27,408 research outputs found
Observational Tests Of Intermediate Mass Star Yields Using Planetary Nebulae
This paper summarizes a project designed to study abundances in a sample of
planetary nebulae representing a broad range in progenitor mass and
metallicity. We collect abundances of C, N, and O determined for the entire
sample and compare them with theoretical predictions of planetary nebula
abundances from a grid of intermediate-mass star models. We find very good
agreement between observations and theory, lending strong support to our
current understanding of nucleosynthesis in stars with progenitor masses below
8 solar masses. This agreement between observation and theory also supports the
validity of published stellar yields of C and N in the study of the abundance
evolution of these two elements.Comment: 2 pages, to appear in the proceedings of ``Cosmic Evolution'', held
at Institut d'Astrophysique de Paris, November 13-17, 200
Gallery of Planetary Nebula Spectra
We present the Gallery of Planetary Nebula Spectra now available at
http://oit.williams.edu/nebulae The website offers high-quality, moderate
resolution (~7-10 A FWHM) spectra of 128 Galactic planetary nebulae from
3600-9600 A, obtained by Kwitter, Henry, and colleagues with the Goldcam
spectrograph at the KPNO 2.1-m or with the RC spectrograph at the CTIO 1.5-m.
The master PN table contains atlas data and an image link. A selected object's
spectrum is displayed in a zoomable window; line identification templates are
provided. In addition to the spectra themselves, the website also contains a
brief discussion of PNe as astronomical objects and as contributors to our
understanding of stellar evolution. We envision that this website, which
concentrates a large amount of data in one place, will be of interest to a
variety of users: researchers might need to check the spectrum of a particular
object of interest; the non-specialist astronomer might simply be interested in
perusing such a collection of spectra; and finally, teachers of introductory
astronomy can use this database to illustrate basic principles of atomic
physics and radiation. To particularly encourage this last use, we have
developed two paper-and-pencil exercises to introduce beginning astronomy
students to the wealth of information that PN spectra contain.Comment: Two pages, two figures. Contributed paper to IAU Symp. 234,
``Planetary Nebulae in our Galaxy and Beyond.'
Seasonal Flight Patterns of Miridae (Hemiptera) in a Southern Illinois Black Walnut Plantation
The seasonal flight patterns of 92 species of Miridae collected in window traps in a southern Illinois black walnut plantation are compared with similar data from a North Carolina black walnut plantation. Flying height distributions and seasonal flight activities of Amblytylus nasutus, Deraeocoris nebulosus, Leptopterna dolabrata, Lopidea heidemanni, Lygus lineolaris, and Plagiognathus politus are considered in detail. Six species are newly recorded for Illinois
Abundances of Disk Planetary Nebulae in M31 and the Radial Oxygen Gradient
We have obtained spectra of 16 planetary nebulae in the disk of M31 and
determined the abundances of He, N, O, Ne, S and Ar. Here we present the median
abundances and compare them with previous M31 PN disk measurements and with PNe
in the Milky Way. We also derive the radial oxygen gradient in M31, which is
shallower than that in the Milky Way, even accounting for M31's larger disk
scale length.Comment: 2 pages, 1 figure, 1 table, to appear in the proceedings of IAU
Symposium No. 283, Planetary Nebulae: An Eye to the Futur
Effects of crucible wetting during solidification of immiscible Pb-Zn
Many industrial uses for liquid phase miscibility gap alloys are proposed. However, the commercial production of these alloys into useful ingots with a reasonable amount of homogeneity is arduous because of their immiscibility in the liquid state. In the low-g environment of space gravitational settling forces are abated, thus solidification of an immiscible alloys with a uniform distribution of phases becomes feasible. Elimination of gravitational settling and coalescence processes in low-g also makes possible the study of other separation and coarsening mechanisms. Even with gravitational separation forces reduced, many low-g experiments have resulted in severely segregated structures. The segregation in many cases was due to preferential wetting of the crucible by one of the immiscible liquids. The objective was to analyze the wetting behavior of Pb-Zn alloys on various crucible materials in an effort to identify a crucible in which the fluid flow induced by preferential wetting is minimized. It is proposed that by choosing the crucible for a particular alloy so that the difference in surface energy between the solid and two liqud phases is minimized, the effects of preferential wetting can be diminished and possibly avoided. Qualitative experiments were conducted and have shown the competitive wetting behavior of the immiscible Pb-Zn system and 13 different crucible materials
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