내용
사진
사진 업로드
DSS Images Other Images
관련 글
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.
| An Extended FUSE Survey of Diffuse O VI Emission in the Interstellar Medium
We present a survey of diffuse O VI emission in the interstellar medium(ISM) obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE).Spanning 5.5 yr of FUSE observations, from launch through 2004 December,our data set consists of 2925 exposures along 183 sight lines, includingall of those with previously published O VI detections. The data wereprocessed using an implementation of CalFUSE version 3.1 modified tooptimize the signal-to-noise ratio and velocity scale of spectra from anaperture-filling source. Of our 183 sight lines, 73 show O VIλ1032 emission, 29 at >3 σ significance. Six of the 3σ features have velocities |vLSR|>120 kms-1, while the others have |vLSR|<=50 kms-1. Measured intensities range from 1800 to 9100 LU (lineunit; 1 photon cm-2 s-1 sr-1), with amedian of 3300 LU. Combining our results with published O VI absorptiondata, we find that an O VI-bearing interface in the local ISM yields anelectron density ne=0.2-0.3 cm-3 and a path lengthof 0.1 pc, while O VI-emitting regions associated with high-velocityclouds in the Galactic halo have densities an order of magnitude lowerand path lengths 2 orders of magnitude longer. Although the O VIintensities along these sight lines are similar, the emission isproduced by gas with very different properties.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer. FUSE is operated for NASA by Johns HopkinsUniversity under NASA contract NAS5-32985.
| Inward Motions of the Compact SiO Masers around VX Sagittarii
We report Very Long Baseline Array (VLBA) observations of 43 GHz v=1,J=1-0 SiO masers in the circumstellar envelope of the M-type semiregularvariable star VX Sgr at three epochs during 1999 April-May. Thesehigh-resolution VLBA images reveal a persistent ringlike distribution ofSiO masers with a projected radius of ~3 stellar radii. The typicalangular size of 0.5 mas for individual maser features was estimated fromtwo-point correlation function analysis of maser spots. We found thatthe apparent size scale of maser features was distinctly smaller thanthat observed in the previous observations by comparing their fractionsof the total power imaged. This change in the size scale of maseremission may be related to stellar activity that caused a large SiOflare during our observations. Our observations confirmed the asymmetricdistribution of maser emission, but the overall morphology has changedsignificantly, with the majority of the masers clustering to thenortheast of the star compared to the majority of the masers lying inthe southwest in 1992. By identifying 42 matched maser featuresappearing in all three epochs, we determined the contraction of an SiOmaser shell toward VX Sgr at a proper motion of -0.507+/-0.069 masyr-1, corresponding to a velocity of about 4 kms-1 at a distance of 1.7 kpc to VX Sgr. Such a velocity is onthe order of the sound speed and can be easily explained by thegravitational infall of material from the circumstellar dust shell.
| The effect of dust obscuration in RR Telescopii on optical and IR long-term photometry and Fe II emission lines
Aims.Infrared and optical photometric and spectroscopic observations ofthe symbiotic nova RR Tel are used to study the effects and propertiesof dust in symbiotic binaries containing a cool Mira component, as wellas showing "obscuration events" of increased absorption, which aretypical for such Miras. Methods: .A set of photometricobservations of the symbiotic nova RR Tel indifferent wavelength bands - visual from 1949 to 2002 and near-infrared({JHKL}) from 1975 to 2002 - are presented. The variability due to thenormal Mira pulsation was removed from the JHKL data, which were thencompared with the American Association of Variable Star Observers'({AAVSO}) visual light curve. The changes of the Fe II emission linefluxes during the 1996-2000 obscuration episode were studied in theoptical spectra taken with the Anglo-Australian telescope. Results: .We discuss the three periods during which the Mira componentwas heavily obscured by dust as observed in the different wavelengthbands. A change in the correlations of J with other infrared magnitudeswas observed with the colour becoming redder after JD 2 446 600.Generally, J-K was comparable, while K-L was larger than typical valuesfor single Miras. A distance estimate of 2.5 kpc, based on the IR data,is given. A larger flux decrease for the permitted than for theforbidden Fe II lines, during the obscuration episode studied, has beenfound. There is no evidence for other correlations with line properties,in particular with wavelength, which suggests obscuration due toseparate optically thick clouds in the outer layers.
