380 research outputs found
Single site observations of \textit{TESS} single transit detections
Context: TESS has been successfully launched and has begin data acquisition.
To expedite the science that may be performed with the resulting data it is
necessary to gain a good understanding of planetary yields. Given the observing
strategy employed by TESS the probability of detecting single transits in long
period systems is increased. These systems require careful consideration.
Aims: To simulate the number of TESS transit detections during its 2 year
mission with a particular emphasis on single transits. Additionally, to
determine the feasibility of ground-based follow-up observations from a single
site.
Methods: A distribution of planets is simulated around the 4 million
stars in the TESS Candidate Target List. These planets are tested for
detectable transits and characterised. Based on simulated parameters the single
transit detections are further analysed to determine which are amenable to
ground-based follow-up.
Results: TESS will discover an approximate lower bound of 4700 planets with
around 460 being single transits. A large fraction of these will be observable
from a single ground-based site. This paper finds that, in a single year,
approximately 1000 transit events of around 320 unique TESS single transit
detections are theoretically observable.
Conclusions: As we consider longer period exoplanets the need for exploring
single transit detections increases. For periods days the number of
single transit detections outnumber multitransits by a factor of 3 (8218
and 257 respectively) a factor which only grows as longer period
detections are considered. Therefore, it is worth expending the extra effort
required to follow-up these more challenging, but potentially very rewarding,
discoveries. Additionally, we conclude that a large fraction of these targets
can be theoretically observed from just a single ground-based site.Comment: 12 pages, 19 figures. To be published in Astronomy and Astrophysic
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
Configuration of the high‐latitude thermosphere neutral circulation for IMF B y negative and positive
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94946/1/grl2864.pd
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
MASCARA-2 b: A hot Jupiter transiting the A-star HD185603
In this paper we present MASCARA-2 b, a hot Jupiter transiting the
A2 star HD 185603. Since early 2015, MASCARA has taken more than 1.6 million
flux measurements of the star, corresponding to a total of almost 3000 hours of
observations, revealing a periodic dimming in the flux with a depth of .
Photometric follow-up observations were performed with the NITES and IAC80
telescopes and spectroscopic measurements were obtained with the Hertzsprung
SONG telescope. We find MASCARA-2 b orbits HD 185603 with a period of
at a distance of , has a radius of and place a
upper limit on the mass of . HD 185603 is a
rapidly rotating early-type star with an effective temperature of
and a mass and radius of
, , respectively. Contrary
to most other hot Jupiters transiting early-type stars, the projected planet
orbital axis and stellar spin axis are found to be aligned with . The brightness of the host star and the high equilibrium
temperature, , of MASCARA-2 b make it a suitable target for
atmospheric studies from the ground and space. Of particular interest is the
detection of TiO, which has recently been detected in the similarly hot planets
WASP-33 b and WASP-19 b.Comment: 8 pages, 4 figures, Accepted for publication in A&
Simulated recovery of LEO objects using sCMOS blind stacking
We present the methodology and results of a simulation to determine the
recoverability of LEO objects using a blind stacking technique. The method
utilises sCMOS and GPU technology to inject and recover LEO objects in real
observed data. We explore the target recovery fraction and pipeline run-time as
a function of three optimisation parameters; number of frames per data-set,
exposure time, and binning factor. Results are presented as a function of
magnitude and velocity. We find that target recovery using blind stacking is
significantly more complete, and can reach fainter magnitudes, than using
individual frames alone. We present results showing that, depending on the
combination of optimisation parameters, recovery fraction is up to 90% of
detectable targets for magnitudes up to 13.5, and then falls off steadily up to
a magnitude limit around 14.5. Run-time is shown to be a few multiples of the
observing time for the best combinations of optimisation parameters,
approaching real-time processing.Comment: 14 pages, 14 figures. Accepted for publication in Advances in Space
Research (ASR
A transiting companion to the eclipsing binary KIC002856960
We present an early result from an automated search of Kepler eclipsing
binary systems for circumbinary companions. An intriguing tertiary signal has
been discovered in the short period eclipsing binary KIC002856960. This third
body leads to transit-like features in the light curve occurring every 204.2
days, while the two other components of the system display eclipses on a 6.2
hour period. The variations due to the tertiary body last for a duration of
\sim1.26 days, or 4.9 binary orbital periods. During each crossing of the
binary orbit with the tertiary body, multiple individual transits are observed
as the close binary stars repeatedly move in and out of alignment with the
tertiary object. We are at this stage unable to distinguish between a planetary
companion to a close eclipsing binary, or a hierarchical triply eclipsing
system of three stars. Both possibilities are explored, and the light curves
presented.Comment: Accepted into A&A Letters (5 pages & 3 figures
Accessible digital ophthalmoscopy based on liquid-lens technology
Ophthalmoscopes have yet to capitalise on novel low-cost miniature optomechatronics, which could disrupt ophthalmic monitoring in rural areas. This paper demonstrates a new design integrating modern components for ophthalmoscopy. Simulations show that the optical elements can be reduced to just two lenses: an aspheric ophthalmoscopic lens and a commodity liquid-lens, leading to a compact prototype. Circularly polarised transpupilary illumination, with limited use so far for ophthalmoscopy, suppresses reflections, while autofocusing preserves image sharpness. Experiments with a human-eye model and cadaver porcine eyes demonstrate our prototype’s clinical value and its potential for accessible imaging when cost is a limiting factor
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