Infrared interferometric observations of T Tauri stars
We present observations of several T. Tauri, stars using long baseline infrared interferometry from the Palomar Testbed Interferometer.
infrared↗
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Winds from T Tauri stars. I - Spherically symmetric models
Line fluxes and profiles are computed for a sequence of spherically symmetric T Tauri wind models. The calculations indicate that the H-alpha emission of T Tauri stars arises in an extended and probably turbulent circumstellar envelope at temperatures above about 8000 K. The models predict that Mg II resonance line emission should be strongly correlated with H-alpha fluxes; observed Mg II/H-alpha ratios are inconsistent with the models unless extinction corrections have been underestimated. The models predict that most of the Ca II resonance line and IR triplet emission arises in dense layers close to the star rather than in the wind. H-alpha emission levels suggest mass loss rates of about 10 to the -8th solar mass/yr for most T Tauri stars, in reasonable agreement with independent analysis of forbidden emission lines. These results should be useful for interpreting observed line profiles in terms of wind densities, temperatures, and velocity fields.
Hartmann, Lee↗
Infrared Spectroscopy and Imaging Polarimetry of the Disk Around the T Tauri Star RNO 91
We present 3-5 micrometer spectra and a 2.2 micrometer polarimetric image of the T Tauri star RNO 91. We report the detection of three absorption bands centered at 3250 per cm (3.08 micrometer), 2139 per cm (4.68 micrometer), and 2165 per cm (4.62 micrometer) in spectra of RNO 91. These features are due to frozen H2O, CO, and possibly XCN along the line of sight toward RNO 91. Our 2187-2107 per cm spectrum of RNO 90, the only other T Tauri star in the dark cloud L43, does not show the CO or XCN absorption bands. By comparing our observed polarimetric image with modeled images of scattered light from bipolar nebulae or circumstellar disks as well as with known morphology of the RNO 91 bipolar outflow, we demonstrate that the reflection nebulosity seen in the near-infrared is most likely a circumstellar disklike structure with a radius of approximately 1700 AU. The location of both RNO 90 and RNO 91 in front of or near the front of L43 suggests that the intracloud optical depths toward both stars are small and, therefore, that the frozen H2O, CO, and XCN molecules are located on grains in circumstellar material around RNO 91 at distances from the central star of perhaps 10-1700 AU. This frozen material may represent precometary grains orbiting RNO 91.
Weintraub, David A.↗
Flat spectrum T Tauri stars: The case for infall
We show that the mid- to far-infrared fluxes of 'flat spectrum' T Tauri stars can be explained by radiative equilibrium emission from infalling dusty envelopes. Infall eliminates the need for accretion disks with non-standard temperature distributions. The simplicity and power of this explanantion indicates that models employing 'active' disks, in which the temperature distribution is a parameterized power law, should be invoked with caution. Infall also naturally explains the scattered light nebulae detected around many flat spectrum sources. To match the observed spectra, material must fall onto a disk rather than the central star, as expected for collapse of a rotating molecular cloud. It may be necessary to invoke cavities in the envelopes to explain the strength of optical and near-infrared emission; these cavities could be produced by the powerful bipolar outflows commonly observed from young stars. If viewed along the cavity, a source may be lightly extincted at visual wavelengths, while still accreting substantial amounts of material from the envelope. Infall may also be needed to explain the infrared-bright companions of many optical T Tauri stars. This picture suggests that many of the flat spectrum sources are 'protostars'-young stellar objects surrounded by dust infalling envelopes of substantial mass.
Calvet, Nuria↗
Emission lines in the spectra of the RV Tauri stars U Monocerotis and AC Herculis
Strong metallic emission lines have been observed in the spectra of the RV Tauri stars U Mon and AC Her near recent light minima. While these two variables differ in a number of significant respects, the metallic emission spectra are quite similar, resembling the emission that was previously reported as present in the spectrum of R Sct at a deep minimum. The data appear to support Baird's shock-wave model for the spectral behavior of RV Tauri stars.
