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Reliability Checks on the Indo-US Stellar Spectral Library Using Artificial Neural Networks and Principal Component Analysis
The Indo-US coudé feed stellar spectral library (CFLIB) madeavailable to the astronomical community recently by Valdes et al. (2004,ApJS, 152, 251) contains spectra of 1273 stars in the spectral region3460 to 9464Å at a high resolution of 1Å (FWHM) and a widerange of spectral types. Cross-checking the reliability of this databaseis an important and desirable exercise since a number of stars in thisdatabase have no known spectral types and a considerable fraction ofstars has not so complete coverage in the full wavelength region of3460-9464Å resulting in gaps ranging from a few Å to severaltens of Å. We use an automated classification scheme based onArtificial Neural Networks (ANN) to classify all 1273 stars in thedatabase. In addition, principal component analysis (PCA) is carried outto reduce the dimensionality of the data set before the spectra areclassified by the ANN. Most importantly, we have successfullydemonstrated employment of a variation of the PCA technique to restorethe missing data in a sample of 300 stars out of the CFLIB.
| New planetary nebulae in the Galactic bulge region with l > 0°- II
The presentation of new results from an [OIII] 5007-Å survey in asearch for planetary nebulae (PNe) in the Galactic bulge is continued. Atotal of 60 objects, including 19 new PNe, have been detected in theremaining 34 per cent of the survey area, while 41 objects are alreadyknown. Deep Hα+[NII] CCD images as well as low-resolution spectrahave been acquired for these objects. Their spectral signatures suggestthat the detected emission originates from photoionized nebulae. Inaddition, absolute line fluxes have been measured and the electrondensities are given. Accurate optical positions and optical diametersare also determined.
| SARG@TNG: asteroseismology of solar like stars.
Since 1995, the extrasolar planet search has driven the high resolutionspectroscopy community to build more and more stable spectrograph inorder to reach the photon statistics limit in radial velocitymeasurements. This situation opened the possibility of asteroseismicobservations of stellar p-mode pulsations in solar - like stars. In thispaper we describe the possible performance of the SARG spectrographitself in asterosimological campaigns on fainter solar-like stars.
| Stellar abundance gradients in galactic discs - I. Method and spectral line gradients
We describe the technique of absorption-line imaging of galaxy discsusing the Taurus Tunable Filter on the Anglo-Australian Telescope anddemonstrate its sensitivity to the behaviour of spectral featuresassociated with Mg and Fe. Radial profiles of Mg2 and Fe5270line strengths are presented for a sample of eight face-on spiralgalaxies spanning a range of Hubble types. Signatures of phenomenaincluding merger-induced star formation, HII rings and galactic bars arealso reported. This study demonstrates the capacity of tunable filtersto measure Mg and Fe line strengths across the face of spiral galaxies,which can ultimately reveal clues about the star formation history andchemical evolution.
| Group, field and isolated early-type galaxies - I. Observations and nuclear data
This is the first paper of a series on the investigation of stellarpopulation properties and galaxy evolution of an observationallyhomogeneous sample of early-type galaxies in groups, field and isolatedgalaxies.Here we present high signal-to-noise ratio (S/N) long-slit spectroscopyof 86 nearby elliptical and S0 galaxies. Eight of them are isolated,selected according to a rigorous criterion, which guarantees a genuinelow-density subsample. The present survey has the advantage of coveringa larger wavelength range than normally found in the literature, whichincludes [OIII]λ5007 and Hα, both lines important foremission correction. Among the 86 galaxies with S/N >= 15 (perresolution element, for re/8 central aperture), 57 have theirHβ-index corrected for emission (the average correction is 0.190Åin Hβ) and 42 galaxies reveal [OIII]λ5007 emission,of which 16 also show obvious Hα emission. Most of the galaxies inthe sample do not show obvious signs of disturbances nor tidal featuresin the morphologies, although 11 belong to the Arp catalogue of peculiargalaxies; only three of them (NGC 750, 751 and 3226) seem to be stronglyinteracting. We present the measurement of 25 central line-strengthindices calibrated to the Lick/IDS system. Kinematic information isobtained for the sample. We analyse the line-strength index versusvelocity dispersion relations for our sample of mainly low-densityenvironment galaxies, and compare the slope of the relations withcluster galaxies from the literature. Our main findings are that theindex-σ0 relations presented for low-density regionsare not significantly different from those of cluster E/S0s. The slopeof the index-σ0 relations does not seem to change forearly-type galaxies of different environmental densities, but thescatter of the relations seems larger for group, field and isolatedgalaxies than for cluster galaxies.
