Оглавление
Изображения
Загрузить ваше изображение
DSS Images Other Images
Публикации по объекту
CCD photometric search for peculiar stars in open clusters. VII. Berkeley 11, Berkeley 94, Haffner 15, Lyngå 1, NGC 6031, NGC 6405, NGC 6834 and Ruprecht 130
Aims.The detection of magnetic chemically peculiar (CP2) stars in openclusters of the Milky Way can be used to study the influence ofdifferent galactic environments on the (non-)presence of peculiarities,which has to be taken into account in stellar evolution models.Furthermore it is still unknown if the CP2 phenomenon evolves, i.e. doesthe strength of the peculiarity feature at 5200 Å increase ordecrease with age. Methods: .We have observed eight young tointermediate age open clusters in the Δ a photometric system. Thisintermediate band photometric system samples the depth of the 5200Å flux depression by comparing the flux at the center with theadjacent regions having bandwidths of 110 Å to 230 Å. TheΔ a photometric system is most suitable to detect CP2 stars withhigh efficiency, but is also capable of detecting a small percentage ofnon-magnetic CP objects. Also, the groups of (metal-weak) λBootis, as well as classical Be/shell stars, can be successfullyinvestigated. This photometric system allows one to determine the age,reddening and distance modulus by fitting isochrones. Results:.Among the presented sample of eight galactic clusters, we have detectedtwenty three CP2, eight Be/Ae and eight metal-weak stars. Another sixobjects show a peculiar behaviour which is most probably due to anon-membership, variability or duplicity. Fitting isochrones to Δa photometry yields estimates of the age, reddening and distance thatare in excellent agreement with published values.
| Searching for links between magnetic fields and stellar evolution. I. A survey of magnetic fields in open cluster A- and B-type stars with FORS1
Context: .About 5% of upper main sequence stars are permeated by astrong magnetic field, the origin of which is still matter of debate. Aims: . With this work we provide observational material to studyhow magnetic fields change with the evolution of stars on the mainsequence, and to constrain theory explaining the presence of magneticfields in A and B-type stars. Methods: . Using FORS1 inspectropolarimetric mode at the ESO VLT, we have carried out a survey ofmagnetic fields in early-type stars belonging to open clusters andassociations of various ages. Results: . We have measured themagnetic field of 235 early-type stars with a typical uncertainty of 100 G. In our sample, 97 stars are Ap or Bp stars. For thesetargets, the median error bar of our field measurements was 80 G.A field has been detected in about 41 of these stars, 37 of which werenot previously known as magnetic stars. For the 138 normal A and B-typestars, the median error bar was 136 G, and no field was detected in anyof them.
| Physical parameters of the Algol system VW Hydrae from simultaneous analysis of GENEVA seven-colour light curves
The semi-detached eclipsing binary system VW Hydrae (P = 2.70 days) hasbeen analysed using the Wilson Devinney program, on the basis of lightcurves obtained in the GENEVA seven-colour photometric system, andradial velocity curves for both components measured with thecross-correlation technique. The physical and orbital parameters havebeen determined through a self-consistent simultaneous solution of lightcurves in seven colours and of the radial velocity curves of bothcomponents. The effective temperature of the primary component isdetermined from the photometric analysis,T=10,650±200K. It is shown that this value can be verywell determined, despite the fact the primary eclipse is partial, by theuse of colour indexes, as e.g. [B2 ‑V1]0. The absolute elements of the components arefor the primary (mass gainer), with the value of T fixed,M1 = 3.10 ± 0.07Mȯ, R1 =2.60 ± 0.01Rȯ, M=0.05±0.01, andfor the secondary (mass loser), M2 = 0.76 ±0.02Mȯ, R2 = 3.38 ±0.01Rȯ,M=2.90±0.01,T=4848±6K. Thesemi-major axis A of the relative orbit is 12.771 ±0.090Rȯ. The estimated spectral types of the componentsare about B8/9 V (primary) and F9 III. The equatorial rotationalvelocity of the primary (54 km s‑1) shows that thesystem is synchronised. The distance to VW Hya is evaluated to 1122± 42 pc, and the colour excess E[B2 ‑V1] to 0.046 ± 0.022.
