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	forbidden line
		An emission line found in the spectrum of a rarefied gas under special conditions, such as those found in some nebulae, the solar corona, and parts of active galactic nuclei.
		When these lines were first seen, in the spectra of planetary nebula in the 1860s, their true nature wasn't recognized and it was thought they might be due to a new element, which was dubbed "nebulium." More than half a century passed before Ira Bowen provided the right explanation.
		Besides forbidden lines of ionized oxygen, others of neon, nitrogen, and other relatively abundant elements are seen making up the light of nebulae, as well as the ordinary, permitted lines of hydrogen and helium.
	www.daviddarling.info /encyclopedia/F/forbidden_line.html (391 words)

	Appendix G
		Greenstein and Schmidt [13] observed "forbidden" spectral lines of oxygen and neon in the quasar spectra.
		To generate the forbidden spectral lines, this power is illuminating a cloud of thin gas equivalent in volume to a sphere with a diameter of 54 light years.
		Therefore, it is clear that the forbidden lines observed in quasar spectra cannot be explained even in a crude sense by the theory that evolved from the study of forbidden lines in gaseous nebulae.
	www.olduniverse.com /appendix_g.htm (2950 words)

	Forbidden line (Site not responding. Last check: 2007-09-18)
		Although they are technically forbidden, there is anon-zero probability of their spontaneous occurrence, should an atom or molecule be raised to an excited state.
		Forbidden emission lines have only been observed in extremely low- density gasesand plasmas, either in outer space or in the extreme upper atmosphere of the Earth.
		Forbidden lines of nitrogen ([N II] at 654.8 and 658.4 nm), sulfur ([S II] at 671.6 and 673.1 nm), and oxygen ([O II] at 372.7 nm, and [O III] at 495.9 and 500.7 nm) are commonly observed inastrophysical plasmas.
	www.therfcc.org /forbidden-line-32819.html (263 words)

	emission line Comparison Table (Site not responding. Last check: 2007-09-18)
		An emission line of Fe XIV, the strongest line in the solar corona.
		An emission line in which the emission is on the violet side of the absorption.
		A spectral line in the X-ray region (α = 0.334 Å), produced by the transition between the lowest level of the K shell and the lowest level of the L shell.
	www.site.uottawa.ca:4321 /astronomy/emissionline_table.html (205 words)

	Hartigan's Research/BAAS Report
		Forbidden Line Emission from T Tauri Stars and Jets: Hartigan, S. Edwards (Smith College), and recently graduated Rice undergrad R. Pierson published a paper in the Astrophysical Journal in 2004 detailing a study of five classical T Tauri stars known to have strong forbidden line emission.
		Several emission lines not previously seen in jets close to the star exist in the HN Tau jet; the [Fe II] 7155A / 8617A ratio is particularly useful because it measures the electron density in the densest regions of stellar jets, where log(N_e) > 6.
		Another useful set of emission lines not seen before in jets close to the star are the quartet of lines of [O II] near 7300A; when combined with [O I] lines at 5577A and 6300A, the quartet makes it possible to estimate the density and ionization fraction in the flow.
	sparky.rice.edu /~hartigan/research/baas.html (1817 words)

	Galaxies and the Universe - Emission -Line Spectra
		This means that certain line ratios are fixed by statistical weights in the atoms - the ratio of photon numbers in the lines is the ratio of statistical weights, and the ratio of line intensities is this value modified by the ratio of frequencies.
		The line ratio is about 1000 at 6000 K, dropping to 100 at 14000 K. However, beware that a one-zone model is seldom appropriate; a small amount of hot gas may skew the results.
		Hydrogen or helium recombination lines are also frequently used to measure reddening; if the temperature is known (and a one-zone model is not too bad) they may be measured over an enormous wavelength range, but are frequently dominated by the tiny BLR or have highly velocity-composite profiles.
	www.astr.ua.edu /keel/galaxies/emission.html (2855 words)

