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Bregman, J.

Publications and source records attributed to Bregman, J..

17 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

The NASA X-Ray Mission Concepts Study

The 2010 Astrophysics Decadal Survey recommended a significant technology development program towards realizing the scientific goals of the International X-ray Observatory (IXO). NASA has undertaken an X-ray mission concepts study to determine alternative approaches to accomplishing IXO's high ranking scientific objectives over the next decade given the budget realities, which make a flagship mission challenging to implement. The goal of the study is to determine the degree to which missions in various cost ranges from $300M to $2B could fulfill these objectives. The study process involved several steps. NASA released a Request for Information in October 2011, seeking mission concepts and enabling technology ideas from the community. The responses included a total of 14 mission concepts and 13 enabling technologies. NASA also solicited membership for and selected a Community Science Team (CST) to guide the process. A workshop was held in December 2011 in which the mission concepts and technology were presented and discussed. Based on the RFI responses and the workshop, the CST then chose a small group of notional mission concepts, representing a range of cost points, for further study. These notional missions concepts were developed through mission design laboratory activities in early 2012. The results of all these activities were captured in the final X-ray mission concepts study report, submitted to NASA in July 2012. In this presentation, we summarize the outcome of the study. We discuss background, methodology, the notional missions, and the conclusions of the study report.

Petre, Robert↗
NASA NTRS2004

Identifying Organic Molecules in Space: The AstroBiology Explorer (ABE) Mission Concept

The AstroBiology Explorer (ABE) mission concept consists of a modest dedicated space observatory having a 60 cm class primary mirror cooled to T less than 50 K equipped with medium resolution cross-dispersed spectrometers having cooled large format near- and mid-infrared detector arrays. Such a system would be capable of addressing outstanding problems in Astrochemistry and Astrophysics that are particularly relevant to Astrobiology and addressable via astronomical observation. The mission's observaticxiai program woiild make fundamental scieztific: prngress in establishing the nature, distribution, formation and evolution of organic and other molecular materials in the following extra-terrestrial environments: 1) The Outflow of Dying Stars; 2) The Diffuse Interstellar Medium (DISM); 3) Dense Molecular Clouds, Star Formation Regions, and Young Stellar/Planetary Systems; 4) Planets, Satellites, and Small Bodies within the Solar System; and 5) The Interstellar Media of Other Galaxies ABE could make fundamental progress in all of these area by conducting a 1 to 2 year mission to obtain a coordinated set of infrared spectroscopic observations over the 2.5 - 20 micron spectral range at a spectral resolution of R greater than 2500 of about 1500 galaxies, stars, planetary nebulae, young stellar objects, and solar system objects.

Ennico, Kimberly↗
NASA NTRS2004

Identifying Organic Molecules in Space: The AstroBiology Explorer (ABE) Mission Concept

The AstroBiology Explorer (ABE) mission concept consists of a dedicated space observatory having a 60 cm class primary mirror cooled to T < 50 K equipped with medium resolution cross-dispersed spectrometers having cooled large format near- and mid-infrared detector arrays. Such a system would be capable of addressing outstanding problems in Astrochemistry and Astrophysics that are particularly relevant to Astrobiology and addressable via astronomical observation. The mission s observational program would make fundamental scientific progress in establishing the nature, distribution, formation and evolution of organic and other molecular materials in the following extra-terrestrial environments: 1) The Outflow of Dying Stars, 2) The Diffuse Interstellar Medium, 3) Dense Molecular Clouds, Star Formation Regions, and Young StellarPlanetary Systems, 4) Planets, Satellites, and Small Bodies within the Solar System, and 5 ) The Interstellar Media of Other Galaxies. ABE could make fundamental progress in all of these areas by conducting a 1 to 2 year mission to obtain a coordinated set of infrared spectroscopic observations over the 2.5-20 micron spectral range at a spectral resolution of R > 2000 of about 1500 objects including galaxies, stars, planetary nebulae, young stellar objects, and solar system objects. Keywords: Astrobiology, infrared, Explorers, interstellar organics, telescope, spectrometer, space, infrared detectors