| Reddening and the Extinction Law at High Galactic Latitude
We present near-infrared (JHKL) photometry of 103 southern stars locatedbehind translucent interstellar clouds at high Galactic latitude. Ourdata are combined with visual photometry and spectral type informationfrom the literature in a detailed analysis of the wavelength dependenceof interstellar extinction by dust in these high-latitude clouds. Weinvestigate the shape of the near-infrared extinction curve and evaluatethe total line-of-sight extinction (AV) and ratio oftotal-to-selective extinction (RV) in each line of sight.Sources of uncertainty in RV arising from photometric errorsand spectral classification errors are carefully assessed and quantifiedas functions of the line-of-sight reddening. We detect appreciabledifferences in our results compared with the average extinction curvefor dust in the diffuse interstellar medium (ISM) close to the Galacticplane. Assuming a power-law form in the near-infrared, we find the meanfor high-latitude clouds to be well described by~λ-2.3, somewhat steeperthan that for the diffuse ISM(~λ-1.8). Our sampleincludes a substantial number of lines of sight with low RVvalues (47% with RV<2.8) relative to the diffuse ISMaverage of 3.05+/-0.15. We conclude that many high-latitude clouds haveenhanced abundances of relatively small grains.
| Heliocentric Dependence of Sodium Emission of Comet Hale-Bopp (C/1995O1)
A sequential spectroscopic observation of comet C/1995 O1 (Hale-Bopp)was performed from 1996 September to 1997 May. After the first positivedetection in early 1997 February, the development of the neutral sodiumemission was monitored during about 4 months around the perihelionpassage. The ratio of the sodium D-line emission relative to thecontinuum emission strength varied with the days from perihelion. Thesodium D-line emission was weak relative to the continuum near theperihelion because of the Swings effect. We corrected the Swings effect,the phase angle dependence of continuum emission, and the differences ingeocentric distance. We found that the corrected sodium-to-continuumratio varied with the dependence of r-k; k=5-6, r denotes aheliocentric distance of the comet. Our result supports the hypothesisof thermal desorption of sodium atoms from dust grains.
| Deep optical observations of the supernova remnants G 126.2+1.6, G 59.8+1.2 and G 54.4-0.3
Optical CCD imaging and spectroscopic observations of three supernovaremnants are presented. Optical emission from G 54.4-0.3 and G 59.8+1.2is detected for the first time, while the first flux calibrated CCDimages of the supernova remnant G 126.2+1.6 were performed in theoptical emission lines of Hα+[N II], [O III] and [S II]. A mixtureof filamentary and diffuse structures is observed in G 54.4-0.3 and G59.8+1.2, mainly in Hα+[N II], while the deep optical images of G126.2+1.6 reveal several new filamentary and diffuse structures insidethe extent of the remnant as defined by its known radio emission. In allcases, the radio emission is found to be well correlated with theoptical filaments. [O III] emission was not detected at G 54.4-0.3 and G59.8+1.2 while in G 126.2+1.6, significant morphological differencesbetween the low and medium ionization images are present suggestingincomplete shock structures. Deep long-slit spectra were taken atdifferent positions of the remnants. Both the flux calibrated images andthe long-slit spectra clearly show that the emission originates fromshock-heated gas, while some spectra of G 126.2+1.6 are characterized bylarge [O III]/Hβ ratios. This remnant's [O III] flux suggests shockvelocities into the interstellar "clouds" between 100 and 120 kms-1, while the [O III] absence in the other two remnantsindicates slower shock velocities. For all remnants, the [SII]λλ 6716/6731 ratio indicates electron densities below600 cm-3 with particularly low densities for G 54.4-0.3(below 50 cm-3). Finally, the Hα emission has beenmeasured to be between 3.0 to 15.2 × 10-17 ergs-1 cm-2 arcsec-2, 3.2 ×10-17 erg s-1 cm-2 arcsec-2and between 6.5 to 16.8 × 10-17 erg s-1cm-2 arcsec-2 for G 54.4-0.3, G 59.8+1.2 and G126.2+1.6, respectively.