| The Reddening of Red Supergiants: When Smoke Gets in Your Eyes
Deriving the physical properties of red supergiants (RSGs) depends onaccurate corrections for reddening by dust. We use our recent modelingof the optical spectra of RSGs to address this topic. First, we findthat previous broadband studies have underestimated the correction forextinction in the visible, and hence the luminosities (if derived fromV); the shift in the effective wavelengths of the standard B and Vbandpasses necessitates using an effective value of the ratioR'V=4.2 to correct broadband photometry of RSGs ifRV=3.1 for early-type stars viewed through the same dust,where we have assumed the standard reddening law of Cardelli andcoauthors. Use of the Fitzpatrick reddening law would lead toR'V=3.8, as well as slightly lower values ofextinction derived from spectrophotometry, but results in slightlypoorer fits. Second, we find that a significant fraction of RSGs inGalactic OB associations and clusters show up to several magnitudes ofexcess visual extinction compared to OB stars in the same regions; weargue that this is likely due to circumstellar dust around the RSGs. Wealso show that the RSG dust production rate (as indicated by the 12μm excess) is well correlated with bolometric luminosity, contrary towhat has been found by earlier studies. The stars with the highestamount of extra visual extinction also show significant near-UV (NUV)excesses compared to the stellar models reddened by the standardreddening law. This NUV excess is likely due to scattering of the star'slight by the dust and/or a larger average grain size than that typicalof grains found in the diffuse interstellar medium. Similar excesseshave been attributed to circumstellar dust around R Coronae Borealisstars. Finally, we estimate that the RSGs contribute dust grains at therate of 3×10-8Msolar yr-1kpc-2 in the solar neighborhood, comparable to what weestimate for late-type WCs, 1×10-7Msolaryr-1 kpc-2. In the solar neighborhood thisrepresents only a few percent of the dust production (which is dominatedby low-mass AGBs), but we note that in low-metallicity starbursts, dustproduction by RSGs would likely dominate over other sources.
| The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not As Cool As We Thought
We use moderate-resolution optical spectrophotometry and the new MARCSstellar atmosphere models to determine the effective temperatures of 74Galactic red supergiants (RSGs). The stars are mostly members of OBassociations or clusters with known distances, allowing a criticalcomparison with modern stellar evolutionary tracks. We find we canachieve excellent matches between the observations and the reddenedmodel fluxes and molecular transitions, although the atomic lines Ca Iλ4226 and Ca II H and K are found to be unrealistically strong inthe models. Our new effective temperature scale is significantly warmerthan those in the literature, with the differences amounting to 400 Kfor the latest type M supergiants (i.e., M5 I). We show that the newlyderived temperatures and bolometric corrections give much betteragreement with stellar evolutionary tracks. This agreement provides acompletely independent verification of our new temperature scale. Thecombination of effective temperature and bolometric luminosities allowsus to calculate stellar radii; the coolest and most luminous stars (KWSgr, Case 75, KY Cyg, HD 206936=μ Cep) have radii of roughly 1500Rsolar (7 AU), in excellent accordance with the largeststellar radii predicted from current evolutionary theory, althoughsmaller than that found by others for the binary VV Cep and for thepeculiar star VY CMa. We find that similar results are obtained for theeffective temperatures and bolometric luminosities using only thedereddened V-K colors, providing a powerful demonstration of theself-consistency of the MARCS models.
| High-Energy Emission from Millisecond Pulsars
The X-ray and γ-ray spectrum of rotation-powered millisecondpulsars is investigated in a model for acceleration and pair cascades onopen field lines above the polar caps. Although these pulsars have lowsurface magnetic fields, their short periods allow them to have largemagnetospheric potential drops, but the majority do not producesufficient pairs to completely screen the accelerating electric field.In these sources, the primary and secondary electrons continue toaccelerate to high altitude, and their Lorentz factors are limited bycurvature and synchrotron radiation reaction. The accelerating particlesmaintain high Lorentz factors and undergo cyclotron resonant absorptionof radio emission that produces and maintains a large pitch angle,resulting in a strong synchrotron component. The resulting spectraconsist of several distinct components: curvature radiation from primaryelectrons dominating from 1 to 100 GeV, synchrotron radiation fromprimary and secondary electrons dominating up to about 100 MeV, and muchweaker inverse Compton radiation from primary electrons at 0.1-1 TeV. Wefind that the relative size of these components depends on pulsarperiod, period derivative, and neutron star mass and radius, with thelevel of the synchrotron component also depending sensitively on theradio emission properties. This model is successful in describing theobserved X-ray and γ-ray spectrum of PSR J0218+4232 as synchrotronradiation, peaking around 100 MeV and extending up to a turnover aroundseveral GeV. The predicted curvature radiation components from a numberof millisecond pulsars, as well as the collective emission from themillisecond pulsars in globular clusters, should be detectable withAGILE and GLAST. We also discuss a hidden population of X-ray-quiet andradio-quiet millisecond pulsars that have evolved below the pair deathline, some of which may be detectable by telescopes sensitive above 1GeV.
