내용
사진
사진 업로드
DSS Images Other Images
관련 글
Abundance analysis of Am binaries and search for tidally driven abundance anomalies - II. HD861, HD18778, HD20320, HD29479, HD96528 and HD108651
The main goal of this paper is to continue a systematic abundanceanalysis of a sample of Am binaries in order to search for possibleabundance anomalies driven by tidal interaction in these binary systems.New CCD observations in two spectral regions (6400-6500 and 6660-6760Å) of HD861, HD18778, HD20320, HD29479, HD96528 and HD108651 wereobtained. Synthetic spectrum analysis was carried out, and basic stellarproperties, effective temperatures, gravities, projected rotationalvelocities, masses, ages and abundances of several elements weredetermined. We conclude that HD861, 29479 and 108651 are typical Amstars, while HD20320 and 96528 are mild Am stars. HD18778 turned out notto be an Am star although its projected rotational velocity is very low(27 kms-1). On the contrary, HD96528 has one of the highestprojected rotational velocities (85 kms-1) among Am binarieswith orbital periods in the range 20-200 d, and yet it exhibits Amanomalies. Pseudo-synchronization and abundance anomalies are discussedin the context of possible tidal effects.
| Observed Orbital Eccentricities
For 391 spectroscopic and visual binaries with known orbital elementsand having B0-F0 IV or V primaries, we collected the derivedeccentricities. As has been found by others, those binaries with periodsof a few days have been circularized. However, those with periods up toabout 1000 or more days show reduced eccentricities that asymptoticallyapproach a mean value of 0.5 for the longest periods. For those binarieswith periods greater than 1000 days their distribution of eccentricitiesis flat from 0 to nearly 1, indicating that in the formation of binariesthere is no preferential eccentricity. The binaries with intermediateperiods (10-100 days) lack highly eccentric orbits.
| Tidal Effects in Binaries of Various Periods
We found in the published literature the rotational velocities for 162B0-B9.5, 152 A0-A5, and 86 A6-F0 stars, all of luminosity classes V orIV, that are in spectroscopic or visual binaries with known orbitalelements. The data show that stars in binaries with periods of less thanabout 4 days have synchronized rotational and orbital motions. Stars inbinaries with periods of more than about 500 days have the samerotational velocities as single stars. However, the primaries inbinaries with periods of between 4 and 500 days have substantiallysmaller rotational velocities than single stars, implying that they havelost one-third to two-thirds of their angular momentum, presumablybecause of tidal interactions. The angular momentum losses increase withdecreasing binary separations or periods and increase with increasingage or decreasing mass.
| Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897
| Ages of A-Type Vega-like Stars from uvbyβ Photometry
We have estimated the ages of a sample of A-type Vega-like stars byusing Strömgren uvbyβ photometric data and theoreticalevolutionary tracks. We find that 13% of these A stars have beenreported as Vega-like stars in the literature and that the ages of thissubset run the gamut from very young (50 Myr) to old (1 Gyr), with noobvious age difference compared to those of field A stars. We clearlyshow that the fractional IR luminosity decreases with the ages ofVega-like stars.
| Research Note Hipparcos photometry: The least variable stars
The data known as the Hipparcos Photometry obtained with the Hipparcossatellite have been investigated to find those stars which are leastvariable. Such stars are excellent candidates to serve as standards forphotometric systems. Their spectral types suggest in which parts of theHR diagrams stars are most constant. In some cases these values stronglyindicate that previous ground based studies claiming photometricvariability are incorrect or that the level of stellar activity haschanged. Table 2 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/367/297
| The proper motions of fundamental stars. I. 1535 stars from the Basic FK5
A direct combination of the positions given in the HIPPARCOS cataloguewith astrometric ground-based catalogues having epochs later than 1939allows us to obtain new proper motions for the 1535 stars of the BasicFK5. The results are presented as the catalogue Proper Motions ofFundamental Stars (PMFS), Part I. The median precision of the propermotions is 0.5 mas/year for mu alpha cos delta and 0.7mas/year for mu delta . The non-linear motions of thephotocentres of a few hundred astrometric binaries are separated intotheir linear and elliptic motions. Since the PMFS proper motions do notinclude the information given by the proper motions from othercatalogues (HIPPARCOS, FK5, FK6, etc.) this catalogue can be used as anindependent source of the proper motions of the fundamental stars.Catalogue (Table 3) is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222
| Does Rotation Alone Determine Whether an A-Type Star's Spectrum Is Abnormal or Normal?
