תוכן
תמונות
הוסף תמונה שלך
DSS Images Other Images
מאמרים קשורים
A Survey of the SO JK=10-01 Transition toward Massive Star-forming Regions
We present the most extensive survey to date of the SO ground statetransition JK=10-01 (30 GHz). Weobserved 49 regions of massive star formation with theMax-Planck-Institut für Radioastronomie (MPIfR) 100 m telescope. Inaddition, the SO JK=43-32 transitionwas observed with the IRAM 30 m telescope toward a subsample of sevensources. Emission in the SO JK=10-01transition most likely arises from the parsec-scale molecular clumpssurrounding ultracompact H II regions. In general, the SOJK=10-01 line has a Gaussian shape andappears to be optically thin. We derive SO column densities between0.58×1014 and 12×1014 cm-2and SO abundances in the range0.18×10-9-4.4×10-9. Our observationsshow that the SO ground state transition is an effective tool to studymassive star-forming clumps, and the data presented in this paperprovide a useful supplement for future multitransition SO studies.
| The Long-Term Behavior of the Semiregular M Supergiant Variable BC Cygni
The long-term brightness changes in the M supergiant, type C semiregularvariable, Type II supernova progenitor BC Cyg from 1890 to the presentare examined using archival data obtained from photographic plates inthe collections of Harvard College Observatory and SternbergAstronomical Institute, in conjunction with AAVSO observations. BC Cygpulsates with a period close to 700 days but underwent a 0.5 magincrease in brightness between 1900 and 2000, in conjunction with adecrease in pulsation period from 699 to 687 days. Such changes appearto be evolutionary in origin, representing a small contraction of thestar associated with a slight decrease in luminosity. Its evolutionarymass is estimated to be ~19 Msolar from its membership inBerkeley 87, a feature that also permits it to be used to test the Msupergiant period-luminosity relation.
| Variability in red supergiant stars: pulsations, long secondary periods and convection noise
We study the brightness variations of galactic red supergiant starsusing long-term visual light curves collected by the AmericanAssociation of Variable Star Observers over the last century. The fullsample contains 48 red semiregular or irregular variable stars, with amean time-span of observations of 61 yr. We determine periods and periodvariability from analyses of power density spectra and time-frequencydistributions. We find two significant periods in 18 stars. Most ofthese periods fall into two distinct groups, ranging from a few hundredto a few thousand days. Theoretical models imply fundamental, first andpossibly second overtone mode pulsations for the shorter periods.Periods greater than 1000 d form a parallel period-luminosity relationthat is similar to the long secondary periods of the asymptotic giantbranch stars. A number of individual power spectra shows a single moderesolved into multiple peaks under a Lorentzian envelope, which weinterpret as evidence for stochastic oscillations, presumably caused bythe interplay of convection and pulsations. We find a strong 1/f noisecomponent in the power spectra that is remarkably similar in almost allstars of the sample. This behaviour fits the picture of irregularphotometric variability caused by large convection cells, analogous tothe granulation background seen in the Sun.
| The Unusual Silicate Dust around HV 2310, an Evolved Star in the Large Magellanic Cloud
The spectrum of HV 2310, an evolved star in the Large Magellanic Cloud,taken with the Infrared Spectrograph (IRS) on the Spitzer SpaceTelescope, reveals the presence of an optically thin shell of silicatedust with unusual spectral structure in the 10 μm feature: anemission peak at 9.7 μm, a saddle at 10.4 μm, and an extendedshoulder to 11.2 μm. This structure is similar to spectra fromcrystalline silicate grains, and of the available optical constants,forsterite provides the best fit. The spectrum also shows structure at14 μm that may arise from an unidentified dust feature.
| The origin of brightness variations in BC Cygni.
