Оглавление
Изображения
Загрузить ваше изображение
DSS Images Other Images
Публикации по объекту
Medium-resolution Isaac Newton Telescope library of empirical spectra - II. The stellar atmospheric parameters
We present a homogeneous set of stellar atmospheric parameters(Teff, logg, [Fe/H]) for MILES, a new spectral stellarlibrary covering the range λλ 3525-7500Å at2.3Å (FWHM) spectral resolution. The library consists of 985 starsspanning a large range in atmospheric parameters, from super-metal-rich,cool stars to hot, metal-poor stars. The spectral resolution, spectraltype coverage and number of stars represent a substantial improvementover previous libraries used in population synthesis models. Theatmospheric parameters that we present here are the result of aprevious, extensive compilation from the literature. In order toconstruct a homogeneous data set of atmospheric parameters we have takenthe sample of stars of Soubiran, Katz & Cayrel, which has very welldetermined fundamental parameters, as the standard reference system forour field stars, and have calibrated and bootstrapped the data fromother papers against it. The atmospheric parameters for our clusterstars have also been revised and updated according to recent metallicityscales, colour-temperature relations and improved set of isochrones.
| Medium-resolution Isaac Newton Telescope library of empirical spectra
A new stellar library developed for stellar population synthesismodelling is presented. The library consists of 985 stars spanning alarge range in atmospheric parameters. The spectra were obtained at the2.5-m Isaac Newton Telescope and cover the range λλ3525-7500 Å at 2.3 Å (full width at half-maximum) spectralresolution. The spectral resolution, spectral-type coverage,flux-calibration accuracy and number of stars represent a substantialimprovement over previous libraries used in population-synthesis models.
| The peculiar variable V838 Monocerotis
Spectroscopic observations of the peculiar variable V838 Mon during theperiod from the second light outburst until the fast dimming arepresented. We describe high resolution (R≈60 000) high S/N spectraobtained a day before the second light maximum and low resolution(R≈6000) spectra covering the whole period. The temporal run ofintensities and radial velocities of various lines is presented. UsingNa I D IS lines we determine the reddening distance of V838 Mon d>3.1kpc, and kinematic distance d>4 kpc. We estimate that V838 Mon isslightly metal deficient but otherwise has a quite solar-like chemicalcomposition except for enhanced abundances of Li, Ba and La.
| The association of IRAS sources and 12CO emission in the outer Galaxy
We have revisited the question of the association of CO emission withIRAS sources in the outer Galaxy using data from the FCRAO Outer GalaxySurvey (OGS). The availability of a large-scale high-resolution COsurvey allows us to approach the question of IRAS-CO associations from anew direction - namely we examined all of the IRAS sources within theOGS region for associated molecular material. By investigating theassociation of molecular material with random lines of sight in the OGSregion we were able to construct a quantitative means to judge thelikelihood that any given IRAS-CO association is valid and todisentangle multiple emission components along the line of sight. Thepaper presents a list of all of the IRAS-CO associations in the OGSregion. We show that, within the OGS region, there is a significantincrease ( ~ 22%) in the number of probable star forming regions overprevious targeted CO surveys towards IRAS sources. As a demonstration ofthe utility of the IRAS-CO association table we present the results ofthree brief studies on candidate zone-of-avoidance galaxies with IRAScounterparts, far outer Galaxy CO clouds, and very bright CO clouds withno associated IRAS sources. We find that ~ 25% of such candidate ZOAGsare Galactic objects. We have discovered two new far outer Galaxystar-forming regions, and have discovered six bright molecular cloudsthat we believe are ideal targets for the investigation of the earlieststages of sequential star formation around HII regions. Finally, thispaper provides readers with the necessary data to compare othercatalogued data sets with the OGS data.Tables 1, 2 and A1 are only available in electronic form at the CDS viaanonymous ftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/399/1083
| Studies of Yellow Semiregular(SRd) Variables
We have used the Hipparcos database of epoch photometry to study thevariability of several yellow semiregular(SRd) variables. For some ofthe stars (V847 Cas, RW Cep, BM Sco, CE Vir), the results wereinconclusive. For SX Lac and TY Vir, the periods found were consistentwith the General Catalogue of Variable Stars (190 and 50 daysrespectively). For UU Her, the known periods of about 45 and 72 dayswere recovered. For WY And, RU Cep, and SX Her, reliable periods werefound; we used archival data to construct (O-C) diagrams to study boththe random and systematic period changes in these three stars.
| Revision and Calibration of MK Luminosity Classes for Cool Giants by HIPPARCOS Parallaxes
The Hipparcos parallaxes of cool giants are utilized in two ways in thispaper. First, a plot of reduced parallaxes of stars brighter than 6.5,as a function of spectral type, for the first time separates members ofthe clump from stars in the main giant ridge. A slight modification ofthe MK luminosity standards has been made so that luminosity class IIIbdefines members of the clump, and nearly all of the class III stars fallwithin the main giant ridge. Second, a new calibration of MK luminosityclasses III and IIIb in terms of visual absolute magnitudes has beenmade.
