Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
Broad- and narrowband visible imaging of comet 9P/Tempel 1 at ESO around the time of the Deep Impact event
Context: On 4 July 2005 at 05:52UT the impactor of NASA's DeepImpact(DI) mission exploded at comet 9P/Tempel 1. The ejecta material of theimpact expanded into the coma that is produced by normal cometaryactivity. The La Silla and Paranal sites of the European SouthernObservatory ESO in Chile participated in the world-wide campaign toobserve this event. Aims: The gas and dust content of thecometary coma is observed around the time of the DI event to identifysignatures of the impact, like changes in the gas production (CN, C{3},C{2}, NH{2} and Na) and in the dust properties. The study also describesthe normal activity pattern in the coma and the expanding ejecta cloud. Methods: The gas production rates and the dust reddening slope aremeasured in images obtained through narrowband cometary filters. Theejecta cloud and the features of normal cometary activity, as imaged innarrow- and broadband filter images, are studied with respect togeometry, intensity, and persistence. Results: The production ofCN, C{3}, and C{2} gas by the nucleus is at similar level on 3 July and9+10 July 2005. The mixing ratios of these gases are in the range ofthose for “typical” comets. NH{2} and Na gas are notdetected above the dust continuum flux in the coma. The reddening slopeof the dust continuum changes from a value of 9%/100 nm, constantthroughout 20 000 km distance around the nucleus, on 3 July to about19-20%/100 nm on 9+10 July 2005. An increase of the slope with radialdistance is found. Both changes might be due to the presence of dustfrom the ejecta cloud. The dust coma of the comet showed a porcupinepattern of 9 coma jets before impact which remained intact after impact.It can be interpreted as being due to embedded fan structures producedby at least 4 active regions on the rotating nucleus. The ejecta cloudcontains dust grains of likely absorbing material and possiblydielectric admixtures with solar radiation pressure factors ? of0.2-1.9 and ejection velocities of 160-370 m s-1. The ejectacloud is optically thin 21 h after impact and shows a higher surfacebrightness and redder color in the sunward sector compared to thetailward side.Based on observations performed at the ESO La Sillaand Paranal Observatories in Chile (program 075.C-0583).
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| The Origins and Evolutionary Status of B Stars Found Far from the Galactic Plane. II. Kinematics and Full Sample Analysis
This paper continues the analysis of faint high-latitude B stars fromMartin. Here we analyze the kinematics of the stars and combine themwith the abundance information from the first paper to classify eachone. The sample contains 31 Population I runaways, 15 old evolved stars(including 5 blue horizontal-branch [BHB] stars, 3 post-HB stars, 1pulsating helium dwarf, and 6 stars of ambiguous classification), 1 Fdwarf, and 2 stars that do not easily fit in one of the othercategories. No star in the sample unambiguously shows thecharacteristics of a young massive star formed in situ in the halo. Thetwo unclassified stars are probably extreme Population I runaways. Thelow binary frequency and rotational velocity distribution of thePopulation I runaways imply that most were ejected from dense starclusters by the dynamic ejection scenario. However, we remain puzzled bythe lack of runaway Be stars. We also confirm that PB 166 and HIP 41979are both nearby solar-metallicity BHB stars.Based on observations made at the 2.1 m Otto Struve Telescope ofMcDonald Observatory, operated by the University of Texas at Austin.
| New Estimates of the Solar-Neighborhood Massive Star Birthrate and the Galactic Supernova Rate
The birthrate of stars of masses >=10 Msolar is estimatedfrom a sample of just over 400 O3-B2 dwarfs within 1.5 kpc of the Sunand the result extrapolated to estimate the Galactic supernova ratecontributed by such stars. The solar-neighborhood Galactic-plane massivestar birthrate is estimated at ~176 stars kpc-3Myr-1. On the basis of a model in which the Galactic stellardensity distribution comprises a ``disk+central hole'' like that of thedust infrared emission (as proposed by Drimmel and Spergel), theGalactic supernova rate is estimated at probably not less than ~1 normore than ~2 per century and the number of O3-B2 dwarfs within the solarcircle at ~200,000.
| New runaway OB stars with HIPPARCOS
A Monte Carlo method for detection of runaway OB stars fromobservational data is proposed. 61 runaway OB star candidates have beendetected by an analysis of Hipparcos proper motions. The peculiartangential and total transverse velocities have been determined forthese stars. A list of the detected runaway star candidates ispresented. The evidence of a discrepancy between photometric andparallactic distances of runaway OB star candidates is presented.
