55 research outputs found
Genetic Evidence on the Origins of Indian Caste Populations
This is the published version, also available here: http://www.dx.doi.org/10.1101/gr.173301.The origins and affinities of the ∼1 billion people living on the subcontinent of India have long been contested.
This is owing, in part, to the many different waves of immigrants that have influenced the genetic structure of
India. In the most recent of these waves, Indo-European-speaking people from West Eurasia entered India from
the Northwest and diffused throughout the subcontinent. They purportedly admixed with or displaced
indigenous Dravidic-speaking populations. Subsequently they may have established the Hindu caste system and
placed themselves primarily in castes of higher rank. To explore the impact of West Eurasians on contemporary
Indian caste populations, we compared mtDNA (400 bp of hypervariable region 1 and 14 restriction site
polymorphisms) and Y-chromosome (20 biallelic polymorphisms and 5 short tandem repeats) variation in ∼265
males from eight castes of different rank to ∼750 Africans, Asians, Europeans, and other Indians. For maternally
inherited mtDNA, each caste is most similar to Asians. However, 20%–30% of Indian mtDNA haplotypes
belong to West Eurasian haplogroups, and the frequency of these haplotypes is proportional to caste rank, the
highest frequency of West Eurasian haplotypes being found in the upper castes. In contrast, for paternally
inherited Y-chromosome variation each caste is more similar to Europeans than to Asians. Moreover, the
affinity to Europeans is proportionate to caste rank, the upper castes being most similar to Europeans,
particularly East Europeans. These findings are consistent with greater West Eurasian male admixture with castes
of higher rank. Nevertheless, the mitochondrial genome and the Y chromosome each represents only a single
haploid locus and is more susceptible to large stochastic variation, bottlenecks, and selective sweeps. Thus, to
increase the power of our analysis, we assayed 40 independent, biparentally inherited autosomal loci (1 LINE-1
and 39 Alu elements) in all of the caste and continental populations (∼600 individuals). Analysis of these data
demonstrated that the upper castes have a higher affinity to Europeans than to Asians, and the upper castes are
significantly more similar to Europeans than are the lower castes. Collectively, all five datasets show a trend
toward upper castes being more similar to Europeans, whereas lower castes are more similar to Asians. We
conclude that Indian castes are most likely to be of proto-Asian origin with West Eurasian admixture resulting
in rank-related and sex-specific differences in the genetic affinities of castes to Asians and Europeans
A chemical survey of exoplanets with ARIEL
Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planet’s birth, and evolution. ARIEL was conceived to observe a large number (~1000) of transiting planets for statistical understanding, including gas giants, Neptunes, super-Earths and Earth-size planets around a range of host star types using transit spectroscopy in the 1.25–7.8 μm spectral range and multiple narrow-band photometry in the optical. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-Z materials compared to their colder Solar System siblings. Said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. Observations of these warm/hot exoplanets, and in particular of their elemental composition (especially C, O, N, S, Si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ARIEL will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ARIEL is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allow us to measure atmospheric signals from the planet at levels of 10–100 part per million (ppm) relative to the star and, given the bright nature of targets, also allows more sophisticated techniques, such as eclipse mapping, to give a deeper insight into the nature of the atmosphere. These types of observations require a stable payload and satellite platform with broad, instantaneous wavelength coverage to detect many molecular species, probe the thermal structure, identify clouds and monitor the stellar activity. The wavelength range proposed covers all the expected major atmospheric gases from e.g. H2O, CO2, CH4 NH3, HCN, H2S through to the more exotic metallic compounds, such as TiO, VO, and condensed species. Simulations of ARIEL performance in conducting exoplanet surveys have been performed – using conservative estimates of mission performance and a full model of all significant noise sources in the measurement – using a list of potential ARIEL targets that incorporates the latest available exoplanet statistics. The conclusion at the end of the Phase A study, is that ARIEL – in line with the stated mission objectives – will be able to observe about 1000 exoplanets depending on the details of the adopted survey strategy, thus confirming the feasibility of the main science objectives.Peer reviewedFinal Published versio
