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Ýlgili Makaleler
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.
| Probable nonradial g-mode pulsation in early A-type stars
Context: . Aims: .Asteroseismology of early A-type stars could bea new tool to test stellar convection theories. Methods: .A surveyfor line profile variability in early A-type stars has been performed inorder to detect nonradial pulsation signatures. Results: .The starHR 6139, with spectral type A2V and estimated T{eff}=8800 K,shows evident line profile variations that can be explained byoscillations in prograde g-modes. This feature and the known photometricvariability are similar to those observed in the Slowly Pulsating B-typestars. However HR 6139 is much cooler than the cool border of theinstability strip of such variables, and it is hotter than the blue edgeof the δ Scuti instability strip. There are indications of a tinyvariability also in other four objects, whose nature is not yetclear. Conclusions: .
| Decay of Planetary Debris Disks
We report new Spitzer 24 μm photometry of 76 main-sequence A-typestars. We combine these results with previously reported Spitzer 24μm data and 24 and 25 μm photometry from the Infrared SpaceObservatory and the Infrared Astronomy Satellite. The result is a sampleof 266 stars with mass close to 2.5 Msolar, all detected toat least the ~7 σ level relative to their photospheric emission.We culled ages for the entire sample from the literature and/orestimated them using the H-R diagram and isochrones; they range from 5to 850 Myr. We identified excess thermal emission using an internallyderived K-24 (or 25) μm photospheric color and then compared allstars in the sample to that color. Because we have excluded stars withstrong emission lines or extended emission (associated with nearbyinterstellar gas), these excesses are likely to be generated by debrisdisks. Younger stars in the sample exhibit excess thermal emission morefrequently and with higher fractional excess than do the older stars.However, as many as 50% of the younger stars do not show excessemission. The decline in the magnitude of excess emission, for thosestars that show it, has a roughly t0/time dependence, witht0~150 Myr. If anything, stars in binary systems (includingAlgol-type stars) and λ Boo stars show less excess emission thanthe other members of the sample. Our results indicate that (1) there issubstantial variety among debris disks, including that a significantnumber of stars emerge from the protoplanetary stage of evolution withlittle remaining disk in the 10-60 AU region and (2) in addition, it islikely that much of the dust we detect is generated episodically bycollisions of large planetesimals during the planet accretion end game,and that individual events often dominate the radiometric properties ofa debris system. This latter behavior agrees generally with what we knowabout the evolution of the solar system, and also with theoreticalmodels of planetary system formation.
| 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 physical properties of normal A stars
Designating a star as of A-type is a result of spectral classification.After separating the peculiar stars from those deemed to be normal usingthe results of a century of stellar astrophysical wisdom, I define thephysical properties of the "normal" stars. The hotter A stars haveatmospheres almost in radiative equilibrium. In the A stars convectivemotions can be found which increase in strength as the temperaturedecreases.
| MARCS: Model Stellar Atmospheres and Their Application to the Photometric Calibration of the Spitzer Space Telescope Infrared Spectrograph (IRS)
We describe state-of-the-art MARCS-code model atmospheres generated fora group of A dwarf, G dwarf, and late-G to mid-K giant standard stars,selected to photometrically calibrate the Spitzer Space TelescopeInfrared Spectrograph (IRS) and compare the synthetic spectra toobservations of HR 6688, HR 6705, and HR 7891. The general calibrationprocesses and uncertainties are briefly described, and the differencesbetween various templated composite spectra of the standards areaddressed. In particular, a contrast between up-to-date modelatmospheres and previously published composite and synthetic spectra isillustrated for wavelength ranges around 8 μm (where the SiOΔv=1 band occurs for the cooler standards) and λ>=20μm, where the use of the Engelke function will lead to increasinglylarge discrepancies as a result of the neglect of gravity in cool stars.At this point, radiometric requirements are being met, absolute fluxcalibration uncertainties (1 σ) are ~20% in the Short-High andLong-High data and ~15% in the Short-Low and Long Low data, andorder-to-order flux uncertainties are ~10% or less. Iteration betweenthe MARCS model atmosphere inputs and the data processing will improvethe S/N ratios and calibration accuracies.