Ennico, K. A.↗
NASA NTRS1996

An Infrared Study of the Juggler Nebula

This work is an examination of the infrared reflection nebula surrounding a protostellar source, IRS 1, in the CRL 2136 region at 2.2, 3.08, and 3.45 micron. The greatest absorption due to water ice occurs within 5 arcsec (10,000 AU, D = 2000 pc) of IRS 1. The water ice absorption decreases with increasing radius from IRS 1. This Tau(sub ice) structure suggests that the water ice is primarily associated with IRS 1. The flux from IRS 1 has a (2.2) - (3.45) color of 5, much redder than the nebula. The color structure combined with the Tau(sub ice) structure suggests the presence of an icy-dusty disk around IRS 1 orientated NE to SW. Radio CO maps presented by Kastner et al. reveal a molecular outflow orientated perpendicular to the disk. The south and east reflection lobes line the conical cavity created by the blueshifted molecular outflow.

Holbrook, J. C.↗
NASA NTRS1996

The infrared spectrum of the Galactic center and the composition of interstellar dust

We have obtained 5-8 micrometers spectra of the Galactic center from the Kuiper Airborne Observatory at resolving powers of approximately 50, approximately 150, and approximately 300. These spectra show absorption features at 5.5, 5.8, 6.1, and 6.8 micrometers. Together with previously observed features in the 3 micrometers region, these features are compared with laboratory spectra of candidate materials. The 3.0 and 6.1 micrometers features are due to the OH stretching and bending variations of H2O and are well fitted by water of hydration in silicates (e.g., talc). The 3.0 micrometer band is equally well fitted by ice mixtures containing 30% H2O, but such mixtures do not provide a good fit to the observed 6.1 micrometer band. The 3.4 and 6.8 micrometers features are identified with the CH stretching and deformation modes in CH2 and CH3 groups in saturated aliphatic hydrocarbons. The 6.1 micrometer band shows a short wavelength shoulder centered on 5.8 micrometer, attributed to carbonyl (C double bond O) groups in this interstellar hydrocarbon dust component. Finally, the narrow 5.5 micrometer feature is also attributed to carbonyl groups, but in the form of metal carbonyls [e.g., Fe(CO)4]. We have derived column densities and abundances along the line of sight toward the Galactic center for the various identified dust components. This analysis shows that hydrocarbon grains contain only 0.08 of the elemental abundance of C and contribute only a relatively minor fraction (0.1) of the total dust volume. Most of the interstellar dust volume is made up of silicates (approximately 0.6). Small graphite grains, responsible for the 2200 angstroms bump, account for 0.07 of the total dust volume. The remaining one-quarter of the interstellar dust volume consists of a material(s) without strong IR absorption features. Likely candidates include large graphite grains, diamonds, or amorphous carbon grains, which all have weak or no IR active modes. Finally, various models for the origin of the hydrocarbon dust component of the interstellar dust are discussed. All of them face some problems in explaining the observations, in particular, the absence of the spectroscopic signature of hydrocrbon grains in sources associated with molecular clouds.

NASA Discipline Exobiology↗
NASA NTRS1995

Simultaneous UV, optical and radio monitoring of the BL Lac object OJ 287 in March 1993

The BL Lacertae object OJ 287 was intensively monitored with the IUE satellite from 1993 March 15 to 20 in the 2000-3000 A wavelength region. The very low emission state of the source hampered the detection during part of the 23 performed exposures. The light curve at 2650 A constructed with the 11 best images exhibits a variable trend with a factor is less than or approximately 2 enhancement of the flux in about 3 hours. Simultaneous ground based observations show an optical flux variability of smaller amplitude, but correlated with the UV light curve without any apparent lag. The radio light curve is nearly constant. The UV emission state is the weakest observed in 15 years for this flaring blazard, being a factor of less than orapproximately 20 lower than the maximum recorded one.

