Оглавление
Изображения
Загрузить ваше изображение
DSS Images Other Images
Публикации по объекту
3D mapping of the dense interstellar gas around the Local Bubble
We present intermediate results from a long-term program of mapping theneutral absorption characteristics of the local interstellar medium,motivated by the availability of accurate and consistent parallaxes fromthe Hipparcos satellite. Equivalent widths of the interstellar NaID-line doublet at 5890 Å are presented for the lines-of-sighttowards some 311 new target stars lying within ~ 350 pc of the Sun.Using these data, together with NaI absorption measurements towards afurther ~ 240 nearby targets published in the literature (for many ofthem, in the directions of molecular clouds), and the ~ 450lines-of-sight already presented by (Sfeir et al. \cite{sfeir99}), weshow 3D absorption maps of the local distribution of neutral gas towards1005 sight-lines with Hipparcos distances as viewed from a variety ofdifferent galactic projections.The data are synthesized by means of two complementary methods, (i) bymapping of iso-equivalent width contours, and (ii) by densitydistribution calculation from the inversion of column-densities, amethod devised by Vergely et al. (\cite{vergely01}). Our present dataconfirms the view that the local cavity is deficient in cold and neutralinterstellar gas. The closest dense and cold gas ``wall'', in the firstquadrant, is at ~ 55-60 pc. There are a few isolated clouds at closerdistance, if the detected absorption is not produced by circumstellarmaterial.The maps reveal narrow or wide ``interstellar tunnels'' which connectthe Local Bubble to surrounding cavities, as predicted by the model ofCox & Smith (1974). In particular, one of these tunnels, defined bystars at 300 to 600 pc from the Sun showing negligible sodiumabsorption, connects the well known CMa void (Gry et al. \cite{gry85}),which is part of the Local Bubble, with the supershell GSH 238+00+09(Heiles \cite{heiles98}). High latitude lines-of-sight with the smallestabsorption are found in two ``chimneys'', whose directions areperpendicular to the Gould belt plane. The maps show that the LocalBubble is ``squeezed'' by surrounding shells in a complicated patternand suggest that its pressure is smaller than in those expandingregions.We discuss the locations of several HI and molecular clouds. Usingcomparisons between NaI and HI or CO velocities, in some cases we areable to improve the constraints on their distances. According to thevelocity criteria, MBM 33-37, MBM 16-18, UT 3-7, and MBM 54-55 arecloser than ~ 100 pc, and MBM 40 is closer than 80 pc. Dense HI cloudsare seen at less than 90 pc and 85 pc in the directions of the MBM 12and MBM 41-43 clouds respectively, but the molecular clouds themselvesmay be far beyond. The above closest molecular clouds are located at theneutral boundary of the Bubble. Only one translucent cloud, G192-67, isclearly embedded within the LB and well isolated.These maps of the distribution of local neutral interstellar NaI gas arealso briefly compared with the distribution of both interstellar dustand neutral HI gas within 300 pc.Tables 1 and 2 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/411/447
| Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897
| Rotational velocities of A-type stars. I. Measurement of v sin i in the southern hemisphere
Within the scope of a Key Programme determining fundamental parametersof stars observed by HIPPARCOS, spectra of 525 B8 to F2-type starsbrighter than V=8 have been collected at ESO. Fourier transforms ofseveral line profiles in the range 4200-4500 Å are used to derivev sin i from the frequency of the first zero. Statistical analysis ofthe sample indicates that measurement error is a function of v sin i andthis relative error of the rotational velocity is found to be about 6%on average. The results obtained are compared with data from theliterature. There is a systematic shift from standard values from\citet{Slk_75}, which are 10 to 12% lower than our findings. Comparisonswith other independent v sin i values tend to prove that those fromSlettebak et al. are underestimated. This effect is attributed to thepresence of binaries in the standard sample of Slettebak et al., and tothe model atmosphere they used. Based on observations made at theEuropean Southern Observatory (ESO), La Silla, Chile, in the frameworkof the Key Programme 5-004-43K. Table 4 is only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5)or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/105
| Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 2 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Coupled Line-Profile and Continuum Variations in EZ Canis Majoris: Implications for the Driving Mechanism of Global Wind Structures in Wolf-Rayet Winds
EZ CMa is an apparently unusual Wolf-Rayet star of the nitrogen sequencethat exhibits strong variations on a period of 3.77 days with coherencylasting typically about 10 cycles. We have used an extensive set ofoptical spectroscopic observations to investigate a possible linkbetween its line-profile and photometric continuum variability. Despitethe strong epoch dependency of the variations, a persistent correlationis found between changes in the wind line profiles (N V lambda lambda4604, 4620 in particular) and in continuum flux emanating near thestellar core. We suggest that these observations give further support tothe idea that the physical conditions prevailing in the vicinity of thestar's photosphere have a significant impact on the wind structure andthat a spatial dependence of these conditions at the base of the outflowinduces the formation of azimuthal wind structures in EZ CMa. Theepoch-dependent nature of the variability could be related to long-termbehavior of corotating magnetic structures, although pulsationalinstabilities constitute a viable alternative.
