We estimate the fraction of mass that is composed of compact objects in gravitational lens galaxies. This study is based on microlensing measurements (obtained from the literature) of a sample of 29 quasar image pairs seen through 20 lens galaxies. We determine the baseline for no microlensing magnification between two images from the ratios of emission line fluxes. Relative to this baseline, the ratio between the continua of the two images gives the difference in microlensing magnification. The histogram of observed microlensing events peaks close to no magnification and is concentrated below 0.6 magnitudes, although two events of high magnification, ∆m ∼ 1.5, are also present. We study the likelihood of the microlensing measurements using frequency distributions obtained from simulated microlensing magnification maps for different values of the fraction of mass in compact objects, α. The concentration of microlensing measurements close to ∆m ∼ 0 can be explained only by simulations corresponding to very low values of α (10% or less). A maximum likelihood test yields α = 0.05 +0.09 −0.03 (90% confidence interval) for a quasar continuum source of intrinsic size r s 0 ∼ 2.6 · 10 15 cm. This estimate is valid in the 0.1 − 10M ⊙ range of microlens masses. We study the dependence of the estimate of α with r s 0 , and find that α 0.1 for r s 0 1.3 · 10 16 cm. High values of α are possible only for source sizes much larger than commonly expected (r s 0 >> 2.6 · 10 16 cm). Regarding the current controversy about Milky Way/LMC and M31 microlensing studies, our work supports the hypothesis of a very low content in MACHOS (Massive Compact Halo Objects). In fact, according to our study, quasar microlensing probably arises from the normal star populations of lens galaxies and there is no statistical evidence for MACHOS in the dark halos.

We discuss the effects of microlensing on the broad emission lines (BELs) of QSOs in the light of recent determinations of the size of the broad-line region (BLR) and its scaling with QSO luminosity. Microlensing by star-sized objects can produce significant amplifications in the BEL of some multiple-imaged QSOs, and could be very relevant for high-ionization lines. We have identified a group of 10 gravitational lens systems ($30% of the selected sample) in which microlensing could be observed. Using standard kinematic models for active galactic nuclei, we have studied the changes induced in the line profile by a microlens located at different positions with respect to the center of the BLR. We found that microlensing could produce important effects such as the relative enhancement of different parts of the line profile or the displacement of the peak of the line. The study of BEL profiles of different ionization in a microlensed QSO image could be an alternative method for probing the BLR structure and size.

The dwarf planet Eris is a trans-Neptunian object with an orbital eccentricity of 0.44, an inclination of 44 degrees and a surface composition very similar to that of Pluto. It resides at present at 95.7 astronomical units (1 AU is the Earth-Sun distance) from Earth, near its aphelion and more than three times farther than Pluto. Owing to this great distance, measuring its size or detecting a putative atmosphere is difficult. Here we report the observation of a multi-chord stellar occultation by Eris on 6 November 2010 UT. The event is consistent with a spherical shape for Eris, with radius 1,163 ± 6 kilometres, density 2.52 ± 0.05 grams per cm(3) and a high visible geometric albedo, Pv = 0.96(+0.09)(-0.04). No nitrogen, argon or methane atmospheres are detected with surface pressure larger than ∼1 nanobar, about 10,000 times more tenuous than Pluto's present atmosphere. As Pluto's radius is estimated to be between 1,150 and 1,200 kilometres, Eris appears as a Pluto twin, with a bright surface possibly caused by a collapsed atmosphere, owing to its cold environment. We anticipate that this atmosphere may periodically sublimate as Eris approaches its perihelion, at 37.8 astronomical units from the Sun.

CCD observations of the gravitational lens system Q0957+561A,B in the BV RI bands are presented in this paper. The observations, taken with the 82 cm IAC-80 telescope, at Teide Observatory, Spain, were made from the beginning of 1996 February to 1998 July, as part of an on-going lens monitoring program. Accurate photometry was obtained by simultaneously fitting a stellar two-dimensional profile on each component by means of DAOPHOT software. This alternative method equals and even improves the results obtained with previous techniques. The final dataset is characterized by its high degree of homogeneity as it was obtained using the same telescope and instrumentation during a period of almost 3 years. The resulting delay, obtained with a new method, the δ 2 -test, is of 425 ± 4 days, slightly higher than the value previously accepted (417 days), but concordant with the results obtained by Pelt et al.

We report the development of a 4-color simultaneous camera for the 1.52 m Telescopio Carlos Sánchez (TCS) in the Teide Observatory, Canaries, Spain. The new instrument, named MuSCAT2, has a capability of 4-color simultaneous imaging in g (400-550 nm), r (550-700 nm), i (700-820 nm), and z s (820-920 nm) bands. MuSCAT2 equips four 1024×1024 pixel CCDs, having a field of view of 7.4×7.4 arcmin 2 with a pixel scale of 0.44 arcsec per pixel. The principal purpose of MuSCAT2 is to perform high-precision multi-color exoplanet transit photometry. We have demonstrated photometric precisions of 0.057%, 0.050%, 0.060%, and 0.076% as root-mean-square residuals of 60 s binning in g, r, i and z s bands, respectively, for a G0 V star WASP-12 (V = 11.57 ± 0.16). MuSCAT2 has started science operations since January 2018, with over 250 telescope nights per year. MuSCAT2 is expected to become a reference tool for exoplanet transit observations, and will substantially contribute to the follow-up of the TESS and PLATO space missions.