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Newly identified very wide low-mass binary systems

A large-scale near-IR survey aiming to identify new brown dwarfs using precise astrometry, uncovering co-moving pairs of late stars. Method involves PM comparison between SIMP, SDSS, and 2MASS. Exciting discoveries and future work detailed.

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Newly identified very wide low-mass binary systems

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  1. Newly identified very wide low-mass binary systems David Lafrenière (U. Montréal) Étienne Artigau (Gemini S.) René Doyon (U. Montréal) Loïc Albert (CFHT) Cassy L. Davison (Gemini S.)

  2. Sondage Infrarouge de Mouvement Propre (SIMP) • Large-scale near-IR imaging survey • Observations • CPAPIR camera • 35′×35′ FOV • 2005-2007 at CTIO 1.5-m • 2007-… at Mégantic 1.6-m • J-band, down to J~17 • 16% of sky covered (d < +20º)

  3. SIMP goal(s) • Identify new BDs in 2MASS data through PM • Astrometric precision of ~0.2″ (1s) and Dt~4-9 years • PM uncertainty ~25-50 mas yr-1 • 30+ new BDs confirmed spectroscopically • 300+ new BD candidates • …uncover new co-moving pairs of late stars • SDSS can also be used as 2nd epoch • Dt up to ~5 years

  4. Search for binaries: method • Initial star list: • NLTT + LSPM catalogs • PM > 0.15″ yr-1 (>3s) • Roughly 60000 stars • ~11500 observed by SIMP • ~15000 observed by SDSS • Compare SIMP & SDSS vs 2MASS • Compute differential PM of sources within 4′ • Candidate companion if < 40 mas yr-1 (~1s)

  5. Search method (cont.) • Spectral type estimate • (I)JHK if only 2MASS • r′i′z′JHK if SDSS as well • Photometric distance estimate • Based on spectral type + J • dphot of both components of candidate binary must overlap within estimated uncertainties

  6. Ex. of discovery: SIMP vs 2MASS • Primary: M3-M4 • VIJHK photometry • Secondary: L4 • GNIRS spectroscopy • Separation: 18.1″ • ~900 AU PM of all sources within 10′ of target star

  7. Ex. of discovery: SIMP vs 2MASS

  8. Ex. of discovery: SIMP vs 2MASS 18″ Blink: 2MASS J-band Vs SIMP J-band

  9. Ex. of discovery: SDSS vs 2MASS • Primary: M5-M6 • r′i′z′JHK photometry • Secondary: L0 • r′i′z′JHK photometry + SDSS spectroscopy • Separation: 7.6″ (~300 AU)

  10. 23 candidate binary systems found

  11. Probability of random alignment • Calculation for 2 stars • of SpT in [M3,L4] • located at 25-75 pc or 75-125 pc • with DPM < 40 mas yr-1 • Can be viewed as upper limits Stars at 75-125 pc Stars at 25-75 pc Expected number of unrelated co-moving pairs

  12. New candidates

  13. Follow-up and future work • Imaging – CPAPIR or SIMON • Improve PM accuracy • Spectroscopy – GNIRS (GMOS?) • Obtain accurate spectral types • Obtain differential RV measurements? • Perform a blind search for binaries • i.e. not just for companions to known high-PM stars • Using SIMP & SDSS vs 2MASS • Could detect VLM systems

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