Search

We report on a multiwavelength campaign on the TeV gamma-ray blazar Mrk 421 performed during 2002 December and 2003 January. These target of opportunity observations were initiated by the detection of X-ray and TeV gamma-ray flares with the All Sky Monitor (ASM) on board the Rossi X-Ray Timing Explorer (RXTE) and the 10 m Whipple gamma-ray telescope. The campaign included observational coverage in the radio (University of Michigan Radio Astronomy Observatory), optical (Boltwood, La Palma KVA 0.6 m; WIYN 0.9 m), X-ray (RXTE pointed telescopes), and TeV gamma-ray (Whipple and HEGRA) bands. At TeV energies, the observations revealed several flares at intermediate flux levels, peaking between 1 and 1.5 times the flux from the Crab Nebula. While the time-averaged spectrum can be fitted with a single power law of photon index Gamma = 2.8 from dN gamma/dE proportional to E-Gamma, we find some evidence for spectral variability. Confirming earlier results, the campaign reveals a rather loose correlation between the X-ray and TeV gamma-ray fluxes. In one case, a very strong X-ray flare is not accompanied by a comparable TeV gamma-ray flare. Although the source flux was variable in the optical and radio bands, the sparse sampling of the optical and radio light curves does not allow us to study the correlation properties in detail. We present a simple analysis of the data with a synchrotron self-Compton model, emphasizing that models with very high Doppler factors and low magnetic fields can describe the data.

Recent R-matrix calculations of electron impact excitation rates among the 3s23p4 levels of Cl II are used to derive the nebular emission-line intensity ratios R1 = I(6161.8 A)/I(8578.7 A) and R2 = I(6161.8 A)/I(9123.6 A) as a function of electron temperature (Te) and density (Ne). The ratios are found to be very sensitive to changes in Te but not Ne for densities lower than 105 cm-3. Hence, they should, in principle, provide excellent optical Te diagnostics for planetary nebulae. The observed values of R1 and R2 for the planetary nebulae NGC 6741 and IC 5117, measured from spectra obtained with the Hamilton echelle spectrograph on the 3 m Shane Telescope, imply temperatures in excellent agreement with those derived from other diagnostic lines formed in the same region of the nebula as [Cl II]. This provides some observational support for the accuracy of the [Cl II] line ratio calculations and hence the atomic data on which they are based. The [Cl II] 8578.7 and 9123.6 A lines are identified for the first time (to our knowledge) in a high-resolution spectrum of the symbiotic star RR Telescopii, obtained with the University College London Echelle Spectrograph on the 3.9 m Anglo-Australian Telescope. However, the 6161.8 A feature is unfortunately too weak to be identified in the RR Telescopii observations, consistent with its predicted line strength.

We have measured the spectral line intensities of the metal poor planetary nebula IC 4634. Using a photo-ionization model calculation, we try to fit the the optical and UV region spectra, i.e., Hamilton Echelle and IUE observations. From direct images, one expects complicated density variations, but the model predicts a range in densities that may be smaller than actually exist. We find N(sub epsilon) approximates 5000 /cubic meter. In spite of the geometrical complexity of the S shaped double-lobed structure, the simple photoionization model with a spherical symmetry can fit most emission lines, fairly well. The derived chemical composition has been compared with previous estimates and also with the Sun - The metallicity in IC 4634 appears to be lower than in the Sun or the average planetary nebula. The most likely temperature of the central ionizing source of IC 4634 appears to be about 55,000 K. We find a central star mass of about 0.55 Solar Mass from comparison with theoretical evolutionary tracks.

Wavelengths and identifications have been provided for approximately 300 lines between 3660 and 10125 A in the spectrum of the archetypal bright, high-excitation planetary nebula NGC 7662. These lines are measured with the Hamilton echelle spectrograph at Lick Observatory and are supplemented by image-tube data. Published results are used to construct diagnostic diagrams and derive ionic concentrations. The electron temperature indicated by [O III] is about 12,500 K; the density regimes consist of N = 5000-17,000 cm-1. Derivation of precise abundances will require appropriate model calculations, but with the aid of homogeneous spherical model procedures we find C to be enhanced, N marginally so if at all, and heavier elements depleted with respect to the Sun. These conclusions are in harmony with those of Barker.

