Садржај
Слике
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
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.
| The Calar Alto lunar occultation program: update and new results
We present an update of the lunar occultation program which is routinelycarried out in the near-IR at the Calar Alto Observatory. A total of 350events were recorded since our last report (Fors et al. 2004, A&A,419, 285). In the course of eight runs we have observed, among others,late-type giants, T-Tauri stars, and infrared sources. Noteworthy was apassage of the Moon close to the galactic center, which produced a largenumber of events during just a few hours in July 2004. Results includethe determinations of the angular diameter of RZ Ari,and the projected separations and brightness ratios for one triple and13 binary stars, almost all of which representing first time detections.Projected separations range from 0farcs09 to 0farcs007. We provide aquantitative analysis of the performance achieved in our observations interms of angular resolution and sensitivity, which reach about 0farcs003and K ≈8.5 mag, respectively. We also present a statisticaldiscussion of our sample, and in particular of the frequency ofdetection of binaries among field stars.
| B Star Rotational Velocities in h and χ Persei: A Probe of Initial Conditions during the Star Formation Epoch?
Projected rotational velocities (vsini) have been measured for 216 B0-B9stars in the rich, dense h and χ Persei double cluster and comparedwith the distribution of rotational velocities for a sample of fieldstars having comparable ages (t~12-15 Myr) and masses (M~4-15Msolar). For stars that are relatively little evolved fromtheir initial locations on the zero-age main sequence (ZAMS) (those withmasses M~4-5 Msolar), the mean vsini measured for the h andχ Per sample is slightly more than 2 times larger than the meandetermined for field stars of comparable mass, and the cluster and fieldvsini distributions differ with a high degree of significance. Forsomewhat more evolved stars with masses in the range 5-9Msolar, the mean vsini in h and χ Per is 1.5 times thatof the field; the vsini distributions differ as well, but with a lowerdegree of statistical significance. For stars that have evolvedsignificantly from the ZAMS and are approaching the hydrogen exhaustionphase (those with masses in the range 9-15 Msolar), thecluster and field star means and distributions are only slightlydifferent. We argue that both the higher rotation rates and the patternof rotation speeds as a function of mass that differentiatemain-sequence B stars in h and χ Per from their field analogs werelikely imprinted during the star formation process rather than a resultof angular momentum evolution over the 12-15 Myr cluster lifetime. Wespeculate that these differences may reflect the effects of the higheraccretion rates that theory suggests are characteristic of regions thatgive birth to dense clusters, namely, (1) higher initial rotationspeeds; (2) higher initial radii along the stellar birth line, resultingin greater spin-up between the birth line and the ZAMS; and (3) a morepronounced maximum in the birth line radius-mass relationship thatresults in differentially greater spin-up for stars that become mid- tolate-B stars on the ZAMS.
| 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.
| Identification and Characterization of Faint Emission Lines in the Spectrum of the Planetary Nebula IC 418
We present high signal-to-noise ratio echelle spectra of the compacthigh surface brightness, low-ionization planetary nebula (PN) IC 418.These reveal 807 emission lines down to intensities less than10-5 that of Hβ for which we determine widths andrelative intensities. We show that line profiles are a valuableparameter for making line identifications and in constraining theexcitation mechanism of the lines. We present evidence that indicatesthat many supposed high-level recombination lines may in fact be excitedby a process other than recombination. We contend from the detection ofdielectronic recombination lines that their relatively low intensitiesargue against their making a significant contribution to levelpopulations of the heavy ions in this object. Following similar analysesof other PNe we find that IC 418 shows a small discrepancy in ionabundances derived from forbidden versus recombination lines of theheavy elements.
| 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.
| 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.
| Catalogue of averaged stellar effective magnetic fields. I. Chemically peculiar A and B type stars
This paper presents the catalogue and the method of determination ofaveraged quadratic effective magnetic fields < B_e > for 596 mainsequence and giant stars. The catalogue is based on measurements of thestellar effective (or mean longitudinal) magnetic field strengths B_e,which were compiled from the existing literature.We analysed the properties of 352 chemically peculiar A and B stars inthe catalogue, including Am, ApSi, He-weak, He-rich, HgMn, ApSrCrEu, andall ApSr type stars. We have found that the number distribution of allchemically peculiar (CP) stars vs. averaged magnetic field strength isdescribed by a decreasing exponential function. Relations of this typehold also for stars of all the analysed subclasses of chemicalpeculiarity. The exponential form of the above distribution function canbreak down below about 100 G, the latter value representingapproximately the resolution of our analysis for A type stars.Table A.1 and its references are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/407/631 and Tables 3 to 9are only available in electronic form at http://www.edpsciences.org
| 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.
