184 research outputs found
Chemical tagging can work: Identification of stellar phase-space structures purely by chemical-abundance similarity
Chemical tagging promises to use detailed abundance measurements to identify
spatially separated stars that were in fact born together (in the same
molecular cloud), long ago. This idea has not yielded much practical success,
presumably because of the noise and incompleteness in chemical-abundance
measurements. We have succeeded in substantially improving spectroscopic
measurements with The Cannon, which has now delivered 15 individual abundances
for ~100,000 stars observed as part of the APOGEE spectroscopic survey, with
precisions around 0.04 dex. We test the chemical-tagging hypothesis by looking
at clusters in abundance space and confirming that they are clustered in phase
space. We identify (by the k-means algorithm) overdensities of stars in the
15-dimensional chemical-abundance space delivered by The Cannon, and plot the
associated stars in phase space. We use only abundance-space information (no
positional information) to identify stellar groups. We find that clusters in
abundance space are indeed clusters in phase space. We recover some known
phase-space clusters and find other interesting structures. This is the
first-ever project to identify phase-space structures at survey-scale by blind
search purely in abundance space; it verifies the precision of the abundance
measurements delivered by The Cannon; the prospects for future data sets appear
very good.Comment: accepted for publication in the Ap
TOI-150: A transiting hot Jupiter in the TESS southern CVZ
We report the detection of a hot Jupiter ($M_{p}=1.75_{-0.17}^{+0.14}\
M_{J}R_{p}=1.38\pm0.04\ R_{J}\log
g=4.152^{+0.030}_{-0.043}\beta=-79.59^{\circ}$). We confirm the
planetary nature of the candidate TOI-150.01 using radial velocity observations
from the APOGEE-2 South spectrograph and the Carnegie Planet Finder
Spectrograph, ground-based photometric observations from the robotic
Three-hundred MilliMeter Telescope at Las Campanas Observatory, and Gaia
distance estimates. Large-scale spectroscopic surveys, such as APOGEE/APOGEE-2,
now have sufficient radial velocity precision to directly confirm the signature
of giant exoplanets, making such data sets valuable tools in the TESS era.
Continual monitoring of TOI-150 by TESS can reveal additional planets and
subsequent observations can provide insights into planetary system
architectures involving a hot Jupiter around a star about halfway through its
main-sequence life.Comment: 13 pages, 3 figures, 2 tables, accepted to ApJ
Identifying Contributions to the Stellar Halo from Accreted, Kicked-Out, and In Situ Populations
[Abridged] We present a medium-resolution spectroscopic survey of late-type
giant stars at mid-Galactic latitudes of (30),
designed to probe the properties of this population to distances of 9
kpc. Because M giants are generally metal-rich and we have limited
contamination from thin disk stars by the latitude selection, most of the stars
in the survey are expected to be members of the thick disk
(-0.6) with some contribution from the metal-rich component of
the nearby halo.
Here we report first results for 1799 stars. The distribution of radial
velocity (RV) as a function of l for these stars shows (1) the expected thick
disk population and (2) local metal-rich halo stars moving at high speeds
relative to the disk, that in some cases form distinct sequences in RV-
space. High-resolution echelle spectra taken for 34 of these "RV outliers"
reveal the following patterns across the [Ti/Fe]-[Fe/H] plane: seventeen of the
stars have abundances reminiscent of the populations present in dwarf
satellites of the Milky Way; eight have abundances coincident with those of the
Galactic disk and more metal-rich halo; and nine of the stars fall on the locus
defined by the majority of stars in the halo. The chemical abundance trends of
the RV outliers suggest that this sample consists predominantly of stars
accreted from infalling dwarf galaxies. A smaller fraction of stars in the RV
outlier sample may have been formed in the inner Galaxy and subsequently kicked
to higher eccentricity orbits, but the sample is not large enough to
distinguish conclusively between this interpretation and the alternative that
these stars represent the tail of the velocity distribution of the thick disk.
