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HST Survey of the Orion Nebula Cluster in the H2O 1.4 µm Absorption Band. II. The Substellar IMF Down to Planetary Masses
Gennaro, Mario; Robberto, Massimo
We utilize the ability of the Hubble Space Telescope to probe near-infrared water absorption present in the atmosphere of low-mass stars and brown-dwarf and planetary-mass objects to create a pure sample of Orion Nebula Cluster (ONC) members, not affected by contamination from background stars and galaxies that lack water absorption. Thanks to the…
NuSTAR observations of four nearby X-ray faint AGNs: low luminosity or heavy obscuration?
Harrison, F. A.; Stern, D.; Alexander, D. M. +20 more
We present NuSTAR (Nuclear Spectroscopic Telescope Array) observations of four active galactic nuclei (AGNs) located within 15 Mpc. These AGNs, namely ESO 121-G6, NGC 660, NGC 3486, and NGC 5195, have observed X-ray luminosities of L2-10 keV,obs ≲ 1039 erg s-1, classifying them as low-luminosity AGN (LLAGN). We per…
Cosmology with quasars: predictions for eROSITA from a quasar Hubble diagram
Lusso, Elisabeta
The effort for understanding the matter and energy content of the Universe and its evolution relies on different probes, such as cosmic background radiation, cluster lensing, supernovae. Yet, we are still far from grasping what dark matter is made of, and what the physical origin of dark energy is. Our group has developed a technique that makes us…
Joining Bits and Pieces of Reionization History
Finelli, Fabio; Paoletti, Daniela; Hazra, Dhiraj Kumar +1 more
Cosmic microwave background (CMB) temperature and polarization anisotropies from Planck have estimated a lower value of the optical depth to reionization (τ ) compared to WMAP. A significant period in the reionization history would then fall within 6 <redshift(z )<10 , where detection of galaxies with Hubble frontier fields program and indep…
OGLE-ing the Magellanic System: RR Lyrae Stars in the Bridge
Udalski, Andrzej; Mróz, Przemek; Szymański, Michał K. +12 more
We use the extended and updated Optical Gravitational Lensing Experiment (OGLE) Collection of Variable Stars to thoroughly analyze the distribution of RR Lyrae stars in the Magellanic Bridge. We use photometric metallicities to derive the absolute Wesenheit magnitude and individual distance of each RR Lyrae star. We confirm results from our earlie…
The Slow Heartbeats of an Ultraluminous X-Ray Source in NGC 3621
Salvaterra, R.; Tiengo, A.; Marelli, M. +6 more
We report on the results of X-ray observations of 4XMM J111816.0-324910, a transient ultraluminous X-ray source located in the galaxy NGC 3621. This system is characterized by a transient nature and marked variability with a characteristic timescale of ≈3500 s, in contract with other ultraluminous X-ray sources, which in the vast majority show lim…
A high-precision abundance analysis of the nuclear benchmark star HD 20
Grebel, Eva K.; Hanke, Michael; Hansen, Camilla Juul +4 more
Metal-poor stars with detailed information available about their chemical inventory pose powerful empirical benchmarks for nuclear astrophysics. Here we present our spectroscopic chemical abundance investigation of the metal-poor ([Fe/H] = -1.60 ± 0.03 dex), r-process-enriched ([Eu/Fe] = 0.73 ± 0.10 dex) halo star
SS433: A massive X-ray binary in an advanced evolutionary stage
Cherepashchuk, Anatol; Postnov, Konstantin; Molkov, Sergey +2 more
INTEGRAL IBIS/ISGRI 18-60 keV observations of SS433 performed in 2003-2011 enabled for the first time the hard X-ray phase-resolved orbital and precessional light curves and spectra to be constructed. The spectra can be fitted by a power-law with photon index ≃ 3.8 and remain almost constant while the X-ray flux varies by a factor of a few. This s…
Matched Photometric Catalogs of GALEX UV Sources with Gaia DR2 and SDSS DR14 Databases (GUVmatch)
Bianchi, Luciana; Shiao, Bernard
We have matched the ultraviolet (UV) sources in GUVcat_AIS with optical databases that have similar depth and wide sky coverage. GUVcat_AIS has Galaxy Evolution Explorer (GALEX) far-UV (FUV, λeff ∼ 1528 Å) and near-UV (NUV, λeff ∼ 2310 Å) photometry of ≈83 million sources, covering 24,788 square degrees of the sky, with a typ…
The Metallicity Gradient and Complex Formation History of the Outermost Halo of the Milky Way
Yoon, Jinmi; Beers, Timothy C.; Placco, Vinicius M. +1 more
We present an examination of the metallicity distribution function of the outermost stellar halo of the Galaxy based on an analysis of both local (within 4 kpc of the Sun, ∼16,500 stars) and non-local (∼21,700 stars) samples. These samples were compiled using spectroscopic metallicities from the Sloan Digital Sky Survey and photometric metalliciti…