866 research outputs found
Spectroscopic Confirmation of the Dwarf Galaxies Hydra II and Pisces II and the Globular Cluster Laevens 1
We present Keck/DEIMOS spectroscopy of stars in the recently discovered Milky
Way satellites Hydra II, Pisces II, and Laevens 1. We measured a velocity
dispersion of 5.4 (+3.6 -2.4) km/s for Pisces II, but we did not resolve the
velocity dispersions of Hydra II or Laevens 1. We marginally resolved the
metallicity dispersions of Hydra II and Pisces II but not Laevens 1.
Furthermore, Hydra II and Pisces II obey the luminosity-metallicity relation
for Milky Way dwarf galaxies ( = -2.02 +/- 0.08 and -2.45 +/- 0.07,
respectively), whereas Laevens 1 does not ( = -1.68 +/- 0.05). The
kinematic and chemical properties suggest that Hydra II and Pisces II are dwarf
galaxies, and Laevens 1 is a globular cluster. We determined that two of the
previously observed blue stars near the center of Laevens 1 are not members of
the cluster. A third blue star has ambiguous membership. Hydra II has a radial
velocity = 303.1 +/- 1.4 km/s, similar to the leading arm of the
Magellanic stream. The mass-to-light ratio for Pisces II is 370 (+310 -240)
M_sun/L_sun. It is not among the most dark matter-dominated dwarf galaxies, but
it is still worthy of inclusion in the search for gamma rays from dark matter
self-annihilation.Comment: Accepted to ApJ. v2 has been revised in response to the referee's
repor
Re-exploration of vertical rectus abdominis myocutaneous flap for vaginal reconstruction: Case report and review of the literature.
The vertical rectus abdominis myocutaneous (VRAM) flap is a versatile and well-established reconstructive technique for many defects created as a result of colorectal and gynecologic extirpation. However, major re-operation in the pelvis following a VRAM flap reconstruction several months later is uncommon, and the safety and integrity of the VRAM flap in this setting has not been described. This case examines VRAM flap preservation during repeat exploratory laparotomy, and a unique view of the VRAM flap during interval exploration. We demonstrate an intact flap after lysis of adhesions with an audible Doppler signal, and maintenance of flap integrity in the postoperative period. This further substantiates its use as a durable rotational flap for perineal tissue defects
Triangulum II: Not Especially Dense After All
Among the Milky Way satellites discovered in the past three years, Triangulum
II has presented the most difficulty in revealing its dynamical status. Kirby
et al. (2015a) identified it as the most dark matter-dominated galaxy known,
with a mass-to-light ratio within the half-light radius of 3600 +3500 -2100
M_sun/L_sun. On the other hand, Martin et al. (2016) measured an outer velocity
dispersion that is 3.5 +/- 2.1 times larger than the central velocity
dispersion, suggesting that the system might not be in equilibrium. From new
multi-epoch Keck/DEIMOS measurements of 13 member stars in Triangulum II, we
constrain the velocity dispersion to be sigma_v < 3.4 km/s (90% C.L.). Our
previous measurement of sigma_v, based on six stars, was inflated by the
presence of a binary star with variable radial velocity. We find no evidence
that the velocity dispersion increases with radius. The stars display a wide
range of metallicities, indicating that Triangulum II retained supernova ejecta
and therefore possesses or once possessed a massive dark matter halo. However,
the detection of a metallicity dispersion hinges on the membership of the two
most metal-rich stars. The stellar mass is lower than galaxies of similar mean
stellar metallicity, which might indicate that Triangulum II is either a star
cluster or a tidally stripped dwarf galaxy. Detailed abundances of one star
show heavily depressed neutron-capture abundances, similar to stars in most
other ultra-faint dwarf galaxies but unlike stars in globular clusters.Comment: accepted to ApJ, Table 5 available as a machine-readable table by
clicking on "Other formats" on the right. Proof corrections reflected in
version
NGC 2419 -- Another Remnant of Accretion by the Milky Way
We isolate a sample of 43 upper RGB stars in the extreme outer halo Galactic
globular cluster NGC 2419 from two Keck/DEIMOS slitmasks. The probability that
there is more than one contaminating halo field star in this sample is
extremely low. Analysis of moderate resolution spectra of these cluster
members, as well as of our Keck/HIRES high resolution spectra of a subsample of
them, demonstrates that there is a small but real spread in Ca abundance of ~
0.2 dex within this massive metal-poor globular cluster. This provides
additional support to earlier suggestions that NGC 2419 is the remnant of a
dwarf galaxy accreted long ago by the Milky Way.Comment: Accepted to the Astrophysical Journa
Triangulum II: Possibly a Very Dense Ultra-faint Dwarf Galaxy
Laevens et al. recently discovered Triangulum II (Tri II), a satellite of the Milky Way. Its Galactocentric distance is 36 kpc, and its luminosity is only 450 L_⊙. Using Keck/DEIMOS, we measured the radial velocities of six member stars within 1'.2 of the center of Tri II, and we found a velocity dispersion of σ_v = 5.1_(-1.4)^(+4.0) km s^(-1). We also measured the metallicities of three stars and found a range of 0.8 dex in [Fe/H]. The velocity and metallicity dispersions identify Tri II as a dark matter-dominated galaxy. The galaxy is moving very quickly toward the Galactic center v_(GSR) = -262 km s^(-1). Although it might be in the process of being tidally disrupted as it approaches pericenter, there is no strong evidence for disruption in our data set. The ellipticity is low, and the mean velocity, 〈|v_(helio)〉 =-382.1 ± 2.9 km s^(-1), rules out an association with the Triangulum–Andromeda substructure or the Pan-Andromeda Archaeological Survey stellar stream. If Tri II is in dynamical equilibrium, then it would have a mass-to-light ratio of 3600_(-2100)^(+3500) M}_⊙ L_⊙^(-1), the highest of any non-disrupting galaxy (those for which dynamical mass estimates are reliable). The density within the 3D half-light radius would be 4.8_(-3.5)^(+8.1) M⊙ pc^(-3), even higher than Segue 1. Hence, Tri II is an excellent candidate for the indirect detection of dark matter annihilation
SUSY Simplified Models at 14, 33, and 100 TeV Proton Colliders
Results are presented for a variety of SUSY Simplified Models at the 14 TeV
LHC as well as a 33 and 100 TeV proton collider. Our focus is on models whose
signals are driven by colored production. We present projections of the upper
limit and discovery reach in the gluino-neutralino (for both light and heavy
flavor decays), squark-neutralino, and gluino-squark Simplified Model planes.
