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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.
| An Atlas of Spectrophotometric Landolt Standard Stars
We present CCD observations of 102 Landolt standard stars obtained withthe Ritchey-Chrétien spectrograph on the Cerro TololoInter-American Observatory 1.5 m telescope. Using stellar atmospheremodels, we have extended the flux points to our six spectrophotometricsecondary standards, in both the blue and the red, allowing us toproduce flux-calibrated spectra that span a wavelength range from 3050Å to 1.1 μm. Mean differences between UBVRI spectrophotometrycomputed using Bessell's standard passbands and Landolt's publishedphotometry were determined to be 1% or less. Observers in bothhemispheres will find these spectra useful for flux-calibrating spectra,and through the use of accurately constructed instrumental passbands,will be able to compute accurate corrections to bring instrumentalmagnitudes to any desired standard photometric system (S-corrections).In addition, by combining empirical and modeled spectra of the Sun,Sirius, and Vega, we calculate and compare synthetic photometry toobserved photometry taken from the literature for these three stars.
| R CrB Candidates in the Small Magellanic Cloud: Observations of Cold, Featureless Dust with the Spitzer Infrared Spectrograph
We observed 36 evolved stars in the Small Magellanic Cloud (SMC) usingthe low-resolution mode of the Infrared Spectrograph (IRS) on theSpitzer Space Telescope. Two of these stars, MSX SMC 014 and 155, havenearly featureless spectral energy distributions over the IRS wavelengthrange (5.2-35 μm) and Fν peaking at ~8-9 μm. Thedata can be fit by sets of amorphous carbon shells or by single 600-700K blackbodies. The most similar spectra found in extant spectraldatabases are of R CrB, although the spectral structure seen in R CrBand similar stars is much weaker or absent in the SMC sources. Both SMCstars show variability in the near-infrared. Ground-based visual spectraconfirm that MSX SMC 155 is carbon-rich, as expected for R CrB (RCB)stars, and coincides with an object previously identified as an RCBcandidate. The temperature of the underlying star is lower for MSX SMC155 than for typical RCB stars. The strength of the C2 Swanbands and the low temperature suggest that it may be a rare DY Per-typestar, only the fifth such identified. MSX SMC 014 represents a new RCBcandidate in the SMC, bringing the number of RCB candidates in the SMCto six. It is the first RCB candidate discovered with Spitzer and thefirst identified by its infrared spectral characteristics rather thanits visual variability.
| Statistical Constraints for Astrometric Binaries with Nonlinear Motion
Useful constraints on the orbits and mass ratios of astrometric binariesin the Hipparcos catalog are derived from the measured proper motiondifferences of Hipparcos and Tycho-2 (Δμ), accelerations ofproper motions (μ˙), and second derivatives of proper motions(μ̈). It is shown how, in some cases, statistical bounds can beestimated for the masses of the secondary components. Two catalogs ofastrometric binaries are generated, one of binaries with significantproper motion differences and the other of binaries with significantaccelerations of their proper motions. Mathematical relations betweenthe astrometric observables Δμ, μ˙, and μ̈ andthe orbital elements are derived in the appendices. We find a remarkabledifference between the distribution of spectral types of stars withlarge accelerations but small proper motion differences and that ofstars with large proper motion differences but insignificantaccelerations. The spectral type distribution for the former sample ofbinaries is the same as the general distribution of all stars in theHipparcos catalog, whereas the latter sample is clearly dominated bysolar-type stars, with an obvious dearth of blue stars. We point outthat the latter set includes mostly binaries with long periods (longerthan about 6 yr).
| An empirical temperature calibration for the Δ a photometric system . I. The B-type stars
We establish an empirical effective temperature calibration of mainsequence, luminosity class V to III B-type stars for the Δ aphotometric system which was originally developed to detect magneticchemically peculiar objects of the upper main sequence (early B-type toearly F-type) at 5200 Å. However, this system provides the index(g_1-y) which shows an excellent correlation with (B-V) as well as (b-y)and can be used as an indicator of the effective temperature. This issupplemented by a very accurate color-magnitude diagram, y or V versus(g_1-y), which can be used, for example, to determine the reddening,distance and age of an open cluster. This makes the Δ aphotometric system an excellent tool to investigate theHertzsprung-Russell-Diagram (HRD) in more detail. Using thereddening-free parameters and already established calibrations withinthe Strömgren uvbyβ, Geneva 7-color and Johnson UBV systems, apolynomial fit of third degree for the averaged effective temperaturesto the individual (g_1-y)0 values was derived. For thispurpose, data from the literature as well as new observations were takenresulting in 225 suitable bright normal B-type objects. The statisticalmean of the error for this sample is 238 K which is sufficient toinvestigate the HRD of distant galactic open clusters as well asextragalactic aggregates in the future.
| 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.