As noted by Abt & Morrell, virtually all of the metallic line (Am)and peculiar A (Ap) stars have equatorial rotational velocities lessthan 120 km s-1, and most of the normal A0-F0 main-sequencestars have equatorial rotational velocities greater than 120 kms-1. However, at all spectral types there are some (10%-20%)of the normal stars that have smaller rotational velocities. If thisoverlap is real, then a star's rotational velocity is insufficient toexplain its abnormal or normal spectra. We studied the A5-F0 and A2-A4stars and found in both cases that there are stars classified as``normal'' that have unusually weak Ca II K lines and/or that occur inshort-period binaries. Therefore, the overlap seems to be due toundetected marginal abnormal stars. Among the A0-A1 stars we find thatour inability to distinguish consistently the class IV from the class Vstars can explain the overlap because the class IV stars have lowerrotational velocities than class V stars. We conclude from statisticalarguments that rotation alone can explain the appearance of an A star aseither abnormal or normal.
| A Second Catalog of Orbiting Astronomical Observatory 2 Filter Photometry: Ultraviolet Photometry of 614 Stars
Ultraviolet photometry from the Wisconsin Experiment Package on theOrbiting Astronomical Observatory 2 (OAO 2) is presented for 614 stars.Previously unpublished magnitudes from 12 filter bandpasses withwavelengths ranging from 1330 to 4250 Å have been placed on thewhite dwarf model atmosphere absolute flux scale. The fluxes wereconverted to magnitudes using V=0 for F(V)=3.46x10^-9 ergs cm^-2 s^-1Å^-1, or m_lambda=-2.5logF_lambda-21.15. This second catalogeffectively doubles the amount of OAO 2 photometry available in theliterature and includes many objects too bright to be observed withmodern space observatories.
| Spectroscopy of Hot Stars in the Galactic Halo. II. The Identification and Classification of Horizontal-Branch and Other A-Type Stars
We discuss a spectroscopic and photometric technique that enables theidentification and classification of field horizontal-branch (FHB) andother A-type stars, even from relatively low signal-to-noise ratiomedium-resolution spectra. This technique makes use of broadband UBVcolors predicted from model atmosphere calculations and Balmer lineprofiles and Ca II K equivalent widths determined from synthetic spectrato estimate the physical parameters T_eff, log g, and [Fe/H] for starsin the effective temperature range 6000-10,000 K. A comparison of ourmethod with high signal-to-noise ratio spectra of standard starsindicates a scatter in the derived parameters of sigma(T_eff)=+/-250 K,sigma(log g)=+/-0.14 dex, and sigma([Fe/H])=+/-0.12 dex. This precisionallows for a separation of low surface gravity FHB and other, generallyhigher surface gravity, A-type (and somewhat later) stars. We alsodevelop a synthetic-template comparison technique, which is veryeffective in the identification of metallic-line and peculiar A-typestars. A detailed investigation of the influence of noise in the spectraon the determination of physical parameters shows that, for spectra withsignal-to-noise ratios in the range 10
| On the HIPPARCOS photometry of chemically peculiar B, A, and F stars
The Hipparcos photometry of the Chemically Peculiar main sequence B, A,and F stars is examined for variability. Some non-magnetic CP stars,Mercury-Manganese and metallic-line stars, which according to canonicalwisdom should not be variable, may be variable and are identified forfurther study. Some potentially important magnetic CP stars are noted.Tables 1, 2, and 3 are available only in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://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
| Behaviour of calcium abundance in Am-Fm stars with evolution
Calcium abundance in the atmosphere of Am stars is examined as afunction of their evolutionary state within the main sequence. Newspectroscopic abundances as well as abundances obtained photometricallyby Guthrie (1987) are used, since they are mutually quite consistent.The main result of this work is that, contrary to earlier suggestions,calcium abundance does not tend to be larger in evolved Am stars than inunevolved ones, for objects distributed along a given evolutionary trackin the HR diagram. The trend appears to be the reverse, if it is presentat all. For our whole sample of Am stars, there is a significantcorrelation between calcium abundance and effective temperature, in thesense that the cooler objects are the most Ca-deficient, hence have themost pronounced Am peculiarity. This implies an apparent correlationbetween calcium deficiency and age, although the lack of Am starsyounger than log t = 8.6 seems real. Our results are fully consistentwith the low rate of Am stars observed in young clusters and withtheoretical predictions of time-dependent radiative diffusion (Alecian1996). Based on observations collected at Observatoire de Haute Provence(CNRS), France, and on data from the ESA HIPPARCOS astrometry satellite.
