Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
The Opaque Nascent Starburst in NGC 1377: Spitzer SINGS Observations
We analyze extensive data on NGC 1377 from the Spitzer Infrared NearbyGalaxies Survey (SINGS). Within the category of nascent starbursts thatwe previously selected as having infrared-to-radio continuum ratios inlarge excess of the average and containing hot dust, NGC 1377 has thelargest infrared excess yet measured. Optical imaging reveals amorphological distortion suggestive of a recent accretion event.Infrared spectroscopy reveals a compact and opaque source dominated by ahot, self-absorbed continuum (τ~20 in the 10 μm silicate band).We provide physical evidence against nonstellar activity being theheating source. H II regions are detected through the single [Ne II]line, probing <1% of the ionizing radiation. Not only is the opticaldepth in different gas and dust phases very high, but >85% ofionizing photons are suppressed by dust. The only other detectedemission features are molecular hydrogen lines, arguably excited mainlyby shocks, besides photodissociation regions, and weak aromatic bands.The new observations support our interpretation in terms of an extremelyyoung starburst (<1 Myr). More generally, galaxies deficient in radiosynchrotron emission are likely observed within a few Myr of the onsetof a starburst and after a long quiescence, prior to the replenishmentof the interstellar medium with cosmic rays. The similar infrared-radioproperties of NGC 1377 and some infrared-luminous galaxies suggest thatNGC 1377 constitutes an archetype that will be useful to betterunderstand starburst evolution. Although rare locally because observedin a brief evolutionary stage, nascent starbursts may represent anonnegligible fraction of merger-induced starbursts that dominate deepinfrared counts. Since they differ dramatically from usual starbursttemplates, they have important consequences for the interpretation ofdeep surveys.
| Statistical Constraints for Astrometric Binaries with Nonlinear Motion
Useful constraints on the orbits and mass ratios of astrometric binariesin the Hipparcos catalog are derived from the measured proper motiondifferences of Hipparcos and Tycho-2 (Δμ), accelerations ofproper motions (μ˙), and second derivatives of proper motions(μ̈). It is shown how, in some cases, statistical bounds can beestimated for the masses of the secondary components. Two catalogs ofastrometric binaries are generated, one of binaries with significantproper motion differences and the other of binaries with significantaccelerations of their proper motions. Mathematical relations betweenthe astrometric observables Δμ, μ˙, and μ̈ andthe orbital elements are derived in the appendices. We find a remarkabledifference between the distribution of spectral types of stars withlarge accelerations but small proper motion differences and that ofstars with large proper motion differences but insignificantaccelerations. The spectral type distribution for the former sample ofbinaries is the same as the general distribution of all stars in theHipparcos catalog, whereas the latter sample is clearly dominated bysolar-type stars, with an obvious dearth of blue stars. We point outthat the latter set includes mostly binaries with long periods (longerthan about 6 yr).
| The physical properties of normal A stars
Designating a star as of A-type is a result of spectral classification.After separating the peculiar stars from those deemed to be normal usingthe results of a century of stellar astrophysical wisdom, I define thephysical properties of the "normal" stars. The hotter A stars haveatmospheres almost in radiative equilibrium. In the A stars convectivemotions can be found which increase in strength as the temperaturedecreases.
| MARCS: Model Stellar Atmospheres and Their Application to the Photometric Calibration of the Spitzer Space Telescope Infrared Spectrograph (IRS)
We describe state-of-the-art MARCS-code model atmospheres generated fora group of A dwarf, G dwarf, and late-G to mid-K giant standard stars,selected to photometrically calibrate the Spitzer Space TelescopeInfrared Spectrograph (IRS) and compare the synthetic spectra toobservations of HR 6688, HR 6705, and HR 7891. The general calibrationprocesses and uncertainties are briefly described, and the differencesbetween various templated composite spectra of the standards areaddressed. In particular, a contrast between up-to-date modelatmospheres and previously published composite and synthetic spectra isillustrated for wavelength ranges around 8 μm (where the SiOΔv=1 band occurs for the cooler standards) and λ>=20μm, where the use of the Engelke function will lead to increasinglylarge discrepancies as a result of the neglect of gravity in cool stars.At this point, radiometric requirements are being met, absolute fluxcalibration uncertainties (1 σ) are ~20% in the Short-High andLong-High data and ~15% in the Short-Low and Long Low data, andorder-to-order flux uncertainties are ~10% or less. Iteration betweenthe MARCS model atmosphere inputs and the data processing will improvethe S/N ratios and calibration accuracies.
