We present a short history of the TAUVEX instrument, conceived to provide multi-band wide-field imaging in the ultraviolet, emphasizing the lack of sufficient and aggressive support on the part of the different space agencies that dealt with this bas
ic science mission. First conceived in 1985 and selected by the Israel Space Agency in 1989 as its first priority payload, TAUVEX is fast becoming one of the longest-living space project of space astronomy. After being denied a launch on a national Israeli satellite, and then not flying on the Spectrum X-Gamma (SRG) international observatory, it was manifested since 2003 as part of ISROs GSAT-4 Indian satellite to be launched in the late 2000s. However, two months before the launch, in February 2010, it was dismounted from its agreed-upon platform. This proved to be beneficial, since GSAT-4 and its launcher were lost on April 15 2010 due to the failure of the carrier rockets 3rd stage. TAUVEX is now stored in ISROs clean room in Bangalore with no firm indications when or on what platform it might be launched.
We have studied small scale (2 arcmin) spatial variation of the diffuse UV radiation using a set of 11 GALEX deep observations in the constellation of Draco. We find a good correlation between the observed UV background and the IR 100 micron flux, in
dicating that the dominant contributor of the diffuse background in the field is the scattered starlight from the interstellar dust grains. We also find strong evidence of additional emission in the FUV band which is absent in the NUV band. This is most likely due to Lyman band emission from molecular hydrogen in a ridge of dust running through the field and to line emissions from species such as C IV (1550 A) and Si II (1533 A) in the rest of the field. A strong correlation exists between the FUV/NUV ratio and the FUV intensity in the excess emission regions in the FUV band irrespective of the optical depth of the region. The optical depth increases more rapidly in the UV than the IR and we find that the UV/IR ratio drops off exponentially with increasing IR due to saturation effects in the UV. Using the positional details of Spitzer extragalactic objects, we find that the contribution of extragalactic light in the diffuse NUV background is 49 +/- 13 photon units and is 30 +/- 10 photon units in the FUV band.
In this paper we have analyzed IUE high resolution spectra of the central star (BD+602522) of the Bubble nebula. We discuss velocities of the different regions along the line of sight to the bubble. We find that the Bubble Nebula is younger (by a fac
tor of 100) than the exciting star suggesting that either the bubble is expanding into an inhomogenuous interstellar medium or that the mechanics of the stellar wind are not fully understood.
Using the GALEX ultraviolet imagers we have observed a region of nebulosity first identified as starlight scattered by interstellar dust by Sandage (1976). Apart from airglow and zodiacal emission, we have found a diffuse UV background of between 500
and 800 phunit in both the galex FUV (1350 -- 1750 AA) and NUV (1750 -- 2850 AA). Of this emission, up to 250 phunit is due to htwo fluorescent emission in the FUV band; the remainder is consistent with scattering from interstellar dust. We have estimated the optical constants to be $a = 0.3; g = 0.7$ in the FUV and $a = 0.5; g = 0.7$ in the NUV, implying highly forward scattering grains, plus an extragalactic contribution of as much as 150 phunit. These are the highest spatial resolution observations of the diffuse UV background to date and show an intrinsic scatter beyond that expected from instrumental noise alone. Further modeling is required to understand the nature of this scatter and its implications for the ISM.