| The Origins and Evolutionary Status of B Stars Found Far from the Galactic Plane. I. Composition and Spectral Features
The existence of faint blue stars far above the Galactic plane that havespectra that are similar to nearby Population I B stars presents severalinteresting questions. Among them are the following: Can a Population IB star travel from the disk to a position many kiloparsecs above theplane in a relatively short main-sequence lifetime? Is it possible thatsingle massive star formation is occurring far from the Galactic plane?Are these objects something else masquerading as main-sequence B stars?This paper (the first of two) analyzes the abundances of a sample ofthese stars and reveals several that are chemically similar to nearbyPopulation I B stars, whereas others clearly have abundance patternsmore like those expected in blue horizontal-branch (BHB) orpost-asymptotic giant branch stars. Several of those with old evolvedstar abundances also have interesting features of note in their spectra.We also consider why this sample does not have any classical Be starsand identify at least two nearby solar-metallicity BHB stars.Based on observations made at the 2.1 m Otto Struve Telescope ofMcDonald Observatory operated by the University of Texas at Austin.
| Catalog of Galactic OB Stars
An all-sky catalog of Galactic OB stars has been created by extendingthe Case-Hamburg Galactic plane luminous-stars surveys to include 5500additional objects drawn from the literature. This work brings the totalnumber of known or reasonably suspected OB stars to over 16,000.Companion databases of UBVβ photometry and MK classifications forthese objects include nearly 30,000 and 20,000 entries, respectively.
| 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.
| 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.
| The HB Narrowband Comet Filters: Standard Stars and Calibrations
We present results concerning the development and calibration of a newset of narrowband comet filters, designated the HB filter set, which wasdesigned and manufactured to replace aging IHW filters. Information isalso presented about the design and manufacturing of the filters,including the reasoning that was used for deciding the final wavelengthsand bandpasses. The new filters are designed to measure five differentgas species (OH, NH, CN, C2, C3), two ions(CO+, H2O+), and four continuum points.An improved understanding of extended wings from emission bands in cometspectra, gained since the development of the IHW filters, wasincorporated into the new design, so that contamination from undesiredspecies is significantly reduced compared to previous filters. Inaddition, advances in manufacturing techniques lead to squarertransmission profiles, higher peak transmission and UV filters withlonger lifetimes. We performed the necessary calibrations so that dataobtained with the filters can be converted to absolute fluxes, allowingfor, among other things, accurate subtraction of the continuum from thegas species. Flux standards and solar analogs were selected andobserved, and the data were used to establish a magnitude system for theHB filters. The star measurements were also used to evaluate which solaranalogs were best representatives of the Sun and to explore how the fluxstandards differed in the UV with respect to their spectral type. Newprocedures were developed to account for the non-linear extinction inthe OH filter, so that proper extrapolations to zero airmass can beperformed, and a new formalism, which can account for mutualcontaminations in two (or more) filters, was developed for reducingcomet observations. The relevant equations and reduction coefficientsare given, along with detailed instructions on how to apply them. Wealso performed a series of tests involving factors that can affecteither the filter transmission profiles or the distribution of theemission lines in the gas species to determine how these effectspropagate through to the calibration coefficients. The results indicatethat there are only two factors that are a concern at a level of morethan a few percent: f-ratios smaller than f/4, and a few individualfilters whose transmission profiles are significantly different from thefilters used in the calibrations.
| He, CNO abundances and v sin i values in He-rich stars
We present projected rotational velocities distribution in He-rich starsagainst normal B type stars as well as the abundance analysis of lightelements and their comparison with results of earlier series. Theanalysis is based on high-resolution observations (R=40000) collected atESO, La Silla, Chile in the optical region and includes 11 stars,amongst them 5 new stars in comparison with an earlier sample. Thedistribution of projected rotational velocities shows a significantexcess of slow rotators, no He-rich stars having v sin i > 130 km/sat the significance level of 99.5%. Based on fully consistent LTEmodels, the helium abundance ranges from 0.1 (solar) to 0.4. Theanalysis on the new sample confirms the results of earlier paper: thelight element abundances display a diverse pattern from under-solar upto above-solar values. Carbon has the same abundance in He-rich and instandard stars for cool He-rich stars, following the predictions ofradiative diffusion in the presence of wind. The star HD149363 appearsrather as He-weak as based on the equivalent widths from R=40 000spectra.
| 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
| 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.
