What can we learn about late-‐stage stellar evolu3on from surveys of the Milky Way and the satellite galaxies? Mikako Matsuura STFC Ernest Rutherford Fellow Cardiﬀ University Post main-‐sequence stellar evolu3on •  AGB stars (1-‐8 M¤) •  Red supergiants AGB AGB RGB Key to understand the post-‐main sequence stellar evolu3on R Sculptoris Mass loss AGB stars in the Milky Way and Magellanic Clouds Post-‐main sequence stellar evolu3on: unresolved problems §  How do stars evolve aRer the main sequence? §  How do stars lose the mass ? 1)  How does metallicity aﬀect the stellar evolu3on? •  Chemistry •  Mass-‐loss rate 2)  Are AGB stars and red-‐supergiants important source of dust? AGB stars in the Milky Way and Magellanic Clouds Observa3ons Milky Way Large & Small Magellanic Clouds Spitzer AKARI 1.2-‐2.5” 9.7” @3.6-‐24 µm @2.4-‐24 µm (5-‐bands) (9-‐bands) 18.3-‐14.2 mag (SN~3) 2MASS ~2” JHK 15.8-‐14.3 mag (S/N~10) Post-‐main sequence stellar evolu3on: unresolved problems §  How do stars evolve aRer the main sequence? §  How do stars lose the mass ? 1)  How does metallicity aﬀect the stellar evolu3on? •  Chemistry •  Mass-‐loss rate 2)  Are AGB stars and red-‐supergiants important source of dust? AGB stars in the Milky Way and Magellanic Clouds AKARI/MIR All Sky photometric Survey Ishihara et al. (2011) 9µm map
Band 9µm 18µm Spa3al resolu3on 9.4” 90mJy Sensi3vity (5σ) 50mJy Num. of 844,649 194,551 sources 870,973 Blue : 9µm Red : 18µm
Classifying AGB stars/YSOs etc C-‐rich AGB (C/O>1) O-‐rich AGB (C/O<1) Ishihara et al. (2011) AGB stars in the Milky Way and Magellanic Clouds Object classiﬁca3ons by colours YSOs Em C-‐AGB T Tau O-‐AGB/RSGs Post-‐AGB PNe S-‐stars AGB stars in the Milky Way and Magellanic Clouds Be Normal galaxies Seyferts O-‐M stars Galac3c distribu3ons of C-‐rich and O-‐rich AGB stars Carbon-‐rich AGB O-‐rich AGB: inner galaxy C-‐rich AGB: outer galaxy Impact of metallicity High metallicity at the inner galaxy -‐> high ini3al O-‐abundance -‐> high O/C ra3o Oxygen-‐rich AGB Oxygen-‐rich AGB Post-‐main sequence stellar evolu3on: unresolved problems §  How do stars evolve aRer the main sequence? §  How do stars lose the mass ? 1)  How does metallicity aﬀect the stellar evolu3on? •  Chemistry •  Mass-‐loss rate 2)  Are AGB stars and red-‐supergiants important source of dust? AGB stars in the Milky Way and Magellanic Clouds How does metallicity aﬀect the mass loss rate? •  Stellar wind (mass loss) •  Radia3on pressure on dust grains •  Hydrodynamical model predic3on •  Low metallicity -‐> smaller mass of dust -‐> lower mass loss rate ¤
yr-‐1) Z=0.01 M=2.5 M¤ Z=0.001 M=2.5 M¤ Mass-‐loss rate 10-‐4 (M
Age Wachter et al.(2008) 6x10-‐5 (M¤yr-‐1) How does metallicity aﬀect the mass loss rate? Theory: stars in galaxies with higher metal content have more dust and CO Metal content: Milky Way (Z¤) > Large Magellanic Cloud (~1/2 Z¤) Flux (Jy) Herschel SPIRE spectra LMC red-‐supergiant IRAS 05280−6910 CO 12-‐11 Flux (Jy) Observa3ons Dust (from SED) Observed frequency (GHz) Wavelength (micron) CO: gas mass-‐loss rate Dust mass-‐loss rate Matsuura et al. (in prepara3on) How does metallicity aﬀect the mass loss rate? Theory: stars in galaxies with higher metal content have more dust and CO Observa3ons Conclusion: No obvious inﬂuence of metal contents on CO or dust Individual stellar property (=luminosity/mass) is the key Mass-‐loss rate (M¤yr-‐1) Metal content: Milky Way (Z¤) > Large Magellanic Cloud (~1/2 Z¤) Luminosity (L¤) Matsuura et al. (in prepara3on) Post-‐main sequence stellar evolu3on: unresolved problems §  How do stars evolve aRer the main sequence? §  How do stars lose the mass ? 