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Why Magnetic Fields Cannot Be the Main Agent Shaping Planetary Nebulae
An increasing amount of the literature reports the detection of magneticfields in asymptotic giant branch (AGB) stars and in central stars ofplanetary nebulae (PNe). These detections lead to claims that themagnetic fields are the main agent shaping the PNe. In this paper, Iexamine the energy and angular momentum carried by magnetic fieldsexpelled from AGB stars, as well as other physical phenomena thataccompany the presence of large-scale fields, such as those claimed inthe literature. I show that a single star cannot supply the energy andangular momentum if the magnetic fields have the large coherentstructure required to shape the circumstellar wind. Therefore, thestructure of nonspherical planetary nebulae cannot be attributed todynamically important large-scale magnetic fields. I conclude that theobserved magnetic fields around evolved stars can be understood withrespect to locally enhanced magnetic loops, which can have a secondaryrole in the shaping of the PN. The primary role, I argue, rests with thepresence of a companion.
| Observable effects of dust formation in dynamic atmospheres of M-type Mira variables
The formation of dust with temperature-dependent non-grey opacity isconsidered in a series of self-consistent model atmospheres at differentphases of an O-rich Mira variable of mass 1.2Msolar.Photometric and interferometric properties of these models are predictedunder different physical assumptions regarding the dust formation. Theiron content of the initial silicate that forms and the availability ofgrain nuclei are found to be critical parameters that affect theobservable properties. For certain plausible parameter values, dustwould form at 2-3 times the average continuum photospheric radius. Thiswork provides a consistent physical explanation for the larger apparentsize of Mira variables at wavelengths shorter than 1μm than thatpredicted by dust-free fundamental-mode pulsation models.
| Time Monitoring Observations of SiO J = 2-1 and J = 3-2 Maser Emission toward Late-Type Stars
We present the results of simultaneous time monitoring observations ofSiO J=2-1 and J=3-2 maser emission for 10 late-type stars (8 Miravariables, 1 OH/IR star, and 1 supergiant) with the 14 m radio telescopeat Taeduk Radio Astronomy Observatory from 1999 January to 2001February. The SiO v=1, J=2-1 and J=3-2 maser emission was detected atalmost all observational epochs. The SiO v=2, J=2-1 maser was detectedfrom 4 late-type stars (VY CMa, R Cas, χ Cyg, R Leo) and the v=2,J=3-2 maser was detected from 7 stars (R Aqr, TX Cam, R Cas, χ Cyg,W Hya, R Leo, IK Tau). The v=3, J=2-1 and J=3-2 masers were alsodetected from χ Cyg and TX Cam, respectively. Based on theseobservational data, line profile and peak velocity variations withrespect to stellar velocity, antenna temperatures, and their ratiovariations as a function of optical phase of central star wereinvestigated. As main results, the line profile and the peak velocityvariation of the v=1, J=3-2 maser with pulsation phase was found todiffer from the v=1, J=2-1 transition. Similarly, the J=2-1 and J=3-2transitions also differ between rovibrational transitions at a givenpulsation phase. However, it is difficult to find significantcorrelations between the peak velocity variation relative to the stellarvelocity of either the J=3-2 or J=2-1 transitions over pulsation phase,due to limited time sampling in these data. The peak and integratedantenna temperature (PT and IT) ratios among rotational ladders andvibrational states are investigated. These ratios between rotationalladders of the v=1, J=2-1, and J=3-2 masers are averaged to be the peakantenna temperature ratio, PT(v=1, J=3-2)/PT(v=1, J=2-1)~0.29, and theintegrated antenna temperature ratio, IT(v=1, J=3-2)/IT(v=1,J=2-1)~0.21, respectively. In the v=2 state, these ratios are PT(v=2,J=3-2)/PT(v=2, J=2-1)~7.94 and IT(v=2, J=3-2)/IT(v=2, J=2-1)~8.50,respectively. The peak and integrated antenna temperature ratios betweenvibrational states are also averaged to be PT(v=2, J=3-2)/PT(v=1,J=3-2)~1.29, IT(v=2, J=3-2)/IT(v=1, J=3-2)~1.02, PT(v=2, J=2-1)/PT(v=1,J=2-1)~0.06, and IT(v=2, J=2-1)/IT(v=1, J=2-1)~0.05, respectively. Theseintensity ratios for the v=2, J=2-1 and v=2, J=3-2 masers suggest thatline overlaps operating in the v=2, J=2-1 transition do not similarlyaffect the v=2, J=3-2 transition.