| An extensive Delta a-photometric survey of southern B and A type bright stars
Photoelectric photometry of 803 southern BS objects in the Deltaa-system as detection tool for magnetic chemically peculiar (=CP2) starshas been carried out and compared to published spectral types. Thestatistical yield of such objects detected by both techniques ispractically the same. We show that there are several factors whichcontaminate the search for these stars, but this contamination is onlyof the order of 10% in both techniques. We find a smooth transition fromnormal to peculiar stars. Our sample exhibits the largest fraction ofCP2 stars at their bluest colour interval, i.e. 10% of all stars in thecolour range -0.19 <= B-V < -0.10 or -0.10 <= b-y < -0.05.No peculiar stars based on the Delta a-criterion were found at bluercolours. Towards the red side the fraction of CP2 stars drops to about3% for positive values of B-V or b-y with red limits roughlycorresponding to normal stars of spectral type A5. The photometricbehaviour of other peculiar stars: Am, HgMn, delta Del, lambda Boo, Heabnormal stars, as well as Be/shell stars and supergiants shows someslight, but definite deviations from normal stars. Spectroscopic andvisual binaries are not distinguished from normal stars in their Delta abehaviour. The results of this work justify larger statistical work(e.g. in open clusters) employing more time-saving photometric methods(CCD). \newpage Based on observations obtained at the European SouthernObservatory, La Silla, Chile. This research has made use of the Simbaddatabase, operated at CDS, Strasbourg, France. Table 2 is only availablein electronic form via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| Optical Spectroscopy of EZ Canis Majoris: Indication for Large-Scale Structures in a Wolf-Rayet Wind
We have carried out optical spectroscopy of the Wolf-Rayet star EZ CMaduring 20 consecutive nights in 1995 January in support of the IUEMega-project. In parallel with this optical spectroscopy, we alsomonitored EZ CMa using narrowband photometry. The light curve was foundto be remarkably stable when folded with the P=3.77 day period, and ithad a peak-to-valley amplitude of 0.1 mag. The P Cygni absorptioncomponents of He I lambda 3889 and He I lambda 5876 display a similarglobal pattern of variability as was found for the simultaneouslyacquired UV profiles. The strengthening of the P Cygni absorptioncomponent of these transitions is associated with the maximum of thecontinuum flux. Conversely, the absorption trough of N V lambda 4604gradually disappears as the star brightens. Although the emission partsof the lines are variable at different levels, they all show the samepattern of variability, which consists of phase-dependent shifts ofextra emission components superposed on the profiles. A strongcorrelation is found between the continuum-light level and theequivalent width of most transitions. The line skewness and thefull-width at half-maximum show a daily recurrence timescale, reflectingthe light curve changes. We have addressed in a rigorous statistical waythe significance of the variations by calculating the "temporal variancespectrum." For any given line, we found enhanced variability at somevelocities, although the whole profile displays a statisticallysignificant level of variability. Arguments against a compact companionas the cause of the observed periodic variability are presented.Instead, our observations strongly support the suggestion in the IUEMega analysis that the atypical level of variability results from therotation of a structured wind. We propose that the wind variability ofEZ CMa is triggered by photospheric activity, or that the wind iscontrolled by a large-scale magnetic field.
| Multi-colour photometric and spectroscopic monitoring of the WN5 star EZ Canis Majoris.
We present and analyse photometric and spectroscopic observations of theWN5 star EZ Canis Majoris obtained over a period of 7years. We discussthe changing light curve, the shift in phase of the maxima and point toflare type variability seen in one night. Small amplitude variations arereported in another night. We have investigated the change of theaverage visual magnitude over a time span of 18years and found atentative cyclic variation with a time scale of 2425d (6.6yr) with arange of ~0.07mag. This, of course, should be verified. If true, aprecession phenomenon may offer an explanation. The trend of the maximumlight amplitude of the 3.766d cycle is also investigated and it shows asaw-tooth character with a timescale of ~400d. A possible relation withthe magnetic activity of the star is discussed. We conclude that theline emission variability can be caused by both a single star model withan ever-changing wind and a binary (WN+NS) model.