Bopp, B. W.↗
A synoptic of H-alpha line profile in the T Tauri star SU Aurigae
We present a catalog of 106 high spectral resolution observations of the H-alpha line profile in the T Tauri star SU Aurigae, obtained during the period from 1986 October through 1990 November. The spectra were acquired during joint synoptic programs to observe selected T Tauri stars using the Hamilton Echelle Spectrometer of the Lick Observatory and the solar-stellar spectrograph at the McMath telescope of the National Solar Observatory on Kitt Peak. A restricted set of Mg II h and k line profiles was also obtained in a coordinated program involving the International Ultraviolet Explorer (IUE) satellite observatory and the McMath solar-stellar facility. Striking variability is evident on a nightly basis. A key result is that the relative intensity in the blue wing of H-alpha spanning a range of velocities bear -150 km/s is modulated at a period of 2.98 +/- 0.4 days. We identify the 2.98 day period with the rotation period of the star. We also find that the occurrence of the periodic modulation of the mass outflow is episodic and most evident during a 2 week sequence of nightly observations. We find two other intervals where the periodic spectroscopic variability is likely present, although at a lower level of significance at a lower level of significance. The variability is otherwise stochastic in nature. The Mg II resonance lines exhibit clear variability that is most pronounced in the blue wing of the k line. A comparison of the Mg II k line profile with H-alpha profiles obtained nearly simultaneous yields no apparent correlation between the variable features in each line. The profile shapes of the Mg II h and k lines are generally indicative of formation in a wind. An analysis of the principal features that appear in the H-alpha profile set suggests that the line is composed of contributions from an enhanced chromosphere; a relatively slow moving, dense, optically thick component of a stellar wind formed relatively close to the star; and an optically thin, high-velocity, expanding stellar wind located further away from the star. An investigation of possible correlations among the principal features in the series of H-alpha profiles suggests that as the density in the wind increases, the wind may become more unstable to large turbulence. This may lead to a reduction in the wind bulk velocity, thus regulating the mass-loss rate. We also find that the position of the main absorption feature which is always present in the H-alpha profiles is not correlated with its depth, indicating that optical depth and wind velocity are not correlated in the denser portions of the wind.
Giampapa, Mark S.↗
The ultraviolet spectrum of the T Tauri star RW Aurigae
Ultraviolet spectra of the T Tauri star RW Aurigae have been obtained with the International Ultraviolet Explorer. Emission lines include Mg II, Fe II, Cr II, Si I, Si II, Si III, Si IV, C II, C IV, and L alpha. The spectrum roughly resembles the solar chromospheric spectrum, but the surface fluxes are 200 times greater. N V and He II appear to be absent, a possible indication of either an extended chromosphere cooled by mass loss or an optically thick, hot shocked region. The ultraviolet excess in RW Aur is strong, consistent with Balmer continuum emission. The observed continuum may be used to set limits on the type and amount of extinction affecting the star.
Imhoff, C. L.↗
Wind-disk shocks around T Tauri stars
It is suggested that the winds of T Tauri stars are heated at distances of 50-100 AU by oblique shocks with circumstellar disks, producing the observed high-velocity forbidden-line emission. The low shock velocities characteristic of this model provide low-excitation emission and line profiles in reasonable agreement with observations. The blueshifted character of the observed emission is explained by a combination of disk occultation of the receding flow, plus a modest collimation of the observable wind by the disk envelope. Instabilities at the wind-disk interface may be important in producing the observed emission.
Hartmann, Lee↗
Density streams in the disc winds of Classical T Tauri stars
ABSTRACT Spectral and photometric variability of the Classical T Tauri stars RY Tau and SU Aur from 2013 to 2022 is analysed. We find that in SU Aur the H α line’s flux at radial velocity RV = −50 ± 7 km s−1 varies with a period P = 255 ± 5 d. A similar effect previously discovered in RY Tau is confirmed with these new data: P = 21.6 d at RV = −95 ± 5 km s. In both stars, the radial velocity of these variations, the period, and the mass of the star turn out to be related by Kepler’s law, suggesting structural features on the disc plane orbiting at radii of 0.2 au in RY Tau and 0.9 au in SU Aur, respectively. Both stars have a large inclination of the accretion disc to the line of sight – so that the line of sight passes through the region of the disc wind. We propose there is an azimuthal asymmetry in the disc wind, presumably in the form of ‘density streams,’ caused by substructures of the accretion disc surface. These streams cannot dissipate until they go beyond the Alfven surface in the disc’s magnetic field. These findings open up the possibility to learn about the structure of the inner accretion disc of CTTS on scales less than 1 au and to reveal the orbital distances related to the planet’s formation.
