Binary and Mul,ple Stars

Transcription

1 Binary and Mul,ple Stars

2 Types of Mul,ple Systems Binaries Visual SB1 SB2 Triples Heirarchical Quadruples Trapezia

3 T Tau triple system Kohler et al 2016

4 Observa,ons Imaging Rayleigh Limit: Resolu,on = λ/d

5 Observa,ons Spectroscopic v = c δλ/λ v = (GM/a) ½ = (2πGM/P) 1/3

6 SB2

7 Observa,ons Contrast Luminosity M 3.5 on upper main sequence Instrumental considera,ons make SNR>100 hard to achieve ΔM ~ 10 (SNR/3.5) = 3.7 for SNR=100

8 What makes a physical pair? An orbit Common space mo,ons and distances

9 Mul,plicity Frac,on MF = (B+T+Q) / (S+B+T+Q) Companion star frac,on CF = (B+2T+3Q) / (S+B+T+Q)

10 Are most Stars in Binaries? Mul,plicity frac,on of F7- G9 stars (164 stars, d<22pc, δ > - 20) Duquennoy & Mayor 1990 Single : double : triple : quadruple 57 : 38 : 4 : 1 56 : 33 : 8 : 1 (Raghavan 2010 update; unc 2%) MF ~ 70% for massive stars MF ~ 30% for M stars

11 Blue: MF Red: CF Duchene & Krause 2013 ARAA 51, 269

12 Eccentricity Distribu,on J. L. Halbwachs, M. Mayor, S. Udry, F. Arenou, 2003, A&A, 397, 159

13 Mass ra,o distribu,on Observed Corrected Mazeh et al, 2003, ApJ, 599, 1344

14 The PMS Mul,plicity Func,on 100% in Taurus About double the MS MF Is the MF the same in T associa,ons and in young clusters? High density SFRs may have lower MFs

15 PMS MF Evolu,on Reipurth et al, 2014, PPVI

16 Binary Frac,on with Mass Observa,ons and simula,ons suggest that most stars form in binary systems (e.g. Duquennoy & Mayor 1991; Goodwin & Kroupa 2005; Kouwenhoven et al. 2005,2007b; Goodwin et al. 2007; Mason et al. 1998; Kobulnicky & Fryer 2007), and that a substan,al frac,on are part of a triple or higher- order system (e.g. Tokovinin & Smekhov 2002; Correia et al. 2006; Tokovinin et al. 2006; Hu et al. 2008). Mul,plicity is thus a fundamental property of the star forming process. Detailed knowledge of a young binary popula,on can be employed to study the outcome of star forma,on, consequently the star forma,on process itself. Surveys indicate that the proper,es of the binary popula,on are a func,on of the spectral type of the primary star. Prac,cally all O- type stars (Mason et al. 1998) and B/A- type stars ( Shatsky & Tokovinin 2002; Kouwenhoven et al. 2007b; Kobulnicky & Fryer 2007) are found in binary or mul,ple systems. Abt & Levy (1976) report a mul,plicity frac,on of 55% among F3- G2 stars, and in their CORAVEL spectroscopic study of F7- G9 stars, Duquennoy & Mayor (1991) find a binary frac,on of. The binary frac,on among M- type stars is (Reid & Gizis 1997; Fischer & Marcy 1992; Leinert et al. 1997). For late M- type stars and brown dwarfs the binary frac,on decreases to (e.g., Close et al. 2003; Bouy et al. 2003; Burgasser et al. 2003; Siegler et al. 2005; Joergens 2008; Ahmic et al. 2007; Maxted et al. 2008; Gizis et al. 2003).

17 Binary Star Forma,on Mechanisms Capture Requires energy dissipa,on N * > 2, or in a cloud Consequence: non- coeval pair Fission Does not work Protostars rotate too slowly Predicts q<0.1 Fragmenta,on

18 Binary Star Forma,on Mechanisms Fragmenta,on In collapsing cloud Scales: Jeans mass In protostellar disk Toomre Q Simula,ons reproduce observa,ons Trouble producing close binaries

19 Role of Gas Physics γ: adiaba,c exponent, γ= c p /c v P (γ-1)ρ T ρ (γ-1) PV γ constant on an adiabat γ: 1: isothermal gas 4/3: photon gas 5/3: ideal monatomic gas 7/5: ideal gas (molecular)

20 Toomre Q Sta,s,c for disk stability Q = κc s /πgσ κ 2 = 2Ω/R d/dr(r 2 Ω) for Keplerian rota,on, κ=ω Stable to axi- symmetric perturba,ons for Q>1

21 Star Forma,on Simula,ons hrps:// people/mbate/cluster/ pr.html

22 hrps:// Marhew R. Bate, Ian A. Bonnell, and Volker Bromm

23 Evolu,on of Binaries Tidal Stripping: Balance stellar/galac,c forces F Gal = GM Gal m/r 2 GC F = GMm/R 2 * R * = R GC (M/M Gal ) ½ For M=1 M, R~0.018 pc = 3600au

24 Evolu,on of Binaries Circulariza,on: Due to,dal dissipa,on cf: Hut, 1981, A&A, 99, 126

25 Later Disk instabili,es

26 Fragmenta,on Simula,ons show: For barotropic EoS (P =f(ρ)), fragmenta,on when cen,fugally- supported - > 100au disks Radia,ve feedback increases scale to 10 3 au Do binaries can spiral in?

27 Issues: Theory Fragmenta,on seems promising, but Very sensi,ve to ini,al condi,ons Role of magne,c fields/ambipolar diffusion? Model simula,ons terminate too soon Will simula,ons produce bound binary star systems? Can this produce close binaries?

28 Issues: Theory Can fragmenta,on produce close binaries? Role of magne,c field: Strength Orienta,on Supression or enhancement? Role of Turbulence How is angular momemtum lost? Reipurth: premature to draw conclusions from fragmenta,on models

29 Spectroscopic Binaries P < 4000 days Metal poor field stars: BF = 18 +/- 4% PMS: ~12% SB a< a few au: Cannot form in situ: must inspiral

30 Interac,ons in PMS Binaries Assume two independent star/disk systems Type 1 encounters: disk perturba,ons during periastron passage FUOrs/Exors? Type 2 encounters:,des/disk dissipa,on results in close circular pair with circumbinary disk V4041 Sgr Type 3 encounters: coalescence Extremely rapidly rota,ng PMS stars Rela,on to HH objects?

31 Origin of Single Stars PMS MF > field MF Frac,on of singles increases with decreasing mass Lowest mass member of triples tend to be ejected Origin of single from evolu,on of higher- order systems? Ejec,on veloci,es ~ 1 km/s (1 pc in 10 6 yrs) Origin of singles in mergers?

32 Issues: Observa,on Are there non- coeval binaries? Is the role of environment quan,fiable?