| The X-Ray Emission of A-Type Stars
From X-ray images in the ROSAT public archives, we determine soft X-rayfluxes, or flux upper limits, for 74 A-type stars, which have beenobserved during deep integrations with the PSPC. Nine supposedly single,late A stars (0.20 < B-V < 0.35) are found to coincide with X-raysources. The X-ray luminosities we infer for these stars range fromlevels comparable to the Active Sun, at log L_x ~27.6, to much brighteremission levels similar to those observed for active late-type binarysystems, near log L_x ~30.1. Another 10 sources are identified withearly A stars (0.0 < B-V < 0.2). Five of these are confirmeddouble stars, the rest are ostensibly single. The maximum luminosity wedetect in the early A stars, log L_x = 30.1, is 3.5 orders of magnitudebrighter than the X-ray upper limits for the nondetected stars.Additional study, including radial velocity monitoring and/or opticalinterferometry, will be needed to determine whether the putativelysingle X-ray emitting stars are in fact single, or whether theiremission is produced entirely or in part by unknown or unresolved binarycompanions. The level of X-ray emission associated with chemicallynormal, single A stars thus far appears to be uncorrelated with anyobvious stellar property, including the rotation rate, which is known togreatly influence the dynamo activity and the X-ray emission levels oflower mass stars. (SECTION: Stars)
| The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..135A&db_key=AST
| A unique period for the WN5 star EZ CMa
We have obtained three months (mid Feb.-mid May 1993) of uninterrupted,precision, narrowband visual, continuum photometry of EZ CMa whichallows a viable search for periodicities at unprecedented highresolution in the frequency domain. We find only one independentsignificant period, P = 3.76d, as first claimed in 1980. The phasedlight curve shows complex structure (3peaks) but a high levelof coherency during the first approximately 8 weeks. A sudden changeleads to a different, but still coherent, light curve during the lastapproximately 4 weeks. Since only one period persists, it must have itsorigin either in rotation as a single WR star (e.g., oblique rotator) orin a binary (e.g., with a compact companion).
| Longterm Photometry of Variables at ESO - Part Two - the Second Data Catalogue 1986-1990
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..102...79S&db_key=AST
| Photometry, polarimetry, spectroscopy, and spectropolarimetry of the enigmatic Wolf-Rayet star EZ Canis Majoris
New observations of the peculiar Wolf-Rayet star EZ Canis Majoriscollected since 1987 are presented, and photometric, polarimetric,spectroscopic, and spectropolarimetric data are discussed. Linearpolarization data are well fitted with an eccentric binary model wherean additional free parameter is included to allow for epoch-dependentchanges of the geometrical electron distribution in the W-R envelope.This yields a set of basic parameters, including an eccentricity e =0.39 +/- 0.02 and an orbital inclination i = 114 deg +/- 3 deg. Thespectroscopic data show global profile variations for all three observedstrong emission lines He II 5412 A, C IV 5807 A, and He I 5876 A. Radialvelocities of the lines vary with the 3.766-day period. Radiallyexpanding inhomogeneities are superposed on the line profiles andvariable polarization in the lines is observed.
| Rapid photometry of EZ Canis Majoris - Searching for flare activity in Wolf-Rayet stars
EZ CMa was chosen for a trial run of high-speed photometry to search forflare activity in W-R stars. Data were collected during UT November27-December 2, 1991 with the 1.0-telescope + ASCAP photometer and the0.6-m telescope + manual photometer of the Cerro Tololo Inter-AmericanObservatory. A period near 22.7 min was found. A brightness increase ofabout 1 percent, lasting for about 10 min in the otherwise smooth lightcurve, was observed. Fourier analysis of the data sets an upper limit of0.0005 mag on any variations with periods less than about 10 min.
| Long-term photometry of variables at ESO. I - The first data catalogue (1982-1986)
This paper presents the catalog of photometric data in the Stromgrensystem obtained during the first four years (October 1982 - September1986) of the Long-Term Photometry of Variables (LTPV) program at ESO.The data are available in computer-readable form.