Pian, E.↗
NASA NTRS1995

The 5-8 Micron Infrared Spectrum of the Galactic Center and the Composition of Interstellar Dust

Interstellar dust is an important component of the interstellar medium which dominates the opacity and, hence, regulates radiative transfer, molecule formation, and thermal balance of the ISM. Much of our knowledge on the composition of interstellar dust results from infrared spect,oscopy. The extinction along the line of sight towards the galactic center is believed to be dominated by dust in the diffuse ISM. Because of the high extinction and high IR flux, IR spectra of galactic center sources have been a prime sampling ground for the characteristics of interstellar dust. We have obtained 5-8 micrometer spectra of the galactic center using the KAO. These spectra show absorption features at 5.5, 5.8, 6.1, and 6.8 micrometers. Together with features in the 3 micrometer region previously observed by us using the IRTF, these features are compared to laboratory spectra of candidate materials. We conclude that the 3.0 and 6.1 micrometer feature are carried by H2O, likely in the form of water of hydration in interstellar silicates. The 3.4, 5.5, 5.8, and 6.8 micrometer features are due to CH2, CH3 and C=O stretching and deformation modes in a hydrocarbon grain component. Comparing derived dust abundances, we conclude that silicates dominate the interstellar dust volume. Hydrocarbon and (small) graphite grains contribute each about 0.1. The remainder of the interstellar dust volume does not show strong IR absorption features and is likely in the form of large graphite, amorphous, carbon, or diamond grains.

Tielens, A. G. G. M.↗
NASA NTRS1994

The Infrared Reflection Nebula Around the Protostellar System in S140

We have studied the protostellar system in S140 at 2.2, 3.1 and 3.45 microns using a 128x128 InSb array at the Lick Observatory 3m telescope. Besides the protostellar sources, the data reveal a bright infrared reflection nebula. We have developed a simple model of this region and derived the physical conditions. IRSI is surrounded by a dense dusty disk viewed almost edge-on. Photons leaking out through the poles illuminate almost directly north and south the inner edge of a surrounding shell of molecular gas, Analysis of the observed colors and intensities of the NIR light, using Mie scattering theory, reveal that the dust grains in the molecular cloud are somewhat larger than in the general diffuse interstellar medium. Moreover, the incident light has a "cool" color temperature, approximately equals 800K, and likely originates from a dust photosphere close to the protostar. Finally, we find little H2O ice associated with the dusty disk around IRSI. Most of the 3.1 micron ice extinction arises instead from cool intervening molecular cloud material. We have compared our infrared dust observations with millimeter and radio observations of molecular gas associated with this region. The large scale structure observable in the molecular gas is indicative of the interaction between the protostellar wind and the surrounding molecular cloud rather than the geometry of the protostellar disk. We conclude that S140 is a young blister formed by this outflow on the side of a molecular cloud and viewed edge-on.

Harker, D.↗
NASA NTRS1993

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 photo-dissociation region at wavelengths corresponding to the carbon-hydrogen stretching mode of polycyclic aromatic hydrocarbons, the 1-0 S(l) 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.

Tielens, A. G. G. M.↗
NASA NTRS1989

Airborne observations of the infrared emission bands

The data concerning low resolution airborne spectra from 5 to 8 microns available for a sample of 40 sources selected from the Infrared Astronomy Satellite low resolution spectral Atlas with polycyclic aromatic hydrocarbon (PAH) emission features, are discussed. A new emission band at 5.2 microns, previously predicted for PAHs, was found in 33 sources; it also correlates with the 7.7 microns band. This extends the spectrum of narrow observed PAH features to 3.3, 5.2, 5.6, 6.2, 6.9, 7.7, 8.7, 11.3, and 12.7 microns. From the data the relative strengths of most of these bands are defined in three separate nebular environments: planetaries, H II regions, and reflection nebulae. The differences in the PAHs spectra in those environments are analyzed.

Cohen, M.↗
NASA NTRS1986

The infrared emission bands. I - Correlation studies and the dependence on C/O ratio

Airborne measurements obtained for the unidentified IR (UIR) 5-8 micron emission bands of eight planetaries, eight locations in five reflection nebulae, and seven locations in four H II regions (including the Orion Bar), are presently compared with existing and new ground-based observations of the 3.3, 8.7, and 11.3 micron bands. The good correlations found between the strengths of all pairs of bands lead to the conclusion that all seven UIR features form a 'generic spectrum', although there are significant variations in the relative strengths of the features among the sources. The fraction of total far-IR luminosity radiated by a planetary in the strongest UIR feature at 7.7 microns is strongly correlated with the nebular C/O ratio, strongly suggesting that hydrocarbons are the carriers of these features.

