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Register a new userA new look into the spectral and light variations of epsilon Aur
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Investigating long series of spectral and photometric observations, we found that the orbital elements of epsilon Aur are subject to much larger uncertainties than usually believed. The H alpha emission is found to move basically with the F primary but its exact location should still be investigated. We also find strong additional absorption and large reddening of the object near the third contact during the eclipse. Episodic atmospheric mass transfer from the F primary towards its companion is tentatively suggested.
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Bright Be star beta CMi has been identified as a non-radial pulsator on the basis of space photometry with the MOST satellite and also as a single-line spectroscopic binary with a period of 170.4 d. The purpose of this study is to re-examine both these findings, using numerous electronic spectra from the Dominion Astrophysical Observatory, Ondv{r}ejov Observatory, Universitatssterwarte Bochum, archival electronic spectra from several observatories, and also the original MOST satellite photometry. We measured the radial velocity of the outer wings of the double Halpha emission in all spectra at our disposal and were not able to confirm significant radial-velocity changes. We also discuss the problems related to the detection of very small radial-velocity changes and conclude that while it is still possible that the star is a spectroscopic binary, there is currently no convincing proof of it from the radial-velocity measurements. Wavelet analysis of the MOST photometry shows that there is only one persistent (and perhaps slightly variable) periodicity of 0.617 d of the light variations, with a double-wave light curve, all other short periods having only transient character. Our suggestion that this dominant period is the stars rotational period agrees with the estimated stellar radius, projected rotational velocity and with the orbital inclination derived by two teams of investigators. New spectral observations obtained in the whole-night series would be needed to find out whether some possibly real, very small radial-velocity changes cannot in fact be due to rapid line-profile changes.
We collected rich series of RV measurements covering last 110 years and photometric observations from the past 6 primary eclipses, complemented them by our new observations and derived a new precise ephemeris and an orbital solution of epsilon Aur.
The concept of local pressure is pivotal to describe many important physical phenomena, such as buoyancy or atmospheric phenomena, which always require the consideration of space-varying pressure fields. These fields have precise definitions within the phenomenology of hydro-thermodynamics, but a simple and pedagogical microscopic description based on Statistical Mechanical is still lacking in present literature. In this paper, we propose a new microscopic definition of the local pressure field inside a classical fluid, relying on a local barometer potential that is built into the many-particle Hamiltonian. Such a setup allows the pressure to be locally defined, at an arbitrary point inside the fluid, simply by doing a standard ensemble average of the radial force exerted by the barometer potential on the gas particles. This setup is further used to give a microscopic derivation of the generalized Archimedess buoyancy principle, in the presence of an arbitrary external field. As instructive examples, buoyancy force fields are calculated for ideal fluids in the presence of: i) a uniform force field, ii) a spherically symmetric harmonic confinement field, and iii) a centrifugal rotating frame.
Over the past years, the lambda-Orionis cluster has been a prime location for the study of young very low mass stars, substellar and isolated planetary mass objects and the determination of the initial mass function and other properties of low mass cluster members. In the continuity of our previous studies of young associations cores, we search for ultracool members and new multiple systems within the central 5.3 (~0.6pc) of the cluster. We obtained deep seeing limited J, Ks-band images of the 5.3 central part of the cluster with NTT/SofI and H-band images with CAHA/Omega2000. These images were complemented by multi-conjugate adaptive optics (MCAO) H and Ks images of the 1.5 central region of the lambda-Orionis cluster obtained with the prototype MCAO facility MAD at the VLT. The direct vicinity of the massive lambda-Ori O8III-star was probed using NACO/SDI at the VLT. Finally, we also retrieved Spitzer IRAC images of the same area and used archival Subaru Suprime-Cam and CFHT CFHT12K i-band images. We report the detection of 9 new member candidates selected from optical and near-IR color-color and color-magnitude diagrams and 7 previously known members. The high spatial resolution images resolve 3 new visual multiple systems. Two of them are most likely not members of the association. The third one is made of a brown dwarf candidate companion to the F8V star HD36861C. The simultaneous differential images allow us to rule out the presence of visual companions more massive than M>0.07Msun in the range 1-2.5, and M>0.25Msun in the range 0.5-2.5
We have imaged GM Aur with HST, detected its disk in scattered light at 1400A and 1650A, and compared these with observations at 3300A, 5550A, 1.1 microns, and 1.6 microns. The scattered light increases at shorter wavelengths. The radial surface brightness profile at 3300A shows no evidence of the 24AU radius cavity that has been previously observed in sub-mm observations. Comparison with dust grain opacity models indicates the surface of the entire disk is populated with sub-micron grains. We have compiled an SED from 0.1 microns to 1 mm, and used it to constrain a model of the star+disk system that includes the sub-mm cavity using the Monte Carlo Radiative Transfer code by Barbara Whitney. The best-fit model image indicates that the cavity should be detectable in the F330W bandpass if the cavity has been cleared of both large and small dust grains, but we do not detect it. The lack of an observed cavity can be explained by the presence of sub-microns grains interior to the sub-mm cavity wall. We suggest one explanation for this which could be due to a planet of mass <9 Jupiter masses interior to 24 AU. A unique cylindrical structure is detected in the FUV data from the Advanced Camera for Surveys/Solar Blind Channel. It is aligned along the system semi-minor axis, but does not resemble an accretion-driven jet. The structure is limb-brightened and extends 190 +/- 35 AU above the disk midplane. The inner radius of the limb-brightening is 40 +/- 10 AU, just beyond the sub-millimeter cavity wall.
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