Садржај
Слике
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
The XMM-Newton serendipitous survey. V. The Second XMM-Newton serendipitous source catalogue
Aims. Pointed observations with XMM-Newton provide the basis forcreating catalogues of X-ray sources detected serendipitously in eachfield. This paper describes the creation and characteristics of the 2XMMcatalogue. Methods: The 2XMM catalogue has been compiled from a newprocessing of the XMM-Newton EPIC camera data. The main features of theprocessing pipeline are described in detail. Results: The catalogue,the largest ever made at X-ray wavelengths, contains 246 897 detectionsdrawn from 3491 public XMM-Newton observations over a 7-year interval,which relate to 191 870 unique sources. The catalogue fields cover a skyarea of more than 500 deg^2. The non-overlapping sky area is ~360deg2 (~1% of the sky) as many regions of the sky are observedmore than once by XMM-Newton. The catalogue probes a large sky area atthe flux limit where the bulk of the objects that contribute to theX-ray background lie and provides a major resource for generating large,well-defined X-ray selected source samples, studying the X-ray sourcepopulation and identifying rare object types. The main characteristicsof the catalogue are presented, including its photometric andastrometric propertiesBased on observations obtained with XMM-Newton, an ESA science missionwith instruments and contributions directly funded by ESA Member Statesand NASA. The catalogue and full Tables D.1 and D.2 are available inelectronic form at the 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/493/339
| Non-thermal emission processes in massive binaries
In this paper, I present a general discussion of several astrophysicalprocesses likely to play a role in the production of non-thermalemission in massive stars, with emphasis on massive binaries. Eventhough the discussion will start in the radio domain where thenon-thermal emission was first detected, the census of physicalprocesses involved in the non-thermal emission from massive stars showsthat many spectral domains are concerned, from the radio to the veryhigh energies. First, the theoretical aspects of the non-thermalemission from early-type stars will be addressed. The main topics thatwill be discussed are respectively the physics of individual stellarwinds and their interaction in binary systems, the acceleration ofrelativistic electrons, the magnetic field of massive stars, and finallythe non-thermal emission processes relevant to the case of massivestars. Second, this general qualitative discussion will be followed by amore quantitative one, devoted to the most probable scenario wherenon-thermal radio emitters are massive binaries. I will show how severalstellar, wind and orbital parameters can be combined in order to makesome semi-quantitative predictions on the high-energy counterpart to thenon-thermal emission detected in the radio domain. These theoreticalconsiderations will be followed by a census of results obtained so far,and related to this topic. These results concern the radio, the visible,the X-ray and the γ-ray domains. Prospects for the very highenergy γ-ray emission from massive stars will also be addressed.Two particularly interesting examples—one O-type and oneWolf-Rayet binary—will be considered in details. Finally,strategies for future developments in this field will be discussed.
| The CH2CN- molecule: carrier of the λ8037 diffuse interstellar band?
The hypothesis that the cyanomethyl anion CH2CN- isresponsible for the relatively narrow diffuse interstellar band (DIB) at8037.8±0.15 Å is examined with reference to newobservational data. The 0_00 absorption band arising from the^1B_1-tildeX ^1A' transition from the electronic ground state to thefirst dipole-bound state of the anion is calculated for a rotationaltemperature of 2.7 K using literature spectroscopic parameters andresults in a rotational contour with a peak wavelength of 8037.78Å. By comparison with diffuse band and atomic line absorptionspectra of eight heavily-reddened Galactic sightlines, CH2CN-is found to be a plausible carrier of the λ8037 diffuseinterstellar band provided the rotational contour is Doppler-broadenedwith a b parameter between 16 and 33 km s-1 that depends onthe specific sightline. Convolution of the calculated CH2CN-transitions with the optical depth profile of interstellar Ti II resultsin a good match with the profile of the narrow λ8037 DIB observedtowards HD 183143, HD 168112 and Cyg OB2 8a. The rotational levelpopulations may be influenced by nuclear spin statistics, resulting inthe appearance of additional transitions from Ka = 1 of orthoCH2CN- near 8025 and 8050 Å that are not seen incurrently available interstellar spectra. For CH2CN- to bethe carrier of the λ8037 diffuse interstellar band, either a)there must be mechanisms that convert CH2CN- from the orthoto the para form, or b) the chemistry that forms CH2CN- mustresult in a population of K_a'' levels approaching a Boltzmanndistribution near 3 K.