Depending on the model a jets + MET, mono-jet, or same-sign di-lepton search is
applied. The impact of pileup is explored. This study utilizes the Snowmass
backgrounds and combined detector. Assuming 3000 fb^{-1} of integrated
luminosity, a gluino that decays to light flavor quarks can be discovered below
2.3 TeV at the 14 TeV LHC and below 11 TeV at a 100 TeV machine.Comment: 81 pages, 55 figures; v2 journal versio
Multi-Element Abundance Measurements from Medium-Resolution Spectra. II. Catalog of Stars in Milky Way Dwarf Satellite Galaxies
We present a catalog of Fe, Mg, Si, Ca, and Ti abundances for 2961 red giant
stars that are likely members of eight dwarf satellite galaxies of the Milky
Way (MW): Sculptor, Fornax, Leo I, Sextans, Leo II, Canes Venatici I, Ursa
Minor, and Draco. For the purposes of validating our measurements, we also
observed 445 red giants in MW globular clusters and 21 field red giants in the
MW halo. The measurements are based on Keck/DEIMOS medium-resolution
spectroscopy combined with spectral synthesis. We estimate uncertainties in
[Fe/H] by quantifying the dispersion of [Fe/H] measurements in a sample of
stars in monometallic globular clusters. We estimate uncertainties in Mg, Si,
Ca, and Ti abundances by comparing our medium-resolution spectroscopic
measurements to high-resolution spectroscopic abundances of the same stars. For
this purpose, our DEIMOS sample included 132 red giants with published
high-resolution spectroscopy in globular clusters, the MW halo field, and dwarf
galaxies. The standard deviations of the differences in [Fe/H] and [alpha/Fe]
(the average of [Mg/Fe], [Si/Fe], [Ca/Fe], and [Ti/Fe]) between the two samples
is 0.15 and 0.16, respectively. This catalog represents the largest sample of
multi-element abundances in dwarf galaxies to date. The next papers in this
series draw conclusions on the chemical evolution, gas dynamics, and star
formation histories from the catalog presented here. The wide range of dwarf
galaxy luminosity reveals the dependence of dwarf galaxy chemical evolution on
galaxy stellar mass.Comment: 26 pages, 22 figures, 4 machine-readable tables (available in the
source file; click "Other formats"); accepted for publication in ApJ
Supplements; updated acknowledgments in v
Preparing Postbaccalaureates for Entry and Success in Biomedical PhD Programs
Certain racial and ethnic groups, individuals with disabilities, and those from low socioeconomic backgrounds remain underrepresented (UR) in the biomedical sciences. This underrepresentation becomes more extreme at each higher education stage. To support UR scholars during the critical transition from baccalaureate to PhD, we established an intensive, 1-yr postbaccalaureate training program. We hypothesized that this intervention would strengthen each participant’s competitiveness for leading PhD programs and build a foundation of skills and self-efficacy important for success during and after graduate school. Scholar critical analysis skills, lab technique knowledge, and Graduate Record Examination scores all improved significantly during the program. Scholars reported significant confidence growth in 21 of 24 categories related to success in research careers. In 5 yr, 91% (41/45) of scholars transitioned directly into PhD programs. Importantly, 40% (18/45) of participating postbaccalaureate scholars had previously been declined acceptance into graduate school; however, 17/18 of these scholars directly entered competitive PhD programs following our training program. Alumni reported they were “extremely well” prepared for graduate school, and 95% (39/41) are currently making progress to graduation with a PhD. In conclusion, we report a model for postbaccalaureate training that could be replicated to increase participation and success among UR scholars in the biomedical sciences
Plants, people and health: Three disciplines at work in Namaqualand
In Paulshoek, Namaqualand, three research projects focusing on medicinal plants were developed concurrently. The projects were based in the disciplines of anthropology, botany and chemistry. In this paper, we explore how these projects related to one another and describe the conversations that occurred in the process of searching for transdisciplinary knowledge. The projects ostensibly shared a common object of knowledge, but it was through working together that the medicinal plants constituted us as a community of scholars. As our insight into our respective disciplinary relationships with the plants grew, so did our understanding of the limitations of our respective disciplinary positions. The process made possible a ‘reimagination’ of both the object of study and our relationships to it and to one another. The research project, conceptualised in 2009, engaged current debates on indigenous knowledge and its historical erasures, and offered an approach that has potential to produce new knowledges while respecting the integrity of the disciplines. This approach requires a non-competitive attitude to research and one that acknowledges the contributions that can be made by multiple approaches
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