A search for new members of the β Pictoris, Tucana–Horologium and ε Cha moving groups in the RAVE data base

Center of excellence SPACE-SI, Ljubljana, Slovenia
Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.52). 02/2011; 411(1):117 - 123. DOI: 10.1111/j.1365-2966.2010.17660.x

ABSTRACT We report on the discovery of new members of nearby young moving groups, exploiting the full power of combining the Radial Velocity Experiment (RAVE) survey with several stellar age diagnostic methods and follow-up high-resolution optical spectroscopy. The results include the identification of one new and five likely members of the β Pictoris moving group, ranging from spectral types F9 to M4 with the majority being M dwarfs, one K7 likely member of the ε Cha group and two stars in the Tucana–Horologium association. Based on the positive identifications, we foreshadow a great potential of the RAVE data base in progressing towards a full census of young moving groups in the solar neighbourhood.

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    ABSTRACT: We describe the results of an ongoing project aimed to identify new members of young associations by searching for common proper-motion companions to already-known members. We have used the Aladin sky atlas of the Virtual Observatory and the 2MASS, USNO-B1 and PPMXL astro-photometric catalogues to look for new faint members in the the Local Association and its young kinematic groups (Tucana-Horologium, β Pictoris, AB Doradus). We have discovered several new late-type stellar companions. For one of the new identified objects, we have taken low-resolution spectroscopy to confirm its young nature and characterise its stellar properties. A detailed study of Tucana-Horologium has provided an unprecedented view of the moving group nucleus around β^{01+02+03} Tuc, which lies at the centre of the remnant of the cluster that originated the group.
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    ABSTRACT: We present a comprehensive investigation of the Epsilon Chamaeleontis association (Epsilon Cha), one of several young moving groups spread across the southern sky. We re-assess the putative membership of Epsilon Cha using the best-available proper motion and spectroscopic measurements, including new ANU 2.3-m/WiFeS observations. After applying a kinematic analysis our final membership comprises 35-41 stars from B9 to mid-M spectral types, with a mean distance of 110+/-7 pc and a mean space motion of (U,V,W)=(-10.9+/-0.8,-20.4+/-1.3,-9.9+/-1.4) km/s. Theoretical evolutionary models suggest Epsilon Cha is 3-5 Myr old, distinguishing it as the youngest moving group in the solar neighbourhood. Fifteen members show 3-22 micron spectral energy distributions attributable to circumstellar discs, including 11 stars which appear to be actively accreting. Epsilon Cha's disc and accretion fractions (29+8-6 and 32+9-7 per cent, respectively) are both consistent with a typical 3-5 Myr-old population. Multi-epoch spectroscopy reveals three M-type members with broad and highly-variable H-alpha 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 Epsilon Cha's connection to the young open cluster Eta Cha and the Sco-Cen OB association. Contrary to earlier studies which assumed Eta and Epsilon Cha are coeval and were born in the same location, we find the groups were separated by ~30 pc when Eta Cha formed 4-8 Myr ago in the outskirts of Sco-Cen, 1-3 Myr before the majority of Epsilon Cha members.
    Monthly Notices of the Royal Astronomical Society 05/2013; 435(2). · 5.52 Impact Factor
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    ABSTRACT: We present a new method based on a Bayesian analysis to identify new members of nearby young kinematic groups. The analysis minimally takes into account the position, proper motion, magnitude, and color of a star, but other observables can be readily added (e.g., radial velocity, distance). We use this method to find new young low-mass stars in the β Pictoris and AB Doradus moving groups and in the TW Hydrae, Tucana-Horologium, Columba, Carina, and Argus associations. Starting from a sample of 758 mid-K to mid-M (K5V-M5V) stars showing youth indicators such as Hα and X-ray emission, our analysis yields 214 new highly probable low-mass members of the kinematic groups analyzed. One is in TW Hydrae, 37 in β Pictoris, 17 in Tucana-Horologium, 20 in Columba, 6 in Carina, 50 in Argus, 32 in AB Doradus, and the remaining 51 candidates are likely young but have an ambiguous membership to more than one association. The false alarm rate for new candidates is estimated to be 5% for β Pictoris and TW Hydrae, 10% for Tucana-Horologium, Columba, Carina, and Argus, and 14% for AB Doradus. Our analysis confirms the membership of 58 stars proposed in the literature. Firm membership confirmation of our new candidates will require measurement of their radial velocity (predicted by our analysis), parallax, and lithium 6708 Å equivalent width. We have initiated these follow-up observations for a number of candidates, and we have identified two stars (2MASSJ01112542+1526214, 2MASSJ05241914-1601153) as very strong candidate members of the β Pictoris moving group and one strong candidate member (2MASSJ05332558-5117131) of the Tucana-Horologium association; these three stars have radial velocity measurements confirming their membership and lithium detections consistent with young age.
    The Astrophysical Journal 12/2012; 762(2):88. · 6.73 Impact Factor