Pulsation, Dust & Death The story of stellar demise as told by wide field surveys

Transcription

1 Pulsation, Dust & Death The story of stellar demise as told by wide field surveys Iain McDonald Jodrell Bank Centre for Astrophysics University of Manchester ATCA

2 Chemical evolution of the Universe Big Bang Today Boring gas Fun things He Stellar evolution He Others Mg Si N Fe Ne C H H O La Silla Observatory

3 Introduction: stellar death WD TP-AGB PN? Post-AGB Early AGB H 2 Mo B MST O MS 0.8 Mo Mass loss Upper RGB 2-10 Myr of evolution 90-99% of total energy output 85-99% of total mass loss RGB Important for galaxies': Spectra Chemical evolution

4 Open questions How does stellar ejecta vary among stars? What is the mass-loss rate for a star at a given M, [Fe/H] & L? What is the ejecta composition? What is the wind momentum? (i.e. what is the wind velocity?) What is the wind-driving mechanism?

5 Introduction: parameter space SM C Sex B Milky Way globular clusters Sgr dsph Milky Way open LM clusters C

6 Introduction: stellar death RGB star H H e shell Large convecti ve envelop e Large convective cells weak pulsation Magnetism heats stellar chromosph eremagnetism + pulsation promotes a slower plasma/molecular outflow IS M

7 Introduction: stellar death TPAGB H2O VO TiO CO C/O < 1 Al2O3 CN Alumina Silicate SiO am. C. C2 C/O > 1 met. Fe? CO IS M met. Fe? PAHs SiC Graphite SiC following Le Bertre (1997)

8 Introduction: stellar death No carbon stars SM C LM C Milky Way Sex B Carbon stars produced Sgr dsph Data: Marigo & Girardi (1997); figure: McDonald et al. (201

9 Method struct spectral energy distributions of stars and look for infrared excess ( = dust product

10 Method struct spectral energy distributions of stars and look for infrared excess ( = dust product APOGEE 2MASS or VISTA/VHS or private surveys WISE Spitzer/IRAC AKARI WISE WISE Spitzer/IRACSpitzer/MIPS IRAS IRAS AKARI Spitzer/MIPS IRAS COBE/DIRBE SDSS UCAC or private surveys Spitzer/IRS IRAS/LRS ISO/SWS

11 Red giant branch mass loss in globular clusters Keck

12 Red giant branch mass loss: always ~10 km/s? km/s Determined 0-20 km/s from H I 6563A line: Stars from CO: ~10 km/s Determined from He I 1.08-um lines: km/s McDonald & van Loon (2007); McDonald et al. (2010); Meszaros et al. (2009); Smith et al. (2004)

13 Red giant branch mass loss in globular clusters Difficult to get sub-mm observations of individual stars... Groenewegen (2014) HIP McDonald et al. (nearly finished) EU Del MT late-type stars survey: Jan Wouterloot (East Asian Observatory) -I: Albert Zijlstra (Manchester) tual work done by: Samira Alharbi (Manchester) or conditions filler project, ~571 sources observed so far, some of which may be RGB sta O(2-1), CO(3-2), 13CO(2-1), 13CO(3-2), HCN(3-2), HCN(4-3)

14 Red giant branch mass loss in globular clusters Measure stellar masses at two evolutionary points. M5 (McDonald et al., in prep.) MSTO HB needs only photometry and stellar evolution models AGB RGB HB MSTO Keck RGB AGB also need spectra

15 Red giant branch mass loss in globular clusters Measure difference between main-sequence turnoff and horizontal branch Initial masses from isochrone fitting Median HB masses from Gratton et al. (2010 White dwarf masses: / Mo Most mass is lost on the RGB, but an apparent variation with metallicity But metal-poor stars evolve faster, so need to divide by evolutionary time McDonald & Zijlstra (2015b)

