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|Infrared Nebulae around Young Stellar Objects|
We present a K-band atlas of 106 reflection nebulae, 41 of which are newdiscoveries. We observed these nebulae with the University of Hawaii 2.2m telescope in the course of an imaging survey of 197 objects that wereselected as nearby young Class I sources. K-band images andflux-calibrated surface brightness contour plots of each nebula arepresented. We found that the near-IR luminosities and physical sizes ofthe nebulae increase with the bolometric luminosity of the illuminatingsources. Only 22 nebulae, about 10% of these candidate Class I sources,have indications of shocked H2 emission. The great variety ofnebulae that we observed prevented us from classifying them based onmorphology. However, we note that as the spectral index decreases, thecentral star is more frequently visible at K band, and the flux from thecentral star tends to be dominant over the flux from the nebula. Forobjects that have a higher spectral index, most of the K-band flux isfrom the reflection nebula, and the central star is less frequentlyvisible. The nebula around IRAS 05450+0019 has a unique morphology, andwe speculate that it may be an example of a disk shadow being projectedinto the surrounding cloud. We present J-, H-, and K-band images of thisobject with surface brightness contours, as well as its spectral energydistribution from 1.2 to 100 μm.
|On the Nature of the Extended Radio Emission Surrounding T Tauri South|
At centimeter wavelengths, the young stellar system T Tauri is known tobe composed of two sources, the northern one associated with the opticalstar T Tau itself, and the southern one related to the infraredcompanion T Tau S. Here we reexamine the origin of the radio emissionfrom these two components using archival 2 cm, 3.6 cm, and 6 cm VLAobservations. The emission from the northern member is confirmed to belargely dominated by free-free radiation from an ionized wind, while thesouthern radio source is confirmed to consist of a compact component ofmagnetic origin, surrounded by an extended halo. Only moderatelyvariable, the extended structure associated with the southern source ismost likely the result of free-free radiation related to stellar winds.However, its flat spectral energy distribution, its extent, and the lackof variation of its size with the frequency of observation areincompatible with the classical picture of a fully ionized wind withconstant velocity and mass-loss rate leading to an electron densitydistribution of ne(r)~r-2. Instead, we propose amodel in which the ionization results from the impact of a supersonicwind driven by T Tau Sb onto dense surrounding material, possiblyassociated with the circumbinary disk recently identified around the TTau Sa/T Tau Sb pair. The timescales for cooling and recombination insuch a situation are in good agreement with the observed morphologicalchanges undergone by the extended structure as its driving source movesthrough the environment.
|The Origins of Fluorescent H2 Emission From T Tauri Stars|
We survey fluorescent H2 emission in HST STIS spectra of theclassical T Tauri stars (CTTSs) TW Hya, DF Tau, RU Lupi, T Tau, and DGTau, and the weak-lined T Tauri star (WTTS) V836 Tau. From each of thosesources we detect between 41 and 209 narrow H2 emissionlines, most of which are pumped by strong Lyα emission.H2 emission is not detected from the WTTS V410 Tau. Thefluorescent H2 emission appears to be common to circumstellarenvironments around all CTTSs, but high spectral and spatial resolutionSTIS observations reveal diverse phenomenon. Blueshifted H2emission detected from RU Lupi, T Tau, and DG Tau is consistent with anorigin in an outflow. The H2 emission from TW Hya, DF Tau,and V836 Tau is centered at the radial velocity of the star and isconsistent with an origin in a warm disk surface. The H 2lines from RU Lupi, DF Tau, and T Tau also have excess blueshiftedH2 emission that extends to as much as -100 kms-1. The strength of this blueshifted component from DF Tauand T Tau depends on the upper level of the transition. In all cases,the small aperture and attenuation of H2 emission by stellarwinds restricts the H2 emission to be formed close to thestar. In the observation of RU Lupi, the Lyα emission and theH2 emission that is blueshifted by 15 km s-1 areextended to the SW by ~0.07", although the faster H2 gas thatextends to ~100 km s-1 is not spatially extended. We alsofind a small reservoir of H 2 emission from TW Hya and DF Tauconsistent with an excitation temperature of ~2.5×104K.
