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Radio study on the mass loss bi-stability jump
By means of radio continuum observations of 29 stars with spectral typesO8-B3 we searched for evidence of the existence of a bi-stability jumpin stellar mass loss around T_{eff} ≈ 21 kK. Although there arequantitative discrepancies, the qualitative behaviour of the windefficiency with effective temperature appears to be in line withtheoretical predictions. Observations of new cases are fundamental toconfirm these results.
| H+3 in Diffuse Interstellar Clouds: A Tracer for the Cosmic-Ray Ionization Rate
Using high-resolution infrared spectroscopy we have surveyed twentysight lines for H+3 absorption.H+3 is detected in eight diffuse cloud sight lineswith column densities varying from 0.6×1014 to3.9×1014 cm-2. This brings to 14 the totalnumber of diffuse cloud sight lines where H+3 hasbeen detected. These detections are mostly along sight linesconcentrated in the Galactic plane but are well dispersed in Galacticlongitude. The results imply that abundant H+3 iscommon in the diffuse interstellar medium. Because of the simplechemistry associated with H+3 production anddestruction, these column density measurements can be used in concertwith various other data to infer the primary cosmic-ray ionization rate,ζp. Values range from 0.5×10-16 to3×10-16 s-1 with an average of2×10-16 s-1. Where H+3is not detected, the upper limits on the ionization rate are consistentwith this range. The average value of ζp is about 1order of magnitude larger than both the canonical rate and ratespreviously reported by other groups using measurements of OH and HD. Thediscrepancy is most likely due to inaccurate measurements of rateconstants and the omission of effects which were unknown when thosestudies were performed. We believe that the observed column density ofH+3 is the most direct tracer for the cosmic-rayionization rate due to its simple chemistry. Recent models of diffusecloud chemistry require cosmic-ray ionization rates on the order of10-16 s-1 to reproduce observed abundances ofvarious atomic and molecular species, in rough accord with ourobservational findings.
| Testing the predicted mass-loss bi-stability jump at radio wavelengths
Context: Massive stars play a dominant role in the Universe, but one ofthe main drivers for their evolution, their mass loss, remains poorlyunderstood. Aims: In this study, we test the theoretically predictedmass-loss behaviour as a function of stellar effective temperatureacross the so-called “bi-stability” jump. Methods: Weobserve OB supergiants in the spectral range O8-B3 at radio wavelengthsto measure their thermal radio flux densities, and complement thesemeasurements with data from the literature. We derive the radiomass-loss rates and wind efficiencies, and compare our results withHα mass-loss rates and predictions based on radiation-driven windmodels. Results: The wind efficiency shows the possible presence of alocal maximum around an effective temperature of 21 000 K - inqualitative agreement with predictions. Furthermore, we find that theabsolute values of the radio mass-loss rates show good agreement withempirical Hα rates derived assuming homogeneous winds - for thespectral range under consideration. However, the empirical mass-lossrates are larger (by a factor of a few) than the predicted rates fromradiation-driven wind theory for objects above the bi-stability jump(BSJ) temperature, whilst they are smaller (by a factor of a few) forstars below the BSJ temperature. The reason for these discrepanciesremains as yet unresolved. A new wind momenta-luminosity relation (WLR)for O8-B0 stars has been derived using the radio observations. Thevalidity of the WLR as a function of the fitting parameter related tothe force multiplier α_eff (Kudritzki & Puls, 2000, ARA&A,629) is discussed. Conclusions: Our most interesting finding is thatthe qualitative behaviour of the empirical wind efficiencies witheffective temperature is in line with the predicted behaviour, and thispresents the first hint of empirical evidence for the predictedmass-loss bi-stability jump. However, a larger sample of stars aroundthe BSJ needs to be observed to confirm this finding.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| LS 5039: A runaway microquasar ejected from the galactic plane
We have compiled optical and radio astrometric data of the microquasarLS 5039 and derived its proper motion. This, togetherwith the distance and radial velocity of the system, allows us to statethat this source is escaping from its own regional standard of rest,with a total systemic velocity of about 150 km s-1 and acomponent perpendicular to the galactic plane larger than 100 kms-1. This is probably the result of an acceleration obtainedduring the supernova event that created the compact object in thisbinary system. We have computed the trajectory of LS5039 in the past, and searched for OB associations andsupernova remnants in its path. In particular, we have studied thepossible association between LS 5039 and thesupernova remnant G016.8-01.1, which, despite ourefforts, remains dubious. We have also discovered and studied an H Icavity in the ISM, which could have been created by the stellar wind ofLS 5039 or by the progenitor of the compact object inthe system. Finally, in the symmetric supernova explosion scenario, weestimate that at least 17 Msun were lost in order to producethe high eccentricity observed. Such a mass loss could also explain theobserved runaway velocity of the microquasar.