| Rotational Velocities of B, A, and Early-F Narrow-lined Stars
Projected rotational velocities for 58 B, A, and early-F stars have beendetermined from high-resolution spectroscopic observations made at KittPeak National Observatory with the coudé feed telescope. All thestars are slowly rotating with vsini<60 km s-1. Because oftheir low rotational velocities, 15 of the stars have been observed asprospective, early-type, radial velocity standards.
| 3D mapping of the dense interstellar gas around the Local Bubble
We present intermediate results from a long-term program of mapping theneutral absorption characteristics of the local interstellar medium,motivated by the availability of accurate and consistent parallaxes fromthe Hipparcos satellite. Equivalent widths of the interstellar NaID-line doublet at 5890 Å are presented for the lines-of-sighttowards some 311 new target stars lying within ~ 350 pc of the Sun.Using these data, together with NaI absorption measurements towards afurther ~ 240 nearby targets published in the literature (for many ofthem, in the directions of molecular clouds), and the ~ 450lines-of-sight already presented by (Sfeir et al. \cite{sfeir99}), weshow 3D absorption maps of the local distribution of neutral gas towards1005 sight-lines with Hipparcos distances as viewed from a variety ofdifferent galactic projections.The data are synthesized by means of two complementary methods, (i) bymapping of iso-equivalent width contours, and (ii) by densitydistribution calculation from the inversion of column-densities, amethod devised by Vergely et al. (\cite{vergely01}). Our present dataconfirms the view that the local cavity is deficient in cold and neutralinterstellar gas. The closest dense and cold gas ``wall'', in the firstquadrant, is at ~ 55-60 pc. There are a few isolated clouds at closerdistance, if the detected absorption is not produced by circumstellarmaterial.The maps reveal narrow or wide ``interstellar tunnels'' which connectthe Local Bubble to surrounding cavities, as predicted by the model ofCox & Smith (1974). In particular, one of these tunnels, defined bystars at 300 to 600 pc from the Sun showing negligible sodiumabsorption, connects the well known CMa void (Gry et al. \cite{gry85}),which is part of the Local Bubble, with the supershell GSH 238+00+09(Heiles \cite{heiles98}). High latitude lines-of-sight with the smallestabsorption are found in two ``chimneys'', whose directions areperpendicular to the Gould belt plane. The maps show that the LocalBubble is ``squeezed'' by surrounding shells in a complicated patternand suggest that its pressure is smaller than in those expandingregions.We discuss the locations of several HI and molecular clouds. Usingcomparisons between NaI and HI or CO velocities, in some cases we areable to improve the constraints on their distances. According to thevelocity criteria, MBM 33-37, MBM 16-18, UT 3-7, and MBM 54-55 arecloser than ~ 100 pc, and MBM 40 is closer than 80 pc. Dense HI cloudsare seen at less than 90 pc and 85 pc in the directions of the MBM 12and MBM 41-43 clouds respectively, but the molecular clouds themselvesmay be far beyond. The above closest molecular clouds are located at theneutral boundary of the Bubble. Only one translucent cloud, G192-67, isclearly embedded within the LB and well isolated.These maps of the distribution of local neutral interstellar NaI gas arealso briefly compared with the distribution of both interstellar dustand neutral HI gas within 300 pc.Tables 1 and 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/411/447
| Radial velocities of early-type stars in the Perseus OB2 association
We present radial velocities for 29 B- and A-type stars in the field ofthe nearby association Perseus OB2. The velocities are derived fromspectra obtained with AURELIE, via cross correlation with radialvelocity standards matched as closely as possible in spectral type. Theresulting accuracy is ~ 2-3 km s-1. We use thesemeasurements, together with published values for a few other early-typestars, to study membership of the association. The mean radial velocity(and measured velocity dispersion) of Per OB2 is 23.5 +/- 3.9 kms-1, and lies ~ 15 km s-1 away from the meanvelocity of the local disk field stars. We identify a number ofinterlopers in the list of possible late-B- and A-type members which wasbased on Hipparcos parallaxes and proper motions, and discuss thecolour-magnitude diagram of the association.Based on observations made at the Observatoire de Haute-Provence (CNRS),France.