|A High Spatial Resolution Infrared View of the T Tauri Multiple System|
We present the results of our monitoring study of the IR photometric andspectroscopic variability of the T Tau multiple system. We also presentdata on the apparent position of T Tau South (T Tau S) with respect to TTau North (T Tau N), and two new spatially resolved observations of theT Tau Sa-Sb binary. T Tau N has not varied by more than 0.2 mag in K andL' flux during the 8 years of our observations, although itsBrγ and Brα emission-line fluxes have varied by nearly afactor of 4 during this time. For the unresolved T Tau S system, we havederived a 20 yr light curve based on our images and on measurementsavailable in the literature. T Tau S varies by 2-3 mag in K- andL'-band brightness in a ``redder when faint'' manner,consistent with changes along the line of sight in the amount ofmaterial that follows an interstellar medium extinction law. Absorptionin the 3.05 μm water ice feature is seen only in the spectra of T TauS, and it displays variations in depth and profile. H2 (2.12μm) emission is also detected only at the position of T Tau S; theH2, Brγ, and Brα emission-line fluxes also vary.We have found that the apparent positions of T Tau S with respect to TTau N and T Tau Sb with respect to Sa are consistent withgravitationally bound orbital motion. The possible orbits of the T Tau Sbinary imply that Sa is likely the most massive component in this youngtriple. A reanalysis of the motion of the radio source associated with TTau S provides no evidence for an ejection event in the T Tau system.
|The Spatial Distribution of Fluorescent H2 Emission near T Tauri|
New subarcsecond far-UV observations of T Tau with Hubble SpaceTelescope STIS show spatially resolved structures in the2''×2'' area around the star. The structuresare apparent in multiline emission of fluorescent H2 pumpedby Lyα. One emission structure follows the cavity walls observedaround T Tau N in scattered light in the optical. A temperature of>=1000 K is required to have a high enough population in theH2 to produce the observed fluorescent lines; in the coolenvironment of the T Tau system, shock heating is required to achievethis temperature at distances of a few tens of AU. FluorescentH2 along the cavity wall represents the best evidence to datefor the action of low-density, wide opening angle outflows drivingcavities into the molecular medium at scales <=100 AU. A southernregion of emission consists of two arcs, with shape and orientationsimilar to the arcs of H2 2.12 μm and forbidden-lineemission crossing the outflow associated with the embedded system T TauS. This region is located near the centroid of forbidden-line emissionat the blueshifted lobe of the north-south outflow.
|The Enigmatic HH 255|
To gain insight into the nature of the peculiar Herbig-Haro object HH255 (also called Burnham's nebula), we use previously publishedobservations to derive information about the emission-line fluxes as afunction of position within HH 255 and compare them with thewell-studied and relatively well behaved bow shock HH 1. There are somequalitative similarities in the Hα and [O III] λ5007 linesin both objects. However, in contrast to the expectation of the standardbow-shock model, the fluxes of the [O I] λ6300, [S II]λ6731, and [N II] λ6583 lines are essentially constantalong the axis of the flow, while the electron density decreases, over alarge distance within HH 255. We also explore the possibility that HH255 represents the emission behind a standing or quasi-stationary shock.The shock faces upwind, and we suggest, using theoretical arguments,that it may be associated with the collimation of the southern outflowfrom T Tauri. Using a simplified magnetohydrodynamic simulation toillustrate the basic concept, we demonstrate that the existence of sucha shock at the north edge of HH 255 could indeed explain its unusualkinematic and ionization properties. Whether or not such a shock canexplain the detailed emission-line stratification remains an openquestion.
