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NASA NTRS1972

Possibility that the far ultraviolet excess in M31 is due to main sequence stars

The far ultraviolet excess in the central region of M31, observed by OAO-2, could be due to young main sequence stars. More than enough such stars are present in the model for the M31 inner disk population derived by Tinsley and Spinrad (1971) to match line- and color-indices at longer wavelengths. If the far ultraviolet radiation of typical galaxies arises from young stars, the theoretical ultraviolet background is enhanced greatly by evolutionary effects. For evolution at the rate of Tinsley and Spinrad's model for M31, or of Arnett's (1971) linear model for our galaxy, the enhancement is a factor 2.5 to 14, depending on the Hubble constant and the spectrum at wavelengths below 1700 A.

Tinsley, B. M.↗
NASA NTRS1981

Stellar winds and mass-loss rates from Be stars

An analysis for the effects of stellar winds concerning Copernicus scans of Si III and Si IV resonance lines in the spectra of 22 early B stars, of which 19 have Be characteristics, yields line asymmetries in all but one of the stars to which theoretical profiles were fitted. The resulting wind parameters were used to calculate mass-loss rates. Most of the silicon in the winds of the cooler stars is in the form of Si III and Si IV, leading to a mass loss rate value ranging from 10 to the -11th to 3 x 10 to the -9th solar masses/year. Equatorial gravity darkening is seen in the relative velocity widths of ultraviolet and visible photospheric lines. The measured photospheric Si III and Si IV resonance-line equivalent widths do not agree with those predicted by current stellar atmosphere calculations. Be star mass loss rates are probably insufficient to affect either their own evolution or that of the galaxy, since their winds do not significantly contribute to the enrichment of the interstellar medium.

Snow, T. P., Jr.↗
NASA NTRS1982

Analysis of the ultraviolet spectrum of RWT 152 - A subluminous O star with a main-sequence visual spectrum

Observations of luminous early-type stars provide one of the most sensitive ways to detect the low density gas of the interstellar medium. As part of an ongoing program studying the gas in the galactic halo, stars believed to be outside the plane of the Milky Way have been observed. In the interest of studying the halo gas in additional directions, a search has been conducted for candidate stars which are bright enough to be observable with the International Ultraviolet Explorer Satellite (IUE) high dispersion mode and far enough from the galactic plane to provide a long line of sight through the halo gas. One such star is star 152 in the catalog of Rubin, Westpfahl, and Tuve (1974), which is called RWT 152 in the investigation. The IUE spectra of RWT 152 were obtained and analyzed. It appears that RWT 152 is not a young massive star, but rather a low mass object in an advanced stage of evolution.

Ebbets, D. C.↗
NASA NTRS1990

Near-infrared mapping of spiral barred galaxies

In external galaxies, near-infrared emission originates from stellar populations, hot dust, free-free emission from H+ regions, gaseous emission, non-thermal nucleus if any. Because of the low extinction compared to the visible, infrared wavelengths are useful to probe regions obscured by dust such as central parts where starburst phenomena can occur because of the large quantity of matter. The results presented were obtained with a 32 x 32 InSb charge injection device (CID) array cooled at 4K, at the f/36 cassegrain focus of the 3m60 Canada-France-Hawaii telescope with a spatial resolution of 0.5 inches per pixel. The objects presented are spiral barred galaxies mapped at J(1.25 microns), H(1.65 microns) and K(2.2 microns). The non-axisymetric potential due to the presence of a bar induces dynamical processes leading to the confinement of matter and peculiar morphologies. Infrared imaging is used to study the link between various components. Correlations with other wavelengths ranges and 2-colors diagrams ((J-H), (H-K)) lead to the identification of star forming regions, nucleus. Maps show structures connected to the central core. The question is, are they flowing away or toward the nucleus. Observations of M83 lead to several conclusions. The star forming region, detected in the visible and the infrared cannot be very compact and must extend to the edge of the matter concentration. The general shape of the near-infrared emission and the location of radio and 10 micron peaks suggest the confinement of matter between the inner Linblad resonances localized from CO measurements about 100 and 400 pc. The distribution of color indices in the arc from southern part to the star forming region suggests an increasing amount of gas and a time evolution eventually triggered by supernova explosions. Close to the direction of the bar, a bridge-like structure connects the arc to the nucleus with peculiar color indices. Perhaps, this structure can be linked to a height velocity component seen in UV and we can attribute it to a jet and/or a matter flow along the bar toward the nucleus, fuelling it. NGC 1068 is the nearest Seyfert 2 galaxy. It has been a subject of many studies at all wavelengths. This object was mapped at J, H, K, L and M, and in polaro-imagery. Results are given.