Our data do not rule out the possibility that a minority of the sample could
have formed from gas {\it in situ} on their current orbits.Comment: 43 pages, 9 figures, 4 tables, published in the Astrophysical Journa
The impact of Ming and Qing dynasty maritime bans on trade ceramics recovered from coastal settlements in northern Sumatra, Indonesia
We review published literature and historical texts to propose that three periods of official Chinese maritime bans impacted the composition and circulation of trade ceramics along Asian trade routes: Ming Ban 1 (1371 – 1509), Ming Ban 2 (1521 – 1529), and Qing Ban (1654 – 1684). We use ceramics collected during a landscape archaeology survey along 40km of coast in Aceh, Indonesia to show how the three ban periods manifest in the ceramic record of settlements along an important stretch of the maritime silk road. All three ban periods overlap with reductions in the quantity of Chinese ceramics. Within several decades of the start of Ming Ban 1, people in Aceh began importing ceramics from production centres in Burma and Thailand as a substitute for Chinese ceramics. Following Ming Ban 2, there is an increase in imports from Chinese production centres, albeit from new kilns sites. While brief, the Qing ban resulted in an almost immediate influx of ceramics from Japan and Vietnam, which maintained some market share until the mid-17th century, after which Chinese ceramics dominate the record until the end of the Qing dynasty. Our data show both the importance of Chinese ceramics within regional trade networks and how those networks and local patterns of consumption adapted to disruptions of supply
The contribution of N-rich stars to the Galactic stellar halo using APOGEE red giants
The contribution of dissolved globular clusters (GCs) to the stellar content
of the Galactic halo is a key constraint on models for GC formation and
destruction, and the mass assembly history of the Milky Way. Earlier results
from APOGEE pointed to a large contribution of destroyed GCs to the stellar
content of the inner halo, by as much as 25, which is an order of magnitude
larger than previous estimates for more distant regions of the halo. We set out
to measure the ratio between N-rich and normal halo field stars, as a function
of distance, by performing density modelling of halo field populations in
APOGEE DR16. Our results show that at 1.5 kpc from the Galactic Centre, N-rich
stars contribute a much higher 16.8 fraction to the total
stellar halo mass budget than the 2.7 ratio contributed at
10 kpc. Under the assumption that N-rich stars are former GC members that now
reside in the stellar halo field, and assuming the ratio between first-and
second-population GC stars being 1:2, we estimate a total contribution from
disrupted GC stars of the order of 27.5 at r = 1.5 kpc
and 4.2 at r = 10 kpc. Furthermore, since our methodology
requires fitting a density model to the stellar halo, we integrate such density
within a spherical shell from 1.5-15 kpc in radius, and find a total stellar
mass arising from dissolved and/or evaporated GCs of =
9.6 10 M.Comment: Paper accepted for Publication in MNRA
Kinematics & Chemistry of Halo Substructures: The Vicinity of the Virgo Over-Density
We present observations obtained with the AAT's 2dF wide field spectrograph
AAOmega of K-type stars located within a region of the sky which contains the
Virgo Over-Density and the leading arm of the Sagittarius Stream. On the basis
of the resulting velocity histogram we isolate halo substructures in these
overlapping regions including Sagittarius and previously discovered Virgo
groups. Through comparisons with N-body models of the Galaxy-Sagittarius
interaction, we find a tri-axial dark matter halo is favoured and we exclude a
prolate shape. This result is contradictory with other observations along the
Sagittarius leading arm, which typically favour prolate models. We have also
uncovered K-giant members of Sagittarius that are notably more metal poor
([Fe/H] = -1.7 +/- 0.3 dex) than previous studies. This suggests a
significantly wider metallicity distribution exists in the Sagittarius Stream
than formerly considered. We also present data on five carbon stars which were
discovered in our sample.Comment: accepted to A
Light Curve Templates and Galactic Distribution of RR Lyrae Stars from Sloan Digital Sky Survey Stripe 82
We present an improved analysis of halo substructure traced by RR Lyrae stars
in the SDSS stripe 82 region. With the addition of SDSS-II data, a revised
selection method based on new ugriz light curve templates results in a sample
of 483 RR Lyrae stars that is essentially free of contamination. The main
result from our first study persists: the spatial distribution of halo stars at
galactocentric distances 5--100 kpc is highly inhomogeneous. At least 20% of
halo stars within 30 kpc from the Galactic center can be statistically
associated with substructure. We present strong direct evidence, based on both
RR Lyrae stars and main sequence stars, that the halo stellar number density
profile significantly steepens beyond a Galactocentric distance of ~30 kpc, and
a larger fraction of the stars are associated with substructure. By using a
novel method that simultaneously combines data for RR Lyrae and main sequence
stars, and using photometric metallicity estimates for main sequence stars
derived from deep co-added u-band data, we measure the metallicity of the
Sagittarius dSph tidal stream (trailing arm) towards R.A.2h-3h and Dec~0 deg to
be 0.3 dex higher ([Fe/H]=-1.2) than that of surrounding halo field stars.