|Merged catalogue of reflection nebulae|
Several catalogues of reflection nebulae are merged to create a uniformcatalogue of 913 objects. It contains revised coordinates,cross-identifications of nebulae and stars, as well as identificationswith IRAS point sources.The catalogue is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (126.96.36.199) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/399/141
|The Variability of T Tauri, RY Tauri, and RW Aurigae from 1899 to 1952|
We present the historical light curve of T Tau derived from photographicplates in the Harvard College Observatory archives. We find that theoptical light of T Tau varied by 2-3 (or more) mag on timescales asshort as a month prior to ~1917, consistent with the 1949 results ofLozinskii. Extreme light fluctuations of greater than 2 mag abruptlyceased in the late 1910s and, to the best of our knowledge, have notrepeated since this time. We compare the observed light variations of TTau with the T Tauri stars RY Tau and RW Aur, whose light curves we alsoconstructed from inspection of the archival plates. We find thatvariable extinction along the line of sight to the star is the mostlikely explanation for the observed light fluctuation of T Tau duringthe early part of the 20th century.
|A Deep Long-Slit Spectroscopic Study of the Two Bipolar Outflows from the T Tauri Binary System|
We present results of a new deep, high-resolution, long-slitspectroscopic study of the extended nebular line emission around theyoung binary T Tauri. The deduced position-velocity diagrams of the [OI], [N II], and [S II] lines have been used to investigate in greatdetail the complex geometric and kinematic structure of the massoutflows from the stellar binary components T Tau N and T Tau S. A largenumber of distinct extended outflow components, each of themcharacterized by its specific spatio-kinematic properties, has beenidentified. In addition to the brighter components (A, B, C, D, E, andF) already described in detail by Böhm & Solf, we have detectedseveral much fainter components (G, H, I, J, K, and L), some of themextending up to ~40" from the central binary. The new data confirm theexistence of two separate bipolar outflow systems associated with thebinary: one of them oriented near the east-west direction and probablyoriginating from the visible binary component T Tau N, the other oneoriented near the north-south direction and probably originating fromthe infrared binary component T Tau S. In the east-west outflow, so farconsidered to be represented only by blueshifted components (B, F, andH) west of T Tau N, we have detected for the first time an indicationfor a redshifted faint counterjet (G) east of T Tau, corresponding tothe known HH 155 jet (H). In the north-south outflow, so far consideredto be represented only by two components (C and D) near the centralsource (<=3"), two additional, rather faint components (I and J) havebeen detected, which are located farther out (8"-15") on opposite sidesof the source. Both faint components present rather low velocities ofopposite sign but rather large velocity dispersions of about 75-100 kms^-1 (FWHM). Using a biconical model for the outflow geometry, we havederived an inclination angle of 79 deg with respect to the line of sightfor the bipolar axis and deduced typical velocities of ~91 and ~280 kms^-1 in the faint outer regions (I and J) and the bright inner regions(C and D) of the north-south outflow, respectively. We have compared thekinematic state (mean radial velocity and velocity dispersion) of the``hot'' (partially) ionized gas of the outflows from the binary T Taudeduced from our forbidden line observations with that of the ``warm''molecular gas determined from the v=1-0 S(1) line of H_2 observations byT. M. Herbst and coworkers. In principal, the [S II] and H_2 emissionregions refer to very different spatial regions of the outflows, andhence the kinematic states of the two regions do not have to be coupledto each other. In particular, it is expected that the velocitydispersion derived from the [S II] lines is much larger than that fromthe H_2 lines. These expectations are generally fulfilled by theobservations, except for the ``core'' region of Burnham's nebula(component E) where the velocity dispersions of both the forbidden andH_2 lines are approximately the same. These findings as well as otherenigmatic properties of Burnham's nebula reported earlier are not yetunderstood.
|ISO spectroscopy of shocked gas in the vicinity of T Tauri|
We present the results of ISO SWS and LWS spectroscopy of the youngbinary system T Tau. The spectrum shows absorption features due to H_2Oice, CO_2 ice, gas-phase CO and amorphous silicate dust, which weattribute to the envelope of T Tau S. We derive an extinction of A_V =17.4m +/- 0.6m towards this source. Detected emission lines from H iarise in the same region which is also responsible for the optical H ilines of T Tau N. These lines most likely arise in a partially ionizedwind. Emission from the infrared fine-structure transitions of [S i],[Ar ii], [Ne ii], [Fe ii], [Si ii], [O i] and [C ii] was also detected,which we explain as arising in a ~ 100 km s(-1) dissociative shock in afairly dense (5 x 10(4) cm(-3) ) medium. Pure rotational andro-vibrational emission from molecular hydrogen was detected as well. Weshow the H_2 emission lines to be due to two thermal components, of 440and 1500 K respectively, which we attribute to emission from thedissociative shock also responsible for the atomic fine-structure linesand a much slower (~ 35 km s(-1) ) non-dissociative shock. The 1500 Kcomponent shows clear evidence for fluorescent UV excitation.Additionally, we found indications for the presence of a deeply embedded(A_V > 40() m) source of warm H_2 emission. We suggest that thiscomponent might be due to a shock, caused by either the outflow from TTau S or by the infall of matter on the circumstellar disk of T Tau S.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries: France, Germany, theNetherlands and the United Kingdom) and with the participation of ISASand NASA.