Recent R-matrix calculations of electron impact excitation rates in Ar IV are used to calculate the emission-line ratio: ratio diagrams (R1, R2), (R1, R3), and (R1, R4), where R1 = I(4711 ?)/I(4740 ?), R2 = I(7238 ?)/I(4711 + 4740 ?), R3 = I(7263 ?)/I(4711 + 4740 ?), and R4 = I(7171 ?)/I(4711 + 4740 ?), for a range of electron temperatures (Te = 5000-20,000 K) and electron densities (Ne = 10-106 cm-3) appropriate to gaseous nebulae. These diagrams should, in principle, allow the simultaneous determination of Te and Ne from measurements of the [Ar IV] lines in a spectrum. Plasma parameters deduced for a sample of planetary nebulae from (R1, R3) and (R1, R4), using observational date obtained with the Hamilton echelle spectrograph on the 3 m Shane Telescope at the Lick Observatory, are found to show excellent internal consistency and to be in generally good agreement with the values of Te and Ne estimated from other line ratios in the echelle spectra. These results provide observational support for the accuracy of the theoretical ratios and, hence, the atomic data adopted in their derivation. In addition, they imply that the 7171 ? line is not as seriously affected by telluric absorption as previously thought. However, the observed values of R2 are mostly larger than the theoretical high-temperature and density limit, which is due to blending of the Ar IV 7237.54 ? line with the strong C II transition at 7236 ?.

Theoretical O V electron-density-sensitive emission line ratios for R = I(2s21S0 - 2s2p3P2)/I(2s21S0 - 2s2p3P1) are presented. Inspection of Goddard High Resolution Spectrograph Hubble Space Telescope spectra of RR Tel reveals the presence of the [O V] 2s21S - 2s2p3P2 line at 1213.80 A, which is 4.62 ± 0.12 A away from the 2s21S - 2s2p3P2 intercombination transition at 1218.42 A, in good agreement with the theoretical prediction of Δλ = 4.54 A. The resultant value of R = 0.82 ± 0.11 implies a logarithmic electron density, log Ne, of 5.2 ± 0.2 cm-3, in good agreement with that found from other ions with high electron temperature, such as Ne VI, which also provides support for the identification.

Among Henry Norris Russell's many achievements were his contributions to solar and stellar spectroscopy, in particular, to an analysis of the chemical composition of the solar atmosphere. The question of composition differences between stars was hotly debated; some distinguished astronomers argued that all stars had the solar composition. Some early challenges to this doctrine are described. Determinations of chemical compositions of gaseous nebulae were much more difficult. If we observe the lines of a given chemical element in one ionization stage in a stellar spectrum, we can deduce readily the abundance of that element. No such luxury is available for a planetary or diffuse gaseous nebula. We must measure lines of as many ionization stages as we can. Furthermore, a nebula is an extended object. Often detailed spectroscopy is at hand only for narrow pencil columns taken through the image. Different observers use a variety of apertures. Fortunately it is possible to calculate theoretical spectra for any arbitrary cross section taken through a symmetrical model, so UV, optical, and IR observations all can be compared properly with a prediction. The value of high-resolution spectra obtained with instruments such as the Hamilton Echelle Spectrograph at Lick Observatory is emphasized. Improved fluxes for weak but important transitions are found. Close blends of lines of different ions can be resolved, and checks can be made on predictions of atomic parameters such as Einstein A-values and collision strengths. High spectral resolution data have been obtained and reduced for 22 planetary nebulae of varying size, structure, stellar population membership, dustiness, level of excitation, evolutionary status, and chemical compositions. The promise seems justified that with such extensive, high quality data, additional insights on nebular genesis and late states of stellar evolution can be found. The present survey is confined to nebulae of high surface brightness, but among these are found some engaging objects such as NGC 7027, IC 4997, and NGC 6572.

Although the asymmetric optical image of IC 2149 does not fall into any standard morphologies (Balick et al. 1993), the overall shape and its radio frequency image show a bilateral symmetry. The central star of spectral class O7.5 is a remarkable object with a rich spectrum showing many Fe ions. We discuss this spectrum in detail. The nebula has been studied utilizing our theoretical photoionization models. Detailed analyses of spectral data are done in both the UV region (lambda less than 3000 A; IUE) and the optical region (3500 A approximately 10500 A; the Hamilton Echelle at Lick Observatory). The plasma diagnostics suggest an electron temperature of 9000 approximately 10,000 K and an electron density near 5600 cm. Our model calculations were carried out with due regard to the above plasma diagnostics. The observations can be interpreted by a model of IC 2149 which consists of two components (an equatorial ring and a polar cone), but the total emission is dominated by the relatively denser equatorial shell. Carbon, nitrogen, and oxygen appear to be depleted by a factor of about 3; ratios of other elements are also lower than in the Sun.

