Beobachtungssergebnisse Bundesdeutsche Arbeitsgemeinschaft fuer Veraenderliche Sterne e.V.
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Secular Evolution in Mira Variable Pulsations
Stellar evolution theory predicts that asymptotic giant branch (AGB)stars undergo a series of short thermal pulses that significantly changetheir luminosity and mass on timescales of hundreds to thousands ofyears. These pulses are confirmed observationally by the existence ofthe short-lived radioisotope technetium in the spectra of some of thesestars, but other observational consequences of thermal pulses are subtleand may only be detected over many years of observations. Secularchanges in these stars resulting from thermal pulses can be detected asmeasurable changes in period if the star is undergoing Mira pulsations.It is known that a small fraction of Mira variables exhibit largesecular period changes, and the detection of these changes among alarger sample of stars could therefore be useful in evolutionary studiesof these stars. The American Association of Variable Star Observers(AAVSO) International Database currently contains visual data for over1500 Mira variables. Light curves for these stars span nearly a centuryin some cases, making it possible to study the secular evolution of thepulsation behavior on these timescales. In this paper we present theresults of our study of period change in 547 Mira variables using datafrom the AAVSO. We use wavelet analysis to measure the period changes inindividual Mira stars over the span of available data. By making linearfits to the period versus time measurements, we determine the averagerates of period change, dlnP/dt, for each of these stars. We findnonzero dlnP/dt at the 2 σ significance level in 57 of the 547stars, at the 3 σ level in 21 stars, and at the level of 6 σor greater in eight stars. The latter eight stars have been previouslynoted in the literature, and our derived rates of period change largelyagree with published values. The largest and most statisticallysignificant dlnP/dt are consistent with the rates of period changeexpected during thermal pulses on the AGB. A number of other starsexhibit nonmonotonic period change on decades-long timescales, the causeof which is not yet known. In the majority of stars, the periodvariations are smaller than our detection threshold, meaning theavailable data are not sufficient to unambiguously measure slowevolutionary changes in the pulsation period. It is unlikely that morestars with large period changes will be found among heretoforewell-observed Mira stars in the short term, but continued monitoring ofthese and other Mira stars may reveal new and serendipitous candidatesin the future.
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Mira kinematics from Hipparcos data: a Galactic bar to beyond the Solar circle
The space motions of Mira variables are derived from radial velocities,Hipparcos proper motions and a period-luminosity relation. Thepreviously known dependence of Mira kinematics on the period ofpulsation is confirmed and refined. In addition, it is found that Miraswith periods in the range 145-200d in the general Solar neighbourhoodhave a net radial outward motion from the Galactic Centre of75+/-18kms-1. This, together with a lag behind the circularvelocity of Galactic rotation of 98+/-19kms-1, is interpretedas evidence for an elongation of their orbits, with their major axesaligned at an angle of ~17° with the Sun-Galactic Centre line,towards positive Galactic longitudes. This concentration seems to be acontinuation to the Solar circle and beyond of the bar-like structure ofthe Galactic bulge, with the orbits of some local Miras probablypenetrating into the bulge. These conclusions are not sensitive to thedistance scale adopted. A further analysis is given of the short-period(SP) red group of Miras discussed in companion papers in this series. InAppendix A the mean radial velocities and other data for 842 oxygen-richMira-like variables are tabulated. These velocities were derived frompublished optical and radio observations.
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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.
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Classification and Identification of IRAS Sources with Low-Resolution Spectra
IRAS low-resolution spectra were extracted for 11,224 IRAS sources.These spectra were classified into astrophysical classes, based on thepresence of emission and absorption features and on the shape of thecontinuum. Counterparts of these IRAS sources in existing optical andinfrared catalogs are identified, and their optical spectral types arelisted if they are known. The correlations between thephotospheric/optical and circumstellar/infrared classification arediscussed.
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Water Masers Associated with Circumstellar Shells
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..106..579B&db_key=AST
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SiO Maser Survey of Late-Type Stars. II. Statistical Study
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111.1987C&db_key=AST
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SiO maser survey of late-type stars. I. Simultaneous observations of six transitions of ^28^SiO and ^29^SiO.
