Search Publications
Explanation of a Special Color-Magnitude Diagram of Star Cluster NGC 1651 from Different Models
Chen, Li; Li, Zhongmu; Mao, Caiyan
The color-magnitude diagram (CMD) of globular cluster NGC 1651 has special structures including a broad main sequence, an extended main sequence turn-off, and an extended red giant clump. The reason for such a special CMD remains unclear. In order to test the difference among the results from various stellar population assumptions, we study a high…
A comparative study of four significance measures for periodicity detection in astronomical surveys
Holl, Berry; Rimoldini, Lorenzo; Mowlavi, Nami +8 more
We study the problem of periodicity detection in massive data sets of photometric or radial velocity time series, as presented by ESA's Gaia mission. Periodicity detection hinges on the estimation of the false alarm probability of the extremum of the periodogram of the time series. We consider the problem of its estimation with two main issues in …
An ionized layer in the upper atmosphere of Mars caused by dust impacts from comet Siding Spring
Gurnett, D. A.; Persoon, A. M.; Morgan, D. D. +4 more
We report the detection of a dense ionized layer in the upper atmosphere of Mars caused by the impact of dust from comet Siding Spring. The observations were made by the ionospheric radar sounder on the Mars Express spacecraft during two low-altitude passes approximately 7 h and 14 h after closest approach of the comet to Mars. During these passes…
Reconciling Planck cluster counts and cosmology? Chandra/XMM instrumental calibration and hydrostatic mass bias
Reiprich, Thomas H.; Massey, Richard; Israel, Holger +2 more
The mass of galaxy clusters can be inferred from the temperature of their X-ray-emitting gas, TX. Their masses may be underestimated if it is assumed that the gas is in hydrostatic equilibrium, by an amount bhyd ∼ (20 ± 10) per cent suggested by simulations. We have previously found consistency between a sample of observed Ch…
How elevated is the dynamical-to-stellar mass ratio of the ultracompact dwarf S999?
Janz, Joachim; Penny, Samantha J.; Forbes, Duncan A. +4 more
Here we present new Keck Echelle Spectrograph and Imager high-resolution spectroscopy and deep archival Hubble Space Telescope/Advanced Camera for Surveys imaging for S999, an ultracompact dwarf in the vicinity of M87, which was claimed to have an extremely high dynamical-to-stellar mass ratio. Our data increase the total integration times by a fa…
History of the clay-rich unit at Mawrth Vallis, Mars: High-resolution mapping of a candidate landing site
Mangold, N.; Bibring, J. -P.; Poulet, F. +4 more
The Mawrth Vallis region is covered by some of the largest phyllosilicate-rich outcrops on Mars, making it a unique window into the past history of Mars in terms of water alteration, potential habitability, and the search for past life. A landing ellipse had been proposed for the Curiosity rover. This area has been extensively observed by the High…
Constraints on the exponential f (R ) model from latest Hubble parameter measurements
Geng, Chao-Qiang; Lee, Chung-Chi; Chen, Yun +2 more
We investigate the viable exponential f (R ) gravity in the metric formalism with f (R )=-β Rs(1 -e-R /Rs). The latest sample of the Hubble parameter measurements with 23 data points is used to place bounds on this f (R ) model. A joint analysis is also performed with the luminosity distances of type Ia supernovae …
Probing Wolf-Rayet Winds: Chandra/HETG X-Ray Spectra of WR 6
Hamann, W. -R.; Huenemoerder, David P.; Ignace, R. +6 more
With a deep Chandra/HETGS exposure of WR 6, we have resolved emission lines whose profiles show that the X-rays originate from a uniformly expanding spherical wind of high X-ray-continuum optical depth. The presence of strong helium-like forbidden lines places the source of X-ray emission at tens to hundreds of stellar radii from the photosphere. …
The WISE Light Curves of Polars
Harrison, Thomas E.; Campbell, Ryan K.
We have extracted the WISE (Wide-field Infrared Survey Explorer) single-exposure data for a sample of 72 polars, which are highly magnetic cataclysmic variables (CVs). We combine these data with both published and unpublished optical and infrared data to explore the origins of the large amplitude variations seen in these systems. In nearly every c…
Gamma-ray activity of Seyfert galaxies and constraints on hot accretion flows
Szanecki, Michał; Niedźwiecki, Andrzej; Xie, Fu-Guo +1 more
Aims: We check how the Fermi/LAT data constrain the physics of hot accretion flows that are most likely present in low-luminosity AGNs.
Methods: Using a precise model of emission from hot flows, we studied the flow γ-ray emission resulting from proton-proton interactions. We explored the dependence of the γ-ray luminosity on the accretio…