| Correlation of Mira's SiO Maser Properties
The v=0, 1, and 2, J=1-0 SiO maser spectra of Mira have been observedwith high phase resolution over approximately three periods of the star.A time lag cross-correlation analysis of the integrated flux density andthe velocity centroid of the emission indicates that the velocitystructure varies in a consistent manner with emission during someoscillation periods of the star. Over two periods of the star the v=1integrated flux density and velocity centroid were correlated at the0.67 level. The velocity centroid reached a maximum 0.066 phase earlierthan the integrated flux density. These quantities were anticorrelatedat the 0.71 level, with the velocity centroid reaching a minimum 0.59phase earlier than the integrated flux density maximum. The other masertransitions show lower levels of correlation and other phaserelationships. The velocity centroids of the spectra have been analyzedand compared with theoretical predictions of shock passage effects.These observations are relevant for kinematic models of the maser regionand for maser-pumping models.
| Infrared Spectra and Visibilities as Probes of the Outer Atmospheres of Red Supergiant Stars
In the light of the recent results of the stellar interferometry, weexamine the nature of the extra molecular layer outside the photosphereof red supergiant stars, so far studied mostly with the use of theinfrared spectra. Although the visibility data are more direct probes ofthe spatial structure of the outer atmosphere, it is essential that theyare analyzed in combination with the spectral data. In the case of theM2 supergiant μ Cephei, several sets of data, both spectra andvisibilities, strongly suggested the presence of an extra molecularlayer (which we referred to as ``MOLsphere'' for simplicity), and thebasic parameters of the MOLsphere are estimated to be excitationtemperature Tex~1600 K, column densities of CO andH2O molecules Ncol~3.0×1020cm-2, and located at about one stellar radius above thephotosphere or Rin~2.0R*. The result showsreasonable agreement with the one based on the infrared spectra alone,and the model inferred from the spectra is now fully supported with therecent visibility data. In the case of the M2 supergiant αOrionis, the infrared spectra and visibilities show a consistent picturein that its MOLsphere is closer to the photosphere(Rin~1.3R*) with higher gas temperature(Tex~2250 K) and lower gas column density(Ncol~1020 cm-2), compared with that ofμ Cep. Some controversy on the interpretation of the mid-infrareddata of α Orionis can be reconciled. Given that the presence ofthe extra molecular layer is reasonably well established, the majorunsolved problem is how to understand the origin of such a rather warmand dense layer in the outer atmosphere.
| Changes in Apparent Size of Giant Stars with Wavelength due to Electron-Hydrogen Collisions
Interferometric measurements of stellar sizes in frequency bands rangingfrom the near-infrared to longer wavelengths give different results.Various explanations have been proposed to account for these variationsin apparent size with wavelength, but none have been entirelyconsistent. We propose that thermal ionization in the stellar atmosphereand resulting opacity, primarily due to free-free electron-hydrogencollisions, play a significant role. Such an opacity has a quadraticdependence on photon wavelength and produces variations in the opacityof the atmosphere with wavelength, consistent with pertinentmeasurements. This may be particularly important for Mira-type stars,and two examples, o Ceti and W Hya, are analyzed as examples. For starsthat are much smaller or with more concentrated mass, it is not likelyto be significant.
| Variations of the v=0, 1, 2, and 3, J=1-0 SiO Masers of Mira
The v=0, 1, 2, and 3, J=1-0 SiO maser spectra of Mira have been observedwith high phase resolution over approximately 2.6 periods of the star.These observations represent the first reported monitoring of the v=0emission over multiple stellar periods. A time cross-correlationanalysis indicates that the variations in the emission of the v=1 andv=0 states were coincident to 0.066 or less of a phase period. Thevariations of the v=1 and v=2 emissions were coincident to less than0.033 of a phase period. The v=0 emission generally had relatively lowcontrast between its maximum and minimum and had several relative maximaduring a stellar period. The relative minima varied by vibrationalstate. The v=3 emission was only observed once during theseobservations, at a time when the v=2 emission was near its absolutemaximum. These observations further constrain possible models of maserpumping.