| X-ray observations of classical and recurrent novae.
X-ray observations of classical and recurrent novae at different stagesafter the outburst are reviewed. The author introduces the threemechanisms of X-ray emission, presents some observations done with ROSATand SAX, and discusses the results of a survey of ROSAT serendipitousobservations of 50 novae.
| Evolutionary sequences for Nova V1974 Cygni using new nuclear reaction rates and opacities
The outburst of Nova V1974 Cyg 1992 is arguably the best observed ofthis century, with realistic estimates now available for the amount ofmass ejected, the composition of the ejecta and the total energy budget.These data strongly support the conclusion that this was indeed a `neon'nova that occurred on an oxygen, neon, magnesium white dwarf. Inaddition, X-ray studies of its outburst imply that the mass of the whitedwarf is about 1.25Msolar. We, therefore, report on the results of newcalculations of thermonuclear runaways on 1.25-Msolar oxygen, neon,magnesium white dwarfs, using our one-dimensional, fully implicit,hydrodynamic stellar evolution code that includes a large nuclearreaction network. We have updated the nuclear reaction network, with theinclusion of new and improved experimental and theoreticaldeterminations of the nuclear reaction rates. We have also incorporatedthe OPAL carbon rich tables and have investigated the effects of changesin convective efficiency on the evolution. Our results show that thechanges in the reaction rates and opacities that we have introducedproduce important changes with respect to our previous studies. Forexample, relevant to nucleosynthesis considerations, a smaller amount of^26Al is produced, while the abundances of ^31P and ^32S increase byfactors of more than two. This change is attributed to the increasedproton-capture reaction rates for some of the intermediate mass nucleinear ^26Al and beyond, such that nuclear fusion to higher mass nuclei isenhanced. The characteristics of our models are then compared toobservations of the outburst of V1974 Cyg 1992 and we find that thepredicted amount of mass ejected is at least a factor of 10 less thanobserved. The low values for the amount of ejected mass are aconsequence of the fact that the OPAL opacities are larger than those wepreviously used, which results in less mass being accreted on to thewhite dwarf. This is a general problem with respect to the comparison ofobservations and theory for ONeMg novae and we suggest a possibleresolution of this discrepancy.
| 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.
| UV turn-off times of classical novae
We present IUE spectra of classical novae obtained at least one yearafter the outburst. The UV luminosities are compared with the ROSAT\observations and significant parameters of the systems. The turn-offtimes derived from the IUE data are in agreement with the ROSAT\results, showing that most novae decline in bolometric luminosity 1-5years after the outburst. This is a signal of the exhaustion of the fuelin the hydrogen-burning layer on top of the white dwarf. There is notany clear dependence of the turn-off time on the speed class, thechemical composition or other parameters of the system. Data indicatethat only a small fraction of the accreted layer is left on the whitedwarf after the outburst. Based on observations made with theInternational Ultraviolet Explorer collected at the VillafrancaSatellite Tracking Station and de-archived from the ESA-VILSPA Database.