TESS spots a mini-neptune interior to a hot saturn in the TOI-2000 system
Hot jupiters (P 60 ) are almost always found
alone around their stars, but four out of hundreds known have inner companion
planets. These rare companions allow us to constrain the hot jupiter's
formation history by ruling out high-eccentricity tidal migration. Less is
known about inner companions to hot Saturn-mass planets. We report here the
discovery of the TOI-2000 system, which features a hot Saturn-mass planet with
a smaller inner companion. The mini-neptune TOI-2000 b (, ) is in a 3.10-day
orbit, and the hot saturn TOI-2000 c (, ) is in a
9.13-day orbit. Both planets transit their host star TOI-2000 (TIC 371188886, V
= 10.98, TESS magnitude = 10.36), a metal-rich ([Fe/H] =
) G dwarf 174 pc away. TESS observed the two planets
in sectors 9-11 and 36-38, and we followed up with ground-based photometry,
spectroscopy, and speckle imaging. Radial velocities from CHIRON, FEROS, and
HARPS allowed us to confirm both planets by direct mass measurement. In
addition, we demonstrate constraining planetary and stellar parameters with
MIST stellar evolutionary tracks through Hamiltonian Monte Carlo under the PyMC
framework, achieving higher sampling efficiency and shorter run time compared
to traditional Markov chain Monte Carlo. Having the brightest host star in the
V band among similar systems, TOI-2000 b and c are superb candidates for
atmospheric characterization by the JWST, which can potentially distinguish
whether they formed together or TOI-2000 c swept along material during
migration to form TOI-2000 b.Comment: v3 adds RV frequency analysis; 25 pages, 11 figures, 14 tables;
revision submitted to MNRAS; machine-readable tables available as ancillary
files; posterior samples available from Zenodo at
https://doi.org/10.5281/zenodo.7683293 and source code at
https://doi.org/10.5281/zenodo.798826
The Magellan-TESS Survey I: Survey Description and Mid-Survey Results
One of the most significant revelations from Kepler is that roughly one-third
of Sun-like stars host planets which orbit their stars within 100 days and are
between the size of Earth and Neptune. How do these super-Earth and sub-Neptune
planets form, what are they made of, and do they represent a continuous
population or naturally divide into separate groups? Measuring their masses and
thus bulk densities can help address these questions of their origin and
composition. To that end, we began the Magellan-TESS Survey (MTS), which uses
Magellan II/PFS to obtain radial velocity (RV) masses of 30 transiting
exoplanets discovered by TESS and develops an analysis framework that connects
observed planet distributions to underlying populations. In the past, RV
measurements of small planets have been challenging to obtain due to the
faintness and low RV semi-amplitudes of most Kepler systems, and challenging to
interpret due to the potential biases in the existing ensemble of small planet
masses from non-algorithmic decisions for target selection and observation
plans. The MTS attempts to minimize these biases by focusing on bright TESS
targets and employing a quantitative selection function and multi-year
observing strategy. In this paper, we (1) describe the motivation and survey
strategy behind the MTS, (2) present our first catalog of planet mass and
density constraints for 25 TESS Objects of Interest (TOIs; 20 in our population
analysis sample, five that are members of the same systems), and (3) employ a
hierarchical Bayesian model to produce preliminary constraints on the
mass-radius (M-R) relation. We find qualitative agreement with prior
mass-radius relations but some quantitative differences (abridged). The the
results of this work can inform more detailed studies of individual systems and
offer a framework that can be applied to future RV surveys with the goal of
population inferences.Comment: 101 pages (39 of main text and references, the rest an appendix of
figures and tables). Submitted to AAS Journal
TOI-1338 : TESS' first transiting circumbinary planet