Relative populations for the 17 fine-structure levels in the 5 D, 3 P, 3 H, 3 F, and 3 G states of the 3d 6 configuration in Fe III, calculated using electron impact excitation rates derived with the R-matrix code, are used to derive theoretical electron temperature and density sensitive emission-line ratios applicable to the spectra of astronomical objects in the 4607-5412 A wavelength range. A comparison of these with high spectral resolution observational data for the planetary nebula IC 4997 reveals generally good agreement between theory and observation. This provides experimental support for the accuracy of the theoretical ratios, and illustrates their usefulness in determining plasma parameters for the Fe III emitting region of a gaseous nebula

An optical and ultraviolet study is presented of object 28 of Sanduleak et al. (1978) in the SMC. This object is an extreme type of I PN which apparently has undergone all three stages of nuclear dredge-up together with an appreciable amount of convective envelope burning. Optical and UV data are well-represented by a model in which the central star has a temperature of 180,000 K and a radius of 0.09 solar radius. A nebular mass of 0.71 solar mass and a central star mass of 0.65-0.71 solar mass are inferred. The object apparently evolved from a massive progenitor with main-sequence mass greater than five solar masses, which underwent both second and third nuclear dredge-up and very efficient hot bottom burning.

The planetary nebula in the Fornax dwarf spheroidal galaxy is carbon rich, according to calculations based on measurements of the 1909 A emission line doublet of semiforbidden C III obtained with the International Ultraviolet Explorer. The ratio N(C)/N(O) is approximately equal to 3.7, comparable to the largest reliably determined carbon/oxygen ratios in high excitation planetaries of the Milky Way. The present result is based on four low-dispersion spectra with a combined exposure time of 27.2 hours; the Fornax planetary nebula is probably the most distant known planetary that can be observed with IUE. The IUE data were analyzed together with visible-wavelength emission-line fluxes reported by Danziger et al. (1978) to compute abundances for various elements. In terms of chemical composition, the Fornax nebula resembles planetary nebulae in the Magellanic Clouds more closely than it does typical or carbon-rich planetaries in the Galaxy.

Measurements of auroral and nebular type transitions in several planetary nebulae of high surface brightness lead to the conclusion that presently available collisional cross sections and transitions probabilities for 3p/sup 3/ configurations in Ar/sup +3/ may be in error. The observed auroral/nebular line ratio is always larger than the predicted value, and the disagreement is further aggravated if auroral lines are weakened by telluric line absorption.

A blue spectral survey and coarse photographic photometry are presented for 21 planetary nebulae, of which eight have not been heretofore observed with any detail. Eight of the nebulae have been observed photoelectrically. Most of the planetaries studied are of intermediate excitation; five present no detectable He ii lines, and two are of high excitation with powerful He ii lambda4686. The chief value of the photographic part of the study is to locate objects deserving of further study. Rough electron densities are derived for the nebulae from either or both of the O ii or Ar iv doublet ratios, and electron temperatures from the O iii lines. Values are generally within the normal range except for Hb 12, for which N/sub e/ may be as high as 4 x 10$sup 5$. (AIP)

On a mesure les raies de fluorescence de Bower de 17 nebuleuses planetaires et on a compare les intensites relatives des raies a celles que prevoit la theorie. O III I(λ3429)/I(λ3444) est beaucoup plus faible que prevu

Image tube observations carried out at the Lick and Mount Wilson Observatories were combined with IUE and infrared observations to study the spectra of the high-excitation planetary nebula NGC 6741. Plasma diagnostics were carried out and ion concentrations were calculated for ions from He I to Ca4(+). The ion densities and plasma diagnostics data were compared with theoretical nebular models to interpret the spectra and to obtain ionization correction factors. It is shown that the exciting star in NGC 6741 has an effective temperature near 160,000 K. The predicted abundance ratios for the lines at 5876/4686 A, 3426/3868 A, and 3727/5007 A conformed well to the observations. The derived logarithmic abundances in NGC 6741 are given in a table. 62 references.

Suitable IUE archival material on planetary nebulae has been examined to determine the log R /F(lambda 1909 C III)/F(lambda 1892 Si III)/ as a discriminant for distinguishing planetary nebulae from symbiotic stars and related objects. The mean value of log R for 73 galactic planetaries is 1.4, while that of extragalactic planetaries appears to be slightly lower, and that for symbiotics is 0.3. The lower value of log R for symbiotics is easily understood as a consequence of their higher densities. A plot of log R versus N-epsilon indicates that 80 percent of the planetaries fall into the range of log R between 1.2 and 1.8, but some of the 'peculiar' and bipolar nebulae fall below log R = 1.2. The corresponding N(C++)/N(Si++) ionic ratio varies over a large range.

