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On the discrepancy between asteroseismic and Gaia DR1 TGAS parallaxes
Gontcharov, George A.; Mosenkov, Aleksandr V.
Recently, a deviation of the Gaia Tycho-Gaia Astrometric Solution (TGAS) parallaxes from the asteroseismic ones for giants was found. We show that for parallaxes ϖ < 1.5 mas it can be explained by a selection effect in favour of bright and luminous giants in the Tycho-2 and TGAS catalogues. Another explanation of this deviation seems to be vali…
Modelling the observed stellar mass function and its radial variation in galactic globular clusters
Vesperini, Enrico; Dalessandro, Emanuele; Ferraro, Francesco R. +3 more
We measure how the slope α of the stellar mass function (MF) changes as a function of clustercentric distance r in five Galactic globular clusters and compare α(r) to predictions from direct N-body star cluster simulations. Theoretical studies predict that α(r) (which traces the degree of mass segregation in a cluster) should steepen with time as …
The Warm Circumgalactic Medium: 105-6 K Gas Associated with a Single Galaxy Halo or with an Entire Group of Galaxies?
Danforth, Charles W.; Stocke, John T.; Keeney, Brian A. +3 more
In preparation for a Hubble Space Telescope (HST) observing project using the Cosmic Origins Spectrograph (COS), the positions of all AGN targets having high-S/N far-UV G130M spectra were cross-correlated with a large catalog of low-redshift galaxy groups homogenously selected from the spectroscopic sample of the Sloan Digital Sky Survey (SDSS). S…
Ultra low frequency waves at Venus: Observations by the Venus Express spacecraft
Fränz, M.; Zhang, T. L.; Dubinin, E. +2 more
The generation of waves with low frequencies (below 100 mHz) has been observed in the environment of most bodies in the solar system and well studied at Earth. These waves can be generated either upstream of the body in the solar wind by ionization of planetary exospheres or ions reflected from a bow shock or in the magnetosheath closer to the mag…
The Small-scale Structure of Photospheric Convection Retrieved by a Deconvolution Technique Applied to Hinode/SP Data
Solanki, S. K.; Shimizu, T.; Quintero Noda, C. +3 more
Solar granules are bright patterns surrounded by dark channels, called intergranular lanes, in the solar photosphere and are a manifestation of overshooting convection. Observational studies generally find stronger upflows in granules and weaker downflows in intergranular lanes. This trend is, however, inconsistent with the results of numerical si…
A Model for Dissipation of Solar Wind Magnetic Turbulence by Kinetic Alfvén Waves at Electron Scales: Comparison with Observations
Saur, Joachim; Schreiner, Anne
In hydrodynamic turbulence, it is well established that the length of the dissipation scale depends on the energy cascade rate, I.e., the larger the energy input rate per unit mass, the more the turbulent fluctuations need to be driven to increasingly smaller scales to dissipate the larger energy flux. Observations of magnetic spectral energy dens…
The Horizontal Branch Population of NGC 1851 as Revealed by the Ultraviolet Imaging Telescope (UVIT)
Stalin, C. S.; Rao, N. Kameswara; Murthy, J. +15 more
We present the UV photometry of the globular cluster NGC 1851 using images acquired with the Ultraviolet Imaging Telescope (UVIT) onboard the ASTROSAT satellite. Point-spread function fitting photometric data derived from images in two far-UV (FUV) filters and one near-UV (NUV) filter are used to construct color-magnitude diagrams (CMDs), in combi…
Study of orbital and superorbital variability of LSI +61° 303 with X-ray data
Tsygankov, S.; Takahashi, H.; Babyk, Iu. +4 more
LSI +61° 303 is one of the few X-ray binaries with a Be star companion from which radio, X-rays and high-energy gamma-ray (GeV and TeV) emission have been observed. The nature of the high-energy activity of the system is not yet fully understood, but it is widely believed that it is generated due to the interaction of the relativistic electrons le…
An extinction-free AGN selection by 18-band SED fitting in mid-infrared in the AKARI NEP deep field
Hashimoto, Tetsuya; Goto, Tomotsugu; Matsuhara, Hideo +2 more
We have developed an efficient active galactic nucleus (AGN) selection method using 18-band spectral energy distribution (SED) fitting in mid-infrared (mid-IR). AGNs are often obscured by gas and dust, and those obscured AGNs tend to be missed in optical, UV and soft X-ray observations. Mid-IR light can help us to recover them in an obscuration-fr…
Molecular clouds as origin of the Fermi gamma-ray GeV excess
Biermann, Peter L.; de Boer, Wim; Bosse, Léo +2 more
The so-called GeV excess of the diffuse Galactic gamma-ray emission, as observed by the Fermi-LAT satellite, is studied with a spectral template fit based on energy spectra for each relevant process of gamma-ray emission. This has the advantage over "conventional" analysis because one includes the spectral knowledge of physical processes into the …