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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.
| Monitoring of Mira Variable Stars
We have begun intensive V- and R-band CCD monitoring of Mira variablestars since early in 2003. This project was initiated in the hopes ofimproving the statistics of putative flaring phenomena among thesestars. This paper will give an update of the project and describe thestrategies being employed.
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| 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
| Envelope tomography of long-period variable stars III. Line-doubling frequency among Mira stars
This paper presents statistics of the line-doubling phenomenon in asample of 81 long-period variable (LPV) stars of various periods,spectral types and brightness ranges. The set of observations consistsof 315 high-resolution optical spectra collected with the spectrographELODIE at the Haute-Provence Observatory, during 27 observing nights atone-month intervals and spanning two years. When correlated with a maskmimicking a K0III spectrum, 54% of the sample stars clearly showed adouble-peaked cross-correlation profile around maximum light, reflectingdouble absorption lines. Several pieces of evidence are presented thatpoint towards the double absorption lines as being caused by thepropagation of a shock wave through the photosphere. The observation ofthe Balmer lines appearing in emission around maximum light in thesestars corroborates the presence of a shock wave. The observed velocitydiscontinuities, ranging between 10 and 25 km s-1, are notcorrelated with the brightness ranges. A comparison with thecenter-of-mass (COM) velocity obtained from submm CO lines originatingin the circumstellar envelope reveals that the median velocity betweenthe red and blue peaks is blueshifted with respect to the COM velocity,as expected if the shock moves upwards. The LPVs clearly exhibitingline-doubling around maximum light with the K0III mask appear to be themost compact ones, the stellar radius being estimated from theireffective temperatures (via the spectral type) and luminosities (via theperiod-luminosity relationship). It is not entirely clear whether or notthis segregation between compact and extended LPVs is an artefact of theuse of the K0III mask. Warmer masks (F0V and G2V) applied to the mostextended and coolest LPVs yield asymmetric cross-correlation functionswhich suggest that line doubling is occurring in those stars as well.Although a firm conclusion on this point is hampered by the largecorrelation noise present in the CCFs of cool LPVs obtained with warmmasks, the occurrence of line doubling in those stars is confirmed bythe double CO Delta v = 3 lines observed around 1.6 mu m by Hinkle etal. (1984, ApJS, 56, 1). Moreover, the Hdelta line in emission, which isanother signature of the presence of shocks, is observed as well in themost extended stars, although with a somewhat narrower profile. This isan indication that the shock is weaker in extended than in compact LPVs,which may also contribute to the difficulty of detecting line doublingin cool, extended LPVs. Based on observations made at Observatoire deHaute Provence, operated by the Centre National de la RechercheScientifique, France. Table 3 is only available in electronic form athttp://www.edpsciences.org and 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/379/305
| Long period variable stars: galactic populations and infrared luminosity calibrations
In this paper HIPPARCOS astrometric and kinematic data are used tocalibrate both infrared luminosities and kinematical parameters of LongPeriod Variable stars (LPVs). Individual absolute K and IRAS 12 and 25luminosities of 800 LPVs are determined and made available in electronicform. The estimated mean kinematics is analyzed in terms of galacticpopulations. LPVs are found to belong to galactic populations rangingfrom the thin disk to the extended disk. An age range and a lower limitof the initial mass is given for stars of each population. A differenceof 1.3 mag in K for the upper limit of the Asymptotic Giant Branch isfound between the disk and old disk galactic populations, confirming itsdependence on the mass in the main sequence. LPVs with a thin envelopeare distinguished using the estimated mean IRAS luminosities. The levelof attraction (in the classification sense) of each group for the usualclassifying parameters of LPVs (variability and spectral types) isexamined. Table 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/374/968 or via ASTRIDdatabase (http://astrid.graal.univ-montp2.fr).
