Smithsonian Astrophysical Observatory

About: Smithsonian Astrophysical Observatory is a facility organization based out in Cambridge, Massachusetts, United States. It is known for research contribution in the topics: Galaxy & Stars. The organization has 1665 authors who have published 3622 publications receiving 132183 citations. The organization is also known as: SAO.

Asteroid spectroscopy: Progress and perspectives

Abstract: A broad understanding of meteorite and asteroidal studies is needed for the most dynamic progress of both disciplines, in their common goal of understanding the origin and early evolution of the solar system. Asteroid compositional investigations are currently shifting from the survey mode to focused investigations of selected targets, in pursuit of specific problems. Attention is presently given the compositional nature and diversity of asteroid taxonomic classes, as addressed by the Small Main-Belt Asteroid Spectroscopic Survey.

Long-wavelength ultraviolet photoproduction of amino acids on the primitive Earth.

Abstract: Long wavelength UV photoproduction of amino acids on primitive earth, using hydrogen sulfide as photon acceptor

HST photometry of the trapezium cluster

Abstract: We have obtained images of 11 fields in the Trapezium cluster with the Planetary Camera (PC) of the Hubble Space Telescope (HST) in order to extend Herbig & Terndrup's (1986) study of this prototype, dense embedded cluster to fainter magnitudes than is possible from the ground. Using these images, we have identified 319 stars within an area of approximately 12 sq arc min corresponding roughly to a volume of approximately 0.065 cu pc assuming the cluster is approximately spherically symmetric. Our completeness limits for star identification in V-band and I-band images are V approximately = 20 and I(sub c) approximately = 19 respectively, corresponding to a mass limit of approximately 0.15 solar mass if the faintest stars have the same average A(sub v) as that estimated for the brighter stars in the cluster. We have compared the V versus V-I color-magnitude diagram derived from the HST photometry to new theoretical isochrones. Star formation in the Trapezium appears to be remarkably coeval, with greater than or = 80% of the stars having inferred ages less than 1 Myr. Over the somewhat limited mass range of the observations, there is no evidence for 'bimodal' star formation-the high- and low-mass stars appear to have the same ages. The sharp cores of the HST images and the small angular size of the PC pixels has allowed us to identify 35 new visual binaries in the cluster with separations from approximately 0.06 arc sec (approximately 26 AU) to approximately 1.0 arc sec (approximately 440 AU). For the range of binary separations that we are sensitive to, the observed binary frequency for the Trapezium is essentially identical to that estimated for field low-mass stars by Duquennoy & Mayor (1991). The most straightfoward inference from this result is that binaries in this separation are unlikely to be formed by a tidal capture process. We have also identified three stars which have associated compact nebulosity visible in the HST images. One of these star + nebulosity cases was previously identified by O'Dell, Wen, & Hu (1993)-these objects appear to form a class of objects whose circumstellar matter is being 'lit up', most likely by Theta(sup 1) Ori C, enabling the gas to be observable at both optical and radio wavelengths (Felli et al. 1993a, b). We provide a brief summary of the optical properties of the other radio sources which appear in our PC images.

Metallicity Gradients and Gas Flows in Galaxy Pairs

Abstract: We present the first systematic investigation into the metallicity gradients in galaxy close pairs. We determine the metallicity gradients for eight galaxies in close pairs using H II region metallicities obtained with high signal-to-noise multi-slit observations with the Keck LRIS Spectrograph. We show that the metallicity gradients in close pairs are significantly shallower than gradients in isolated spiral galaxies such as the Milky Way, M83, and M101. These observations provide the first solid evidence that metallicity gradients in interacting galaxies are systematically different from metallicity gradients in isolated spiral galaxies. Our results suggest that there is a strong relationship between metallicity gradients and the gas dynamics in galaxy interactions and mergers.

Collisional cascades in planetesimal disks. ii. embedded planets

Abstract: We use a multiannulus planetesimal accretion code to investigate the growth of icy planets in the outer regions of a planetesimal disk. In a quiescent minimum-mass solar nebula, icy planets grow to sizes of 1000–3000 km on a timescale tP ≈ (15–20)[a/(30 AU)]3 Myr, where a is the distance from the central star. Planets form faster in more massive nebulae. Newly formed planets stir up leftover planetesimals along their orbits and produce a collisional cascade in which icy planetesimals are slowly ground to dust. The dusty debris of planet formation has physical characteristics similar to those observed in β Pic and HR 4796A and other debris disks. The computed dust masses are Md(r 1 mm) ~ 1026(M0/MMMSN) g and Md(1 mm r 1 m) ~ 1027(M0/MMMSN) g, where r is the radius of a particle, M0 is the initial mass in solids, and MMMSN is the mass in solids of a minimum-mass solar nebula at 30–150 AU. The luminosity of the dusty disk relative to the stellar luminosity is LD/L0 ~ Lmax(t/t0)-m, where Lmax ~ 10-3(M0/MMMSN), t0 ≈ 10–1000 Myr, and m ≈ 1–2. Our calculations produce bright rings and dark gaps with sizes Δa/a ≈ 0.1. Bright rings occur where planets 1000 km and larger have recently formed. Dark gaps are regions where planets have cleared out dust, or shadows where planets have yet to form. Planets can also grow in a planetesimal disk perturbed by the close passage of a star. Stellar flybys initiate collisional cascades, which produce copious amounts of dust. The dust luminosity following a modest perturbation is 3–4 times larger than the maximum dust luminosity of a quiescent planet-forming disk. In 10 Myr or less, large perturbations remove almost all of the planetesimals from a disk. After a modest flyby, collisional damping reduces planetesimal velocities and allows planets to grow from the remaining planetesimals. Planet formation timescales are then 2–4 times longer than timescales for undisturbed disks; dust luminosities are 2–4 times smaller.