A B S T R A C TWe present contemporaneous optical and infrared (IR) photometric observations of the Type IIn SN 1998S covering the period between 11 and 146 d after discovery. The IR data constitute the first ever IR light curves of a Type IIn supernova. We use blackbody and spline fits to the photometry to examine the luminosity evolution. During the first 2±3 months, the luminosity is dominated by the release of shock-deposited energy in the ejecta. After ,100 d the luminosity is powered mostly by the deposition of radioactive decay energy from 0X150X05 M ( of 56 Ni which was produced in the explosion. We also report the discovery of an astonishingly high IR excess, K 2 L H 2X5Y that was present at day 130. We interpret this as being due to thermal emission from dust grains in the vicinity of the supernova. We argue that to produce such a high IR luminosity so soon after the explosion, the dust must be preexisting and so is located in the circumstellar medium of the progenitor. The dust could be heated either by the UV/optical flash (IR echo) or by the X-rays from the interaction of the ejecta with the circumstellar material.
We present a parallax measurement for the very cool degenerate WD 0346+246, the serendipitous discovery of which was reported by Hambly et al. We find an absolute parallax of 36±5 mas, yielding a distance estimate of 28±4 pc. The resulting absolute visual magnitude of the object is MV=16.8±0.3, making it the second‐lowest luminosity white dwarf currently known. We use the distance estimate and measured proper motion to show that the object has kinematics consistent with membership of the Galactic halo. WD 0346+246 is therefore by far the coolest and least luminous of only a handful of plausible halo white dwarf candidates. As such, the object has relevance to the ongoing debate concerning the results of microlensing experiments and the nature of any baryonic dark matter component to the Galactic halo residing in stellar remnants.
observations lying on either side of M13 and having a two-component structure ; the broad component (FWHM B 32 km s~1) has an H I column density of B5 ] 1019 cm~2, while the narrow component (FWHM B 8 km s~1) has a column density of B6 ] 1018 cm~2 as seen in the Synthesis Telescope observations. The cloudlets have an angular size B2@ and are only partially resolved in the synthesis telescope data. Fine-scale gas structure is also evident from the cluster star spectroscopy with variations in Na I column density of a factor of observed across the several arcminutes of the cluster face ; Z10 there is also evidence for structure on an angular scale of several arcseconds. A column density ratio Na I/H I B 4 ] 10~8 is measured for a cloudlet in the foreground of the cluster near the strongest Na I detection. Estimates are made of cloudlet gas density that are comparable with those reported for highvelocity cloud (HVC) concentrations. However, the present observations emphasize further the need for higher spatial resolution H I studies to provide Ðrmer estimates of cloud properties.
Using H I spectra obtained with the Lovell telescope (FWHM ∼ 12 arcmin) we present maps showing the H I distribution and velocity structure of an intermediate‐velocity cloud (IVC; vLSR ∼ 70 km s−1) which is observed in the general direction of the globular cluster M15. The gas is shown to be clumpy in nature and we examine its position and velocity structure. The IVC is detected in absorption in the Ca II K line towards five cluster stars in intermediate resolution spectra obtained with ISIS/WHT and in high resolution UES/WHT Na I D line spectra of two cluster stars (II‐75; IV‐38). The clumpy nature of the gas is indicated by the Na I and K I spectra obtained in the II‐75 and IV‐38 sightlines, which have angular separation ∼ 3.5 arcmin. The IVC is detected in K I in the higher column density II‐75 sightline; this appears to be the first detection of IVC or HVC gas in K I. The IVC gas towards M15 has a similar velocity to that observed towards HD 203664, some 3.1° away from the cluster. Similarities in the IVC gas velocity suggest a gas structure that extends across both sightlines, although gas column densities are considerably higher towards M15. For a common feature, this would place the M15 IVC at a height above the Galactic plane (z‐distance) of ≲ 1.5 kpc based on the Little et al. estimate of the HD 203664 distance. From the fine‐scale structure and column density observations, estimates are made of the space density of the small‐scale concentrations. However, these remain uncertain and the present observations emphasize the need for higher spatial and spectral resolution studies to provide firmer estimates of cloud properties. We report also on a radio H I and Ca II line survey towards a sample of 24 stars over a wider field. This was carried out in an attempt to detect any wider distribution of the IVC gas and to place better limits on its distance. Although these observations are of sufficient spectral quality, no new optical detections are reported.
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