Not Available
| 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.
| CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/431/773
| The Impact of Space Experiments on our Knowledge of the Physics of the Universe
With the advent of space experiments it was demonstrated that cosmicsources emit energy practically across all the electromagnetic spectrumvia different physical processes. Several physical quantities givewitness to these processes which usually are not stationary; thosephysical observable quantities are then generally variable. Thereforesimultaneous multifrequency observations are strictly necessary in orderto understand the actual behaviour of cosmic sources. Space experimentshave opened practically all the electromagnetic windows on the Universe.A discussion of the most important results coming from multifrequencyphotonic astrophysics experiments will provide new inputs for theadvance of the knowledge of the physics, very often in its more extremeconditions. A multitude of high quality data across practically thewhole electromagnetic spectrum came at the scientific community'sdisposal a few years after the beginning of the Space Era. With thesedata we are attempting to explain the physics governing the Universeand, moreover, its origin, which has been and still is a matter of thegreatest curiosity for humanity. In this paper we will try to describethe last steps of the investigation born with the advent of spaceexperiments, to note upon the most important results and open problemsstill existing, and to comment upon the perspectives we can reasonablyexpect. Once the idea of this paper was well accepted by ourselves, wehad the problem of how to plan the exposition. Indeed, the exposition ofthe results can be made in different ways, following several points ofview, according to: - a division in diffuse and discrete sources; -different classes of cosmic sources; - different spectral ranges, whichimplies in turn a sub-classification in accordance with differenttechniques of observations; - different physical emission mechanisms ofelectromagnetic radiation; - different vehicles used for launching theexperiments (aircraft, balloons, rockets, satellites, observatories). Inorder to exhaustively present The Impact of Space Experiments on ourKnowledge of the Physics of the Universe it would then have beennecessary to write a kind of Encyclopaedia of the Astronomical SpaceResearch, which is not our desire. On the contrary, since our goal is toprovide an useful tool for the reader who has not specialized in spaceastrophysics and for the students, we decided to write this paper in theform of a review, the length of which can be still consideredreasonable, taking into account the complexity of the argumentsdiscussed. Because of the impossibility of realizing a complete pictureof the physics governing the Universe, we were obliged to select how toproceed, the subjects to be discussed the more or the less, or those tobe rejected. Because this work was born in the Ph.D. thesis of one of us(LSG) (Sabau-Graziati, 1990) we decided to follow the `astronomicaltradition' used there, namely: the spectral energy ranges. Although suchenergy ranges do not determine physical objects (even if in many casessuch ranges are used to define the sources as: radio, infrared, optical,ultraviolet, X-ray, γ-ray emitters), they do determine themethods of study, and from the technical point of view they define thetechnology employed in the relative experiments. However, since then wehave decided to avoid a deep description of the experiments, satellites,and observatories, simply to grant a preference to the physical results,rather than to technologies, however fundamental for obtaining thoseresults. The exposition, after an introduction (Section 1) and somecrucial results from space astronomy (Section 2), has been focussed intothree parts: the physics of the diffuse cosmic sources deduced fromspace experiments (Section 3), the physics of cosmic rays from ground-and space-based experiments (Section 4), and the physics of discretecosmic sources deduced from space experiments (Section 5). In this firstpart of the paper we have used the logic of describing the main resultsobtained in different energy ranges, which in turn characterize theexperiments on board space vehicles. Within each energy range we havediscussed the contributions to the knowledge of various kind of cosmicsources coming from different experiments. And this part is mainlyderived by the bulk of the introductory part of LSG's Ph.D. thesis. Inthe second part of the paper, starting from Section 6, we have preferredto discuss several classes of cosmic sources independently of the energyranges, mainly focussing the results from a multifrequency point ofview, making a preference for the knowledge of the physics governing thewhole class. This was decided also because of the multitude of new spaceexperiments launched in the last fifteen years, which would haverendered almost impossible a discussion of the results divided intoenergy ranges without weakening the construction of the entire puzzle.We do not pretend to cover every aspect of every subject consideredunder the heading of the physics of the universe. Instead a crosssection of essays on historical, modern, and philosophical topics areoffered and combined with personal views into tricks of the spaceastrophysics trade. The reader is, then, invited to accept this papereven though it obviously lacks completeness and the arguments discussedare certainly biased by a selection effect owed essentially to ourknowledge, and to it being of a reasonable length. Some parts of itcould seem, in certain sense, to belong to an older paper, in which the`news' is not reported. But this is owed to our own choice, just in fullaccord with the goals of the text: we want to present those resultswhich have, in our opinion, been really important, in the development ofthe science. These impacting results do not necessarily constitute thelast news. This text was formally closed just on the day of the launchof the INTEGRAL satellite: October 17, 2002. After that date onlyfinishing touches have been added.