| The Dearth of Massive, Helium-rich White Dwarfs in Young Open Star Clusters
Spectra have been obtained of 21 white dwarfs (WDs) in the direction ofthe young, rich open star cluster NGC 2099. This represents anappreciable fraction (>30%) of the cluster's total WD population. Themean derived mass of the sample is 0.8 Msolar-about 0.2Msolar larger than the mean seen among field WDs. Asurprising result is that all of the NGC 2099 WDs have hydrogen-richatmospheres (DAs); none exhibit helium-rich ones (DBs) or any otherspectral class. The number ratio in the field at the temperatures of theNGC 2099 WDs is DA/DB ~ 3.5. While the probability of seeing no DB WDsin NGC 2099 solely by chance is ~2%, if we include WDs in other openclusters of similar age it then becomes highly unlikely that the dearthof DB WDs in young open clusters is just a statistical fluctuation. Weexplore possible reasons for the lack of DBs in these clusters andconclude that the most promising scenario for the DA/DB number ratiodiscrepancy in young clusters is that hot, high-mass WDs do not developlarge enough helium convection zones to allow helium to be brought tothe surface and turn a hydrogen-rich WD into a helium-rich one.Based on observations with Gemini (run ID GN-2002B-Q-11) and Keck.Gemini is an international partnership managed by the Association ofUniversities for Research in Astronomy, Inc., under a cooperativeagreement with the National Science Foundation. The W. M. KeckObservatory, which is operated as a scientific partnership among theCalifornia Institute of Technology, the University of California, andNASA, was made possible by the generous financial support of the W. M.Keck Foundation.
| Astrophysical parameters of Galactic open clusters
We present a catalogue of astrophysical data for 520 Galactic openclusters. These are the clusters for which at least three most probablemembers (18 on average) could be identified in the ASCC-2.5, a catalogueof stars based on the Tycho-2 observations from the Hipparcos mission.We applied homogeneous methods and algorithms to determine angular sizesof cluster cores and coronae, heliocentric distances, mean propermotions, mean radial velocities, and ages. For the first time we derivedistances for 200 clusters, radial velocities for 94 clusters, and agesof 196 clusters. This homogeneous new parameter set is compared withearlier determinations, where we find, in particular, that the angularsizes were systematically underestimated in the literature.
| The last born at La Silla: REM, The Rapid Eye Mount
Cerro La Silla in June welcomed a new small telescope on its top: TheRapid Eye Mount (REM) Italian Telescope: a telescope which has beenconceived and designed to immediately point and observe the Gamma-RayBursts detected by satellites. Its immediate data gathering capabilityand its accurate astrometry in the optical and in the near-infrared willalso allow an early alert and pointing of the Very Large Telescope.
| Proper Motions of Open Star Clusters and the Rotation Rate of the Galaxy
The mean proper motions of 167 Galactic open clusters withradial-velocity measurements are computed from the data of the Tycho-2catalog using kinematic and photometric cluster membership criteria. Theresulting catalog is compared to the results of other studies. The newproper motions are used to infer the Galactic rotation rate at the solarcircle, which is found to be ω0=+24.6±0.8 km s-1 kpc-1.Analysis of the dependence of the dispersion of ω0 estimates onheliocentric velocity showed that even the proper motions of clusterswith distances r>3 kpc contain enough useful information to be usedin kinematic studies demonstrating that the determination of propermotions is quite justified even for very distant clusters.
