Jesse D. Bregman

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

Mid-Infrared Observation of Mass Loss in Elliptical Galaxies

Early-type galaxies exhibit thermal and molecular resonance emission from dust that is shed and heated through stellar mass loss as a subset of the population moves through the asymptotic giant branch (AGB) phase of evolution. Because this emission can give direct insight into stellar evolution in addition to galactic stellar mass loss and interstellar medium injection rates, we conducted a program to search for this signature emission with CAM on the Infrared Space Observatory. We obtained 6-15 μm imaging observations in six narrow bands for nine elliptical galaxies; every galaxy is detected in every band. For wavelengths shorter than 9 μm, the spectra are well matched by a blackbody originating from the K and M stars that dominate the integrated light of elliptical galaxies. At wavelengths between 9 and 15 μm, however, the galaxies display excess emission relative to the stellar photospheric radiation. Additional data taken with the fine-resolution circular variable filter on one source clearly shows broad emission from 9 to 15 μm, peaking around 10 μm. This result is consistent with the known broad silicate feature at 9.7 μm originating in the circumstellar envelopes of AGB stars. This emission is compared with studies of Galactic and Large Magellanic Cloud AGB stars to derive cumulative mass-loss rates. In general, these mass-loss rates agree with the expected ~0.8 M☉ yr-1 value predicted by stellar evolutionary models. Both the photospheric and circumstellar envelope emission follow a de Vaucouleurs R1/4 law, supporting the conclusion that the mid-infrared excess emission originates in the stellar component of the galaxies and acts as a tracer of AGB mass loss and mass injection into the interstellar medium.

The dust coma of periodic Comet Churyumov-Gerasimenko (1982 VIII)

Abstract The dust coma of Comet P/Churyumov-Gerasimenko was monitored in the infrared (1–20 μm) from September 1982 to March 1983. Maximum dust production rate of ∼2 × 10 5 g/sec occured in December, 1 month postperihelion. The ratio of dust/gas production was higher than that in other short-period comets. No silicate feature was visible in the 8- to 13-μm spectrum on 23 October. The mean geometric albedo of the grains was ∼0.04 at 1.25 μm and ∼0.05 at 2.2 μm.

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.

Cold Dust in Early-Type Galaxies. I. Observations*

We describe far-infrared observations of early-type galaxies selected from the Infrared Space Observatory (ISO) archive. This rather inhomogeneous sample includes 39 giant elliptical galaxies and 14 S0 (or later) galaxies. These galaxies were observed with the array photometer PHOT on-board the ISO satellite using a variety of different observing modes—sparse maps, mini-maps, oversampled maps, and single pointings—each of which requires different and often rather elaborate photometric reduction procedures. The ISO background data agree well with the COBE-DIRBE results to which we have renormalized our calibrations. As a further check, the ISO fluxes from galaxies at 60 and 100 μm agree very well with those previously observed with IRAS at these wavelengths. The spatial resolution of ISO is several times greater than that of IRAS, and the ISO observations extend out to 200 μm, which views a significantly greater mass of colder dust not assessable to IRAS. Most of the galaxies are essentially point sources at ISO resolution, but a few are clearly extended at FIR wavelengths with image sizes that increase with FIR wavelength. The integrated far-infrared luminosities do not correlate with optical luminosities, suggesting that the dust may have an external, merger-related origin. In general, the far-infrared spectral energy distributions can be modeled with dust at two temperatures, ~43 and ~20 K, which probably represent limits of a continuous range of temperatures. The colder dust component dominates the total mass of dust, 106-107 M⊙, which is typically more than 10 times larger than the dust masses previously estimated for the same galaxies using IRAS observations. For S0 galaxies we find that the optically normalized far-infrared luminosity LFIR/LB correlates strongly with the mid-infrared luminosity L15 μm/LB, but that correlation is weaker for elliptical galaxies.