| First Resolved Images of the Mira AB Symbiotic Binary at Centimeter Wavelengths
We report the first spatially resolved radio continuum measurements ofthe Mira AB symbiotic binary system, based on observations obtained withthe Very Large Array (VLA). This is the first time that a symbioticbinary has been resolved unambiguously at centimeter wavelengths. Wedescribe the results of VLA monitoring of both stars over a 10 monthperiod, together with constraints on their individual spectral energydistributions, variability, and radio emission mechanisms. The emissionfrom Mira A is consistent with originating from a radio photosphere,while the emission from Mira B appears best explained as free-freeemission from an ionized circumstellar region~(1-10)×1013 cm in radius.
| Changes in the Velocity Centroid of SiO Maser Emission
The v=1, J=1-0 silicon monoxide maser emission from 85 stars wasresurveyed in 2005 and 2006. The emission from these stars hadpreviously been measured in 1979 and/or 1983. For the detected stars thevelocity centroids were determined and compared with the previousvalues. If supergiant stars, known binary stars, and S Virginis wereremoved from the data set, 76 sources remained. Seven of these sourceswere not of sufficient flux density to be claimed as detections. Themean difference in the velocity centroids of the remaining sources was0.065 km s-1, and the standard deviation was 2.00 km s-1. It is important to determine the standard deviation of SiOmaser time variations in order to identify the level of the timevariability of the sources, possible binary stars, unusual emissionpatterns, or perhaps planets. The velocity centroid of S Virginisdiffered by 13.5 km s-1 from its 1983 value. This differenceindicates that S Virginis is probably part of a multiple-star system. Anaive analysis of the present data combined with earlier publishedobservations indicates a revolution period of 14.8 yr.
| Searching for Flickering Variability in Several Symbiotic Stars and Related Objects: BX Mon, V471 Per, RS Oph, V627 Cas, CI Cam, V886 Her, Z And, T CrB, MWC 560, V407 Cyg
UBVRI photometric observations of 10 symbiotic stars and related objectsobtained in the period 2002-2003 are presented. Analyzing differentiallight curves we found rapid light variations with timescales of tens ofminutes and significant amplitudes in the well-known flickers MWC 560,RS Oph, V407 Cyg and T CrB. MWC 560 and V407 Cyg demonstrate quasiperiodic oscillations (QPO) with similar amplitudes and timescales. Flickering and unusual flare in V627 Cas as well as some indications offlickering presence in BX Mon are detected. The existence of 29 minoscillations in Z And with an amplitude approx 0.02 mag in the U-band isconfirmed. Only one symbiotic star, V471 Per, and both non symbiotic, CICam and V886 Her, seem to be constant on flickering timescales. Nevertheless, small night to night changes in the brightness of V886 Herwere observed as well.
| CO(4-3) and CO(7-6) maps of the nucleus of NGC 253
Context: .Molecular line excitation studies of the nuclei of nearbystarburst galaxies yield important information on the starburstphenomena, in particular on the temperature and density of thestar-forming gas. Such studies also provide templates for high redshiftgalaxies with even more extreme star formation. Aims: .Fundamentalconstraints on the physical properties in the nuclear regions ofexternal galaxies can be derived from the spectral energy distribution(i.e., integrated flux density vs. rotational quantum number) of COrotational emission arising from warm gas. Methods: .Theresolution and sensitivity of the APEX telescope makes it feasible toperform spatially resolved studies of submillimeter (submm) CO emissionfrom the warm, dense gas in nearby starburst nuclei. Using the FLASHdual-channel heterodyne receiver we mapped emission in the CO J=4-3 and7-6 lines toward the archetypical nuclear starburst galaxy NGC 253. Results: .Combining our new observations with data from theliterature, we derive the CO line SED in the central 250 pc of NGC 253,which peaks near the 6-5 transition and has a shape very similar to thatof M 82. All CO transitions in the central region can well be fittedwith a single temperature/density Large Velocity Gradient (LVG) model. Agood match to the observations is found by assuming kinetic gastemperatures that are comparable to the dust temperature({T}kin ≈ 60 K) and a H2 density of order 104cm-3. Conclusions: .Our very first APEX submm study ofa nearby starburst nucleus (NGC 253) meaningfully constrains thephysical properties of the star-forming molecular gas it contains. Withbroader band spectrometers and a chopping secondary coming soon, theimpact of APEX on extragalactic astrophysics will be foreseeablysignificant.
