Search results for "Local Group"
showing 6 items of 6 documents
On the exhaust of electromagnetic drive
2016
Recent reports about propulsion without reaction mass have been met on one hand with enthusiasm and on the other hand with some doubts. Namely, closed metal cavities, when fueled with microwaves, have delivered thrust that could eventually maintain satellites on orbits using solar power. However, the measured thrust appears to be without any apparent exhaust. Thus the Law of Action-Reaction seems to have been violated. We consider the possibility that the exhaust is in a form that has so far escaped both experimental detection and theoretical attention. In the thruster's cavity microwaves interfere with each other and invariably some photons will also end up co-propagating with opposite pha…
On the nature of a shell of young stars in the outskirts of the Small Magellanic Cloud
2019
Understanding the evolutionary history of the Magellanic Clouds requires an in-depth exploration and characterization of the stellar content in their outer regions, which ultimately are key to tracing the epochs and nature of past interactions. We present new deep images of a shell-like over-density of stars in the outskirts of the Small Magellanic Cloud (SMC). The shell, also detected in photographic plates dating back to the fifties, is located at ~1.9 degr from the center of the SMC in the north-east direction.The structure and stellar content of this feature were studied with multi-band, optical data from the Survey of the MAgellanic Stellar History (SMASH) carried out with the Dark Ene…
Optical and X-ray Observations of M31N 2007-12b: An Extragalactic Recurrent Nova with a Detected Progenitor?
2009
We report combined optical and X-ray observations of nova M31N 2007-12b. Optical spectroscopy obtained 5 days after the 2007 December outburst shows evidence of very high ejection velocities (FWHM H$\alpha \simeq 4500$ km s$^{-1}$). In addition, Swift X-ray data show that M31N 2007-12b is associated with a Super-Soft Source (SSS) which appeared between 21 and 35 days post-outburst and turned off between then and day 169. Our analysis implies that $M_{\rm WD} \ga 1.3 $M$_{\odot}$ in this system. The optical light curve, spectrum and X-ray behaviour are consistent with those of a recurrent nova. Hubble Space Telescope observations of the pre-outburst location of M31N 2007-12b reveal the prese…
The First Precise Determination of an Optical–Far‐Ultraviolet Extinction Curve Beyond the Local Group ( \documentclass{aastex} \usepackage{amsbsy} \u…
2005
We present the optical-far-ultraviolet extinction curve of the dust in the lens galaxy of the gravitational lens system SBS 0909+532 (z = 0.83). Extending our previous optical-UV estimate (from λ ~ 2 to 5 μm-1) into the far ultraviolet (from λ ~ 5 to 8 μm-1) is crucial for comparing with the extinction curves measured for Local Group galaxies in the spectral region where the differences are greatest. The SBS 0909+532 curve is similar to that of the LMC2 supershell, with a weaker 2175 A feature and a steeper rise into the UV than that observed in the Milky Way. The shapes of the extinction curve inferred from the quasar continuum and emission lines are in very good agreement. There is, howev…
The imprints of the Great Attractor and the Virgo cluster on the microwave background
1993
A fully non-linear model based on the Tolman-Bondi solution of the Einstein equations is used to describe the Great Attractor and the Virgo cluster. The background is a Friedmann-Robertson-Walker universe, and the inhomogeneity develops from physically motivated initial profiles of the energy density and the peculiar velocity. Accurate numerical integrations of the field equations of the null geodesics are carried out, and thus the angular temperature distribution of the microwave background produced by the chosen overdensities is found. The observer is located in the Local Group. The quadrupole Q produced by each overdensity is computed and divided into two parts: the relativistic Doppler …
Long Term Radio Monitoring of SN 1993J
2007
We present our observations of the radio emission from supernova (SN) 1993J, in M 81 (NGC 3031), made with the VLA, from 90 to 0.7 cm, as well as numerous measurements from other telescopes. The combined data set constitutes probably the most detailed set of measurements ever established for any SN outside of the Local Group in any wavelength range. Only SN 1987A in the LMC has been the subject of such an intensive observational program. The radio emission evolves regularly in both time and frequency, and the usual interpretation in terms of shock interaction with a circumstellar medium (CSM) formed by a pre-SN stellar wind describes the observations rather well considering the complexity o…