ALBERT

Description: We describe our efforts to seek "closure" in our infrared absolute calibration scheme by comparing spectra of asteroids, absolutely calibrated through reference stars, with "Standard Thermal Models" and "Thermophysical Models" for these bodies. Our use of continuous 5-14 microns airborne spectra provides complete sampling of the rise to, and peak, of the infrared spectral energy distribution and constrains these models. Such models currently support the absolute calibration of ISO-PHOT at far-infrared wave- lengths (as far as 300 microns), and contribute to that of the Mid-Infrared Spectrometer on the "Infrared Telescope in Space" in the 6-12 microns region. The best match to our observed spectra of Ceres and Vesta is a, standard thermal model using a beaming factor of unity. We also report the presence of three emissivity features in Ceres which may complicate the traditional model extrapolation to the far-infrared from contemporaneous ground-based N-band photometry that is used to support calibration of, for example, ISO-PHOT. While identification of specific materials that cause these features is not made, we discuss families of minerals that may be responsible.

Description: SOFIA (Stratospheric Observatory for Infrared Astronomy) will be a telescope with 2.5 m effective aperture operating at altitudes of 12.5 to 13.7 km in a Boeing 747 aircraft. It will enable astronomers on board to make observations which are impossible from the ground at wavelengths between 0.3 microns and 1.5 mm. Diffraction-limited imaging will be possible at wavelengths beyond about 10 microns. SOFIA's mobility will assure all-sky coverage and access to transient events from anywhere in the world. Some of the science topics to be studied will be star and planet formation, origin and evolution of biogenic materials, comets and planetary atmospheres in the solar system, the interstellar media of other galaxies, and phenomena at our galactic center. The SOFIA concept is based on 21 years of experience with NASA's Kuiper Airborne Observatory (KAO), which has been retired to help fund the project. As with the KAO, state-of-the-art focal plane instruments and a vigorous educational outreach program will be features of this new airborne astronomy facility. A more intensive flight program, approximately 150 flights per year, will accommodate many more guest investigators however. Planned as a collaboration between the United States and Germany, SOFIA is scheduled to begin a 20 year operating lifetime in 2001.

Description: The possibility of extra-solar planets has been a very popular topic with the general public for years. Considerable media coverage of recent detections has only heightened the interest in the topic. School children are particularly interested in learning about space. Astronomers have the knowledge and responsibility to present this information in both an understandable and interesting format. Since most classrooms and homes are now equipped with computers this media can be utilized to provide more than a traditional "flat" presentation. An interactive "stack" has been developed using Hyperstudio (TM). The major topics include: "1996 - The Break Through Year In Planet Detection"; "What Determines If A Planet Is Habitable?"; "How Can We Find Other Planets (Search Methods)"; "All About the Kepler Mission: How To Find Earth-Sized Planets"; and "A Mission Simulator". Using the simulator, the student records simulated observations and then analyzes and interprets the data within the program stacks to determine the orbit and planet size, the planet's temperature and surface gravity, and finally determines if the planet is habitable. Additional related sections are also included. Many of the figures are animated to assist in comprehension of the material. A set of a dozen lesson plans for the middle school has also been drafted.

Description: Herbig Ae/Be stars are intermediate mass pre-main sequence stars, the higher mass analogues to the T Tauri stars. Because of their higher mass, they are expected form more rapidly than the T Tauri stars. Whether the Herbig Ae/Be stars accrete only from collapsing infalling envelopes or whether accrete through geometrically flattened viscous accretion disks is of current debate. When the Herbig Ae/Be stars reach the main sequence they form a class called Vega-like stars which are known from their IR excesses to have debris disks, such as the famous beta Pictoris. The evolutionary scenario between the pre-main sequence Herbig Ae/Be stars and the main sequence Vega-like stars is not yet revealed and it bears on the possibility of the presence of Habitable Zone planets around the A stars. Photometric studies of Herbig Ae/Be stars have revealed that most are variable in the optical, and a subset of stars show non-periodic drops of about 2 magnitudes. These drops in visible light are accompanied by changes in their colors: at first the starlight becomes reddened, and then it becomes bluer, the polarization goes from less than 0.1 % to roughly 1% during these minima. The theory postulated by V. Grinnin is that large cometary bodies on highly eccentric orbits occult the star on their way to being sublimed, for systems that are viewed edge-on. This theory is one of several controversial theories about the nature of Herbig Ae/Be stars. A 5 year mid-IR spectrophotometric monitoring campaign was begun by Wooden and Butner in 1992 to look for correlations between the variations in visible photometry and mid-IR dust emission features. Generally the approximately 20 stars that have been observed by the NASA Ames HIFOGS spectrometer have been steady at 10 microns. There are a handful, however, that have shown variable mid-IR spectra, with 2 showing variations in both the continuum and features anti-correlated with visual photometry, and 3 showing variations in the emission features only while the continuum level remained unchanged. The first 2 stars mentioned probably have reprocessing envelopes. The other 3 stars gives important clues to the controversy over the geometry of the gas and dust around these pre-main sequence stars: the steady underlying 10 microns continuum and variable features indicates that an optically thick continuum probably arising from an accretion disk is decoupled from the optically thin emission features which may arise in a disk atmosphere. Bernadette Rodgers has joined this monitoring campaign in the near-IR using GRIMII with the goal of detecting variations in the hot dust continuum and the gas density in the dense accretion region close to these stars.

Description: The mid- and far-infrared (IR) spectra of the nebular phase of SM 987A spans 250 days through more than 1000 days after the event. Analysis of the spectra, largely obtained from the Kuiper Airborne Observatory, leads to a rich picture of the structure of the supernebula. The evidence for dust grain formation. In the nebula after about 580 days will be reviewed. The dust continuum emission spectrum was gray and dust appears to have condensed in optically thick 'clumps' throughout a significant fraction of the nebula. Additional information is contained in the original extended abstract.