| Non-thermal radio emission from O-type stars. II. HD 167971
HD 167971 is a triple system consisting of a 3.3-day eclipsing binary(O5-8 V + O5-8 V) and an O8 supergiant. It is also a well knownnon-thermal radio emitter. We observed the radio emission of HD 167971with the Very Large Array (VLA) and the Australia Telescope CompactArray (ATCA). By combining these data with VLA archive observations weconstructed a radio lightcurve covering a 20-yr time-range. We searchedfor, but failed to find, the 3.3-day spectroscopic period of the binaryin the radio data.This could be due to the absence of intrinsic synchrotron radiationin the colliding-wind region between the two components of the eclipsingbinary,or due to the largeamount of free-free absorption that blocks the synchrotronradiation. We are able to explain many of the observed characteristicsof the radio dataif the non-thermal emission is produced in a colliding-wind regionbetween the supergiant and the combined winds of the binary.Furthermore, if the system is gravitationally bound, the orbital motionoccurs over a period of ~20 years or longer, as suggested by thelong-term variability in the radio data. We argue that the variabilityis due to the free-free absorption that changes with orbital phase ormay also in part be due to changes in separation, should the orbit beeccentric.Table A.1 is only available in electronic form at http://www.aanda.org
| XMM-Newton observations of the massive colliding wind binary and non-thermal radio emitter CygOB2#8A [O6If + O5.5III(f)]
We report on the results of four XMM-Newton observations separated byabout ten days from each other of CygOB2#8A [O6If + O5.5III(f)]. Thismassive colliding wind binary is a very bright X-ray emitter - one ofthe first X-ray emitting O-stars discovered by the Einstein satellite -as well as a confirmed non-thermal radio emitter whose binarity wasdiscovered quite recently. The X-ray spectrum between 0.5 and 10.0keV isessentially thermal, and is best fitted with a three-component modelwith temperatures of about 3, 9 and 20MK. The X-ray luminosity correctedfor the interstellar absorption is rather large, i.e. about1034ergs-1. Compared to the `canonical'LX/Lbol ratio of O-type stars, CygOB2#8A was afactor of 19-28 overluminous in X-rays during our observations. The EPICspectra did not reveal any evidence for the presence of a non-thermalcontribution in X-rays. This is not unexpected considering that thesimultaneous detections of non-thermal radiation in the radio and softX-ray (below 10.0keV) domains is unlikely. Our data reveal a significantdecrease in the X-ray flux from apastron to periastron with an amplitudeof about 20 per cent. Combining our XMM-Newton results with those fromprevious ROSAT-PSPC and ASCA-SIS observations, we obtain a light curvesuggesting a phase-locked X-ray variability. The maximum emission leveloccurs around phase 0.75, and the minimum is probably seen shortly afterthe periastron passage. Using hydrodynamic simulations of the wind-windcollision, we find a high X-ray emission level close to phase 0.75, anda minimum at periastron as well. The high X-ray luminosity, the strongphase-locked variability and the spectral shape of the X-ray emission ofCygOB2#8A revealed by our investigation point undoubtedly to X-rayemission dominated by colliding winds.Based on observations with XMM-Newton, an ESA Science Mission withinstruments and contributions directly funded by ESA Member states andthe USA (NASA).E-mail: debecker@astro.ulg.ac.be ‡Research Associate FNRS (Belgium).
| Can single O stars produce non-thermal radio emission?
