Transcript pptx
Stellar Astrophysics: Things That Are Too Hard for Keck Judy Cohen (Caltech)+ Evan Kirby, the 0Z team and Branimir Sesar Astronomy in the TMT Era Tokyo, Oct 2013 1 Four Problems Gravitational 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 1 M13 HB, grav settling, rad levitation Behr, Cohen + 2 Vrot vs Teff, M13 HB, vrot drops rapidly as Teff up Behr, Cohen, +, ~2000, big effect ! 3 Richard, Michaud et al predict diffusion in low Fe/H dwarfs Size of effect reduced in response to our and others early work. 4 M92 CMD + HIRES sample, reaches MSTO 5 M92 [Fe/H] vs Teff, upper RGB to MSTO, HIRES 6 M92, same for Ti12, can’t achieve needed accuracy, spent > 4 HIRES/Keck nights on MSTO. HIRES with multiplex would be great ! 7 0Z project, 122 EMP/HES, [C(CH)/Fe] vs [Fe/H] 8 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 9 122 EMP stars, HES 0Z, new class found: low-Ca stars 10 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 11 Kirby et al Local Group Sample 12 Sculptor, 375 RGB stars, ~100/slitmask 13 [Fe/H] distributions, 7 isolated dIrr 14 MDF for 4 most luminous dSph 15 <[Fe/H]> vs Luminosity. All Deimos. 16 Now add in SDSS data, <[Fe/H]> vs M(star) 17 Combined MDF for luminous dSph and dIrr 18 CMD Segue 2 SDSS, not many stars bright enough 19 ACS CMDs for nearby UF galaxies Brown et al 2013 20 WTPC2/HST Leo T (415 kpc) Clementini et al 2013 21 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 22 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 kpc A 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 ? 23 Palomar Transient Factory RR Lyrae Stars (~900 RR Lyr 30 < R < 100 kpc) RR Lyrae stars between 70 and 100 kpc Se~~ 8 RR Lyrae Stars at ~85 kpc in 45 deg2 RR Ly 70-100 kpc (~90 in Draco dSph) 26 Histogram – distances of outer halo RR Lyr, excludes RR Lyr in known MW satellites 27 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 !!! 28