| The faint supernova remnant G 116.5+1.1 and the detection of a new candidate remnant
The extended supernova remnant G 116.5+1.1 was observed in the opticalemission lines of Hα+[N II], [S II] and [O III}]; deep long slitspectra were also obtained. The morphology of the remnant's observedemission is mainly diffuse and patchy in contrast to the knownfilamentary emission seen along the western limb. The bulk of thedetected emission in the region appears unrelated to the remnant butthere is one area of emission in the south-east which is characterizedby a [S II]/Hα ratio of ~0.5, implying a possible relation to G116.5+1.1. If this is actually the case, it would imply a more extendedremnant than previously realized. Emission in the [O III] 5007 Åline image is not detected, excluding moderate or fast velocity shocksrunning into ionized interstellar clouds. Our current estimate of thedistance to G 116.5+1.1 of ~3 kpc is in agreement with earlier estimatesand implies a very extended remnant (69 pc × 45 pc). Observationsfurther to the north-east of G 116.5+1.1 revealed a network offilamentary structures prominent in Hα+[N II] and [S II] butfailed to detect [O III] line emission. Long slit spectra in a number ofpositions provide strong evidence that this newly detected emissionarises from shock heated gas. Typical Hα fluxes lie in the rangeof 9 to 17 × 10-17 erg s-1 cm-2arcsec-2, while low electron densities are implied by theintensities of the sulfur lines. Weak emission from the mediumionization line at 5007 Å is detected in only one spectrum. Cooldust emission at 60 and 100 microns may be correlated with the opticalemission in a limited number of positions. Surpisingly, radio emissionis not detected in published surveys suggesting that the new candidateremnant may belong to the class of “radio quiet” supernovaremnants.
| The Indo-US Library of Coudé Feed Stellar Spectra
We have obtained spectra for 1273 stars using the 0.9 m coudéfeed telescope at Kitt Peak National Observatory. This telescope feedsthe coudé spectrograph of the 2.1 m telescope. The spectra havebeen obtained with the no. 5 camera of the coudé spectrograph anda Loral 3K×1K CCD. Two gratings have been used to provide spectralcoverage from 3460 to 9464 Å, at a resolution of ~1 Å FWHMand at an original dispersion of 0.44 Å pixel-1. For885 stars we have complete spectra over the entire 3460 to 9464 Åwavelength region (neglecting small gaps of less than 50 Å), andpartial spectral coverage for the remaining stars. The 1273 stars havebeen selected to provide broad coverage of the atmospheric parametersTeff, logg, and [Fe/H], as well as spectral type. The goal ofthe project is to provide a comprehensive library of stellar spectra foruse in the automated classification of stellar and galaxy spectra and ingalaxy population synthesis. In this paper we discuss thecharacteristics of the spectral library, viz., details of theobservations, data reduction procedures, and selection of stars. We alsopresent a few illustrations of the quality and information available inthe spectra. The first version of the complete spectral library is nowpublicly available from the National Optical Astronomy Observatory(NOAO) via ftp and http.
| Optical and IUE Spectra of the Planetary Nebula NGC 7026
We investigated spectroscopic data of the extended planetary nebula NGC7026 in the wavelengths 3700-10,050 Å, secured with the HamiltonEchelle Spectrograph at Lick Observatory. This optical wavelengthspectrum has been analyzed along with the International UltravioletExplorer (IUE) UV spectral data. The diagnostic diagram indicates thatthe planetary nebula has very complex electron densities ofNɛ~3000-10,000 cm-3. The electrontemperatures are relatively low: around Tɛ=8000-9500K, probably as a result of an enhanced heavy elemental cooling. Theelectron temperature variation also indicates that the low-excitationline region is slightly higher than the high-excitation line regionsperhaps as a result of the hardening of escaped UV ionizing photons intothe outer shell part of low-excitation lines. We construct aphotoionization model, with the central star of the planetary nebula ata temperature of Teff=80,000 K, to fit most of the relativelystrong line intensities and the observed physical conditions. With thisphotoionization model construction and with a semiempirical ionizationcorrection method, we derived the elemental abundances of the nebula.Compared to the average or normal planetary nebula, most elementalabundances of He, C, N, O, Ne, S, Ar, and Cl appear to be enhanced.