We present a model for the non-thermal radio emission from presumablysingle O stars, in terms of synchrotron emission from relativisticelectrons accelerated in wind-embedded shocks. These shocks areassociated with an unstable, chaotic wind. The main improvement withrespect to earlier models is the inclusion of the radial dependence ofthe shock velocity jump and compression ratio, based on one-dimensionaltime-dependent hydrodynamical simulations. The decrease of the velocityjump and the compression ratio as a function of radius produces arapidly decreasing synchrotron emissivity. This effectively prohibitsthe models from reproducing the spectral shape of the observednon-thermal radio emission. We investigate a number of “escaperoutes” by which the hydrodynamical predictions might bereconciled with the radio observations. We find that the observedspectral shape can be reproduced by a slower decline of the compressionratio and the velocity jump, by the re-acceleration of electrons in manyshocks or by adopting a lower mass-loss rate. However, none of theseescape routes are physically plausible. In particular, re-accelerationby feeding an electron distribution through a number of shocks, is incontradiction with current hydrodynamical simulations. Thesehydrodynamical simulations have their limitations, most notably the useof one-dimensionality. At present, it is not feasible to performtwo-dimensional simulations of the wind out to the distances requiredfor synchrotron-emission models. Based on the current hydrodynamicmodels, we suspect that the observed non-thermal radio emission from Ostars cannot be explained by wind-embedded shocks associated with theinstability of the line-driving mechanism. The most likely alternativemechanism is synchrotron emission from colliding winds. That would implythat all O stars with non-thermal radio emission should be members ofbinary or multiple systems.
| Radio Detection of Colliding Wind Binaries
Four massive, early-type stars, three of which are confirmed binaries,have been observed with the Australia Telescope Compact Array at 1.4,2.4, 4.8, and 8.6 GHz. The earliest star cataloged so far, HD 93129A,was also observed at 17.8 and 24.5 GHz. Here we present an analysis ofthe spectra as well as the structure of the stellar systems. All fourspectra show clear evidence of non-thermal emission, indicative of abinary system with a colliding wind region. We discuss the magneticfield of the emitting region of HD 93129A and make predictions on theradiation at high energies. Archive X-ray observations towards thetarget sources are also investigated and interpreted in the light of thenon-thermal emission detected.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| An XMM-Newton observation of the multiple system HD 167971 (O5-8V + O5-8V + (O8I)) and the young open cluster NGC 6604
We discuss the results of two XMM-Newton observations of the opencluster NGC 6604 obtained in April and September 2002. We concentratemainly on the multiple system HD 167971 (O5-8V + O5-8V + (O8I)). Thesoft part of the EPIC spectrum of this system is thermal with typicaltemperatures of about 2 × 106 to 9 ×106 K. The nature (thermal vs. non-thermal) of the hard partof the spectrum is not unambiguously revealed by our data. If theemission is thermal, the high temperature of the plasma (~2.3 ×107 to 4.6 × 107 K) would be typical of whatshould be expected from a wind-wind interaction zone within a longperiod binary system. This emission could arise from an interactionbetween the combined winds of the O5-8V + O5-8V close binary system andthat of the more distant O8I companion. Assuming instead that the hardpart of the spectrum is non-thermal, the photon index would be rathersteep (~3). Moreover, a marginal variability between our two XMM-Newtonpointings could be attributed to an eclipse of the O5-8V + O5-8V system.The overall X-ray luminosity points to a significant X-ray luminosityexcess of about a factor 4 possibly due to colliding winds. ConsideringHD 167971 along with several recent X-ray and radio observations, wepropose that the simultaneous observation of non-thermal radiation inthe X-ray (below 10.0 keV) and radio domains appears rather unlikely.Our investigation of our XMM-Newton data of NGC 6604 reveals a rathersparse distribution of X-ray emitters. Including the two brightnon-thermal radio emitters HD 168112 and HD 167971, we present a list of31 X-ray sources along with the results of the cross-correlation withoptical and infrared catalogues. A more complete spectral analysis ispresented for the brightest X-ray sources. Some of the members of NGC6604 present some characteristics suggesting they may be pre-mainsequence star candidates.
