Lawrence John Caroff

Early science with SOFIA, the stratospheric observatory for infrared astronomy

The Stratospheric Observatory For Infrared Astronomy (SOFIA) is an airborne observatory consisting of a specially modified Boeing 747SP with a 2.7 m telescope, flying at altitudes as high as 13.7 km (45,000 ft). Designed to observe at wavelengths from 0.3 μm to 1.6 mm, SOFIA operates above 99.8% of the water vapor that obscures much of the infrared and submillimeter. SOFIA has seven science instruments under development, including an occultation photometer, near-, mid-, and far-infrared cameras, infrared spectrometers, and heterodyne receivers. SOFIA, a joint project between NASA and the German Aerospace Center Deutsches Zentrum fur Luft und-Raumfahrt, began initial science flights in 2010 December, and has conducted 30 science flights in the subsequent year. During this early science period three instruments have flown: the mid-infrared camera FORCAST, the heterodyne spectrometer GREAT, and the occultation photometer HIPO. This Letter provides an overview of the observatory and its early performance.

Far-infrared spectrophotometry of Saturn and its rings

Abstract The spectrum of Saturn was measured from 80 to 350 cm −1 (29 to 125 μm) with ≈6- cm −1 resolution using a Michelson interferometer aboard NASAs Kuiper Airborne Observatory. These observations are of the full disk, with little contribution from the rings. For frequencies below 300 cm −1 , Saturns brightness temperature rises slowly, reaching ≈111°K at 100 cm −1 . The effective temperature is 96.8 ± 2.5°K, implying that Saturn emits 3.0 ± 0.5 times as much energy as it receives from the Sun. The rotation-inversion manifolds of NH 3 that are prominent in the far-infrared spectrum of Jupiter are not observed on Saturn. Our models predict the strengths to be only ≈2 to 5°K in brightness temperature because most of the NH 3 is frozen out; this is comparable to the noise in our data. By combining our data with those of an earlier investigation when the Saturnicentric latitude of the Sun was B ′ = 21.2°, we obtain the spectrum of the rings. The high-frequency end of the ring spectrum ( ν > 230 cm −1 ) has nearly constant brightness temperature of 85°K. At lower frequencies, the brightness temperature decreases roughly as predicted by a simple absorption model with an optical depth proportional to ν 1.5 . This behavior could be due to mu-structure on the surface of the ring particles with a scale size of 10 to 100 μm and/or to impurities in their composition.

The brightness temperatures of Saturn and its rings at 39 microns

We have resolved the relative rings-to-disk brightness (specific intensity) of Saturn at 39 μm (δλ ≃ 8 μm) using the 224-cm telecscope at Mauna Kea Oservatory, and have also measured the total flux of Saturn relative to Jupiter in the same bandpass from the NASA Learjet Observatory. These two measurements, which were made in early 1975 with Saturns rings near maximum inclination (b′ ≃ 25°), determine the disk and average ring (A and B) brightness in terms of an absolute flux calibration of Jupiter in the same bandpass. While present uncertainties in Jupiters absolute calibration make it possible to compare existing measurementsunambiguously, it is nevertheless possible to conclude the following: (1) observations between 20 and 40 μm are all compatible (within 2σ) of a disk brightness temperature of 94°K, and do not agree with the radiative equilibrium models of Trafton; (2) the rings at large tilt contribute a flux component comparable to that of the planet itself for λ ≲ 40 μm and (3) there is a decrease of ∼22% in the relative ring: disk brightness between effective wavelengths of 33.5 and 39 μm.

Spectrum of the Kleinmann-Low nebula from 29 to 125 micrometers

The infrared spectrum of the Kleinmann-Low nebula in M42 has been measured from 80 to 350 cm/sup -1/ (approx.29--125 ..mu..m) with a Michelson interferometer aboard the NASA G. P. Kuiper Airborne Observatory. The frequency spectrum peaks at approx.185 cm/sup -1/. A simple model of the emission implies that the temperature is in the range 70--95 K, and that the optical depth is > or =0.2 at the peak frequency. A possible absorption is seen at approx.176 cm/sup -1/. Thermal emission by dust at a temperature of 71 K, with the absorption cross section proportional to frequency, provides a good fit to the data. Other thermal emission models can also fit the spectrum. The data are compared with previous broad-band measurements. Upper limits are placed on expected line emission from the surrounding H II region at the position of the nebula.

