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The True Shapes of the Dumbbell and the Ring
Using images centered around the 2.12 ?m line of molecular hydrogenobtained with the Wide Field Infrared Camera on the Canada-France-HawaiiTelescope, we show that in spite of the different apparent morphologies,the Dumbbell Nebula and the Ring Nebula share the same intrinsicthree-dimensional triple biconic structure.
| Adaptive Optics Imaging of IRAS 18276-1431: A Bipolar Preplanetary Nebula with Circumstellar ``Searchlight Beams'' and ``Arcs''
We present high angular resolution images of the post-AGB nebula IRAS18276-1431 (also known as OH 17.7-2.0) obtained with the Keck IIadaptive optics (AO) system in its natural guide star (NGS) mode in theKp, Lp, and Ms near-infrared bands. Wealso present supporting optical F606W and F814W HST images as well asinterferometric observations of the 12CO J=1-0, 13CO J=1-0, and 2.6 mm continuum emission with OVRO. The envelopeof IRAS 18276-1431 displays a clear bipolar morphology in our opticaland NIR images with two lobes separated by a dark waist and surroundedby a faint 4.5''×3.4'' halo. OurKp-band image reveals two pairs of radial ``searchlightbeams'' emerging from the nebula center and several intersecting,arclike features. From our CO data we derive a mass of M>0.38(D/3kpc)2 Msolar and an expansion velocityVexp=17 km s-1 for the molecular envelope. Thedensity in the halo follows a radial power law ~r-3, which isconsistent with a mass-loss rate increasing with time. Analysis of theNIR colors indicates the presence of a compact central source of~300-500 K dust illuminating the nebula in addition to the central star.Modeling of the thermal IR suggests a two-shell structure in the dustenvelope: (1) an outer shell with inner and outer radiusRin~1.6×1016 andRout>~1.25×1017 cm, dust temperatureTdust~105-50 K, and a mean mass-loss rate ofM˙~10-3 Msolar yr-1 and (2) aninner shell with Rin~6.3×1014 cm,Tdust~500-105 K, and M˙~3×10-5Msolar yr-1. An additional population of big dustgrains (radius a>~0.4 mm) with Tdust=150-20 K and massMdust=(0.16-1.6)×10-3(D/3 kpc)2Msolar can account for the observed submillimeter andmillimeter flux excess. The mass of the envelope enclosed withinRout=1.25×1017 cm derived from SED modelingis ~1(D/3 kpc)2 Msolar.
| A Variable Infrared Counterpart to the Soft Gamma-Ray Repeater SGR 1806-20
We present K'-band (2.12 ?m) imaging observations of theSGR 1806-20 field taken during its very active phase in mid-2004 theseobservations reveal brightening of sources within the Chandra X-rayerror circle when compared with earlier images obtained in 2002. Onesource brightened by more than a factor of 2, and so we consider this tobe the probable infrared counterpart to SGR 1806-20. The other twosources are located in close proximity to the probable counterpart andshow marginal brightening, which may suggest that the high-energyphotons emitted from the soft gamma-ray repeater (SGR) during its activephase have induced dust sublimation or brightening of the unresolvedbackground around the SGR.Based on data collected at the Subaru Telescope, which is operated bythe National Astronomical Observatory of Japan.
| L' and M' standard stars for the Mauna Kea Observatories Near-Infrared system
We present L' and M' photometry, obtained at the United Kingdom InfraredTelescope (UKIRT) using the Mauna Kea Observatories Near-Infrared(MKO-NIR) filter set, for 46 and 31 standard stars, respectively. The L'standards include 25 from the in-house `UKIRT Bright Standards' withmagnitudes deriving from Elias et al. and observations at the InfraredTelescope Facility in the early 1980s, and 21 fainter stars. The M'magnitudes derive from the results of Sinton and Tittemore. We estimatethe average external error to be 0.015 mag for the bright L' standardsand 0.025 mag for the fainter L' standards, and 0.026 mag for the M'standards. The new results provide a network of homogeneously observedstandards, and establish reference stars for the MKO system, in thesebands. They also extend the available standards to magnitudes whichshould be faint enough to be accessible for observations with moderndetectors on large and very large telescopes.
| JHK standard stars for large telescopes: the UKIRT Fundamental and Extended lists
We present high-precision JHK photometry with the 3.8-m UK InfraredTelescope (UKIRT) of 82 standard stars, 28 from the widely usedpreliminary list known as the `UKIRT Faint Standards', referred to hereas the Fundamental List, and 54 additional stars referred to as theExtended List. The stars have 9.4
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