| Multi-aperture photometry of extended IR sources with ISOPHOT. I. The nature of extended IR emission of planetary Nebulae
Context: .ISOPHOT multi-aperture photometry is an efficient method toresolve compact sources or to detect extended emission down torelatively faint levels with single detectors in the wavelength range 3to 100 μm. Aims: .Using ISOPHOT multi-aperture photometry andcomplementary ISO spectra and IR spectral energy distributions wediscuss the nature of the extended IR emission of the two PNe NGC 6543and NGC 7008. Methods: .In the on-line appendix we describe thedata reduction, calibration and interpretation methods based on asimultaneous determination of the IR source and background contributionsfrom the on-source multi-aperture sequences. Normalized profiles enabledirect comparison with point source and flat-sky references. Modellingthe intensity distribution offers a quantitative method to assess sourceextent and angular scales of the main structures and is helpful inreconstructing the total source flux, if the source extends beyond aradius of 1 arcmin. The photometric calibration is described and typicalaccuracies are derived. General uncertainty, quality and reliabilityissues are addressed, too. Transient fitting to non-stabilised signaltime series, by means of combinations of exponential functions withdifferent time constants, improves the actual average signals andreduces their uncertainty. Results: .The emission of NGC 6543 inthe 3.6 μm band coincides with the core region of the optical nebulaand is homogeneously distributed. It is comprised of 65% continuum and35% atomic hydrogen line emission. In the 12 μm band a resolved butcompact double source is surrounded by a fainter ring structure with allemission confined to the optical core region. Strong line emission of[ArIII] at 8.99 μm and in particular [SIV] at 10.51 μm shapes thisspatial profile. The unresolved 60 μm emission originates from dust.It is described by a modified (emissivity index β = 1.5) blackbodywith a temperature of 85 K, suggesting that warm dust with a mass of 6.4× 10-4 Mȯ is mixed with the ionisedgas. The gas-to-dust mass ratio is about 220. The 25 μm emission ofNGC 7008 is characterised by a FWHM of about 50´´ with anadditional spot-like or ring-like enhancement at the bright rim of theoptical nebula. The 60 μm emission exhibits a similar shape, but isabout twice as extended. Analysis of the spectral energy distributionsuggests that the 25 μm emission is associated with 120 K warm dust,while the 60 μm emission is dominated by a second dust component with55 K. The dust mass associated with this latter component amounts to 1.2× 10-3 Mȯ, significantly higher thanpreviously derived. The gas-to-dust mass ratio is 59 which, compared tothe average value of 160 for the Milky Way, hints at dust enrichment bythis object.
| CO line emission from circumstellar envelopes
Aims.We present the results of a multi-transition CO observationalprogram conducted on a sample of AGB and post-AGB stars envelopes. Wehave collected maps and single pointing observations of these envelopesin 5 rotational transitions ranging from J = 1-0 to J = 6-5, includingin particular new observations of the CO line at 691 GHz at the CSO. Theuse of such a set of mm and submm CO line on stellar envelopes is rareand limited to the work of some authors on IRC+10216. Methods:.Using a model for the CO emission of an AGB circumstellar envelope, incombination with a standard LVG approach, we have conducted a systematicmodelling analysis using the whole set of CO data collected for a sampleof 12 sources. We simultaneously fit all five transitions, taking intoaccount the spatial information provided by the maps. Results: .Wefind mass-loss rates in the range 1 × 10-7 to 4 ×10-4 M_ȯ/yr, and envelope temperatures ranging from 20 Kto 1000 K at a radius of 1016 cm. There seem to be a generalanti-correlation between mass loss rates and temperature, the high massloss rate AGBs having low temperatures, and vice versa. We show thatmost AGB data can be fitted using a constant mass loss rate, at leastwithin the calibration uncertainties associated with the data collectedat different frequencies. For some cases though (e.g. CIT 6, R Hya,χ Cyg), a change in the mass loss rate history needs to be invokedto reconcile data at low- and high-J, a scenario already mentioned byseveral authors to explain observations of WX Psc.