| Non-thermal radio emission from O-type stars. I. HD168112
We present a radio lightcurve of the O5.5 III(f^+) star HD 168112, basedon archive data from the Very Large Array (VLA) and the AustraliaTelescope Compact Array (ATCA). The fluxes show considerable variabilityand a negative spectral index, thereby confirming that HD 168112 is anon-thermal radio emitter. The non-thermal radio emission is believed tobe due to synchrotron radiation from relativistic electrons that havebeen Fermi accelerated in shocks. For HD 168112, it is not known whetherthese shocks are due to a wind-wind collision in a binary system or tothe intrinsic instability of the stellar wind driving mechanism.Assuming HD 168112 to be a single star, our synchrotron model shows thatthe velocity jump of the shocks should be very high, or there should bea very large number of shocks in the wind. Neither of these iscompatible with time-dependent hydrodynamical calculations of O starwinds. If, on the other hand, we assume that HD 168112 is a binary, thehigh velocity jump is easily explained by ascribing it to the wind-windcollision. By further assuming the star to be an eccentric binary, wecan explain the observed radio variability by the colliding-wind regionmoving in and out of the region where free-free absorption is important.The radio data presented here show that the binary has a period ofbetween one and two years. By combining the radio data with X-ray data,we find that the most likely period is ~1.4 yr.
| Quasi-simultaneous XMM-Newton and VLA observation of the non-thermal radio emitter HD 168112 (O5.5III(f+))
We report the results of a multiwavelength study of the non-thermalradio emitter HD 168112 (O5.5III(f+)). The detailed analysisof two quasi-simultaneous XMM-Newton and VLA observations reveals strongvariability of this star both in the X-ray and radio ranges. The X-rayobservations separated by five months reveal a decrease of the X-rayflux of 30%. The radio emission on the other hand increases by afactor 5-7 between the two observations obtained roughly simultaneouslywith the XMM-Newton pointings. The X-ray data reveal a hard emissionthat is most likely produced by a thermal plasma at kT 2-3 keVwhile the VLA data confirm the non-thermal status of this star in theradio waveband. Comparison with archive X-ray and radio data confirmsthe variability of this source in both wavelength ranges over a yet illdefined time scale. The properties of HD 168112 in the X-ray and radiodomain point towards a binary system with a significant eccentricity andan orbital period of a few years. However, our optical spectra reveal nosignificant changes of the star's radial velocity suggesting that if HD168112 is indeed a binary, it must be seen under a fairly lowinclination.Based on observations with XMM-Newton, an ESA Science Mission withinstruments and contributions directly funded by ESA Member states andthe USA (NASA). Also based on observations collected with the VLA, aninstrument of the National Radio Astronomy Observatory, which is afacility of the National Science Foundation operated by AssociatedUniversities, Inc. Optical data were collected at the European SouthernObservatory (La Silla, Chile), and at the ObservatorioAstronómico Nacional of San Pedro Mártir (Mexico).
| A Galactic O Star Catalog
We have produced a catalog of 378 Galactic O stars with accuratespectral classifications that is complete for V<8 but includes manyfainter stars. The catalog provides cross-identifications with othersources; coordinates (obtained in most cases from Tycho-2 data);astrometric distances for 24 of the nearest stars; optical (Tycho-2,Johnson, and Strömgren) and NIR photometry; group membership,runaway character, and multiplicity information; and a Web-based versionwith links to on-line services.