The far-infrared spectrum of the core of Sagittarius B2

A Michelson interferometer aboard NASAs Kuiper Airborne Observatory has been used to measure the spectrum of Sgr B2 from 40 to 200 kaysers with 5-kayser resolution in a 1.4-arcmin beam. The measured spectrum is smooth and featureless with a broad maximum at about 85 kaysers. The data can be fitted analytically with a model corresponding to thermal emission by a uniform sla of dust filling the beam, with an average temperature of approximately 32 K, an optical depth at 100 microns of about 1.6, and a spectral index of the dust emissivity about 1.5. The absence of features implies either that the source is optically thick or that the emission spectrum of the individual grains is smooth in the passband. The possible physical significance of this model is discussed.

Infrared spectrum of the Orion Nebula between 55 and 200 microns

The infrared spectrum of the Trapezium region of the Orion Nebulala has been measured between the wavelengths of 55 mu and 200 mu Observations were made at 44,000 feet (13,500 m) using a 12-inch (30-cm) telescope, Michelson interferometer, and a gallium-doped germanium detector aboard a Lear jet. The shape of the spectrum is compatible with a color temperature of 70 deg K. (auth)

Application of the collective approach to the thermodynamics of an electron gas

The collective approach of Pines & Bohm has been applied to the problem of the thermodynamics of the N -particle electron gas including transverse radiation. Partitioning of the internal energy and certain of the other thermodynamic quantities is discussed generally. The system is seen to divide itself into three approximately independent subsystems: (1) an infinite set of free harmonic oscillators, corresponding to the transverse field, with an energy spectrum given by ω T (κ), where ω T (κ), is given by the dispersion relation for transverse electromagnetic waves in a plasma; (2) a set of 8 free harmonic oscillators corresponding to the longitudinal (plasma) oscillations, with an energy spectrum ω T (κ), given by the dispersion relation for plasma oscillations; and (3) a set of (N — 2s/3) quasi-particles of mass approximately equal to the electron mass, interacting via a short-range potential which is essentially screened Coulomb. Analytical expressions for the energy, pressure, and constant-volume specific heat of the transverse oscillators are given, together with approximate expressions applicable to the high-density—low-temperature and low-density—high-temperature limits. Detailed numerical calculations of the internal energy and pressure of the longitudinal modes are presented. In addition, the contributions to the energy and pressure from the particle portion are evaluated in the low-density—high-temperature limit as functions of the cut-off wave vector κ c ; κ c is the maximum k-vector of the longitudinal oscillators.

Water vapor absorption spectra of the upper atmosphere (45–185 cm −1 )

The far ir nighttime absorption spectrum of the earths atmosphere above 14 km is determined from observations of the bright moon. The spectra were obtained using a Michelson interferometer attached to a 30-cm telescope aboard a high-altitude jet aircraft. Comparison with a single-layer model atmosphere implies a vertical column of 3.4 +/- 0.4 mum of percipitable water on 30 August 1971 and 2.4 +/- 0.3 mum of precipitable water on 6 January 1972.

The far-infrared spectrum of S140 IR

The spectrum of S140 IR from 65 to 345 kaysers (155-29 microns) has been measured with 9.4-kayser resolution. The emission in this spectral range is consistent with a 9-arcsec-diameter blackbody radiating at a temperature of 70 K. Attempts at finding a self-consistent radiative-transfer model of the source suggest that the near- and far-infrared observations cannot result from a spherically symmetric nebula with a continuous density distribution and a central exciting source. A number of compact near-infrared sources may be embedded in the cloud.

Far Infrared Spectral Observations of the Galactic Center Region from the Gerard P. Kuiper Airborne Observatory

Low resolution spectra in the region 45–250 microns of SgrA and SgrB2 were obtained in July/August, 1975, with the 91 cm telescope on the Gerard P. Kuiper Airborne Observatory. The spectra were taken with a single-beam Michelson interferometer utilizing a Mylar beam-splitter and a Ge-Ga bolometer with a beam diameter of 1.4 min. FWHM. Preliminary results give mean brightness temperatures for SgrA of roughly 90°K and for SgrB2 of roughly 40°K. SgrA was observed with a resolution of approximately 6 cm-1, while the resolution for B2 is approximately 3 cm-1. In addition, the HII region NGS 7538 was also observed at approximately 9 cm-1 resolution. The data will be presented and discussed.