16 Red giant branch mass loss in globular clusters Need to adopt a mass-loss law (4 x Mo yr-1) Choose: Reimers (1975) Calibrate eta Eta = / (including systematic errors) Very little metallicity dependence (Assuming constant age of ~11.5 Gyr makes the line flat) McDonald & Zijlstra (2015b)

17 Red giant branch mass loss in globular clusters Or take a direct approach... & Teff from fitting spectral energy distribution photometric surveys & log(g) from spectral line fitting spectroscopic surveys eff olve for mass NGC 5139 Omega Cen Metal-poor stars 0.83 Mo RGB Mo AGB 0.53 Mo WD 0.09 Fits will with predictions. Similar data for 47 Tuc shows: / Mo lost between RGB and AGB eta = / McDonald et al. (2011)

18 Asymptotic giant branch mass loss La Silla

19 Asymptotic giant branch mass loss parcos: modelled SED of 110,000 stars; made an H-R diagram and looked for infrared exc 62 dusty giant stars with accurate distances, almost all known variables Pulsation comes before dust production Future: Gaia McDonald et al. (2012)

20 Asymptotic giant branch mass loss dsph with VISTA: 12 epochs of Z-band images, looking for variability among 4 million sta Every star is variable at some level (as Kepler tells us too) Pulsation amplitude does not correlate with dust production in oxygen-rich stars Pulsation alone is not enough for dust production RGB stars pulsate the same as AGB stars but don't(?) produce dust Future: PAN-STARRS McDonald et al. (2013,2014,2016)

21 Asymptotic giant branch mass loss (Luminosity) LMC OGLE + SAGE: periodic variability plus dust-production rates for all LMC giants ss rate depends on pulsation period. lsations are needed to levitate material far from the surface of the star so that it forms d mass dependent nset of dust production should initiate a mass dependence in the mass-loss rate & wind Boyer et al. (2015)

22 AGB dust production No silicate features Silicate features 37 No dust production Flux (RayleighJeans units) Spitzer spectral survey: Metallicity dependence of the onset of puslation and dust production. Dust composition may change considerably too McDonald et al. ( )

23 AGB dust production Crystalline silicates become simpler and more oxygen-rich at low metallicity. MgSiO3 [Fe/H] SMC LMC Galaxy Mg2SiO4 Jones et al. (2012)

24 What next? No carbon stars SM C LM C Milky Way Sex B Carbon stars produced Sgr dsph Data: Marigo & Girardi (1997); figure: McDonald et al. (201

25 DUSTiNGS: Dust in Nearby Galaxies with Spitzer Warm Spitzer mission 3.6 & 4.5 um imaging of 50 nearby dwarf galaxies with Spitzer Multi-epoch photometry to separate variable stars from background galaxies Two epochs already, with more planned on some galaxies in variable stars found so far, 526 with very red Spitzer colours stars near the AGB tip Masses: 1 to >8 Msun; metallicities: [Fe/H] = -2.7 to -0.5 proxies for early Universe Boyer et al. (2015)

26 Conclusions understanding of stellar mass loss requires a statistical sample of stars with varying par an approach which is: Multi-wavelength: need the entire SED to measure stellar properties & dust production Multi-epoch: want to identify the amplitude and period of stellar pulsation hotometric and spectroscopic: spectra confirm membership, abundances, nd can be used to trace atmospheric motions mostly used archival data, supplemented by targetted observations to measure dust pro ar clusters and the Magellanic Clouds, and are now expanding our search to high-mass, m s in nearby dwarf galaxies. k has made use of many existing surveys: Hipparcos, SDSS, ASAS, 2MASS, AKARI, WISE, ook forward to using many new surveys in the future: Gaia, SDSS/APOGEE, LSST, IPHAS/V AS, VISTA/VHS+VIKING+VVV,... That's all folks!

27 Clearing globular clusters Simple model... L2 Milky Way Vacuum Stop Gas Tidal radius Cluster gravity dominates Galactic gravity dominates Material leaves by Jeans escape McDonald & Zijlstra (2015a)