| Discovery of Two New, Carbon-rich Proto-Planetary Nebulae:IRAS Z02229+6208 and IRAS 07430+1115
We report the discovery of two new carbon-rich proto-planetary nebulae(PPNs), IRAS Z02229+6208 and 07430+1115. Optical spectroscopy of thesesources and another previously discovered PPN, IRAS 05431+0852, revealsthe presence of C_2 and C_3 in absorption. All three objects have thespectra of G-K supergiants, consistent with the expectations of theirbeing PPNs. New ground-based optical and infrared photometry, combinedwith the IRAS measurements, show double-peak spectral energydistributions for each; this suggests that the asymptotic giant branch(AGB) mass loss has ended and these objects are in the post-AGB phase ofevolution. The remnant of the molecular envelope is detected in COemission for the first time in all three objects, using the CO (3-2)line. The 3.3 and 11.3 μm emission features commonly attributed tothe polycyclic aromatic hydrocarbon molecules have been detected in IRAS07430+1115. Strikingly absent in IRAS 07430+1115, however, is the 21μm emission feature, found in the other two and in all but one of theother PPNs known to show C_2 in absorption.
| Accurate Two-dimensional Classification of Stellar Spectra with Artificial Neural Networks
We present a solution to the long-standing problem of automaticallyclassifying stellar spectra of all temperature and luminosity classeswith the accuracy shown by expert human classifiers. We use the 15Angstroms resolution near-infrared spectral classification systemdescribed by Torres-Dodgen & Weaver in 1993. Using the spectrum withno manual intervention except wavelength registration, artificial neuralnetworks (ANNs) can classify these spectra with Morgan-Keenan types withan accuracy comparable to that obtained by human experts using 2Angstroms resolution blue spectra, which is about 0.5 types (subclasses)in temperature and about 0.25 classes in luminosity. Accuratetemperature classification requires a hierarchy of ANNs, whileluminosity classification is most successful with a single ANN. Wepropose an architecture for a fully automatic classification system.
| Colour excesses of F-G supergiants and Cepheids from Geneva photometry.
A reddening scale for F-G supergiants and Cepheids is presented.Supergiants with low reddenings or in clusters form the basis of thecalibration. In this sense, it is entirely empirical. The data have beenobtained in the Geneva photometric system. Comparisons with otherreddening scales show no disagreement. The only problem is with Fernie'sscale for Cepheids (1990), where a systematic trend exists. Its originis not clear. It is suggested to extend the number of supergiants withindependently obtained colour excesses in order to test the existence ofa possible luminosity dependence of the calibration. A period-colourrelation for Cepheids is deduced, on the basis of the present reddeningcorrections. It gives strong support for V473 Lyr being a secondovertone pulsator.
| Classification of Population II Stars in the Vilnius Photometric System. I. Methods
The methods used for classification of Population II stars in theVilnius photometric system are described. An extensive set of standardswith known astrophysical parameters compiled from the literature sourcesis given. These standard stars are classified in the Vilnius photometricsystem using the methods described. The accuracy of classification isevaluated by a comparison of the astrophysical parameters derived fromthe Vilnius photometric system with those estimated from spectroscopicstudies as well as from photometric data in other systems. For dwarfsand subdwarfs, we find a satisfactory agreement between our reddeningsand those estimated in the uvbyscriptstyle beta system. The standarddeviation of [Fe/H] deter mined in the Vilnius system is about 0.2 dex.The absolute magnitude for dwarfs and subdwarfs is estimated with anaccuracy of scriptstyle <=0.5 mag.
| HD6474: an UU Her Spectrum Variable?
Not Available
| Optical spectroscopy of carbon-rich proto-planetary nebulae
In this paper, we present a medium-resolution (3 A) spectroscopic studyof six proto-planetary nebulae (PPN), post-asymptotic giant branch (AGB)objects with large infrared excesses. All six are found to display thespectra of G supergiants. However, they also show molecular carbonfeatures, C2 and in most cases C3, and strong absorption lines due tos-process elements. Other evidences of a carbon-rich nature are found inpublished molecular-line millimeter emissions (CO and HCN) and 3.3micrometer features attributed to polycyclic aromatic hydrocarbons.These properties are all in accord with what one would expect in apost-AGB star in which carbon-rich materials formed in thermal pulses isdredged up to the surface of a mass-losing object. A correlation isfound between the presence of molecular C2 absorption and the presenceof the unidentified 21 micrometer emission feature. This strengthens thesuggestion that carbon is a major component of the molecule producingthis unidentified feature. Four additional proto-planetary nebulae whichshare some of these properties are also discussed.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| The pulsations of yellow semi-regular variables II. The F supergiant in the high-latitude binary BL Telescopii
Photoelectric observations of the F-type component of the high-latitudeeclipsing binary BL Telescopii outside eclipse were analysed. Twoperiods (92.5d and 64.8)d were found to be present in the light curve.They are identified as belonging to the fundamental mode and the firstovertone. It seems that BL Telescopii prefers overtone pulsation. Thepresence of the two periods and their ratio indicates that the high-massinterpretation of the variable could be valid. Together with UU Her andV487 Cas it belongs to the re-defined UU Herculis group of stars.