|Submillimeter Imaging of T Tauri's Circumbinary Disk and the Discovery of a Protostar in Hind's Nebula|
We have obtained images at 2.2, 450, and 850 μm of thepre-main-sequence binary T Tauri and of Hind's Nebula, which is locatedless than 1' west of T Tauri. The three maps reveal that the nebulosityaround T Tauri is extended, with an FWHM size of several hundred AU inthermal emission and more than 1000 AU in reflected light. Dust clearlyconnects the circumstellar nebula around T Tauri to the southwestern tipof Hind's Nebula, where we have identified a secondary intensity peak inthe submillimeter maps. Calculations of the long-wavelength emissivitydemonstrate that the dust emissivity index beta is ~2 for the largenebula but is ~1.2 for the secondary intensity peak. These results forbeta suggest that we have found a class I protostar 30" southwest of TTauri and that star formation is more active in the vicinity of T Taurithan previously had been thought. This protostar is detected directly atsubmillimeter wavelengths; however, polarization mapping at 2.2 μmdemonstrates that the disk-shaped dust cloud around the protostar isilluminated externally at short wavelengths, making it similar to theOrion proplyds.
|Infrared spectra of T Tauri stars.|
|Hubble Space Telescope Imaging of the Circumstellar Nebulosity of T Tauri|
Short-exposure Planetary Camera images of T Tauri have been obtainedusing broadband filters spanning the wavelength range 0.55-0.80 mum. Theoptically visible star lies very close to an arc of reflectionnebulosity. The arc's northern arm extends approximately 5" from thestar, while its southwestern arm appears brighter and extends only 2".The arc shows an approximate symmetry along an axis toward thewest-northwest, the direction of Hind's Nebula and the blueshiftedmolecular outflow. The morphology of the reflected light is similar tomodels of scattered light within an illuminated, axisymmetric outflowcavity in a circumbinary envelope, viewed ~45 deg from the outflow axis.However, our model images do not successfully account for the amount oflimb brightening that is seen. No optical counterpart to the infraredcompanion is seen to a limiting magnitude of V = 19.6, which suggestsA_V > 7 mag toward this source. There is no evidence for an opticaltertiary, to a limiting DeltaV = 5.1 mag fainter than the primary, atthe position where such an object has been previously reported.
|Imaging and Kinematic Studies of Young Stellar Object Jets in Taurus|
We report on an imaging and kinematic study of the jets and outflowsemanating from DG Tau, DG Tau B, FS Tau B, T Tau, and CoKu Tau 1. Thekinematic data are based on proper-motion measurements and long-slitspectroscopy, and the imaging data on deep narrowband [S ii]lambdalambda6716, 6731, Hα, and continuum images. The individualobjects and their peculiarities are discussed in detail. The sixinvestigated jets and flows differ from each other in their morphology,spatial extent, and their degree of variations in velocity and in theratio zeta between the knot pattern speed and the flow speed. Possiblereasons for these large differences are briefly discussed. In DG Tau, FSTau B, and T Tau strong velocity variations are indicated, while for DGTau B very small velocity variations, if any, are observed (<=7% insome flow sections). The small velocity variations in DG Tau B, togetherwith large variations in the zeta-values in this and other young stellarobject (YSO) jets, pose severe difficulties for any model that explainsthe observed knots by internal shocks resulting from velocityvariations. Our results from DG Tau B and other YSO jets stronglyindicate that for a significant fraction of knots in YSO jets othermechanisms probably excite the internal shocks. The bipolar outflow fromFS Tau B apparently shows indications of a highly collimated and apoorly collimated flow in both outflow lobes. To our knowledge, L1551IRS 5 is the only other case where such an unusual situation is alsoindicated. About 60" northeast of FS Tau B we have found an independentfaint 150"-long jetlike outflow oriented approximately perpendicular tothe FS Tau B jet, which we have designated FS Tau C (HH 276).