Together with a similar result for another major halo substructure, the
Monoceros stream, these results support theoretical predictions that an early
forming, smooth inner halo, is metal poor compared to high surface brightness
material that have been accreted onto a later-forming outer halo. The mean
metallicity of stars in the outer halo that are not associated with detectable
clumps may still be more metal-poor than the bulk of inner-halo stars, as has
been argued from other data sets.Comment: Submitted to ApJ, 68 pages, 26 figures, supplemental material (light
curves, templates, animation) can be downloaded from
http://www.astro.washington.edu/bsesar/S82_RRLyr.htm
Taking the Measure of the Universe: Precision Astrometry with SIM PlanetQuest
Precision astrometry at microarcsecond accuracy has application to a wide
range of astrophysical problems. This paper is a study of the science questions
that can be addressed using an instrument that delivers parallaxes at about 4
microarcsec on targets as faint as V = 20, differential accuracy of 0.6
microarcsec on bright targets, and with flexible scheduling. The science topics
are drawn primarily from the Team Key Projects, selected in 2000, for the Space
Interferometry Mission PlanetQuest (SIM PlanetQuest). We use the capabilities
of this mission to illustrate the importance of the next level of astrometric
precision in modern astrophysics. SIM PlanetQuest is currently in the detailed
design phase, having completed all of the enabling technologies needed for the
flight instrument in 2005. It will be the first space-based long baseline
Michelson interferometer designed for precision astrometry. SIM will contribute
strongly to many astronomical fields including stellar and galactic
astrophysics, planetary systems around nearby stars, and the study of quasar
and AGN nuclei. SIM will search for planets with masses as small as an Earth
orbiting in the `habitable zone' around the nearest stars using differential
astrometry, and could discover many dozen if Earth-like planets are common. It
will be the most capable instrument for detecting planets around young stars,
thereby providing insights into how planetary systems are born and how they
evolve with time. SIM will observe significant numbers of very high- and
low-mass stars, providing stellar masses to 1%, the accuracy needed to
challenge physical models. Using precision proper motion measurements, SIM will
probe the galactic mass distribution and the formation and evolution of the
Galactic halo. (abridged)Comment: 54 pages, 28 figures, uses emulateapj. Submitted to PAS
Identification of the first ATRIP-deficient patient and novel mutations in ATR define a clinical spectrum for ATR-ATRIP Seckel Syndrome
A homozygous mutational change in the Ataxia-Telangiectasia and RAD3 related (ATR) gene was previously reported in two related families displaying Seckel Syndrome (SS). Here, we provide the first identification of a Seckel Syndrome patient with mutations in ATRIP, the gene encoding ATR-Interacting Protein (ATRIP), the partner protein of ATR required for ATR stability and recruitment to the site of DNA damage. The patient has compound heterozygous mutations in ATRIP resulting in reduced ATRIP and ATR expression. A nonsense mutational change in one ATRIP allele results in a C-terminal truncated protein, which impairs ATR-ATRIP interaction; the other allele is abnormally spliced. We additionally describe two further unrelated patients native to the UK with the same novel, heterozygous mutations in ATR, which cause dramatically reduced ATR expression. All patient-derived cells showed defective DNA damage responses that can be attributed to impaired ATR-ATRIP function. Seckel Syndrome is characterised by microcephaly and growth delay, features also displayed by several related disorders including Majewski (microcephalic) osteodysplastic primordial dwarfism (MOPD) type II and Meier-Gorlin Syndrome (MGS). The identification of an ATRIP-deficient patient provides a novel genetic defect for Seckel Syndrome. Coupled with the identification of further ATR-deficient patients, our findings allow a spectrum of clinical features that can be ascribed to the ATR-ATRIP deficient sub-class of Seckel Syndrome. ATR-ATRIP patients are characterised by extremely severe microcephaly and growth delay, microtia (small ears), micrognathia (small and receding chin), and dental crowding. While aberrant bone development was mild in the original ATR-SS patient, some of the patients described here display skeletal abnormalities including, in one patient, small patellae, a feature characteristically observed in Meier-Gorlin Syndrome. Collectively, our analysis exposes an overlapping clinical manifestation between the disorders but allows an expanded spectrum of clinical features for ATR-ATRIP Seckel Syndrome to be define
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