| Radio observations of stellar winds from early type stars
Fifteen O and B supergiants have been observed with the Very Large Array(VLA) at 4.85, 8.45, and 14.95 GHz in order to make a detailedcomparative study of the mass loss rates evaluated from Hα andradio continuum observations and reveal and quantify possible departuresfrom standard wind conditions. We detected 12 sources, 7 of which forthe first time, thus increasing by 30% the total number of detections ofOB supergiants in the northern sky. Radio spectral slopes indicate thatthe radio emission is mainly of thermal origin in all objects with oneexception (HD 190603) out of the 12 detections. Our results demonstratethe value of using Hα for mass loss rate determinations,especially for stars that are too distant or too faint to be detectedwith radio techniques. The relationship dot {M} - L for supergiantsturns out to be appreciably flatter than commonly reported, i.e. log{dot {M}} =3D (1.25\pmm0.30) log {L}. Based on observations with theVery Large Array. The VLA is a facility of the National Radio AstronomyObservatory which is operated by the Associated Universities Inc. undercooperative agreement with the National Science Foundation.
| The yellow hypergiants
We list the main stellar data of known hypergiants and similarlyluminous stars, and then concentrate on a review of the yellowhypergiants. These stars are post-red supergiants evolving alongblueward loops in the Hertzsprung-Russell diagram. Their properties,their location in the Hertzsprung-Russell diagram and their occasionalmass ejections are related to a region of atmospheric instability in theH-R diagram, the Yellow Void. The `bouncing against the border of theVoid' of three objects: ρ Cas, HR8752 and IRC+10420, is described.The apparent atmospheric instability of yellow hypergiants is related tothe atmospheric pulsations. There are indications that the approach tothe Void is associated with an increased amplitude of the pulsation andwith enhanced mass loss. The observed small-scale motion field is onlyapparently strongly supersonic; the observed large stochastic velocitiesare the quasi-stochastically varying thermal motions in the many hotsheets that occur in the wakes of many small shocks, while the realhydrodynamic velocity component is small and subsonic. This shock-wavefield is also responsible for the observed rate of mass loss and foremission in the wings of Hα . Most yellow hypergiants haveenvelopes containing gas and dust, but a thick extended envelope,presumably dissipating and showing bipolar outflow, is only known aroundIRC+10420. At the interface of the bipolar wind and the interstellarmedium one or more stationary shocks may develop as is observed in thecase of IRC+10420 and suspected with ρ Cas.
| 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.
| H-beta Photometry of Southern Luminous Stars
H-beta photometry for 116 stars listed in Stephenson and Sanduleak's(1971) catalog of _Luminous Stars in the Southern Milky Way_ isreported. The vast majority of these objects are O and B-type stars; afew are A, F, or Wolf-Rayet stars. A systematic difference of on theorder of 30 mmag between the present results and those of otherinvestigators is noted. (SECTION: Stars)
| Stroemgren and H beta photometry of OB stars in Serpens
Stroemgren and H beta photometry of 25 stars in the field of Serpens arepresented. The excesses, the absolute magnitude and the temperatures ofthe stars are obtained. The masses and the ages are also estimated.
| Millimetre observations of southern translucent clouds
Millimetre emission line observations of ^12^CO J=1-0 are presented fora sample of translucent molecular clouds previously studied by opticalabsorption lines towards background stars. The CO maps provideinformation on the extent, structure, mass and kinematics of theregions. In some clouds, the emission is characterized by a singlecomponent which does not vary much across the region. In other cases,multiple close-lying components or sheets are found, which may vary in aself-similar manner across the cloud. None of the clouds is close tosimple virial equilibrium. Sensitive searches for ^13^CO and C^18^OJ=1-0 emission have been made towards the stellar positions. C^18^O hasbeen detected in only 5 clouds, most of which have extinctions well inexcess of 2 mag. The inferred ^13^CO/C^18^O abundance ratios range from7-25, and the lower limits from >13 to >35. These values are asmuch as five times larger than the overall interstellar([^13^C].[^16^O])/([^12^C] .[^18^O]) ratio, suggesting thatisotope-selective photodissociation plays a role in at least some of theclouds. Searches for other molecules at millimetre wavelengths have beenmade for a few of the best characterized clouds. Surprisingly, noemission was detected from the C_2_H or C_3_H_2_ molecules, even thoughthe abundances of diatomic C_2_ and CH are quite large. On the otherhand, the abundance of HCO^+^ appears comparable to that found in denserclouds, and the abundance of HCN may be up to an order of magnitudelarger than the predictions of models in two clouds.