| On Space Velocities of Binary Stars in Which One Component Has Experienced a Supernova Explosion
When one component of an evolved binary loses a significant fraction ofits initial mass in a symmetric supernova explosion but remains bound toits companion, the remnant binary recoils with a velocity that can becomparable to the orbital velocity of the supernova precursor. Thisvelocity is enough to explain the observed peculiar space velocitiesand/or distances from the Galactic plane of most X-ray binaries andbinary OB runaway stars. Some exceptions certainly occur, butuncertainties in estimates of velocities and distances, as well asmechanisms other than a popular asymmetric kick, may be responsible formost of the exceptions.
| Red and infrared colours of B stars and the reddening law in the Galaxy
The red and infrared intrinsic colours of B stars are derived fromphotometric observations through the UBV(RI)_CJHK and Hβ filters of257 early-type stars. Those stars for which the UBV and Hβmeasurements match the published spectral class, and which show no othersigns of peculiarity, are used to determine the intrinsic photometriccolours of B stars in the red and infrared. From these intrinsic coloursthe interstellar reddening relationships for the red and infraredcolours are evaluated, and the results are compared with previousestimates of these quantities. The values of R, E(B-V) and the distanceare then determined for the individual stars. R is confirmed to be closeto 3.1 in most cases, but was found to be much larger in somedirections. The relationship between R and the location of a star in theGalaxy is investigated. Usually the abnormally reddened stars seemed tobe associated with known regions of star formation. The paper alsoidentifies seven likely variable stars and a number of stars withpossible dust shells.
| A Search for Pulsar Companions to OB Runaway Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...461..357S&db_key=AST
| DO OB Runaway Stars Have Pulsar Companions?
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111.1220P&db_key=AST
| New spectroscopic and photometric observations of the ellipsoidal variable V600 HER (HD 149881): solution of the light curves and the radial-velocity curve by the method of synthesis.
Not Available
| 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.
| Evidence for an extended neutral Galactic halo
Singly ionized titanium is the dominant ionization stage in H I regionsand provides an excellent tracer of the neutral interstellar medium.Here we present new interstellar Ti II absorption line observationstoward six halo stars located at absolute value of z greater than 1 kpc.Although the gas distribution is probably patchy, significant neutralgas does exist beyond 1 kpc from the Galactic plane and the projectedcolumn density, N(Ti II) sin (b), continues to increase out to the mostdistant star observed, at z = 8.7: kpc. Along this line of sight, the TiII absorption is the strongest yet detected and also has the highestgas-phase abundance of titanium seen in interstellar gas. Ti IIabsorption observed toward halo stars may arise from a new component ofthe halo interstellar medium which contains low column density neutralgas over a wide velocity range and which may extend beyond several H Iscale heights from the plane. The scale height of this component has yetto be determined, but could be well beyond several kpc, coincident withor even farther than the highly ionized gas observed in C IV and Si IV.Observations toward a large sample of extragalactic sources are neededto determine the actual scale height of neutral halo gas.
| Secondary photometric standard stars for the Thuan-Gunn and Johnson-Kron-Cousins systems
CCD photometry is presented for 119 stars observed in the Thuan-Gunnphotometric system (the passbands vgr). The sample includes 82 stars forwhich magnitudes in this system have not previously been published.Photometry in the Johnson-Kron-Cousins photometric system (BV or UBV)has been obtained for a subsample of 85 of the stars. Of those starswhich are not primary standard stars for the Thuan-Gunn system 70observed in Gunn r, 48 observed in Gunn g, and 37 observed in Gunn vhave sufficient repeat measurements that they may be used as secondarystandard stars for CCD photometry. The typical uncertainties for themagnitudes of these stars are 0.006 mag.
| A high-resolution optical and radio study of Milky Way halo gas
Optical interstellar absorption lines of Ti II and Ca II and the 21 cmemission line of H I were observed at high-resolution (6 and 1 km/s,respectively) and high detection sensitivity along 25 lines of sight inthe Galactic halo. The sample includes 16 distant halo stars matchedwith one or more nearly aligned foreground stars as well as local starsalong five extragalactic sight lines. The data show substantialinterstellar material, at both low and intermediate velocities, between250 and 1000 pc beyond the Galactic plane. As much as one-third of thetotal gas observed in Ca II absorption may be beyond 1 kpc, and thegaseous Ti II may lie in an even thicker layer. The directly determinedgaseous Ti abundance above the Galactic plane exceeds that in the disk,on the average, by a factor of 4 to 6 and, for individual cloudcomponents, is further enhanced at higher LSR velocity. Thirty threediscrete high-latitude clouds are detected in Ca II absorption, and 17discrete clouds, including three high-velocity clouds, are identified inH I emission. The kinematics of the high-latitude gas observed in Ti IIand Ca II absorption is characterized by significant peculiar velocitieswith respect to a model corotating halo.
