The Lowest Mass Young Star Spectroscopic Binaries

1. The Lowest Mass Young Star Spectroscopic Binaries Lisa Prato Lowell Observatory Multiplicity in Star Formation -- Toronto -- May 17, 2007

2. What happens to young star spectroscopic multiplicity below 0.6 M ? PRE-MAIN-SEQUENCE DOUBLE-LINED SBS Visible light SB2s IR identified SB2s Prato et al. (2002) • Desert of brown dwarf spectroscopic companions to higher mass stars (e.g., Marcy & Butler 2000) • Small fraction of low-mass wide separation visual binaries (e.g., Gizis et al. 2003; Burgasser et al. 2003) • Few planets around the lowest mass stars (e.g., Butler et al. 2004; Endl et al. 2006)

3. ~ main-sequence  Primary Mass Separation 

4. But need to add more dimensions: age (many), metallicity (Boden), secondary mass… • …and to take into account variations between diverse star-forming regions: • Binary fraction & separation distribution a function of stellar density (e.g., Simon 1997; Kraus & Hillenbrand 2007) Lada et al. (2000) Orion Serpens NASA/JPL-Caltech/L. Cieza (UT Austin)  Talk at 2:40pm today!

5. Impact of surveys for VLM stellar and substellar young spectroscopic binaries: • Implications for stellar binary formation, substellar binary formation, and planet formation (e.g., Goodwin, Bate, Clarke, et al.) • Enables measurement of dynamical quantities such as mass ratios and eventually masses (e.g., Boden) • Quantitative tests of formation models • Quantitative SFR comparisons Mazeh et al. 2003

6. “A comprehensive theory of star formation must account not only for the stellar/substellar initial mass function, but also the frequency and orbital distributions of binary systems.” Gizis et al. (2003)  Talk at 2:20pm today! “There are a lot of M stars out there…” Lada (2006), Endl et al. (2006), Boss (2006), Prato (MSF, 2007), et al.

7. NIRSPEC+Keck2 / H-band /R=30,000 1 2 A tale of two Keck surveys: First large IR radial velocity survey of young stars (1) Young early M stars in Ophiuchus • Homogeneous sample (from Martín et al. 1998) • X-ray sources • Spectral types K7 - M4 • Selected from 4 regions of Ophiuchus • 31 targets - average H=9.8 mag (2) Young late M type objects in Taurus, TW Hya, and Ophiuchus • Sample from White & Basri; Jayawardhana et al.; Muzerolle et al. 2003; Briceño et al. 2002 • Spectral types M6 - M9 • Combination of non-accretors and accretors • 18 targets - average H=12.2 mag • Why IR observations? • M stars peak at >1m • Better chance of detecting spectra of faint, red 2ndaries

8. 1” 1” Young, early M star results: Prato (2007) (130 AU) • Variety of multiple scales identified!

9. 4/31 objects observed are spectroscopic binaries • Two double-lined systems, one located within a quadruple system • Two single-lined systems • At least one radial velocity variable candidate • Five subarcsecond visual binaries serendipitously discovered • Average vsini ~ 20 km/s (range <10 to >50 km/s) 8.0 3.5 %: • Overall spectroscopic multiplicity = 12± Consistent with higher mass young star + field star fractions

10. Young, late M objects: Preliminary results • Three epochs’ observations of (almost) every target • Some of the highest SNR, high-resolution spectra to date • Similar M6—M9 homogeneity in features as high-resolution J-band data on field brown dwarfs (McLean et al. 2007)

11. Analysis of third epoch of radial velocity shifts (∆vr) incomplete; results from initial analysis of first two epochs only: 4-13 months • Average ∆vr = –0.11±0.83 km/s (all 18 targets) Average ∆vr = –0.02±0.45 km/s (targets w/ ∆vr < 1 km/s) Precision ~ 0.5 km/s • Joergens (2006): M2.5 – M8  2/12 candidate RV variables  Talk at 4:30pm today! • Kurosawa et al. (2006): M5 – M8.5  4/17 candidate RV variables  Talk at 4:00pm today!

12. Candidate RV Variables?? only 2 epochs! ~10-20 epochs on variable candidates Joergens (2006) Prato in prep. • Are chromospheres active enough to produce spots and thus faux radial velocity noise? “Young BDs of spectral type M are sufficiently warm to sustain an active corona.” (Grosso et al. 2006)

13. Three interesting cases: KPNO-Tau 8 Broadest lines in sample • In general vsini’s systematically < than for early M stars: ave ~10 km/s  longer-lived disks as suggested by Bouy et al. (2007)? MHO 5 False hope from literature! White & Basri (2003): RV = 20.8±0.7 km/s Muzerolle et al. (2003): RV = 12.3±1.2 km/s NIRSPEC data: 4 epochs  ~16±0.5 km/s 2MASS 1207 Very low-mass companion at 55 AU: maximum induced RV only 0.15 km/s — nothing detected

14. What to do next! • Observational biases a huge problem (IR vs. visible, etc) • Completeness of samples in different SFRs lacking • Need a lot of observations with optimized sampling • Plenty to do before the next workshop!

15. Conclusions • Spectroscopic multiplicity of young, early and late M stars is important to study for comprehensive knowledge of parameter space and for assumption-free dynamical data • Early Ophiuchus M stars have spectroscopic multiplicity comparable to that of field stars and higher mass young stars • Late M (≥M6) sample yields 3 candidate SBs — need to be confirmed with multiple epoch observations! • Late M vsini’s systematically lower than for early Ms • Homogeneous, large samples within individual SFRs are important — if challenging — to compile This research was supported by the NASA KPDA fund & the NSF