AGB Stars as Tracers of Stellar Populations.

This slides is for my paper talk about how astronomers use AGB stars as tracers of stellar populations. Much of the content is from the first three sections in Chapter 8 of Habing et al. (2003). In the end, I tried to cover some recent works of Japanese researchers. As far as I know, they’ve conducted lots of photometric surveys in the infrared wavelength.

Transcript

1. AGB Stars as Tracers of Stellar Populations From the Milky Way to the Magellanic Clouds
3. The structure of AGB stars. The dredge-up: stellar surface enriched in nuclear burning products, especially carbon. The atmosphere: molecules formation; shocks develop; grain condensation. The circumstellar envelop: mass loss & super wind; escaping gas & dust particles.
4. Introduction: Why can we use AGB stars as tracers? • The most luminous red stars in any galaxy • At their brightest in the near-infrared (extinction unimportant) • Rarity (short-lived) For convenience: study those brighter than tRGB
5. The (I,V-I) diagram for stars in the LMC. tRGB: Mbol = -3.9
6. • Defining feature of OH/IR stars: powerful OH maser action at 1612 MHz; ΔV/2 (Vexp) ~ gas expansion velocity of the CSE; ΔV: indicator of initial mass of the star. • Age: Mbol: upper limit of a single star’s age; Cluster: highest luminosity ~ AGB star with the age of the cluster (M-type) LPVs: longer period, younger age. ΔV: rough age indicator. P < 255d , > 5 Gyr; 255 < P < 450d , 1 ~ 3 Gyr; P > 450d , < 1 Gyr. ∆V > 38km/s, < 1Gyr ∆V < 36km/s, > 4Gyr
7. Wood et al. (1999) The PL relations for optically visible red variables in a O.5xO.5 degree area of the LMC. Luminosity of tRGB and TPAGB min for a star of M ≈ 1⨀ indicated by arrows. Data from MACHO.
8. The MWG • Solar neighborhood Z: distance from the Galactic plane for Miras. Conclusion: Shorter period, greater heights; so Shorter period, lower main-sequence mass. (because they’re older?) The kinematics of LPVs depend on the period. Conclusion: Miras with period longer than 200d are disk stars. Shorter period, lower main-sequence mass. (quick rotation — lower mass?)
9. • The Galactic Nucleus: the center & its surroundings (l, V) diagram of OH/IR stars near the Galactic center. Conclusion: Vrad = A*l, A = 30km/(s*pc) ➡ Uniform mass density ~ 1.3*10^5⨀ /(pc^3) ∆V < 36km/s, older ∆V > 38km/s, younger Distribution of OH/IR stars within a few hundred pc from the center Same A = 2.5km/(s*pc) ➡ Uniform mass density ~ 1.1*10^4⨀/(pc^3) Younger group suggests different origin.
10. Period distribution of OH/IR stars (shaded) Vexp distribution of different samples. P < 255d , > 5 Gyr; 255 < P < 450d , 1 ~ 3 Gyr; P > 450d , < 1 Gyr. ∆V > 38km/s, < 1Gyr ∆V < 36km/s, > 4Gyr
11. The Inner MWG: -30˚ < l < 30˚; the Bar and the Bulge (l, V) diagram of interstellar CO and OH/IR stars Near-IR maps of the MWG made by the COBE satellite. Evidence of the Bar from AGB stars.
12. The distribution of IRAS Miras in distance modulus. Open circles: negative longitude. Closed triangles: positive longtitude.
13. Ishihara, 2011 The Galactic Disk
14. Marigo, 2008 Evolutionary tracks of AGB stars Orange: M-type stars; Green: Carbon stars
15. • PL relation (Miras in metal-rich clusters obey sequence C) All brighter than tRGB are Miras Matsunaga et al. (2006) NIR survey for red variables in GCs Filled circles: variables in metal-rich clusters ([Fe=H] > 1) Star symbols: those in metal-poor ones Gray points: data of the LMC Globular clusters
16. Yoshifusa Ita et al. (2003) Upper: LMC; Bottom: SMC Data from OGLE-II & SIRIUS θ<0.55: ‘regularly pulsating variables’; θ>0.55: ‘less regularly pulsating variables’. J-K > 1.4: mostly C-rich AGB stars; J-K < 1.4: mostly O-rich AGB stars. The Magellanic Clouds