feigelson E. D., Lawson W. A., Garmire G. P., 2003, ApJ,599, 1207Fern´andez D., Figueras F., Torra J., 2008, A&A, 480, 735Gontcharov G. A., 2006, AstL, 32, 759Holmberg J., Nordstr¨om B., Andersen J., 2007, A&A, 475,519Jilinski E., Ortega V. G., de la Reza R., 2005, ApJ, 619,945L´epine S., Simon M., 2009, AJ, 137, 3632L´opez-Santiago J., Micela G., Montes D., 2009, A&A, 499,129Kastner J. H., et al., 2003, ApJ, 585, 878Kasper M., et al., 2007, A&A, 472, 321Kharchenko N. V., Scholz R.-D., Piskunov A. E., R¨oser S.,Schilbach E., 2007, AN, 328, 889Makarov V. V., 2007, ApJS, 169, 105Mentuch E., Brandeker A., van Kerkwijk M. H., Jayaward-hana R., Hauschildt P. H., 2008, ApJ, 689, 1127Mo´or A., et al., 2006, ApJ, 644, 525Ortega V. G., de la Reza R., Jilinski E., Bazzanella B.,2002, ApJ, 575, L75Rebull L. M., et al., 2008, ApJ, 681, 1484Riaz B., Gizis J. E., Harvin J., 2006, AJ, 132, 866Schlieder J. E., L´epine S., Simon M., 2010, AJ, 140, 119Schmitt J. H. M. M., Fleming T. A., Giampapa M. S., 1995,ApJ, 450, 392Shkolnik E., Liu M. C., Reid I. N., 2009, ApJ, 699, 649Song I., Zuckerman B., Bessell M. S., 2003, ApJ, 599, 342Steinmetz, M., et al., 2006, AJ, 132, 1645 Terranegra L., Morale F., Spagna A., Massone G., LattanziM. G., 1999, A&A, 341, L79Torres C. A. O., et al., 2006, A&A, 460, 695Torres C. A. O., et al., 2008, Handbook of Star FormingRegions, Vol. II, ASP Monograph Publications, Vol. 5,757van Leeuwen, F. 2007, Astrophysics and Space Science Li-brary, 350, by F. van LeeuwenVoges W., et al., 1999, A&A, 349, 389Voges W., et al., 2000, IAUC, 7432, 1Zacharias N., et al., 2010, AJ, 139, 2184Zuckerman B., et al., 2001, ApJ, 562, L87Zuckerman B., Song I., Webb R. A., 2001, ApJ, 559, 388Zuckerman B., Song I., 2004, ARA&A, 42, 685Zwitter T., et al., 2008, AJ, 136, 421 c (cid:13)000