	FORBIDDEN LINE
		A line in a spectrum resulting from a transition from a metastable state within an atom.
		Forbidden lines are not found in ordinary sources, but may be conspicuous in very large bodies of rarefied gas where the time interval between collisions of atoms is long.Forbidden lines of oxygen appear, for example, in the aurora.
		A spectral line due to transition from the metastable state (metastable atom) of the neutral atom or an atom which has been ionized several times; emitted by very low-density plasmas.
	www.websters-online-dictionary.org /fo/forbidden+line.html (473 words)

	nebula lines (Site not responding. Last check: 2007-09-18)
		The radiation per unit volume in the nebula from forbidden transitions is not much changed from the (small) thermal emission rate.
		For the forbidden lines, 1> is usually the lowest energy level.
		The lower level of permitted lines is often not the ground level of the atom.
	www.aoc.nrao.edu /~jweather/physics425/node18.html (147 words)

	High-ionization (coronal) emission lines (Site not responding. Last check: 2007-09-18)
		Previous studies of the coronal lines in Seyfert galaxies have found them to have line widths intermediate between that of the lower-excitation forbidden narrow lines (such as [OIII]) and the permitted broad lines (Grandi 1978).
		These studies have also found the coronal lines to be slightly blueshifted with respect to the narrow forbidden lines.
		to examine the coronal line emission from the inner and outer warm absorber.
	www.astro.umd.edu /~chris/publications/html_papers/aat/node22.html (564 words)

	Donald R Garnett: Annual Report 2001
		This is part of a larger project to understand why recombination lines and forbidden lines from heavy element ions often yield very different abundances; recombination lines often yield much larger derived ion abundances than the forbidden lines.
		The puzzling discrepancies between recombination line and forbidden line abundances introduce uncertainty into the interpretation of emission line spectra of H II regions and planetary nebulae in our own and in distant galaxies.
		The goal of the project is to derive accurate sulfur abundances from and emission line measurements, comparing the abundances derived from the IR lines with those derived from optical spectra.
	www.as.arizona.edu /steward/annrep01/Donald_Garnett.html (1123 words)

	Forbidden line -- Facts, Info, and Encyclopedia article (Site not responding. Last check: 2007-09-18)
		Although they are technically forbidden, there is a non-zero probability of their spontaneous occurrence, should an ((physics and chemistry) the smallest component of an element having the chemical properties of the element) atom or ((physics and chemistry) the simplest structural unit of an element or compound) molecule be raised to an excited state.
		Even the hardest laboratory (An electrical home appliance that cleans by suction) vacuum on Earth is still too dense for forbidden line emission to occur before atoms are (Click link for more info and facts about collisionally) collisionally de-excited.
		These lines are extremely important to the (Click link for more info and facts about energy balance) energy balance of such things as (Click link for more info and facts about planetary nebulae) planetary nebulae and (Click link for more info and facts about H II regions) H II regions.
	www.absoluteastronomy.com /encyclopedia/f/fo/forbidden_line.htm (282 words)

	Energy levels, wavelengths, transition probabilities
		Atomic data for permitted resonance lines of atoms and ions from H to Si, and S, Ar, Ca and Fe.
		Ionization thresholds and strongest lines of atoms and ions.
		Observed lines and lines in the CHIANTI database between 50 and 1100 A Dere et al.
	www.pa.uky.edu /~verner/lines.html (557 words)

	[60.10] [O III] Outflows in QSOs (Site not responding. Last check: 2007-09-18)
		It is often assumed that the redshift of the narrow forbidden lines in QSOs indicate the systemic velocity of the object.
		The narrow-line region is thought to have a large physical extent, in part because the forbidden lines come from low density gas and in part because of the small velocity width of the lines, which is thought to predominantly reflect the stellar velocity dispersion of the host galaxy.
		It is found that the low-ionization lines all indicate a consistent redshift with a dispersion of about 20 km/sec.
	www.aas.org /publications/baas/v36n2/aas204/576.htm (257 words)

	Ph. D. Thesis Wolfgang Braun February 1996
		The absence of lines belonging to reflections in the other half sphere therefore is a direct consequence of the truncation of the crystal.
		The reciprocal lattice needed for the construction of the Kikuchi line pattern shows the same truncation as the real lattice it belongs to, which means that the reciprocal lattice points in one half sphere correspond to real-space points in the same half sphere, at least for cubic crystal symmetry.
		This provides further evidence that Kikuchi lines are generated in the surface layer, where the extinction of certain reflections is lifted.
	asumbe.eas.asu.edu /formermembers/wolfgang/thesis/sect223.html (1151 words)

