Stellar Astrophysics: Things That Are Too Hard for Keck

Judy Cohen (Caltech)+ Evan Kirby, the 0Z team and Branimir Sesar

Astronomy in the TMT EraTokyo, Oct 2013

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Four ProblemsGravitational settling in the Sun & solar modeling

Extremely metal-poor stars: CNO

Chemical Evolution in Nearby Galaxies

The total mass of the Milky Way + finding more ultra-faint galaxies – RR Lyr + HSC/Subaru

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M13 HB, grav settling, rad levitation Behr, Cohen +

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Vrot vs Teff, M13 HB, vrot

drops rapidly as

Teff upBehr,

Cohen, +, ~2000,

big effect !

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Richard, Michaud et al predict diffusion in low

Fe/H dwarfs

Size of effect reduced in response to our and

others early work.

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M92 CMD + HIRES sample, reaches MSTO

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M92 [Fe/H] vs Teff, upper RGB to MSTO, HIRES

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M92, same for Ti12, can’t

achieve needed

accuracy, spent > 4

HIRES/Keck nights on

MSTO. HIRES with multiplex

would be great !

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0Z project, 122 EMP/HES, [C(CH)/Fe] vs [Fe/H]

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Adding N and O

• C from 4300 strong CH band. N,O not so easy

• N from NH band, 3360 A• O from OH bands, 3200 A or near 1.6 microns• Weak lines, in regions hard to observe

• Really need full set of CNO abundances for best understanding

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122 EMP stars, HES 0Z, new class found: low-Ca stars

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Chemical Evolution of the Local Group, Kirby, Cohen + many, Deimos/Keck

• 2850 RGB stars in 8 dSph MW satellites, most distant Leo I at 260 kpc

• 108 stars in 7 Ultra-Faint MW satellites, most distant CVnII at 160 kpc

• 629 in 7 Local Group isolated dIrr, most distant VV 124 at 1,400 kpc

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Kirby et al Local Group Sample

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Sculptor, 375 RGB stars, ~100/slitmask

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[Fe/H] distributions, 7 isolated dIrr

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MDF for 4 most luminous dSph

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<[Fe/H]> vs Luminosity. All Deimos.

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Now add in SDSS data, <[Fe/H]> vs M(star)

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Combined MDF for luminous dSph and dIrr

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CMD Segue 2 SDSS, not many stars bright enough

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ACS CMDs for nearby UF galaxies Brown et al 2013

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WTPC2/HST Leo T (415 kpc)

Clementini et al 2013

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We are now at the limit of Keck

• Can’t do ultra-faints better – very few bright giants and can’t reach more numerous MS

• No group has had success in finding more UF, PanStars none so far, PTF not suitable for this

• Kirby, Cohen + no more MW satellites left close enough for Deimos

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RR Lyr: Total Mass of the Milky Way with dark matter, and finding more UF MW satellites

RR Lyrae can be found in the PTF to ~100 kpcA period + a rough Fe/H determines an accurate luminosity and distance

We have found ~100 RR Lyr at 70 < D < 100 kpc excluding more than 100 in the known dSph, with vr can infer total mass of MW out to 100 kpc.

Using RR Lyr as lamp-posts can we find the very low luminosity stellar systems/streams in which they presumably live ?

Palomar Transient Factory RR Lyrae Stars (~900 RR Lyr 30 < R < 100 kpc)

Se~~

RR Lyrae stars between 70 and 100 kpc

8 RR Lyrae Stars at ~85 kpc in 45 deg2

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RR Ly 70-100 kpc (~90 in Draco dSph)

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Histogram – distances of outer halo RR Lyr, excludes RR Lyr in known MW satellites

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How to get beyond 100 kpc – HSC !!

• Find the RR Lyr using HSC wide survey• Get periods using Keck (cadence project)• Get vr + rough Fe/H using Keck• Use known RR Lyr distance + matched filter

algorithm to search HSC multi-color catalog for main sequence stars in the underlying low luminosity stellar system or stream

• HSC is the ONLY way to do this !!!