| On the Galactic Disk Metallicity Distribution from Open Clusters. I. New Catalogs and Abundance Gradient
We have compiled two new open cluster catalogs. In the first one, thereare 119 objects with ages, distances, and metallicities available, whilein the second one, 144 objects have both absolute proper motion andradial velocity data, of which 45 clusters also have metallicity dataavailable. Taking advantage of the large number of objects included inour sample, we present an iron radial gradient of about -0.063+/-0.008dex kpc-1 from the first sample, which is quite consistentwith the most recent determination of the oxygen gradient from nebulaeand young stars, about -0.07 dex kpc-1. By dividing clustersinto age groups, we show that the iron gradient was steeper in the past,which is consistent with the recent result from Galactic planetarynebulae data, and also consistent with inside-out galactic diskformation scenarios. Based on the cluster sample, we also discuss themetallicity distribution, cluster kinematics, and space distribution. Adisk age-metallicity relation could be implied by those properties,although we cannot give conclusive result from the age- metallicitydiagram based on the current sample. More observations are needed formetal-poor clusters. From the second catalog, we have calculated thevelocity components in cylindrical coordinates with respect to theGalactic standard of rest for 144 open clusters. The velocitydispersions of the older clusters are larger than those of youngclusters, but they are all much smaller than that of the Galactic thickdisk stars.
| Urban Astronomy: Observing the Messier Objects from the City
Not Available
| TOPS Telescope Projects on Variable Stars and Other Objects
Teachers and high school students who attended the University ofHawaii's "Toward Other Planetary Systems" workshop in June 2002 gavepresentations on introductory telescope projects on lunar photography,variable stars, and Messier Objects at the AAVSO 91st Spring meeting inJuly 2002. Other participants discussed advanced projects on photometry,CCDs, and spectroscopy. Former student participants presented thediscovery of a new variable star and an on-going remote observingproject utilizing the Lowell Observatory 31-inch telescope. Thesevarious projects are described and/or summarized.
| The rise and rise of the deep sky image
Presidential Address to the British Astronomical Association, 2000October 25
| Intense accretion and mass loss of a very low mass young stellar object
We present visible and near-infrared photometry and spectroscopy ofLS-RCrA 1, a faint, very late-type object (M 6.5-M 7) seen in thedirection of the R Coronae Australis star forming complex. While itsemission spectrum shows prominent features of accretion and mass losstypical of young stellar objects, its underlying continuum andphotometric properties are puzzling when trying to derive a mass and agebased on pre-main sequence evolutionary tracks: the object appears to befar too faint for a young member of the R Coronae Australis complex ofits spectral type. We speculate that this may be due to either itsevolution along pre-main sequence tracks being substantially altered bythe intense accretion, or to a combination of partial blocking andscattering of the light of the object by a nearly edge-on circumstellardisk. The rich emission line spectrum superimposed on the stellarcontinuum is well explained by an intense accretion process: theHalpha , CaII infrared triplet, and HeI 6678 lines showequivalent widths typical of very active classical T Tauri stars. Thenear-infrared observations show anomalously weak spectral features andno significant excess emission in the K band, which we tentativelyinterpret as indicating line filling due to emission in a magneticaccretion funnel flow. At the same time, numerous, strong forbiddenoptical lines ([OI], [NII] and [SII]) and H2 emission at 2.12mu m suggest that the object is simultaneously undergoing mass loss,providing another example that shows that mass loss and accretion areclosely related processes. Such an intense accretion and mass lossactivity is observed for the first time in a young stellar object in thetransition region between low mass stars and brown dwarfs, and providesa valuable observational test on the effects of accretion on theevolution of objects with such low masses. Based on observationscollected at the European Southern Observatory in La Silla and CerroParanal (Chile), in programs 59.E-0679, 63.I-0546, 264.I-5723,64.L-0049, 65.H-0492, and 67.C-0109.
| Proper motions of open clusters within 1 kpc based on the TYCHO2 Catalogue
We present mean absolute proper motions of 112 open clusters, determinedusing the data from the Tycho2 Catalogue. For 28 clusters, this is thefirst determination of proper motion. The measurements made use of alarge number of stars (usually several tens) for each cluster. The totalnumber of stars studied in the fields of the 164 open clusters is 5016,of which 4006 were considered members. The mean proper motions of theclusters and membership probability of individual stars were obtainedfrom the proper motion data by applying the statistical method proposedby Sanders (\cite{Sanders71}). Based on observations of the ESAHipparcos satellite. Tables 1, 2 and 5 to 117 are only 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/376/441
| 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
| Variations of the Ap star HDE 318107
The rotation period of the Ap star HDE 318107 has been determined frommagnetic and photometric observations obtained between August 1992 andSeptember 1998.