| 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.
| 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.
| 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.
| Elemental abundance analyses with DAO spectrograms. XXVII. The superficially normal stars theta And (A2 IV), epsilon Del (B6 III), epsilon Aqr (A1.5 V), and iota And (B9 V)
The superficially normal stars theta And (A2 V), epsilon Del (B6 III),epsilon Aqr (A1.5 V), and iota And (B9 V), which have rotationallybroadened line profiles, are analyzed in a manner consistent withprevious studies of this series using 2.4 Åmm-1spectrograms obtained with CCD detectors and S/N >=200. Theirvariable radial velocities strongly suggest they are spectroscopicbinaries. As no evidence is seen for lines of their companions they areanalyzed as single stars. Their derived abundances are generally nearsolar. But those for theta And suggest that it is possibly a fastrotating Am star.Table 5 is only 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/406/975
| 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.
| Automated spectroscopic abundances of A and F-type stars using echelle spectrographs. II. Abundances of 140 A-F stars from ELODIE
Using the method presented in Erspamer & North (\cite{erspamer},hereafter Paper I), detailed abundances of 140 stars are presented. Theuncertainties characteristic of this method are presented and discussed.In particular, we show that for a S/N ratio higher than 200, the methodis applicable to stars with a rotational velocity as high as 200 kms-1. There is no correlation between abundances and Vsin i,except a spurious one for Sr, Sc and Na which we explain by the smallnumber of lines of these elements combined with a locally biasedcontinuum. Metallic giants (Hauck \cite{hauck}) show larger abundancesthan normal giants for at least 8 elements: Al, Ca, Ti, Cr, Mn, Fe, Niand Ba. The anticorrelation for Na, Mg, Si, Ca, Fe and Ni with Vsin isuggested by Varenne & Monier (\cite{varenne99}) is not confirmed.The predictions of the Montréal models (e.g. Richard et al.\cite{richard01}) are not fulfilled in general. However, a correlationbetween left [(Fe)/(H)right ] and log g is found for stars of 1.8 to 2.0M_sun. Various possible causes are discussed, but the physical realityof this correlation seems inescapable.Based on observations collected at the 1.93 m telescope at theObservatoire de Haute-Provence (St-Michel l'Observatoire, France) andCORALIE.Based on observations collected at the Swiss 1.2 m Leonard Eulertelescopes at the European Southern Observatory (La Silla, Chile).Tables 5 and 6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u.strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/1121
| 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.
| 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
| On the effective temperatures and surface gravities of superficially normal main sequence band B and A stars
Effective temperatures and surface gravities for 48 main sequence band Band A stars were found by matching optical region spectrophotometry andHγ profiles with the predictions of ATLAS9 solar composition modelatmospheres. When these values were compared with those found usingStrömgren uvbybeta photometry based on ATLAS6 model atmospheres, wefound a difference (photometry-spectrophotometry) of 25+/- 118 K for 29stars with 8000 K le Teff <= 10 050 K compared to 76 +/-105 K for 14 stars with 10 050 K <= Teff <= 17 000 K.The surface gravity scales are in agreement. These stars aresufficiently hot that their effective temperatures and surface gravitydeterminations are unaffected by discrepancies due to the choice ofMixing-Length or Canuto-Mazzitelli convection theories.
| 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.
