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71.
We present observations of a sample of Herbig AeBe stars, as well as the FU Orionis object V1057 Cygni. Our K-band (2.2μm)
observations from the Palomar Testbed Interferometer (PTI) used baselines of 110 m and 85 m, resulting in fringe spacings
of ∼4 mas and 5 mas, respectively. Fringes were obtained for the first time on V1057 Cygnias well as V594 Cas. Additional
measurements were made of MWC147, while upper limits to visibility-squared are obtained for MWC297, HD190073, and MWC614.
These measurements are sensitive to the distribution of warm, circumstellar dust in these sources. If the circumstellar infrared
emission comes from warm dust in a disk, the inclination of the disk to the line of sight implies that the observed interferometric
visibilities should depend upon hour angle. Surprisingly, the observations of Millan-Gabet, Schloerb and Traub (2001)(hereafter
MST) did not show significant variation with hour angle. However, limited sampling of angular frequencies on the sky was possible
with the IOTA interferometer, motivating us to study a subset of their objects to further constrain these systems.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
72.
W.W. Zeilinger S. De Rijcke H. Dejonghe G.K.T. Hau 《Astrophysics and Space Science》2003,284(2):607-610
Deep imaging and long-slit spectroscopy was obtained for a sample of dwarf ellipticals in the Fornax cluster, NGC 5044 and
NGC 5898 groups using the ESO VLT. The observational data extend out to typically 1.5–2 effective radii and indicate a kinematic
dichotomy in the family of ellipticals. The observed stellar kinematics indicate a luminosity–velocity dispersion relation
largely supporting Supernova-driven stellar mass loss scenarios for the formation of dwarf ellipticals. Stellar dynamical
models favour dark matter halos with typical mass-to-light ratios in the range of 3 to 9 solar units.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
73.
74.
A flare of maser radio emission in the 1665-MHz OH line with a flux density of about 1000 Jy was discovered in the star-forming region W75 N in 2003. At the time of its observations, it was the strongest OH maser in the entire history of research since the discovery of cosmic OH masers in 1965. The linear polarization of the flare emission reached 100%. A weaker flare with a flux density of 145 Jy was observed in this source in 2000–2001; this was probably a precursor of the intense flare. The intensity of two other spectral features decreased when the flare emerged. This change in the intensity of the emission from maser condensations (a brightening of some of them and a weakening of others) can be explained by the passage of a magnetohydrodynamic shock through regions of enhanced gas concentration. 相似文献
75.
76.
77.
78.
E. I. Ekwue 《地球表面变化过程与地形》1990,15(2):175-181
The influence of organic matter on splash detachment was investigated using soils with grass and peat treatments. The relationship between organic matter and aggregate stability to water disruption was positive for soils with grass treatment while it was negative for those with peat treatment. Organic matter from both treatments, however, reduced splash detachment by rainfall. Soils with grass did this by increasing aggregate stability while peat acted as a mulch on the soil surface. This implies that though organic matter always reduces splash detachment, different processes may be involved, depending on the form of the organic material. Because of the different processes involved, both negative and positive relationships between splash detachment and aggregate stability as reported in literature were obtained for the soils with grass and peat respectively. 相似文献
79.
Annamaria Borriello Paolo Salucci 《Monthly notices of the Royal Astronomical Society》2001,323(2):285-292
We use high-quality optical rotation curves of nine low-luminosity disc galaxies to obtain the velocity profiles of the surrounding dark matter haloes. We find that they increase linearly with radius at least out to the edge of the stellar disc, implying that, over the entire stellar region, the density of the dark halo is about constant.
The properties of the mass structure of these haloes are similar to those found for a number of dwarf and low surface brightness galaxies, but provide a more substantial evidence of the discrepancy between the halo mass distribution predicted in the cold dark matter scenario and those actually detected around galaxies. We find that the density law proposed by Burkert reproduces the halo rotation curves, with halo central densities ( ρ0 ∼1–4×10−24 g cm−3 ) and core radii ( r 0 ∼5–15 kpc) scaling as ρ 0 ∝ r 0 −2/3 . 相似文献
The properties of the mass structure of these haloes are similar to those found for a number of dwarf and low surface brightness galaxies, but provide a more substantial evidence of the discrepancy between the halo mass distribution predicted in the cold dark matter scenario and those actually detected around galaxies. We find that the density law proposed by Burkert reproduces the halo rotation curves, with halo central densities ( ρ
80.
S. S. Kaisin A. V. Kasparova A. Yu. Knyazev I. D. Karachentsev 《Astronomy Letters》2007,33(5):283-291
We present our Hα observations of 11 isolated southern galaxies: SDIG, PGC 51659, E 222-010, E 272-025, E 137-018, IC 4662, Sag DIG, IC 5052, IC 5152, UGCA 438, and E 149-003, with distances from 1 to 7 Mpc. We have determined the total Hα fluxes from these galaxies. The star formation rates in these galaxies range from 10?1 (IC 4662) to 10?4 M ⊙ yr?1 (SDIG) and the gas depletion time at the observed star formation rates lies within the range from 1/6 to 24 Hubble times H 0 ?1 . 相似文献