目录
图像
上传图像
DSS Images Other Images
相关文章
The central kinematics of NGC 1399 measured with 14 pc resolution
We present near-infrared (NIR) adaptive optics-assisted spectroscopicobservations of the CO(Δμ= 2) absorption bands towards thecentre of the giant elliptical galaxy NGC 1399. The observations weremade with NAOS-CONICA (on the European Southern Observatory's Very LargeTelescope) and have a full width at half-maximum resolution of0.15arcsec (14pc). Kinematic analysis of the observations reveals adecoupled core and strongly non-Gaussian line-of-sight velocity profilesin the central 0.2arcsec (19pc). NIR imaging also indicates anasymmetric elongation of the central isophotes in the same region.We use spherical orbit-superposition models to interpret the kinematics,using a set of orthogonal `eigen-velocity profiles' that allow us to fitmodels directly to spectra. The models require a central black hole ofmass 1.2+0.5-0.6× 109Msolar, with a strongly tangentially biased orbitdistribution in the inner 40pc.
| B Star Rotational Velocities in h and χ Persei: A Probe of Initial Conditions during the Star Formation Epoch?
Projected rotational velocities (vsini) have been measured for 216 B0-B9stars in the rich, dense h and χ Persei double cluster and comparedwith the distribution of rotational velocities for a sample of fieldstars having comparable ages (t~12-15 Myr) and masses (M~4-15Msolar). For stars that are relatively little evolved fromtheir initial locations on the zero-age main sequence (ZAMS) (those withmasses M~4-5 Msolar), the mean vsini measured for the h andχ Per sample is slightly more than 2 times larger than the meandetermined for field stars of comparable mass, and the cluster and fieldvsini distributions differ with a high degree of significance. Forsomewhat more evolved stars with masses in the range 5-9Msolar, the mean vsini in h and χ Per is 1.5 times thatof the field; the vsini distributions differ as well, but with a lowerdegree of statistical significance. For stars that have evolvedsignificantly from the ZAMS and are approaching the hydrogen exhaustionphase (those with masses in the range 9-15 Msolar), thecluster and field star means and distributions are only slightlydifferent. We argue that both the higher rotation rates and the patternof rotation speeds as a function of mass that differentiatemain-sequence B stars in h and χ Per from their field analogs werelikely imprinted during the star formation process rather than a resultof angular momentum evolution over the 12-15 Myr cluster lifetime. Wespeculate that these differences may reflect the effects of the higheraccretion rates that theory suggests are characteristic of regions thatgive birth to dense clusters, namely, (1) higher initial rotationspeeds; (2) higher initial radii along the stellar birth line, resultingin greater spin-up between the birth line and the ZAMS; and (3) a morepronounced maximum in the birth line radius-mass relationship thatresults in differentially greater spin-up for stars that become mid- tolate-B stars on the ZAMS.
| An empirical temperature calibration for the Δ a photometric system . I. The B-type stars
We establish an empirical effective temperature calibration of mainsequence, luminosity class V to III B-type stars for the Δ aphotometric system which was originally developed to detect magneticchemically peculiar objects of the upper main sequence (early B-type toearly F-type) at 5200 Å. However, this system provides the index(g_1-y) which shows an excellent correlation with (B-V) as well as (b-y)and can be used as an indicator of the effective temperature. This issupplemented by a very accurate color-magnitude diagram, y or V versus(g_1-y), which can be used, for example, to determine the reddening,distance and age of an open cluster. This makes the Δ aphotometric system an excellent tool to investigate theHertzsprung-Russell-Diagram (HRD) in more detail. Using thereddening-free parameters and already established calibrations withinthe Strömgren uvbyβ, Geneva 7-color and Johnson UBV systems, apolynomial fit of third degree for the averaged effective temperaturesto the individual (g_1-y)0 values was derived. For thispurpose, data from the literature as well as new observations were takenresulting in 225 suitable bright normal B-type objects. The statisticalmean of the error for this sample is 238 K which is sufficient toinvestigate the HRD of distant galactic open clusters as well asextragalactic aggregates in the future.
