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מאמרים קשורים
Caroline Herschel's catalogue of nebulae
Not Available
| The epoch of the constellations on the Farnese Atlas and their origin in Hipparchus's lost catalogue
Not Available
| Pulsating Stars in the ASAS-3 Database. I. beta Cephei Stars
We present results of an analysis of the ASAS-3 data for short-periodvariables from the recently published catalog of over 38000 stars. Usingthe data available in the literature we verify the results of theautomatic classification related to \beta Cep pulsators. In particular,we find that 14 stars in the catalog can be classified unambiguously asnew beta Cep stars. By means of periodogram analysis we derive thefrequencies and amplitudes of the excited modes. The main modes in thenew beta Cep stars have large semi-amplitudes, between 35 and 80 mmag.Up to four modes were found in some stars. Two (maybe three) new betaCep stars are members of southern young open clusters: ASAS164409-4719.1 belongs to NGC 6200, ASAS 164630-4701.2 is a member ofHogg 22, and ASAS 164939-4431.7 could be a member of NGC 6216.We also analyze the photometry of four known beta Cep stars in theASAS-3 catalog, namely IL Vel, NSV 24078, V1449 Aql and SY Equ. Finally,we discuss the distribution of beta Cep stars in the Galaxy.
| The Star Formation History and Mass Function of the Double Cluster h and χ Persei
The h and χ Per ``double cluster'' is examined using wide-field(0.98d×0.98d) CCD UBV imaging supplemented by optical spectra ofseveral hundred of the brightest stars. Restricting our analysis to nearthe cluster nuclei, we find identical reddenings [E(B-V)=0.56+/-0.01],distance moduli (11.85+/-0.05), and ages (12.8+/-1.0 Myr) for the twoclusters. In addition, we find an initial mass function slope for eachof the cluster nuclei that is quite normal for high-mass stars,Γ=-1.3+/-0.2, indistinguishable from a Salpeter value. We derivemasses of 3700 Msolar (h) and 2800 Msolar (χ)integrating the present-day mass function from 1 to 120Msolar. There is evidence of mild mass segregation within thecluster cores. Our data are consistent with the stars having formed at asingle epoch; claims to the contrary are very likely due to theinclusion of the substantial population of early-type stars located atsimilar distances in the Perseus spiral arm, in addition tocontamination by G and K giants at various distances. We discuss theuniqueness of the double cluster, citing other examples of suchstructures in the literature but concluding that the nearly identicalnature of the two cluster cores is unusual. We fail to settle thelong-standing controversy regarding whether or not the double cluster isthe core of the Per OB1 association and argue that this may beunanswerable with current techniques. We also emphasize the need forfurther work on the pre-main-sequence population of this nearby andhighly interesting region.
| Physical Conditions in the Foreground Gas of Reflection Nebulae: NGC 2023, vdB 102, and NGC 7023
High-resolution optical spectra of HD 37903 and HD 147009, whichilluminate the reflection nebulae NGC 2023 and vdB 102, were obtainedfor comparison with our results for HD 200775 and NGC 7023. Ground-basedmeasurements of the molecules CH, C2, and CN and the atoms NaI and K I were analyzed to extract physical conditions in the foregroundcloud. Estimates of the gas density, gas temperature, and flux ofultraviolet radiation were derived and were compared with the resultsfrom infrared and radio studies of the main molecular cloud. Theconditions are similar to those found in studies of diffuse clouds. Theforeground material is less dense than the gas in the molecular cloudbehind the star(s). The gas temperature was set at 40 K, the temperaturedetermined for the foreground gas in NGC 7023. The flux of ultravioletradiation was found to be less intense than in the molecular materialbehind the star(s). The column densities of Na I and K I were reproducedreasonably well when the extinction curve for the specific line of sightwas adopted. We obtained NEWSIPS data from the IUE archive for HD 37903and HD 200775. The ultraviolet data on C I and CO allow extraction ofthe physical conditions by alternate methods. General agreement amongthe various diagnostics was found, leading to self-consistent picturesof the foreground photodissociation regions. An appendix describeschecks on the usefulness of IUE NEWSIPS data for interstellar studies.Equivalent widths are compared with a previous analysis of IUEobservations for interstellar gas toward 20 Aql. Excellent agreement isfound with NEWSIPS results having smaller errors. A comparison ofNEWSIPS data for C I toward X Per with data acquired with the HubbleSpace Telescope shows similar levels of agreement in equivalent widthsand that the derived column densities from IUE results are accurate tobetter than a factor of 2 for absorption lines of moderate strength.
