Contents
Images
Upload your image
DSS Images Other Images
Related articles
MOST Detects SPBe Pulsations in HD 127756 and HD 217543: Asteroseismic Rotation Rates Independent of vsini
The MOST (Microvariability and Oscillations of Stars ) satellite hasdiscovered SPBe (slowly pulsating Be) oscillations in the stars HD127756 (B1/B2 Vne) and HD 217543 (B3 Vpe). For HD 127756, 30 significantfrequencies are identified from 31 days of nearly continuous photometry;for HD 217543, up to 40 significant frequencies from 26 days of data. Inboth cases, the oscillations fall into three distinct frequency ranges,consistent with models of the stars. The variations are caused bynonradial g-modes (and possibly r-modes) distorted by rapid rotation andexcited by the opacity mechanism near the iron opacity bump. Acomparison of pulsation models and observed frequency groups yields arotation frequency for each star, independently of vsini. The rotationrates of these stars, as well as those of the SPBe stars previouslydiscovered by MOST, HD 163868 and ? CMi, are all close to theircritical values.Based on data from the MOST satellite, a Canadian Space Agency mission,jointly operated by Dynacon, Inc., the University of Toronto Instituteof Aerospace Studies, and the University of British Columbia with theassistance of the University of Vienna.
| A photometric study of Be stars located in the seismology fields of COROT
Context: In preparation for the COROT mission, an exhaustive photometricstudy of Be stars located in the seismology fields of the mission hasbeen performed. The very precise and long-time-spanned photometricobservations gathered by the COROT satellite will give important clueson the origin of the Be phenomenon. Aims: The aim of this work is tofind short-period variable Be stars located in the seismology fields ofCOROT, and to study and characterise their pulsational properties. Methods: Light curves obtained at the Observatorio de Sierra Nevada,together with data from Hipparcos and ASAS-3 for a total of 84 Be stars,were analysed in order to search for short-term variations. We appliedstandard Fourier techniques and non-linear least-square fitting to thetime series. Results: We found 7 multiperiodic, 21 mono-periodic and 26non-variable Be stars. Short-term variability was detected in 74% ofearly-type Be stars and in 31% of mid- to late-type Be stars. We showthat non-radial pulsations are more frequent among Be stars than inslow-rotating B stars of the same spectral range.Appendix A is only available in electronic form at http://www.aanda.org
| Multiperiodic pulsations in the Be stars NW Serpentis and V1446 Aquilae
Aims:We present accurate photometric time series of two Be stars:NW Ser and V1446 Aql. Both starswere observed at the Observatorio de Sierra Nevada (Granada) in July2003 with an automatic four-channel Strömgren photometer. We alsopresent a preliminary theoretical study showing that the periodicvariations exhibited by these stars can be due to pulsation. Methods: An exhaustive Fourier analysis together with a least-squarefitting has been carried out on the time series for all fourStrömgren bands. Several independent frequencies and non-periodictrends explain most of the variance. A theoretical non-adiabatic codeapplied to stellar models for these stars shows that g-modes areunstable. Results: Both stars show rapid variations in amplitude,probably due to a beating phenomenon. Four significant frequencies havebeen detected for each star. Comparison of the observed amplitude ratiosfor each pulsational frequency with those calculated from theoreticalpulsation codes allows us to estimate the pulsation modes associatedwith the different detected frequencies. NW Ser seems also to showunstable p-modes and thus could be one of the newly discovered βCephei and SPB hybrid stars. Further spectroscopic observations areplanned to study the stability of the detected frequencies.Tables A.1 and A.2 are 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/472/565
| Multiperiodicity in the newly discovered mid-late Be star V2104?Cygni
Aims:We obtained the first long, homogenous time-series of V2104 Cyg,consisting of 679 datapoints, with the uvby? photometers of theSierra Nevada and San Pedro Mártir Observatories. Our aim was todetect and subsequently interpret the intrinsic frequencies of thispreviously unstudied variable star, which turned out to be a Be star. Weevaluate its place among the variable B stars on the upper MainSequence. To obtain additional information on physical parameters wecollected a few spectra with the Elodie and FIES instruments. Methods: We searched for frequencies in the uvby passbands using 2different frequency analysis methods and used the S/N > 4 criterionto select the significant periodicities. We obtained an estimate of thephysical parameters of the underlying B star of spectral type between B5and B7, by correcting for the presence of a circumstellar disk using aformalism based on the strength of the H? line emission. Results: We detected 3 independent frequencies with amplitudes below0.01 mag, ?1 = 4.7126 d-1 , ?2 =2.2342 d-1 and ?3 = 4.671 d-1 , anddiscovered that V2104 Cyg is a Be star. The fast rotation (vsin i =290±10 km s-1, and 27°< i < 45°)hampered the investigation of the associated pulsational parameters ell.Conclusions: The most plausible explanation for the observedvariability of this mid-late type Be star is a non-radial pulsationmodel.Based on observations obtained at the Observatorio AstronómicoNacional San Pedro Mártir (Mexico), Observatorio de Sierra Nevada(Spain) and Observatoire de Haute Provence (France), and on observationsmade with the Nordic Optical Telescope, operated on the island of LaPalma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in theSpanish Observatorio del Roque de los Muchachos of the Instituto deAstrofísica de Canarias. Full Fig. 1 is only available inelectronic form at http://www.aanda.org
| Fundamental parameters of Be stars located in the seismology fields of COROT
In preparation for the COROT space mission, we determined thefundamental parameters (spectral type, temperature, gravity, V sin i) ofthe Be stars observable by COROT in its seismology fields (64 Be stars).We applied a careful and detailed modeling of the stellar spectra,taking into account the veiling caused by the envelope, as well as thegravitational darkening and stellar flattening due to rapid rotation.Evolutionary tracks for fast rotators were used to derive stellar massesand ages. The derived parameters will be used to select Be stars assecondary targets (i.e. observed for 5 consecutive months) and short-runtargets of the COROT mission. Furthermore, we note that the main part ofour stellar sample falls in the second half of the main sequence lifetime, and that in most cases the luminosity class of Be stars isinaccurate in characterizing their evolutionary status.