| The nature of ultraviolet spectra of AG Pegasi and other symbiotic stars: locations, origins, and excitation mechanisms of emission lines
A detailed study of ultraviolet spectra of the symbiotic star AG Peg hasbeen undertaken to derive the atomic excitation mechanisms and origin offormation for the lines common in symbiotic systems. More than 600emission lines are observed in spectra from {IUE}, {HST} and {FUSE} ofwhich 585 are identified. Population mechanisms and origin of formationare given for a majority of those lines. Based on the understanding ofthe AG Peg spectra {IUE} data of 19 additional symbiotic stars areinvestigated and differences and similarities of their spectra arediscussed. Fe II fluorescence lines pumped by strong emission linesbetween 1000 and 2000 Å are observed in 13 of these systems. Someof the symbiotic systems belonging to the subclass symbiotic novae havemore than 100 Fe II fluorescence lines in the ultraviolet wavelengthregion. Forbidden lines are detected for 13 of the stars, mostly fromhighly-ionized spectra such as Ar V, Ne V and Mg V. Further, [Mg VI] and[Mg VII] lines are observed in a symbiotic star (AG Dra) for the firsttime. Five of the symbiotic stars have broad white-dwarf wind profiles({FWHM} > 400 km s-1) for a few lines in their spectra.The stars with no such broad lines can be divided into two similarlysized groups, one where all lines have FWHM less than 70 kms-1 and the other where one, a few or all of the broad({FWHM} > 400 km s-1) lines of AG Peg have an enhancedbroad wing (110-140 km s-1).
| Hydrodynamical simulations of the jet in the symbiotic star MWC 560. II. Simulations beyond density balance
Context: .In the first paper of this series, we presented hydrodynamicalsimulations with radiative cooling of jet models with parametersrepresentative of the symbiotic system MWC 560. These were jetsimulations of a pulsed, initially underdense jet in a high-densityambient medium. They were stopped when the jet reached a length of 50AU. There, however, a transition of the initially underdense jet towardsan overdense jet should occur, which should result in changedkinematics. A few minor differences between the models and theobservations were thought to be solved by a model with an increased jetdensity during the pulses which was calculated only with purelyhydrodynamical means in the former paper. Aims: .Therefore, wedescribe two hydrodynamical simulations with cooling beyond this densitybalance, one with the same parameters as model i in Paper I (now calledmodel i´), which was presented there with and without cooling, andthe second with higher gas densities in the jet pulses (modeliv´). Methods: .Hydrodynamical simulations, with a furtherapproximated cooling treatment compared to Paper I, were used to be ableto enlarge the computational domain. Results: .The transitioncauses changes in the expansion of the cocoon and therefore themorphology of the jet, e.g. a larger radial width of the jet knots. Weinvestigate the radiation properties of the jets, the bremsstrahlung andoptical emissivities, integrated emission maps, and synthetic absorptionline profiles. Conclusions: .The conclusion that the high observedvelocities in CH Cygni, R Aquarii, and MWC 560 favor the models withcooling is unchanged by the transition. The observed parallel featuresin R Aquarii can be produced by the internal knots or by a variabledense radiative shell of shocked ambient medium. The absorption lineprofiles show that the real parameters in MWC 560 are closer to modeliv´ than to model i´.
| The OH 1612 MHz maser pump rates of stellar, interstellar and post-AGB OH masers
(Pseudo) radiative pumprate of OH 1612 MHz masers is defined for asample of 44 OH/IR sources (infrared sources with OH 1612 MHz maser),irrespective of the real maser pumping mechanisms. The correlationbetween the (pseudo) maser pumprates and the evolutionary status of themaser sources reveals that the radiative pumprates of stellar OH masersare nearly fixed, which agrees with the theoretical prediction forradiatively pumped OH maser. The (pseudo) radiative pumprates ofinterstellar OH masers are not only very small but also varying broadlyover two orders of magnitude, which is argued to be the manifestation ofvarying number of quiet absorbing OH cloudlets and/or various OH maserpumping mechanisms and/or competitive gain between mainline and 1612 MHzOH masers and/or anisotropy of the maser emission. The radiativepumprates of post-AGB OH masers very possibly decrease with increasingIRAS C32 color indices and distribute in an interim regionbetween the stellar and interstellar OH masers in the pumprate-colordiagram.
| 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.
| Ausbruch von Roentgenstrahlen von Mira A.
