125 research outputs found
K2 Variable Catalogue: Variable Stars and Eclipsing Binaries in K2 Campaigns 1 and 0
We have created a catalogue of variable stars found from a search of the
publicly available K2 mission data from Campaigns 1 and 0. This catalogue
provides the identifiers of 8395 variable stars, including 199 candidate
eclipsing binaries with periods up to 60d and 3871 periodic or quasi-periodic
objects, with periods up to 20d for Campaign 1 and 15d for Campaign 0.
Lightcurves are extracted and detrended from the available data. These are
searched using a combination of algorithmic and human classification, leading
to a classifier for each object as an eclipsing binary, sinusoidal periodic,
quasi periodic, or aperiodic variable. The source of the variability is not
identified, but could arise in the non-eclipsing binary cases from pulsation or
stellar activity. Each object is cross-matched against variable star related
guest observer proposals to the K2 mission, which specifies the variable type
in some cases. The detrended lightcurves are also compared to lightcurves
currently publicly available. The resulting catalogue is made available online
via the MAST archive at https://archive.stsci.edu/prepds/k2varcat/, and gives
the ID, type, period, semi-amplitude and range of the variation seen. We also
make available the detrended lightcurves for each object.Comment: Accepted by A&A. 6 pages, 6 figures. Catalogue and lightcurves are
available online via MAST at https://archive.stsci.edu/prepds/k2varcat
A systematic map of research exploring the effect of greenspace on mental health
The past 35 years has seen an accumulation of empirical evidence suggesting a positive association between greenspace and mental health. Existing reviews of evidence are narrow in scope, and do not adequately represent the broad range of disciplines working in this field. This study is the first systematic map of studies investigating greenspace effects on mental health. A total of 6059 papers were screened for their relevance, 276 of which met inclusion criteria for the systematic map.The map revealed several methodological limitations hindering the practical applications of research findings to public health. Critically, the majority of studies used cross-sectional mental health data which makes causal inference about greenspace effects challenging. There are also few studies on the micro-features that make up greenspaces (i.e., their âqualityâ), with most focussing only on âquantityâ effects on mental health. Moreover, few studies adopted a multi-scale approach, meaning there is little evidence about at which spatial scale(s) the relationship exists. A geographic gap in study location was also identified, with the majority of studies clustered in European countries and the USA.Future research should account for both human and ecological perspectives of âqualityâ using objective and repeatable measures, and consider the potential of scale-dependent greenspace effects to ensure that management of greenspace is compatible with wider scale biodiversity targets. To establish the greenspace and metal health relationship across a life course, studies should make better use of longitudinal data, as this enables stronger inferences to be made than more commonly used cross-sectional data
K2 Variable Catalogue II: Machine Learning Classification of Variable Stars and Eclipsing Binaries in K2 Fields 0-4
We are entering an era of unprecedented quantities of data from current and
planned survey telescopes. To maximise the potential of such surveys, automated
data analysis techniques are required. Here we implement a new methodology for
variable star classification, through the combination of Kohonen Self
Organising Maps (SOM, an unsupervised machine learning algorithm) and the more
common Random Forest (RF) supervised machine learning technique. We apply this
method to data from the K2 mission fields 0-4, finding 154 ab-type RR Lyraes
(10 newly discovered), 377 Delta Scuti pulsators, 133 Gamma Doradus pulsators,
183 detached eclipsing binaries, 290 semi-detached or contact eclipsing
binaries and 9399 other periodic (mostly spot-modulated) sources, once class
significance cuts are taken into account. We present lightcurve features for
all K2 stellar targets, including their three strongest detected frequencies,
which can be used to study stellar rotation periods where the observed
variability arises from spot modulation. The resulting catalogue of variable
stars, classes, and associated data features are made available online. We
publish our SOM code in Python as part of the open source PyMVPA package, which
in combination with already available RF modules can be easily used to recreate
the method.Comment: Accepted for publication in MNRAS, 16 pages, 13 figures. Updated with
proof corrections. Full catalogue tables available at
https://www2.warwick.ac.uk/fac/sci/physics/research/astro/people/armstrong/
or at the CD
Non-detection of He I in the atmosphere of GJ1214b with Keck/NIRSPEC, at a time of minimal telluric contamination
Observations of helium in exoplanet atmospheres may reveal the presence of
large gaseous envelopes, and indicate ongoing atmospheric escape. Orell-Miquel
et al. (2022) used CARMENES to measure a tentative detection of helium for the
sub-Neptune GJ 1214b, with a peak excess absorption reaching over 2% in transit
depth at 10830 Angstroms. However, several non-detections of helium had
previously been reported for GJ 1214b. One explanation for the discrepancy was
contamination of the planetary signal by overlapping telluric absorption- and
emission lines. We used Keck/NIRSPEC to observe another transit of GJ 1214b at
10830 Angstroms, at a time of minimal contamination by telluric lines, and did
not observe planetary helium absorption. Accounting for correlated noise in our
measurement, we place an upper limit on the excess absorption size of 1.22%
(95% confidence). We find that the discrepancy between the CARMENES and NIRSPEC
observations is unlikely to be caused by using different instruments or stellar
activity. It is currently unclear whether the difference is due to correlated
noise in the observations, or variability in the planetary atmosphere.Comment: Accepted for publication in ApJ
Erratum: A library of ATMO forward model transmission spectra for hot Jupiter exoplanets
This is the final version. Available from OUP via the DOI in this recordThe article to which this is the erratum is in ORE at http://hdl.handle.net/10871/30324The paper âA library of ATMO forward model transmission spectra for hot Jupiter exoplanetsâ was published in MNRAS 474, 4, 5158â5185.