New infrared observations of Ne II, Ar III, and S IV are used in optical observations of other ionization states of the considered elements to evaluate the abundances of neon, argon, and sulfur in 18 planetary nebulae. Attention is also given to one or more of the infrared lines in 18 other nebulae. It is pointed out that S IV was detected in approximately 90% of the observed objects, while Ar III was found in about 80%, and Ne II in roughly one-third. It is noted that optical observations typically include only a limited region of the nebula, while the infrared measurements frequently involve integration over the entire nebular image.

Ultraviolet spectra of the high excitation planetary nebulas LMC P40, SMC N2, and SMC N5 are presented in an investigation of their chemical composition in an effort to make reliable estimates of the carbon abundance in extragalactic planetary nebulas. The carbon abundance is found to be almost 40 times more abundant in the SMC planetaries than in the SMC interstellar medium, and is about 6 times more abundant in the LMC planetary than in the LMC interstellar medium. The net result of carbon synthesis and convective dredgeup in the progenitors of planetary nebulas as reflected in the nebular carbon abundance is roughly the same in the Galaxy, the LMC, and the SMC.

The double-ring planetary nebula IC 1297 resembles NGC 7662 in appearance, although it is of much lower surface brightness. What is remarkable is the great strength of the dielectronic recombination O V line. Although this line is seen as a P Cygni feature in a number of planetary nebulae, it is in those instances accompanied by a strong continuum and other easily recognized features of stellar origin. No star is visible on CCD images of IC 1297. Optical region measurements are supplemented by IUE observations. The following logarithmic abundance values are found: log N(He) = 11.065; log N(forbidden C) = 8.6; log N(N) = 8.1; log N(O) = 8.74; log N(Ne) = 8.16; log N(S) = 7.0; log N(Cl) = 5.4; log N(Ar) = 6.2. The nebula shows no dramatic pattern of nucleogenesis events.

L'etude concerne 139 nebuleuses planetaires parmi lesquelles 108 sont non stellaires, ∼50% presentent une symetrie bipolaire et ∼30% yne symetrie elliptique

Spectral scans of NGC 6720 obtained with the Robinson-Wampler image-tube scanner on the Lick 3.0 m reflector have been analyzed to obtain electron temperatures from the (N ii) lambdalambda5755/6584 ratio and electron densities from the (S ii) lambdalambda6717/6731 and (Cl III) lambdalambda5517/5537 ratios. Comparison of these data with those obtained by previous observers for (O II), (O III), and (S II) support the following model: The (S II), (Cl III), and presumably also the (N II) radiation originates in filaments somewhat denser and cooler than the (O i) emitting region, while the (O iii) radiation comes primarily from interior zones that are at least 1000 K hotter than the (N II) emitting regions. It also suggests that the (N ii) and (S ii) emission observed near the center of the nebula emission observed near the center of the nebula is produced by outer shell material seen in projection. (AIP)

Physical parameters of the central stars of the planetary nebulae (PN) P40, N2, and N5 are determined from UV observations by the IUE spacecraft and emission line-data. The observations took place on May 23 and 26, 1981. Derived properties, such as the H-beta, color excess, nebular hydrogen emission, helium emission, and stellar continuum emission, the stellar radius, surface gravity, Zanstra temperature, luminosity, absolute bolometric magnitude, apparent visual magnitude, mass, and Zanstra parameter for the three PN central stars are presented. All the masses were over one solar mass, suggesting a specific PN nuclei mass. The finding was corroborated by all luminosities exceeding the Eddington luminosity for a 0.6 solar mass star, which has previously been calculated for the white dwarf core of a PN.

Planetary nebula are now recognized as a penultimate stage in the evolution of many stars. Me 2-1 offers advantages meriting a detailed analysis. A description is presented of measurements regarding this object which have been conducted with a photoelectric scanner and a 3 m telescope Cassegrain image tube scanner. The chemical composition of Me 2-1 appears to fit well that of other planetaries. The values for N, O, and Ne fall slightly above those for an 'average' planetary, but Me 2-1 would not qualify as a nitrogen-rich object. When a comparison is made with the sun, there appears to be an enhancement of carbon, possibly slight enhancements of nitrogen and neon, but a slight reduction in oxygen.

