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

What happens to young star spectroscopic multiplicity below 0.6 M ? Visible light SB2s PRE-MAIN-SEQUENCE DOUBLE-LINED SBS Prato et al. (2002) IR identified SB2s 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)

G many lots some K M L ? rare T ~ main-sequence  Primary Mass spectroscopic small-separation visual wider-separation visual wide  Primary Mass Separation 

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!

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

“There are a lot of M stars out there…” “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.

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 2 NIRSPEC+Keck2 / H-band /R=30,000 1 Why IR observations? M stars peak at >1m Better chance of detecting spectra of faint, red 2ndaries

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

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) Overall spectroscopic multiplicity = 12± 8.0 3.5 %: Consistent with higher mass young star + field star fractions

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)

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!

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)

Broadest lines in sample 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

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!

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