| The total-to-selective extinction ratio determined from near IR photometry of OB stars
The paper presents an extensive list of the total to selectiveextinction ratios R calculated from the infrared magnitudes of 597 O andB stars using the extrapolation method. The IR magnitudes of these starswere taken from the literature. The IR colour excesses are determinedwith the aid of "artificial standards" - Wegner (1994). The individualand mean values of total to selective extinction ratios R differ in mostcases from the average value R=3.10 +/-0.05 - Wegner (1993) in differentOB associations. The relation between total to selective extinctionratios R determined in this paper and those calculated using the "methodof variable extinction" and the Cardelli et al. (1989) formulae isdiscussed. The R values presented in this paper can be used to determineindividual absolute magnitudes of reddened OB stars with knowntrigonometric parallaxes.
| VLA Radio Continuum and IRAS Observations of the Ring Nebulae around WR 101 and WR 113
We report radio continuum observations at 1465 MHz obtained with theVery Large Array (VLA) in the DnC configuration toward the ring nebulaeassociated with the stars WR 101 and WR 113, with resolutions of ~38"and 30", respectively. IRAS images of the nebulae with resolutions ofabout 2' (90 Msolar, 40 cm-3) are also analyzed. Aremarkable resemblance among the optical, infrared, and radio images ofthese ring nebulae is observed. The VLA data indicate that Anon. WR 101is thermal in nature. An ionized mass of ~230+/-40 Msolar andelectron densities in the range ~40-55 cm-3 were estimatedfor Anon. WR 101. The derived ionized masses and electron densities inthe inner and outer shells of the nebula related to WR 113 are ~20+/-10Msolar, 180-500 cm-3 and ~90 Msolar 40cm-3, respectively. Based on infrared data at 60 and 100μm, the derived masses and temperatures for the dust component in thering nebula around WR 101 are 0.3-1 Msolar and ~40 K. Theassociated masses suggest that the ring nebula related to WR 101 and theouter arc associated with WR 113 consist of swept-up interstellarmatter, while the relatively low ionized mass associated with the innershell of the nebula around WR 113 may contain a nonnegligiblecontribution of expelled ejecta material. The derived electron densitiesfor the nebula around WR 101 and the inner shell around WR 113 arecomparable to electron densities for other W-R ring nebulae. Low fillingfactors are inferred for both nebulae. The nebulae probably originatedduring the current W-R phase of the stars.
| Atlas of Interstellar Extinction Curves of OB Stars Covering the Whole Available Wavelength Range
The paper presents a collection of 436 extinction curves covering thewhole available range of wavelengths from satellite UV to near-IR. Thedata were taken from the ANS photometric catalogue and from thecompilations of IR photometric measurements. The data curves have beenobtained with the aid of ``artificial standards": Papaj et al. (1993)and Wegner (1994, 1995). The visual magnitudes and spectralclassifications of O and B type stars with EB-V>= 0.05were taken from the SIMBAD database. The curves are given in the form ofplots and tables E{lambda - V} / EB-V versus1/λ. The observed variety of extinction laws among slightlyreddened stars is apparently due to the various physical parameters ofinterstellar clouds.
| 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
| The Serpens OB2 Association and Its Thermal ``Chimney''
UBVRI photometry and MK spectral types have been obtained for a nearlycomplete sample of the massive star population of the Serpens OB2association. This relatively neglected association is found to containover 100 OB stars at a distance of 1.9+/-0.3 kpc and with a common ageof 5+/-1 Myr. These stars illuminate the large H II region S54, and aredirectly connected to the unusual thermal ``chimney'' detected byMüller et al. Evidence is given of continuing star formation withinthe association, and the relationship between the association stars andthe chimney is discussed.
