1 / 38

Dark Matters

Dark Matters. Red dwarfs, low-mass stars & brown dwarfs. Neill Reid, Univ. of Pennsylvania in association with 2MASS Core project: Davy Kirkpatrick, Jim Liebert, Conard Dahn, Dave Monet, Adam Burgasser. Shameless plug…. Now available from Amazon.com and in all the best bookstores.

urbana
Download Presentation

Dark Matters

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Dark Matters Red dwarfs, low-mass stars & brown dwarfs Neill Reid, Univ. of Pennsylvania in association with 2MASS Core project: Davy Kirkpatrick, Jim Liebert, Conard Dahn, Dave Monet, Adam Burgasser

  2. Shameless plug…. Now available from Amazon.com and in all the best bookstores

  3. Cool dwarf evolution (1) Low-mass stars: H fusion establishes equilibrium configuration Brown dwarfs: no long-term energy supply T ~ 2 million K required for lithium fusion

  4. Cool dwarf evolution (2) Rapid luminosity evolution for substellar-mass dwarfs

  5. Cool dwarf evolution (3) Brown dwarfs evolve through spectral types M, L and T L dwarfs encompass stars and brown dwarfs Cooling rate decreases with increasing mass

  6. Cool dwarf spectra (1) Early-type M dwarfs characterised by increasing TiO absorption CaOH present for sp > M4

  7. Cool dwarf spectra (2) Late M dwarfs: increasing TiO VO at sp > M7 FeH at sp > M8

  8. Cool dwarf spectra (3) Spectral class L: decreasing TiO, VO - dust depletion increasing FeH, CrH, water lower opacities - increasingly strong alkali absorption Na, K, Cs, Rb, Li

  9. Cool dwarf spectra (4) Low opacity leads to high pressure broadening of Na D lines cf. Metal-poor subdwarfs

  10. Optical HR diagram Broad Na D lines lead to increasing (V-I) at spectral types later than L3.5/L4 Latest dwarf - 2M1507-1627 L5 Astrometry/photometry courtesy of USNO (Dahn et al)

  11. The near-infrared HR diagram K I absorption leads to increasing (I-J) at sp > L7

  12. Cool dwarf spectra (5) : near-IR K, Fe, Na atomic lines water, CO molecular bands

  13. The L/T transition Onset of methane absorption at T~1200/1300 K leads to reduced flux at H, K Radical change in colours (cf. Tsuji, 1964) [Burgasser - this meeting]

  14. The near-IR HR diagram (2) Methane absorption eliminates JHK-only search for T dwarfs

  15. Brown dwarf atmospheres Non-grey atmospheres - flux peaks at 1, 5 and 10 microns - bands and zones? - “weather”?

  16. Brown dwarf “weather” Observations suggest that brown dwarfs have rapid rotation - v ~ 40 to 80 km/sec - P ~ 4 hrs to 90 mins If brown dwarfs had spots (giant storms?), what would we see?

  17. Clouds on an L8? Gl 584C - r ~ 17 pc - 2 G dwarf companions - a ~ 2000 AU - age ~ 100 Myrs - Mass ~ 0.045 M(sun) - M(J) ~ 15.0 Gl 229B M(J) ~ 15.4

  18. Low mass binaries Why binaries? - dynamical mass estimates - coeval: calibration of relative properties Finding binary systems - direct imaging: wide systems ( > 5 AU) - HST + ground-based AO imaging - radial velocities: close systems - Keck spectroscopy, optical + IR Targets - low mass stars in open clusters - nearby low-luminosity dwarfs

  19. The Hyades cluster Age ~ 625 Myrs Distance ~ 45.3 parsecs Diameter ~ 12 parsecs > 400 known members Uniform space motion V ~ 46.7 km/sec

  20. Binary surveys: the Hyades (1) Targets: 55 late-type M dwarfs Mv > 12, Mass < 0.3 M(sun) HST imaging (with John Gizis, IPAC) - resolution 0.09 arcseconds, ~ 4 AU - capable of detecting 0.06 M(sun) brown dwarfs expect 2 to 3 detections - nine new stellar binaries detected - no brown dwarf companions

  21. Binary surveys: the Hyades (3) Spectroscopic survey (Reid & Mahoney) Rhy 403 - Period ~ 1.25 days - amplitude 40 km/sec Primary mass ~ 0.15 M(sun) single-lined system The secondary has a mass between 0.06 and 0.095 solar masses. 70% probability M < 0.075 -> 1st candidate brown dwarf

  22. Binary surveys: the Hyades (4) Summary: 25% of low-mass Hyads have a stellar companion 1 candidate brown dwarf Another brown dwarf desert?