| Statistical parallaxes and kinematical parameters of classical Cepheids and young star clusters
The statistical-parallax method is applied for the first time to spacevelocities of 270 classical Cepheids with proper motions adopted fromHIPPARCOS (1997) and TRC (Hog et al. 1998) catalogs and distances basedon the period-luminosity relation by Berdnikov et al. (1996). Thedistance scale of short-period Cepheids (with periods less than 9 days)is shown to require an average correction of 15-20%, whereas statisticalparallaxes of Cepheids with periods > 9 days are found to agree wellwith photometric distances. It is shown that the luminosities ofshort-period Cepheids must have been underestimated partly due to thecontamination of this subsample by a substantial (20 to 40%) fraction offirst-overtone pulsators. The statistical-parallax technique is alsoapplied for the first time to 117 open clusters younger than 100 millionyears and with proper motions reduced to the HIPPARCOS reference system.It is concluded that a 0.12-0.15 mag increase of the distance scales ofopen clusters and Cepheids would be sufficient to reconcile thestatistical-parallax results inferred for these two types of objects.Such approach leads to an LMC distance modulus of less than 18.40 mag,which agrees, within the errors, with the short distance scale for RRLyrae variables and is at variance with the conclusions by Feast andCatchpole (1998) and Feast et al. (1998), who argue that the LMCdistance modulus should be increased to 18.70 mag. The distance scalebased on the Cepheid period-luminosity relation by Berdnikov and Efremov(1985) seems to be a good compromise. Extragalactic distances, whichrely on long-period Cepheids, seem to require no substantial correction.In addition to statistical parallaxes, kinematical parameters have beeninferred for the combined sample consisting of Cepheids andopen-clusters: solar-motion components (U0 ,V0,W0) = (9, 12, 7) km/s (+/- 1 km/s); velocity-ellipsoid axes(σU; σV; σW) = (15.0,10.3, 8.5) km/s (+/- 1 km/s); the angular velocity of rotation of thesubsystem, ω0 = 28.7 +/- 1 km/s/kpc, the Oort constantA = 17.4 +/- 1.5 km/s, and the second derivative of angular velocity,⋰ω0= 1.15 +/- 0.2 km/s/kpc3.
| Search for variable stars in the open cluster NGC 7654
Time-series CCD photometry of the open cluster NGC 7654 was performedover five nights from October 2nd to 18th, 1997 U.T., in order to searchfor new variable stars. We also carried out UBV photometric observationsto obtain physical parameters of variable stars in the cluster. We havederived the distance modulus of (V-M_V)deg = 10.9 +/- 0.2 andthe interstellar reddening of E(B-V) = 0.62 +/- 0.05 by fitting the ZAMSto the observed color-color and color-magnitude diagrams of the cluster.Using the theoretical isochrones with solar metal abundance by Bertelliet al. (1994), an age of the cluster, log t = 8.0, was estimated.Applying the ensemble normalization technique to the observed 1215time-series data, light variations of 284 stars, fainter than 11\fm0 inthe observed field, were carefully examined. As a result, three slowlypulsating B stars and one eclipsing binary were discovered in thecluster. We also confirmed the light variation of a low amplitude deltaSct star which has been recently discovered by Viskum et al. (1997).
| Open clusters with Hipparcos. I. Mean astrometric parameters
New memberships, mean parallaxes and proper motions of all 9 openclusters closer than 300 pc (except the Hyades) and 9rich clusters between 300 and 500 pc have been computed using Hipparcosdata. Precisions, ranging from 0.2 to 0.5 mas for parallaxes and 0.1 to0.5 mas/yr for proper motions, are of great interest for calibratingphotometric parallaxes as well as for kinematical studies. Carefulinvestigations of possible biases have been performed and no evidence ofsignificant systematic errors on the mean cluster parallaxes has beenfound. The distances and proper motions of 32 more distant clusters,which may be used statistically, are also indicated. Based onobservations made with the ESA Hipparcos astrometry satellite
| Parameters of open star clusters from uvby-beta photometry.