|A Variable Star and a Variable Nebula|
|Tracing the Envelopes around Embedded Low-Mass Young Stellar Objects with HCO + and Millimeter-Continuum Observations|
The envelopes and disks around embedded low-mass young stellar objects(YSOs) are investigated through millimeter-continuum and HCO+ lineemission. Nine sources, selected on the basis of their HCO+ 3-2 emissionfrom an IRAS flux- and color-limited sample of 24 objects, are observedin lambda = 3.4 and 2.7 mm continuum emission with the Owens ValleyMillimeter Array and in the HCO+ and H13CO+ 4-3, 3-2, and 1-0transitions at the James Clerk Maxwell and IRAM 30 m telescopes. Allnine sources are detected at 3.4 and 2.7 mm in the interferometer beam,with total fluxes between 4 and 200 mJy. The visibilities can be fitwith an unresolved (<3") point source and, in about half of thesources, with an extended envelope. The point sources, presumablythermal dust emission from circumstellar disks, typically contribute30%-75% of the continuum flux observed at 1.1 mm in a 19" beam, assuminga spectral slope of 2.5. The fact that at least two-thirds of oursources show point-source emission indicates that circumstellar disksare established early in the embedded phase. The remainder of the 1.1 mmsingle-dish flux is attributed to an extended envelope, with a mass of0.001-0.26 Mȯ within a 19" beam. In HCO+, the J = 1-0 line is seento trace the surrounding cloud, while the emission from J = 3-2 and 4-3is concentrated toward the sources. All sources look marginally resolvedin these lines, indicative of a power-law brightness distribution. Abeam-averaged HCO+ abundance of (1.2 +/- 0.4) x 10-8 with respect to H2is derived. The 1.1 mm continuum fluxes and HCO+ line intensities of theenvelopes correlate well and are modeled with the simple inside-outcollapse model of Shu (1977) and with power-law density distributions ofslopes p = 1-3. All models provide satisfactory fits to theobservations, indicating that HCO+ is an excellent tracer of theenvelopes. Of the 15 sources of the original sample that were eitherundetected in HCO+ 3-2 or too weak to be selected, seven show 1.1 mmsingle-dish fluxes comparable to our objects. It is proposed that all ofthe 1.1 mm flux of the former sources should be attributed to compactcircumstellar disks. The relative evolutionary phase of a YSO, definedas the current ratio of stellar mass over envelope mass, is traced bythe quantity ∫ Tmb dV(HCO+3-2)/Lbol. Sources that are undetected inHCO+ are found to have significantly lower values in this tracer than dothe objects of our subsample, indicating that the former objects aremore evolved. The sources that are weak in HCO+ 3-2 areindistinguishable from our subsample in this tracer and haveintrinsically low masses. It is concluded that HCO+, especially in its3-2 and 4-3 transitions, is a sensitive tracer of the early embeddedphase of star formation.