| Rotational velocities of A-type stars. I. Measurement of v sin i in the southern hemisphere
Within the scope of a Key Programme determining fundamental parametersof stars observed by HIPPARCOS, spectra of 525 B8 to F2-type starsbrighter than V=8 have been collected at ESO. Fourier transforms ofseveral line profiles in the range 4200-4500 Å are used to derivev sin i from the frequency of the first zero. Statistical analysis ofthe sample indicates that measurement error is a function of v sin i andthis relative error of the rotational velocity is found to be about 6%on average. The results obtained are compared with data from theliterature. There is a systematic shift from standard values from\citet{Slk_75}, which are 10 to 12% lower than our findings. Comparisonswith other independent v sin i values tend to prove that those fromSlettebak et al. are underestimated. This effect is attributed to thepresence of binaries in the standard sample of Slettebak et al., and tothe model atmosphere they used. Based on observations made at theEuropean Southern Observatory (ESO), La Silla, Chile, in the frameworkof the Key Programme 5-004-43K. Table 4 is only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5)or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/105
| Far-Ultraviolet Spectra of B Stars near the Ecliptic
Spectra of B stars in the wavelength range of 911-1100 Å have beenobtained with the Espectrógrafo Ultravioleta de RadiaciónDifusa (EURD) spectrograph on board the Spanish satellite MINISAT-01with ~5 Å spectral resolution. International Ultraviolet Explorer(IUE) spectra of the same stars have been used to normalize Kuruczmodels to the distance, reddening, and spectral type of thecorresponding star. The comparison of eight main-sequence stars studiedin detail (α Vir, ɛ Tau, λ Tau, τ Tau, αLeo, ζ Lib, θ Oph, and σ Sgr) shows agreement withKurucz models, but observed fluxes are 10%-40% higher than the models inmost cases. The difference in flux between observations and models ishigher in the wavelength range between Lyα and Lyβ. Wesuggest that Kurucz models underestimate the far-ultraviolet (FUV) fluxof main-sequence B stars between these two Lyman lines. Computation offlux distributions of line-blanketed model atmospheres including non-LTEeffects suggests that this flux underestimate could be due to departuresfrom LTE, although other causes cannot be ruled out. We found that thecommon assumption of solar metallicity for young disk stars should bemade with care, since small deviations can have a significant impact onFUV model fluxes. Two peculiar stars (ρ Leo and ɛ Aqr) and twoemission-line stars (ɛ Cap and π Aqr) were also studied. Ofthese, only ɛ Aqr has a flux in agreement with the models. The resthave strong variability in the IUE range and/or uncertain reddening,which makes the comparison with models difficult. Based on thedevelopment and utilization of the Espectrógrafo Ultravioleta deRadiación Difusa, a collaboration of the Spanish InstitutoNacional de Técnica Aeroespacial and the Center for EUVAstrophysics, University of California, Berkeley.
| Stellar populations in Seyfert 2 galaxies. I. Atlas of near-UV spectra
We have carried out a uniform spectroscopic survey of Seyfert 2 galaxiesto study the stellar populations of the host galaxies. New spectra havebeen obtained for 79 Southern galaxies classified as Seyfert 2 galaxies,7 normal galaxies, and 73 stars at a resolution of 2.2 Å over thewavelength region 3500-5300 Å. Cross-correlation between thestellar spectra is performed to group the individual observations into44 synthesis standard spectra. The standard groups include a solarabundance sequence of spectral types from O5 to M3 for dwarfs, giants,and supergiants. Metal-rich and metal-weak F-K giants and dwarfs arealso included. A comparison of the stellar data with previouslypublished spectra is performed both with the individual spectra and thestandard groups. For each galaxy, two distinct spatial regions areconsidered: the nucleus and the external bulge. Spectroscopic variationsfrom one galaxy to another and from the central to the external regionare briefly discussed. It is found that the central region of a Seyfert2 galaxy, after subtracting the bulge stellar population, always shows anear-UV spectrum similar to one of three representative categories: a)many strong emission lines and only two visible absorption lines (Ca IiK and G band) (Sey2e); b) few emission lines, many absorption lines, anda redder continuum than the previous category (Sey2a); c) an