| Settling onto the Main Sequence: ROSAT Observations of H and χ Persei
We have studied X-rays from the double cluster h and χ Per with an11 ks ROSAT position-sensitive proportional counter (PSPC) observation.Emission is concentrated toward the two cluster centers. Whether theemission is diffuse emission or from a population of unresolved faintsources is uncertain because the resolution is poor at the distance ofthe clusters (2.4 kpc). Twenty-three sources were found with an X-rayluminosity of logL=31.5 ergs s-1 or greater. These sourceswere found in the cluster nuclei, between the clusters, and in a haloaround the cluster pair. The ROSAT PSPC error circle is too large forthe identification of X-ray sources with individual optical objects.However, because of a lack of correlation between X-ray sources and Bstars, we conclude that the X-rays are produced by late spectral typepre-main-sequence stars. The X-ray sources are brighter than all but thevery brightest sources in the younger Orion Nebula cluster, which makesthem important in tracing the final stages approaching the mainsequence. Based on observations made with the ROSAT satellite.
| NGC 7419: An open cluster rich in Be stars
The results of our CCD photometric Hα observations of NGC7419 are presented. The observations resulted in a discoveryof 17 new Be stars and two other emission-line objects. In consequence,the number of known Be stars in this young cluster increased more thantwofold and equals now to 31. This is at present the largest number ofBe stars known in any galactic open cluster. Moreover, we estimate thatthese 31 Be stars constitute 36 +/- 7% of all cluster B-type starsbrighter than R_C = 16.1 mag. This locates NGC 7419 among these openclusters which are richest in Be stars such as galactic NGC663, NGC 330 in SMC, and NGC1818A in LMC.
| Radiative lifetimes, branching fractions and transition probabilities in GeI - solar implications
New radiative lifetimes have been measured for the 5s ^3P^o_0,1,2 and 5s^1P^o_1 levels of GeI using a laser-produced plasma subject to selectivelaser excitation. A diffraction grating based emission spectrometer ofmoderately high resolution has been used to remeasure the branchingratios of the 4p-5s depopulating transitions. The oscillator strengthsof astrophysical interest, which have been derived from these new data,are compared with theoretical values calculated within apseudo-relativistic Hartree-Fock approach. The new set of f-values hasbeen compared with the few results available in the literature, whichare generally characterized by a large scatter and a low accuracy. Thesolar photospheric abundance of germanium deduced from the new atomicdata of the present work is A_Ge = 3.58 +/- 0.05, on the usuallogarithmic scale, in agreement with the meteoritic value.
| A catalog of rotational and radial velocities for evolved stars
Rotational and radial velocities have been measured for about 2000evolved stars of luminosity classes IV, III, II and Ib covering thespectral region F, G and K. The survey was carried out with the CORAVELspectrometer. The precision for the radial velocities is better than0.30 km s-1, whereas for the rotational velocity measurementsthe uncertainties are typically 1.0 km s-1 for subgiants andgiants and 2.0 km s-1 for class II giants and Ib supergiants.These data will add constraints to studies of the rotational behaviourof evolved stars as well as solid informations concerning the presenceof external rotational brakes, tidal interactions in evolved binarysystems and on the link between rotation, chemical abundance and stellaractivity. In this paper we present the rotational velocity v sin i andthe mean radial velocity for the stars of luminosity classes IV, III andII. Based on observations collected at the Haute--Provence Observatory,Saint--Michel, France and at the European Southern Observatory, LaSilla, Chile. Table \ref{tab5} also available in electronic form at CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The ROSAT all-sky survey catalogue of optically bright late-type giants and supergiants
We present X-ray data for all late-type (A, F, G, K, M) giants andsupergiants (luminosity classes I to III-IV) listed in the Bright StarCatalogue that have been detected in the ROSAT all-sky survey.Altogether, our catalogue contains 450 entries of X-ray emitting evolvedlate-type stars, which corresponds to an average detection rate of about11.7 percent. The selection of the sample stars, the data analysis, thecriteria for an accepted match between star and X-ray source, and thedetermination of X-ray fluxes are described. Catalogue only available atCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| EUV activity in late-type stars during the ROSAT WFC All-Sky Survey - I. Techniques and initial results
We study 127 active late-type stars, including the well-known flarestars, in the extreme ultraviolet (EUV) region of the electromagneticspectrum, using the ROSAT Wide Field Camera (WFC) survey observations.Our analysis includes photometry for all the stars in the sample, timinganalysis of the observed photon events, and a statistical analysis forpossible small-scale, low-level variability. 49 stars in our sample weredetected in one or both EUV wavebands. A total of 35 flares were seen,from 23 stars, not all of them well-known flare stars. In addition,about half of the detections exhibited low-level variability. Furtheranalysis reveals that the observed low-level variability was not due torotational or orbital modulation, but rather was related to small-scaleactivity on the stars, possibly in the form of small-amplitude,flare-like events which were too faint to be recognized as individualflares at the sensitivity of the WFC. We call this low-level activity`milliflaring'. We also give estimated upper-limit count rates for thenon-detections.
