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Topic I what can we learn about very metal-poor stars with H- and K- band IR spectra?
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IGRINS for Stellar Abundances & Nucleosynthesis
Chris Sneden, Natalie Gosnell, Dan Jaffe, Greg Mace, Richard Seifert (UT Austin)
Hwihyun Kim + IGRINS team members (KASI)Melike Afşar (Ege U, Izmir Turkey)
Caty Pilachowski (Indiana U)
Topics for today two famous very low metallicity stars
is there anything left to discover? red horizontal-branch stars
better CNO will help solve their existence puzzle open cluster stars:
IR data can refine their evolutionay states
Abundance Definitions log ε(X) = log10(NX/NH) + 12 for element “X” [X/Y] = log10(NX/NY)★– log10(NX/NY)
Topic I
what can we learn about very metal-poor stars with H- and K-
band IR spectra?
Two famous very bright, very metal-poor stars
HD 122563 B = 7.10 V = 6.19 H = 3.76 K = 3.73 575 papers in the literature have something about this star red giant: Teff = 4500K, log(g) = 0.8, [Fe/H] = –2.9 40+ years after my PhD, I’m still working on this same star
HD 140283 B = 7.11 V = 7.21 H = 5.70 K = 5.59 first high-res metal-poor star: Chamerlain & Aller (1952) warm: Teff = 5650K, log(g) = 3.4, [Fe/H] = –2.7 a legendary “cheat” on metallicity; a moral lesson for us
Afşar et al. 2015, ApJ, submitted
most of the IGRINS H-band in our stars
HIP 54048 is a solar metallicity red horizontal branch star
✔
✔
staytuned
and most of the IGRINS K Band
✔✔
ends of orders with lots of tellurics have been chopped here
reductions & analyses in brief
IGRINS pipeline, and IRAF “telluric” package standard analysis techniques using MOOG code NIST transition probabilities when available,
otherwise Kurucz database line-to-line scatter is reasonable: σ ≈ 0.1 happiest results: better abundances for “alpha”
elements (Mg, Si, S, Ca) OH, CO molecular lines visible in HD 122563 probably detections of 1 Na line and 2 Al lines, but
we are not confident of abundances
some lines are obvious, withsome unexpected detections
simple extrapolations from Arcturus spectrum predict that Mg I will be strong at low metallicity
good question for thesis defenses: why is weak,
fragile molecule OH visible in HD 122563?
Note the 1% deep S I lines; these are real
Si I lines are BETTER in the IR
analysis issues; watch out!
lines are too weak
lines are just right for reliable abundances
IGRINS alpha abundances are
trustworthy
No possibility of getting sulfur in the
optical
much of the line-line scatter must be in the (NIST) basic line data
HD 140283 gives similar results, but
there are fewer lines in that warmer star
optical IGRINS
how low in metallicity can we go???we could have added
in more CO lines
only a simple mean was done here
arbitrary C, O to fit observed line
the syntheses differ by 0.3 dex in C
abundan ce
Topic II
Application of H- and K-band IGRINS spectra to the curious case of field red horizontal-
branch stars
red clump vs red horizontal branch
http://spiff.rit.edu/classes/phys373/lectures/colors/colors.html
young, higher-mass metal-rich field stars: the red clump
https://en.wikipedia.org/wiki/Horizontal_branch
old, low mass, usually metal-poor stars: the blue and red horizontal branch
why are there so many bright RHB field stars?
Afşar et al. 2012
RC
HR diagram of color-selected sample of bright G-type giants
Many with Hipparcos parallaxes
that confirm their “giant” status
filled circles and x symbols have
“evolved” carbon isotopic ratios:
12C/13C < 30
they are not very metal-poor; they are often thin disk; they really(?) are chemically evolved
this is a“Toomre” diagram for the field RHB stars
low 12C/13C is a telltale sign of CN-
cycle H-burning and envelope mixing
many are low velocity thin disk starsAfşar et al. 2012
But believing carbon isotopes from one very weak transition is very risky
Afşar et al. 2012
IGRINS to the rescue!one 2%-deep CN optical feature versus
a whole IR CO bandheads
and for HIP 54048, better light-element abundances in the IR than in the optical
note especially P I, S I, K I only in IR; good agreement between Ti I & Ti II
Afşar et al. ,in prep
Topic III
Some uses of IGRINS spectra for fundamental evolution of open
cluster stars
our first effort used optical spectra of NGC 752
http://www.employees.org/~ddavison/Astro/astro.php?image=ngc752-2.jpg&images=NGC
Böcek Topcu et al. 2015
light elements + HR-diagram = stellar evolutionopen cluster NGC 752
Böcek Topcu et al. 2015
fred
http://www.alsonwongastro.com/ngc6940.htm
red symbols are stars observed by IGRINS
Now attack with IGRINS
fred
http://cs.astronomy.com/asy/m/starclusters/464451.aspx
red symbols are stars observed by IGRINS
Now attack with IGRINS
CNOLi abundances in open cluster giantsELEMENT OPTICAL LINES
IGRINS LINES
lithium Li I 6707Åno features
carbon CH 4300Å – saturated CO all over
C2 5160, 5630Å – weak
nitrogen CN mostly >8000ÅCN strong in H
oxygen [O I] 6300,6363Å - ?? OH all over
some other considerations red giants typically 2-3 mag brighter in K than in V H and K bands have drastically reduced extinction mostly can get around gravity worries with CMD
a first IGRINS look at an exotic light element in M67
mostly an easy victory: 12C/13C = 25
but what are the things that don’t “fit”?
?
????
where IR spectrum analyses struggle: ions
also in the heavy neutron-capture elements
IGRINS spectra of cool stars are dazzling –let’s be half as good as our data!
from Pierre Magain’s contribution at IAU Symp 132 (1988):
It is just a matter of will: do we intend to continue to provide the Galactic evolution theorists with data we cannot reasonably guarantee their reliability, or will we concentrate part of our efforts on checking the validity of our assumptions?
the good news is that IGRINS will bring qualitative advances to our knowledge of stellar chemical
compositions ... and employment for us for many years!
Many thanks for this excellent meeting!
fred
fred
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