The binary millisecond radio pulsar PSR J1023+0038 has been recently the subject of multi-wavelength monitoring campaigns which revealed that an accretion disc has formed around the neutron star (since 2013 June). We present here the results of Xray and UV observations carried out by the Swift satellite between 2013 October and 2014 May, and of optical and NIR observations performed with the REM telescope, the Liverpool Telescope, the 2.1-m telescope at the San Pedro Mártir Observatory and the 1.52-m telescope at the Loiano observing station. The X-ray spectrum is well described by an absorbed power law, which is softer than the previous quiescent epoch (up to 2013 June). The strong correlation between the X-ray and the UV emissions indicates that the same mechanism should be responsible for part of the emission in these bands. Optical and infrared photometric observations show that the companion star is strongly irradiated. Double-peaked emission lines in the optical spectra provide compelling evidence for the presence of an outer accretion disc too. The spectral energy distribution from IR to X-rays is well modelled if the contributions from the companion, the disc and the intra-binary shock emission are all considered. Our extensive data set can be interpreted in terms of an engulfed radio pulsar: the radio pulsar is still active, but undetectable in the radio band due to a large amount of ionized material surrounding the compact object. X-rays and gamma-rays are produced in an intra-binary shock front between the relativistic pulsar wind and matter from the companion and an outer accretion disc. The intense spin-down power irradiates the disc and the companion star, accounting for the UV and optical emissions.

ABSTRACT. Three optical telescopes located at the San Pedro Mártir National Observatory were used for the first time to obtain multifilter defocused photometry of the transiting extrasolar planets WASP-39b and WASP-43b. We observed WASP-39b with the 2.12 m telescope in the U filter for the first time, and additional observations were carried out in the R and I filters using the 0.84 m telescope. WASP-43b was observed in V RI with the same instrument, and in the i filter with the robotic 1.50 m telescope. We reduced the data using different pipelines and performed aperture photometry with the help of custom routines in order to obtain the light curves. The fit of the light curves (1.5-2.5 mmag rms), and of the period analysis, allowed a revision of the orbital and physical parameters, revealing for WASP-39b a period (4:0552947 AE 9:65 × 10 À7 days) which is 3:084 AE 0:774 seconds larger than previously reported. Moreover, we find for WASP-43b a planet/star radius (0:1738 AE 0:0033) which is 0:01637 AE 0:00371 larger in the i filter with respect to previous works, and that should be confirmed with additional observations. Finally, we confirm no evidence of constant period variations in WASP-43b.

Forty transits of the exoplanets HAT-P-12b, HAT-P-13b, HAT-P-16b, HAT-P-23b and WASP-10b were recorded with the 0.36m telescope at the Universidad de Monterrey Observatory. The images were captured with a standard Johnson-Cousins Rc and Ic and Sloan z' filters and processed to obtain individual light curves of the events. These light curves were successfully combined for each system to obtain a resulting one of higher quality, but with a slightly larger time sampling rate. A reduction by a factor of about four in per-point scatter was typically achieved, resulting in combined light curves with a scatter of ~1 mmag. The noise characteristics of the combined light curves were verified by comparing Allan variance plots of the residuals. The combined light curves for each system, along with radial velocity measurements from the literature when available, were modeled using a Monte Carlo method to obtain the essential parameters that characterize the systems. Our results for all these systems confirm the derived transit parameters (the planet-to-star radius ratio, R p /R * ; the scaled semi-major axis, a/R * ; the orbital inclination, i; in some cases the eccentricity, e; and argument of periastron of the orbit, ω), validating the methodology. This technique can be used by small college observatories equipped with modest-sized telescopes to help characterize known extrasolar planet systems. In some instances, the uncertainties of the essential transit parameters are also reduced. For HAT-P23b, in particular, we derive a planet size 4.5 ± 1.0% smaller. We also derive improved linear periods for each system, useful for scheduling observations.

We present high-resolution smoothed particle hydrodynamics simulations of a region of gas flowing in a spiral arm and identify dense gas clouds to investigate their kinematics with respect to a Milky Way model. We find that, on average, the gas in the arms can have a net radial streaming motion of v R ≈ −9 km s −1 and rotate ≈ 6 km s −1 slower than the circular velocity. This translates to average peculiar motions towards the Galaxy centre and opposite to Galactic rotation. These results may be sensitive to the assumed spiral arm perturbation, which is ≈ 3% of the disc potential in our model. We compare the actual distance and the kinematic estimate and we find that streaming motions introduce systematic offsets of ≈ 1 kpc. We find that the distance error can be as large as ±2 kpc and the recovered cloud positions have distributions that can extend significantly into the inter-arm regions. We conclude that this poses a difficulty in tracing spiral arm structure in molecular cloud surveys.