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
| Photometric evidence for sudden emission line strength variations in the WN 5 star HD 50896
Two months of Stromgren photometry confirms the basic 3.763 daylight-curve period of the WN 5 star HD 50896. Superposed on that periodare occasionally found in the four pass bands four secondary maxima, andone dramatic flux change. The periodic and semiperiodic lightvariability is caused by continuum variations, but the sudden fluxchange is more likely caused by emission line strength variations.Although pulsation cannot be ruled out, the continuum variations arepossibly caused by brightness discontinuities on the surface of thecorotating WR star.
| Photometry and polarimetry of the unusual WN5 star EZ Canis Majoris
New high-precision polarimetric data (based on four observing runsspanning 16 months and a nearly contiguous 62-night photometric run) arepresented for the unique Wolf-Rayet star of type WN5, EZ CMa. Eventhough the shape of the polarization curve changes from one run to thenext, the previously known 3.77-d period is always present in each runof data; no significant circular polarization variation is detected. Thedata are interpreted in terms of a binary system with a low-mass(probably compact) companion or rotating spots on a single star. Theformer is preferred; if correct, EZ CMa would fill the heretoforemissing link in the evolution of massive binaries.
| A high precision photometric investigation of the micro-variations of Wolf-Rayet stars
VBLUW photometric observations of seven WR stars, obtained with standarddeviation less than about 0.002 mag using the 90-cm Dutch telescope atESO during March-April 1986, are reported. The observation anddata-reduction techniques are discussed, and the results are presentedin extensive tables and graphs and characterized in detail. Some of thelight and color variations are tentatively attributed totemperature-induced changes in the continuum emission (e.g., nonuniformillumination of the pseudophotosphere due to dynamical inhomogeneitiessuch as temporarily hotter eddies or blobs). Particular attention isgiven to the contrast between the strong W-band (323.6-nm) excesspresently observed in WR 6 (EZ CMa) and the FUV deficiency observed byvan der Hucht et al. in 1974-1976; an explanation based on increasedouter-envelope transparency is proposed.
| Periodic variability of HD 50896 - A Wolf-Rayet star associated with a ring nebula
Photoelectric UBV observations of the Wolf-Rayet star HD 50896, which isassociated with a ring nebula, are reported which confirm the 3.76-dayperiodicity of the star. The observations were made with apulse-counting UBV photoelectric photometer on a 24-in. reflector overthe course of 20 nights. The light curves obtained exhibit a complexstructure which is similar in all filters, and agree well with theperiod of 3.763 days discovered by Firmani et al. (1979) and McLean(1980). The results are found to be in agreement with a model of HD50896 as a binary system containing an accreting neutron star movingthrough the extended atmosphere of the Wolf-Rayet star.
| The region of NGC 2287 and CR 121
Intermediate band and H-beta observations of 135 stars in the regions ofthe clusters NGC 2287 and Cr 121 are discussed, and a luminositycalibration of photometric parameters for late G- to early K-type brightgiants and supergiants is introduced. Results indicate that NGC 2287 isat a distance of 740 pc, very little reddened, 100-million years old,and contains three or four G8-K2 bright giants and supergiants and ablue straggler. Cr 121 is 1.17 kpc distant, very little reddened, 1.5million years old and an extension of CMa OB1. Cr 121 contains a nearerconcentration of stars at the same distance as NGC 2287, and theassociation appears to be the same age as CMa OB1, although presequencestars may exist. Intermingling of stars in CMa OB2 and NGC 2287 is alsoconsidered possible, and a test of the calibration of two methods ofluminosity determination of early A-type stars using photometricparameters shows them to be entirely consistent.
| The binary nature of the single-line Wolf-Rayet star EZ Canis Majoris equals HD 50896
Results of spectral photoelectric observations of HD 50896 obtained inthe period 1975 February-1978 March are presented. The variations inemission-line profiles, radial velocities and light are found to beconsistent with the 3.76 day period. It is concluded that the binaryhypothesis is the most likely one to explain the periodic variations,and that the companion is probably a neutron star of mass m2 equals 1.3plus or minus 0.4 solar mass. In addition, it is found that theeccentricity differs considerably from zero. It is suggested that thiseccentricity is responsible for some of the more extraordinaryvariations observed in HD 50896.
| Collinder 121: a Young Southern Open Cluster Similar to H and χ Persei
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1967ApJ...149..107F&db_key=AST
|
Добавить новую статью
Внешние ссылки
- - Внешних ссылок не найдено -
Добавить внешнюю ссылку
Группы:
|
Наблюдательные данные и астрометрия
| Созвездие: | Большой Пёс |
| Прямое восхождение: | 06h53m55.30s |
| Склонение: | -24°32'21.0" |
| Видимая звёздная величина: | 6.21 |
| Расстояние: | 144.718 парсек |
| Собственное движение RA: | -3 |
| Собственное движение Dec: | 1.2 |
| B-T magnitude: | 6.246 |
| V-T magnitude: | 6.222 |
Каталоги и обозначения:
|