	Search Results for off-line - Encyclopædia Britannica
		in astronomical spectroscopy, bright emission lines in the spectra of certain nebulae (H II regions), not observed in the laboratory spectra of the same gases, because on Earth the gases cannot be...
		Imagine a line, not necessarily straight, drawn between two points A and B and marked off in innumerable small elements like l in, which is to be thought of as a vector.
		A lines plan, usually a life-size scale drawing of a ship, is used by designers to calculate required hydrostatic, stability, and capacity conditions.
	www.britannica.com /search?query=off-line&submit=Find&source=MWTEXT (598 words)

	Perry's AGN Page
		Seyfert 1 galaxies are characterized by the presence of both narrow and broad emission lines, superposed onto a relatively featureless blue continuum.
		The emission lines are formed when atoms in the gas clouds are photo-ionized by the continuum radiation from the central source.
		The huge line widths from the doppler broadening (1000's km/sec) imply that the line forming regions are moving at high velocities around a compact, massive object.
	cfa-www.harvard.edu /~pberlind/whipple/agn.html (728 words)

	Properties of Planetary Nebula (Site not responding. Last check: 2007-09-18)
		The green lines, strongest at 4959Å and 5007Å, however, remained a mystery until 1928 when I. Bowen associated them with the forbidden lines of [OIII].
		Forbidden lines of sulphur ([SII]) and nitrogen ([NII]) are also visible.
		From the relative intensities of the forbidden lines, the temperature, density, and chemical compositions of the PN can be found.
	www.owlnet.rice.edu /~jdowell/astr350/project/properties.html (226 words)

	U Budky -Be stars
		The appereance of absorption cores in H I and/or metallic absorption lines lead to the conclusion that the star pass through the shell episode.
		The line wings are often broadened due to scattering in the circumstellar disks.
		The Ca II triplet (8498, 8542 and 8662) appears sometimes in emission but the emission strength is apparently not related to the behavior of the lines, nor is it concentrated in the early type stars.
	www.asu.cas.cz /~andrea/be.html (1151 words)

	Line emission mechanisms (Site not responding. Last check: 2007-09-18)
		However, the non-detection of forbidden lines, [OIII] 4959, 5007Å, the strong presence of lines and the small Balmer decrement argue for line emission by collisional de-excitation rather than a low density nebular recombinational region.
		In addition, if the lines are produced near the white dwarf, one should expect to see high excitation absorption lines such as NV, CIV and SiIV in the ultraviolet (Fontaine and Michaud 1979, Vauclair 1979) as observed in G191-B2B (Bruhweiler and Kondo 1981).
		There are none of the broad emission lines typical of interacting binaries, such as those produced by an accretion disk or infalling gas close to the white dwarf surface.
	www.star.ucl.ac.uk /~cmj/thesis/node64.html (1293 words)

	No Title (Site not responding. Last check: 2007-09-18)
		The reason is the 21 cm line corresponding to the hyperfine splitting of the ground state.
		The extremely low transition probability of this transition and the consequently narrow width of this line have led to its widespread use in measuring galaxy dynamics and kinematics.
		Classically forbidden spectral lines play a special role as diagnostics of these post-mortem plasmas which include planetary nebulae and supernova remnants.
	www.phys.unm.edu /~duric/phy537/ann/ann.html (541 words)

	Quasars
		From the Doppler effect, spectral lines that are broad in wavelength are emitted from gas clouds moving with high velocities.
		Forbidden lines are spectral lines which are very improbable (not really forbidden).
		Seyfert 1 galaxies are bright in the optical, and have both broad and narrow lines in their spectra.
	jersey.uoregon.edu /~js/ast123/lectures/lec12.html (1071 words)

