David M. Rank

Airborne spectrophotometry of SN 1987A from 1.7 to 12.6 microns: time history of the dust continuum and line emission

Spectrophotometric observations (1.7-12.6 μm) of SN 1987A from the Kuiper Airborne Observatory are presented for five epochs at 60, 260, 415, 615, and 775 days after the explosion. A variety of emission lines is seen, including members of the hydrogen Humphreys, Pfund, Brackett, and Paschen series, fine-structure lines of metals (including (Ni II] 6.634 μm, (Ni I] 7.507 μm, (Ar II] 6.985 μm, and [Co II] 10.521 μm), and CO and SiO molecular bands. The temporal evolution of the seven strongest H lines follows case C recombination theory and yields large values of τ(Hα) at 260 and 415 days. A mass of ∼ 2 × 10 −3 M ○. is derived for stable nickel, and the ratio of the [Ni I] 7.507 μm and [Ni II] 6.634 μm line intensities yields a high ionization fraction of 0.9 in the nickel zone

Anatomy of the photodissociation region in the orion bar.

Much of the interstellar gas resides in photodissociation regions whose chemistry and energy balance is controlled by the flux of far-ultraviolet radiation upon them. These photons can ionize and dissociate molecules and heat the gas through the photoelectric effect working on dust grains. These regions have been extensively modeled theoretically, but detailed observational studies are few. Mapping of the prominent Orion Bar photodissociation region at wavelengths corresponding to the carbon-hydrogen stretching mode of polycyclic aromatic hydrocarbons, the 1-0 S(1) line of molecular hydrogen, and the J = 1-0 rotational line of carbon monoxide allows the penetration of the far-ultraviolet radiation into the cloud to be traced. The results strongly support the theoretical models and show conclusively that the incident far-ultraviolet radiation field, not shocks as has sometimes been proposed, is responsible for the emission in the Orion Bar.

Airborne and groundbased spectrophotometry of comet P/Halley from 5–13 micrometers

Spectrophotometry from 5-10 micrometers (delta lambda/lambda approximately 0.02) of comet Halley was obtained from the Kuiper Airborne Observatory on 1985 December 12.1 and 1986 April 8.6 and 10.5, UT. 8-13 micrometers data were obtained on 17.2 December 1985 from the Nickel Telescope at Lick Observatory. The spectra show a strong broad emission band at 10 micrometers and a weak feature at 6.8 micrometers. We do not confirm the strong 7.5 micrometers emission feature observed by the Vega 1 spacecraft. The 10 micrometers band, identified with silicate materials, has substructure indicative of crystalline material. The band can be fitted by combining spectra data from a sample of interplanetary dust particles. The primary component of the silicate emission is due to olivine. The 6.8 micrometers emission feature can be due either to carbonates or the C-H deformation mode in organic molecules. The lack of other emission bands is used to place limits on the types of organic molecules responsible for the emission observed by others at 3.4 micrometers. Color temperatures significantly higher than the equilibrium blackbody temperature indicate that small particles are abundant in the coma. Significant spatial and temporal variations in the spectrum have been observed and show trends similar to those observed by the spacecraft and from the ground. Temporal variability of the silicate emission relative to the 5-8 micrometers continuum suggests that there are at least two physically separated components of the dust.

3.3 and 11.3 micron images of HD 44179 : evidence for an optically thick polycyclic aromatic hydrocarbon disk

Images of HD 44179 (the Red Rectangle) obtained in the 3.3 and 11.3 micron emission bands show two different spatial distributions. The 3.3 micron band image is centrally peaked and slightly extended N-S while the 11.3 micron image shows a N-S bipolar shape with no central peak. If the 3.3 micron band image shows the intrinsic emission of the 11.3 micron band, then the data suggest absorption of the 11.3 micron emission near the center of HD 44179 by a disk with an optical depth of about one, making HD 44179 the first object in which the IR emission bands have been observed to be optically thick. Since there is no evidence of absorption of the 3.3 micron emission band by the disk, the absorption cross section of the 3.3 micron band must be substantially less than for the 11.3 micron band. Since the 3.3 and 11.3 micron bands are thought to arise from different size PAHs, the similar N-S extents of the two images implies that the ratio of small to large PAHs does not change substantially with distance from the center.