Not Available
| Axial Symmetry and Rotation in the SiO Maser Shell of IK Tauri
We observed v=1, J=1-0 43 GHz SiO maser emission toward the Miravariable IK Tauri (IK Tau) using the Very Long Baseline Array (VLBA).The images resulting from these observations show that SiO masers form ahighly elliptical ring of emission approximately 58×32 mas with anaxial ratio of 1.8:1. The major axis of this elliptical distribution isoriented at a position angle of ~59°. The line-of-sight velocitystructure of the SiO masers has an apparent axis of symmetry consistentwith the elongation axis of the maser distribution. Relative to theassumed stellar velocity of 35 km s-1, the blue- andredshifted masers were found to lie to the northwest and southeast ofthis symmetry axis, respectively. This velocity structure suggests anorthwest-southeast (NW-SE) rotation of the SiO maser shell with anequatorial velocity, which we determine to be ~3.6 km s-1.Such a NW-SE rotation is in agreement with a circumstellar envelopegeometry invoked to explain previous H2O and OH maserobservations. In this geometry, H2O and OH masers arepreferentially created in a region of enhanced density along the NE-SWequator orthogonal to the rotation/polar axis suggested by the SiO maservelocities.
| Diameters of Mira Stars Measured Simultaneously in the J, H, and K' Near-Infrared Bands
We present the first spatially resolved observations of a sample of 23Mira stars simultaneously measured in the near-infrared J, H, and K'bands. The technique used was optical long-baseline interferometry, andwe present for each star visibility amplitude measurements as a functionof wavelength. We also present characteristic sizes at each spectralband, obtained by fitting the measured visibilities to a simple uniformdisk model. This approach reveals the general relation J diameter < Hdiameter < K' diameter.
| Colliding Winds in Symbiotic Binary Systems. I. Analytic and Numerical Solutions
We present new formulations of binary colliding wind models appropriateto symbiotic star systems. The derived models differ from previousformulations in assuming mixing of the shocked material from bothincoming streams, rather than postulating a self-sustaining contactdiscontinuity. The CWb model (colliding winds, binary) extends the workof Girard and Willson by the derivation of an adiabatic temperature, theconsideration of radiative cooling, the inclusion of thermal pressuresin the incoming winds, and the treatment of interaction shells of finitethickness and density. The finite thickness of the interaction shellallows for calculation of its radiative intensity distribution. The CWcmodel (colliding winds, concentric) is a similar extension of the modelof Kwok, Purton, and Fitzgerald. It is derived in a manner parallel tothat of the CWb model, thereby facilitating a unification of the twomodels. A unified model is desired since wind collisions in symbioticsystems should include aspects of both CWb and CWc interactions. Twoexamples of model applications are presented: a comparison of the fluxdensities arising from colliding winds (CWb model) with those arisingfrom the ionization of the surrounding medium (STB model) in thegalactic population of symbiotic stars, and model imaging of thesymbiotic nova HM Sge.
| 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.
| The spectroscopic orbits and other parameters of the symbiotic binary FN Sgr
We present a study of the eclipsing symbiotic binary FN Sgr with aperiod of 568.3 days determined photometrically and confirmedspectroscopically. The hot component underwent a 2.5 mag eruptioncovered by most of our spectroscopic observations. In particular, wehave determined for the first time spectroscopic orbits based on theradial velocity curves for both components. A set of blue absorptionlines resembling an A-F type star is present in all our spectra and theyseem to be associated with the hot component. Based on the light curve,we derive the red giant's radius (140~ Rȯ) and theorbital inclination (i = 80°). We find that FN Sgr is similar toother S-type symbiotic binaries, composed by an M 5-type giant (M_g=1.5Mȯ) and a hot white dwarf (Mh = 0.7~Mȯ, R_h= 0.2~ Rȯ) with a binaryseparation of ~1.6 AU. The red giant is just filling its Roche lobe anda geometrically and optically thick accretion disk is likely to bepresent around the low-mass accretor. The evolution of Th andLh along the active phase argues in favour of accretion diskinstabilities similar to those of Z And. We have also studied spectralchanges and photometric variations as a function of both the hotcomponent activity and the orbital motion.
| Nebular abundances of southern symbiotic stars
We have calculated relative element abundances for a sample of 43symbiotic stars. Helium abundances and the relative elemental abundancesN/O, Ne/O, Ar/O were derived from new spectra collected in the opticalrange through low dispersion spectroscopy. The He ionic abundances werederived taking into account self-absorption effects in Balmer lines. Wefound that the symbiotic stars in the galactic bulge have heavy elementabundances showing the same wide distribution as other bulge objects. Inthe galactic disk, the symbiotic stars follow the abundance gradient asderived from different kinds of objects.