| Deep Fading of the New Herbig Be Star MisV1147
We report on the discovery of a new variable star, MisV1147, by theMISAO Project and its unusual photometric variations. The light curve ofthe object is characterized by two distinct states, that is, arelatively calm, bright state and an active state during whichrepetitive fadings with large amplitudes of 2 mag were observed.The fading events were associated with optical reddening. The object isidentified with a catalogued Hα emission star, which has beenconfirmed by our spectroscopic observations. The Hα emission lineis narrow and symmetric both in the bright and faint phases. The objecthas infrared colors analogous to T Tau stars or Herbig Ae/Be stars. Inconjunction with the detection of a NaD absorption line and its positionclose to Cep OB1, we conclude that MisV1147 is a Herbig Be star with itsspectral type of B2. Its optical-infrared spectral energy distributionis typical for Herbig Ae/Be stars, which supports this classification.The overall properties of the light curve are reminiscent of a UX Orisub-group, showing Algol-type minima. The most noteworthy feature ofMisV1147 is that it has a spectral type B2, whereas known UX Ori starshave spectral types later than B8. The object, furthermore, has one ofthe largest amplitudes of variations among known Herbig Ae/Be stars.Hence the object breaks the very strong correlation between thevariation amplitude and the spectral type. This implies that dust clumpsin circumstellar matter can significantly obscure a central object evenin the early-type system.
| Ground-based photometric observations of Jupiter's inner satellites Thebe, Amalthea, and Metis at small phase angles
We present the results of photometric measurements of the inner joviansatellites Thebe, Amalthea and Metis based on extensive opticalobservations taken from October 1999 to January 2002. The observationswere made in the phase angle range from 8.1° to 0.3°. TheTwo-Channel Focal Reducer of the Max-Planck Institute for Aeronomyattached to the 2-m RCC telescope at Terskol Observatory (Pik Terskol,Northern Caucasus) was used in coronagraph mode. The observations wereperformed at a wavelength of 0.887 μm. Mean observationaluncertainties corresponding to 1σ rms errors were 3% for theleading and trailing sides of Amalthea, 7 and 9% for the leading andtrailing sides of Thebe and 9% for the leading side of Metis aftertaking into account the longitude brightness variations. Photometricdata calibrated on an absolute scale were used to evaluate thenear-opposition behavior of satellite brightness. All three satellitesexhibit significant opposition brightening, but the strength of thiseffect, measured as the ratios of intensities atα1=1.6° and α2=6.7° does notvary significantly among these satellites. In order to measure theopposition surge parameters the empirical law proposed by Karkoschka andHapke's model were used. The parameters of the satellite oppositioneffects are presented and discussed. The values of geometric albedoscalculated with best-fit Hapke parameters are 0.096, 0.157, and 0.24 forThebe, Amalthea, and Metis respectively. We found that the averageleading/trailing ratios of surface reflectance at the measured phaseangles are 1.53+/-0.05, 1.25+/-0.04, 1.04+/-0.08 for Amalthea, Thebe,and Metis.Until June 30, 2004: Max-Planck-Institut für Aeronomie.
| Spectrophotometry of the comet C/2002 V1 (NEAT)
We took spectrophotometric observations of the coma of the comet C/2002V1 (NEAT) on January 24, 25 and February 4, 2003, with 104-cm telescopeof the State Observatory, Nainital. CN (3883 A) and C2 swan bands (4695,5165 and 5538 A) were identified. An estimate of CN and C2 abundancesand their production rates were made. Dust production rates have alsobeen determined.
| 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.
| 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.
| High-Precision Near-Infrared Photometry of a Large Sample of Bright Stars Visible from the Northern Hemisphere
We present the results of 8 yr of infrared photometric monitoring of alarge sample of stars visible from Teide Observatory (Tenerife, CanaryIslands). The final archive is made up of 10,949 photometric measuresthrough a standard InSb single-channel photometer system, principally inJHK, although some stars have measures in L'. The core of this list ofstars is the standard-star list developed for the Carlos SánchezTelescope. A total of 298 stars have been observed on at least twooccasions on a system carefully linked to the zero point defined byVega. We present high-precision photometry for these stars. The medianuncertainty in magnitude for stars with a minimum of four observationsand thus reliable statistics ranges from 0.0038 mag in J to 0.0033 magin K. Many of these stars are faint enough to be observable with arraydetectors (42 are K>8) and thus to permit a linkage of the bright andfaint infrared photometric systems. We also present photometry of anadditional 25 stars for which the original measures are no longeravailable, plus photometry in L' and/or M of 36 stars from the mainlist. We calculate the mean infrared colors of main-sequence stars fromA0 V to K5 V and show that the locus of the H-K color is linearlycorrelated with J-H. The rms dispersion in the correlation between J-Hand H-K is 0.0073 mag. We use the relationship to interpolate colors forall subclasses from A0 V to K5 V. We find that K and M main-sequence andgiant stars can be separated on the color-color diagram withhigh-precision near-infrared photometry and thus that photometry canallow us to identify potential mistakes in luminosity classclassification.