Description: The Galactic Center H(II) region, G0.18-0.04, the 'Sickle', is located where the nonthermal 'Arc' crosses the Galactic plane. The Sickle appears to be the ionized edge of a dense molecular cloud. The source of ionization has been ascribed to both the interaction of the cloud with the magnetic field of the Arc and to the hot stars in the adjacent cluster, AFGL 2004, also known as the 'Quintuplet Cluster'. This paper addresses the relative locations of the stars, the ionized and molecular gas, and the sources of gas excitation and dust heating. Using NASA's Kuiper Airborne Observatory, we have observed the far infrared forbidden lines of [S(III)] 18.7 and 33.5 micrometers, [Si(II)] 34.8 micrometers, [Ne(III)] 36.0 micrometers, [O(III)] 51.8 and 88.4 micrometers, [N(III)] 57.3 micrometers, [O(II)] 63.2 and 146 micrometers, [C(II)] 158 micrometers, and [N(II)] 205 micrometers and the adjacent continua at 11 positions around G0.18-0.04, including G0.15-0.05, the 'Pistol', in a beamsize of 40 - 60 arcsec. The electron density, the ionic abundances, and the ionization structure of the H(II) region are estimated from the doubly ionized line fluxes. The density and radiation field found in the photodissociation region (PDR) between the H(II) region and the molecular cloud are estimated from the [C(II)] and [O(I)] line fluxes and the far-infrared continuum. We compare the ionization structure and the PDR properties to shell models of H(II) regions with varying distances from their exciting stars. The agreement of observations and models indicates that the hot stars of AFGL 2004 are the likely source of ionization of the Sickle. Additional hot stars are necessary to ionize the more outlying positions. However, because of its low ionization and high PDR radiation field, the Pistol cannot be as close to AFGL 2004 as indicated by its close proximity on the sky. Instead, the Pistol is probably ionized by the luminous blue variable candidate, Pistol Source A. We estimated the extinction to the region from the distribution of the J, H, and K' magnitudes of the stars in the field that we measured from the Anglo-Australian telescope and from the IRAS LRS spectrum of AFGL 2004. The extinction is fairly uniform, with no enhancement from the molecular cloud. The strength of Brackett gamma, the 19-micrometer lines and continuum, and the IRAS 25-micrometer continuum are all consistent with the absence of a dense, foreground molecular cloud. We conclude that the H(II) region is on the near side of the dense cloud.

Description: NASA's airborne astronomy program offers a unique opportunity for K-12 science teacher enrichment and for NASA to reach out and serve the educational community. Learning from a combination of summer workshops, curriculum supplement materials, training in Internet skills and ultimately flying on NASA's C-141 airborne observatory, the teachers are able to share the excitement of scientific discovery with their students and convey that excitement from first hand experience rather than just from reading about science in a textbook. This year the program has expanded to include teachers from the eleven western states served by NASA Ames Research Center's Educational Programs Office as well as teachers from communities from around the country where the scientist who fly on the observatory reside. Through teacher workshops and inservice presentations, the FOSTER (Flight Opportunities for Science Teacher EnRichment) teachers are sharing the resources and experiences with many hundreds of other teachers. Ultimately, the students are learning first hand about the excitement of science, the scientific method in practice, the team work involved, the relevance of science to their daily lives and the importance of a firm foundation in math and science in today's technologically oriented world.

Description: We present five new absolutely calibrated continuous stellar spectra from 1.2 to 35 microns, constructed as far as possible from actual observed spectral fragments taken from the ground, the Kuiper Airborne Observatory (KAO), and the IRAS Low Resolution Spectrometer (LRS). These stars, Beta Peg, Delta Boo, Beta And, Beta Gem, and Delta Hya, augment our already created complete absolutely calibrated spectrum for a Tau. All these spectra have a common calibration pedigree. The wavelength coverage is ideal for calibration of many existing and proposed ground-based, airborne, and satellite sensors.

Description: We have obtained narrow-band images of M17 SW and the Orion Bar in the PAH emission bands and pedestal (3.29, 3. 36, 3. 42 microns) The emission bands at 3.3 and 3.4 microns arise from the photodissociation regions (PDRs) between ionized gas and molecular clouds. In both M17 SW and the Orion Bar, the PDRs are nearly edge-on, providing excellent opportunities for comparing models of PDRs with observations. We observe an exponential drop in the strength of the 3.3 micron emission with a 1/e distance of 9 arcsec in Orion and 5 arcsec in M17 SW, in good agreement with previous observations. These results show that the two regions are very similar, and they imply that the mean density is 2.4 times higher in the Orion Bar than in the M17 SW PDR. However, we also find that in the Orion Bar, the ratio of the 3.4 micron emission to the 3.3 micron emission is consistent with the 1/e distance of 3 arcsec determined from PDR models fit to the molecular H and CO in the Orion Bar. We are presently investigating how the main band can imply that the UV field is dropping with a 1/e distance of 9 arcsec while the model PDR predicts a 1/e distance of 3 arcsec.

Description: Rocket and satellite IR sky surveys have revealed vast populations of extreme AGB stars with substantial circumstellar dust shells. It is normally assumed that these shells permit essentially no light to escape. However, using the Lick 3 meter reflector we have been able to secure and analyze a large number of spectra of a well-defined sample of these extreme evolved stars. From this archive we have determined that these objects are all long period Mira variables and have estimated their periods, correlated these with IR photometric variations, and deduced distances to the stars. The data reveal a population of disk carbon-giants, typically of 1-2 yr periods, mostly within 2 kpc of the sun. We have also been able to quantify the thickness of their dust shells.