122 research outputs found
US National Gemini Office in the NOIRLab era
This article presents an overview of the US National Gemini Office (US NGO)
and its role within the International Gemini Observatory user community.
Throughout the years, the US NGO charter changed considerably to accommodate
the evolving needs of astronomers and the observatory. The current landscape of
observational astronomy requires effective communication between stakeholders
and reliable/accessible data reduction tools and products, which minimize the
time between data gathering and publication of scientific results. Because of
that, the US NGO heavily invests in producing data reduction tutorials and
cookbooks. Recently, the US NGO started engaging with the Gemini user community
through social media, and the results have been encouraging, increasing the
observatory's visibility. The US NGO staff developed tools to assess whether
the support provided to the user community is sufficient and effective, through
website analytics and social media engagement numbers. These quantitative
metrics serve as the baseline for internal reporting and directing efforts to
new or current products. In the era of the NSF's National Optical-Infrared
Astronomy Research Laboratory (NOIRLab), the US NGO is well-positioned to be
the liaison between the US user base and the Gemini Observatory. Furthermore,
collaborations within NOIRLab programs, such as the Astro Data Lab and the Time
Allocation Committee, enhance the US NGO outreach to attract users and develop
new products. The future landscape laid out by the Astro 2020 report confirms
the need to establish such synergies and provide more integrated user support
services to the astronomical community at large.Comment: 15 pages, 8 figures, published in the Journal of Astronomical
Telescopes, Instruments, and System
SD 1313-0019 -- Another second-generation star with [Fe/H] = -5.0, observed with the Magellan Telescope
We present a Magellan/MIKE high-resolution (R ~ 35,000) spectrum of the
ancient star SD 1313-0019 which has an iron abundance of [Fe/H] = -5.0, paired
with a carbon enhancement of [C/Fe] ~ 3.0. The star was initially identified by
Allende Prieto et al. in the BOSS survey. Its medium-resolution spectrum
suggested a higher metallicity of [Fe/H] = -4.3 due to the CaII K line blending
with a CH feature which is a common issue related to the search for the most
iron-poor stars. This star joins several other, similar stars with [Fe/H] <
-5.0 that all display a combination of low iron and high carbon abundances.
Other elemental abundances of SD 1313-0019 follow that of more metal-rich halo
stars. From fitting the abundance pattern with yields of Population III
supernova, we conclude that SD 1313-0019 had only one massive progenitor star
with 20 - 30 M_sun that must have undergone a mixing and fallback episode.
Overall, there are now five stars known with [Fe/H] < -5.0 (1D LTE abundances).
This population of second-generation stars strongly suggests massive first
stars that almost exclusively produced large amounts of carbon through stellar
winds and/or their mixing and fallback supernova explosions. As a consequence,
their natal clouds -- presumably some early minihalo structures -- contained
ample amounts of carbon and oxygen that likely facilitated the formation of
these first low-mass stars.Comment: 7 pages and 3 figures, accepted by ApJ
2MASS J18082002-5104378: The brightest (V=11.9) ultra metal-poor star
Context. The most primitive metal-poor stars are important for studying the
conditions of the early galaxy and are also relevant to big bang
nucleosynthesis. Aims. Our objective is to find the brightest (V<14) most
metal-poor stars. Methods. Candidates were selected using a new method, which
is based on the mismatch between spectral types derived from colors and
observed spectral types. They were observed first at low resolution with EFOSC2
at the NTT/ESO to obtain an initial set of stellar parameters. The most
promising candidate, 2MASS J18082002-5104378 (V=11.9), was observed at high
resolution (R=50 000) with UVES at the VLT/ESO, and a standard abundance
analysis was performed. Results. We found that 2MASS J18082002-5104378 is an
ultra metal-poor star with stellar parameters Teff = 5440 K, log g = 3.0 dex,
vt = 1.5 km/s, [Fe/H] = -4.1 dex. The star has [C/Fe]<+0.9 in a 1D analysis, or
[C/Fe]<=+0.5 if 3D effects are considered; its abundance pattern is typical of
normal (non-CEMP) ultra metal-poor stars. Interestingly, the star has a binary
companion. Conclusions. 2MASS J1808-5104 is the brightest (V=11.9) metal-poor
star of its category, and it could be studied further with even higher S/N
spectroscopy to determine additional chemical abundances, thus providing
important constraints to the early chemical evolution of our Galaxy.Comment: A&A Letter
The R-Process Alliance: A Comprehensive Abundance Analysis of HD 222925, a Metal-Poor Star with an Extreme R-Process Enhancement of [Eu/H] = -0.14
We present a detailed abundance analysis of the bright (V = 9.02), metal-poor
([Fe/H] = -1.47 +/- 0.08) field red horizontal-branch star HD 222925, which was
observed as part of an ongoing survey by the R-Process Alliance. We calculate
stellar parameters and derive abundances for 46 elements based on 901 lines
examined in a high-resolution optical spectrum obtained using the Magellan
Inamori Kyocera Echelle spectrograph. We detect 28 elements with 38 <= Z <= 90;
their abundance pattern is a close match to the Solar r-process component. The
distinguishing characteristic of HD 222925 is an extreme enhancement of
r-process elements ([Eu/Fe] = +1.33 +/- 0.08, [Ba/Eu] = -0.78 +/- 0.10) in a
moderately metal-poor star, so the abundance of r-process elements is the
highest ([Eu/H] = -0.14 +/- 0.09) in any known r-process-enhanced star. The
abundance ratios among lighter (Z <= 30) elements are typical for metal-poor
stars, indicating that production of these elements was dominated by normal
Type II supernovae, with no discernible contributions from Type Ia supernovae
or asymptotic giant branch stars. The chemical and kinematic properties of HD
222925 suggest it formed in a low-mass dwarf galaxy, which was enriched by a
high-yield r-process event before being disrupted by interaction with the Milky
Way.Comment: Accepted for publication in the Astrophysical Journal (17 pages, 4
figures, 3 tables
Population Studies. XIII. A New Analysis of the Bidelman-MacConnell "Weak-Metal" Stars - Confirmation of Metal-Poor Stars in the Thick Disk of the Galaxy
A new set of very high signal-to-noise (S/N > 100/1), medium-resolution
(R~3000) optical spectra have been obtained for 302 of the candidate
"weak-metal" stars selected by Bidelman & MacConnell. We use these data to
calibrate the recently developed generalization of the SEGUE Stellar Parameter
Pipeline, and obtain estimates of the atmospheric parameters (Teff, log g , and
[Fe/H]) for these non-SDSS/SEGUE data; we also obtain estimates of [C/Fe]. The
new abundance measurements are shown to be consistent with available
high-resolution spectroscopic determinations, and represent a substantial
improvement over the accuracies obtained from the previous photometric
estimates reported in Paper I of this series. The apparent offset in the
photometric abundances of the giants in this sample noted by several authors is
confirmed by our new spectroscopy; no such effect is found for the dwarfs. The
presence of a metal-weak thick-disk (MWTD) population is clearly supported by
these new abundance data. Some 25% of the stars with metallicities -1.8 <
[Fe/H] <= -0.8 exhibit orbital eccentricities e < 0.4, yet are clearly
separated from members of the inner-halo population with similar metallicities
by their location in a Lindblad energy vs. angular momentum diagram. A
comparison is made with recent results for a similar-size sample of RAVE stars
from Ruchti et al. We conclude, based on both of these samples, that the MWTD
is real, and must be accounted for in discussions of the formation and
evolution of the disk system of the Milky Way.Comment: 45 pages, 14 figures; accepted for publication in Ap
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