|Wind-Disk-Ambient Cloud Interactions in the Near Environment of T Tauri|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114..744H&db_key=AST
|Near-Infrared Spectropolarimetry of T Tauri|
We present near-infrared spectropolarimetric data between 0.9 and 4.2 mum for T Tauri. The data clearly show two polarization components: onehas a position angle of ~90 deg at wavelengths shortward of ~1.6 mu m,while the other has a position angle of ~20 deg at wavelengths longwardof ~1.6 mu m. The degree of polarization of the former componentdecreases as the wavelength increases, while the reverse occurs for thelatter component. Because the polarization position angle rotatesgradually from 1.4 to 1.8 mu m, the rotation can probably be explainedby a combination of several scattering components and/or dichroicextinction. In addition, an enhancement of the polarization of thelonger wavelength component was clearly observed in 1990 January, when TTau's infrared companion, T Tau S, was in the outburst phase. Thepolarization increased to about 3 times that of the quiescent phase at1.4--2.4 mu m. The enhancement of the polarization in the brighter phaseof T Tau S means that T Tau S is a highly polarized source. We estimatethe polarization of T Tau S in the K band (2.2 mu m) at 5.7% +/- 1.3%,assuming that the polarization is constant in both the quiescent and theoutburst phase. This high polarization suggests that the polarizationoriginates from scattering by a compact nebulosity in the vicinity of TTau S. In view of the high polarization resulting from the scattering,we suggest that the infrared companion T Tau S is an embeddedprotostellar object.
|The molecular envelope around T Tauri and the nature of NGC 1555.|
We present maps of the ^12^CO(3-2) and C^18^O(2-1) emission around TTauri. By comparison of the two lines measured with similar spatialresolution we are able to discriminate between the different componentsof molecular circumstellar material and to derive constraints forpossible source models. In particular we are able to trace theoutflowing molecular components. We propose a multiple outflow systemwith stellar wind envelope interaction to explain the morphology anddynamics of the ^12^CO(3-2) and C^18^O(2-1) emitting gas.
|Large-scale magnetic fields in the outflow from the young stellar object T Tauri S|
T Tauri stars are young stellar objects, similar in mass to the Sun,that are completing the transition between a collapsing cloud and amain-sequence star powered by hydrogen fusion1. Many of theseobjects are associated with circumstellar (and, presumably,protoplanetary) disks2, as well as energetic outflows of gasthat can extend several light years away from the youngstar3. These outflows are thought to be collimated bymagnetic fields4, but direct observational evidence for suchfields has hitherto been lacking. Here we show that the infraredcompanion5 (T Tau S) of the prototypical T Tauri star (T Tauitself) recently ejected in opposite directions two large lobes ofmildly relativistic particles. The radio emission from the two lobesexhibits strong circular polarization of opposite helicity, implying theexistence of a strong, ordered magnetic field at a surprisingly largedistance from the source. We also find that the T Tau system may containthree stars, rather than two as previously thought.
|The Dispersing Cloud Core around T Tauri|
Abstract image available at:http://adsabs.harvard.edu/abs/1996ApJ...470.1001M
|The (v, B-V Diagram and the Driving Sources of Herbig-Haro Objects|
|Proper Motion Measurements in Various Young Stellar Object Jets in Taurus|
|Briefly noted: Irish astronomy (poem)|
|The Hα environment of T Tauri resolved by speckle interferometry.|
T Tauri, the prototype of a class of low-mass pre-main sequence stars,was observed with the 3.6m Canada-France-Hawaii telescope (CFHT) and theCP40 photon-counting camera in November 1989. The data have beenanalysed using techniques of Speckle Interferometry to obtaindiffraction-limited information on the spatial extent of T Tauri innarrow passbands centered on the Hα line and the nearby redcontinuum. The object appears unresolved in the continuum passband,while it is resolved in Hα. The Hα emission is fitted with amodel consisting of two strongly flattened two-dimensional gaussians. Inthis model ~80% of the flux lies in a component (A) which is onlymarginally resolved, and ~20% lies in a component (B) with a semi-majoraxis FWHM of ~0.09". After subtraction of continuum, 2/3 of the Hαemission is spatially unresolved and 1/3 is resolved. The position angleof component B is 192deg+/-5deg, which approximates the direction of theperpendicular to the jet known in the [OI] and [SII] lines; this jetextends 30" westwards up to the Herbig-Haro object HH1555. Thecorresponding linear size of the Hα emitting region B is ~6 by15AU FWHM assuming a distance of T Tauri of d=140pc. We argue that thisemission arises either from the interaction between a weakly collimatedwind with a circumstellar flaring disc, or from the basis of thewestward jet which is seen on a larger scale.