Spectral imaging of the Orion Bar at 3.3, 8.4, and 11.3 microns: Comparison with a fluorescent polycyclic aromatic hydrocarbon model

Spectral images were obtained of the Orion Bar which sample polycyclic aromatic hydrocarbon (PAH) emission at 3.3, 8.4, and 11.3 micrometers. The images are strikingly different even though they all sample PAH emission. In particular, the 3.3 and 11.3 micrometers images sample PAH emission from C-H bonds, yet the 3.3 micrometers image contains many small bright knots while the 11.3 micrometers image is much more uniform. For comparison with a fluorescent PAH model, a data set was created from the measured intensities of 250 locations in each image. From the comparison, we conclude that: (1) the size distribution of PAHs varies within the Bar, with the bright 3.3 micrometers knots containing the largest proportion of small PAHs; (2) the points along the front of the Bar have emission cross sections characteristic of neutral PAHs while within the Bar, the emission cross sections are different, consistent with the PAHs being charged; (3) the PAHs along the front of the Bar are larger than average for the Bar; (4) emission along the back of the Bar is consistent with PAH emission in an attenuated UV radiation field; (5) there is no evidence for PAH dehydrogenation.

2-12.5 micron imaging of IRAS 21282+5050 : the structure of a young planetary nebula

We present 3.3, 8.5, 10.0, 11.3, and 12.5 μm narrow-band (Δλ/λ ≃3%-10%) and K-band (2.2 μm) high spatial resolution images of IRAS 21282+5050 and a 6 cm flux density measurement. The new infrared images reveal a toroidal dust nebula, 4″.5×6″, P.A. 165°, with two prominent emission peaks aligned almost E-W and separated by 1″.7-2″.1; a remarkably similar structure to that observed in NGC 7027. From the 6 cm flux density and the dust nebula size, we derive an electron density of 3.6× 10 3 cm −3 for the central ionized region. Comparison of these images with a published CO 1-0 map suggests that the structure of this dusty, ionization-bounded planetary nebula may reflect the density inhomogeneities of the progenitors wind

Spectral imaging of the 3.3 and 11.3 micron emission bands in NGC 1333 - Discovery of spatially separate band emissions

Spectral images and aperture spectra were obtained of the nebula around the star SVS 3 in the star formation region NGC 1333. The spectra contain strong infrared emission bands originating from carbonaceous material. The spectra show the presence of the characteristic 3.3 and 11.3 μm emission features thought to be associated with C-H stretching and C-H out-of-plane bending modes, respectively, of polycyclic aromatic hydrocarbons (PAHs). The distribution of the 3.3 μm emission is suggestive of limb brightening from the edge of an emitting shell. The 3.3 and 11.3 μm emission features come from spatially distinct regions, with the 3.3 μm emission occurring outside the region of strongest 11.3 μm emission

3 micron spectrophotometry of comet Halley: evidence for water ice

Structure has been observed in the 3-3.6 micron preperihelion spectrum of Comet Halley consistent with either an absorption band near 3.1 microns or emission near 3.3 microns. The results suggest that a large fraction of the water molecules lost by the comet are initially ejected in the form of small ice particles rather than in the gas phase. 24 references.

Observations of infrared emission from a fast-moving knot in Cassiopeia A

Broadband (10 microns) and spectroscopic (8.99, 10.52 and 12.81 microns) scans were made of the metal-rich knots in Cas A using instrumentation at the NASA IR Telescope Facility. The observations were performed to distinguish between thermal continuum emission and other features of the metal-rich knots. A faint, forbidden Si IV line was detected, and upper limits were set on the forbidden Ar III and forbidden Ne II emissions, which are now expected to be completely due to lines that may be accessible to the 12 microns sensor on the IRAS. The implications of the measurements for the interpretation of broadband data on metal-rich remnants are discussed. 44 references.

The Lick Observatory Two Micron Camera

Lick Observatory has recently developed a near infrared camera for astronomical imaging. The new camera has been built around a Rockwell NICMOSII 256 x 256 HgCdTe focal plane array. The dewar and optics were manufactured by Infrared Laboratories in Tucson, Arizona while the electronics and data system were designed and fabricated at Lick Observatory.