Xiaobin Wang

Physical properties of the planetary systems WASP-45 and WASP-46 from simultaneous multiband photometry

Accurate measurements of the physical characteristics of a large number of exoplanets are useful to strongly constrain theoretical models of planet formation and evolution, which lead to the large variety of exoplanets and planetary-system configurations that have been observed. We present a study of the planetary systems WASP-45 and WASP-46, both composed of a main-sequence star and a close-in hot Jupiter, based on 29 new high-quality light curves of transits events. In particular, one transit of WASP-45 b and four of WASP-46 b were simultaneously observed in four optical filters, while one transit of WASP-46 b was observed with the NTT obtaining a precision of 0.30 mmag with a cadence of roughly 3 min. We also obtained five new spectra of WASP-45 with the FEROS spectrograph. We improved by a factor of 4 the measurement of the radius of the planet WASP-45 b, and found that WASP-46 b is slightly less massive and smaller than previously reported. Both planets now have a more accurate measurement of the density (0.959 +/- 0.077 rho Jup instead of 0.64 +/- 0.30 rho Jup for WASP-45 b, and 1.103 +/- 0.052 rho Jup instead of 0.94 +/- 0.11 rho Jup for WASP-46 b). We tentatively detected radius variations with wavelength for both planets, in particular in the case of WASP-45 b we found a slightly larger absorption in the redder bands than in the bluer ones. No hints for the presence of an additional planetary companion in the two systems were found either from the photometric or radial velocity measurements.

High-precision photometry by telescope defocussing – VIII. WASP-22, WASP-41, WASP-42 and WASP-55

We present 13 high-precision and four additional light curves of four bright southern-hemisphere transiting planetary systems: WASP-22, WASP-41, WASP-42 and WASP-55. In the cases of WASP-42 and WASP-55, these are the first follow-up observations since their discovery papers. We present refined measurements of the physical properties and orbital ephemerides of all four systems. No indications of transit timing variations were seen. All four planets have radii inflated above those expected from theoretical models of gas-giant planets; WASP-55 b is the most discrepant with a mass of 0.63u2009MJup and a radius of 1.34u2009RJup. WASP-41 shows brightness anomalies during transit due to the planet occulting spots on the stellar surface. Two anomalies observed 3.1 d apart are very likely due to the same spot. We measure its change in position and determine a rotation period for the host star of 18.6 ± 1.5 d, in good agreement with a published measurement from spot-induced brightness modulation, and a sky-projected orbital obliquity of λ = 6 ± 11°. We conclude with a compilation of obliquity measurements from spot-tracking analyses and a discussion of this technique in the study of the orbital configurations of hot Jupiters.

Exploring the crowded central region of ten Galactic globular clusters using EMCCDs - Variable star searches and new discoveries

Aims. We aim to obtain time-series photometry of the very crowded central regions of Galactic globular clusters; to obtain better angular resolution thanhas been previously achieved with conventional CCDs on ground-based telescopes; and to complete, or improve, the census of the variable star population in those stellar systems. n nMethods. Images were taken using the Danish 1.54-m Telescope at the ESO observatory at La Silla in Chile. The telescope was equipped with an electron-multiplying CCD, and the short-exposure-time images obtained (ten images per second) were stacked using the shift-and-add technique to produce the normal-exposure-time images (minutes). Photometry was performed via difference image analysis. Automatic detection of variable stars in the field was attempted. n nResults. The light curves of 12u2009541 stars in the cores of ten globular clusters were statistically analysed to automatically extract the variable stars. We obtained light curves for 31 previously known variable stars (3 long-period irregular, 2 semi-regular, 20 RR Lyrae, 1 SX Phoenicis, 3 cataclysmic variables, 1 W Ursae Majoris-type and 1 unclassified) and we discovered 30 new variables (16 long-period irregular, 7 semi-regular, 4 RR Lyrae, 1 SX Phoenicis and 2 unclassified). Fluxes and photometric measurements for these stars are available in electronic form through the Strasbourg astronomical Data Center.

Photometric analysis for the spin and shape parameters of the C-type main-belt asteroids (171) Ophelia and (360) Carlova

Aims. Two C-type main-belt asteroids (171) Ophelia and (360) Carlova are studied for their spin parameters and shapes in the present paper. Although it was suspected that Ophelia was a binary system owing to the eclipse features in the light curve obtained in 1977, no direct evidence has been obtained to confirm the binarity. To verify the previous findings, the spin parameters and shape of Ophelia are derived by analyzing the photometric data. To understand the dispersion in the previous determination of Carlovas spin parameters, new observational data and existing photometric data are reanalyzed to find a homogenous solution for its spin parameters and shape. Methods. The spin parameters and shapes of two asteroids were determined from photometric data using the convex inversion technique. The simplified virtual-observation Markov chain Monte Carlo method was applied to estimate the uncertainties of the spin parameters and to understand the divergence of derived shapes. Results. A pair of possible poles for Ophelia are derived, the spin periods corresponding to the two poles are nearly the same. The convex shape of Ophelia shows binary characteristics. For Carlova, a unique pole solution and its convex shape are ascertained together with the occultation observations. The convex shape of Carlova shows that it is a rough ellipsoid.