| 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.
| The abundance of CH(+) in translucent molecular clouds - Further tests of shock models
Observations of interstellar absorption lines of CH(+) in the (0, 0) and(1, 0) bands of the A 1Pi - X 1Sigma(+) system are presented for 17stars with reddenings up to E(B-V) about 1.5 mag. Complementary data oninterstellar CH in the (0, 0) bands of the A 2Delta - X 2Pi and B2Sigma(-) - X 2Pi systems and C2 in the A 1Pi(u) - X 1Sigma(g)(+) redsystem have been obtained as well. The derived CH(+) column densitiescontinue to increase with total column density, and values up to 10 exp14/sq cm are reported for highly-reddened lines of sight. In most cases,the CH(+) and CH absorptions are dominated by a single strong component,with weaker features displaced by a few km/s. No significant velocitydifference is found between CH(+) and neutral species such as CH and CNfor this sample of randomly oriented lines of sight. In contrast withCN, the CH(+) abundance does not increase with the density in the cloudas derived from the observed C2 excitation. For the two clouds with thelargest density, HD 62542 and HD 94413, no CH(+) absorption is foundwith CH(+)/CH less than 0.03 and 0.14, respectively. The CH(+) findingsdo not support a single-shock origin for the formation of the ion.
| A study of reddened luminous stars in the southern Milky Way. IV. JHK photometry.
Not Available
| A study of reddened luminous stars in the southern Milky Way. III. VRI photometry.
Not Available
| A study of reddened luminous stars in the southern Milky Way. II. H-beta photometry, reddening and distances.
Not Available
| A study of reddened luminous stars in the southern Milky Way. UVBY photometry.
Not Available
| High-velocity interstellar gas toward HD 169454
The interstellar spectrum of HD 169454 reveals Na D and Ca K absorptionat about + 100 km/s. Measurements made at high resolution resolve 4narrow (about 2-3 km/s) features whose N(Ca II)/N(Na I) ratios aresmall. This high-velocity gas is, therefore, unique in that it resembleslocal quiescent gas, not shocked gas. Redshifted gas is also seen inmoderate-resolution spectra of faint stars lying in the same portion ofthe sky as HD 169454. The resulting picture is one in which a supernovaexplosion or stellar winds within the Sct OB3 association at a distanceof about 1.5 kpc is pushing quiescent gas away from the sun. The gas isseen only in stars estimated to be at most 3 kpc, but greater than 2kpc, away. If HD 169454 is at this greater distance, its absolutemagnitude would be about -9, making it the second most luminous B starin the Galaxy.
| A multi-wavelength analysis of interstellar CN - Comparison of red and violet absorption line observations
New measurements of interstellar CN in translucent molecular clouds arepresented. The CN is observed by optical absorption lines in both the B2Sigma(+) violet and A 2Pi - X 2Sigma(+) red systems and through the N =1-0 emission lines at 113.491 GHz. It is shown how the unsaturated linesof the red system can be used to determine the Doppler parameter b andthus to assess the saturation corrections in the analysis of thestronger lines of the violet system. In all cases, the Doppler parameteris small, b less than about 1 km/s, and agrees well with the velocitydispersion obtained from (C-13)O millimeter emission of lines in thesame direction but averaged over a different volume of gas.
| Has interstellar forbidden Fe X been detected in the spectrum of SN 1987 A?