| The Power of Archival Astronomy
Examples are given of the extreme usefulness of the Harvard CollegeObservatory Photographic Plate Collection for the study of variablestars that possess only limited published observational data. Programobjects studied with the aid of archival photographic data include: (i)the eclipsing binary HD 174403, (ii) the semiregular variable BC Cygni,(iii) V439 Cygni, now recognized as a gamma Cassiopeiae variable, and(iv) the classical Cepheid T Antliae. In the Case of T Antliae, theplate archives yielded not only data for the star's brightnessvariations but also for the spectral characteristics of all starsbrighter than B = 12 in the field.
| Really Cool Stars and the Star Formation History at the Galactic Center
We present λ/Δλ=550-1200 near-infrared H and Kspectra for a magnitude-limited sample of 79 asymptotic giant branch andcool supergiant stars in the central ~5 pc (diameter) of the Galaxy. Weuse a set of similar spectra obtained for solar neighborhood stars withknown Teff and Mbol that is in the same range asthe Galactic center (GC) sample to derive Teff andMbol for the GC sample. We then construct the H-R diagram forthe GC sample. Using an automated maximum likelihood routine, we derivea coarse star formation history of the GC. We find that (1) roughly 75%of the stars formed in the central few parsecs are older than 5 Gyr; (2)the star formation rate (SFR) is variable over time, with a roughly 4times higher SFR in the last 100 Myr compared to the average SFR; (3)our model can match dynamical limits on the total mass of stars formedonly by limiting the initial mass function to masses above 0.7Msolar (this could be a signature of mass segregation or ofthe bias toward massive star formation from the unique star formationconditions in the GC); (4) blue supergiants account for 12% of the totalsample observed, and the ratio of red to blue supergiants is roughly1.5; and (5) models with isochrones with [Fe/H]=0.0 over all ages fitthe stars in our H-R diagram better than models with lower [Fe/H] in theoldest age bins, consistent with the finding of Ramírez et al.that stars with ages between 10 Myr and 1 Gyr have solar [Fe/H].
| Guilt by Association: The 13 Micron Dust Emission Feature and Its Correlation to Other Gas and Dust Features
A study of all full-scan spectra of optically thin oxygen-richcircumstellar dust shells in the database produced by the ShortWavelength Spectrometer on ISO reveals that the strength of severalinfrared spectral features correlates with the strength of the 13 μmdust feature. These correlated features include dust features at 19.8and 28.1 μm and the bands produced by warm carbon dioxide molecules(the strongest of which are at 13.9, 15.0, and 16.2 μm). The databasedoes not provide any evidence for a correlation of the 13 μm featurewith a dust feature at 32 μm, and it is more likely that a weakemission feature at 16.8 μm arises from carbon dioxide gas ratherthan dust. The correlated dust features at 13, 20, and 28 μm tend tobe stronger with respect to the total dust emission in semiregular andirregular variables associated with the asymptotic giant branch than inMira variables or supergiants. This family of dust features also tendsto be stronger in systems with lower infrared excesses and thus lowermass-loss rates. We hypothesize that the dust features arise fromcrystalline forms of alumina (13 μm) and silicates (20 and 28 μm).Based on observations with the ISO, a European Space Agency (ESA)project with instruments funded by ESA member states (especially thePrincipal Investigator countries: France, Germany, the Netherlands, andthe United Kingdom) and with the participation of the Institute of Spaceand Astronautical Science (ISAS) and the National Aeronautics and SpaceAdministration (NASA).
| MSX mid-infrared imaging of massive star birth environments - I. Ultracompact HII regions
We present mid-infrared 21-μm images of a sample of radio-selectedultracompact HII (UCHII) regions, obtained with the Midcourse SpaceExperiment (MSX). With one possible exception, all are detected atmid-infrared wavelengths, sampling the warm dust emission of the cocoonsof the OB star central exciting sources. Many of the UCHII regions havenearby (up to ~ few pc distant) companion dust emission sources, whichrepresent other potential star birth sites. In some objects thecompanion dominates the IRAS point source catalogue entry for the UCHIIregion. We compare the mid- and far-infrared dust emission, measuringthe embedded hot star luminosity, with published UCHII radio emission,measuring the Lyman continuum (LyC) luminosity. We find a spectral typedependence, as predicted by the standard model of an ultracompactionized hydrogen region, surrounded by a natal dust shell, with somescatter, which can be understood by consideration of (1) dust absorptionof some fraction of the emitted Lyman continuum photons; (2) faintercompanion stars within the UCHII region; and (3) the structure of theUCHII regions differing from star to star. Overall, the higher spatialresolution offered by MSX alleviates difficulties often encountered bycomparison of IRAS far-infrared fluxes with radio-derived ionizingfluxes for UCHII regions.
| How many Hipparcos Variability-Induced Movers are genuine binaries?