| 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
| On the effective temperatures and surface gravities of superficially normal main sequence band B and A stars
Effective temperatures and surface gravities for 48 main sequence band Band A stars were found by matching optical region spectrophotometry andHγ profiles with the predictions of ATLAS9 solar composition modelatmospheres. When these values were compared with those found usingStrömgren uvbybeta photometry based on ATLAS6 model atmospheres, wefound a difference (photometry-spectrophotometry) of 25+/- 118 K for 29stars with 8000 K le Teff <= 10 050 K compared to 76 +/-105 K for 14 stars with 10 050 K <= Teff <= 17 000 K.The surface gravity scales are in agreement. These stars aresufficiently hot that their effective temperatures and surface gravitydeterminations are unaffected by discrepancies due to the choice ofMixing-Length or Canuto-Mazzitelli convection theories.
| V, I_C Observations of the Variable Antipin V71
We present VI_C CCD photometry of the variable Antipin V71 stated asfast variable of unknown type by the discoverer.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| 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
| A-shell stars in the Geneva system
Among the various kinds of A stars having a peculiar spectrum, we findthe A-shell stars. Many questions are still open concerning these stars,including their evolutionary status. In the present study we have useddata from the Hipparcos catalogue to examine this point. We have foundthat the majority of A-shell stars are well above the main sequence. Nodifferences could be established between A-shell stars in luminosityclasses III and I and those in luminosity class V as regardsvariability, duplicity, or the importance of the shell feature.
| Speckle Interferometry of New and Problem HIPPARCOS Binaries
The ESA Hipparcos satellite made measurements of over 12,000 doublestars and discovered 3406 new systems. In addition to these, 4706entries in the Hipparcos Catalogue correspond to double star solutionsthat did not provide the classical parameters of separation and positionangle (rho,theta) but were the so-called problem stars, flagged ``G,''``O,'' ``V,'' or ``X'' (field H59 of the main catalog). An additionalsubset of 6981 entries were treated as single objects but classified byHipparcos as ``suspected nonsingle'' (flag ``S'' in field H61), thusyielding a total of 11,687 ``problem stars.'' Of the many ground-basedtechniques for the study of double stars, probably the one with thegreatest potential for exploration of these new and problem Hipparcosbinaries is speckle interferometry. Results are presented from aninspection of 848 new and problem Hipparcos binaries, using botharchival and new speckle observations obtained with the USNO and CHARAspeckle cameras.
| The nature of the sharp-lined A1V star HD 72660
In order to specify the nature of the sharp-lined A1V star HD 72660, itseffective temperature and surface gravity have been determined using twodifferent methods. First, the ultraviolet energy distribution of HD72660 has been compared with that of the normal A0 star HD 10939 andwith the predictions of two model atmospheres. Secondly, the parametershave been derived from Moon & Dworetsky's (1985) calibration of uvbycolors. Both methods yield consistent values Teff = 9750 +/-\200 K, logg = 4.00 +/-\ 0.20 dex. In a second part, high resolution highsignal to noise optical spectra centered on <~mbda4500 Angstroms,<~mbda5080 Angstroms and <~mbda6160 Angstroms have beensynthesized using Gray's (1995) and Takeda's (1995) LTE codes. Theabundances of 13 elements were derived. C and O are found to beunderabundant with respect to the solar value (-0.60 and -0.52 dexrespectively) whereas Ti, Cr, Fe, Ni are overabundant (between +0.37 and+0.72 dex). Ca appears to be moderately overabundant (+0.16 dex). Theseresults suggest that HD 72660 is a hot Am star. Based on observationscollected at Observatoire de Haute Provence (France)
| Elemental abundance analyses with DAO spectrograms - XX. The early A stars epsilon Serpentis, 29 Vulpeculae and sigma Aquarii
Elemental abundances of the early A stars epsilon Ser, 29 Vul and sigmaAqr are derived consistently with previous studies of this series usingspectrograms obtained with Reticon and CCD detectors. The derivedabundances confirm that epsilon Ser is a definite Am star. 29 Vul showsevidence for a weakly operating Am star phenomenon. sigma Aqr, a hot Amstar prototype, has abundances similar to those of o Peg, another classprototype.
| 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.