| At the 2.6 m telescope of Byurakan Perot-Fabry observations of gas emission in nebulae with cigale
During the summer of 1985, the CIGALE Perot-Fabry scanninginterferometer of Marseilles Observatory was installed at the primefocus of the 2.6 m telescope of Byurakan Observatory. The long run (twonew moons) was successful and gave matereial for numerous publications.
| French-Armenian scientific cooperation on study of some HII-regions with cigale
The results of the scientific cooperation between astronomers of theByurakan and Marseille observatories on the study of diffuse matter inthe Galaxy are presented.H -emission is discovered in the direction of hand x Per. Fabry-Perot observations of three HII-regions, Sh2-152, 153,and 106, show the expansion of the diffuse matter relative to theexciting stars. In the Sh2-106 region a probable jet is found. It isshown that in star forming regions the diffuse matter takes part inexpansion motions together with 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.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| Chemical transitions for interstellar C2 and CN in cloud envelopes
Observations were made of absorption from CH, C2, and CN towardmoderately reddened stars in Sco, OB2, Ceo OB3, and Taurus/Auriga. Forthese directions, most of the reddening is associated with a singlecloud complex, for example, the rho Ophiuchus molecular cloud, and as aresult, the observations probe moderately dense material. When combinedwith avaliable data for nearby directions, the survey provides the basisfor a comprehensive analysis of the chemistry for these species. Thechemical transitions affecting C2 and CN in cloud envelopes wereanalyzed. The depth into a cloud at which a transition takes place wascharacterized by tauuv, the grain optical depth at 1000 A.One transition at tauuv approx. = 2, which arises from, theconversion of C(+) into CO, affects the chemistries for both moleculesbecause of the key role this ion plays. A second one involvingproduction terms in the CN chemistry occurs at tauuv ofapprox. = 3; neutral reactions which C2 and CH is more important atlarger values for tauuv. The transition fromphotodissociation to chemical destruction takes place attauuv approx. = 4.5 for C2 and CN. The observational data forstars in Sco OB2, Cep OB3, and Taurus/Auriga were studied with chemicalrate equations containing the most important production and destructionmechanisms. Because the sample of stars in Sco OB2 includes sight lineswith Av ranging from 1-4 mag, sight lines dominated byphotochemistry could be analyzed separately from those controlled bygas-phase destruction. The analysis yielded values for two poorly knownrate constants for reactions involved in the production of CN; thereactions are C2 + N yields CN + C and C(+) + NH yields all products.The other directions were analyzed with the inferred values. Thepredicted column densities for C2 and CN agree with the observed valuesto better than 50%, and in most instances 20%. When combining theestimates for density and temperature derived from chemical modeling andmolecular excitation for a specific cloud, such as the rho Ophiuchusmolecular cloud, the portion of the cloud envelope probed by C2 and CNabsorption was found to be in pressure equilibrium.
| On variation of the emission in the spectra of some Be-stars: theta CrB, phi Per, psi Per.
Not Available
| Redshifts of high-luminosity stars - The K effect, the Trumpler effect and mass-loss corrections
The Trumpler effect is demonstrated in B and A supergiants in h + ChiPersei, as well as in other associations of young luminous stars. TheK-Trumpler effect is also shown in O, B, and A supergiants in theMagellanic Clouds, as well as in nearby galaxies such as NGC 1569 and2777 and in blue irregular variables in M31 and M33. Mass outflow inluminous stars is shown to require an average correction of about 20km/s and to increase the excess redshifts of the stars in the MagellanicClouds to a significance level of 6 sigma. Completely empirical andindependent measurements show that mass-loss corrections of this sizeare required on average for supergiants in both the SMC and LMC and alsoin the Milky Way.