Hipparcos observations of some variable stars, and especially oflong-period (e.g. Mira) variables, reveal a motion of the photocentercorrelated with the brightness variation (variability-induced mover -VIM), suggesting the presence of a binary companion. A re-analysis ofthe Hipparcos photometric and astrometric data does not confirm the VIMsolution for 62 among the 288 VIM objects (21%) in the Hipparcoscatalogue. Most of these 288 VIMs are long-period (e.g. Mira) variables(LPV). The effect of a revised chromaticity correction, which accountsfor the color variations along the light cycle, was then investigated.It is based on ``instantaneous'' V-I color indices derived fromHipparcos and Tycho-2 epoch photometry. Among the 188 LPVs flagged asVIM in the Hipparcos catalogue, 89 (47%) are not confirmed as VIM afterthis improved chromaticity correction is applied. This dramatic decreasein the number of VIM solutions is not surprising, since the chromaticitycorrection applied by the Hipparcos reduction consortia was based on afixed V-I color. Astrophysical considerations lead us to adopt a morestringent criterion for accepting a VIM solution (first-kind risk of0.27% instead of 10% as in the Hipparcos catalogue). With this moresevere criterion, only 27 LPV stars remain VIM, thus rejecting 161 ofthe 188 (86%) of the LPVs defined as VIMs in the Hipparcos catalogue.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997).Table 1 is also available in electronic form at the CDS, via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/399/1167
| SiO Maser Survey of Cold IRAS Sources
We present the results of observations of cold IRAS sources in theGalactic disk area, -10° < l < 100° and |b| < 5°,in the SiO J = 1 -- 0, v = 1 and 2 maser lines. SiO masers were detectedin 51 out of 143 observed sources; 45 were new detections in SiO masers.The selected IRAS sources were objects with dust temperatures of between160 and 280K. According to a confirmation using 2MASS near-infraredimages, a majority of the sample are AGB or post-AGB stars, althoughdense cores in the star-forming regions (or dusty H II regions) are involved in part of the sample. Among newdetections, two were candidates for post-AGB stars: IRAS 18450 - 0148(W43A), and 19312 + 1950. We found that the intensity ratios of the SiOJ = 1 -- 0, v = 2 to the v = 1 line of the objects clearly correlatewith those IRAS colors. The detection rates of SiO masers tend toincrease toward the Galactic center as we ll as the cases of previousSiO maser surveys of typical AGB stars. No strong associations of theobjects to the spiral arms were found. The radial-velocity dispersion ofthe present sample is comparable with the dispersion of the SiO masersample of typical AGB stars. These facts suggest that the present sampleof cold IRAS sources with SiO masers has a kinematic property verysimilar to that of typical AGB stars.
| Hipparcos red stars in the HpV_T2 and V I_C systems
For Hipparcos M, S, and C spectral type stars, we provide calibratedinstantaneous (epoch) Cousins V - I color indices using newly derivedHpV_T2 photometry. Three new sets of ground-based Cousins V I data havebeen obtained for more than 170 carbon and red M giants. These datasetsin combination with the published sources of V I photometry served toobtain the calibration curves linking Hipparcos/Tycho Hp-V_T2 with theCousins V - I index. In total, 321 carbon stars and 4464 M- and S-typestars have new V - I indices. The standard error of the mean V - I isabout 0.1 mag or better down to Hp~9 although it deteriorates rapidly atfainter magnitudes. These V - I indices can be used to verify thepublished Hipparcos V - I color indices. Thus, we have identified ahandful of new cases where, instead of the real target, a random fieldstar has been observed. A considerable fraction of the DMSA/C and DMSA/Vsolutions for red stars appear not to be warranted. Most likely suchspurious solutions may originate from usage of a heavily biased color inthe astrometric processing.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997).}\fnmsep\thanks{Table 7 is onlyavailable 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/qcat?J/A+A/397/997
| CHARM: A Catalog of High Angular Resolution Measurements
The Catalog of High Angular Resolution Measurements (CHARM) includesmost of the measurements obtained by the techniques of lunaroccultations and long-baseline interferometry at visual and infraredwavelengths, which have appeared in the literature or have otherwisebeen made public until mid-2001. A total of 2432 measurements of 1625sources are included, along with extensive auxiliary information. Inparticular, visual and infrared photometry is included for almost allthe sources. This has been partly extracted from currently availablecatalogs, and partly obtained specifically for CHARM. The main aim is toprovide a compilation of sources which could be used as calibrators orfor science verification purposes by the new generation of largeground-based facilities such as the ESO Very Large Interferometer andthe Keck Interferometer. The Catalog is available in electronic form atthe 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/386/492, and from theauthors on CD-Rom.