1)  How does metallicity aﬀect the stellar evolu3on? •  Chemistry •  Mass-‐loss rate 2)  Are AGB stars and red-‐supergiants important source of dust? AGB stars in the Milky Way and Magellanic Clouds Are AGB stars important dust sources of galaxies? (1, 2) Msun kpc-‐2 Myear-‐1 (3) 10-‐2 Msun yr-‐1 In case of the Milky Way Tielens (2005) Dwek (1998) Gehrz (1985) AGB stars Novae SN Ia Red supergiants 8.0 0.3 2.3 0.2 6.5 <0.006 3.6 1.1-‐6.8 0.01 SN II Wolf Rayet 12 0.06 8.5 0.02 0.02-‐0.5 AGB stars in the Milky Way and Magellanic Clouds 0.1-‐0.6 0.01 Large & Small Magellanic Clouds Lirle ambiguity of distances to AGB stars LMC SMC AGB stars in the Milky Way and Magellanic Clouds Spitzer Magellanic Clouds photometric & spectroscopic surveys 3.6 micron: blue 8.0 micron: green 24 micron: red Spitzer Space Telescope Detec3ng almost en3re dust embedded AGB stars in LMC & SMC Dust thermal emission Meixner et al. (2006) AGB stars in the Milky Way and Magellanic Clouds Matsuura et al. (2009) Spitzer LMC & SMC spectroscopic surveys LMC: > 250 sources; SMC: >200 sources Kemper et al. (2010); Woods et al. (2011); Ruﬄe et al. (2015) YSOs Carbon-‐rich AGB Oxygen-‐rich AGB Object classiﬁca3ons Matsuura et al. (2011; 2014); Woods et al. (2011); Ruﬄe et al. (2015) Mass-‐loss rate analysis SED modelling of 40 AGB/RSGs –> dust mass-‐loss rate Empirical formula of mass-‐loss rate vs colour -3
Dust mass-‐loss rate 3.1x10-‐8 M¤ yr-‐1 Log mass-‐loss rate) log ((mass-loss
rate)
-4
-5
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-9
0
1
2
3
4
5
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7
K-[8.0]
K-‐[8.0] Groenewegen et al. (2007, 2009) Matsuura et al. (2009; 2013) y = (m1/(m0+m2)+m3)
First census of dust from evolved stars in a galaxy Carbon-‐rich Oxygen-‐rich Detec3ng AGB stars in Magellanic Clouds, and measuring their dust mass, using Spitzer Matsuura et al. (2009; 2013) AGB stars in the Milky Way and Magellanic Clouds Global dust budget in the Magellanic Clouds •  Caveat –  AGB dust: dust injec3on rate from AGB stars X Dust life3me was es3mated to be 4-‐8x108 yrs (Jones et al. 1994) –  Life3me of dust is uncertain; eﬀects of SN shocks ISM dust 2x106 M¤ AGB dust (2-‐9)x104 M¤ LMC ISM dust 3x105 M¤ AGB (3-‐7)x103 M¤ Over (4-‐8)x108 years SMC Matsuura et al. (2009, 2013) Sta3s3cally... •  Majority of stars are low-‐mass loss rate stars •  A few ten high mass-‐loss rate stars (=intermediate mass origin?) dominates the dust inputs from AGB stars Mass-‐loss rate C.f. C-‐AGB only AGB stars in the Milky Way and Magellanic Clouds Matsuura et al. (2009) Does the past star-‐forma3on histories of galaxies (=age of stars) impact on dust inputs? Key: Spa3al distribu3on of stars Census of dust producing stars Low mass-‐loss rate High mass-‐loss rate Spa3ally resolved stellar popula3ons Disk: >11 Gyrs & <1 Gyrs old Bar: 3-‐5 Gyrs ago Spitzer – dust Op3cal survey 3-‐5 Gyrs old stars are numerous some <1 Gyrs old are important for current dust inputs C.F. GAIA: Milky Way Matsuura et al. (2009; 2013) Constraints on stellar evolu3on models Theore3cal isochrones, including dust + star-‐forma3on history <0.5 Gyrs old Spitzer observa3ons AGB stars in the Milky Way and Magellanic Clouds Dell'Agli et al. (2015) Summary •  Within the range of 1-‐1/2 Z¤, metallicity dependence of mass-‐
loss rate is not obvious •  Magellanic Clouds: the ﬁrst census of mass-‐losing AGB stars in the en3re galaxies –  In the LMC & SMC, AGB stars alone are insuﬃcient to account for dust in the ISM •  Other dust sources (SNe or ISM grain growth?) •  Star-‐forma3on histories of galaxies •  Evolu3on of mass-‐loss rate is about to be resolved by theories AGB stars in the Milky Way and Magellanic Clouds