| V487 Cassiopeiae (HD 6474): a UU Herculis variable in the galactic plane?
New photoelectric photometry of V487 Cassiopeiae (HD 6474) made between1984 and 1992 is presented. The star has a rather complicated lightvariation: at least two periods (P1 = 160.3 days andP2 = 99.6 days) are present in the light curve, one of thempossibly with variable amplitude. The period ratio(P2/P1 = 0.62) and the nature of the lightvariation (i.e. the simultaneous presence of two modes, the amplitudechange) are both very similar to that of UU Herculis. This similarityindicates that V487 Cassiopeiae is a UU Her-type variable though it isin the galactic plane. A distinction between the UU Her-type and 89Her-type variables is suggested.
| High resolution spectroscopy of the semi-regular variable LR SCO
A detailed spectroscopic investigation of LR Sco which was earliermisclassified as R CrB star is made. Atmospheric parameters andelemental abundances are determined using detailed depth-dependent modelatmospheres and line synthesis technique. Most of the elements shownear-solar abundances. The strength of circumstellar components seen inNa D lines are used to derive the mass loss rate. Another independentestimate of mass loss rate is made using the observed infrared flux from1-100 microns. These two approaches lead to nearly the same value ofmass loss rate when M(v) is assumed to be -4.5 for this star.
| Luminosities of yellow supergiants from near-infrared spectra - Calibration through Magellanic Cloud stars
The possibility of using medium resolution spectrograms in the nearinfrared region to determine luminosities of A-G supergiants has beenexplored. A sample of 49 of these stars has been observed in the twoMagellanic Clouds, and using the intensities of the O I 7774 triplet andan index (CP), which is a combination of the Ca II triplet and Paschenlines intensities, a preliminary luminosity calibration, based on LMCstars, has been obtained. Such a calibration predicts reliableluminosities for Galactic supergiants, and offers the advantage of beingcompletely reddening independent. The reddening free CP index combinedwith BVRI color indices has also been used to estimate the interstellarreddenings of Magellanic Cloud stars.
| Galactic OB associations in the northern Milky Way Galaxy. I - Longitudes 55 deg to 150 deg
The literature on all OB associations was reviewed, and their IRAS pointsource content was studied, between galactic longitude 55 and 150 deg.Only one third of the 24 associations listed by Ruprecht et al. (1981)have been the subject of individual studies designed to identify thebrightest stars. Distances to all of these were recomputed using themethod of cluster fitting of the B main sequence stars, which makes itpoossible to reexamine the absolute magnitude calibration of the Ostars, as well as for the red supergiant candidate stars. Also examinedwas the composite HR diagram for these associations. Associations withthe best defined main sequences, which also tend to contain very youngclusters, referred to here as OB clusters, have extremely few evolved Band A or red supergiants. Associations with poorly defined mainsequences and few OB clusters have many more evolved stars. They alsoshow an effect in the upper HR diagram referred to as a ledge byFitzpatrick and Garmany (1990) in similar data for the Large MagellanicCloud. It is suggested that the differences in the associations are notjust observational selection effects but represent real differences inage and formation history.
| Photometry of F-K type bright giants and supergiants. I - Intermediate band and H-Beta observations
Over 1500 observations of 560 bright giants and supergiants of types F-Kare presented and compared to the observations by Gray and Olsen (1991).The present results include intermediate-band which is slightlydifferent from the Stromgren data by Gray and Olsen due to a differentwidth for the v filter. A systematic difference in m(1) - M(1) withdecreasing temperature is noted in the two H-Beta data sets, and thecorrelations are defined.
| Classification of Population II supergiants and related stars in the Vilnius system
The results of photometric classification in the Vilnius system of 117Population II supergiants, suspected supergiants, and related stars aregiven. Their photometric spectral types, intrinsic color indices (Y-V)0,color excesses E(Y-V), metallicities Fe/H, and absolute magnitudes MVare determined. It is shown that the system allows us to detect the UUHerculis-type supergiants photometrically. The analyzed SRd star samplefalls into two groups of metallicity and luminosity. Our photometricclassification assigns luminosity classes from III to V to 37 F-K starswith /b/ greater than 16 deg classified by Bartaya (1979) from objectiveprism spectra as supergiants.
