lamost study of li-rich stars in the milky way disk and

LAMOST study of Li-rich stars in theMilky way disk and halo: Is Li-rich

episode(s) in giants universal ?

Yerra Bharat Kumar

NAOC, Beijing

Stellar Archaeology as a Time Machine to the First StarsKavli IPMU, Tokyo, 3rd Dec 2018

in Collaboration withLi, H & Zhao, G (China), Aoki, W., Matsuno, T., Suda, T., (Japan)

Reddy, B.E. & Singh, R. (India), Lambert, D. L. (US)

Yerra Bharat Kumar Li-rich disk and halo stars in Milky Way

I Product of Big-Bang Nucleosynthesis

I Isotope - 6Li

I Fragile element - destroys at 2.5×106 Kin stellar interiors


Evolution of Li in the Universe

Matteucci+2010

Primordial LiP 2.72±0.06 Cyburt et al. 2008Primordial LiO 2.27±0.03 Lind et al. 2009Turn-off stars 3.20 Lambert & Reddy 2004ISM 3.25 Knauth et al. 2000;2003Meteoritic 3.28 Lodders et al. 2003Sun 1.05 Asplund et al. 2009

A(Li) = logε(Li/H)+12

I Sources for Galactic Li enrichmentI Cosmic ray spallationI SupernovaeI NovaeI AGB Stars

I RGB stars

Role of RGB stars in Galactic Li

enrichment is not well understood !


Li in RGB stars

I Li gets depleted in low mass stars during first dredge-updue to expanding convective envelope on red giant branch

Iben (1967) Lind+2009


Li-rich giants, A(Li) >1.5 - 1% of RGB stars

Some of these Li-rich giants show other anomalies like low carbonisotopic ratios, infrared excess, and rapid rotation

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No clear correlations are found between Li and other peculiarities !


Li-rich giants in Milky way disk & halo, dwarf spheroidals

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Literature

Others Carbon et al. 2018Smiljanic et al. 2018Li et al. 2018Casey et al. 2016Carlberg et al. 2016Delgado Mena et al. 2016Kirby et al. 2016Adamow et al. 2014Liu et al. 2014Martell et al. 2013Kirby et al. 2012Lebzelter et al. 2012Ruchti et al. 2011Monaco et al. 2011Kumar et al. 2011Gonzalez et al.2009Gregoriao-Hetem et al.1992Brown et al. 1989Wallerstein et al. 1982

Does Li-rich episode(s)during low mass star’sevolution is universal ?

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LAMOST survey sample

Large Sky Area Multi-Object Fibre Spectroscopic Telescope(LAMOST) DR5 contains 8 million spectra.

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LAMOST spectra with strong Li line in stars on various parameterspace.


Identifying Li-rich giants: Line Ratio method fromKumar+18

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Estimated errors for LAMOST spectral resolution spectra ≈ 0.35dex


New Li-rich giants from LAMOST

Disk Halo


Observations of high resolution spectra

I High resolution (R∼60000) spectra of LAMOST Li-rich diskstars are mostly observed using three telescopes: Subarutelescope at Hawaii, 2.7-m Harlan J.Smith telescope atMcDonald Observatory, and 2-m HCT at Hanle

I All Li-rich halo stars are observed from Subaru telecope

I Near-UV high resolution spectra for Be measurements are alsoobtained from Subaru HDS


Low and high resolution spectra of Li-rich giants

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Abundance measurements from high resolution spectra

Standard procedure: Teff , logg, [Fe/H], ξt and synthetic spectrafrom well tested linelist, LTE Kurucz model atmospheres, MOOG,NLTE Li corrections from Lind et al. (2009). Samplemeasurements are shown below,


Li abundances from low and high resolution spectra

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Li abundances from high resolution spectra are also used tocalibrate relations from Lamost spectra.


New Li-rich giants from Disk and Halo

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Li-rich Halo giants: preservation from its progenitors ?

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I Li-rich turn-offstars/subgiants

I Internalmechanism -Diffusion ?

I Planet Ingestion?

I External pollution:Novae/UpperRGB/ AGB


Li-rich Halo giants: preservation from its progenitors ?

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I It is clear from figurethat high Li in RGBstars are preservedfrom its progenitorsafter experiencing thefirst dredge-up

I Li-rich episode onRGB in halo stars ?


Li-rich disk stars: Increasing Red clump stars

Kumar+11, ApJL

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Bharat Kumar+18, ApJL)

Singh+18

4200460050005400Teff [K]

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Bharat Kumar+(in preparation)


Li-rich Halo & Disk giants: planet engulfment scenario -Unlikely

Aguilera-Gomez+2016

I Our Be analysis fromnear-UV Subaruspectra of Li-rich diskgiants also shown theabsence ofBe-enrichment.


Summary

I LAMOST survey increased Li-rich stars to 10 fold to existing catalog spanninglarge metallicity range covering disk and Halo of Milky Way

I Added more Li-rich stars to turnoff/subgiant branch and red clump phase of lowmass star’s evolution

I High Li in halo RGB stars seems to be preserved from its progenitors. However,need more Li-rich turnoff/subgiants to confirm it. Li-rich episode on RGB ofhalo stars needs more investigation.

I More Li-rich stars in disk are found to be at red clump

I External pollution through novae or binary mergers seems to be a possiblesources for Li anomaly in Li-rich turn-off stars/subgiants in halo and Li-rich coreHe-burning stars in disk, respectively

I Need a revisit to ”1% of RGB stars are Li-rich”, which may put constraints onRGB star’s Li contribution to Galactic Li enhancement


Thanks for your attention


lamost study of li-rich stars in the milky way disk and

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