| Comparison of dynamical model atmospheres of Mira variables with mid-infrared interferometric and spectroscopic observations
We present a comparison of dynamical model atmospheres with mid-infrared(~11 μm) interferometric and spectroscopic observations of the Miravariable o Cet. The dynamical model atmospheres of Mira variablespulsating in the fundamental mode can fairly explain, without assumingad-hoc components, the seemingly contradictory mid-infraredspectroscopic and interferometric observations of o Cet: the 11 μmsizes measured in the bandpass without any salient spectral features areabout twice as large as those measured in the near-infrared. Ourcalculations of synthetic spectra show that the strong absorption due toa number of optically thick H2O lines is filled in by the emission ofthese H2O lines originating in the geometrically extended layers,providing a possible physical explanation for the picture proposed byOhnaka (2004a) based on a semi-empirical modeling. This filling-ineffect results in rather featureless, continuum-like spectra in roughagreement with the observed high-resolution 11 μm spectra, althoughthe models still predict the H2O lines to be more pronounced than theobservations. The inverse P-Cyg profiles of some strong H2O linesobserved in the 11 μm spectra can also be reasonably reproduced byour dynamical model atmospheres. The presence of the extended H2O layersmanifests itself as mid-infrared angular diameters much larger than thecontinuum diameter. The 11 μm uniform-disk diameters predicted by ourdynamical model atmospheres are in fair agreement with those observedwith the Infrared Spatial Interferometer (ISI), but still somewhatsmaller than the observed diameters. We discuss possible reasons forthis discrepancy and problems with the current dynamical modelatmospheres of Mira variables.
| Forty Years of Spectroscopic Stellar Astrophysics in Japan
The development of Japanese spectroscopic stellar astrophysics in therecent 40 years is reviewed from an observational point of view. In thisarticle, the research activities are provisionally divided into fourfields: hot stars, hot emission-line (Be) stars, cool stars, and otherstars. Historical developments of the observational facilities atOkayama Astrophysical Observatory (spectrographs and detectors) are alsosummarized in connection with the progress in scientific researchactivities.
| Beam Size, Shape and Efficiencies for the ATNF Mopra Radio Telescope at 86-115 GHz
We present data characterising the performance of the Mopra RadioTelescope during the period 2000-2004, including measurements of thebeam size and shape, as well as the overall beam efficiency of thetelescope. In 2004 the full width half maximum of the beam was measuredto be 36+/-3'' at 86GHz, falling to 33+/-2'' at 115GHz. Based on ourobservations of Jupiter we measured the beam efficiency of the Gaussianmain beam to be 0.49+/-0.03 at 86GHz and 0.42+/-0.02 at 115GHz. Sourceswith angular sizes of ~80'' couple well to the main beam, while sourceswith angular sizes between ~80'' and ~160'' couple to the both the mainbeam and inner error beam. Measurements indicate that the inner errorbeam contains approximately one-third the power of the main beam. Wealso compare efficiency corrected spectra to measurements made atsimilar facilities and present standard spectra taken towards themolecular clouds Orion-KL and M17-SW.
| Recent astrophysical results from the VLTI.
Not Available
| Bipolar jet growth and decline in Hen 3-1341: a direct link to fast wind and outburst evolution*
We report on and investigate the evolution and disappearance in thesymbiotic star Hen 3-1341 of collimated bipolar jets, which take theform of symmetrically displaced components of emission lines. Frommodelling of the emission-line spectrum it turns out that the accretingwhite dwarf (WD) in quiescence has TWD~ 1.2 ×105 K and RWD~ 0.14 Rsolar, for aluminosity of 3.8 × 103 Lsolar, and it isstably burning hydrogen on the surface at a rate of , feeding ionizingphotons to a radiation bounded circumstellar nebula extending for ~17au. The WD underwent a multimaxima outburst lasting from 1998 to 2004during which its H-burning envelope reacted to a probable small increasein the mass accretion by expanding and cooling to Teff~ 1× 104 K and R~ 20 Rsolar, mimicking anA-type giant that radiated a total of ~6 × 1044 erg, atan average rate of ~1 × 103 Lsolar. Bipolarjets developed at the time of outburst maximum and their strengthdeclined in parallel with the demise of the fast wind from the inflatedWD, finally disappearing when the wind stopped halfway to quiescence,marking a 1:1 correspondence between jets presence and feeding action ofthe fast wind. The total mass in the jets was Mjet~ 2.5× 10-7 Msolar for a kinetic energy ofEkinjet~ 1.7 × 1042(sini)-1 erg, corresponding to ~0.3(sini)-1 percent of the energy radiated during the whole outburst. We suggest thatthe spectroscopic search for jets in symbiotic stars could pay higherdividends if focused on the outburst phases characterized by maximumwind intensity.
