765 research outputs found
The high-field polar RX J1007.5-2017
We report optical and X-ray observations of the high-field polar
RXJ1007.5-2017 performed between 1990 and 2012. It has an orbital period of
208.60 min determined from the ellipsoidal modulation of the secondary star in
an extended low state. The spectral flux of the dM3- secondary star yields a
distance of 790+-105 pc. At low accretion levels, \RX{} exhibits pronounced
cyclotron emission lines. The second and third harmonic fall in the optical
regime and yield a field strength in the accretion spot of 94 MG. The source is
highly variable on a year-to-year basis and was encountered at visual
magnitudes between V \sim 20 and V \sim 16. In the intermediate state of 1992
and 2000, the soft X-ray luminosity exceeds the sum of the luminosities of the
cyclotron source, the hard X-ray source, and the accretion stream by an order
of magnitude. An X-ray high state, corresponding to the brightest optical
level, has apparently not been observed so far.Comment: To be published in A&
Comparative Study of Slickspots in Grant County, Oklahoma
This thesis was organized to achieve the two parts of the objective without duplicating Chapter II, Consequently, Chapters III and IV deal with the objective of comparing a slickspot and two slightly-affected soils with an adjacent soil unaffected by salts. Chapters V and VI pertain to the second objective of comparing four different slickspots which have developed on different parent materials and physiographic locations.Agronom
Genesis and Lateral Variability of Sand- and Silt-Mantled Soils in North Central Oklahoma
Soil Scienc
Neglected X-ray discovered polars: III. RX J0154.0-5947, RX J0600.5-2709, RX J0859.1+0537, RX J0953.1+1458, and RX J1002.2-1925
We report results on the ROSAT-discovered noneclipsing short-period polars RX
J0154.0-5947, RX J0600.5-2709, RX J0859.1+0537, RX J0953.1+1458, and RX
J1002.2-1925 collected over 30 years. We present accurate linear orbital
ephemerides that allow a correct phasing of data taken decades apart. Three of
the systems show cyclotron and Zeeman lines that yield magnetic field strengths
of 36 MG, 19 MG, and 33 MG for the last three targets, respectively. RX
J0154.0-5947, RX J0859.1+0537, and RX J1002.2-1925 show evidence for part-time
accretion at both magnetic poles, while RX J0953.1+1458 is a polar with a
stable one-pole geometry. RX J1002.2-1925 shows large variations in the shapes
of its light curves that we associate with an unstable accretion geometry.
Nevertheless, it appears to be synchronized. We determined the bolometric soft
and hard X-ray fluxes and the luminosities at the Gaia distances of the five
stars. Combined with estimates of the cyclotron luminosities, we derived
high-state accretion rates that range from
yr to yr for white
dwarf masses between 0.61 and 0.82 , in agreement with predictions
based on the observed effective temperatures of white dwarfs in polars and the
theory of compressional heating. Our analysis lends support to the hypothesis
that different mean accretion rates appply for the subgroups of short-period
polars and nonmagnetic cataclysmic variables.Comment: 24 pages, 11 figures, and 13 tables, accepted for publication in A&
Foaming Species and Trapping Mechanisms in Barium Silicate Glass Sealants
Barium silicate glass powders 4 h milled in CO2 and Ar and sintered in air are studied with microscopy, total carbon analysis, differential thermal analysis (DTA), vacuum hot extraction mass spectroscopy (VHE-MS), Fourier-transformed infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary-ion mass spectrometry (TOF−SIMS). Intensive foaming of powder compacts is evident, and VHE studies prove that foaming is predominantly caused by carbonaceous species for both milling gases. DTA shows that the decomposition of BaCO3 particles mix-milled with glass powders occurs at similar temperatures as foaming of compacts. However, no carbonate at the glass surface could be detected by FTIR spectroscopy, XPS, and TOF−SIMS after heating to the temperature of sintering. Instead, CO2 molecules unable to rotate identified by FTIR spectroscopy after milling, probably trapped by mechanical dissolution into the glass bulk. Such a mechanism or microencapsulation in cracks and particle aggregates can explain the contribution of Ar to foaming after intense milling in Ar atmosphere. The amount of CO2 molecules and Ar, however, cannot fully explain the extent of foaming. Carbonates mechanically dissolved beneath the surface or encapsulated in cracks and micropores of particle aggregates are therefore probably the major foaming source. © 2021 The Authors. Advanced Engineering Materials published by Wiley-VCH GmbH
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