  23. What about brown dwarf binaries? The alternative model for browm dwarfs

  24. Binary surveys: L dwarfs (1) Several L dwarfs are wide companions of MS stars: e.g. Gl 584C, G196-3B, GJ1001B (& Gl229B in the past). What about L-dwarf/L-dwarf systems? - initial results suggest a higher frequency >30% for a > 3 AU (Koerner et al, 1999) - all known systems have equal luminosity --> implies equal mass Are binary systems more common amongst L dwarfs? or are these initial results a selection effects?

  25. Binary surveys: L dwarfs (2) HST imaging survey of 160 ultracool dwarfs (>M8) over cycles 8 & 9 (Reid + 2MASS/SDSS consortium) Successful WFPC2 observations of 20 targets to date --> only 4 binaries detected 2M0746 - L0.5 (brightest known L dwarf) 2M1146 - L3 2M0920 - L6.5 2M0850 - L6

  26. Binary systems: L dwarfs (5) 2M0850: I-band V-band

  27. Binary surveys: L dwarfs (6) Binary components lie close to L dwarf sequence: 2M0850B M(I) ~0.7 mag fainter than type L8 M(J) ~0.3 mag brighter than Gl 229B

  28. 2M0850AB (1) 2M0850A has strong lithium absorption --> implies a mass below 0.06 M(sun) 2M0920A - no detectable lithium --> M > 0.06 M(sun)

  29. 2M0850AB(2) Mass limits: 2M0850A: M < 0.06 M(sun) q(B/A) ~ 0.75 2M0920A: M > 0.06 M(sun) q(B/A) ~ 0.95

  30. 2M0850AB (3) Constraining brown dwarf models - primaries have similar spectral type (Temp) -> similar masses ~0.06 2M0850B ~ 0.045 M(sun) age ~ 1.7 Gyrs

  31. L dwarf binary statistics (1) Four detections from 20 targets --> comparable with detection rate in Hyades but … <r> ~ 20 parsecs for L dwarfs ~ 46 parsecs for Hyades M dwarfs Only 1 of the 4 L dwarf binaries would be resolved at the distance of the Hyades => L dwarf binaries rarer/smaller <a> than M dwarfs

  32. L dwarf binary statistics (2) Known L dwarf binaries - high q, small <a> a < 10 AU except Pl - low q, large <a> -> lower binding energy - preferential disruption? Wide binaries as minimal moving groups?

  33. Binary surveys: T dwarfs A digression: chromospheric activity is due to acoustic heating, powered by magnetic field. H-alpha emission traces activity in late-type dwarfs.

  34. Binary surveys: T dwarfs H-alpha activity declines sharply beyond spectral type M7

  35. Binary surveys: T dwarfs ..but 2M1237+68, a T dwarf, has strong H-alpha emission - no variation observed July, 1999 - February, 2000 Possible mechanisms: - Jovian aurorae? - flares? - binarity?

  36. 2M1237 : a vampire T dwarf Brown dwarfs are degenerate - increasing R, decreasing M - ensures continuous Roche lobe overflow

  37. Summary 1. Photometric/spectroscopic characteristics of ultracool dwarfs are now well characterised 2. Gl584C provides the first detection of brown dwarf “weather” 3. Rhy 403B is a candidate Hyades brown dwarf, but substellar-mass companions remain rare 4. First results from HST L dwarf survey - 4 of 20 are binary - 1 candidate L/T transition dwarf - L dwarf/L dwarf binaries rare disruption of primordial systems?

  38. And our goal.. an eclipsing system

More Related