| Infall and SiO emission in V838 Mon
We present moderate- and high-resolution infrared spectroscopy of thepeculiar eruptive variable V838 Mon, which underwent a series ofremarkable outbursts in early 2002. During the period covered by ourobservations, 2002 December-2003 December, the near-infrared spectrumcontinued to show many of the characteristics of a very cool supergiant.However, throughout this period the spectrum also revealed strong andvariable SiO first overtone emission, and Paβ emission. The 2003December spectrum contained a series of TiI lines with inverse P Cygniprofiles. This is clear evidence that some material is falling inwardtowards the star.
| Vibrato, ma non troppo.
Not Available
| Visual Star Colours from Instrumental Photometry
In order to display graphically the visual colours of stars and otherastronomical objects, photometric broadband R, V, B colours are used toproxy for the r, g, b colours of the three visual sensors of the eye.From photometric Johnson B-V and V-R colour indices, R, V, and Bmagnitudes (V = 0) are calculated, and from these the respectivebrightnesses (r, v = 1 = g, and b) are calculated. After suitablenormalization these are then placed in a ternary diagram having r, g,and b as the vertices. All B-V and V-R are adjusted so that the Sunfalls in the same place as a blackbody at 5800 K. The resulting ternaryplot shows all of its objects (stars, planets) in their visual coloursat their relative positions in the ternary diagram. The star coloursdisplayed on a computer monitor screen or as a print with a colourprinter are more vivid than the usual visual impressions of isolatedstars, undoubtedly because of properties of the dark-adapted eye, butdouble-star pairs with contrasting colours correspond nicely totelescopic visual impressions.
| Helioseismology
The sun being the nearest star, seismic observations with high spatialresolution are possible, thus providing accurate measurement offrequencies of about half million modes of solar oscillations covering awide range of degree. With these data helioseismology has enabled us tostudy the solar interior in sufficient detail to infer the large-scalestructure and rotation of the solar interior. With the availability ofhigh quality helioseismic data over a good fraction of a solar cycle itis also possible to study temporal variations in solar structure anddynamics. Some of these problems and recent results will be discussed.
| Ausbruch von Roentgenstrahlen von Mira A.
Not Available
| Interpretation of angular diameter measurements of Mira variables: role of water
For stars with atmospheres as complex as those of Miras, determinationof fundamental stellar parameters remains a challenge. Occurrence ofwater "shells" and their implication on the interpretation of theangular diameter measurements will be discussed in this talk. The roleof a spectrophotometric index of water in estimating the continuumdiameter will be highlighted.
| The Dust Cloud around the White Dwarf G29-38
We present new observations of the white dwarf G29-38 with the camera(4.5 and 8 μm), photometer (24 μm), and spectrograph (5.5-14μm) of the Spitzer Space Telescope. This star has an exceptionallylarge infrared excess, amounting to 3% of the bolometric luminosity. Thespectral energy distribution (SED) has a continuum peak around 4.5 μmand a 9-11 μm emission feature 1.25 times brighter than thecontinuum. A mixture of amorphous olivine and a small amount offorsterite in an emitting region 1-5 Rsolar from the star canreproduce the shape of the 9-11 μm feature. The SED also appears torequire amorphous carbon to explain the hot continuum. Our newmeasurements support the idea that a relatively recent disruption of acomet or asteroid created the cloud.
