Ages of Our Stellar Neighbors Tom Ayres (CASA)

Z/Z~ 1 Prot~ 23 d Age~ 2 Gyr Z/Z~ 1.8 Prot~ 30 d Age~ 6 Gyr PROCYON L P CEN Prot~ 30 d Age~ 6 Gyr

ALPHA CEN PROCYON A B A B PORB~ 41 yr PORB~ 80 yr α CMi B [WD: DQZ]

Breakthrough Starshot “To boldly go where no nanobot has gone before...”

Flannery & Ayres 1978 t~ 6 ± 1 Gyr A A B B

π (marcs) MA MB Age (Gyr) Flannery & Ayres 1978 1.11 0.92 746 Kamper+‘78 6±1 Pourbaix+‘99 1.17-1.09 (0.97) 737 self-determined 2.7-6.2 Guenther & Demarque ‘00 1.10 747 Söderhjelm ‘99 6.8-7.6 Morel+2000 1.16-1.10 0.97-0.92 2.7-5.6 Pourbaix+‘02 & Several** 0.93 assumed 6.4-6.8 Porto de Mello+‘08; Pourbaix+‘16 1.13 (0.89)-0.97 743 (Hipp: 742) 4.5-5.3 bottom line 2017 6±1 ?? **Thoul+2003; Eggenberger+2004; Miglio+2005; Seismic; Vis orbit + RVs

Alpha Cen AB: Two Decades of X-rays +20 0 −20 A ?? ROSAT XMM-Newton Chandra Year Note: brighter source (B) located at 0” on y-axis (Δdec), and at date of observation (x-axis); relative AB orientation and separation maintained

Iconic view of solar X-ray cycle (Yohkoh: 1990’s)

Ups & Downs of Alpha Centauri   X-ray Index is LX/Lbol in units of 10-7

Ups & Downs of Alpha Centauri 8.4 yr  Sun: 14 yr ?! PROCYON ?? 19.5 yr ?  X-ray Index is LX/Lbol in units of 10-7

Stellar Ca II HK cycles (Mt Wilson) seem to split into two Ricky Egeland (HAO/MSU)+2016 (CS19) Sun unique? maybe not… A A A 20 y Cycle Period (some are double-period) B B B 30 d young old Rotation Period Stellar Ca II HK cycles (Mt Wilson) seem to split into two branches, Active (A) and Inactive (I), with Sun in middle

 faster Rotation Period (days) 10 20 30 40  4 6 8 10 Age (Gyr) Spin-Down Law 4 6 8 10 Age (Gyr) Metcalfe & van Saders (2017): older solar analogs not slowing down as fast as Skumanich law; shift in character of Dynamo?

 faster Rotation Period (days) 10 20 30 40  4 6 8 10 Age (Gyr) Spin-Down Law 4 6 8 10 Age (Gyr) Metcalfe & van Saders (2017): older solar analogs not slowing down as fast as Skumanich law; shift in character of Dynamo?

Conclusions Nearby, visual binary systems offer prospect for accurately determining ages: benchmarks for stellar population studies, rotation-activity connection, Dynamos, etc. However, best case scenario -- α Centauri -- shows that slight uncertainties in mass of more evolved star, mainly from disputed distance, can affect age estimates significantly. Nevertheless, α Cen appears to be perhaps 1 Gyr older than Sun, consistent with magnetic activity signatures. Caveat for rotation-activity is that middle-aged stars might be in a somewhat unstable transition between long and short cycling states. Coronal wind braking then possibly affected by changes in the global field.

Alpha Centauri at a Crossroads Chandra Spring 2017 Newsletter