| CCD surface photometry for E and S0 galaxies in the Coma cluster
The paper presents CCD surface photometry in Johnson B and Gunn r for 33galaxies in the Coma cluster and for 13 galaxies in the field or inother clusters, obtained with the Danish 1.54-m telescope at the ESO, LaSilla, Chile in the period April 3-10, 1989. The data were calibratedwith standard stars. Data for all galaxies include derivations ofeffective radius, mean surface brightness, and total magnitude. Goodagreement was found between the photometry and the global parameterspresented with data of Dressler, Faber, Burstein and theircollaborators, indicating that the quality of the CCD data is fullyadequate for studies of the large-scale motions in the universe.
| Analysis of high-latitude blue stars. VI
Reticon spectroscoy at 50 and 100 A/mm and Stromgren uvby photometry areused to determine Teff, log g and V sin i for a sample of stars from theLuminous Stars in the Northern Milky Way catalogue and several 'faintblue star' catalogues. Four hot subdwarfs (and one probable hotsubdwarf) are discovered, two of them helium-rich. Four other stars,apparently of Population I, are found to be helium-rich and three stars,including two of the helium-rich stars, appear to have distances fromthe galactic plane greater than 4 kpc.
| Selection of standard stars for photometric observations with the 91-cm reflector at Okayama
Not Available
| Runaway stars from young star clusters containing initial binaries. II - A mass spectrum and a binary energy spectrum
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990AJ.....99..608L&db_key=AST
| The spectral energy distribution of early-type stars. II - The extinction law towards O-type stars
Photometric measurements through different pass-bands are used todetermine the color-excess E(B-V) for O-type stars in the UV and IRspectral regions. The results are used to examine the extinctioncharacter of the stars. It is found that, in the UV, each O-type starhas its own extinction character. In general, the visual and NIRextinction in the direction of O-type stars are normal.
| Empirical temperature calibrations for early-type stars
Three temperature calibrations of suitable photometric quantities havebeen derived for O and B stars. A sample of 120 stars with reliableT(eff.) determinations has been used for establishing each calibration.The different calibrations have been critically discussed and compared.Temperature determinations for 1009 program stars have been obtainedwith an accuracy of the order of 10 percent.
| First detection of the astrometric orbit of the single-lined spectroscopic binary epsilon Librae
The Multichannel Astrometric Photometer of the University ofPittsburgh's Allegheny Observatory was used to successfully measure forthe first time the astrometric orbit of the single-lined spectroscopicbinary epsilon Lib. Solution of the orbit indicates that the secondarycomponent is a 0.5-solar-mass star, assuming that the F5 IV primary is1.3 solar mass. If the secondary is on the main sequence, then it islater than a K5 star, but earlier than an M2 star. In addition todetection of the astrometric orbit of epsilon Lib, two references starsused in the observations, AO 754 and AO 755, are found to be acommon-proper-motion pair.
| The spectral energy distribution of early type stars. I - A catalogue of photometric data of 259 stars from 0.15 to 4.8 microns
For the derivation of physical parameters (e.g., effective temperatureand radius) of early-type stars from their intrinsic spectral-energydistribution, and for the study of foreground interstellar and/orcircumstellar matter, a sample of 237 O, B, and A stars was chosen fromthe ANS catalog (Wesselius et al., 1982). The ANS ultraviolet and theJohnson UBV data (mostly from Nicolet's catalog, 1978) of these starswere supplemented with visual Walraven WULBV, red VRI, and near-infraredJHKLM measurements. All these data are given in the present catalog.Data for 22 stars of spectral type later than A are also included.
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Yilanci |
| Sað Açýklýk: | 16h34m28.28s |
| Yükselim: | -06°08'10.3" |
| Görünürdeki Parlaklýk: | 7.766 |
| Uzaklýk: | 6250 parsek |
| özdevim Sað Açýklýk: | -6.7 |
| özdevim Yükselim: | -15 |
| B-T magnitude: | 7.749 |
| V-T magnitude: | 7.765 |
Kataloglar ve belirtme:
|
INHABITED SKY