Not Available
| Absolute proper motions of 181 young open clusters.
Not Available
| The origin of strong magnetic fields in circumstellar SiO masers.
We suggest that the Parker instability, acting in the regions whereshocks form in response to stellar pulsations, gives rise to thefragments in which SiO masers exist in the atmospheres of evolved stars.The production of maser fragments in this manner is compatible with theAlfven speeds in them greatly exceeding their kinematic and thermalspeeds. The magnetic structure in an evolved star's envelope probablyresults in momentum transfer to gas from grains subject to radiationpressure being widely distributed even to regions where grains have notyet formed; the consequences for mass loss of the magneticredistribution of momentum transfer require exploration.
| Observations of Clusters Using the Stromvil System. I. Standard Areas
A set of standard areas of the Stromvil system is described. Preliminaryvalues of the color indices for standard stars for photoelectric workmay be obtained from their published values in both parent (uvby andVilnius) systems. Stars in 19 open clusters already observed in bothsystems may be used as preliminary standards. Standard areas for the CCDwork are to be measured anew. For this, a set of 12 compact openclusters and globular clusters have been selected, six areas in eachhemisphere, mostly at declinations +30 deg and --30 deg. The 10--20arcmin areas will contain standard stars of 10--16 mag. They will begood for fixing the zero-point of magnitudes and color indices, for thedetermination of extinction coefficients in the Earth's atmosphere andfor the determination of color equations between instrumental CCDsystems and the standard Stromvil system. The first observations in thisprogram are planned with the new 1.8-m Vatican telescope on Mt. Graham,Arizona.
| Far-Ultraviolet Stellar Photometry: Fields Centered on rho Ophiuchi and the Galactic Center
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..104..101S&db_key=AST
| Hybrid stars and the reality of "dividing lines" among G to K bright giants and supergiants.
We present results of pointed ROSAT PSPC observations of 15 hybridstars/candidates, which have been analyzed in a homogenous way. 7 ofthese stars were observed in X-rays for the first time. 12 out of 15hybrid stars have been detected as X-ray sources, some of them close tothe detection limit. We conclude that essentially all hybrid stars asdefined by the simultaneous presence of transition region line emissionand cool stellar winds are X-ray sources if exposed sufficiently deep.The X-ray luminosities of hybrid stars cover a range between 2x10^27^and ~10^30^erg/s. Their X-ray surface fluxes can be as low as =~20erg/cm^2^/s and thus considerably lower than those of normal luminosityclass (LC) III giants. X-ray spectra of hybrid stars tend to be harderthan that of normal LC III giants, moreover, the X-ray brightest starshave the hardest spectra. We find that for K II giants the normalizedX-ray flux versus C IV flux obeys a power law with an exponent a=2.9,steeper than among normal giants (1.5). Hybrid K II stars are X-rayunderluminous by a factor of 5 to 20 compared to LC III giants at thesame level of normalized CIV flux f_CIV_/f_bol_; hybrid G supergiantsare even more X-ray deficient. We reanalyze the CaII wind dividing lineand find it vertical at B-V=1.45 for LC III giants. It is nearlyhorizontal between B-V=1.45 and 1.0 (at M_bol_=~-2...-3), and not welldefined for supergiants with B-V<1.0. We therefore suggest thatpossibly all LC II and Ib G and K giants are hybrid stars and that the"dividing line" concept in its simplest form is not valid for G/K giantsbrighter than M_bol_=~-2. Hybrid stars are supposed to be evolvedintermediate mass stars and their coronal activity may in principle bedetermined by the individual history of each star.
| New list of OB associations of our galaxy.
Not Available
| Briefly noted: Irish astronomy (poem)
Not Available
| Characteristics of spectral type distribution for stars in the solar neighborhood
We discuss the distribution of stars by MK spectral types and B-V colorindices based on published catalog data. It is shown that thedistribution of field B stars is nonmonotonic because of contaminationby stars of OB associations and Gould's belt. Statistical analysis ofstars in photometric catalogs confirms the deficit of A5-F5 dwarfs.
|
Добавить новую статью
Внешние ссылки
- - Внешних ссылок не найдено -
Добавить внешнюю ссылку
Группы:
|
Наблюдательные данные и астрометрия
Каталоги и обозначения:
|
INHABITED SKY