| STELIB: A library of stellar spectra at R ~ 2000
We present STELIB, a new spectroscopic stellar library, available athttp://webast.ast.obs-mip.fr/stelib. STELIB consists of an homogeneouslibrary of 249 stellar spectra in the visible range (3200 to 9500Å), with an intermediate spectral resolution (la 3 Å) andsampling (1 Å). This library includes stars of various spectraltypes and luminosity classes, spanning a relatively wide range inmetallicity. The spectral resolution, wavelength and spectral typecoverage of this library represents a substantial improvement overprevious libraries used in population synthesis models. The overallabsolute photometric uncertainty is 3%.Based on observations collected with the Jacobus Kaptein Telescope,(owned and operated jointly by the Particle Physics and AstronomyResearch Council of the UK, The Nederlandse Organisatie voorWetenschappelijk Onderzoek of The Netherlands and the Instituto deAstrofísica de Canarias of Spain and located in the SpanishObservatorio del Roque de Los Muchachos on La Palma which is operated bythe Instituto de AstrofÃsica de Canarias), the 2.3 mtelescope of the Australian National University at Siding Spring,Australia, and the VLT-UT1 Antu Telescope (ESO).Tables \ref{cat1} to \ref{cat6} and \ref{antab1} to A.7 are onlyavailable in electronic form at http://www.edpsciences.org. The StellarLibrary STELIB library is also available at the CDS, via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/402/433
| 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
| Tridimensional Spectroscopic Observation of the Interacting System NGC 7592
We performed a tridimensional spectroscopic study of NGC 7592, aninfrared-luminous interacting system of three galaxies, one of whichcontains a Seyfert 2 nucleus. Narrow-band images of Hα and [O III] were obtained using an imaging Fabry-Perot interferometer with atunable filter. An area-spectroscopic observation was also made by aslit scan in a direction perpendicular to the slit. The Seyfert nucleuswas found to be surrounded by a knotty star-forming region of disk- orring-shape. Along the axis of the disk or ring, a highly-ionized bipolargaseous region was identified. From kinematical analyses, it has beensuggested that this system is composed of two galaxies; one apparentnucleus is considered to be a giant H II region belonging to one galaxy.This result is supported by the morphological properties innear-infrared. Further, it has been suggested that one galaxy is anearly-type spiral, whereas the other is a late-type one, and the twogalaxies show a marked difference in the distribution of thestar-forming regions within each. The cause of the difference was arguedin relation with the dynamical perturbation between the two galaxies.
| JHK Standards for Small Telescopes
The AAVSO Futures meeting, held in Madison, WI, in May 2001, proposedthat the AAVSO support near-infrared research with small telescopes. Aphotometer, the SSP-4, has been developed to provide J- and H-bandcapability for a reasonable cost. However, proper calibrated photometryrequires a set of standard stars. This paper describes such a set ofstars, suitable for small telescopes, and with accurate coordinates,proper motions, and high-quality magnitudes.
| Photometry of Mercury from SOHO/LASCO and Earth. The Phase Function from 2 to 170 deg.
CCD observations of Mercury were obtained with the large anglespectrometric coronograph (LASCO) on the solar and heliosphericobservatory spacecraft, near superior and inferior solar conjunctions.Whole disk photometry was extracted from the orange and blue filterimages and transformed to V magnitudes on the UBV system. The LASCO datawere combined with ground-based, V-filter photometry acquired at largerelongation angles. The resulting photometric phase function covers thegreatest span of angles to date and is the first wide-range function tobe obtained since the era of visual observation. We analyzed the datausing a polynomial fit and a Hapke function fit, and derived thefollowing photometric results. Mercury's fully lit brightness, adjustedto a distance of 1.0 AU from the Sun and observer, was found to beV=-0.694(+/-0.030), which is more luminous than previously measured. Thecorresponding geometric albedo is 0.142(+/-0.005). The phase integral is0.478(+/-0.005) and resulting spherical albedo is 0.068(+/-0.003). Theupper limit of a possible rotational brightness variation is about 0.05magnitude. Mercury's brightness surges by more than 40% between phaseangles 10 and 2°, while the illuminated fraction of the diskincreases by less than 1%. A set of coefficients for Hapke's functionthat fit most of the phase curve includes h=0.065+/-0.002 indicatingthat Mercury and the Moon have similar regolith compaction states andparticle size distributions, and θ-bar=16°+/-1° implyinga macroscopically smoother surface than the Moon. However, we foundother solutions that fit the observations nearly as well withsignificantly smaller and larger values of h, and with values ofθ-bar around 25°. The wide range for θ-bar is due tothe inability of the model to fit the photometry obtained at large phaseangles. .
| 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.
| 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.
| The latitude of the observer of the Almagest star catalogue.
Not Available
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הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | לויתן |
| התרוממות ימנית: | 02h28m09.50s |
| סירוב: | +08°27'36.0" |
| גודל גלוי: | 4.28 |
| מרחק: | 53.967 פארסק |
| תנועה נכונה: | 37.5 |
| תנועה נכונה: | -7.2 |
| B-T magnitude: | 4.223 |
| V-T magnitude: | 4.261 |
קטלוגים וכינוים:
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INHABITED SKY