A preliminary analysis of International Ultraviolet Explorer (IUE) low-dispersion spectrograms of NGC 2346, obtained at various phases of the eclipsing nucleus, shows features typical of a high-excitation planetary nebula. Variations in line profiles, intensities, and stellar continuum are observed as a function of time. An orbital period of 16.0 days was determined from 1.8m(v) variations measured by the IUE Fine Error Sensor (FES) and agrees with the period derived from radial velocity measurements by Mendez.

New measurements of the optical and ultraviolet emission-line intensities of the high-excitation planetary nebula NGC 2440 in the wavelength range 1240-8578 A are analyzed with the aid of photoionization models. The observed O III and N II forbidden-line temperatures (13,800 K and 10,000 K, respectively) differ by more than the models predict. Inclusion of charge-transfer reactions at published rates improves agreement between calculated and observed abundances of many ions, but worsens the agreement for several highly ionized ions. Nitrogen shows a larger overabundance N(N)/N(O) approximately equal to 1.0, whereas ultraviolet lines give a carbon abundance close to the solar value. The refractory elements magnesium, calcium, and iron have similar gas-phase depletions of approximately 1.5 dex. The abundances of oxygen, neon, sodium, sulfur, chlorine, potassium, and argon are rougly solar.

Nebular and central star parameters and elemental abundances of C, N, O, Ne, S, and Ar are presented for the planetary nebulae N2, N5, N43, N54, and N67 in the SMC and P2, P7, P9, P25, P33, and P40 in the LMC. The nebular chemical compositions are affected by nuclear processes in the precursor stars, which may not have been sufficiently massive to synthesize Ne, S, or Ar, which appear to be deficient with respect to their solar abundances by factors of roughly four and five for the LMC and SMC, respectively. Even after excluding nebulae formed by stars in which O apparently was destroyed by nuclear processes, O depletion in the LMC and SMC nebulae is significantly greater than in galactic planetaries. The estimated masses of the 12 remnant central stars range from 0.58 to 0.71 solar mass. 31 references.

Spectroscopic analysis of nebula NGC 6302 for identification as highly excited gaseous nebula, noting He-H ratio

Solar abundance of Y derived from Y II lines by computing transition probabilities and oscillator strength involving several configurations

The three field stars, HD 122563, HD 165195, and HD 221170, similar to giants in metal-poor globular clusters, show decreases in the average metal/ hydrogen ratios by factors of 800, 500, and 500, respectively, compared with the sun. The abundance ratios of other elements to iron resemble those in the sun, with important exceptions. Manganese and vanadium are deficient with respect to iron, by a factor of 3. In HD 122563 all elements heavier than zinc are deficient compared with iron by a factor of 50, yielding a total deficiency of about 50000 for the heavy elements. These observations are interpreted by assuming that the elements were synthesized from hydrogen early in the history of our Galaxy. These stars were formed when the interstellar medium was almost entirely hydrogen, between 10/sup 7/ and 10/sup 9/ years after star formation began. Their metallic constituents were formed and ejected from massive, rapidly evolving stars of extremely low metal content. Processing at high temperatures synthesized the elements from sodium through nickel which are now present in all three stars. The material that went into HD 122563 is drastically deficient in all elements produced by the addition of neutrons to the iron peak, whereasmore » light elements produced by neutron addition---aluminum and scandium--exist in normal amounts or are only slightly deficient. We interpret this to mean that when a flux of free neutrons became available, the progenitors of the light s-process elements were present, but the iron peak elements were rare or absent. The europium in HD 122563 may have been produced by the s-process, a very unexpected result. The presence of europium in HD 165195, in at least the normal ratio to the other elements, raises difficulties concerning r-process nucleosynthesis, since type I supernovae of small mass may not have begun to appear at the early epoch when the star was formed. 37 references. (auth)« less

The chemical composition of the atmosphere of the manganese star 53 Tauri was studied with the aid of data secured with the coude spectrograph of a 120-inch reflector. Transition probabilities required for the problem were obtained from laboratory sources whenever possible, but some were obtained by the calibration of stellar data. The temperature of the star, deduced from ionization equilibria, is near 11,000 deg K approximates -a value in good agreement with that found from spectral energy scans by Sargent and Jugaku. The electron pressure in the atmosphere, deduced from the total intensities of the hydrogen lines, appears to lie in the neighborhood of 500 dynes cm/sup -2/. Several striking abundance anomalies are found; they cannot be explained by deviations from local thermodynamic equilibrium. Manganese seems to be the most abundant metal in the star, but gallium appears to show the greatest enhancement of abundance over the normal value. Strontium, yttrium, and zirconium are also enhanced in abundance, while chromium and calcium seem to be depleted. (auth)