| A Near-Infrared Survey of Radio-selected Ultracompact H II Regions
A near-infrared (NIR) survey of 63 radio-selected, ultracompact (UC) HII regions representing 47 different star-forming sites has beencompleted. The survey was obtained using H-band imaging andmoderate-resolution, R=1200, K-band spectroscopy, centered on the radioemission peak of the UC H II regions. The goal of this survey was todetermine the fraction of radio-selected UC H II regions that can bestudied with NIR observations and analysis. Approximately 50% of the 63radio-selected UC H II regions appear to be detected at NIR wavelengthsin Brγ emission (107 ergs s-1cm-2 sr-1). Typical line-of-sight extinctiontoward the detected UC H II regions ranged from AV=30 to 50,though one source was measured to have AV=80. For a few ofthese UC H II regions, the central ionizing sources are detected throughhigh signal-to-noise ratio NIR spectra of photospheric transitions. Thispreliminary survey suggests that perhaps 5%-10% of UC H II regionsshowing NIR counterparts will have directly detectable central ionizingsources. Using the ratio of He I 2.11 to Brγ, the effectivetemperatures of the central ionizing stars in 25 UC H II regions havebeen estimated. While He I is not always detected in UC H II regions,when it was found or a meaningful upper limit determined, the spectraltype implied by the ratio of He I 2.11 to Brγ closely matchedsimilar estimates of spectral type derived from radio. Model predictionsbased on mid-infrared measurements appear to underestimate thetemperature of the central ionizing stars for which we have directlydetected spectral types. The line ratios of H2 2-1 S(1) and1-0 S(0) relative to the 1-0 S(1) line in our sample of UC H II regionsare generally indicative of dense photodissociation regions rather thanshocks, similar to what is seen in the Orion Bar. This was true even forUC H II regions showing very weak Brγ emission. While Brγwas generally found to be spatially correlated with the radio emission,H2 showed little correlation with the UC H II regions,typically lying >~10" from the central radio emission. A discussionof each UC H II region studied is included in an extensive appendix.
| The impact of multifrequency observations on knowledge of the young open clusters: galactic gamma-ray and cosmic-ray contributors.
Not Available
| A Methyl Cyanide Search for the Earliest Stages of Massive Protostars
Forty-eight candidate massive protostar regions were surveyed for methylcyanide (CH3CN) emission using the Heinrich Hertz Telescope(HHT) on Mount Graham, AZ. CH3CN J=12-11 emission at 220 GHzwas detected toward 25 regions. Thirteen of these are new detections,yielding a substantial number of new candidates for massive protostars.The CH313CN (J=12-11) isotopomer was included inthe bandpass of all observed sources and was detected toward eightsources in our sample. These sources are probably optically thick insome of the CH3CN lines. CH3CN J=25-24 emission at460 GHz was detected in at least one K-component toward five of 11sources observed in this transition. Using a rotational equilibriumtemperature analysis we estimate the CH3CN rotationtemperatures and beam-averaged column densities for 20 of the sources.