| Proper Motion and Kinematics of the Ansae in NGC 7009
We have measured the proper motion (PM) and kinematics of the ansae inNGC 7009 using high-dispersion echelle spectra and archive narrowbandHubble Space Telescope images. Assuming that the ansae are moving atequal and opposite velocities from the central star, we obtain a systemradial velocity of -53+/-2 km s-1, the eastern ansaapproaching and the western ansa receding at vr=5.3+/-1 kms-1 with respect to this value. The PM of the eastern ansa is28+/-8 mas yr-1, which, with our weighted distance to NGC7009 of 0.86+/-0.34 kpc, gives Vexp=114+/-32 kms-1. The electron temperature and density in both ansae weredetermined to be Te~9000+/-400 K and ne~2300+/-400cm-3. The dynamic age of the ansae is ~910+/-260 yr, and theimplied PM of the central star is μCS=1+/-0.5 masyr-1. This is in qualitative but not quantitative agreementwith previous work.
| Empirically Constrained Color-Temperature Relations. II. uvby
A new grid of theoretical color indices for the Strömgren uvbyphotometric system has been derived from MARCS model atmospheres and SSGsynthetic spectra for cool dwarf and giant stars having-3.0<=[Fe/H]<=+0.5 and 3000<=Teff<=8000 K. Atwarmer temperatures (i.e., 8000-2.0. To overcome thisproblem, the theoretical indices at intermediate and high metallicitieshave been corrected using a set of color calibrations based on fieldstars having well-determined distances from Hipparcos, accurateTeff estimates from the infrared flux method, andspectroscopic [Fe/H] values. In contrast with Paper I, star clustersplayed only a minor role in this analysis in that they provided asupplementary constraint on the color corrections for cool dwarf starswith Teff<=5500 K. They were mainly used to test thecolor-Teff relations and, encouragingly, isochrones thatemploy the transformations derived in this study are able to reproducethe observed CMDs (involving u-v, v-b, and b-y colors) for a number ofopen and globular clusters (including M67, the Hyades, and 47 Tuc)rather well. Moreover, our interpretations of such data are verysimilar, if not identical, with those given in Paper I from aconsideration of BV(RI)C observations for the sameclusters-which provides a compelling argument in support of thecolor-Teff relations that are reported in both studies. Inthe present investigation, we have also analyzed the observedStrömgren photometry for the classic Population II subdwarfs,compared our ``final'' (b-y)-Teff relationship with thosederived empirically in a number of recent studies and examined in somedetail the dependence of the m1 index on [Fe/H].Based, in part, on observations made with the Nordic Optical Telescope,operated jointly on the island of La Palma by Denmark, Finland, Iceland,Norway, and Sweden, in the Spanish Observatorio del Roque de losMuchachos of the Instituto de Astrofisica de Canarias.Based, in part, on observations obtained with the Danish 1.54 mtelescope at the European Southern Observatory, La Silla, Chile.