Gallais, P.↗
NASA NTRS1993

Starburst ages in HII galaxies

The age of the starbursts of a few H2 galaxies is derived from optical photometry and compared with previous results from radio continuum spectra. H2 galaxies are gas rich and characterized by the dominance of giant H2 regions, blue stellar colors, high surface brightness, and narrow emission lines. The presently observed high abundances of bright young stars must be the result of a recent -or even ongoing- starburst. The question, whether the observed starburst is the first one or if it is a recurrent phenomenon, is still open. If the starburst is the first one, H2 galaxies can be interpreted as being among the most unevolved galaxies known - their star formation characteristics possibly paralleling that of normal galaxies early in their evolution. A sample of five H2 galaxies was observed with B, R, and I broadband filters. They have been observed previously at several radio continuum frequencies. The photometric data are given. The results of the photometry and a comparison with radio continuum spectra are given.

Deeg, Hans-Joerg↗
NASA NTRS1993

The detectability of brown dwarfs - Predictions and uncertainties

In order to determine the likelihood for the detection of isolated brown dwarfs in ground-based observations as well as in future spaced-based astronomy missions, and in order to evaluate the significance of any detections that might be made, we must first know the expected surface density of brown dwarfs on the celestial sphere as a function of limiting magnitude, wavelength band, and Galactic latitude. It is the purpose of this paper to provide theoretical estimates of this surface density, as well as the range of uncertainty in these estimates resulting from various theoretical uncertainties. We first present theoretical cooling curves for low-mass stars that we have computed with the latest version of our stellar evolution code. We use our evolutionary results to compute theoretical brown-dwarf luminosity functions for a wide range of assumed initial mass functions and stellar birth rate functions. The luminosity functions, in turn, are utilized to compute theoretical surface density functions for brown dwarfs on the celestial sphere. We find, in particular, that for reasonable theoretical assumptions, the currently available upper bounds on the brown-dwarf surface density are consistent with the possibility that brown dwarfs contribute a substantial fraction of the mass of the Galactic disk.

Nelson, L. A.↗
NASA NTRS1993

Hydrodynamics of winds from irradiated companion stars in low-mass X-ray binaries

We study the hydrodynamics of evaporative winds driven by X-rays and/or soft gamma-rays irradiating the outer layers of companion stars in low-mass X-ray binaries (LMXBs). We consider several irradiating fluxes and spectra for LMXBs with white dwarf and main-sequence companion stars. The thermal structure of the base of the coronal region, the position of the sonic point, and the value of the mass-loss rate are calculated in the case of spherical geometry. We consider photospheric and coronal heating from both X-ray photoionization and Compton scattering of X-rays and soft gamma-rays with energy about 1 MeV possibly irradiating the companion star in LMXBs. Evaporative winds may play a relevant role for the evolution of a special class of radiation-driven LMXBs, and this study is a step toward a quantitative understanding of the mechanism driving LMXB evolution.

Tavani, Marco↗
NASA NTRS1994

UBV stellar photometry of the 30 Doradus region of the large Magellanic Cloud with the Hubble Space Telescope