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| 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.
| Infrared colours for Mira-like long-period variables found in the (Mȯ<~10-7 Msolar yr-1) Hipparcos Catalogue
Near-infrared, JHKL, photometry is presented for 193 Mira andsemi-regular variables that were observed by Hipparcos; periods,bolometric magnitudes and amplitudes are derived for 92 of them. Becauseof the way in which the Hipparcos targets were selected, this group ofstars provides a useful data base of Miras with low mass-loss rates(Mȯ<~10-7Msolaryr-1).Various period-colour relationships are discussed in detail. The colour,particularly BCK = 10.86 - 38.10 K (J - K)0 +64.16(J - K)20 - 50.72(J -K)30 + 19, K-L, at a given period is found todepend on the pulsation amplitude of the star. A comparison with modelssuggests that this is a consequence of atmospheric extension, in thesense that large-amplitude pulsators have very extended atmospheres andredder Mȯ<10-7Msolaryr-1, K-L and H-K but bluerJ-H than their lower amplitude counterparts. The stars with veryextended atmospheres also have higher values of K-[12] and hence highermass-loss rates. This finding provides further evidence for the causalconnection between pulsation and mass loss. Two sequences are identifiedin the Hp-K versus logP diagram (where Hp is the Hipparcos broad-bandmagnitude) at short periods (logP<2.35). At a given period these twogroups have, on average, the same pulsation amplitude, but differentJHKL colours and spectral types. The short-period stars in the bluersequence have similar near-infrared colours to the Miras found inglobular clusters. Long-term trends in the infrared light curves arediscussed for stars that have sufficient data.
| 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.
| Period-Luminosity-Colour distribution and classification of Galactic oxygen-rich LPVs. I. Luminosity calibrations
The absolute K magnitudes and kinematic parameters of about 350oxygen-rich Long-Period Variable stars are calibrated, by means of anup-to-date maximum-likelihood method, using Hipparcos parallaxes andproper motions together with radial velocities and, as additional data,periods and V-K colour indices. Four groups, differing by theirkinematics and mean magnitudes, are found. For each of them, we alsoobtain the distributions of magnitude, period and de-reddened colour ofthe base population, as well as de-biased period-luminosity-colourrelations and their two-dimensional projections. The SRa semiregulars donot seem to constitute a separate class of LPVs. The SRb appear tobelong to two populations of different ages. In a PL diagram, theyconstitute two evolutionary sequences towards the Mira stage. The Mirasof the disk appear to pulsate on a lower-order mode. The slopes of theirde-biased PL and PC relations are found to be very different from theones of the Oxygen Miras of the LMC. This suggests that a significantnumber of so-called Miras of the LMC are misclassified. This alsosuggests that the Miras of the LMC do not constitute a homogeneousgroup, but include a significant proportion of metal-deficient stars,suggesting a relatively smooth star formation history. As a consequence,one may not trivially transpose the LMC period-luminosity relation fromone galaxy to the other Based on data from the Hipparcos astrometrysatellite. Appendix B is only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Photometry of Hipparcos Variable Stars
Among the discoveries reported by the Hipparcos team was the detectionof short-term photometric fluctuations in several long period, or Mira,variables (de Laverny et al. 1998). Nearly 15 percent of the 250 Mirassurveyed in the broadband 380 to 800 nm filter showed variation of 0.2to 1.1 magnitudes on timescales of 2 to 100 hours, preferentially aroundminimum light phases. We have begun an observational effort to confirmthese variations. We seek to correlate the behavior with ancillaryinformation, such as optical and infrared spectra plus maser data, todetermine whether the fluctuations can be understood as thermalinstabilities or so-called molecular catastrophe (cf. Muchmore et al1987; Stencel et al. 1990). A progress report and call for observationcoordination are given.
| Detection of short-term variations in Mira-type variables from HIPPARCOS photometry
The Hipparcos photometric observations carried out over 37 months havebeen investigated in detail for ~ 250 Miras. This leads to an unexpectedby-product of the mission that we already suspected from ESOC real-timereductions: the first detection from space of photometric short-termbrightness variations in Mira-type variables. Altogether, 51 events in39 M-type Miras are detected and no similar variations are found for Sand C-type Miras. Their amplitude ranges from 0.23 mag up to 1.11 magand their duration extends from 2 hours up to almost 6 days. Theseevents seem to occur preferentially in late spectral types. We suggestthat they might be related to molecular opacity effects. Based on datafrom the \HIP astrometry ESA satellite
| 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.
| 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.
