52 research outputs found
Experiments with synchronized sCMOS cameras
Scientific-CMOS (sCMOS) cameras can combine low noise with high readout speeds and do not suffer the charge multiplication noise that effectively reduces the quantum efficiency of electron multiplying CCDs by a factor 2. As such they have strong potential in fast photometry and polarimetry instrumentation. In this paper we describe the results of laboratory experiments using a pair of commercial off the shelf sCMOS cameras based around a 4 transistor per pixel architecture. In particular using a both stable and a pulsed light sources we evaluate the timing precision that may be obtained when the cameras readouts are synchronized either in software or electronically. We find that software synchronization can introduce an error of ~ 200-msec. With electronic synchronization any error is below the limit (~ 50-msec) of our simple measurement technique. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only
Transit timing variation and transmission spectroscopy analyses of the hot Neptune GJ3470b
GJ3470b is a hot Neptune exoplanet orbiting an M dwarf and the first sub-Jovian planet to exhibit Rayleigh scattering. We present transit timing variation (TTV) and transmission spectroscopy analyses of multiwavelength optical photometry from 2.4-m and 0.5-m telescopes at the Thai National Observatory, and the 0.6-m PROMPT-8 telescope in Chile. Our TTV analysis allows us to place an upper mass limit for a second planet in the system. The presence of a hot Jupiter with a period of less than 10 d or a planet with an orbital period between 2.5 and 4.0 d are excluded. Combined optical and near-infrared transmission spectroscopy favour an H/He-dominated haze (mean molecular weight 1.08 ± 0.20) with high particle abundance at high altitude. We also argue that previous near-infrared data favour the presence of methane in the atmosphere of GJ3470b
TransitFit:an exoplanet transit fitting package for multi-telescope datasets and its application to WASP-127~b, WASP-91~b, and WASP-126~b
TransitFit: an exoplanet transit fitting package for multi-telescope datasets and its application to WASP-127~b, WASP-91~b, and WASP-126~b
We present TransitFit, an open-source Python~3 package designed to fit
exoplanetary transit light-curves for transmission spectroscopy studies
(Available at https://github.com/joshjchayes/TransitFit and
https://github.com/spearnet/TransitFit, with documentation at
https://transitfit.readthedocs.io/). TransitFit employs nested sampling to
offer efficient and robust multi-epoch, multi-wavelength fitting of transit
data obtained from one or more telescopes. TransitFit allows per-telescope
detrending to be performed simultaneously with parameter fitting, including the
use of user-supplied detrending alogorithms. Host limb darkening can be fitted
either independently ("uncoupled") for each filter or combined ("coupled")
using prior conditioning from the PHOENIX stellar atmosphere models. For this
TransitFit uses the Limb Darkening Toolkit (LDTk) together with filter
profiles, including user-supplied filter profiles. We demonstrate the
application of TransitFit in three different contexts. First, we model SPEARNET
broadband optical data of the low-density hot-Neptune WASP-127~b. The data were
obtained from a globally-distributed network of 0.5m--2.4m telescopes. We find
clear improvement in our broadband results using the coupled mode over
uncoupled mode, when compared against the higher spectral resolution GTC/OSIRIS
transmission spectrum obtained by Chen et al. (2018). Using TransitFit, we fit
26 transit observations by TESS to recover improved ephemerides of the
hot-Jupiter WASP-91~b and a transit depth determined to a precision of 170~ppm.
Finally, we use TransitFit to conduct an investigation into the contested
presence of TTV signatures in WASP-126~b using 126 transits observed by TESS,
concluding that there is no statistically significant evidence for such
signatures from observations spanning 31 TESS sectors.Comment: 14 pages, 5 figures, 5 tables, submitted to MNRAS. Temporary data
address at https://cdsarc.u-strasbg.fr/ftp/vizier.submit/wasp-127b/ (Final
address to be included in accepted paper
The binary millisecond pulsar PSR J1023+0038 during its accretion state - I. Optical variability
We present time-resolved optical photometry of the binary millisecond ‘redback’ pulsar
PSR J1023+0038 (=AY Sex) during its low-mass X-ray binary phase. The light curves
taken between 2014 January and April show an underlying sinusoidal modulation due to the
irradiated secondary star and accretion disc. We also observe superimposed rapid flaring on
time-scales as short as ∼20 s with amplitudes of ∼0.1–0.5 mag and additional large flare events
on time-scales of ∼5–60 min with amplitudes of ∼0.5–1.0 mag. The power density spectrum
of the optical flare light curves is dominated by a red-noise component, typical of aperiodic
activity in X-ray binaries. Simultaneous X-ray and UV observations by the Swift satellite
reveal strong correlations that are consistent with X-ray reprocessing of the UV light, most
likely in the outer regions of the accretion disc. On some nights we also observe sharp-edged,
rectangular, flat-bottomed dips randomly distributed in orbital phase, with a median duration
of ∼250 s and a median ingress/egress time of ∼20 s. These rectangular dips are similar to the
mode-switching behaviour between disc ‘active’ and ‘passive’ luminosity states, observed in
the X-ray light curves of other redback millisecond pulsars. This is the first time that the optical
analogue of the X-ray mode-switching has been observed. The properties of the passive- and
active-state light curves can be explained in terms of clumpy accretion from a trapped inner
accretion disc near the corotation radius, resulting in rectangular, flat-bottomed optical and
X-ray light curves
Lightweight, aluminum, mirror design optimization for conventional and additive manufacturing processes
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