We report on Planetary Camera observations of the central region of 30 Doradus in the Large Magellanic Cloud (LMC). These images of 30 Doradus are the first `deep' Hubble Space Telescope (HST) exposures that have appropriate photometric calibration. The B band (F439W) image, which shows R136a at the center of the PC6 charge coupled device (CCD) chip, reveals over 200 stars within 3 sec of the center of R13a, and over 800 stars in a 35 sec x 35 sec area. We used Malumuth et al.'s (1991) Point Spread Function (PSF)-fitting method to measure the magnitudes of all stars on the PC6 chip. These new B magnitudes, along with U and V magnitudes from archival PC images, yield a luminosity function, mass density profile, and initial mass function of the 30 Doradus ionizing cluster. The mass distribution is well fit by a King model with a core radius, R(sub c) = 0.96 sec (0.24 pc), a tidal radius, R(sub t) = 110 sec (28 pc), and a total mass, Mass = 16,800 solar mass. Both the luminosity function and initial mass function show evidence for mass segregation, in the sense that the central region has a higher fraction of massive stars than the outer regions. This is the first observational evidence for mass segregation in a very young cluster (age approximately 3 million years). The observations admit the hypothesis that the mass segregation occurred in the process of star formation and/or that the mass segregation is the result of dynamical evolution.

Malumuth, Eliot M.↗
NASA NTRS2002

The Evolution of Dust in the Multiphase Interstellar Medium

Interstellar dust has a profound effect on the structure and evolution of the interstellar medium (ISM) and on the processes by which stars form from it. Dust obscures regions of star formation from view, and the uncertain quantities of elements in dust makes it difficult to measure accurately the abundances of the elements in low density regions. Despite the central importance of dust in astrophysics, we cannot answer some of the most basic questions about it: Why is it that most of the refractory elements are in dust grains? What determines the sizes of interstellar grains? In our theoretical investigations we have addressed these questions by studying the destruction of interstellar grains. We describe here the investigations that we have completed to date. As part of our original proposal we proposed additional projects that have not been completed. We are requesting a no-cost extension to carry out those investigations and describe those in our request.

Slavin, J.↗
NASA NTRS2003

The Evolution of Dust in the Multiphase Interstellar Medium

Interstellar dust has a profound effect on the structure and evolution of the interstellar medium (ISM) and on the processes by which stars form from it. Dust obscures regions of star formation from view, and the uncertain quantities of elements in dust makes it difficult to measure accurately the abundances of the elements in low density regions. Despite the central importance of dust in astrophysics, we cannot answer some of the most basic questions about it: Why is it that most of the refractory elements are in dust grains? What determines the sizes of interstellar grains? It has been the goal of our proposed theoretical investigations to address these questions by studying the destruction of interstellar grains, and to develop observational diagnostics that can test the models we develop.

Oliversen, Ronald J.↗
NASA NTRS2005

The Star Formation History of Orion and its Environs

During the period of performance, we have obtained the following observations and carried out the analysis of the Orion associations itemized below: 1) Detailed analysis of newly discovered stars in strips at declinations +1 degree and -1 degree; 2) Disk evolution in the Ori OB1 association; 3) Spitzer proposal; 4) Multifiber echelle spectroscopy; 5) Slit spectroscopy of bright candidates; 6) Other multifiber spectroscopy; 7) UBVRI photometry; 8) Near and mid-IR photometry.

Calvert, Nuria↗
NASA NTRS2005

NASA's Challenges in Optics for Future Space-Based Science Missions

NASA's mission is: "To understand and project our home planet, To explore the universe and search for life, To inspire the next generation of explorers ... as only NASA can." These mission concepts are further defined in our recently published"Strategic Objectives for 2005 and Beyond" , which include conducting advanced telescope searches for Earth-like planets and habitable environments around the stars, as well as exploring the universe to understand its origin, structure, evolution, and destiny. This presentation will summarize several future space-based missions currently in formulation to meet these objectives, and will outline some of the principal challenges in the field of optics to their success.