| 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.
| 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.
| Statistical analysis of intrinsic polarization, IR excess and projected rotational velocity distributions of classical Be stars
We present the results of statistical analyses of a sample of 627 Bestars. The parameters of intrinsic polarization (p*),projected rotational velocity (v sin i), and near IR excesses have beeninvestigated. The values of p* have been estimated for a muchlarger and more representative sample of Be stars (~490 objects) thanpreviously. We have confirmed that most Be stars of early spectral typehave statistically larger values of polarization and IR excesses incomparison with the late spectral type stars. It is found that thedistributions of p* diverge considerably for the differentspectral subgroups. In contrast to late spectral types (B5-B9.5), thedistribution of p* for B0-B2 stars does not peak at the valuep*=0%. Statistically significant differences in the meanprojected rotational velocities (/line{vsin i}) are found for differentspectral subgroups of Be stars in the sense that late spectral typestars (V luminosity class) generally rotate faster than early types, inagreement with previously published results. This behaviour is, however,not obvious for the III-IV luminosity class stars. Nevertheless, thecalculated values of the ratio vt/vc of the truerotational velocity, vt, to the critical velocity forbreak-up, vc, is larger for late spectral type stars of allluminosity classes. Thus, late spectral type stars appear to rotatecloser to their break-up rotational velocity. The distribution of nearIR excesses for early spectral subgroups is bi-modal, the position ofthe second peak displaying a maximum value E(V-L)~ 1 . m 3for O-B1.5 stars, decreasing to E(V-L)~0. m8 for intermediatespectral types (B3-B5). It is shown that bi-modality disappears for latespectral types (B6-B9.5). No correlations were found betweenp* and near IR excesses and between E(V-L) and vsin i for thedifferent subgroups of Be stars. In contrast to near IR excesses, arelation between p* and far IR excesses at 12 mu m is clearlyseen. A clear relation between p* and vsin i (as well asbetween p* and /line{vsin i}/vc) is found by thefact that plots of these parameters are bounded by a ``triangular"distribution of p*: vsin i, with a decrease of p*towards very small and very large vsin i (and /line{vsini}/vc) values. The latter behaviour can be understood in thecontext of a larger oblateness of circumstellar disks for the stars witha rapid rotation. From the analysis of correlations between differentobservational parameters we conclude that circumstellar envelopes forthe majority of Be stars are optically thin disks with the range of thehalf-opening angle of 10degr
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| 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.
| Rotational Velocity Determinations for 164 Be and B Stars
Rotational velocities, v sin i, have been obtained for 96 Be and 68normal B stars by measurements of the FWHM of the He I lambda-4471 line(for spectral types B0-B4.5) and Mg II lambda-4481 (for types B5-B9.5).The consistency of various published sources is examined. (SECTION: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.
| Early-type stars detected on UK Schmidt objective-prism plates - III. UKST area 881.
Not Available
| Distances, reddenings and distribution of emission B-stars in the galactic centre region /l/ not greater than 45 deg
The distribution of Be stars in the region surrounding the Galacticcenter and their correlation to the spiral structure of the Galaxy hasbeen studied. The results are discussed in terms of reddenings anddistances of these stars. Data are presented on the Galacticcoordinates, colors, interstellar color excesses, reddening-freemagnitudes and colors, adopted absolute magnitudes, distances in kpc,distances from the Galactic plane, and MK spectral type.
| Photometric observations of emission B-stars in the southern Milky Way
In order to study the distribution of Be stars and their correlation tothe local spiral structure of the Galaxy photoelectric UBV photometrywas carried out for a total of 488 Be stars located in the southernMilky Way between galactic longitudes 315 and 45 deg. UBV magnitudes arepresented for these stars.
| UBV photometry of OB+ stars north of 1950.0 declinaison -15.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975AJ.....80..128D&db_key=AST
| Luminous Stars in the Northern Milky Way
Not Available
| Kinematic studies of early-type stars. I. Photometric survey, space motions, and comparison with radio observations.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1962AJ.....67..491R&db_key=AST
| General Catalogue of Stellar Radial Velocities
Not Available
| Supplement to the Mount Wilson Catalogue and Bibliography of Stars of Classes B and a whose Spectra have Bright Hydrogen Lines.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1943ApJ....98..153M&db_key=AST
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Aquila |
| Right ascension: | 19h12m40.26s |
| Declination: | -06°27'31.7" |
| Apparent magnitude: | 9.14 |
| Proper motion RA: | 0.9 |
| Proper motion Dec: | -6.8 |
| B-T magnitude: | 9.479 |
| V-T magnitude: | 9.168 |
Catalogs and designations:
|