	[No title]
		The aim of this proposal is to use infrared recombination lines of Hydrogen and Helium, as well as forbidden lines, to study the velocity field in Be star discs.
		Infrared recombination line widths depend strongly on the details of the velocity law (both rotational and radial) as a function of distance.
		The line strengths are sensitive probes of the density structure, both in the radial and in the vertical direction.
	www.ipac.caltech.edu /iso/gtotext/RWATERS.BESTARS.txt (653 words)

	Chapter Appendix B of Stars by A.S. Eddington
		Thus in the tranquillity of a nebula we observe light which is not emitted in the commotion of a vacuum tube.
		It must not be overlooked that the enormous extension of the nebulae has a great deal to do with the apparition of these forbidden lines.
		This identification of nebulium is confirmed by the fact that the other conspicuous unknown lines in the spectra of nebulae have been identified with forbidden lines.
	www.bibliomania.com /2/1/67/114/21324/2.html (493 words)

	Astron. Astrophys. 347, 617-629 (1999)
		It seems to be a paradox: the permitted lines typically have radiative transition probabilities 4...
		In both considered limiting cases, the radiative cooling by spectral lines does not depend on the strength of the lines, e.
		the number of lines in case 2 and especially the low excitation energy in case 1) in fact suggest that forbidden and fine-structure lines are more important in both limiting cases.
	aa.springer.de /papers/9347002/2300617/sc6.htm (474 words)

	Energy Citations Database (ECD) - Energy and Energy-Related Bibliographic Citations (Site not responding. Last check: 2007-09-18)
		A survey is made of theoretical and experimental studies of forbidden lines in atomic spectra.
		General regularities and classifications of spontaneous forbid den lines, forbidden emissions of celestial bodies, and lines impelled by various fields are discussed.
		The problems of producing forbidden lines under laboratory conditioms and a series of unsolved important problems related to forbidden atomtic emissions sre analyzed.
	www.osti.gov /energycitations/product.biblio.jsp?osti_id=4277807 (116 words)

	Forbidden Spectral Lines from the Solar Corona Below 1000 \AA (Site not responding. Last check: 2007-09-18)
		Visible wavelength spectral lines formed in the solar corona created great interest when their origin in the forbidden transitions of highly ionized atoms was first discovered by W. Grotrian and B. Edlen, because that origin implied a temperature of about one million degrees K for the corona.
		Additional forbidden lines in the 1000 to 2000 \AA\ spectral region have since been discussed by Feldman and Doschek, and other authors.
		Besides their intrinsic interest, they may serve in combination with the permitted lines as density diagnostics when the coronal density is not too high.
	www.aas.org /publications/baas/v26n4/aas185/abs/S4413.html (257 words)

	Ionized zones and PDRs of planetary nebulae
		The ISO SWS and LWS observations of the mid- and far-IR ionic fine structure lines, which, unlike their counterpart in UV and optical, have excitation energies of less than 1100 K and cover a wide range in critical densities, provide fresh input for a better understanding of this fundamental discrepancy in nebular abundance determinations.
		An example on this respect is illustrated by the detections of CH and CH in the ISO LWS spectrum of NGC7027.
		The majority of the unidentified lines are however likely to be real and probably arise from unknown molecular species.
	www.iso.vilspa.esa.es /meetings/isopeaks/liu (332 words)

	Another Quasar Enigma
		It is not the "forbidden" character of the spectral likes that disturb the astronomers.
		("Forbidden" simply means "improbable" in spectroscopy!) Rather, it is the half-hour variations that pose the dilemma.
		This is because most astronomers are convinced that the said forbidden lines are emitted by regions of the quasar that are 100-10,000 light years across.
	www.science-frontiers.com /sf029/sf029p03.htm (254 words)

	Seyfert Galaxies & Active Galaxies (Site not responding. Last check: 2007-09-18)
		The nuclear regions are so luminous that they account for much of the galaxy's light, often having the appearance of stars in photographic plates because they so strongly outshine their spiral host galaxies [Seyfert, 1943].
		The widths of the forbidden lines are typically >~1000 km/s.
		The permitted lines of hydrogen and helium sometimes have the same width, and sometimes are much broader with widths corresponding to a few percent of the speed of light.
	taltos.pha.jhu.edu /~jonathan/papers/proposal/node1.html (406 words)

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