| NaI and CaII absorption components observed towards the Orion-Eridanus Superbubble
We present medium-resolution spectra (R ~ 7.5 km s-1) of theinterstellar NaI and CaII interstellar absorption lines observed towards16 early-type stars with distances of 160-1 kpc in the line-of-sighttowards the Orion-Eridanus Superbubble (OE-S). These data have beensupplemented with measurements of NaI absorption towards a further 13stars with similar sight-lines taken from the literature. We detect twomajor absorption components with velocities of Vlsr ~ +7.0and -8.0 km s-1. The former component, seen in 70% of thesight-lines is associated with the boundary to the Local Bubble cavitylocated at a distance of 140-150 pc. The other absorption component isonly detected towards a limited region of the sky bounded by (190°< l < 215°) and (-50° < b < -30°). If gas withthis velocity is associated with an outer expansion shell of the OE-S,then we can place its distance at 163-180 pc in agreement with theestimate by Guo et al. (1995, ApJ, 453, 256). Several other negativevelocity components at Vlsr ~ -20.4, -28.5 and -33.5 kms-1 have also been detected for sight-line distances > 220pc within an area coincident with that of the 0.75 keV X-ray enhancementof the OE-S. Column density ratios, N(NaI)/N(CaII), for the mostnegative velocity components have values < 1.0, suggesting that thisgas has been disrupted by a possible shock event. Our data do notsupport a simple model for the OE-S that involves a single stellarbubble cavity that stretches from the Orion Nebula to high galacticlatitudes. Instead, our detection of multiple positive and negativevelocity components suggests the presence of several gas shells producedby supernovae and/or stellar wind-driven shocks. We also confirm thatthe prominent "hook-like" feature of H-α emission thatcharacterizes the OE-S, in in fact composed of two physically separateemission arcs, with the brighter Arc A being at a distance > 500 pc.Finally, we place a similar distance limit for any coherently structuredrear shell of neutral gas associated with expansion of the OE-S towardsthe galactic halo.
| Surface abundances of light elements for a large sample of early B-type stars - III. An analysis of helium lines in spectra of 102 stars
Non-local thermodynamic equilibrium analysis of He I lines in spectraof 102 B stars is implemented in order to derive the helium abundanceHe/H, the microturbulent parameter Vt and the projectedrotation velocity v sini. A simultaneous determination of He/H andVt for the stars is effected by analysing equivalent widthsof the 4471- and 4922-Å lines primarily as indicators of He/H andthe 4713-, 5016-, 5876- and 6678-Å lines primarily as indicatorsof Vt. The rotation velocities v sini are found from profilesof the same lines. It is shown that, when Vt > 7 kms-1, the Vt(He I) values determined from He Ilines are systematically overestimated as compared with theVt(OII, NII) values derived from OII and NII lines. Thisdiscrepancy is especially appreciable for hot evolved B giants withVt(He I) = 16-23 km s-1 and may indicate a failureof classical model atmospheres to represent the strong He I lines forthese stars.Two programme stars, HR 1512 and 7651, are found to be helium-weakstars. The remaining 100 stars are divided into three groups accordingto their masses M. The microturbulent parameter Vt(He I) islow for all stars of group A (M= 4.1-6.9 Msolar) and for allstars with the relative ages t/tMS < 0.8 of group B (M=7.0-11.2 Msolar). Their Vt(He I) values are withinthe 0 to 5 km s-1 range, as a rule; the mean value isVt= 1.7 km s-1. Only evolved giants of group B,which are close to the termination of the main-sequence (MS)evolutionary phase (t/tMS > 0.8), show Vt(He I)up to 11 km s-1. The helium abundance He/H is correlated withthe relative age t/tMS in both groups; the averaged He/Henhancement during the MS phase is 26 per cent. For group C, containingthe most massive stars (M= 12.4-18.8 Msolar), theVt(He I) values display a correlation with t/tMS,varying from 4 to 23 km s-1. The He/H determination for hotevolved B giants of the group with Vt(He I) > 15 kms-1 depends on a choice between the Vt(He I) andVt(OII, NII) scales. The mean He/H enrichment by 67 per centduring the MS phase is found, if the abundances He/H are based on theVt(OII, NII) scale; however, two evolved giants withespecially high v sini, HR 7446 and 7993, show the He/H enhancement byabout a factor of 2.5. When using the same Vt scale, we founda trend of He/H with projected rotational velocities v sini a largedispersion for v sini > 150 km s-1 can result fromdifferences in masses M.A comparison with the stellar model computations with rotationallyinduced mixing shows that the observed helium enrichment during the MSphase can be explained by rotation with initial velocities 250-400 kms-1. The He/H distribution on M and v sini based on theVt(OII, NII) scale seems to be in better agreement with thetheory than one based on the Vt(He I) scale. The mean valueHe/H = 0.10 derived for stars in the zero age main sequence (ZAMS)vicinity can be adopted as the typical initial helium abundance forearly B stars in the solar neighbourhood.