Cohen, M.↗
NASA NTRS1986

Interstellar grain mantles

Interstellar molecular grain mantles are an important component of the interstellar dust inside dense molecular clouds as evidenced by the detection of absorption bands at 2.97, 3.08, 4.61, 6.0 and 6.8 microns. Mantles may also be the precursors of more complex grain mantles in the diffuse interstellar medium. The molecular composition of these icy grain mantles were calculated employing gas phase as well as grain surface reactions. The calculated mixtures consist mainly of the molecules H2O, H2CO, N2, CO, O2, H2O2, NH2, and their deuterated counterparts in varying ratios. The exact compositions depend strongly on the physical conditions in the gas phase. The absorption spectra of H2O with other molecules was studied in the laboratory. Optical constants were determined for a few selected mixtures. Extinction and polarization cross sections across the 3 micron ice band were calculated. A comparison with the observations towards BN shows that the low frequency wing observed on this feature is due to absorption by a mixture of H2O and other molecules rather than scattering by large, pure H2O ice grains.

Bregman, J.↗
NASA NTRS1984

Absorption features in the 5-8 micron spectra of protostars

High signal-to-noise ratio spectra in the range of 5-8 microns of four sources embedded in molecular clouds are examined using low-temperature laboratory measurements of the 5-8-micron spectra of simple molecules and their mixtures. The absorption, apparent in all four sources, is characterized by highly distinct features ranging from two relatively narrow bands at 6.0 and 6.8 microns in W33A to a broad, shallow, and partially structured feature extending from 5.2 to 7.8 microns in Mon R2-IRS2, BN, and NGC2264. The first feature (W33A) is explained by the OH bending mode in H2O and the CH deformation modes in saturated hydrocarbons; while the second feature (Mon R2-IRS2-type) is explained by the presence of a mixture of saturated and unsaturated hydrocarbons possibly containing strongly electronegative groups.

Tielens, A. G. G. M.↗
NASA NTRS1984

The Unidentified Emission Features: a Study of the Orion Bar and Planetary Nebulae

The unidentified emission features which are a group of broad emission bands found between 3.3 and 11.3 micro m in many objects which emit UV radiation and are associated with dust were studied. The features emit a substantial fraction of the energy in this wavelength range, and must therefore be an important constituent of the material around these objects. A two phase approach to the problem to better define the factors affecting the features was undertaken. The number of objects with good spectra between 3 and 13 micro m to look for correlations of the features with each other and with chemical and physical conditions were expanded and several positions in a single region, the Orion Bar, where the chemical composition was homogeneous, but the physical conditions varied are examined.

Bregman, J.↗
NASA NTRS1984

Interstellar Grain Mantles

Techniques for determining the composition of small dust grains in interstellar matter are discussed. The best way to study the composition of interstellar grain mantles is by infrared spectroscopy. The absorption features in a complete infrared spectrum from 2 to 15 microns can be used as fingerprints to identify the absorbing molecule. Ground-based observations around 3 microns confirmed the presence of H2O ice in interstellar grain mantles, through the detection of the 3.08 micron OH stretching vibration. The detection of other molecules, in particular the carbon bearing molecules, is however hampered by atmospheric absorption in the 5-8 micron region and the presence of the strong ice and silicate bands, which dominate the 3 and 10 micron region respectively. Kuiper Airborne Observatory observations of the 5-8 micron region of the spectrum are therefore extremely important to determine the composition of interstellar grain mantles. The 5 to 8 micron spectra of molecular cloud sources was obtained using a 24 detector grating spectrometer. An important characteristic of this spectrometer is that the whole spectrum is obtained simultaneously. It is therefore relatively easy to correct for atmospheric transmission.

Witteborn, F.↗
NASA NTRS1972

Circumstellar shells in the young cluster NGC 2264. II - Infrared and further optical observations.

Flux measurements at 1.6, 2.2, and 3.4 microns for 42 stars in the young cluster NGC 2264 suggest that a significant number of these stars are surrounded by circumstellar material which produces observable infrared excesses. Hydrogen line profiles are used to estimate surface gravities and thereby to predict visual luminosities for a number of pre-main-sequence A stars. Those stars which appear faintest as compared with their predicted luminosities all have infrared excesses.

Strom, S. E.↗