VARIATIONS OF THE MID-INFRARED EMISSION SPECTRUM IN REFLECTION NEBULAE

Using spatial-spectral data cubes of reflection nebulae obtained by ISOCAM, we have observed a shift in the central wavelength of the 7.7 μm band within several reflection nebulae. This band, composed of components at 7.85 and 7.65 μm, shows a centroid shift from 7.75 μm near the edge of the nebulae to 7.65 μm toward the center of the nebulae as the shorter wavelength component becomes relatively stronger. The behavior of the 7.7 μm band center can be explained by assuming either that anions are the origin of the 7.85 μm band and cations the 7.65 μm band, or that the band center wavelength depends on the chemical nature of the polycyclic aromatic hydrocarbons (PAHs). The ratio of the 11.3/7.7 μm bands also changes with distance from the central star, first rising from the center toward the edge of the nebula, then falling at the largest distances from the star, consistent with the 11.3/7.7 μm band ratio being controlled by the PAH ionization state.

The Ages of Elliptical Galaxies from Infrared Spectral Energy Distributions

The mean ages of early-type galaxies obtained from the analysis of optical spectra give a mean age of 8 Gyr at z = 0, with 40% being younger than 6 Gyr. Independent age determinations are possible by using infrared spectra (5-21 μm), which we have obtained with the Infrared Spectrograph on Spitzer. This age indicator is based on the collective mass-loss rate of stars, in which mass loss from AGB stars produces a silicate emission feature at 9-12 μm. This feature decreases more rapidly than the shorter wavelength continuum as a stellar population ages, providing an age indicator. From observations of 30 nearby early-type galaxies, 29 show a spectral energy distribution dominated by stars, and one has significant emission from the ISM and is excluded. The infrared age indicators for the 29 galaxies show them all to be old, with a mean age of about 10 Gyr and a standard deviation of only a few Gyr. This is consistent with the ages inferred from the values of M/LB, but is inconsistent with the ages derived from the optical line indices, which can be much younger. All of these age indicators are luminosity weighted and should be correlated, even if multiple-age components are considered. The inconsistency indicates that there is a significant problem with either the infrared and the M/LB ages, which agree, or with the ages inferred from the optical absorption lines.

Discovery of the 11.2 Micron Polycyclic Aromatic Hydrocarbon Band in Absorption toward Monoceros R2 IRS 3

Interpretation of the infrared emission bands is difficult because these bands likely arise from a mixture of ionized and neutral polycyclic aromatic hydrocarbon (PAH) molecules. Modeling the emission process is also difficult because the size distribution of the molecules, their ionization state and excitation, and the geometry of the emitting regions are generally unknown. If these molecular bands could be found in absorption, many of these factors would be eliminated, making it much easier to interpret the data. We have discovered an absorption band in Monoceros R2 IRS 3 centered at 11.25 μm that we identify with a C–H out-of-plane vibrational mode of PAH molecules. The shape and position of the band are very similar to that seen in emission in planetary nebulae, H II regions, and the interstellar medium.

Spectral irradiance calibration in the infrared. III - The influence of CO and SiO

We describe first efforts to establish a network of calibrated infrared spectra of «standard stars» suitable for calibration of at least low-resolution infrared spectrometers using ground-based, airborne, and satellite-borne broadband sensors. The focus of this paper is on the crucial 5-8 μm region, inaccessible from the ground, in K and M giants. In this region the fundamental bands of CO and SiO cause substantial departures from featureless pseudo-continua. These departures are, of course, well-known to stellar atmosphere theorists. However, they are still ignored by many astronomical infrared photometrists and spectroscopists who assume that these bright stars can be represent by blackbodies at their effective temperatures

Gas-Phase Polycyclic Aromatic Hydrocarbons in Absorption toward Protostellar Sources?*

One of the major criticisms of identifying the infrared emission bands with polycyclic aromatic hydrocarbon (PAH) molecules has been the lack of a match between laboratory spectra of individual PAHs and the emission features. Part of the difficulty arises from the complexity of modeling the emission mechanism with an a priori unknown mixture of ionized and neutral PAHs. A direct comparison between laboratory spectra of PAHs and astronomical sources is possible for absorption spectra. However, because of poor atmospheric transmission, ground-based spectra of the PAH absorption band in the C-H stretch region are too noisy to make a detailed comparison with laboratory spectra. In this paper we show that ISO Short Wavelength Spectrometer spectra of a few protostars that show a 3.25 μm absorption band can be well matched by laboratory absorption spectra of a mixture of isolated PAHs.