| The Search for Interstellar C60
The optical region of a number of reddened O-type stars has beenexamined on Keck I HIRES spectrograms (R=45,000) for evidence ofinterstellar C60. No absorption features were detected nearthe laboratory C60 wavelengths 3857 and 3980 Å. Aninterstellar feature is present at 6220.8 Å, but it isunacceptably far from the laboratory gas-phase wavelength of 6217.5Å. It is probably just another of the weak diffuse interstellarbands (DIBs), which are numerous in that spectral region. The mostastronomically promising C60 feature was measured in thelaboratory at 3284 Å in liquid or solid matrices. Its gas-phasewavelength can be inferred either from matrix shifts of C60features at longer wavelengths or from high-temperature gas-phasemeasurements. On that evidence, the interstellar feature could fallanywhere between about 3244 and 3306 Å. Its width is uncertain buthere is taken to be about 1 Å . No interstellar absorption fittingthese specifications and as strong as 16 mÅ has been detected inthe stars observed, including Cyg OB2/8A of E(B-V)=1.60. It follows thatin that particular line of sight and for the assumed FWHM of 1 Å ,N(C60)<4.5×1011 cm-2. However,some recent laboratory spectroscopy suggests that its width may be verymuch larger, in which case this limit would be invalid. At this upperlimit, the corresponding number of carbon atoms contained in neutralC60 indicates that that molecule would be only a minorcontributor to the total amount of C in that direction, and would beless than 1% of the amount that may be tied up in the DIBs. StrongerC60 bands are known in the laboratory at approximately 2110and 2566 Å, but the upper limit on 3284 Å suggests that theywill not be easy to detect without high resolution, high signal-to-noiseratio (S/N) satellite spectroscopy and better laboratory gas-phasewavelengths. An estimate of the column density ofC+60, under the assumption that the 9577, 9632Å bands are indeed due to C+60 and that thelaboratory f-value is correct, indicates that theC+60/C60 abundance in that line ofsight is greater than 100.
| 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
| Observational Evidence of Supershell Blowout in GS 018-04+44: The Scutum Supershell
Emission in the H I 21 cm line has been mapped for a region of theGalaxy that includes two known supershells, GS 018-04+44 and GS034-06+65. We focus on the GS 018-04+44, hereafter referred to as theScutum Supershell, which is an elongated shell about 5 deg in diameterextending to -7 deg below the Galactic plane. The Scutum shell lies at akinematic distance of ~3300 pc, implying a shell diameter of ~290 pcwith a vertical extension of ~400 pc away from the Galactic plane. TheScutum shell contains 6.2x105 Msolar swept intothe walls. We observe that the top of the shell is missing, and asubstantial column of H I rises from the shell walls tob=-11deg, culminating in a large cloud of neutral hydrogen,3.74x104 Msolar, located ~630 pc from the plane.ROSAT data show X-ray emission that closely anticorrelates with the 21cm emission. This emission probably originates from hot gas within theScutum Supershell. After approximately correcting for the foregroundabsorption, we find that the 1.5 keV X-rays peak at the base of theshell, the 0.75 keV emission peaks in the interior and at the top of theshell, and the 0.25 keV emission extends to high latitudes above theshell. The X-ray luminosity is roughly ~5x1036 ergss-1. The Wisconsin Hα Mapper (WHAM) survey shows thepresence of Hα emission that exhibits a morphology similar to thatof the H I. Spectra indicate the presence of ionized hydrogen atvelocities similar to the H I, placing ionized material at the samekinematic distance as the neutral material. IRAS images in the 60 and100 μm wavebands reveal the presence of dust correlated with theneutral hydrogen. Infrared surface brightness indicates an excess in the100 μm emission, which could indicate a molecular hydrogen componentwith a column density of 2.4x1021 cm-2 in thedensest regions of the high-latitude cloud of neutral hydrogen. IUEultraviolet high dispersion spectra of HD 177989 (l=17.89d, b=-11.88d)and HD 175754 (l=16.40d, b=-9.92d) reveal the presence of very strongabsorption by highly ionized gas at a velocity that associates theabsorption with the ejecta of the Scutum Supershell. In the case of HD177989, the high ion column density ratios suggest an origin in aturbulent mixing layer where hot and cool gases mix in the presence ofshear flows. The Hα and X-ray emission suggest that a multitude ofenergetic phenomena exist in this region, providing the necessaryionizing radiation. Indeed, there are multiple supernova remnants, H IIregions, and hot stars, which could all contribute sizeable amounts ofenergy and ionizing radiation. The combination of these data setsindicates observational evidence of a ``blowout'' phenomena whereby hotmaterial produced within the Scutum Supershell has blown through the topof the shell and been pushed to high latitude. Based on observationsfrom the Green Bank 43m radio telescope, the ROSAT All-Sky Survey, theWHAM All-Sky Survey, IRAS, and IUE.