| The supernova remnant G 6.4-0.1 and its environment
Flux calibrated CCD images, in the Hα+[N II], S II, and [O III]emission lines, of a wide field around the supernova remnant G 6.4-0.1are presented. The low ionization images identify a front of enhanced SII/Hα+[N II] ratio along the east-west direction. This front isvery well correlated with the filamentary radio emission of the remnantas well as with molecular CO emission and may indicate the interactionof the primary blast wave with molecular clouds present in the vicinityof the remnant. We estimate a total Hα flux, corrected forinterstellar extinction, of 2 × 10-8 erg s-1cm-2, and a total S II flux of 1.1 × 10-8erg s-1 cm-2. The Hα+[N II] and S II imagesprovide evidence for the presence of emission from shock heated gas tothe south-west and to the east of the bulk of the known opticalemission, implying that the primary shock wave is able to driveradiative shocks into the interstellar clouds. The image in the mediumionization line of [O III] 5007 Å does not reveal any filamentarystructures. On the contrary, the emission is diffuse and very weak,close to our detection limit of 5 × 10-17 ergs-1 cm-2 arcsec-2 (3 σ), andappears to be mainly present in the south-east to north-west areas ofthe remnant. The long-slit spectra indicate significant extinction inall positions observed, while the measured variations are within the 3σ error. The [O III] emission in the spectra, whenever present, isweaker than the ^hbeta flux suggesting shock velocities around 70 kms-1 or less all around the remnant in accordance with the [OIII] imagery. Thus, the low shock velocities are a common characteristicof G 6.4-0.1 and not just of the areas where the spectra were acquired.The average sulfur line ratio suggests postshock electron densitiesbelow 120 cm-3 at the 3 σ limit.
| Library of flux-calibrated echelle spectra of southern late-type dwarfs with different activity levels
We present Echelle spectra of 91 late-type dwarfs, of spectral typesfrom F to M and of different levels of chromospheric activity, obtainedwith the 2.15 m telescope of the CASLEO Observatory located in theArgentinean Andes. Our observations range from 3890 to 6690 Å, ata spectral resolution from 0.141 to 0.249 Å per pixel(R=λ/δ λ ≈ 26 400). The observations were fluxcalibrated with the aid of long slit spectra. A version of thecalibrated spectra is available via the World Wide Web.Table 2 is also available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/414/699The spectra are available as FITS and ascii-files at the URL:http://www.iafe.uba.ar/cincunegui/spectra/Table2.html. They are alsoavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/414/699. When convertingthe fits to ascii, the spectra were oversampled to a constant δλ ≈ 0.15 Å.Table 2 is also available in electronic form at the CDS via anonymous
| New planetary nebulae in the Galactic bulge region with l > 0°- I. Discovery method and first results
We present the first results of an [OIII] 5007 Å interferencefilter survey for planetary nebulae (PNe) in the Galactic bulge.Covering (at first) the 66 per cent of the survey area, we detected atotal of 90 objects, including 25 new PNe, 57 known PNe and eight knownPNe candidates. Deep Hα+[NII] CCD images have been obtained aswell as low-resolution spectra for the newly discovered PNe. Theirspectral signature suggests that the detected emission originates from aphotoionized nebula. In addition, absolute line fluxes have beenmeasured and the electron densities are given. Accurate opticalpositions and optical diameters have also been determined.
| Optical Spectrum of CI Aql in the Plateau Phase
Not Available
| High-Resolution Observations of Interstellar Ca I Absorption-Implications for Depletions and Electron Densities in Diffuse Clouds
We present high-resolution (FWHM~0.3-1.5 km s-1) spectra,obtained with the AAT UHRF, the McDonald Observatory 2.7 m coudéspectrograph, and/or the KPNO coudé feed, of interstellar Ca Iabsorption toward 30 Galactic stars. Comparisons of the column densitiesof Ca I, Ca II, K I, and other species-for individual componentsidentified in the line profiles and also when integrated over entirelines of sight-yield information on relative electron densities anddepletions (dependent on assumptions regarding the ionizationequilibrium). There is no obvious relationship between the ratio N(CaI)/N(Ca II) [equal to ne/(Γ/αr) forphotoionization equilibrium] and the fraction of hydrogen in molecularform f(H2) (often taken to be indicative of the local densitynH). For a smaller sample of sight lines for which thethermal pressure (nHT) and local density can be estimated viaanalysis of the C I fine-structure excitation, the average electrondensity inferred from C, Na, and K (assuming photoionizationequilibrium) seems to be independent of nH andnHT. While the electron density (ne) obtained fromthe ratio N(Ca I)/N(Ca II) is often significantly higher than the valuesderived from other elements, the patterns of relative nederived from different elements show both similarities and differencesfor different lines of sight-suggesting that additional processesbesides photoionization and radiative recombination commonly andsignificantly affect the ionization balance of heavy elements in diffuseinterstellar clouds. Such additional processes may also contribute tothe (apparently) larger than expected fractional ionizations(ne/nH) found for some lines of sight withindependent determinations of nH. In general, inclusion of``grain-assisted'' recombination does reduce the inferred ne,but it does not reconcile the ne estimated from differentelements; it may, however, suggest some dependence of ne onnH. The depletion of calcium may have a much weakerdependence on density than was suggested by earlier comparisons with CHand CN. Two appendices present similar high-resolution spectra of Fe Ifor a few stars and give a compilation of column density data for Ca I,Ca II, Fe I, and S I.