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| Systematic Errors in the FK5 Catalog as Derived from CCD Observations in the Extragalactic Reference Frame.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114..850S&db_key=AST
| On the nature of the AM phenomenon or on a stabilization and the tidal mixing in binaries. II. Metallicity and pseudo-synchronization.
We reveal sufficient evidences that for Am binaries the metallicitymight depend on their orbital periods, P_orb_, rather than on vsini. Inparticular, δm_1_ index seems to decrease with increasing orbitalperiod up to at least P_orb_=~50d, probably even up to P_orb_=~200d.This gives further support to our "tidal mixing + stabilization"hypothesis formulated in Part I. Moreover, while the most metallic Amstars seem to have rather large periods the slowest rotators are foundto exhibit substantially shorter P_orb_. A questioning eye is thus caston the generally adopted view that Am peculiarity is caused by asuppressed rotationally induced mixing in slowly rotating `single'stars. The observed anticorrelation between rotation and metallicity mayhave also other than the `textbook' explanation, namely being the resultof the correlation between metallicity and orbital period, as themajority of Am binaries are possibly synchronized. We further argue thatthere is a tendency in Am binaries towards pseudo-synchronization up toP_orb_=~35d. This has, however, no serious impact on our conclusionsfrom Part I; on the contrary, they still hold even if this effect istaken into account.
| On the nature of the AM phenomenon or on a stabilization and the tidal mixing in binaries. I. Orbital periods and rotation.
The paper casts a questioning eye on the unique role of the diffusiveparticle transport mechanism in explaining the Am phenomenon and arguesthat the so-called tidal effects might be of great importance incontrolling diffusion processes. A short period cutoff at =~1.2d as wellas a 180-800d gap were found in the orbital period distribution (OPD) ofAm binaries. The existence of the former can be ascribed to the state ofthe primaries with the almost-filled Roche lobes. The latter couldresult from the combined effects of the diffusion, tidal mixing andstabilization processes. Because the tidal mixing might surpassdiffusion in the binaries with the orbital periods P_orb_ less thanseveral hundred days and might thus sustain the He convection zone,which would otherwise disappear, no Am stars should lie below thisboundary. The fact that they are nevertheless seen there implies theexistence of some stabilization mechanism (as, e.g., that recentlyproposed by Tassoul & Tassoul 1992) for the binaries with orbitalperiods less than 180d. Further evidence is given to the fact that theOPD for the Am and the normal binaries with an A4-F1 primary arecomplementary to each other, from which it stems that Am stars are closeto the main sequence. There are, however, indications that they haveslightly larger radii (2.1-3 Rsun_) than expected for theirspectral type. The generally accepted rotational velocity cutoff at=~100km/s is shown to be of little value when applied on Am binaries ashere it is not a single quantity but, in fact, a function of P_orb_whose shape is strikingly similar to that of the curves of constantmetallicity as ascertained from observations. This also leads to thewell known overlap in rotational velocities of the normal and Am starsfor 402.5d.We have exploited this empirical cutoff function to calibrate thecorresponding turbulent diffusion coefficient associated with tidalmixing, having found out that the computed form of the lines of constantturbulence fits qualitatively the empirical shape of the curves ofconstant metallicity. As for larger orbital periods(20d55km/s found by Burkhart(1979) would then be nothing but a manifestation of insufficientlypopulated corresponding area of larger P_orb_.
| The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..135A&db_key=AST
| 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.
| An atlas of southern MK standards from 5800 to 10200 A
An atlas of stellar spectra covering the wavelength range from 5800 to10,200 A is presented of 126 southern MK standard stars, covering theluminosity classes I, III, and V. Some peculiar stars are included forcomparison purposes. The spectra were obtained at a resolution of 4.3 Aper pixel using a Cassegrain-mounted Boller and Chivens spectrographequipped with a Reticon detector. The quality and utility of the dataare discussed and examples of the spectra are presented. The atlas isavailable in digital format through the NSSDC.
| Second astrolabe catalogue of Santiago.