| Korean nova records in A.D. 1073 and A.D. 1074: R Aquarii
R Aqr is known to be a symbiotic binary system with an associatedextended emission nebula, possibly produced by a historic outburst. Tofind the associated historic records, we searched for and compiled allGuest Star and Peculiar Star records in three Korean official historybooks that cover almost two thousand years, Samguksagi, Goryeosa,Joseonwangjosillok. In addition to the record of A.D. 1073, previouslynoted by Li (1985, Chin. Astron. Astrophys., 9, 322), we have found inGoryeosa another candidate record of A.D. 1074, which has the samepositional description as that of A.D. 1073 with an additionalbrightness description. We examined various aspects of the two recordsand conclude that they both are likely to be the records of outburst ofR Aqr. This means that there were two successive outbursts in A.D. 1073and in A.D. 1074, separated by approximately one year. Based on theserecords, we estimate the distance to R Aqr to be 273 pc if the expansionof the nebula has been at a constant rate. The brightness record of A.D.1074 corresponds to the absolute magnitude at outburst ofMoutburst = -6.2m -5.2m at thisdistance. The two Korean records associated with R Aqr may provideastronomically meaningful constraints to the outburst model of R Aqr andthe formative process of its nebulosity.
| Search for radiative pumping lines of OH masers. I. The 34.6 m absorption line towards 1612 MHz OH maser sources
The 1612 MHz hydroxyl maser in circumstellar envelopes has long beenthought to be pumped by 34.6 μm photons. Only recently, the InfraredSpace Observatory has made possible spectroscopic observations whichenable the direct confirmation of this pumping mechanism in a few cases.To look for the presence of this pumping line, we have searched theInfrared Space Observatory Data Archive and found 178 spectra with dataaround 34.6 μm for 87 galactic 1612 MHz masers. The analysisperformed showed that the noise level and the spectral resolution of thespectra are the most important factors affecting the detection of the34.6 μm absorption line. Only 5 objects from the sample (3 redsupergiants and 2 galactic center sources) are found to show clear 34.6μm absorption (all of them already known) while two additionalobjects only tentatively show this line. The 3 supergiants show similarpump rates and their masers might be purely radiatively pumped. The pumprates of OH masers in late type stars are found to be about 0.05, only1/5 of the theoretical value of 0.25 derived by Elitzur (1992). We havealso found 16 maser sources which, according to the analysis assumingElitzur's pump rate, should show the 34.6 μm absorption line but donot. These non-detections can be tentatively explained by far-infraredphoton pumping, clumpy nature of the OH masing region or a limb-fillingemission effect in the OH shell.
| Are jets in symbiotic stars driven by magnetic fields?
We compare two scenarios to launch jets - formation by MHD processes orformation by thermal pressure in the boundary layer (BL) - with respectto their compatibility with observational data of jets in symbioticstars, especially in the well studied jet source MWC 560. Finally, wediscuss points of further research to be done.
| SiO masers in TX Cam. Simultaneous VLBA observations of two 43 GHz masers at four epochs
We present the results of simultaneous high resolution observations of v= 1 and v = 2, J = 1-0 SiO masers toward TX Cam at four epochs coveringa stellar cycle. We used a new observing technique to determine therelative positions of the two maser maps. Near maser maximum (Epochs IIIand IV), the individual components of both masers are distributed inring-like structures but the ring is severely disrupted near stellarmaser minimum (Epochs I and II). In Epochs III and IV there is a largeoverlap between the radii at which the two maser transitions occur.However in both epochs the average radius of the v = 2 maser ring issmaller than for the v = 1 maser ring, the difference being larger forEpoch IV. The observed relative ring radii in the two transitions, andthe trends on the ring thickness, are close to those predicted by themodel of Humphreys et al. ([CITE], A&A, 386, 256). In manyindividual features there is an almost exact overlap in space andvelocity of emission from the two transitions, arguing against pureradiative pumping. At both Epochs III and IV in many spectral featuresonly 50% of the flux density is recovered in our images, implyingsignificant smooth maser structure. For both transitions we find thatred- and blue-shifted masers occur in all parts of the rings, withrelatively few masers at the systemic velocity. Thus there is noevidence for rotation, although the blue-shifted masers are somewhatmore prominent to the west. At all four epochs red-shifted componentsare generally brighter than blue-shifted ones. Blue-shifted masersbecome very weak at some stellar phases but never completely disappear.At Epochs III and IV, we see many filamentary or spoke-like features inboth v = 1 and v = 2 masers, especially in the red-shifted gas. Thesespokes show systematic velocity gradients consistent with a deceleratingoutward flow with increasing radius. We outline a possible model toexplain why, given the presence of these spokes, there is a deficit ofmaser features at the systemic velocity. The breaking of sphericalsymmetry by spoke-like features may explain the high-velocity wings seenin SiO maser single dish spectra.
| CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/431/773
| Hydrodynamical simulations of the jet in the symbiotic star MWC 560. I. Structure, emission and synthetic absorption line profiles
We performed hydrodynamical simulations with and without radiativecooling of jet models with parameters representative of the symbioticsystem MWC 560. For symbiotic systems we have to perform jet simulationsof a pulsed underdense jet in a high density ambient medium. We presentthe jet structure resulting from our simulations and calculate emissionplots which account for expected radiative processes. In addition, ourcalculations provide expansion velocities for the jet bow shock, thedensity and temperature structure in the jet, and the propagation andevolution of the jet pulses. In MWC 560 the jet axis is parallel to theline of sight so that the outflowing jet gas can be seen as blueshifted, variable absorption lines in the continuum of the underlyingjet source. Based on our simulations we calculate and discuss syntheticabsorption profiles. Based on a detailed comparison between modelspectra and observations we discuss our hydrodynamical calculations fora pulsed jet in MWC 560 and suggest improvements for future models.Figures \ref{skizze}, \ref{modi_det}, \ref{slice_cool_p},\ref{NV_3.0_synch}, \ref{modelicool_greyscale},\ref{line_rem}-\ref{line_dv} and \ref{line_zmax} are only available inelectronic form at http://www.edpsciences.org
| X-Ray Jets in R Aquarii (poster)
Not Available
| QX Pup (OH 231-8+4.2) - a Post-AGB/PPN or a Symbiotic Mira?
Not Available
| Fe II fluorescence in symbiotic stars
Fe 0 fluorescence by PAR has been investigated in eight symbiotic starshaving a wide range in temperature of the hot component and orbitalperiod. The data used are spectra obtained from the IUE archive. Allpumping lines investigated in this work are in the short wavelengthregion of IUE (1200-2000 Å), except for He 0 λ 1084.942 andO 0 λ 1032.041. The resulting Fe 0 fluorescence lines are mainlyin the long wavelength region (2000-3300 Å), but a few fall in thesame region as the pumping lines. The aim is to understand the optimalconditions for formation of Fe 0 fluorescence lines caused by PAR. Threeof the selected systems, RR Tel, AG Peg and V1016 Cyg, have 10-30 activeFe 0 channels. Two conditions connect those systems to each other: Thehot component is a white dwarf of extreme temperature (80 .103-150 . 103 K) and all three systems are socalled symbiotic novae and have had outbursts during the last 150 years.Three systems, AG Dra, RW Hya and R Aqr, have only 2-3 active Fe 0channels. In the two remaining systems, CI Cyg and T CrB, Fe 0fluorescence lines were totally absent. These two systems have twofeatures in common: The emission strength of highly ionized elements isless than in most symbiotic systems, and the hot component is suspectedto be an accreting main sequence star rather than a white dwarf.
| Jets from Accreting White Dwarfs
Collimated outflows from accreting white dwarfs have a vital role toplay in the study of astrophysical jets.
| Spectroscopic Diagnostics of Symbiotic Stars. II. Statistical Analyses of Highly Resolved Emission-Line Profiles
We obtained highly resolved spectroscopic data of 34 symbiotic stars atHα, He II λ 4686, and [O III ] λ 5007. We analyzed the line profilesstatistically to obtain clear common characteristics of the emissionnebulae in symbiotic stars. We first carried out coarse analyses, whichsuggested differences in the line profiles between the quiescent andoutburst phases. Second, we de-convolved the line profiles with multipleGaussian components, and statistically dealt with each component inorder to extract certain characteristics as a group. In the case ofalmost edge-on binary orbits, the relation between the characteristicvelocities of the main, the broad wing, and the absorption components ofHα versus the orbital phase can be explained by the existence andinteraction of stellar winds from cool and hot stars. The difference inthe width of the main component of He II λ4686 between the quiescent and the outburst phases and the changes intheir radial velocities with the orbital phase support the idea thatHe++ gas would distribute around a hot star. Double-peakedprofiles of [O III ] λ 5007 lines and theirrelation to the orbital phase can be explained by bi-conical flows.
