1,252 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
A study of the kinematics and binary-induced shaping of the planetary nebula HaTr 4
We present the first detailed spatio-kinematical analysis and modelling of
the planetary nebula HaTr 4, one of few known to contain a post-common-envelope
central star system. Common envelope evolution is believed to play an important
role in the shaping of planetary nebulae, but the exact nature of this role is
yet to be understood. High spatial- and spectral- resolution spectroscopy of
the [OIII]5007 nebular line obtained with VLT-UVES are presented alongside deep
narrowband Ha+[NII]6584 imagery obtained using EMMI-NTT, and together the two
are used to derive the three-dimensional morphology of HaTr 4. The nebula is
found to display an extended ovoid morphology with an enhanced equatorial
region consistent with a toroidal waist - a feature believed to be typical
amongst planetary nebulae with post-common-envelope central stars. The nebular
symmetry axis is found to lie perpendicular to the orbital plane of the central
binary, concordant with the idea that the formation and evolution of HaTr 4 has
been strongly influenced by its central binary.Comment: 9 pages, 5 figures, accepted for publication in MNRA
The Ever Changing Circumstellar Nebula Around UW Centauri
We present new images of the reflection nebula surrounding the R Coronae
Borealis Star, UW Cen. This nebula, first detected in 1990, has changed its
appearance significantly. At the estimated distance of UW Cen, this nebula is
approximately 0.6 ly in radius so the nebula cannot have physically altered in
only 8 years. Instead, the morphology of the nebula appears to change as
different parts are illuminated by light from the central star modulated by
shifting thick dust clouds near its surface. These dust clouds form and
dissipate at irregular intervals causing the well-known declines in the R
Coronae Borealis (RCB) stars. In this way, the central star acts like a
lighthouse shining through holes in the dust clouds and lighting up different
portions of the nebula. The existence of this nebula provides clues to the
evolutionary history of RCB stars possibly linking them to the Planetary
Nebulae and the final helium shell flash stars.Comment: To be published in ApJ Letters. 5 pages, 3 figures (2 in color
Transit shapes and self organising maps as a tool for ranking planetary candidates : application to Kepler and K2
A crucial step in planet hunting surveys is to select the best candidates for follow up observations, given limited telescope resources. This is often performed by human âeyeballingâ, a time consuming and statistically awkward process. Here we present a new, fast machine learning technique to separate true planet signals from astrophysical
false positives. We use Self Organising Maps (SOMs) to study the transit shapes of Kepler and K2 known and candidate planets. We find that SOMs are capable of distinguishing known planets from known false positives with a success rate of 87.0%, using the transit shape alone. Furthermore, they do not require any candidates to be dispositioned prior to use, meaning that they can be used early in a missionâs
lifetime. A method for classifying candidates using a SOM is developed, and applied to previously unclassified members of the Kepler KOI list as well as candidates from the K2 mission. The method is extremely fast, taking minutes to run the entire KOI list on a typical laptop. We make Python code for performing classifications publicly available, using either new SOMs or those created in this work. The SOM technique represents a novel method for ranking planetary candidate lists, and can be used both alone or as part of a larger autovetting code
RISE: a fast-readout imager for exoplanet transit timing
By the precise timing of the low amplitude (0.005 - 0.02 magnitude) transits
of exoplanets around their parent star it should be possible to infer the
presence of other planetary bodies in the system down to Earth-like masses. We
describe the design and construction of RISE, a fast-readout frame transfer
camera for the Liverpool Telescope designed to carry out this experiment. The
results of our commissioning tests are described as well as the data reduction
procedure necessary. We present light curves of two objects, showing that the
desired timing and photometric accuracy can be obtained providing that
autoguiding is used to keep the target on the same detector pixel for the
entire (typically 4 hour) observing run.Comment: Published in PROC SPIE, vol 7014, 70416
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
On the Abundance of Circumbinary Planets
We present here the first observationally based determination of the rate of
occurrence of circumbinary planets. This is derived from the publicly available
Kepler data, using an automated search algorithm and debiasing process to
produce occurrence rates implied by the seven systems already known. These
rates depend critically on the planetary inclination distribution: if
circumbinary planets are preferentially coplanar with their host binaries, as
has been suggested, then the rate of occurrence of planets with
orbiting with \ d is \% (95\% confidence limits),
higher than but consistent with single star rates. If on the other hand the
underlying planetary inclination distribution is isotropic, then this
occurrence rate rises dramatically, to give a lower limit of 47\%. This implies
that formation and subsequent dynamical evolution in circumbinary disks must
either lead to largely coplanar planets, or proceed with significantly greater
ease than in circumstellar disks. As a result of this investigation we also
show that giant planets () are significantly less common in
circumbinary orbits than their smaller siblings, and confirm that the proposed
shortfall of circumbinary planets orbiting the shorter period binaries in the
Kepler sample is a real effect.Comment: Accepted for publication in MNRAS (1st August 2014). 12 pages. Update
to match final version, including clarifications and new figures. Results are
unchange
A Buffer Stocks Model for Stabilizing Price of Staple Food with Considering the Expectation of Non Speculative Wholesaler
This paper is a study of price stabilization in the
staple food distribution system. All stakeholders experience
market risks due to some possibility causes of price volatility.
Many models of price stabilization had been developed by
employing several approaches such as floor-ceiling prices,
buffer funds, export or import taxes, and subsidies. In the
previous researches, the models were expanded to increase the
purchasing price for producer and decrease the selling price
for consumer. Therefore, the policy can influence the losses for
non-speculative wholesaler that is reflected by the descending
of selling quantity and ascending of the stocks. The objective of
this model is not only to keep the expectation of both producer
and consumer, but also to protect non-speculative wholesaler
from the undesirable result of the stabilization policy. A
nonlinear programming model was addressed to determine the
instruments of intervention program. Moreover, the result
shows that the wholesaler behavior affects the intervention
costs.
Index Terms Buffer stocks, Price stabilization, Nonlinear
programming, Wholesaler behavior
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