| The 10 μm Feature of M-Type Stars in the Large Magellanic Cloud and the Dust Condensation Sequence
We present 7-14 μm Infrared Space Observatory (ISO) spectroscopy of12 M-type evolved stars in the Large Magellanic Cloud (LMC), in order tostudy the dust mineralogy and condensation process around these stars.The sample stars show a broad dust feature in the 7-14 μm region,which is seen in either emission or (self-) absorption. The shape of thefeature changes with increasing mass-loss rate, M˙, suggesting achange in dust mineralogy as the central star evolves. At low mass-lossrates amorphous alumina and amorphous silicates are observed, while athigh mass-loss rates only amorphous silicates are seen, in agreementwith the classical condensation sequence expected for these materials.We find a clear correlation between M˙ and the peak wavelengthposition of the broad dust feature. Our data suggest a strong dependenceof the dust mineralogy on the temperature at the dust condensationradius.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries: France, Germany, theNetherlands and the UK) and with the participation of ISAS and NASA.
| A Large X-Ray Outburst in Mira A
We report the Chandra ACIS-S detection of a bright soft X-ray transientin the Mira AB interacting symbiotic-like binary. We have resolved thesystem for the first time in X-rays. Using Chandra and Hubble SpaceTelescope images, we determine that the unprecedented outburst is likelyassociated with the cool asymptotic giant branch (AGB) star, Mira A, theprototype of the Mira class of variables. X-rays have never before beendetected from an AGB star, and the recent activity signals that thesystem is undergoing dramatic changes. The total X-ray luminosity of thesystem is several times higher than the luminosity estimated usingprevious XMM-Newton and ROSAT observations. The outburst may be causedby a giant flare in Mira A associated with a mass ejection or a jet andmay have long-term consequences on the system.We dedicate this paper to the memory of Janet A. Mattei, who inspiredthis work and made these observations possible for many years.
| Joint VLBA/VLTI Observations of the Mira Variable S Orionis
We present the first coordinated Very Long Baseline Array (VLBA) / VeryLarge Telescope Interferometer (VLTI) measurements of the stellardiameter and circumstellar atmosphere of a Mira variable star.Observations of the v=1, J=1-0 (43.1 GHz) and v=2, J=1-0 (42.8 GHz) SiOmaser emission toward the Mira variable S Ori were conducted using theVLBA. Coordinated near-infrared K-band measurements of the stellardiameter were performed using VLTI-VINCI closely spaced in time to theVLBA observations. Analysis of the SiO maser data recorded at a visualvariability phase 0.73 shows the average distance of the masers from thecenter of the distribution to be 9.4 mas for the v=1 masers and 8.8 masfor the v=2 masers. The velocity structure of the SiO masers appears tobe random, with no significant indication of global expansion/infall orrotation. The determined near-infrared, K-band, uniform disk (UD)diameters decreased from ~10.5 mas at phase 0.80 to ~10.2 mas at phase0.95. For the epoch of our VLBA measurements, an extrapolated UDdiameter of ΘKUD=10.8+/-0.3 mas wasobtained, corresponding to a linear radius ofRKUD=2.3+/-0.5 AU orRKUD=490+/-115 Rsolar. Our coordinatedVLBA/VLTI measurements show that the masers lie relatively close to thestellar photosphere at a distance of ~2 photospheric radii, consistentwith model estimates. This result is virtually free of the usualuncertainty inherent in comparing observations of variable stars widelyseparated in time and stellar phase.
| A new look at the position of the 1604 Supernova (V843 Ophiuchi)
The position of the supernova of 1604 (V843 Oph) is re-assessed, withrelevant discussion pertaining to the present-day remnant, 3C 358.
| Angular Diameter Measurements of Evolved Variables by Lunar Occultations at 2.2 and 3.8 Microns
We report the angular diameters of two Mira variables (U Ari and Z Sco),three semiregular (SR) and irregular variables (SW Vir, η Gem, andμ Gem), and a supergiant SR variable (TV Gem) by lunar occultationobservations in the near-IR broad K band (2.2 μm). Lunar occultationsof η Gem and μ Gem were also observed for the first timesimultaneously in both the K and L' bands, yielding angular diameters at2.2 and 3.8 μm. Effective temperatures and linear radii are alsoderived for all the observed sources and compared with earliermeasurements. The mode of pulsation of both Mira and SR sources in oursample is discussed.
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