| On the behavior of the Cii 4267.261, 6578.052 and 6582.882 Å lines in chemically peculiar and standard stars
With the aim of investigating the possible particular behavior of carbonin a sample of chemically peculiar stars of the main sequence withoutturning to modeling, we performed spectroscopic observations of threeimportant and usually prominent single ionized carbon lines: 4267.261,6578.052 and 6582.882 Å. In addition, we observed a large numberof standard stars in order to define a kind of normality strip, usefulfor comparing the observed trend for the peculiar stars. We paidparticular attention to the problem of the determination of fundamentalatmospheric parameters, especially for the chemically peculiar stars forwhich the abundance anomalies change the flux distribution in such a waythat the classical photometric methods to infer effective temperaturesand gravities parameter cannot be applied. Regarding CP stars, we founda normal carbon abundance in Hg-Mn, Si (with some exceptions) and Hestrong stars. He weak stars are normal too, but with a large spread outof the data around the mean value. A more complicated behavior has beennoted in the group of SrCrEu stars: four out of seven show a strongoverabundance, being the others normal.
| Rotational Velocities of B Stars
We measured the projected rotational velocities of 1092 northern B starslisted in the Bright Star Catalogue (BSC) and calibrated them againstthe 1975 Slettebak et al. system. We found that the published values ofB dwarfs in the BSC average 27% higher than those standards. Only 0.3%of the stars have rotational velocities in excess of two-thirds of thebreakup velocities, and the mean velocity is only 25% of breakup,implying that impending breakup is not a significant factor in reducingrotational velocities. For the B8-B9.5 III-V stars the bimodaldistribution in V can be explained by a set of slowly rotating Ap starsand a set of rapidly rotating normal stars. For the B0-B5 III-V starsthat include very few peculiar stars, the distributions in V are notbimodal. Are the low rotational velocities of B stars due to theoccurrence of frequent low-mass companions, planets, or disks? Therotational velocities of giants originating from late B dwarfs areconsistent with their conservation of angular momentum in shells.However, we are puzzled by why the giants that originate from the earlyB dwarfs, despite having 3 times greater radii, have nearly the samerotational velocities. We find that all B-type primaries in binarieswith periods less than 2.4 days have synchronized rotational and orbitalmotions; those with periods between 2.4 and 5.0 days are rotating withina factor 2 of synchronization or are ``nearly synchronized.'' Thecorresponding period ranges for A-type stars are 4.9 and 10.5 days, ortwice as large. We found that the rotational velocities of the primariesare synchronized earlier than their orbits are circularized. The maximumorbital period for circularized B binaries is 1.5 days and for Abinaries is 2.5 days. For stars of various ages from 107.5 to1010.2 yr the maximum circularized periods are a smoothexponential function of age.
| 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.
| 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.
| Electron temperature fluctuations in 30 Doradus
We present an observational study of the spatial variation of theelectron temperature in the 30 Doradus Nebula. Weused the [ion {O}{iii}] (lambda 4959 + lambda 5007)/lambda 4363 ratio toestimate the electron temperature at 135 positions in the nebula acrossthree different directions. We analysed long-slit spectrophotometricdata of high signal-to-noise in the range of 4100 to 5030 Åobtained with the Cassegrain spectrograph attached to the 1.60 mtelescope of the Laboratório Nacional de Astrofísica,Brazil. No large-scale electron temperature gradient was detected in 30Doradus. The electron temperature estimates obtained are fairlyhomogeneous with a mean value of 10 270 +/- 140 (3sigma ) K. Thecompatibility between the present estimates with optical and radiotemperature determinations found in the literature for other positionsor for the entire nebula corroborates this conclusion. Temperaturefluctuations of small amplitude were observed with a variance relativeto the mean of ts2= 0.0025 or equivalently with adispersion of only 5%. The areas with lower surface brightness seem topresent slightly higher electron temperatures. This would indicate thatthe bright arcs of 30 Doradus, which correspond to the densest regions,would have lower electron temperatures than the most diffuse areas.
| 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.