| A New Semiregular Variable S10934 in Corona Borealis
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| Period update of 40 Mira stars
Current periods and new epochs are presented for 40 very poorly studiedMira variables. The average periods of these stars were also determinedusing earlier epochs found in the literature. The current period differssignificantly from the average period value in 4 cases. The importanceof the period variation study of Mira stars is also briefly discussed.
| 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.
| IRAS low resolution spectrograph spectral class and M and S Miras
A large sample of 177 M and S Miras, as revealed by their IRAS LRSspectral class, have been examined to determine the dependence ofsilicate emission on the visual light curve asymmetry factor, f. It isconfirmed that 9.7-micron silicate emission feature not only in M but inS Miras also occurs only when f is not greater than 0.45. However, notall stars with f of not greater than 0.45 show the silicate emission;this nondetection reveals dependence on other parameters like the meanvisual light amplitude. Though strong emission feature in M Miras mayoccur for any value of f, very weak features are absent for small valuesof f, and the strongest features tend to appear for larger values of f.Infrared excess tends to increase with the strength of the silicateemission as well as with decrease in the value of f. The probability ofdetection of silicate emission is very high for the visual light curveclasses (Ludendorff, 1928) alpha 1, alpha 2, and alpha 3, decreases foralpha 4 and gamma 1, and is negligible for the beta class.
| 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.
| SiO maser emission in evolved stars - Relation to IR continuum
The present observations of SiO masers at 43 GHz have detected 11 newSiO stars; an analysis of these SiO and mid-IR measurements yields agood correlation between maser intensity and 8-micron continuum foroxygen-rich Mira variables and late-type supergiants. This correlationimplies a maser radiative pump mechanism rather than collisional models,and is useful in the characterization of the SiO maser emitters; thecomparison of the respective regions occupied by these groups of objectsin the SiO-IR diagram shows that the emission of the C stars is morethan about 100 times weaker than that of the oxygen-rich objects.
| 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.
| Luminosities and mass loss rates of OH/H2O maser stars
It has been found that approximately 130 Mira variables, semiregular(SR) variables, or M supergiants have associated circumstellar H2Omasers. Such H2O masers are commonly associated with oxygen-rich Miravariables which have OH or SiO maser emission. However, it is not knownif a star which has one of these maser species also will have theothers. The present investigation is concerned with the results of anH2O survey of late-type stars, in which efforts have been made tominimize limitations related to the correlation of the properties of H2Oemission with stellar properties. Attention is given to H2O luminositiesfor the nearby stars, the relation of H2O luminosity to mass loss rate,the ratio of H2O to OH luminosities, and the pump mechanism for H2Omasers.
| OH maser luminosity and expansion velocity gradient in Mira envelopes
Eleven newly-detected Mira variables in which hydroxyl emission has beendetected (OH-Miras), together with the 37 other known sources, arestudied in order to investigate OH maser emission from the circumstellarenvelopes of Mira variables. The search for OH emission from Miravariables was conducted at frequencies of 1612 and 1667 MHz. Peakintrinsic luminosities of the sources are found to range from 5 x 10 tothe 15th to 5 x 10 to the 17th W for Type I OH-Miras and from 10 to the17th to 5 x 10 to the 18th W for Type II OH-Miras. The more luminousType II sources are considered rarer, and thus are found at greaterdistances. The mean velocity separation between the two main OH peaks isfound to be smaller for OH-Miras than for OH-IR sources, howver thevelocity gradient in OH-Mira envelopes is higher. The maser action ofOH-Miras can be explained in terms of infrared pumping models in whichthe main lines are excited by hot dust grains of 350 to 450 K.
| A search for 18-cm OH radio emission from miras and semiregular variables.
Not Available
| An 0BSERVATIONAL Study of Mira Variables. I. The Near-Infrared Photometry
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973ApJS...25..369B&db_key=AST
| 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
| 44 variables stars.
Not Available
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| Csillagkép: | Ökörhajcsár |
| Rektaszcenzió: | 15h17m14.71s |
| Deklináció: | +36°21'33.4" |
| Vizuális fényesség: | 11.379 |
| RA sajátmozgás: | -13 |
| Dec sajátmozgás: | -2.2 |
| B-T magnitude: | 12.509 |
| V-T magnitude: | 11.473 |
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