Funding: Funding for the DPAC has been provided by national institutions, in particular, the institutions participating in the Gaia Multilateral Agreement. W.F.W. and J.A.O.thank John Hood Jr. for his generous support of exoplanet research at SDSU. Support was also provided and acknowledged through NASA Habitable Worlds grant 80NSSC17K0741 and NASA XRP grant 80NSSC18K0519. This work is partly supported by NASA Habitable Worlds grant 80NSSC17K0741. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under grant No.(DGE-1746045). A.H.M.J.T. has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 803193/BEBOP) and from a Leverhulme Trust Research Project grant No. RPG-2018-418. A.C. acknowledges support by CFisUC strategic project (UID/FIS/04564/2019).We report the detection of the first circumbinary planet (CBP) found by Transiting Exoplanet Survey Satellite (TESS). The target, a known eclipsing binary, was observed in sectors 1 through 12 at 30 minute cadence and in sectors 4 through 12 at 2 minute cadence. It consists of two stars with masses of 1.1 M⊙ and 0.3 M⊙ on a slightly eccentric (0.16), 14.6 day orbit, producing prominent primary eclipses and shallow secondary eclipses. The planet has a radius of ∼6.9 R⊕ and was observed to make three transits across the primary star of roughly equal depths (∼0.2%) but different durations—a common signature of transiting CBPs. Its orbit is nearly circular (e ≍ 0.09) with an orbital period of 95.2 days. The orbital planes of the binary and the planet are aligned to within ∼1°. To obtain a complete solution for the system, we combined the TESS photometry with existing ground-based radial-velocity observations in a numerical photometric-dynamical model. The system demonstrates the discovery potential of TESS for CBPs and provides further understanding of the formation and evolution of planets orbiting close binary stars.Publisher PDFPeer reviewe
The TESS Grand Unified Hot Jupiter Survey. II. Twenty New Giant Planets
NASA's Transiting Exoplanet Survey Satellite (TESS) mission promises to
improve our understanding of hot Jupiters by providing an all-sky,
magnitude-limited sample of transiting hot Jupiters suitable for population
studies. Assembling such a sample requires confirming hundreds of planet
candidates with additional follow-up observations. Here, we present twenty hot
Jupiters that were detected using TESS data and confirmed to be planets through
photometric, spectroscopic, and imaging observations coordinated by the TESS
Follow-up Observing Program (TFOP). These twenty planets have orbital periods
shorter than 7 days and orbit relatively bright FGK stars ().
Most of the planets are comparable in mass to Jupiter, although there are four
planets with masses less than that of Saturn. TOI-3976 b, the longest period
planet in our sample ( days), may be on a moderately eccentric orbit
(), while observations of the other targets are consistent
with them being on circular orbits. We measured the projected stellar obliquity
of TOI-1937A b, a hot Jupiter on a 22.4 hour orbit with the Rossiter-McLaughlin
effect, finding the planet's orbit to be well-aligned with the stellar spin
axis (). We also investigated the possibility that
TOI-1937 is a member of the NGC 2516 open cluster, but ultimately found the
evidence for cluster membership to be ambiguous. These objects are part of a
larger effort to build a complete sample of hot Jupiters to be used for future
demographic and detailed characterization work.Comment: 67 pages, 11 tables, 13 figures, 2 figure sets. Resubmitted to ApJS
after revision
A planet within the debris disk around the pre-main-sequence star AU Microscopii
AU Microscopii (AU Mic) is the second closest pre main sequence star, at a
distance of 9.79 parsecs and with an age of 22 million years. AU Mic possesses
a relatively rare and spatially resolved3 edge-on debris disk extending from
about 35 to 210 astronomical units from the star, and with clumps exhibiting
non-Keplerian motion. Detection of newly formed planets around such a star is
challenged by the presence of spots, plage, flares and other manifestations of
magnetic activity on the star. Here we report observations of a planet
transiting AU Mic. The transiting planet, AU Mic b, has an orbital period of
8.46 days, an orbital distance of 0.07 astronomical units, a radius of 0.4
Jupiter radii, and a mass of less than 0.18 Jupiter masses at 3 sigma
confidence. Our observations of a planet co-existing with a debris disk offer
the opportunity to test the predictions of current models of planet formation
and evolution.Comment: Nature, published June 24th [author spelling name fix
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