The detection of forbidden Fe X is found to be inconsistent with the lowlevels of diffuse X-ray flux identified with the Einstein and RosatX-ray satellites. The observed line can be interpreted as the slightlyredshifted wavelength 6379.3 of the diffuse interstellar band, in whichcase the velocity would equal that of the strong interstellar atomiclines in the spectrum of SN 1987 A. The unique feature is interpreted tobe evidence of variations in the ratios of interstellar lines forabsorbing clouds.
| UBV photometry of OB+ stars in the southern Milky Way
One thousand two hundred and twenty six new observations are combinedwith previously published results of the author to yield an internalyconsistent set of magnitudes and colors on the international UBV systemfor 666 stars classified as OB+ in the Stephenson-Sanduleak OB starsurvey. The U - B, B - V diagram indicates that these stars consistprimarily of O-type stars and early B-type supergiants, reddened by upto E(B - V) = 2.1 mag.
| CO J = 3-2 observations of translucent and high-latitude molecular clouds
Measurements were carried out on the CO J = 3-2 emission line at 345 GHzfrom a number of translucent and high-latitude molecular clouds, as wellas on the J = 2-1 and J = 1-0 lines of both the (C-12)O and (C-13)O. Itis shown that the physical conditions in the high-latitude clouds arevery similar to those in the translucent clouds. The densities derivedfrom measured (C-12)O 1-0/3-2 ratios were often found to be higher thanthose based on the C2 excitation, while densities derived from measured3-2/(C-13)O 1-0 ratios were similar to those based on C2.
| Interstellar C2, CH, and CN in translucent molecular clouds
Optical absorption-line techniques have been applied to the study of anumber of translucent molecular clouds in which the total columndensities are large enough that substantial molecular abundances can bemaintained. Results are presented for a survey of absorption lines ofinterstellar C2, CH, and CN. Detections of CN through the A 2Pi-X2Sigma(+) (1,O) and (2,O) bands of the red system are reported andcompared with observations of the violet system for one line of sight.The population distributions in C2 provide diagnostic information ontemperature and density. The measured column densities of the threespecies can be used to test details of the theory of molecule formationin clouds where photoprocesses still play a significant role. The C2 andCH column densities are strongly correlated with each other and probablyalso with the H2 column density. In contrast, the CN column densitiesare found to vary greatly from cloud to cloud. The observations arediscussed with reference to detailed theoretical models.
| The maximum amplitude of the optical micro-variations of massive O-F type stars (or Alpha Cygni variables, including LBV's or S DOR variables) across the HR diagram
The maximum light amplitude (MLA) of the microvariations of nearly 100massive stars with spectral type O 3-F8 are collected from theliterature and unpublished material. These variables, called the AlphaCygni variables, also include the LBVs or S Dor type variables. The SDor type variables must be in a quiescent stage to detect theirintrinsic variations properly. The log T(eff)/MLA diagram exhibits aclear separation between S Dor type variables and the normal Alpha Cygnivariables (the majority). The results suggest that the outer layers ofboth types of stars where gravity waves presumably occur, differphysically from each other.
| Mass loss from stars : the universal formula for mass loss rate
Not Available
| Miscellaneous spectroscopic notes
Results of slit-spectrograph observations are reported for approximately260 stars. The data presented range from recognition of many new Ap, Am,and other unusual stars to H-alpha observations of early-typesupergiants and Be stars. The material discussed was obtained over thepast 40 years at a number of U.S. observatories and at the DominionAstrophysical Observatory in Victoria, B.C.
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Osservazione e dati astrometrici
| Costellazione: | Scudo |
| Ascensione retta: | 18h25m06.18s |
| Declinazione: | -14°38'57.7" |
| Magnitudine apparente: | 8.328 |
| Distanza: | 625 parsec |
| Moto proprio RA: | 0.9 |
| Moto proprio Dec: | -4.1 |
| B-T magnitude: | 9.824 |
| V-T magnitude: | 8.452 |
Cataloghi e designazioni:
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