| Searching for radiative pumping lines of OH masers: II. The 53.3 μm absorption line towards 1612 MHz OH maser sources
This is the second paper in a series aiming at searching for infraredpumping lines for galactic 1612 MHz OH masers. Our paper I is devoted tothe 34.6 μm absorption lines in ISO SWS spectra towards a largesample of galactic OH/IR sources. This paper analyzes the 53.3 μmline in the ISO LWS spectra towards a similar sample of OH/IR sources. Asearch with position radius of 1 arcmin in ISO Data Archive (IDA)results in 137 LWS spectra covering 53.3 μm associated with 47galactic OH/IR sources and 4 ones associated with megamasers Arp 220 andNGC 253. (These two magamasers are included for comparison purposeonly.) Ten of these galactic OH/IR sources are found to show and another5 ones tentatively show the 53.3 μm absorption while another 7sources (our group U1 and U2 sources) highly probably do not show thisline. The source class is found to be correlated with the type ofspectral profile: red supergiants (RSGs) and AGB stars tend to showstrong blue-shifted filling emission in their 53.3 μm absorption lineprofiles while H II regions tend to show a weak red-shifted fillingemission in the line profile. GC sources and megamasers mainly showsymmetrical profile in the line core while megamasers tend to show anadditional absorption tail on the blue side of the line profile. It isargued that the filling emission might be the manifestation of anunresolved half emission half absorption profile of the 53.3 μmdoublet which might be produced by the transitions among the two levels:2Π1/2(J=3/2) and2Π1/2(J=5/2) and their closely related levels.The 53.3 to 34.6 μm equivalent width (EW) ratio is close to unity forRSGs but much larger than unity for GC sources and megamasers while H IIregions only show the 53.3 μm line. The pump rate defined as maser toIR photon flux ratio is approximately 5% for RSGs. The pump rates of GCsources are three order of magnitude smaller. Both the large 53.3 to34.6 μm EW ratio and the small pump rate of the GC OH masers reflectthat the two detected `pumping lines' in these sources are actually ofinterstellar origin. The pump rate of Arp 220 is 32% - much larger thanthat of RSGs, which indicates that the contribution of other pumpingmechanisms to this megamaser is important. A handful of non-detectionsof the 34.6 or 53.3 μm line or both can be explained partly by thegenuinely weakness of the OH masers and partly by some other mechanismsweakening the IR pumping lines, such as clumpy OH shell or limb fillingemission.
| A radio jet in the prototypical symbiotic star Z And?
As part of a multiwavelength campaign to observe the 2000-2002 outburstof the prototypical symbiotic star Z Andromedae, we observed this objectsix times each with the Multi-Element Radio Linked InterferometerNetwork (MERLIN) and Very Large Array (VLA). The radio flux variedsignificantly during the course of the optical outburst at all threeobservation frequencies (1.4, 5, and 15 GHz). A jet-like extension waspresent in the 2001 September MERLIN image and appeared to be alignedperpendicularly to the plane of the binary orbit. Assuming that theejection took place at the beginning of the optical outburst, the0.06-arcsec separation between the peak of the extended emission and thecentral core implies that the ejected material was moving with avelocity of ~400 km s-1. This extended emission faded on atime-scale of ~ months and was not detected at any other epoch. Weconsider the implications of jets being a component of a `prototypical'symbiotic system and compare properties of the observed jet of Z Andwith those of the jets in X-ray binary systems.
| Astrophysical Jets
The acceleration and collimation mechanisms of jets probably are thesame in all the classes of astrophysical objects which exhibit them:active galactic nuclei, young stellar objects, massive X-ray binaries,low mass X-ray binaries, black hole X-ray transients, gamma-ray bursts,symbiotic systems, planetary nebulae, supersoft X-ray sources andpossibly recurrent novae and pulsars. An attempt is made to identify thenecessary ingredients for the acceleration and collimation mechanisms.Most likely, the jets are produced at the center of accretion disks andare accelerated and collimated hydromagnetically.
|
새 글 등록
관련 링크
새 링크 등록
다음 그룹에 속해있음:
|
관측 및 측정 데이터
천체목록:
|
INHABITED SKY
