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Evolution of depressions on Comet 67P/Churyumov Gerasimenko: Role of ice metamorphism
Kossacki, Konrad J.; Leliwa-Kopystyński, Jacek; Szutowicz, Slawomira
This work is intended to investigate the influence of temperature-dependent metamorphism of ice on the shape of small depressions in the surface of cometary nuclei. We are mainly interested in the role of initial cohesivity of a nucleus. For this purpose we simulate sublimation of ice from the facets of initially cylindrical depressions in ice of …
Tracing the Dynamical History of the Globular Cluster 47 Tucanae
Sills, Alison; Beccari, Giacomo; Guhathakurta, Puragra +3 more
We use two stellar populations in the globular cluster 47 Tucanae to trace its dynamical history: blue stragglers and low-mass main-sequence stars. We assumed that the blue stragglers were formed through stellar collisions in all regions of the cluster. We find that in the core of the cluster, models of collisional blue stragglers agree well with …
X-rays from the radio-quiet quasar PG 1407+265: relativistic jet or accretion disc emission?
Gallo, L. C.
We present two XMM-Newton observations of the luminous (Lx > 1046ergs-1), radio-quiet quasar PG 1407+265, separated by 11 months. The data indicate two distinct states: a highly variable, bright state (first epoch); and a quiescent, low-flux one (second epoch). During the low-flux state the spectrum is consisten…
Bistatic observations of Titan's surface with the Huygens probe radio signal
Lorenz, R. D.; Lebreton, J. -P.; Floury, N. +2 more
Huygens provided an unanticipated bistatic radio scattering experiment from Titan's surface. After a successful entry and descent on Titan, on 14 January 2005, the probe remarkably survived the landing and continued radioing from the surface to the overflying Cassini, until the orbiter set below Titan's local horizon. Here we report high-quality m…
On the Fraction of X-Ray-obscured Quasars in the Local Universe
Wang, J. X.; Jiang, P.
Recent wide-area hard X-ray and soft gamma-ray surveys have shown that the fraction of X-ray-obscured active galactic nuclei (AGNs) in the local universe significantly decreases with intrinsic luminosity. In this Letter we point out that two corrections have to be made to the samples: (1) radio-loud AGNs have to be excluded, since their X-ray emis…
Multiwavelength Studies of the Optically Dark Gamma-Ray Burst 001025A
Cline, T.; Hurley, K.; Schartel, N. +18 more
We identify the fading X-ray afterglow of GRB 001025A from XMM-Newton observations obtained 1.9-2.3 days, 2 yr, and 2.5 yr after the burst. The nondetection of an optical counterpart to an upper limit of R=25.5, 1.20 days after the burst, makes GRB 001025A a ``dark'' burst. Based on the X-ray afterglow spectral properties of GRB 001025A, we argue …
Variable Unidentified Emission near 6307 Å in η Carinae
Weis, K.; Stahl, O.; Davidson, K. +2 more
We have discovered a conspicuous unidentified variable feature near 6307 Å in the spectrum of η Carinae that is spatially unresolved from the central star and its wind (r<~200-300 AU). It is significant for two reasons: first, such prominent unidentified lines are now rare in this object, and second, this feature varies strongly and systematica…
DDO 44 and UGC 4998: Distances, Metallicities, and Star Formation Histories
Mateo, Mario; Aparicio, Antonio; Alonso-García, Javier
We have obtained deep HST imaging of two candidate dwarf systems in the nearby M81 Group, DDO 44 and UGC 4998. Both are isolated, low surface brightness systems, but with likely very different star formation histories based on their mean colors and color fluctuations. The color-magnitude diagrams of these galaxies have been used to estimate their …
UV Capabilities to Probe the Formation of Planetary Systems: From the ISM to Planets
Cernicharo, José; Gómez de Castro, Ana I.; Linsky, Jeffrey L. +2 more
Planetary systems are angular momentum reservoirs generated during star formation. Solutions to three of the most important problems in contemporary astrophysics are needed to understand the entire process of planetary system formation: The physics of the ISM. Stars form from dense molecular clouds that contain ∼ 30% of the total interstellar medi…
Is V899 Herculis an unsolved quadruple system containing double close binary stars?
Qian, S. -B.; Liao, W. -P.; He, J. -J. +2 more
Orbital period variation of the W UMa-type eclipsing binary, V899 Herculis, discovered by the Hipparcos satellite was investigated based on all available photoelectric and CCD times of light minimum. It is discovered that the orbital period of the binary shows a cyclic change with an amplitude of 0.0117 days. The cyclic period change can be explai…