| 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.
| Five-colour photometry of OB-stars in the Southern Hemisphere
Observations of OB-stars, made in 1959 and 1960 at the Leiden SouthernStation near Hartebeespoortdam, South Africa, with the VBLUW photometerattached to the 90 cm light-collector, are given in this paper. They arecompared with photometry obtained by \cite[Graham (1968),]{gra68}\cite[Walraven & Walraven (1977),]{wal77} \cite[Lub & Pel(1977)]{lub77} and \cite[Van Genderen et al. (1984).]{gen84} Formulaefor the transformation of the present observations to those of\cite[Walraven & Walraven (1977)]{wal77} and \cite[Lub & Pel(1977)]{lub77} are given. Table 4 is only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/Abstract.html
| Interstellar extinction.
Not Available
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
| A Radial Velocity Database for Stephenson-Sanduleak Southern Luminous Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....113..823R&db_key=AST
| Derivation of the Galactic rotation curve using space velocities
We present rotation curves of the Galaxy based on the space-velocitiesof 197 OB stars and 144 classical cepheids, respectively, which rangeover a galactocentric distance interval of about 6 to 12kpc. Nosignificant differences between these rotation curves and rotationcurves based solely on radial velocities assuming circular rotation arefound. We derive an angular velocity of the LSR of{OMEGA}_0_=5.5+/-0.4mas/a (OB stars) and {OMEGA}_0_=5.4+/-0.5mas/a(cepheids), which is in agreement with the IAU 1985 value of{OMEGA}_0_=5.5mas/a. If we correct for probable rotations of the FK5system, the corresponding angular velocities are {OMEGA}_0_=6.0mas/a (OBstars) and {OMEGA}_0_=6.2mas/a (cepheids). These values agree betterwith the value of {OMEGA}_0_=6.4mas/a derived from the VLA measurementof the proper motion of SgrA^*^.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Diffuse interstellar bands and UV extinction curves. The missing link.
The connection between diffuse interstellar bands and components of theinterstellar ultraviolet extinction curve, decomposed according to theFitzpatrick & Massa scheme, is analysed from new observations ofseveral DIBs in the line of sight to 28 stars measured by IUE. We findthat the strength of the 217.5nm bump positively correlates with DIBstrength, whereas correlations with a negative slope exist with the FUVnon-linear rise and the width of the bump. There is no correlation withlinear rise. The relation of bump height versus DIB strength does notpass through zero. The results are interpreted within the polycyclicaromatic hydrocarbon (PAH) framework. They strengthen the hypothesisthat the FUV non-linear rise is produced by neutral PAHs, whereas DIBcarriers are found among some ionised or radical PAHs.
| A spectroscopic database for Stephenson-Sanduleak Southern Luminous Stars
A database of published spectral classifications for objects in theStepenson-Sanduleak Luminous Stars in the Southern Milky Way catalog hasbeen compiled from the literature. A total of 6182 classifications for2562 stars from 139 sources are incorporated.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
| Сазвежђа: | Змија |
| Ректацензија: | 18h18m40.87s |
| Deклинација: | -12°06'23.4" |
| Apparent магнитуда: | 8.563 |
| Даљина: | 10000000 parsecs |
| Proper motion RA: | 2.1 |
| Proper motion Dec: | -2.8 |
| B-T magnitude: | 9.231 |
| V-T magnitude: | 8.619 |
Каталог и designations:
|
