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Herbig Ae/Be Multiplicity Study

Herbig Ae/Be Multiplicity Study. Bernadette Rodgers , Gemini Observatory Nicole van der Bliek , NOAO CTIO Sandrine Thomas , UCO Lick Observatory Greg Doppmann , NOAO Tucson Jerôme Bouvier , University of Grenoble. Special Thanks to our summer students. Claudia Araya (PIA, 2007)

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Herbig Ae/Be Multiplicity Study

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  1. Herbig Ae/Be Multiplicity Study Bernadette Rodgers, Gemini Observatory Nicole van der Bliek, NOAO CTIO Sandrine Thomas, UCO Lick Observatory Greg Doppmann, NOAO Tucson Jerôme Bouvier, University of Grenoble

  2. Special Thanks to our summer students • Claudia Araya (PIA, 2007) • Maria José Cordero (PIA, 2006) • Anne Sweet (REU, 2006) • Ben Brandvig (REU, 2005) • Lara Pierpoint (REU, 2003) MSF Toronto

  3. Why study Herbig Ae/Be stars? • Herbig Ae/Be stars (HAEBEs) are intermediate-mass (2-8 solar masses) pre-main sequence stars • Bridge the gap between low-mass T Tauri’s and high-mass YSOs • star formation as a function of mass • Studies to date scattered, incomplete • Much less than studies of T Tauri stars • Why not? heterogeneous sample, large distance range for significant sample MSF Toronto

  4. Why study their multiplicity? • Stars do not form in isolation, nor in homogeneous mass environments • HAEBE binary frequency comparable to, or greater than, T Tauri frequency • Constrain star formation models as a function of mass • Do high mass stars form like low mass stars? • IF there is a break, it occurs in HAEBE class • T Tauri binary studies support fragmentation • Effect of HAEBE stars on their companions • “zone of influence” as function of primary mass Note: difficult because of large delta-magnitude MSF Toronto

  5. Our project Broaden the sample of multiple HAEBE systems, and investigate their characteristics • Known Sample: Previous Surveys • Broaden Sample: AO Imaging • Verify companionship • Investigate Companions: NIR Photometry & Spectroscopy, and Mid-IR Imaging MSF Toronto

  6. HAEBE Sample MSF Toronto

  7. AO Imaging • GN+NIRI/Altair & VLT+NACO • Deeper and Closer • dK=2 @0.1” • dK=8 @ 1” • Larger Sample • Nearly doubled candidate multiples 35->66 • ≈50% are multiples (>2) Note: dK(B0-K0) ≈7, while dK(A0-K0) ≈ 3 MSF Toronto

  8. HAEBE Multiplicity surveys – previous & ours - MSF Toronto

  9. Physically bound? • Spectral energy distribution Photometry only SED unconstraint Uncertain IR excess MSF Toronto

  10. Physically bound? • Spectral energy distribution • Proper motion • PM available for 72 stars • Altair-NIRI images: 0,056’’ => 5,6 mas/yr for a 10 yr baseline • 17 objects with enough pm • 6 have ang.sep. and PA in literature MSF Toronto

  11. HIP 114995 pmRA = -18,63 mas/yr pmDEC = -14,84 mas/yr MSF Toronto

  12. Physically bound? • Spectral energy distribution • Proper motion • PM available for 72 stars • Altair-NIRI images: 0,056’’ => 5,6 mas/yr for a 10 yr baseline • 17 objects with enough pm • 6 have ang.sep. and PA in literature 3 companion candidates are moving together with primary; 2 are located within error bars; 1 companion is definitely not moving with HAEBE star MSF Toronto

  13. Physically bound? • Spectral energy distribution • Proper motion • Statistical analysis • Probability of finding at least one unrelated source at an angular separation : • Depends on angular separation  surface density  (30’) (secondary magnitude) MSF Toronto

  14. P is probability to find at least one unrelated source within θ MSF Toronto

  15. Physically bound? • Spectral energy distribution • Proper motion • Statistical analysis • Probability of finding at least one unrelated source at an angular separation : • Depends on angular separation  surface density  (30’) (secondary magnitude) 80 pairs of stars (45 primaries) 2/3 of companions have a certainty of 95% of being related MSF Toronto

  16. Physically bound? • Spectral energy distribution • Uncertain circumstellar extinction • Proper motion • Multiple observations are needed • Only works for stars with fairly large proper motion • Not definitive in clusters • Probability based on surface density • Applicable to large sample • Depends mainly on K magnitude of secondary • Not definitive in clusters • Fold in surface density, as function of spectral type MSF Toronto

