172 research outputs found
Spectral analysis of the background in ground-based, long-slit spectroscopy
This paper examines the variations, because of atmospheric extinction, of
broad-band visible spectra, obtained from long-slit spectroscopy, in the
vicinity of some stars, nebulae, and one faint galaxy.Comment: 12 figure
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.'
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
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
Abundances of PNe in the Outer Disk of M31
We present spectroscopic observations and chemical abundances of 16 planetary
nebulae (PNe) in the outer disk of M31. The [O III] 4363 line is detected in
all objects, allowing a direct measurement of the nebular temperature essential
for accurate abundance determinations. Our results show that the abundances in
these M31 PNe display the same correlations and general behaviors as Type II
PNe in the Milky Way Galaxy. We also calculate photoionization models to derive
estimates of central star properties. From these we infer that our sample PNe,
all near the peak of the Planetary Nebula Luminosity Function, originated from
stars near 2 M_sun. Finally, under the assumption that these PNe are located in
M31's disk, we plot the oxygen abundance gradient, which appears shallower than
the gradient in the Milky Way.Comment: 48 pages, including 12 figures and 8 tables, accepted by
Astrophysical Journa
ELSA: An Integrated, Semi-Automated Nebular Abundance Package
We present ELSA, a new modular software package, written in C, to analyze and
manage spectroscopic data from emission-line objects. In addition to
calculating plasma diagnostics and abundances from nebular emission lines, the
software provides a number of convenient features including the ability to
ingest logs produced by IRAF's splot task, to semi-automatically merge spectra
in different wavelength ranges, and to automatically generate various data
tables in machine-readable or LaTeX format. ELSA features a highly
sophisticated interstellar reddening correction scheme that takes into account
temperature and density effects as well as He II contamination of the hydrogen
Balmer lines. Abundance calculations are performed using a 5-level atom
approximation with recent atomic data, based on R. Henry's ABUN program.
Improvements planned in the near future include use of a three-region
ionization model, similar to IRAF's nebular package, error propagation, and the
addition of ultraviolet and infrared line analysis capability. Detailed
documentation for all aspects of ELSA are available at
http://www.williams.edu/Astronomy/research/PN .Comment: 2 pages, contributed paper, IAU Symp. 234, Planetary Nebulae in Our
Galaxy and Beyon
Alpha Element Abundances in a Large Sample of Galactic Planetary Nebulae
We present emission line strengths, abundances, and element ratios (X/O for
Ne, S, Cl, and Ar) for a sample of 38 Galactic disk planetary nebulae (PNe)
consisting primarily of Peimbert classification Type I. Spectrophotometry for
these PNe incorporates an extended optical/near-IR range of 3600-9600 angstroms
including the [S III] lines at 9069 and 9532. We have utilized Emission Line
Spectrum Analyzer, a five-level atom abundance routine, to determine T_e, N_e,
ionization correction factors, and total element abundances. With a compilation
of data from >120 Milky Way PNe, we present results from our most recent
analysis of abundance patterns in Galactic disk PNe. We have examined the alpha
elements against H II regions and blue compact galaxies (H2BCG) to discern
signatures of depletion or enhancement in PNe progenitor stars, particularly
the destruction or production of O and Ne. We present evidence that many PNe
have higher Ne/O and lower Ar/Ne ratios compared to H2BCGs within the range of
8.5-9.0 for 12 + log(O/H). This suggests that Ne is being synthesized in the
low- and intermediate-mass progenitors. Sulfur abundances in PNe continue to
show great scatter and are systematically lower than those found in H2BCG at a
given metallicity. Although we find that PNe do show some distinction in alpha
elements when compared to H2BCG, within the Peimbert classification types
studied, PNe do not show significant differences in alpha elements amongst
themselves, at least to an extent that would distinguish in situ
nucleosynthesis from the observed dispersion in abundance ratios.Comment: 12 pages, 18 figures, 7 tables (note: tables 2-5 are available online
only in machine-readable form
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