|Coronographic imaging of T Tauri: discovery of an optical jet in Burnham nebula.|
We present coronographic images of T Tauri and its surrounding nebula(Burnham nebula) obtained with the STScI coronograph at Calar Alto(Spain) and with the STScI-Torino coronograph at ESO-NTT in Hα6563, [SII] 6716-6731 and 6670/80 A satellite continuum filters. Takingadvantage of the subarcsec seeing conditions, we mapped thecircumstellar environment down to 2" from the star, corresponding to320A.U. at the T Tauri distance of 160pc. Both the Hα and [SII]images reveal a complex morphology, characterized by several clumps ofshock-excited gas superimposed on large scale continuum emission. Inparticular, we detected a jet-like feature departing from the immediatesurroundings of the star in a southly direction that leads to a regionof shock excited clumps. A curved filament departs from this region,crossing Burnham nebula up to the previously known Herbig-Haro object HHA (Schwartz 1990). The south-western part of Burnham nebula ischaracterized by a number of small, nearly circular clumps. A faint,isolated HH object is also present in the northern part of the nebula.Taking into account all the available data, we suggest that the opticaljet is emitted by T Tau S roughly along the plane of the sky. The jet atfirst moves into the neutral components originating the shock excitedknots and then impacts with the edges of the cavity associated to theoutflows. The jet wiggling due to the orbital motion of the emittingsource and/or to precession phenomena could explain the peculiarexcitation status of the Burnham nebula.
|A sub-arcecond-scale spectroscopic study of the complex mass outflows in the vicinity of T Tauri|
High-resolution, long-slit spectra in the 6250-6800 A range, obtained atvarious position angles from the emission nebulosities around T Tau, arepresented. Using a method recently developed by Solf, we have eliminatedthe contribution of the stellar continuum spectrum to the detectedemission lines and determined position-velocity diagrams of the (O I),(N II), and (S II) lines to the immediate vicintiy of the star. Weidentify at least five individual components (A, B, C, D, and E) in thecomplex emission-line structure which are distinguished by their spatialdistribution and their related kinematic properties. Each line componentcan be attributed to a separate nebular condensation in the massoutflows associated with the T Tau system.
|The enigmatic T Tauri radio source|
We have analyzed eight high angular resolution images of the prototypelow mass pre-main-sequence star T Tauri obtained with the Very LargeArray between 1987 and 1990. Our objectives were to confirm a recentreport that the radio emission is both variable and circularlypolarized, to determine whether this behavior originates in the opticalstar or in the infrared source lying 0.6 sec to its south, and toidentify possible emission mechanisms. No variability or circularpolarization was detected in the weak (approximately equals 1 mJy) radioemission associated with the visible star, down to levels ofapproximately equals 10%. The observed flux can be accounted for byfree-free emission from an ionized wind with a mass-loss rate M = 3.7 x10-8 solar mass yr-1, but a more accuratedetermination of the spectral index is needed to test the validity ofsperical wind models. In sharp contrast, the 3.6 cm emission of theinfrared source is variable (approximately equals 4-7 mJy) on timescales less than or equal to 3 days and circularly polarized at lowlevels of approximately equals 3% - 5%. The polarization was leftcircular when detected during periods of low radio activity but changedto right circular during a radio outburst, similar to the reversals thathave been seen in some RS CVn binary systems. The spectral index isnegative during 'quiescence,'and we argue that the emission isnonthermal gyrosynchrotron radiation. The detection of magnetic radioactivity in this optically invisible infrared source sparks new interestin clarifying its evolutionary status. Sensitive 3.6 cm images revealweak emission extending approximately equals 1 sec west of the T Tausystem that is probably associated with high-velocity shock-excited gasflowing toward HH-1555. We find no radio evidence for a putative thirdcomponent north of the visible star.
|Warm IRAS sources. II - Optical spectroscopy of objects from the point source catalog|
Optical spectra are presented for a sample of 563 high latitude IRASsources exhibiting relatively warm 25-60 micron colors, with a view tothe efficient identification of Seyfert galaxies. Spectroscopic data areobtained on 358 extragalactic objects. The present census is consistentwith an obscuration scheme for producing both types of Seyfert objectfrom a single parent population, although the origin of excess cool IRradiation from many Seyferts remains unclear.
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