| The faint supernova remnant G 34.7-0.4 (W44)
Flux calibrated images of the known supernova remnant G 34.7-0.4 inbasic optical emission lines are presented. The low ionization imagesshow a relatively flat flux distribution. The diffuse and patchymorphology of the detected optical emission may indicate the presence ofturbulent magnetic fields. Typical observed Hnii fluxes are 8× 10-17 erg s-1 cm-2arcsec-2, while the Sii fluxes are lower around 4 ×10-17 erg s-1 cm-2 arcsec-2.Emission in the medium ionization line of [ion {O}{iii}] 5007 Å isnot detected within our sensitivity limits, probably due to the heavyextinction towards the remnant. The long-slit spectra reveal strong Siiand [ion {N}{ii}] emission relative to Ha and moderate [ion {O}i] 6300Å emission. Shock velocities in the range of 110-150 kms-1 and low electron densities are estimated. Archival MSXinfrared data show emission in the south and west areas of the remnantmatching rather well the optical and radio emission.
| Spectral evolution of Nova (V1494) Aql and its high velocity jets
Spectral evolution of the fast nova V1494 Aql was monitored soon afterits discovery in December 1999 to September 2000. The first spectrashowed prominent emission lines of H I and Fe II, while He I was seen inabsorption. The radial velocities of the absorption components of H I,He I and N II rapidly increased (in the negative sense) during the earlydecline stage, while those of Fe II remained nearly constant. When a newspectrum was taken on February 6, 2000 after the seasonal interruption,this nova was in the transition stage. The spectra in the transitionstage showed emission lines of H I, He I, He II, N II, N III, Si II, [NII], [O I], [O III], [Fe II], [Fe VI], [Ca V] etc., hence the emissionlines of Fe II had disappeared. A quasi-periodic oscillation ofluminosity with a time scale of about 16.5+/- 1 days and a meanamplitude of about 1.2 mag in V band was seen from February to themiddle of April 2000. The emission lines of He II and [Ca V] disappearedaround a light maximum of the oscillation, while the emission lines of NII and N III strengthened. At the same time high velocity (-2900 and+2830 km s-1) broad emission wings of H I lines appeared,which suggest an ejection of high velocity jets. The excitation stateincreased throughout the nebular stage. The last spectra taken inSeptember 2000 showed highly excited emission lines up to [Fe VII] and[Fe X] ł6374.5.The interstellar extinction is estimated as E(B-V)=0.6+/- 0.1 from theequivalent widths of the interstellar absorption components of Na I D1and D2. Using this result, the distance to the nova is estimated as 1.6+/- 0.2 kpc. The mass and the helium abundance of the ejecta areestimated as 6.2 +/- 1.4 x 10-5 Msun andN(He)/N(H) = 0.13 +/- 0.01, respectively. The electron density of theejecta decreased as Ne ~ t-0.8 during the nebularstage, where t is time from light maximum. This low decline ratesuggests that the ejecta had a ring like shape as well a large mass losswhich may have continued throughout the nebular stage.Table 1 is only available in electronic form athttp://www.edpsciences.org
| Optical line emission from the supernova remnant G 73.9+0.9
Flux calibrated images of the field around the known supernova remnant G73.9+0.9 in the Hiα+[N Ii], [S Ii], [O Ii], and [O Iii] emissionlines are presented. The low ionization images are characterized bydiffuse emission both within and outside the extent of the remnant. Theflux calibrated images revealed a few small scale structures in the eastareas of G 73.9+0.9. The long-slit spectra identify the emission fromone of them as emission from shock heated gas. This patchy structure is 3 arcmin long and emits Hα flux at a level of 33× 10-17 erg s-1 cm-2arcsec-2. The bright diffuse arc-like structure in the centerof the field seems to be associated to G 73.9+0.9 given its spectralsignature and positional relation with the non-thermal radio emission. A8 arcmin long filamentary structure with an absolute Hα fluxof 9 × 10-17 erg s-1 cm-2arcsec-2 is detected in the [O Iii] emission line to thesouth of G 73.9+0.9 but is probably unrelated. The deep long-slitspectra suggest complete recombination zones, shock velocities below 90km s-1, low electron densities (<50 cm-3) andnon-negligible magnetic field strengths.
