A low-mass stellar companion of the planet host star HD75289

We report on the detection of a new low-mass stellar companion of HD75289, a G0V star that harbors one known radial-velocity planet (Udry et al. 2000). Comparing an image of 2MASS with an image we obtained with SofI at the ESO 3.58m NTT three years later, we detected a co-moving companion located 21.465+-0.023arcsecs (621+-10AU at 29pc) east of HD75289. A second SofI image taken 10 months later confirmed the common proper motion of HD75289B with its host star. The infrared spectrum and colors of the companion are consistent with an M2 to M5 main-sequence star at the distance of HD75289. No further (sub)stellar companion down to H = 19mag could be detected. With the SofI detection limit we can rule out additional stellar companions beyond 140AU and substellar companions with masses m > 0.050Msun from 400AU up to 2000AU.Comment: accepted in A&

Orion revisited. II. The foreground population to Orion A

Following the recent discovery of a large population of young stars in front of the Orion Nebula, we carried out an observational campaign with the DECam wide-field camera covering ~10~deg^2 centered on NGC 1980 to confirm, probe the extent of, and characterize this foreground population of pre-main-sequence stars. We confirm the presence of a large foreground population towards the Orion A cloud. This population contains several distinct subgroups, including NGC1980 and NGC1981, and stretches across several degrees in front of the Orion A cloud. By comparing the location of their sequence in various color-magnitude diagrams with other clusters, we found a distance and an age of 380pc and 5~10Myr, in good agreement with previous estimates. Our final sample includes 2123 candidate members and is complete from below the hydrogen-burning limit to about 0.3Msun, where the data start to be limited by saturation. Extrapolating the mass function to the high masses, we estimate a total number of ~2600 members in the surveyed region. We confirm the presence of a rich, contiguous, and essentially coeval population of about 2600 foreground stars in front of the Orion A cloud, loosely clustered around NGC1980, NGC1981, and a new group in the foreground of the OMC-2/3. For the area of the cloud surveyed, this result implies that there are more young stars in the foreground population than young stars inside the cloud. Assuming a normal initial mass function, we estimate that between one to a few supernovae must have exploded in the foreground population in the past few million years, close to the surface of Orion A, which might be responsible, together with stellar winds, for the structure and star formation activity in these clouds. This long-overlooked foreground stellar population is of great significance, calling for a revision of the star formation history in this region of the Galaxy.Comment: Accepted for publication in A&

Dynamics and Constraints of the Massive Gravitons Dark Matter Flat Cosmologies

We discuss the dynamics of the universe within the framework of Massive Graviton Dark Matter scenario (MGCDM) in which gravitons are geometrically treated as massive particles. In this modified gravity theory, the main effect of the gravitons is to alter the density evolution of the cold dark matter component in such a way that the Universe evolves to an accelerating expanding regime, as presently observed. Tight constraints on the main cosmological parameters of the MGCDM model are derived by performing a joint likelihood analysis involving the recent supernovae type Ia data, the Cosmic Microwave Background (CMB) shift parameter and the Baryonic Acoustic Oscillations (BAOs) as traced by the Sloan Digital Sky Survey (SDSS) red luminous galaxies. The linear evolution of small density fluctuations is also analysed in detail. It is found that the growth factor of the MGCDM model is slightly different ($\sim1-4$) from the one provided by the conventional flat $\Lambda$CDM cosmology. The growth rate of clustering predicted by MGCDM and $\Lambda$CDM models are confronted to the observations and the corresponding best fit values of the growth index ($\gamma$) are also determined. By using the expectations of realistic future X-ray and Sunyaev-Zeldovich cluster surveys we derive the dark-matter halo mass function and the corresponding redshift distribution of cluster-size halos for the MGCDM model. Finally, we also show that the Hubble flow differences between the MGCDM and the $\Lambda$CDM models provide a halo redshift distribution departing significantly from the ones predicted by other DE models. These results suggest that the MGCDM model can observationally be distinguished from $\Lambda$CDM and also from a large number of dark energy models recently proposed in the literature.Comment: Accepted for publication in Physical Review D (12 pages, 4 figures

Alguns insetos úteis ao algodoeiro.

bitstream/item/126637/1/Alguns-Insetos-uteis-ao-algoodoeiro.pd