Observa6ons of Brown Dwarfs

Transcription

1 Observa6ons of Brown Dwarfs Image credit: Don Dixon Kevin L. Luhman Penn State University

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3 M J Log 10 (L/L sun ) M J 13 M J 73 M J 0.3 M J 8 Burrows et al Age (yr)

4 brown dwarf planet

5 Chabrier et al. (2014) brown dwarf BD if star s composi6on planet if different composi6on

6 Hatzes & Rauer 2015

7 density and radii do not depend on the presence/absence of rocky core at >1 M Jup 25 M E 100 M E 50 M E no core Fortney et al. 2007

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9 What makes it possible for brown dwarfs to form? Barnard 68 Alves et al. 2001

10 What makes it possible for brown dwarfs to form? gravity gas pressure Barnard 68 Alves et al. 2001

11 Turbulent fragmenta6on? e.g., Padoan & Nordlund 2004 gravity gas pressure Barnard 68 Alves et al. 2001

12 Turbulent fragmenta6on? e.g., Padoan & Nordlund 2004 Barnard 68 Alves et al. 2001

13 Dynamical interac6ons? e.g., Reipurth & Clarke 2001, Bate et al Barnard 68 Alves et al. 2001

14 Dynamical interac6ons? e.g., Boss 2001, Stamatellos et al. 2007

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16 If dynamical interac6ons determine masses, then IMF should be broader at higher stellar densi6es (more BDs) high density low density Bonnell et al. 2011

17 Taurus Orion

18 Width of IMF & abundance of BDs similar across a factor of 1000 in stellar density Taurus Luhman et al IC Orion 348 Muench et al. 2002

19 IMF sensi6ve to spectral classifica6ons different classifica6on system

20 IMF sensi6ve to T eff scale & models different T eff scale/models

21 IMF sensi6ve to field size IC 348 core halo no convincing evidence of significant varia6ons in the substellar IMF Muench et al. 2003

22 Chamaeleon I star- forming region Luhman 2007 See also: Bejar et al Briceno et al Slesnick et al Lodieu et al Alves de Oliveira et al Scholz et al. 2012

23 the field Reid et al Bochanski et al. 2010

24 Metchev et al Pinfield et al Burningham et al Reyle et al Kirkpatrick et al. 2011

25 Chabrier 2005

26 1 BD for every 5 stars

27 free- floaters in field at >10 M Jup dominated by BDs rather than ejected companions

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29 Cummings et al Howard et al <20 AU

30 Cummings et al Johnson et al Clanton & Gaudi 2014 Montet et al. 2014

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32 Metchev & Hillenbrand AU

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34 giant planets and BDs overlap in mass

35 5 M Jup planets & BDs exist in similar numbers

36 free- floaters should be called BDs rather than rogue planets

37 microlensing free- floaters (Sumi et al. 2011)

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39 Easiest method of detecting disks: IR imaging

40 Disks detected around solar-type stars with JHKL J H K L Furlan et al. 2011

41 Longer wavelengths needed for most BD disks J H K L Furlan et al. 2011

42 ISO detected a 4.5 µm excess from a young BD J H K 4.5μm Comeron et al. 1998

43 A few BD disks detected at >4 µm from ground Mohanty et al. 2004

44 A few BD disks detected at >4 µm from ground Apai et al. 2004

45 Spitzer detected disks for smallest known BDs (~8 M Jup ) Cha I: Luhman et al. 2005a,b, 2008a,b Cha II: Allers et al. 2006, 2007 σ Ori: Zapatero et al. 2007; Scholz & Jayawardhana 2008; Luhman et al. 2008c

46 Spitzer detected disks in large numbers & at faint levels disks no disks Cha I: Luhman 2008

47 BDs and low- mass stars have similar disk frac6ons Disk frac6on BDs stars see also Carpenter 2006 Luhman 2012

48 Disk life6mes from disk frac6ons vs. age Haisch et al. 2001

49 Disk life6mes longer for lower stellar masses Luhman 2012 see also Carpenter 2006 Disk frac6on BDs stars

50 UV excess emission from accre6ng BDs data template+model excess template Herczeg & Hillenbrand 2008; Herczeg et al. 2009