| Near-infrared imaging of compact HII regions in Cygnus X
We present a near-infrared imaging survey of compact HII regions in thedirection of the Cygnus X complex, for which no previous observations atthose wavelengths have been published so far. The targets have beenselected from a catalog of sources in that region having a thermalspectral energy distribution between 408 and 4800 MHz (Wendker et al.1991), and an inferred angular size smaller than 5 arcmin across. Wepresent images in the JHK filters, color-magnitude, and color-colordiagrams for each region. We also suggest and apply a method forestimating the distance by comparing the dereddened H-band flux from allthe stars in the area of the HII region and the radio-continuum flux.Many of the regions imaged are clearly associated with stellaraggregates with different degrees of concentration, whose componentsshow varying amounts of extinction. Some objects are often found in theregion of the (J-H), (H-K) diagram indicating excess emission ofcircumstellar nature. A detailed discussion on each object is providedin the context of existing published observations at differentwavelengths, in particular regarding the existence of ultracompactcomponents. A number of ultracompact HII regions are found to haveclearly visible unresolved or nearly unresolved K-band counterpartscharacterized by very red H-K colors, suggesting that the extinction maybe low enough in their direction so as to allow the direct observationof the star ionizing the ultracompact component. Based on observationscollected at the Observatorio del Teide (Tenerife, Spain). The completeFig. 1 is available in electronic form at http://www.edpsciences.org andTable 2 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/375/539
| Speckle Interferometry of New and Problem Hipparcos Binaries. II. Observations Obtained in 1998-1999 from McDonald Observatory
The Hipparcos satellite made measurements of over 9734 known doublestars, 3406 new double stars, and 11,687 unresolved but possible doublestars. The high angular resolution afforded by speckle interferometrymakes it an efficient means to confirm these systems from the ground,which were first discovered from space. Because of its coverage of adifferent region of angular separation-magnitude difference(ρ-Δm) space, speckle interferometry also holds promise toascertain the duplicity of the unresolved Hipparcos ``problem'' stars.Presented are observations of 116 new Hipparcos double stars and 469Hipparcos ``problem stars,'' as well as 238 measures of other doublestars and 246 other high-quality nondetections. Included in these areobservations of double stars listed in the Tycho-2 Catalogue andpossible grid stars for the Space Interferometry Mission.
| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| Dust features in the 10-mu m infrared spectra of oxygen-rich evolved stars
We have analyzed the 8-13.5 mu m UKIRT CGS3 spectra of 142 M-type starsincluding 80 oxygen-rich AGB stars and 62 red supergiants, with a viewto understanding the differences and similarities between the dustfeatures of these stars. We have classified the spectra into groupsaccording to the observed appearance of the infrared features. In eachcase the normalized continuum-subtracted spectrum has been compared tothose of the other stars to find similarities and form groups. The dustfeatures of the AGB stars are classified into six groups: broad AGB,where the feature extends from 8 mu m to about 12.5 mu m with littlestructure; broad+sil AGB, which consists of a broad feature with anemerging 9.7 mu m silicate bump; and four silicate AGB groups in which a``classic'' 9.7 mu m silicate feature gets progressively narrower.Likewise, the supergiant spectra have also been classified into groups,however these do not all coincide with the AGB star groups. In thesupergiant case we again have six groups: featureless, where there islittle or no emission above the continuum; broad Super, where thefeature extends from about 9 mu m to about 13 mu m; and four silicateSuper groups, which again show a progression towards the narrowest``classic'' 9.7 mu m silicate feature. We compare the mean spectrum foreach group, which yields two main results. Firstly, while the``classic'' silicate feature is essentially identical for both AGB starsand red supergiants, the broad features observed for these two stellartypes are quite different. We suggest that the dust in these twoenvironments follows different evolutionary paths, with the dust aroundMira stars, whose broad feature spectra can be fit by a combination ofalumina (Al2O3) and magnesium silicate,progressing from this composition to dust dominated by magnesiumsilicate only, while the dust around supergiants, whose broad featurecan be fit by a combination of Ca-Al-rich silicate andAl2O3, progresses from this initial composition toone eventually also dominated by magnesium silicate. The reason for thedifference in the respective broad features is not clear as yet, butcould be influenced by lower C/O ratios and chromospheric UV radiationfields in supergiant outflow environments. The second result concernsthe 12.5 - 13.0 mu m feature discovered in IRAS LRS spectra and widelyattributed to Al2O3. This feature is seenpredominantly in the spectra of semiregular variables, sometime in Mirasand only once (so far) in supergiant spectra. We argue that it isunlikely that this feature is due to Al2O3 or, ashas more recently been suggested, spinel(MgAl2O4), but could be associated with silicondioxide or highly polymerized silicates (not pyroxenes or olivines).