The refined physical properties of transiting exoplanetary system WASP-11/HAT-P-10

The transiting exoplanetary system WASP-11/HAT-P-10 was observed using the CCD camera at Yunnan Observatories, China from 2008 to 2011, and four new transit light curves were obtained. Combined with published radial velocity measurements, the new transit light curves are analyzed along with available photometric data from the literature using the Markov Chain Monte Carlo technique, and the refined physical parameters of the system are derived, which are compatible with the results of two discovery groups, respectively. The planet mass is M-p = 0.526 +/- 0.019 M-J, which is the same as West et al.s value, and more accurately, the planet radius R-p = 0.999(-0.018) (+0.029) R-J is identical to the value of Bakos et al. The new result confirms that the planet orbit is circular. By collecting 19 available mid-transit epochs with higher precision, we make an orbital period analysis for WASP11b/HAT-P-10b, and derive a new value for its orbital period, P = 3.72247669 days. Through an (0 C) study based on these mid-transit epochs, no obvious transit timing variation signal can be found for this system during 2008-2012.

Refined system parameters and TTV study of transiting exoplanetary system HAT-P-20

This work is supported by National Natural Science Foundation of China through grants No. U1531121, No. 10873031 and No. 11473066.

Study of photometric phase curve with new brightness model: Refining phase function system parameters of asteroid (107) Camilla.

We characterize the morphology of the photometric phase curve model of an asteroid with a three-parameter magnitude phase function H — G1 — G2 system by considering the effect of brightness variation arising from a triaxial ellipsoid representing the asteroids shape. Applying this new model and a Markov Chain Monte Carlo method, we refine the photometric phase curve of asteroid (107) Camilla and obtain its absolute magnitude H = 7.026−0.054+0.052 mag, and phase function parameters G1 = 0.489−0.044+0.043 and G2 = 0.259−0.023+0.023. Meanwhile, we also determine (107) Camillas orientation of pole (74.1°−4.5°+4.3°, 50.2°−5.0°+5.4°) with rotational period of 4.843928−0.00001+0.000001 h, and axial ratios a/b = 1.409−0.020+0.020 and b/c = 1.249−0.060+0.063. Furthermore, according to the values of phase function parameters G1 and G2, we infer that asteroid (107) Camilla is an X-type asteroid.

Long-term transit timing monitoring and homogenous study of WASP-32

We report new photometric observations of the transiting exoplanetary system WASP-32 made by using CCD cameras at Yunnan Observatories and Ho Koon Nature Education cum Astronomical Centre, China from 2010 to 2012. Following our usual procedure, the observed data are corrected for systematic errors according to the coarse decorrelation and SYSREM algorithms so as to enhance the signal of the transit events. Combined with radial velocity data presented in the literature, our newly observed data and earlier photometric data in the literature are simultaneously analyzed to derive the physical parameters describing the system by employing the Markov chain Monte Carlo technique. The derived parameters are consistent with the result published in the original paper about WASP-32b, but the uncertainties of the new parameters are smaller than those in the original paper. Moreover, our modeling result supports a circular orbit for WASP-32b. Through the analysis of all available mid-transit times, we have refined the orbital period of WASP-32b; no evident transit timing variation is found in these transit events.

The refined physical parameters of transiting exoplanet system HAT-P-24

The transiting exoplanet system HAT-P-24 was observed by using CCD cameras at Yunnan Observatory and Hokoon Astronomical Centre, China in 2010 and 2012. In order to enhance the signal to noise ratio of transit events, the observed data are corrected for systematic errors according to Collier Cameron et al.s coarse decorrelation and Tamuz et al.s SYSREM algorithms. Three new complete transit light curves are analyzed by means of the Markov chain Monte Carlo technique, and the new physical parameters of the system are derived. They are consistent with the old ones from the discovered paper except for a new larger radius R-p = 1.364 R-J of HAT-P-24b, which confirms its inflated nature. By combining the five available epochs of mid-transit derived from complete transit light curves, the orbital period of HAT-P-24b is refined to P = 3.3552479 d and no obvious transit timing variation signal can be found from these five transit events during 2010-2012.

New CCD photometry of asteroid (1028) Lydina

New CCD photometric observations for asteroid (1028) Lydina, carried out with the 1-m and 2.4-m telescopes at Yunnan Observatory from 2011 December 19 to 2012 February 3, are presented. Using the new light curves, the rotation period of 11.680 +/- 0.001 hours is derived with the Phase Dispersion Minimization (PDM) method. In addition, using the Amplitude-Aspect method, the elementary results of the pole orientation of asteroid (1028) Lydina are obtained: lambda(p) = 111 degrees(+4 degrees)(-4 degrees), beta(p)=31 degrees(+4 degrees)(-5 degrees). Meanwhile, the axial ratios of the tri-axial ellipsoid are estimated: a/b = 1.77(-0:08)(+0.10) and b/c = 1.17(-0.09)(+0.07).