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

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