Post on 27-Mar-2021
Brown Dwarfs as Chronometers
1 © 2009 Adam J. Burgasser
IAU 258: Ages of Stars
Brown Dwarfs
Adam J. Burgasser Massachusetts Institute of
Technology
as Galactic Chronometers
© 2009 Adam J. Burgasser
Brown Dwarfs as Chronometers
2 © 2009 Adam J. Burgasser
IAU 258: Ages of Stars
~0.075 M
Eff
ectiv
e T
empe
ratu
re (
K)
“Planemos”
Brown Dwarfs
Stars
Time (Gyr)
(Z dependent)
M L
T
Y?
Spectral classes
models from Burrows et al. (2001)
Brown Dwarfs as Chronometers
3 © 2009 Adam J. Burgasser
IAU 258: Ages of Stars
Magnetic Activity: �A Poor Diagnostic
Fleming et al. (2003); Burgasser & Putman (2006) see also Gizis et al. (2000); West et al. (2004); Osten et al. (2005); Berger (2006); Audard et al. (2007); Schmidt et al. (2007)
M5 L0 L5
X-rays
Hα
radio
log
LR/L
bol log L
Hα /L
bol lo
g L
X/L
bol
(next) talk by A. West
Brown Dwarfs as Chronometers
4 © 2009 Adam J. Burgasser
IAU 258: Ages of Stars
No slow rotators for SpT > L2, evidence of mass & temperature dependent spindown timescale (ωcrit → 0).
Do Brown Dwarfs ever spin down? Halo L subdwarf vsini = 65 km/s
Reiners & Basri (2008) see also Mohanty et al. (2002), Mohanty & Basri (2003), Bailer-Jones (2004); Reiners & Basri (2006), Blake et al. (2007)
Brown Dwarfs as Chronometers
5 © 2009 Adam J. Burgasser
IAU 258: Ages of Stars
Method 1: Companions and Clusters
Gliese 570D (2-5 Gyr) Burgasser et al. (2000)
HD 3651B (0.7-4.7 Gyr) Luhman et al. (2006) Mugrauer et al. (2006)
G 196-3B (30-300 Myr) Rebolo et al. (1998)
Young clusters
MK
J-K
Upp Sco α Per Pleiades Ursa Major & Hyades
Jameson et al. (2008)
Brown Dwarfs as Chronometers
6 © 2009 Adam J. Burgasser
IAU 258: Ages of Stars
Method 2: �The Li clock
Li is fused to exhaustion in the core for M > 0.065 M, ages > 500 Myr
50-200 Myr “sweet spot”: degree of Li depletion depends on age and mass - the Li depletion boundary.
see Rebolo et al. (1992); Bildsten et al. (1997)
Li I 6708 Å
models from Burrows et al. (2001)
Brown Dwarfs as Chronometers
7 © 2009 Adam J. Burgasser
IAU 258: Ages of Stars
Pleiades 125 Myr
Luminosity at which Li I line disappears can be matched to a corresponding mass
& age
Stauffer et al. (1998) see also Barrado y Navascués et al. (1999); Stauffer et al. (1999); Oliveira et al. (2003); Manzi et al. (2008)
Brown Dwarfs as Chronometers
8 © 2009 Adam J. Burgasser
IAU 258: Ages of Stars
Li depletion line
⇒ t > 0.4 Gyr
Time (Gyr)
models from Burrows et al. (2001)
No Li I detected
Li
LiCl
Eff
ecti
ve T
empe
ratu
re (
K)
Brown Dwarfs as Chronometers
9 © 2009 Adam J. Burgasser
IAU 258: Ages of Stars
Li depletion line
⇒ t > 1 Gyr
Time (Gyr)
Li I detected
models from Burrows et al. (2001)
Li
LiCl
Eff
ecti
ve T
empe
ratu
re (
K)
Brown Dwarfs as Chronometers
10 © 2009 Adam J. Burgasser
IAU 258: Ages of Stars
Li I detected
⇒ 0.4 < t < 1 Gyr
A Li clock Binary
see Liu & Leggett (2005); Burgasser et al. (2005); Zapatero Osorio et al. (2008)
Eff
ecti
ve T
empe
ratu
re (
K)
Time (Gyr)
No Li I detected
Li depletion line
models from Burrows et al. (2001)
Li
LiCl
Brown Dwarfs as Chronometers
11 © 2009 Adam J. Burgasser
IAU 258: Ages of Stars
Method 3: Mass Standards
A growing number of brown dwarf binaries have orbital (dynamic) mass measurements.
Binary companions to age-dated stars/in clusters provide tests of evolutionary models.
see also Lane et al. (2001), Bouy et al. (2004); Zapatero Osorio et al. (2004); Stassun et al. (2006); Bouy et al. (2008); Liu et al. (2008)
Talk by T. Dupuy, Poster by M. Liu
Dupuy, Liu & Ireland (2008)
~0.8 Gyr
Brown Dwarfs as Chronometers
12 © 2009 Adam J. Burgasser
IAU 258: Ages of Stars
models from Burrows et al. (2001) Effective Temperature (K)
Log
Sur
face
Gra
vity
(cg
s)
Method 4: Surface Gravity
Brown Dwarfs as Chronometers
13 © 2009 Adam J. Burgasser
IAU 258: Ages of Stars
Teff & gravity → mass & age can be made for individual field objects
Caveat: metallicity
Burgasser, Burrows & Kirkpatrick (2006) see also Knapp et al. (2004); Burgasser (2007); Liebert & Burgasser (2007); Liu et al. (2007); Looper et al. (2007); Warren et al. (2007); Delorme et al. (2008); Leggett et al. (2008); Burningham et al. (2008)
Surface Gravity Diagnostics
Poster by S. Leggett
Brown Dwarfs as Chronometers
14 © 2009 Adam J. Burgasser
IAU 258: Ages of Stars
Method 5: Kinematics
Are local brown dwarfs young? Zapatero Osorio et al. (2007): 21 L & T dwarfs w/ UVW ⇒ <age> ~ 0.5-4 Gyr
Faherty et al. (2008): >800 M7-T8 dwarfs w/ Vtan ⇒ <age> ~ 3-8 Gyr see also Schmidt et al. (2007); Jameson et al. (2007); Casewell et al. (2008)
Faherty et al. (2008) - 20 pc Zapatero Osorio et al. (2007)
Brown Dwarfs as Chronometers
15 © 2009 Adam J. Burgasser
IAU 258: Ages of Stars
Cluster members & companions - distant and/or rare, can encompass any spectral type, useful benchmarks
Li clock - optimal for 50-200 Myr & resolved binaries (rare); limits for Teff > 1300 K (M and L dwarfs)
Mass standards - very rare, long-term time investment, critical for testing models, challenging benchmarks
Surface gravity - useful in principle any source, ideal for T dwarfs, requires benchmarks
Kinematics - appropriate for large samples, current results controversial (single sources caveat emptor)