51 X- shooter: UV excess + many lines + near- IR excess Stelzer et al. 2013

52 X- shooter: UV excess + many lines + near- IR excess Rigliaco et al. 2011

53 Accre6on rates decrease steadily from stars to BDs Alcala et al. 2014

54 Harvey et al Far- IR and mm: BD disk masses ~ M Jup Far- IR: Harvey 2012a,b; Alves de Oliveira 2013 mm: Klein 2003; Scholz 2006; Ricci 2012, 2013; Mohanty 2013; Andrews 2013

55 Disk mass/star mass roughly constant at ~ 0.4% Tau Oph TWA Mohanty et al. 2013

56 Disk mass/star mass roughly constant at ~ 0.4% all Taurus class II <M8 Andrews et al. 2013

57 Companions that are young, wide, and <20 M Jup 2M 1207B Chauvin et al CHXR73B Luhman et al CT Cha B Schmidt et al DH Tau B Itoh et al B Lafreniere et al. 2008

58 Accre6on detected in wide M Jup companions Ireland et al AU Bowler et al. 2011

59 Accre6on detected in wide M Jup companions Zhou et al. 2014

60 Bowler et al ALMA non- detec6on: M disk < 0.05 M Jup

61 Bowler et al ALMA non- detec6on: M disk /M BD < 0.3%

62 Do brown dwarfs undergo the protostellar phases like stars? Class 0 Class I Class II Class III

63 Spitzer has found possible protostellar brown dwarfs, which are not predicted by dynamical models Spitzer image of L1014 CO ouulow in L1014 Young et al Bourke et al See also: Huard et al. 2006, Dunham et al. 2006, 2008, André et al. 2012

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65 Most binary brown dwarfs have small separa6ons (<20 AU) Burgasser et al. 2007

66 But a few binary brown dwarfs are wide (>100 AU) Young Clusters Luhman 2004 Field Burningham et al Scholz et al. 2010

67 But a few binary brown dwarfs are wide (>100 AU) brown dwarfs in wide, fragile systems unlikely to have formed by ejec6on Burgasser et al. 2007

68 Binary frequency decreases steadily with lower mass Duchene & Kraus 2013

69 Indicator of forma6on mechanism: mass ra6o (M 2 /M 1 ) 25 M Jup 4 M Jup 2M 1207B Chauvin et al Large mass ra6o è formed like a binary star

70 Indicator of forma6on mechanism: mass ra6o (M 2 /M 1 ) HST+WFPC2 PSF subtracted 20 M Jup 7 M Jup 2M044144B Todorov et al Large mass ra6o è formed like a binary star

71 Indicator of forma6on mechanism: configura6on of orbits HR8799bcd Marois et al Three small objects orbi6ng a much larger primary è forma6on in a disk

72 Indicator of forma6on mechanism: configura6on of orbits HST+WFPC2 Gemini+ALTAIR 2M044144B Todorov et al. 2010

73 Indicator of forma6on mechanism: configura6on of orbits Gemini+ALTAIR AO 6p- 6lt star

74 Indicator of forma6on mechanism: configura6on of orbits Gemini+ALTAIR 40 M Jup 20 M Jup 0.15 M 7 M Jup Hierarchical configura6on è cloud core fragmenta6on

75 imaging RV lensing exoplanet.eu

76 exoplanet.eu

77 2M0441 2M1207 HR8799 exoplanet.eu

78 exoplanet.eu

79 solar- mass stars cloud core fragmenta&on forma&on in disks exoplanet.eu

80 solar- mass stars cloud core fragmenta&on IMF minimum forma&on in disks exoplanet.eu

81 low- mass stars cloud core fragmenta&on IMF minimum forma&on in disks exoplanet.eu

82 brown dwarfs binary star forma&on IMF minimum forma&on in disks exoplanet.eu

83 Summary IMF, disks, & binarity indicate that BDs form like stars without the need for dynamical interac6ons BDs and giant planets overlap in mass and exist in similar numbers at 5 M jup Free- floa6ng objects are probably BDs unless there is evidence indica6ng forma6on in a disk Binary star forma6on extends down to 5 M jup