| Asymptotic giant branch stars near the sun
Available red and near-infrared photometry and apparent motions of M, S,and C asymptotic giant branch (AGB) stars in the Bright Star Catalogueare tabulated and discussed. It is shown that the red and near infraredindices normally used for late-type stars are interchangeable except forcarbon stars. The M-type giants are variable with visual amplitudegreater than 0.05 mag. The reddening-free parameter m2 from Genevaphotometry is essentially a temperature parameter for M giants, whilethe reddening-free parameter d is a sensitive detector of blue stellarcompanions. The space density of AGB stars near the sun decreases by afactor of 35 in a temperature range 3800 to 3400 K. Two of the S starsnear the sun were found to have nearly equal space motions and may becomembers of the Arcturus group.
| New Measurements of 12C/13C Toward ζ Oph and ξ Per
Not Available
| Groups of stars with common motion in the Galaxy - Groups of red supergiants of the luminosity classes I and II
Not Available
| An atlas of Hubble Space Telescope photometric, spectrophotometric, and polarimetric calibration objects
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990AJ.....99.1243T&db_key=AST
| Third preliminary catalogue of stars observed with the photoelectric astrolabe of the Beijing Astronomical Observatory.
Not Available
| Photometry of BL Lac objects and optically violently variable quasars
A photon-counting photometer has been used to observe BL Lac objects andoptically violently variable (OVV) quasars. The development,construction, and performance of the photometer are discussed and thephotometer configuration is illustrated. The observations were made onfive nights in September 1986 using a 1-m telescope. Results arepresented for observations of seven OVV objects and the star Chi Persei.No statistically significant variation were detected in the sources ontimescales ranging from 0.1 sec to 5 days.
| Be-9 abundances in dwarfs of intermediate metal deficiency - Implications for galactic evolution
This paper presents observations of the 3130 A Be II resonance doubletin stars of intermediate metal deficiency, with Fe/H values between -0.6and -1.1, obtained with the Intermediate Dispersion Spectrographs andIPCS detector at the 2.5 m Isaac Newton Telescope on La Palma. Thederived beryllium abundances range from 5.6 x 10 to the -12th (one halfsolar) to 2 x 10 to the -12th (one sixth solar). These values,interpolated between the sets of previous beryllium measurements athigher and at lower metallicities, serve to confirm the monotonicvariation of the Be abundance with Fe during the evolution of thegalactic disk. It is found that there was no extreme burst of Beproduction in the halo. To circumvent the effects of depletion, astatistical set of data is needed, for which the upper envelope can beused to trace galactic Be evolution. It is noted that no observationswith sufficient sensitivity to detect Be in the extremely metaldeficient stars of the halo have been reported to date.
| Journeys on the H-R diagram.
Not Available
| Analysis of the correlations between polarimetric and photometric properties of young stars
The results of an investigation of the correlations between polarimetricand photometric characteristics of a sample of young Ae/Be Herbig, FUOrion, and T Taurus-type young stars are presented. It is shown that acommon dependence between polarization and IR excesses exists for 80percent of the stars in the sample. A comparison is made between the ageof the stars and the magnitude of their radiation polarization.
| The helium abundance in the atmospheres of the stars in the clusters NGC 869, 884 and 2264
The effective temperature, acceleration due to gravity, atmospherichelium abundance, and rotational velocity of 23 B-stars are determinedusing the model atmosphere method. Photographic spectra in the 3900-4900A range obtained on the main stellar spectrograph of the 6-m telescopewere used. It is concluded that significant differences in the meanhelium abundance do not exist from cluster to cluster.
| A medieval reference to the Andromeda nebula.
Not Available
| Multivariate statistical analysis of OB stars around H and Chi Persei
A multivariate statistical analysis has been carried out on 49 OB starshaving radial velocities and distance moduli in a field around h and ChiPersei. A hierarchical cluster analysis, combined with discriminantanalysis, has revealed the probable presence of two groups: onebelonging to the Perseus spiral arm (mean distance 2100 pc), the otherlocated at a distance of 1150 pc. Comparison of the difference in meanradial velocities of the groups with the value predicted by the formulaof Oort also supports the result obtained.
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הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | פרסאוס |
| התרוממות ימנית: | 02h18m04.50s |
| סירוב: | +57°31'00.0" |
| גודל גלוי: | 5.98 |
| מרחק: | 217.865 פארסק |
| תנועה נכונה: | -13.1 |
| תנועה נכונה: | -2.1 |
| B-T magnitude: | 7.319 |
| V-T magnitude: | 6.113 |
קטלוגים וכינוים:
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