Stahl, H. Phil↗
NASA NTRS2004

The Companion to the Central Mira Star of the Protoplanetary Nebula OH 231.8+4.2

We present deep optical long-slit spectra of the peculiar protoplanetary nebula (PPN) OH 231.8+4.2 obtained with the 6.5 m Baade Telescope at Las Campanas Observatory (Chile). In addition to the molecular absorption bands characteristic of the M9-10 III star inside OH 231.8+4.2 (QX Pup), we identify lines of the Balmer series in absorption, which do not form in the cool atmospheres of late M-type stars. We also confirm the presence of a blue continuum excess with an intensity that is a factor 30 larger than that expected for an M9-10 III star. Our results indicate the presence of a source hotter than QX Pup illuminating OH 231.8+4.2 that is likely a main-sequence star with spectral type A. We discuss how the formation and nebular evolution of OH 231.8+4.2 could have been affected by the presence of a binary system in its core.

binaries↗
NASA NTRS2013

Carbon in the Universe

Over the past few decades, NASA missions have revealed that we live in a Universe that is not a hydrogen-dominated, physicist's paradise, but in a molecular Universe with complex molecules directly interwoven into its fabric. These missions have shown that molecules are an abundant and important component of astronomical objects at all stages of their evolution and that they play a key role in many processes that dominate the structure and evolution of galaxies. Closer to home in our galaxy, the Milky Way, they have revealed a unique and complex organic inventory of regions of star and planet formation that may well represent some of the prebiotic roots to life. Astrobiology emerges from the great interest in understanding astrochemical evolution from simple to complex molecules, especially those with biogenic potential and the roles they may play as primordial seeds in the origin of life on habitable worlds. The first part of this talk will highlight how infrared spectroscopic studies of interstellar space, combined with dedicated laboratory simulations, have revealed the widespread presence of complex organics across deep space. The remainder of the presentation will focus on the evolution of these materials and astrobiology.

Astrobiology↗
NASA NTRS2022

Measurement of Galactic 26Al with the Compton Spectrometer and Imager

The Compton Spectrometer and Imager (COSI) is a balloon-borne compact Compton telescope de-17signed to survey the 0.2–5 MeV sky. COSI’s energy resolution of ∼0.2% at 1.8 MeV, single-photon reconstruction, and wide field of view make it capable of studying astrophysical nuclear lines, particularly the 1809 keVγ-ray line from decaying Galactic 26Al. Most 26Al originates in massive stars and core-collapse supernova nucleosynthesis, but the path from stellar evolution models to Galaxy-wide emission remains unconstrained. In 2016, COSI had a successful 46-day flight on a NASA super pressure balloon. Here, we detail the first search for the 1809 keV26Al line in the COSI 2016 balloon flight using a maximum likelihood analysis. We find a Galactic 26Al flux of (8.6±2.5) ×10−4ph cm−2s−124 within the Inner Galaxy (|ℓ|≤30◦,|b|≤10◦) with 3.7σ significance above background. Within uncertainties, this flux is consistent with expectations from previous measurements by SPI and COMPTEL. This analysis demonstrates COSI’s powerful capabilities for studies of γ-ray lines and underscores the scientific potential of future compact Compton telescopes. In particular, the next iteration of COSI as a NASA Small Explorer satellite has recently been approved for launch in 2025.

Gamma-ray lines↗
NASA NTRS1994

Gas flow in a two component galactic disk

Numerical simulations of two-component (stars + gas) self-gravitating galactic disks show that the interstellar gas can significantly affect the dynamical evolution of the disk even if its mass fraction (relative to the total galaxy mass) is as low as several percent. Aided by efficient energy dissipation, the gas becomes gravitationally unstable on local scale and forms massive clumps. Gravitational scattering of stars by these clumps leads to suppression of bar instability usually seen in heavy stellar disks. In this case, gas inflow towards the galactic center is driven by dynamical friction which gas clumps suffer instead of bar forcing.

Noguchi, M.↗
NASA NTRS1991

The shock process and light-element production in supernova envelopes

Detailed hydrodynamic modeling of the passage of supernova shocks through the hydrogen enevlopes of blue and red progenitor stars was carried out to explore the sensitivity to model conditions of light element production (specifically Li7 and B-11) which was noted by Dearborn, Schramm, Steigman and Truran (1989) (DSST). It is found that, for stellar models with M is less than or approximately 100 M solar mass, current state of the art supernova shocks do not produce significant light element yields by hydrodynamic processes alone. The dependence of this conclusion on stellar models and on shock strengths is explored. Preliminary implications for Galactic evolution of lithium are discussed, and it is suspected that intermediate mass red giant stars may be the most consistent production site for lithium.

Brown, Lawrence E.↗