# Presentation: 865774

## The 0Z Project Team

- Core group: Norbert Christlieb (Hamburg), Judy Cohen (Caltech)
- Andy McWilliam, Steve Shectman and Ian Thompson (Carnegie)
- Past & Present Postdocs: Innocenza Busa, Franz-Joseph Zickgraf, Inese Ivans, Jorge Melendez & Solange Ramirez, Torgny Karlsson & Mattias Dehn
- Hamburg/ESO Survey: Lutz Wizotski and Dieter Reimers
- Associates for the Keck Pilot Project of 2001: E. Carretta and R.Gratton
- Undergrad: Amber Swenson (Caltech)
- Theoretical Support: G. Wasserburg & Y.Qian
- Also: Model atmospheres – Bob Kurucz, MOOG (abund. anal. Code) – Chris Sneden, MAKEE (HIRES anal. code) –Tom Barlow, atomic data – NIST and Bob Kurucz, HIRES at Keck – Steve Vogt, Jerry Nelson, Gerry Smith and their teams.

## Outline/Summary – Discovery of New Extreme EMP Stars

- We have obtained mod. res. spectra of 1539 candidate EMP stars from the HES (+ 26 objects which turned out not to be metal poor stars)
- From this we have isolated 4 new extreme EMP giants with [Fe/H] < -3.5 dex, one at -4 dex, and quite a few giants and dwarfs below -3.0 dex
- Two of  these are strong outliers in [X/Fe] for iron-peak elements and sometimes lighter elements too.  Details for 3 Fe-peak outliers will be presented. (see ApJL published and ApJ submitted, Cohen et al 2007)
- ****NEW*** previous outliers were restricted to CNO and  elements
- We can find even modest outliers because we have significantly enlarged the sample of EMP stars, our data and analyses are quite accurate and homogenous.

## Outline/Summary – the [Fe/H] distribution for the Galactic Halo

- Based on mod res spectra of 1504 stars and HIRES spectra of ~90 of them, we find that the EMP tail of the  [Fe/H](HES) distribution is full of objects that do not belong there and are in general significantly more metal rich.
- Today we could do better with mod res spectra at eliminating the mistakes at the EMP end. We now know not to trust [Fe/H] for C-rich stars.
-  SEGUE has  more spectral coverage (no M dwarfs or QOs), and better more uniform photometry.  This helps too.
- Our [Fe/H](HES) distribution for ~1500 candidates is identical for dwarfs and for giants, suggesting NO gradient of metallicity in the Galactic halo.
-  BUT there may be differential issues  between the calibration of [Fe/H] for giants versus dwarfs

## Offset Between 0Z and First Stars (Cayrel et al) VLT Project

- We have done a comparison and find the following:
- Our Teff scale for giants is hotter.  Our adopted reddening values are in the mean  larger.
- For a given stellar spectrum and broad band colors, [Fe/H](HIRES) ~ [Fe/H](1st Stars) + 0.3 dex
- Thus our extreme EMP stars with [Fe/H] < -3.5 dex would be [Fe/H < -3.8 dex if analyzed by the 1st Stars Project
- The gf values are not an issue

## Outlier: HE1424-0241  Teff=5190K,  [Fe/H] -4.0 dex

## [Si/Fe] vs [Fe/H] for halo stars and globular clusters – outlier HE1424-0241

## [Ca/Fe] vs [Fe/H] for halo stars and globular clusters, outlier HE1424-0241

## Outlier – HE0132-2429, Teff 5295K, [Fe/H] -3.6 dex

## Outlier HE2344-2800, Teff = 6380K, [Fe/H] ~ -2.7 dex

## Cr/Fe vs Mn/Fe for HES VMP & EMP dwarfs, outlier – HE2344-2800  Teff = 6380K,  [Fe/H] = -2.7 dex

## First Abundance for Copper in Extreme EMP Stars

## Theoreticians and modelers of SNII

- Start your CPUs –
- Can you find individual SNII whose predicted nucleosynthesis yields match these stars ?