| Chemical Abundances of NGC 5461 and NGC 5471 Derived from Echelle Spectrophotometry
We present high resolution spectroscopic data of the two giantextragalactic H II regions NGC 5461 and NGC 5471 in M101, which havebeen obtained with the 2.1-m telescope of the Observatorio AstronómicoNacional in San Pedro Mártir, Baja California. We measured theintensities of several H and He recombination lines, and of forbiddenlines of a large number of ions. We calculate the physical conditions inthe two nebulae with a large number of diagnostics and determine theirchemical abundances by applying ionization correction factors (icf's) to the observed ionic abundances. For NGC 5461, theicf's are based on a tailored photoionization model of the region(Luridiana & Peimbert 2001), while for NGC 5471 they are computedfrom those predicted by a photoionization model of NGC 2363 (Luridiana,Peimbert, & Leitherer 1999), a region which is similar to NGC 5471in the ionization structure. For both regions, the icf's arecompared to those computed following the prescriptions by Mathis &Rosa (1991). Such comparison shows large discrepancies for severalelements, including nitrogen, neon, and chlorine.
| New optical filamentary structures in Pegasus
Deep Hα N II CCD images have been obtained in the area of thePegasus Constellation. The resulting mosaic covers an extent of ~ 7.5deg × 7.5 and filamentary and diffuse emission was discovered.Several long filaments (up to ~ 1 deg ) are found within the field,while diffuse emission is present mainly in the central and northernareas. The filaments show variations in intensity along their extentsuggesting inhomogeneous interstellar clouds. Faint soft X-ray emissionwas also detected in the ROSAT All-Sky Survey. It is mainly concentratedin the central areas of our field and overlaps the optical emission. Thelow ionization images of [S II] of selected areas mainly show faintdiffuse emission, while in the medium ionization images of [O III]diffuse and faint filamentary structures are present. Spectrophotometricobservations were performed on the brightest filaments and indicateemission from photoionized or shock-heated gas. The sulfur line ratiosindicate electron densities below ~ 600 cm-3, while theabsolute Hα emission lies in the range of 1.1 - 8.8 ×10-17 erg s-1 cm-2 arcsec-2.The detected optical line emission could be part of a single or multiplesupernova explosions.
| Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897
| Deep optical observations of G 65.3+5.7
We present the first CCD mosaic of the supernova remnant {G 65.3+5.7} inthe optical emission lines of [O Ii] and [O Iii]. The new images revealseveral diffuse and filamentary structures both inside and outside theextent of the remnant as defined by its X-ray and radio emission. Themedium ionization line of [O Iii] 5007 Å provides the sharpestview to the system, while the remnant appears less filamentary in theemission line of [O Ii]. There are significant morphological differencesbetween the two images strongly suggesting the presence of incompleteshock structures. Deep long-slit spectra were taken at several differentpositions of G 65.3+5.7. All spectra originate from shock heated gas,while the majority of them is characterized by large [O Iii]/hbetaratios. The sulfur line ratios indicate electron densities below ~200cm-3, while estimates of the shock velocities lie in therange of 90-140 km s-1. Finally, the observed variations ofthe ^ha/^h$beta ratios may reflect the presence of intrinsic absorptionaffecting the optical spectra.