| 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 physical structure of the planetary nebula NGC 6781
The planetary nebula NGC 6781 was imaged in major optical emissionlines. These lines allow us to construct maps of the projected, twodimensional Balmer decrement, electron density, electron temperature,ionization and abundance structure. The average electron density,determined from the [S Ii] lines, is ~500 cm-3, while theelectron temperature distribution, determined from the [N Ii] lines, isflat at ~10 000 K. The Balmer decrement map shows that there arevariations in extinction between the north and south areas of theplanetary nebula. The higher extinction observed to the north of thecentral star is probably caused by dust spatially associated with COemission at blue-shifted velocities. The [N Ii] image reveals the knownoptical halo, at a flux level of ~0.2% of the strong shell emission inthe east, but now the angular extent of 216 arcsec x 190 arcsec is muchlarger than previous measurements. The halo is also present in [O Iii],where we measure an extent of 190 arcsec x 162 arcsec. The ionizationmaps indicate substantial ionization along the caps of the ellipsoid aswell as in the halo. The maps also show a sharp decrease in ionizationalong the outer edge of the shell in the west and the east, south-east.The typical log abundances measured for He, N, O and S are 10.97, 8.14,8.72 and 6.90, respectively.
| Search for spectroscopical signatures of transiting HD 209458b's exosphere
Following recent attempts to detect the exosphere of the extra-solarplanet 51 Pegb in the infrared (Coustenis et al. \cite{cou97},\cite{cou98}; Rauer et al. \cite{rau00a}), we discuss here a search foroptical spectroscopic signatures from a gaseous extended envelope(called exosphere) surrounding the planet HD 209458b. This planet has ademonstrated photometric transit (Charbonneau et al. \cite{cha00a};Henry et al. \cite{hen00}), thus offering an increased probability forthe spectroscopic detection of such an envelope. Therefore it is thebest known candidate for probing the exospheric composition of a giantplanet, orbiting a Sun-like star at a short distance. The observationswere performed with UVES at the VLT and cover most of the 328-669 nmrange. We did not detect HD 209458b's exosphere at a level of 1%, avalue close to the predictions. We discuss here the first resultsobtained and their limitations, as well as future prospective. Based onpublic data from the UVES Commissioning at the ESO 8.2~m Kueyentelescope operated on Paranal Observatory, Chile.
| 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
| Oxygen and helium abundances in Galactic Hii regions - I. Observations
Absolute integrated line fluxes of Hii regions have been measured usinga Fabry-Perot spectrophotometer. We describe the observations andcalibration procedures. Fluxes are given for 36 Hii regions withGalactocentric distances ranging from 6.6 to 17.7kpc. Several emissionlines have been measured, mainly [Oii] λλ3726 and 3629,Hβ, [Oiii] λ5007, Hei λ5876 and Hα. The veryfaint [Oiii] λ4363 line has been measured in six regions,allowing a direct determination of the electron temperature. Newphotometric distances have been derived based on data from theliterature. A discussion of these results in terms of extinction,electron density and temperature, and oxygen and helium abundances isgiven in Paper II.
| Chemical composition of HD 179821 (IRAS 19114+0002)
A LTE analysis of medium resolution spectra of {HD 179821} has beenmade. Derived atmospheric parameters of {HD 179821} are T_eff=5660 K,log g=-1.0 and [Fe/H]=-0.5. The position of the star in the H-R diagram,its high radial velocity (Vr=100 km s-1), its farinfrared excess similar to PNe and its chemical composition suggest that{HD 179821} is a low mass post-AGB carbon-poor supergiant and not apopulation I massive red supergiant. The underabundance of carbon and ofthe s-process element zirconium shows that HD 179821 has not gonethrough the third dredge-up. We emphasize the similarity of the chemicalpattern of the post-AGB star HD 179821 and the C-poor halo PN DDDM-1.Based on observations obtained at the Observatoire de Haute-Provence,France
| Spectrophotometry: Revised Standards and Techniques
The telluric features redward of 6700 Å have been removed from theaccurate spectrophotometric standards of Hamuy et al. to permit morereliable relative and absolute spectrophotometry to be obtained from CCDspectra. Smooth fluxes from 3300 to 10500 Å are best determined bydividing the raw spectra of all objects taken in a night by the rawspectrum of a ``smooth'' spectrum star before deriving the instrumentalresponse function using the revised standard star fluxes. In this waythe telluric features and any large instrumental variation withwavelength are removed from the raw data, leaving smooth spectra thatneed only small corrections to place them on an absolute flux scale.These small corrections with wavelength are well described by alow-order polynomial and result in very smooth flux-calibrated spectra.
| Commissioning FEROS, the new high-resolution spectrograph at La Silla.
Not Available
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
| Сазвежђа: | Рибе |
| Ректацензија: | 00h01m49.40s |
| Deклинација: | -03°01'39.0" |
| Apparent магнитуда: | 5.1 |
| Даљина: | 125.313 parsecs |
| Proper motion RA: | 19.2 |
| Proper motion Dec: | -9.9 |
| B-T magnitude: | 4.939 |
| V-T magnitude: | 5.082 |
Каталог и designations:
|