  17. Summary of results AO Imaging • Combining those results with previous ones, the total number of HAEBE multiple candidates is 66. We nearly doubled the previously known sample.  Survey continues... • About 50% have more than one possible companion, suggesting a binary fraction potentially greater than 1. • Proper motion study for 6 stars shows that 3 out of 6 stars move together, 1 does not. • Statistical analysis based on surface density shows that 2/3 of candidates are likely to be companions, with 95% certainty. • For stars in clusters it is more difficult to say something conclusive, both based on proper motion and on the statistics. MSF Toronto

  18. Understanding the Nature of HAEBE Companions

  19. Motivation • Just counting companions is not enough… • Need spectroscopy to classify companion • Can help establish true binarity • Look for correlations with primary mass • Mass ratio, multiplicity frequency by mass,… • Compare data with theory in detail • Investigate late-type companions • Are they “typical” T Tauri stars? • What is effect of environment? MSF Toronto

  20. NIR Spectroscopy • GNIRS - cross-dispersed (1-2.5um) R=1700 and R=6000, and K-band R=18000 (for late type companions) • Spectral Type Identification • Improved SED modeling, detect IR excess • Emission Line detection • Indicates accretion, winds • Veiling, rotational velocity, gravity • For resolved lines MSF Toronto

  21. Early type and Late type MSF Toronto

  22. Independent distance Test • Photometry only-- SED unconstrained • Don’t know true Spectral Type • Don’t know about IR excess MSF Toronto

  23. Independent distance Test • Photometry only-- SED constrained to primary distance • G0-G2 with excess MSF Toronto

  24. Spectrum: • SECONDARY shows H I absorption, no late type features • Anomalous HeI, H I emission • ≈G0 (or earlier) • G0 Consistent with distance of primary and moderate excess MSF Toronto

  25. Spectra obtained so far • Taken from literature and Bouvier & Corporon (2001) sample • 9 “Hot” stars, < B7; 5-40 solar masses • 11 “Warm” stars, >B7 and <G0; 1-4 solar masses MSF Toronto

  26. Spectra obtained so far • Taken from literature and Bouvier & Corporon (2001) sample • 9 “Hot” stars, < B7; 5-40 solar masses • 11 “Warm” stars, >B7 and <G0; 1-4 solar masses MSF Toronto

  27. Hot Star: HD76534 • Primary strong emitter • SECONDARY has no emission • Spectral type B3 • Same as primary MSF Toronto

  28. Hot Star: HD76534 • Delta-V = 1.5 • DM ≈ 200pc • Background?(not likely) • Gray extinction? • But no MIR emission • Over-luminous primary? MSF Toronto

  29. Warm Stars and Cool Companions • 11 “Warm” stars, >B7 and <G0; 1-4 solar masses • 12 companions; 9 have strong probability (>98%) of physical association MSF Toronto

  30. CO Ori • SECONDARY is strong emission star • Primary is known variable (UXOR) • Similar spectral type (late F/G0) • May be effected by veiling MSF Toronto

  31. Cool Companions • Often lack emission lines • Not actively accreting? MSF Toronto

  32. Fit spectral type empirically using SpeX Library (Cushing et al) • Simultaneously fit multiple wavelength regions • Line strengths not always well matched MSF Toronto

  33. *also see Carmona et al A&A 2007 (lithium detected) MSF Toronto

  34. Mass Ratio as function of Primary Mass (2004) Theory: • Does mass ratio decrease with increasing primary mass? MSF Toronto

  35. Mass Ratio as function of Primary Mass Data: • Maybe MSF Toronto

  36. Teff: Primary vs Secondary MSF Toronto

  37. Conclusions • Hot Pairs (B+B): • Most likely associated (not necessarily bound) • Why magnitude difference? differential extinction or accretion luminosity? • Lack of Hot-Cool pairs could be sensitivity effect in current spectral sample • Warm-Cool Pairs (A+K/M): • A+A pairs apparently rare; mass ratio for A primaries <0.5 for 7/9 of all sample • No confirmed proper motion pairs (yet) but statistically likely associated • Companions are not “typical” pre-MS • At least 50% lack strong emission • Need to interpret SEDs carefully • “Disk lifetimes shorter” (Bouvier & Corporon 2001) • “Disks last longer” (Carmona et al 2007) MSF Toronto

  38. Summary • AO Imaging survey: Over 100 stars so far; have NIR photometry for over 30 • NIR spectral follow-up: spectral typing, emission lines, distance, IR excess; ~20 so far • Pursuing AO-fed spectroscopy with NIFS for closer pairs • Also high-resolution spectroscopy and MIR imaging for subset • Final product: most extensive HAEBE binary database by far; multiplicity statistics and thorough investigation of companion properties • Test star formation theory in 1-20 solar mass regime • Study effects of “moderate” luminosity neighbors on low mass star formation MSF Toronto

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