| Optical observations of the supernova remnant G 69.4+1.2
We performed deep optical observations of the area of the new supernovaremnant G 69.4+1.2 in the emission lines of [O Iii], Hα+[N Ii] and[S Ii]. The low ionization images reveal diffuse and filamentaryemission in the central and south, south-west areas of our field.Estimates of the [S Ii]/Hα ratio suggest that the detectedemission in these areas originates from shock heated gas, while thestrong extended source in the north must be an H Ii region. The mediumionization image of [O Iii] shows a single filament close to the fieldcenter. Emission from [O Iii] is not detected elsewhere in the field butonly in the north from LBN 069.96+01.35. Deep long-slit spectra taken atthe position of the [O Iii] filament suggest shock velocities ~120 kms-1, while in other areas velocities around 50 kms-1 are expected. The sulfur lines ratio indicates electrondensities less than 120 cm-3. The absolute Hα flux is~5 × 10-17 erg s-1 cm-2arcsec-2. The optical emission is very well correlated withthe radio emission, especially in the south west. The soft X-rayemission detected in the ROSAT All-Sky survey shows a satisfactorydegree of correlation with the optical data in the south-west suggestingtheir association.
| First optical light from the supernova remnant G 17.4-2.3
Deep optical CCD images of the supernova remnant G 17.4-2.3 wereobtained and faint emission has been discovered therein. The images,taken in the emission lines of Hα+[N Ii], [S ii] and [O Iii],reveal filamentary structures in the east, south-east area, whilediffuse emission in the south and central regions of the remnant is alsopresent. The radio emission in the same area is found to be wellcorrelated with the brightest optical filament. The flux calibratedimages suggest that the optical filamentary emission originates fromshock-heated gas ([S ii]/Hα) > 0.4), while the diffuse emissionseems to originate from an H Ii region ([S ii]/Hα) < 0.3).Furthermore, deep long-slit spectra were taken at the bright [O Iii]filament and clearly show that the emission originates from shock heatedgas. The [O Iii] flux suggests shock velocities into the interstellar``clouds'' greater than 100 km s-1, while the [S Ii] lambda6716/6731 ratio indicates electron densities ~240 cm-3.Finally, the Hα emission has been measured to be between 7 to 20× 10-17 erg s-1 cm-2arcsec-2.
| Imaging and spectroscopy of the faint remnant G 114.3+0.3
We present the first calibrated CCD images of the faint supernovaremnant {G 114.3+0.3} in the emission lines of [O Ii], [O Iii],Hα+NII and [S Ii]. The deep low ionization CCD imagesreveal diffuse emission in the south and central areas of the remnant.These are correlated with areas of intense radio emission, whileestimates of the [S Ii]/Hα ratio suggest that thedetected emission originates from shock heated gas. In the mediumionization image of [O Ii]i we discovered a thin filament in the southmatching very well the outer radio contours. This filament is notcontinuous over its total extent but shows variations in the intensity,mainly in the south-west, suggesting inhomogeneous interstellar clouds.Deep long-slit spectra were also taken along the [O Iii] filamentclearly identifying the observed emission as emission from shock heatedgas. The Hα emission is a few times 10-17erg s-1 cm-2 arcsec-2, while thevariations seen in the [O Iii] flux suggest shock velocities into theinterstellar clouds around or below 100 km s-1. The sulfurline ratio approaches the low density limit, implying electron densitiesless than ~500 cm-3.
| A new candidate supernova remnant in Cygnus
Deep optical CCD imaging and spectroscopic observations of four newnebular structures have been performed for the first time. Filamentaryand diffuse emission is detected in this field located to the north-eastof the CTB 80 supernova remnant (SNR). Two longfilaments are discovered to the north of LBN 156, while a 23 arcmin longfilament, emitting strongly in the [O Ii]i line, is present to the eastof LBN 156. A complex and compact network of filaments is located closeto the center of our field. Finally, the last new source of lineemission detected in this field is mainly diffuse and patchy and itsmorphology displays a semi-circular shape. The long-slit spectra ofthese structures indicate emission from shock-heated gas and theobserved variations in the [O Ii]i fluxes most likely reflectdifferences in the shock velocities. Weak radio emission at 4850 MHzseems correlated with almost all of the new structures. It is proposedthat all these structures, with the possible exception of the brightestone, are part of a single supernova remnant. Detailed radio observationsshould allow the determination of the nature of the radio emission andprovide a crucial test of our suggested intepretation.
| SARG: the high resolution spectrograph of TNG.
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