Simultaneous observations of the ^28^SiO v=0, 1, 2, and 3, J=1-0 and^29^SiO v=0 and 1, J=1-0 transitions for 102 late-type stars were madewith a sensitivity of about 2Jy at the 3σ level using the 45 mtelescope of Nobeyama Radio Observatory (NRO). SiO maser emission wasdetected in 83 stars; seven of them being new detections. The v=3 maserwas detected in 12 stars with eight new detections. Most of the v=3masers occur at the same radial velocity of the strongest spikes of thev=1 and 2 masers. We also newly found the ^29^SiO v=0 maser in sixstars. The ^29^SiO v=0 line is stronger and narrower than the ^28^SiOv=0 line, indicating that the ^29^SiO line is masing. In most cases, the^29^SiO line shows a single narrow profile (FWHM=1 to 3km/s), with peakradial velocities coincident with the stellar velocity derived from OHmaser and/or SiO/CO thermal lines within 1km/s. Therefore, this maserline provides excellent means to measure the stellar velocities oflate-type stars. The ^28^SiO v=0, J=1-0 line was detected in elevenstars, with three new detections.
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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.
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Mainline OH detection rates from blue circumstellar shells.
We identified 240 accessible circumstellar shells with water and/or SiOmasers, and used the Arecibo and Nancay radio telescopes to search formainline OH emission from them. Our targets are often Mira variableswithout previously known mainline masers. This search results in 89detections, of which 77 are new. The probability of detecting a maser islarger once a water maser is known, and becomes progressively larger thethicker and redder the shell. Nevertheless, almost all of our examplesof solitary 1665MHz masers, rather than the joint occurrence of both1665 and 1667MHz masers, are in the bluest shells. The IRAS lowresolution spectral type is the strongest factor correlating with themainline detection rate. We find that 67% of objects with a silicateemission feature exhibit masers, whereas only 27% of objects with acomparatively featureless 1n type do. These rates are colourinsensitive. We ascribe this clearcut difference to differing UVextinction properties of the two grain types, which is likely to resultfrom differing grain-size distributions. The IR colour sensitivity ofthe overall mainline detection rate is thus almost entirely anincidental artifact of the changing proportion of the two grain typeswith colour. Inferentially, since 90% of the sample exhibit watermasers, and the proportion of blue sources with silicate features issubstantially larger than an unbiased selection from the IRAS PointSource Catalog would give, the incidence of water masers is similarlysensitive to spectral type.
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Supplement to the Arecibo 1612 MHz survey of color-selected IRAS sources
The completeness of the Arecibo 1612 MHz survey of color-selected IRASsources is extended to (25-12) micrometer greater than -0.7. In addition(1) most IR sources with spectral types normally associated with OH/IRstars and colors outside the coverage of the original survey have beenexamined; (2) most ambiguous observations during the survey have beenreobserved; (3) most single peaked sources have been reexamined, and 17found with second peaks. We report 39 new 1612 MHz detections, of which34 are original. These are also surveyed in the mainlines. Analysis ofthe complete flux-limited survey confirms the existence of a longitudesensitivity effect in the detection of sources, which reduces the totalnumber detected by approximately equals 4%. This analysis sets an upperlimit of 16% on the proportion of a color-selected sample that may beidentified with carbon stars and/or star-formation regions.
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Short- and intermediate-period oxygen-rich Miras
Available IR photometry and the period-IR luminosity relationship areused to analyze a nearly complete sample of oxygen-rich Miras atGalactic latitudes with /b/ greater than 30 deg. In agreement withprevious kinematic studies, a marked difference is found in the spatialdistributions between the stars with periods less than and those withperiods greater than 300 d. For stars with periods in the range 300-400d, the exponential scale height from the Galactic plane is close to 240pc, the projected surface density is about 100/sq kpc, and the localspace density is about 210/cu kpc. The progenitors of the Miras withperiods greater than 300 d appear to be disk dwarfs with typicalmain-sequence masses of between 1.0 and 1.2 solar masses. The masses ofthe main-sequence progenitors of the short-period Miras are 1.1 solarmasses or less. The duration of the Mira phase for theintermediate-period stars is estimated to be about 20,000 yr, somewhatlonger than other recent estimates. Both short- and intermediate-periodoxygen-rich Miras characteristically lose mass at about 10 exp -7 solarmass/yr.