almost flatcontinuum and high-order Balmer lines seen in absorption (Sey2b). Theproportion of Seyfert 2 galaxies belonging to each class is found to be22%, 28%, and 50% respectively. We find no significative differencesbetween morphology distributions of Seyfert 2 galaxies with Balmer linesdetected in absorption and the rest of the sample. This quick lookthrough the atlas indicates that half of Seyfert 2 galaxies harbour ayoung stellar population (about or less than 100 Myr) in their centralregion, clearly unveiled by the high order Balmer series seen inabsorption. Based on observations collected at the European SouthernObservatory, Chile (ESO 65.P-0014(A)). Tables 1-3 and 8 and Fig. A.1(Appendix A) are only available in electronic form athttp://www.edpsciences.org
| The supernova remnants G 67.7+1.8, G 31.5-0.6 and G 49.2-0.7
Optical CCD imaging and spectroscopic observations of three supernovaremnants have been performed for the first time. Filamentary and diffuseemission is discovered from the supernova remnant G 67.7+1.8 located ~82arcmin to the south of CTB 80's pulsar. The Hα and sulfur emissionare almost equally strong at a level of ~ 20 10-17 ergs-1 cm-2 arcsec-2 suggestingshock-heated emission. Electron densities less than 240 cm-3are estimated, while the weak [ion {O}{iii}] emission suggests shockvelocities in the range of 60-80 km s-1. Emission can also beseen in the ROSAT All Sky Survey data which indicate an extended hardX-ray source. Emission from G 31.5-0.6 is detected only in theHα+[ion {N}{ii}] image at a typical flux level of 3510-17 erg s-1 cm-2 arcsec-2.The morphology of the observed radiation is diffuse and partiallycorrelated with the non-thermal radio emission. Deep long-slit spectradetect sulfur line emission which is not strong enough to identify it asemission from shocked gas. Finally, optical emission from G 49.2-0.7 isobscured by several dark nebulae which probably give rise to significantX-ray attenuation. The Hα+[ion {N}{ii}] flux is typically ~4010-17 erg s-1 cm-2 arcsec-2while the [ion {S}{ii}] flux is very weak, not allowing itsidentification as shock-heated. However, a small area of ~3 arcmin× 1 arcmin emits strong sulfur flux relative to Hα ([ion{S}{ii}]/Hα ~ 0.6). This area is located in the south-east of G49.2-0.7, close to the outer boundaries of the X-ray and radio emission.However, deep optical spectra would be required to firmly establish thenature of this emission and its association to G 49.2-0.7.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable 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/qcar?J/A+A/367/521
| Research Note Hipparcos photometry: The least variable stars
The data known as the Hipparcos Photometry obtained with the Hipparcossatellite have been investigated to find those stars which are leastvariable. Such stars are excellent candidates to serve as standards forphotometric systems. Their spectral types suggest in which parts of theHR diagrams stars are most constant. In some cases these values stronglyindicate that previous ground based studies claiming photometricvariability are incorrect or that the level of stellar activity haschanged. Table 2 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/367/297
| The proper motions of fundamental stars. I. 1535 stars from the Basic FK5
A direct combination of the positions given in the HIPPARCOS cataloguewith astrometric ground-based catalogues having epochs later than 1939allows us to obtain new proper motions for the 1535 stars of the BasicFK5. The results are presented as the catalogue Proper Motions ofFundamental Stars (PMFS), Part I. The median precision of the propermotions is 0.5 mas/year for mu alpha cos delta and 0.7mas/year for mu delta . The non-linear motions of thephotocentres of a few hundred astrometric binaries are separated intotheir linear and elliptic motions. Since the PMFS proper motions do notinclude the information given by the proper motions from othercatalogues (HIPPARCOS, FK5, FK6, etc.) this catalogue can be used as anindependent source of the proper motions of the fundamental stars.Catalogue (Table 3) is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222
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| Takýmyýldýz: | Kova |
| Sað Açýklýk: | 20h47m40.60s |
| Yükselim: | -09°29'45.0" |
| Görünürdeki Parlaklýk: | 3.77 |
| Uzaklýk: | 70.373 parsek |
| özdevim Sað Açýklýk: | 33.1 |
| özdevim Yükselim: | -35.7 |
| B-T magnitude: | 3.769 |
| V-T magnitude: | 3.758 |
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