| Surface abundances of light elements for a large sample of early B-type stars - II. Basic parameters of 107 stars
Effective temperatures Teff, surface gravities logg andinterstellar extinctions AV are found for 107 B stars.Distances d of the stars, which are based on the derivedTeff, logg and AV values, show good agreement withthose obtained from the Hipparcos parallaxes. Comparing theTeff and logg values with evolutionary computations, we infermasses, radii, luminosities, ages and relative ages of the stars.Empirical relations between the Teff and logg parameters, onthe one hand, and the photometric indices Q, [c1] and β,on the other hand, are constructed; these relations give a fast methodfor the Teff and logg estimation of early and medium B stars.Inclusion of the infrared J, H and K colours into the Teff,logg and AV determination shows that (i) the Teffand logg parameters are altered only slightly; (ii) the AVvalue is rather sensitive to these colours, so an accuracy better than0.05mag in the JHK data is necessary for precise AVevaluation.
| Rotational Velocities of B Stars
We measured the projected rotational velocities of 1092 northern B starslisted in the Bright Star Catalogue (BSC) and calibrated them againstthe 1975 Slettebak et al. system. We found that the published values ofB dwarfs in the BSC average 27% higher than those standards. Only 0.3%of the stars have rotational velocities in excess of two-thirds of thebreakup velocities, and the mean velocity is only 25% of breakup,implying that impending breakup is not a significant factor in reducingrotational velocities. For the B8-B9.5 III-V stars the bimodaldistribution in V can be explained by a set of slowly rotating Ap starsand a set of rapidly rotating normal stars. For the B0-B5 III-V starsthat include very few peculiar stars, the distributions in V are notbimodal. Are the low rotational velocities of B stars due to theoccurrence of frequent low-mass companions, planets, or disks? Therotational velocities of giants originating from late B dwarfs areconsistent with their conservation of angular momentum in shells.However, we are puzzled by why the giants that originate from the earlyB dwarfs, despite having 3 times greater radii, have nearly the samerotational velocities. We find that all B-type primaries in binarieswith periods less than 2.4 days have synchronized rotational and orbitalmotions; those with periods between 2.4 and 5.0 days are rotating withina factor 2 of synchronization or are ``nearly synchronized.'' Thecorresponding period ranges for A-type stars are 4.9 and 10.5 days, ortwice as large. We found that the rotational velocities of the primariesare synchronized earlier than their orbits are circularized. The maximumorbital period for circularized B binaries is 1.5 days and for Abinaries is 2.5 days. For stars of various ages from 107.5 to1010.2 yr the maximum circularized periods are a smoothexponential function of age.
| Surface abundances of light elements for a large sample of early B-type stars - I. Spectral observations of 123 stars; measurements of hydrogen and helium lines; infrared photometry
High-resolution spectral observations of 123 B0-B5 stars in the mainsequence evolutionary phase were obtained at two observatories, namelythe McDonald Observatory (McDO) and the Crimean AstrophysicalObservatory (CrAO). Accurate equivalent widths W of two Balmer lines,Hβ and Hγ, and ten Hei lines were obtained for all the stars,as well as of the Heiiλ4686 line for the hottest ones. A carefulanalysis of the measured equivalent widths was performed. It is shownthat there is a very good agreement between the W values derived fromthe McDO and CrAO spectra for 14 common stars. A comparison withpublished data leads to the conclusion that the W values measuredearlier by some authors for strong Hei lines are very likely to beunderestimated. Infrared photometric observations in the J, H, and Kbands were performed for 70 programme stars. All these data will be usedin other papers: in particular for the Teff and loggdetermination and for the He, C, N and O abundance analyses.
| 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
| 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
| A Holistic View of the Magnetic Field in the Eridanus/Orion Region
We present observations of 21 cm emission-line Zeeman splitting at 217positions in the Orion/Eridanus loop region and incorporate them withstellar polarization data in a partially successful attempt to develop aholistic interpretation of the magnetic field structure on small andlarge size scales. We develop the "paraboloidal model" to describe theidealized perturbation to ambient magnetic field lines expected for aworm/chimney structure. We compare the magnetic field data to this modeland find fair agreement for part of the region. On the small scale ofone of the molecular clouds, previous interpretations invoke a helicalfield; in contrast, our interpretation invokes the Eridanus shock andits interaction with dense molecular clouds, in which the observedreversal in the line-of-sight field occurs naturally.
| The ROSAT all-sky survey catalogue of optically bright OB-type stars.