Positions for 350 FK5 and 164 FK5 Extension stars as determined with theDanjon astrolabe of Santiago and differences astrolabe-catalogue aregiven for Equinox J2000.0 and for the mean observation epoch of eachstar. The average mean error in alpha is +/-0.005s and +/-0.07" indelta. The mean epoch of observation of the catalogue is J1979.96.
| Speckle observations of visual and spectroscopic binaries. V.
Not Available
| High-resolution mid-infrared imaging and astrometry of the nucleus of the Seyfert galaxy NGC 1068
The Goddard Infrared Array Camera was used to obtain a high resolutionimage of the nucleus of NGC 1068 at 12.4 microns. In addition, the peakemission at 12.4 microns relative to the peak of the optical continuumwas determined. The distribution of the 12.4 micron emission relates toboth the forbidden O III 5007A 'ionization cone' and the opticalcontinuum emission imaged by HST. This distribution is also found tohave an alignment perpendicular to the plane of a putative moleculartorus. It is suggested that the extended mid-infrared emission isthermal radiation from dust in circumnuclear clouds heated by thecollimated optical/UV AGN source. A portion of the unresolved 12.4micron emission possibly originates from the torus. The infraredemission peak is found to coincide with the apex of the ionization cone,which is presumed to be the location of the torus.
| Optical Polarization of 1000 Stars Within 50-PARSECS from the Sun
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..101..551L&db_key=AST
| The Atmospheric Parameters of A-Stars and F-Stars - Part One - Comparison of Various Methods
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...271..515S&db_key=AST
| Corrections to the right ascension to be applied to the apparent places of 1217 stars given in "The Chinese Astronomical Almanach" for the year 1984 to 1992.
Not Available
| Santiago Fundamental Catalogue - A catalogue of 1105 FK5 stars (equinox J2000.0)
The positions in right ascension and declination of 1105 FK5 stars,observed with a Meridian Circle during the period 1979 to 1991, aregiven. The average mean square error of a position, for the wholecatalog, is +/- 0.009 s in right ascension and +/- 0.10 arcsec indeclination. The mean epoch of the catalog is 1983.148.
| MK morphology of AM stars
We present the results of an analysis of the spectra obtained for asample of 27 Am stars. We find evidence for the presence of groups amongthese stars and argue that all Am stars exhibit a pseudoluminosityeffect.
| MK morphological study of AM stars at 66 A/mm
The pseudoluminosity effect in the metallic line A-type stars found byAbt and Morgan (1976) is confirmed in a random sample of 27 Am stars.From a morphological study of their spectra in the wavelength interval3850-4400 A at a reciprocal dispersion of 66 A/mm, revised spectraltypes are given on the MK system for their K-line and metallic-linespectra. This shows that: (1) the segregation of weak Am from the Amstars largely agrees with that by Cowley et al. (1969); (2) all thestars in the sample are dwarfs according to their K-line classification;(3) more than 80 percent exhibit the pseudoluminosity effectsignificantly, with their metallic-line spectra resembling a giant oreven a supergiant in the violet (3850-4100 A), and a giant rather than adwarf in the blue region (4260-4400 A); and (4) in two-thirds of thestars under (3), the Sr II 4077 A line is found to have a markedlybrighter luminosity class compared to any region, and in more thanone-third of the sample it is comparable to that in Ap stars. Moreover,at least five stars exhibit characteristics which might suggest aspectrum variability; among these, the most striking example is 41 SexA. The metallic-line spectra of another five stars appear to be similarto A-shell type in different degrees. Less than 20 percent of the samplecomprises stars which do not show any significant differentialluminosity effect; these stars might have been misclassified or perhapsthey are in a quiescent state.
| Physical data of the fundamental stars.
Not Available
|
새 글 등록
관련 링크
새 링크 등록
다음 그룹에 속해있음:
|
관측 및 측정 데이터
천체목록:
|
INHABITED SKY