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Intrinsic Energy Distribution in Stellar Spectra in the Wavelength Interval 320--760 NM
The intrinsic energy distributions in the interval 320--760 nm ofspectral types B5--G8 of luminosity V, F0--F5 of luminosity IV andG8--M2 of luminosity III, determined by authors, are intercompared withthe catalogue of the mean energy distribution data published bySviderskiene (1988).
| 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
| Reality Tests of Superclusters in the Young Disk Population
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.2862E&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.
| SANTIAGO 91, a right ascension catalogue of 3387 stars (equinox J2000).
The positions in right ascension of 3387 stars belonging to the Santiago67 Catalogue, observed with the Repsold Meridian Circle at Cerro Calan,National Astronomical Observatory, during the period 1989 to 1994, aregiven. The average mean square error of a position, for the wholeCatalogue, is +/-0.009 s. The mean epoch of the catalogue is 1991.84.
| Compositional differences among the A-type stars. 2: Spectrum synthesis up to V sin i = 110 km/s
The results of an abundance analysis of 15 early A-type stars arepresented here. These stars have u sin i on the range 6 to 109 km/s andall but one of them (an Am star) are classified as normal. Reliableabundances (uncertainties about a quarter dex or less) are obtained fortwelve elements. Considerable star-to-star abundance variations arepresent among both the narrow lined and broader lined stars. Mostelements have abundances which scale with those of iron. Carbon andcalcium are interesting exceptions. Carbon abundances seem to beanti-correlated with those of iron, while calcium abundances may exhibita more complex behavior. Heavy elements seem enhanced for most stars.
| The second Quito astrolabe catalogue
The paper contains 515 individual corrections {DELTA}α and 235corrections {DELTA}δ to FK5 and FK5Supp. stars and 50 correctionsto their proper motions computed from observations made with theclassical Danjon astrolabe OPL-13 at Quito Astronomical Observatory ofEcuador National Polytechnical School during a period from 1964 to 1983.These corrections cover the declination zone from -30deg to +30deg. Meanprobable errors of catalogue positions are 0.047" in αcosδand 0.054" in δ. The systematic trends of the catalogue{DELTA}αalpha_cosδ,{DELTA}αdelta_cosδ,{DELTA}δalpha_, {DELTA}δdelta_ arepresented for the observed zone.
| A survey for rapid variability among early main-sequence A stars
A survey of nonpeculiar early (A0-A5) main-sequence A stars for rapid,low-amplitude variability is presented. The survey is also anindependent test of the main-sequence mass-loss theory proposed byWillson et al. (1986). All observations were gathered with theUniversity of Wisconsin Two-Star Photometer. Several period-searchingmethods are used to analyze time series of differential-photometricdata. This instrument coupled with a computerized high-speed datacollection system was used with small telescopes at Pine BluffObservatory and Table Mountain Observatory. Several period-searchmethods are used to analyze time series of differential-photometricdata. This instrument and data-reduction technique allow millimagnitudelight variations to be detected. The survey also discovered severallow-amplitude Delta Sct stars, all of which are in or blueward of therecognized instability strip.
| Corrections to FK4 Positions of Stars Observed at Paris Astrolabe
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..102..389N&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
| Catalog of stars observed with the photoelectric CERGA astrolabe (March 1988 - July 1991)
From Mars 1988 to July 1991 the photoelectric CERGA astrolabe ASPHO wasused to observe 11 star groups. During each annual cycle, each star wasobserved sufficiently to allow an early determination of FK5 catalogcorrections with a precision of 0.03 and 0.04 arcsec in right ascensionand declination respectively. The results are given here in the form ofa combined catalog for the three years of observations, and correctionsto the FK5 positions computed for the epoch 1990.0 and corrections tothe FK5 proper motions are also given. Errors are estimated as acombination of the internal yearly error and of the nonlinearity of itsapparent motion during the three years. The results are discussed,showing that the catalog is well linked to the FK5 system without shiftin alpha or delta. It is concluded that the corrections in positions andproper motions given here are significant within estimated errors.
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
| Csillagkép: | Kis Róka |
| Rektaszcenzió: | 20h38m31.30s |
| Deklináció: | +21°12'04.0" |
| Vizuális fényesség: | 4.82 |
| Távolság: | 65.488 parszek |
| RA sajátmozgás: | 70.6 |
| Dec sajátmozgás: | 2.8 |
| B-T magnitude: | 4.774 |
| V-T magnitude: | 4.798 |
Katalógusok és elnevezések:
|
INHABITED SKY