For the detailed statistical analysis of the X-ray emission of hot starswe selected all stars of spectral type O and B listed in the Yale BrightStar Catalogue and searched for them in the ROSAT All-Sky Survey. Inthis paper we describe the selection and preparation of the data andpresent a compilation of the derived X-ray data for a complete sample ofbright OB stars.
| 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.
| The distribution of interstellar dust in the solar neighborhood
We surveyed the IRAS data base at the positions of the 1808 O6-B9.5stars in The Bright Star Catalog for extended objects with excessemission at 60 microns, indicating the presence of interstellar dust atthe location of the star. Within 400 pc the filling factor of theinterstellar medium, for dust clouds with a density greater than 0.5/cucm is 14.6 + or - 2.4%. Above a density of 1.0/cu cm, the densitydistribution function appears to follow a power law index - 1.25. Whenthe dust clouds are mapped onto the galactic plane, the sun appears tobe located in a low-density region of the interstellar medium of widthabout 60 pc extending at least 500 pc in the direction of longitudes 80deg - 260 deg, a feature we call the 'local trough'.
| A multiwavelength study of the Eridanus soft X-ray enhancement
We present soft X-ray, N(H), and IR maps of the Eridanus soft X-rayenhancement. Soft X-ray maps from the HEAO 1 A-2 LED experiment,processed with a maximum entropy method (MEM) algorithm, show that theenhancement consists of two distinct components: a large hook-shapedcomponent and a small circular component at different temperatures. Bothof these are located in 'holes' in the IR emission, and they correspondto N(H) features at very different velocities. The dust surrounding theX-ray enhancements appears to be associated with several high-latitudemolecular clouds, which allow us to obtain a probable distance of about130 pc to the near edge of the main enhancement. The total power emittedby the hot gas is then about 10 exp 35 to 10 exp 36 ergs/s. We consideralternative interpretations of these objects as adiabatic supernovaremnants or as stellar wind bubbles and conclude that they are morelikely to be stellar wind bubbles, possibly reheated by a SN explosionin the case of the main, hook-shaped object.
| Optical studies of interstellar material in low density regions of the Galaxy. I - A survey of interstellar NA I and CA II absorption toward 57 distant stars
We present high-resolution spectra of the Na I D and Ca II K linestoward 57 late-O and early-B stars along extended (d greater than 1 kpc)low-density paths through the Milky Way disk and halo. The sight linespreferentially sample diffuse gas in the interstellar medium (ISM) alonginterarm, Galactic center, and high latitude directions. We measureequivalent widths, apparent column densities, and absorption componentstructure. The Ca II to Na I ratios presented as a function of velocityfor each sight line exhibit variations due to elemental depletion,ionization, and density enhancements. Absorption along high latitudesight lines is kinematically simpler than it is along interarm andGalactic center sight lines. Galactic rotation noticeably broadens theabsorption profiles of distant stars located in these latter directions.Along several sight lines, we see Ca II absorption at velocitiescorresponding to large distances (/z/ about 1 kpc) from the Galacticplane. The effects of differences in the Ca II and Na I scale heightsand nonzero velocity dispersions are readily apparent in the data. Briefnotes are given for several sight lines with interesting absorptionproperties.
| Secondary UVBY standards in the Harvard E-regions
Photoelectric uvby photometry for 201 stars which are already UBV (RI)cstandards is presented. The photoelectric data are closely tied to theCousins uvby standards and the stars should be suitable for use asfainter (7-11 mag) secondary standards.
| Broad-band photometry of selected southern ultraviolet-bright stars.
Not Available
| Secondary standards for H-beta photometry in the E regions.
Not Available
| Secondary standards for the Stromgren UVBY system
Observations of 158 E region stars have been made in the Stromgrensystem, using the 46-cm reflector at Cape Town. They are mostly brighterthan eighth magnitude and are intended for use as secondary standardsfor the four-color system. The E region relative zero points are definedwith a precision of + or - 0.001 mag, and the internal standard errorsof the colors life between + or - 0.001 and + or - 0.002 mag.
| Catalog of O-B stars observed with Tokyo Meridian Circle
A catalog of the O-B stars, selected from 'Blaauw-Parenago' list andRubin's catalog, has been compiled on the FK4 system by the observationsmade with Gautier 8-inch Meridian Circle at the Tokyo AstronomicalObservatory during the period, 1971 to 1979. It contains 1059 stars andwas compiled for the future establishment of high precision propermotions of O-B stars.
| Interstellar polarization from observations of A and F stars in high and intermediate galactic latitudes, and from stars in the Mathewson and Ford polarization catalogue
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1986A&AS...64..487K&db_key=AST
| A catalog of ultraviolet interstellar extinction excesses for 1415 stars
Ultraviolet interstellar extinction excesses are presented for 1415stars with spectral types B7 and earlier. The excesses with respect to Vare derived from Astronomical Netherlands Satellite (ANS) 5-channel UVphotometry at central wavelengths of approximately 1550, 1800, 2500, and3300 A. A measure of the excess extinction in the 2200-A extinction bumpis also given. The data are valuable for investigating the systematicsof peculiar interstellar extinction and for studying the character of UVinterstellar extinction in the general direction of stars for which theextinction-curve shape is unknown.
