On the observational properties of He-burning stars: some clues on the tilt of the HB in metal rich clusters

We investigate the predicted Color-Magnitude distribution of metal-rich Horizontal Branch (HB) stars, discussing selected theoretical models computed under various assumptions about the star metallicity and the efficiency of super-adiabatic convection. We find that canonical Zero Age Horizontal Branches with metallicity larger or of the order of Z=0.002 should be all affected by a tilt, by an amount which increases when the metallicity is increased and/or the mixing length is decreased, reaching a tilt of $\Delta V \sim$0.2 mag in the case of solar metallicity when a mixing length value $\alpha$=1.6 is assumed ($\Delta V$ is the magnitude difference between the top of the blue HB and the fainter magnitude reached by the red HB). Uncertainties in the luminosity of the red HB due to uncertainty in the mixing length value are discussed. We finally discuss the much larger tilt observed in the clusters NGC 6441 and NGC 6388, reporting additional evidence against suggested non-canonical evolutionary scenarios. Numerical experiments show that differential reddening could produce such sloped HBs. Further, HST-PC imaging of NGC 6441 gives clear indications about the occurrence of differential reddening across the cluster. However, the same imaging shows that the observed slope of the red HB {\em is not} an artifact of differential reddening. We finally show that sloping red HBs in metal rich clusters are a common occurrence not necessarily correlated with the appearance of extended blue HB.Comment: 14 pages, 9 figures, Accepted by Ap

The blue sky of GJ3470b: the atmosphere of a low-mass planet unveiled by ground-based photometry

GJ3470b is a rare example of a "hot Uranus" transiting exoplanet orbiting a nearby M1.5 dwarf. It is of crucial interest for atmospheric studies because it is one of the most inflated low-mass planets known, bridging the boundary between "super-Earths" and Neptunian planets. We present two new ground-based light curves of GJ3470b gathered by the LBC camera at the Large Binocular Telescope. Simultaneous photometry in the ultraviolet (lambda_c = 357.5 nm) and optical infrared (lambda_c = 963.5 nm) allowed us to detect a significant change of the effective radius of GJ3470b as a function of wavelength. This can be interpreted as a signature of scattering processes occurring in the planetary atmosphere, which should be cloud-free and with a low mean molecular weight. The unprecedented accuracy of our measurements demonstrates that the photometric detection of Earth-sized planets around M dwarfs is achievable using 8-10m size ground-based telescopes. We provide updated planetary parameters, and a greatly improved orbital ephemeris for any forthcoming study of this planet.Comment: 8 pages, 6 figures, 1 table; accepted for publication in A&

Deep HST-WFPC2 photometry of NGC 288. II. The Main Sequence Luminosity Function

The Main Sequence Luminosity Function (LF) of the Galactic globular cluster NGC 288 has been obtained using deep WFPC2 photometry. We have employed a new method to correct for completeness and fully account for bin-to-bin migration due to blending and/or observational scatter. The effect of the presence of binary systems in the final LF is quantified and is found to be negligible. There is a strong indication of the mass segregation of unevolved single stars and clear signs of a depletion of low mass stars in NGC 288 with respect to other clusters. The results are in good agreement with the prediction of theoretical models of the dynamical evolution of NGC 288 that take into account the extreme orbital properties of this cluster.Comment: 16 pages, 6 .ps figures. Low resolution version of fig. 1; full resolution figure soon available at http://www.bo.astro.it/bap/BAPhome.html l. Latex. emulateapj5.sty macro included. Accepted for publication by The Astronomical Journa

Absolute proper motion of the Galactic open cluster M67

We derived the absolute proper motion (PM) of the old, solar-metallicity Galactic open cluster M67 using observations collected with CFHT (1997) and with LBT (2007). About 50 galaxies with relatively sharp nuclei allow us to determine the absolute PM of the cluster. We find (mu_alpha cos(delta),mu_delta)_J2000.0 = (-9.6+/-1.1,-3.7+/-0.8) mas/yr. By adopting a line-of-sight velocity of 33.8+/-0.2 km/s, and assuming a distance of 815+/-50 pc, we explore the influence of the Galactic potential, with and without the bar and/or spiral arms, on the galactic orbit of the cluster.Comment: 7 pages, 5 figures, and 3 tables. Published in Astronomy and Astrophysics, Volume 513, id.A51

A real CKM matrix?

The hypothesis of a real Cabibbo-Kobayashi-Maskawa matrix has been considered and found to be disfavoured by present measurements even when neglecting results from CP violation in neutral Kaon decay. This result contradicts statements reported in hep-ph/9810333.Comment: 7 pages, no figure

Radial extent of the SGB in NGC 1851

Recent HST-ACS observations revealed the presence of a double subgiant branch (SGB) in the core of the Galactic globular cluster NGC 1851. This peculiarity was tentatively explained by the presence of a second population with either an age difference of about 1 Gyr, or a higher C+N+O abundance, probably due to pollution by the first generation of stars. In the present Letter, we analyze VLT-FORS V,I images, covering 12.7x12.7 arcmin, in the southwest quadrant of the cluster, allowing us to probe the extent of the double SGB from ~1.4 to ~13 arcmin from the cluster center. Our study reveals, for the first time, that the "peculiar" population is the one associated to the fainter SGB. Indeed, while the percentage of stars in this sequence is about 45% in the cluster core (as previously found on the basis of HST-ACS data), we find that it drops sharply, to a level consistent with zero in our data, at ~2.4 arcmin from the cluster center, where the brighter SGB, in our sample, still contains ~100 stars. Implications for the proposed scenarios are discussed.Comment: Revised text, 1 new figure. No major chang

Peculiar Multimodality on the Horizontal Branch of the Globular Cluster NGC 2808

We present distributions of colors of stars along the horizontal branch of the globular cluster NGC 2808, from Hubble Space Telescope WFPC2 imaging in B, V, and an ultraviolet filter (F218W). This cluster's HB is already known to be strongly bimodal, with approximately equal-sized HB populations widely separated in the color-magnitude diagram. Our images reveal a long blue tail with two gaps, for a total of four nearly distinct HB groups. These gaps are very narrow, corresponding to envelope-mass differences of only \sim 0.01 Msun. This remarkable multimodality may be a signature of mass-loss processes, subtle composition variations, or dynamical effects; we briefly summarize the possibilities. The existence of narrow gaps between distinct clumps on the HB presents a challenge for models that attempt to explain HB bimodality or other peculiar HB structures.Comment: LaTeX, including compressed figures. To appear in ApJL. Larger (851k) PostScript version, including high-quality figures, available from http://astro.berkeley.edu/~csosin/pub