| Photometry of F-K type bright giant and supergiants. II - Calibration on indices in terms of luminosity reddening and abundance of F-type stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1991AJ....102.1826E&db_key=AST
| Near infrared spectra of RV Tauri stars
Medium resolution spectrograms of the near infrared spectral region in asample of RV Tauri stars with spectral types F and early G have beencompared with those of a sample of population I objects. It is shownthat the equivalent widths of Ca II infrared triplet and Paschen linesallow to separate RV Tauri stars from population I supergiants.Moreover, the possibility of using the O I triplet at 7774 A as a toolfor testing the period-luminosity relation for RV Tauri stars isdiscussed.
| The carbon-rich proto-planetary nebula IRAS 22272 + 5435
Ground-based photometry and spectroscopy is presented for IRAS 22272 +5435, a 9th mag star with a large infrared excess. The flux distributionis 'double-peaked', with a visible and near-infrared component due tothe reddened photosphere and a far-infrared component presumably due toa detached dust shell. About equal amounts of energy are detected fromeach. The spectrum is that of a peculiar G supergiant, Gp Ia. Inaddition, strong molecular bands of C3 and C2 are observed. The fluxdistribution is modeled and, together with published molecular-lineradio observations, allows the determination of basic parameters of thecentral star and the dust shell. The source has the characteristics onewould expect of a proto-planetary nebula, an object in transition fromthe asymptotic giant branch to the planetary nebula phase.
| Colour excesses and absolute magnitudes for non-Cepheid F-G supergiants from uvbybeta photometry
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990A&A...239..205A&db_key=AST
| Is LR SCO and RCB star?
Not Available
| Photoelectric Photometry of 241 Stars in the Vilnius System
Not Available
| Supergiants and the Galactic metallicity gradient. II - Spectroscopic abundances for 64 distant F- to M-type supergiants
The metallicity gradient in the Galactic disk from in situ stars withvisual magnitude ranging from 6 to 10 is analyzed. Atmosphericparameters and detailed chemical abundances for 64 Population Isupergiants of spectral types F through M and luminosity classes Iathrough II have been determined. The derived Fe/H ratios ranging from-0.5 to + 0.7 show a mean value of +0.13 with an estimated uncertaintyof + or - 0.2. A subset of 25 supergiants fainter than 7th magnitudelying in the direction of the Galactic center shows a Fe/H mean of +0.18+ or - 0.04, while a similar sample of 15 faint supergiants lying in thedirection of the Galactic anticenter shows a lower Fe/H mean of +0.07 +or - 0.06. For a sample of bright supergiants analyzed by Luck andLambert (1985), the mean abundance pattern for all 64 stars showed thefollowing: deficient C and O along with enhancement of N, indicatingmixing of CNO-cycled material to the stellar surfaces; an apparent Srenhancement attributed to departures from LTE; and an essentially solarpattern of other chemical elements.
| The Perkins catalog of revised MK types for the cooler stars
A catalog is presented listing the spectral types of the G, K, M, and Sstars that have been classified at the Perkins Observatory in therevised MK system. Extensive comparisons have been made to ensureconsistency between the MK spectral types of stars in the Northern andSouthern Hemispheres. Different classification spectrograms have beengradually improved in spite of some inherent limitations. In thecatalog, the full subclasses used are the following: G0, G5, G8, K0, K1,K2, K3, K4, K5, M0, M1, M2, M3, M4, M5, M6, M7, and M8. Theirregularities are the price paid for keeping the general scheme of theoriginal Henry Draper classification.
| A list of MK standard stars
Not Available
| Infrared circumstellar shells - Origins, and clues to the evolution of massive stars
The infrared fluxes, spatial and spectral characteristics for a sampleof 111 supergiant stars of spectral types F0 through M5 are tabulated,and correlations examined with respect to the nature of theircircumstellar envelopes. One-fourth of these objects were spatialyresolved by IRAS at 60 microns and possess extended circumstellar shellmaterial, with implied expansion ages of about 10 to the 5th yr.Inferences about the production of dust, mass loss, and the relation ofthese characteristics of the evolution of massive stars, are discussed.
|
Добавить новую статью
Внешние ссылки
- - Внешних ссылок не найдено -
Добавить внешнюю ссылку
Группы:
|
Наблюдательные данные и астрометрия
| Созвездие: | Кассиопея |
| Прямое восхождение: | 01h06m59.74s |
| Склонение: | +63°46'23.4" |
| Видимая звёздная величина: | 7.584 |
| Расстояние: | 10000000 парсек |
| Собственное движение RA: | -2.1 |
| Собственное движение Dec: | -0.9 |
| B-T magnitude: | 9.557 |
| V-T magnitude: | 7.747 |
Каталоги и обозначения:
|
INHABITED SKY