| The local system of early type stars - Spatial extent and kinematics
Published uvby and H-beta photometric data and proper motions arecompiled and analyzed to characterize the structure and kinematics ofthe bright early-type O-A0 stars in the solar vicinity, with a focus onthe Gould belt. The selection and calibration techniques are explained,and the data are presented in extensive tables and graphs and discussedin detail. The Gould belt stars of age less than 20 Myr are shown togive belt inclination 19 deg to the Galactic plane and node-lineorientation in the direction of Galactic rotation, while the symmetricaldistribution about the Galactic plane and kinematic properties (purecircular differential rotation) of the belt stars over 60 Myr oldresemble those of fainter nonbelt stars of all ages. The unresolveddiscrepancy between the expansion observed in the youngest nearby starsand the predictions of simple models of expansion from a point isattributed to the inhomogeneous distribution of interstellar matter.
| The galactic reddening law - The evidence from uvby-beta photometry of B stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1985A&A...142..189T&db_key=AST
| Be stars in binaries
The known companions to 80 Be stars and 355 B stars listed in the BrightStar Catalogue in the range B1-B7 III-V and north of delta = -30 deg areconsidered. The known near-absence of Be binaries with periods less than1/10 yr is confirmed. For longer periods up to the limit of 10,000 AU ofthis survey, the Be and B stars do not differ in binary frequencies.This result implies that during pre-main-sequence contraction, the tidalbraking in binaries wider than 0.5 AU was inadequate to prevent theformation of stars with nearly the break-up rotational velocities. Thefraction of Be and B stars that have companions is higher in clustersand associations (38 percent) than among field stars (25 percent),confirming that escapees from clusters tend to be single stars. There issome evidence that the companions of Be stars that occur in the sameluminosity range tend also to be Be stars; that result was expectedbecause in visual binaries there is a known tendency for rapidlyrotating primaries to have rapidly rotating secondaries.
| Four-colour photometry of B stars north of B = + 45 deg and comparison with the south
Four-color photometry of 33 Henry Draper B stars north of b = + 45 degis presented. Most are little-reddened B or intermediate-A stars. A newAm star is discovered. The new measures essentially complete uvbyphotometry of all HD B stars within 45 deg of either galactic pole. Thenorthern and southern cones of HD B stars are compared, and selectioneffects deduced. Far from the galactic plane, it appears that B starsmay be equally distributed north and south of the plane; closer to thesun, an asymmetry associated with Gould's Belt is evident.
| Optical observations of ultraviolet objects. I - Spectral classification of 103 stars /l = 200-275 deg/
Results are presented of a program of spectral classification of 103stars originally selected as ultraviolet objects from TD-1 satellitephotometry with the S2/68 experiment. Most of the objects appear to bespectroscopically normal stars; the method of selection yielded a sampleof relatively unreddened B stars at distances up to about 2 kpc. Thisresult is compared with recent studies of the spatial distribution ofinterstellar extinction in the same regions of the sky.
| Geneva photometric boxes. II - The reddening towards the galactic poles
It is noted that photometric boxes allow a very accurate estimation ofindividual reddenings for B- and early A-type stars. A catalog of 129stars with galactic latitudes higher than 30 deg is given. A small butsignificant reddening is seen in the direction of both the northern andsouthern galactic poles: E(B-V) approximately 0.04.
| Photometric search for AP stars among blue stragglers in open clusters
A photometric study of 27 blue stragglers in 9 open clusters ispresented. Besides uvby data fluxes in Maitzen's (1976) g1and g2 passbands where g2 is centered in the 5200A flux depression of Ap stars are obtained. The investigated clustersare older than 10 to the eighth years. Their blue stragglers show(b-y)zero values in the spectral range between B 3 and F 0,the typical region of peculiar A-type stars. The percentage of starswith 5200 A peculiarity among the blue stragglers turned out to be 8.3%.Another 15% of the investigated stars show mild photometric peculiarity.The value of definite peculiar stars agrees with the percentage of Apstars of the same spectral class range in open clusters of similar age(greater than 10 to the eighth years) and in the Galactic field.
|
提交文章
相关链接
提交链接
下列团体成员
|
观测天体数据
目录:
|
INHABITED SKY