In the original manuscript (Goyal et al. 2018), we presented a grid of forward model transmission spectra for hot Jupiter exoplanets. However, we recently identified an error in the treatment of rainout in our 1D atmosphere model ATMO. The correction of this error led to changes in the equilibrium chemical abundances using rainout condensation and thereby the transmission spectra. We note that this error only affects the online library2,3 that includes rainout condensation, the library with local condensation (without rainout) is unaffected. We further note that the gas phase equilibrium scheme used in ATMO has been compared by Drummond et al. (2016) with the analytical schemes of Burrows & Sharp (1999) and Heng & Tsai (2016). The gas phase chemistry with and without local condensation has also been verified in Baudino et al. (2017) against the petitCODE (MolliĂšre et al. 2015, 2017) and Exo-REM (Baudino et al. 2015) models. Therefore, issues with the previous version of the grid were confined to the implementation of rainout
Single transit candidates from K2 : detection and period estimation
Photometric surveys such as Kepler have the precision to identify exoplanet and eclipsing binary candidates from only a single transit. K2, with its 75 d campaign duration, is ideally suited to detect significant numbers of single-eclipsing objects. Here we develop a Bayesian transit-fitting tool (âNamaste: An Mcmc Analysis of Single Transit Exoplanetsâ) to extract orbital information from single transit events. We achieve favourable results testing this technique on known Kepler planets, and apply the technique to seven candidates identified from a targeted search of K2 campaigns 1, 2 and 3. We find EPIC203311200 to host an excellent exoplanet candidate with a period, assuming zero eccentricity, of 540+410 â230 d and a radius of 0.51 ± 0.05RJup. We also find six further transit candidates for which more follow-up is required to determine a planetary origin. Such a technique could be used in the future with TESS, PLATO and ground-based photometric surveys such as NGTS, potentially allowing the detection of planets in reach of confirmation by Gaia
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A robust and readily implementable method for the meta-analysis of response ratios with and without missing standard deviations
The log response ratio, lnRR, is the most frequently used effect size statistic for meta-analysis in ecology. However, often missing standard deviations (SDs) prevent estimation of the sampling variance of lnRR. We propose new methods to deal with missing SDs via a weighted average coefficient of variation (CV) estimated from studies in the dataset that do report SDs. Across a suite of simulated conditions, we find that using the average CV to estimate sampling variances for all observations, regardless of missingness, performs with minimal bias. Surprisingly, even with missing SDs, this simple method outperforms the conventional approach (basing each effect size on its individual study-specific CV) with complete data. This is because the conventional method ultimately yields less precise estimates of the sampling variances than using the pooled CV from multiple studies. Our approach is broadly applicable and can be implemented in all meta-analyses of lnRR, regardless of âmissingnessâ
One of the closest exoplanet pairs to the 3:2 Mean Motion Resonance: K2-19b \& c
The K2 mission has recently begun to discover new and diverse planetary
systems. In December 2014 Campaign 1 data from the mission was released,
providing high-precision photometry for ~22000 objects over an 80 day timespan.
We searched these data with the aim of detecting further important new objects.
Our search through two separate pipelines led to the independent discovery of
K2-19b \& c, a two-planet system of Neptune sized objects (4.2 and 7.2
), orbiting a K dwarf extremely close to the 3:2 mean motion
resonance. The two planets each show transits, sometimes simultaneously due to
their proximity to resonance and alignment of conjunctions. We obtain further
ground based photometry of the larger planet with the NITES telescope,
demonstrating the presence of large transit timing variations (TTVs), and use
the observed TTVs to place mass constraints on the transiting objects under the
hypothesis that the objects are near but not in resonance. We then
statistically validate the planets through the \texttt{PASTIS} tool,
independently of the TTV analysis.Comment: 18 pages, 10 figures, accepted to A&A, updated to match published
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