Cover picture: When a source, e. g., a QSO, lies behind a foreground galaxy, its light bundle is affected by the individual stars of this galaxy. This microlensingeffect, so far observed in at least one QSO (see Sect. 12.4), leads to a change in the flux we observe from the source, relative to an unlensed source. The flux magnification depends sensitively on the position of the source relative to the stars in the galaxy. Here we see the magnification as a function of the relative source position; red and yellow indicates high magnification, green and blue low magnification. The superimposed white curves are the caustics produced by the stars, projected into the source plane. The figure (which is taken from Wambsganss, Witt, and Schneider. Astr. Astophys., 258. 591 (1992)) has been produced by combining the ray-shooting method (Sects. 10.6. and 11.2.5) with the parametric representation of caustics (Sect. 8.3.4). The parameters for the star field are 1(.=0.5. y =1(,= O. with all stars having the same mass. The shape of the acoustics is analyzed in Chap. 6.

Cover picture: When a source, e.g., a QSO, lies behind a foreground galaxy, its light boundle is affected by the individual stars ofthis galaxy. This microlensing effect, so far observed in at least one QSO (see Sect. 12.4), leads to a change in the flux we observe from the source, relative to an lInlensed source. The flux magnification depends sensitively on the position of the source relative to the stars in the galaxy. Here we see the magnification as a function of the relative source position: red and yellow indicates high magnification, green and blue low magnification. The superimposed white curves are the caustics produced by the stars, projected into the source plane. The figure (taken from Wambsganss, Witt, and Schneider, Asfr. Astrophys., 258, 591 (1992)) has been produced by combining the ray-shooting method (Sects. 10.6 and 11.2.5) with the parametric representation of caustics (Sect. 8.3.4). The parameters for the star field are K. = 0.5, ' Y = Kc= 0, with all stars having the same mass. The shape of the acoustics is analyzed in Chap. 6.

We measured the K-band luminosity function using a complete sample of 4192 morphologically-typed 2MASS galaxies with µ Ks = 20 mag/arcsec 2 isophotal magnitudes 7 < K 20 < 11.25 mag spread over 2.12 str. Early-type (T ≤ −0.5) and late-type (T > −0.5) galaxies have similarly shaped luminosity functions, α e = −0.92 ± 0.10 and α l = −0.87 ± 0.09. The early-type galaxies are brighter, M * e = −23.53 ± 0.06 mag compared to M * l = −22.98 ± 0.06 mag, but less numerous, n * e = (0.45 ± 0.06) × 10 −2 h 3 Mpc −3 compared to n * l = (1.01 ± 0.13) × 10 −2 h 3 Mpc −3 for H 0 = 100h km s −1 Mpc −1 , such that the late-type galaxies slightly dominate the K-band luminosity density, j late /j early = 1.17 ± 0.12. Our morphological classifications are internally consistent, consistent with previous classifications and lead to luminosity functions unaffected by the estimated uncertainties in the classifications. These luminosity functions accurately predict the K-band number counts and redshift distributions for K < ∼ 18 mag, beyond which the results depend on galaxy evolution and merger histories.

times Earth's radius (R ⊕ ), indicating that it is intermediate in stature betweenEarth and the ice giants of the Solar System. We find that the planetary mass and radius are consistent with a composition of primarily water enshrouded by a hydrogen-helium envelope that is only 0.05% of the mass of the planet. The atmosphere is probably escaping hydrodynamically, indicating that it has undergone significant evolution during its history.As the star is small and only 13 parsecs away, the planetary atmosphere is amenable to study with current observatories.The recently commissioned MEarth Project 10,11 uses an array of eight identical 40-cm automated telescopes to photometrically monitor 2,000 nearby M dwarfs with masses between

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