## Histogram: [Fe/H](HES) Q1 and Q2 are identical for giants and dwarfs Q1 , median, Q3 -2.32, -1.91, -1.43 dwarfs,                                                   -2.36, -1.96, -1.18 giants)

## [Fe/H](HES) < -3.5 dex of 1565 mod res spectra, EMP stars from HES, 12 objects

- HE1159-0525    -3.52  dex  [Fe/H](HES)
- HE1150-0428    -3.57
- HE2209-3909    -3.59
- HE1031-0020    -3.61
- HE0122-1616    -3.63
- HE0305-5442    -3.68
- HE0313-3640    -3.72
- HE0911-0512    -3.84     M dwarf
- HE2323-0256    -3.96
- HE0208-5335    -4.14     QSO
- HE1030+0137   -4.37     M dwarf
- HE1432-1819    -4.43
- Score so far: 12 – 2 M dwarfs – 1 QSO = 9 possible [Fe/H] < -3.5 stars

## [Fe/H](HES) < -3.5 dex of 1565 mod res spectra, EMP stars from HES, 12 objects

-     ID                   [Fe/H](HES)   [Fe/H](HIRES) (dex)  Comments
- HE1159-0525    -3.52             ...                 Extreme C-star
- HE1150-0428    -3.57             -3.27             C-star
- HE2209-3909    -3.59             ...     near MSTO, hot,  [Fe/H] >> -3.6 dex
- HE1031-0020    -3.61             -2.88             C-star
- HE0122-1616    -3.63             -2.8
- HE0305-5442    -3.68             -3.56 (Cayrel) Rediscovery CS22968-014
- HE0313-3640    -3.72             ...     near MSTO, hot,  [Fe/H] >> -3.6 dex
- HE0911-0512    -3.84     M dwarf
- HE2323-0256    -3.96            -3.78   Rediscovery CS22949-037
- HE0208-5335    -4.14     QSO
- HE1030+0137   -4.37     M dwarf
- HE1432-1819    -4.43            -2.51

## Effect of Using HIRES Abundances, 1565 mod res spectra 

- Of 12 stars [Fe/H](HES) < -3.5 dex, 2 M dwarfs, 1 QSO
- 2 are rediscoveries of known EMP stars from HK Survey
- 4 have HIRES analysis, with  [Fe/H] >> -3.5 dex
- 3 left all appear from examining mod res spectra not to be extreme EMP stars,
- Net result of 1555 mod res spectra = NO NEW EXTREME EMP STARS

## The Extreme EMP End of the [Fe/H] histogram with raw [Fe/H](HES) and with HIRES [Fe/H] substituted when available – all objects below [Fe/H] -3.7 dex disappear.

## Outline/Summary – Discovery of New Extreme EMP Stars

- We have obtained mod. res. spectra of 1539 candidate EMP stars from the HES (+ 26 objects which turned out not to be metal poor stars)
- From this we have isolated 4 new extreme EMP giants with [Fe/H] < -3.5 dex, one at -4 dex, and quite a few giants and dwarfs below -3.0 dex
- Two of  these are strong outliers in [X/Fe] for iron-peak elements and sometimes lighter elements too.  Details for 3 Fe-peak outliers will be presented. (see ApJL published and ApJ submitted, Cohen et al 2007)
- ****NEW*** previous outliers were restricted to CNO and  elements
- We can find even modest outliers because we have significantly enlarged the sample of EMP stars, our data and analyses are quite accurate and homogenous.

## Outline/Summary – the [Fe/H] distribution for the Galactic Halo

- Based on mod res spectra of 1504 stars and HIRES spectra of ~90 of them, we find that the EMP tail of the  [Fe/H](HES) distribution is full of objects that do not belong there and are in general significantly more metal rich.
- Today we could do better with mod res spectra at eliminating the mistakes at the EMP end. We now know not to trust [Fe/H] for C-rich stars.
-  SEGUE has  more spectral coverage (no M dwarfs or QOs), and better more uniform photometry.  This helps too.
- Our [Fe/H](HES) distribution for ~1500 candidates is identical for dwarfs and for giants, suggesting NO gradient of metallicity in the Galactic halo.
-  BUT there may be differential issues  between the calibration of [Fe/H] for giants versus dwarfs

## Backup slides

## Comparison [Fe/H](HIRES) with almost up-to-date Beers et al, still positive overall

## Region of 4030 A Mn triplet in 3 EMP stars, the top one is the most Fe-poor.These outliers are REAL !

## Histograms of [Fe/H](HIRES, or HES) for giants and dwarfs

## Our samples are more than 90% complete for Dec > -25 deg, and are fairly complete in the south, the [Fe/H] histogram is unbiased