| 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
| Observational investigation of mass loss of M supergiants
We present the analysis of infrared photometry and millimeterspectroscopy of a sample of 74 late-type supergiants. These observationsare particularly suitable to study the mass loss and the circumstellarenvelopes of evolved massive stars. In particular, we quantify thecircumstellar infrared excess, the relation of mass loss with stellarproperties, using the K-[12] colour index as mass-loss indicator. We donot find any clear correlation between mass loss rate and luminosity. Wealso show that the K-band magnitude is a simple luminosity indicator,because of the relative constancy of the K-band bolometric correction.Based on observations collected at the European Southern Observatory, LaSilla, Chile within program ESO 54.E-0914, and on observations collectedwith the IRAM 30m telescope. Tables A1 to A3 are only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| A survey of the 6.7 GHz methanol maser emission from IRAS sources. I. Data
We report the first results of a search for 6.7 GHz methanol masers inthe direction of 1399 IRAS objects north of declination-20deg with the flux densities greater than 100 Jy at 60 mu mand the flux density ratio F60/F25>1.Observations were made with the sensitivity of 1.7 Jy and the velocityresolution of 0.04 km s-1 using the 32-m Toruń radiotelescope. Maser emission was found in 182 sources, including 70 newdetections. 32 new sources were identified with objects of radioemission associated with star-forming regions. Comparison of the presentdata set with other observations suggests that about 65% of methanolmasers exhibit moderate or strong variations on time-scales of about 4and 8 years. 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/Abstract.html
| Old spectral type stars in young clusters.
Not Available
| Silicate and hydrocarbon emission from Galactic M supergiants
Following our discovery of unidentified infrared (UIR) band emission ina number of M supergiants in h and chi Per, we have obtained 10-μmspectra of a sample of 60 galactic M supergiants. Only three newsources, V1749 Cyg, UW Aql and IRC+40 427, appear to show the UIR bands;the others show the expected silicate emission or a featurelesscontinuum. The occurrence of UIR-band emission in M supergiants istherefore much higher in the h and chi Per cluster than in the Galaxy asa whole. Possible explanations for the origin and distribution of UIRbands in oxygen-rich supergiants are discussed. We use our spectra toderive mass-loss rates ranging from 10^-8 to 10^-4 M_solar yr^-1 for thenew sample, based on the power emitted in the silicate feature. Therelationship between mass-loss rate and luminosity for M supergiants isdiscussed, and correlations are explored between their mid-infraredemission properties.
| The Infrared Spectral Classification of Oxygen-rich Dust Shells
This paper presents infrared spectral classifications for a flux-limitedsample of 635 optically identified oxygen-rich variables includingsupergiants and sources on the asymptotic giant branch (AGB). Severalclasses of spectra from oxygen-rich dust exist, and these can bearranged in a smoothly varying sequence of spectral shapes known as thesilicate dust sequence. Classification based on this sequence revealsseveral dependencies of the dust emission on the properties of thecentral star. Nearly all S stars show broad emission features fromalumina dust, while most of the supergiants exhibit classic featuresfrom amorphous silicate dust. Mira variables with symmetric light curvesgenerally show broad alumina emission, while those with more asymmetriclight curves show classic silicate emission. These differences may arisefrom differences in the photospheric C/O ratio.
| V 439 Cyg: the smallest LBV?
The emission line star V 439 Cyg (MWC 1015) dramatically changed itsspectrum from late to early type in a few decades with line variabilitypresent at various levels. The star is a member of the peculiar youngopen cluster Berkeley 87 that contains, besides V 439 Cyg, a fewpeculiar objects in a late stage of stellar evolution. A strong IRsource is associated with the region surrounding V 439 Cyg. The star hasa peculiar position in the cluster HR diagram possibly due to anomalousreddening. We have analysed a collection of historical observations andcollected new spectroscopic and photometric data on this unique object.We find several indications suggesting that the star has passed, in thelast decades, through an instability phase with several features of theLBV behaviour. We suggest that its spectral change could be accountedfor in the light of recent stellar models. Based on data collected atthe Bologna Astronomical Observatory, Loiano (Italy); TelescopioInfraRosso Italiano al Gornergrat (TIRGO), Gornergrat (Switzerland);Juan Sanchez Telescope (JST) and INT (Canary Inslands), SharruObservatory, Covo (Italy) and on archive plates from the OHP
|
הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
|
תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | ברבור |
| התרוממות ימנית: | 20h21m38.55s |
| סירוב: | +37°31'59.0" |
| גודל גלוי: | 9.239 |
| מרחק: | 352.113 פארסק |
| תנועה נכונה: | -2.5 |
| תנועה נכונה: | 1.1 |
| B-T magnitude: | 13.114 |
| V-T magnitude: | 9.559 |
קטלוגים וכינוים:
|
INHABITED SKY