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Emission features in IRAS LRS spectra of M Mira variables
A total of 291 M Mira variables with IRAS low-resolution spectrometer(LRS) spectra that have 8-micron fluxes greater than 15 Jy have beenanalyzed. After subtraction of a 2500 K blackbody energy distributionfrom the spectrum, the remaining difference spectra can be classifiedinto seven groups, depending on the shape of their spectral emissionfeatures around 10 microns: Sil, Sil(+) Sil(2+), S, three-component,'broad', and no feature. The spectral emission features are interpretedas being produced primarily by amorphous silicates with differingamounts of crystalline olivine. A weak broad feature at 9-13 microns ispossibly produced by aluminum oxide and/or a size distribution ofsilicate particles that favors larger grains. The 8-22-micron IR excess,defined as the fraction of energy above the 2500 K continuum, shows onlya slight tendency to correlate with period and no tendency to correlatewith mass loss rate. Maser emission from OH and H2O is much morefrequently detected in stars that show the Sil or Sil(+) emissionfeature, but SiO maser emission is detected with the same percentage inall emission feature classes with the exception of the S feature. Starsshowing the S feature appear to be closely related to the MS and Sstars.
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Criteria for OH maser emission from circumstellar envelopes of oxygen-rich Mira-type red giants
A large and representative sample of oxygen-rich Mira stars was selectedand observed in the 18 cm OH lines at their optical maximum. A total of14 new OH sources were detected. The OH maser emission is found in theintrinsically bright far-IR objects with late M spectral type. Othercharacteristics of the Miras are high (H-K) and (K-L) colors. Theirperiods are on average longer and their (25-12) colors on average redderthan those of non-OH Miras. The (J-H) and (60-25) colors are the samefor OH and non-OH stars. In most cases, OH and H2O masers existsimultaneously. The observed stars form a sequence along which theperiod and the stellar luminosity increase, the stellar radiusincreases, the dust shell radius increases by a smaller factor, thephotospheric temperature decreases but the dust shell temperature isroughly constant, and the mass loss rate and thus the thickness and thebrighntess of the envelope increase considerably.
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Additional late-type stars with technetium
The results of a survey of 279 late-type giants and supergiants for thespectral lines of the radioactive element technetium (Tc I) at 4297,4262, and 4238 A are presented. The following conclusions are reached:(1) the presence of Tc correlates very strongly with the existence oflight variability; (2) evolutionary MS stars show Tc and spectroscopicMS stars do not show Tc; (3) single S stars show Tc; (4) SC stars showTc; (5) about 75 percent of the C stars show Tc; and (6) Ba II stars donot show Tc. The findings are compatible with predictions from stellarevolution theory.
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IRAS catalogues and atlases - Atlas of low-resolution spectra
Plots of all 5425 spectra in the IRAS catalogue of low-resolutionspectra are presented. The catalogue contains the average spectra ofmost IRAS poiont sources with 12 micron flux densities above 10 Jy.
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The brightest high-latitude 12-micron IRAS sources
The Infrared Astronomical Satellite (IRAS) Point Source catalog wassearched for sources brighter than 28 Jy (0 mag) at 12 microns withabsolute galactic latitude greater than 30 deg excluding the LargeMagellanic Cloud. The search resulted in 269 sources, two of which arethe galaxies NGC 1068 and M82. The remaining 267 sources are identifiedwith, or have infrared color indices consistent with late-type starssome of which show evidence of circumstellar dust shells. Seven sourcesare previously uncataloged stars. K and M stars without circumstellardust shells, M stars with circumstellar dust shells, and carbon starsoccupy well-defined regions of infrared color-color diagrams.
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First observations with the Effelsberg Radio Telescope at 7-mm wavelength. II - A survey of stars in the vibrationally excited J equals 1-0 SiO lines
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1981AJ.....86..392S&db_key=AST
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A low-detection limit search for OH emission from infrared stars
We have used the 300 m telescope of the Arecibo Observatory to examine154 cool luminous stars for 18 cm OH emission. Six of the stars (RU Ari,R Com, T Com, RX Oph, UU Peg, and RT Vir) were found to show OHemission. For the stars without OH emission, we have establisheddetection limits several times smaller than those of previous surveys.
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Revised Catalog of Spectra of Mira Variables of Types ME and Se
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974ApJS...28..271K&db_key=AST
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New OH sources associated with IR-late-type stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972A&A....21..317F&db_key=AST
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Characteristics of OH emission from infrared stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972A&A....17..385W&db_key=AST
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Proper motions of long-period variable Stars. II
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A Catalogue of Spectra of Mira Variables of Types ME and Se
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1966ApJS...13..333K&db_key=AST
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Catalogue and Bibliography of Emission-Line Stars of Types Later than B.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1954ApJS....1..175B&db_key=AST
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