Petrov, P. P. (ORCID:0000000155514963)↗
The disks of T Tauri stars with flat infrared spectra
The energy distributions of T Tauri stars with flat infrared spectra is modeled by assuming that they have spatially thin disks with unorthodox radial gradients of temperature. Derived model parameters show that the disks associated with the flat-spectrum sources must contain intrinsic luminosity in addition to the energy intercepted and reprocessed from the central star, i.e., the disks must be active. Self-gravity may provide a possible source for this activity.
Adams, Fred C.↗
A near infrared speckle imaging study of T Tauri stars
The results of a speckle imaging survey of T Tauri stars suggest that most, if not all, young low mass stars have companions. Repeated observations of these young binary stars have revealed orbital motion in the closest pairs (less than or = 0.3 sec), providing that these systems are indeed gravitationally bound and providing the basis for mass estimates in the upcoming years. These mass estimates are necessary to distinguish between the various binary star formation mechanisms that have been proposed to date.
Ghez, A. M.↗
The Disk and Jet of the Classical T Tauri Star AA Tau
Previous studies of the classical T-Tauri star AA Tau have interpreted the UX Ononis-like photopolarimetric variability as being due to a warp in the inner disk caused by an inclined stellar magnetic dipole field. We test that these effects are macroscopically observable in the inclination and alignment of the disk. We use HST/STIS coronagraphic detection of the disk to measure the outer disk radius and inclination and find that the inner disk is both misinclined and misaligned with respect to the outer disk. AA Tau drives a faint jet which is also misaligned with respect to the outer disk minor axis. The jet is also poorly colimated near the sun. The measured inclination 71 +/- 1 deg is above the inclination range suggested for stars with UX Ononis-like variability, indicating that dust grains in the disk have grown and settled toward the disk midplane.
Grady, Carol A.↗
X-ray photometry and spectroscopy of T Tauri stars
Follow-up Einstein X-ray observations of four fields containing pre-main-sequence stars are presented. A search has been made for evidence of variability on time scales of hours and of 1 year. A large, slow flare in AS 205, and the X-ray disappearance of AA Tau are reported. Otherwise, T Tauri stars appear no more variable in X-rays than do active solar-like stars. An attempt has been made to determine spectral parameters for a number of the brighter sources. X-ray absorption column densities are consistent with those inferred from A(v), and T(x) of about 10-million K, in all cases. The importance of these observations for models of T Tauri stars and their coronae is considered.
Walter, F. M.↗
The envelopes of RV Tauri stars. I - Linear polarimetric and spectroscopic observations
Simultaneous spectroscopic and polarimetric observations are presented for five RV Tauri stars and one RV Tauri-like semiregular variable. Time-dependent variations are found in the polarizations for four of the objects, as are wavelength-dependent variations in two and possibly three stars. In general, the largest polarizations and strongest wavelength dependences in the polarization occur immediately following primary light minima.
Nook, Mark A.↗
Observations of ultraviolet variability in RV Tauri stars
An IUE program to monitor the ultraviolet variability in RV Tauri stars was initiated. The Mg II region was investigated as a potential probe of atmospheric shocks, which are believed to be associated with the pulsational variability of this class of objects. Observations, a description of the spectra, and findings for V Vul and AC Her are presented. The Mg II emission does vary significantly during the cycle; major changes in the emission line strength occur on a time scale much less than 0.2 in phase; and as the UV (and optical) continuum flux increases, the Mg II lines decrease and increased emission may be seen at 2823, 2844, and 2900 A.
Brugel, Edward W.↗
Optical veiling, disk accretion, and the evolution of T Tauri stars
High-resolution spectra of 31 K7-M1 T Tauri stars (TTs) in the Taurus-Auriga molecular cloud demonstrate that most of these objects exhibit substantial excess emission at 5200 A. Extrapolations of these data consistent with low-resolution spectrophotometry indicate that the extra emission is comparable to the stellar luminosity in many cases. If this continuum emission arises in the boundary layers of accreting disks, more than about 30 percent of all TTs may be accreting material at a rate which is sufficiently rapid to alter their evolution from standard Hayashi tracks. It is estimated that roughly 10 percent of the final stellar mass is accreted in the TT phase. This amount of material is comparable to the minimum gravitationally unstable disk mass estimated by Larson and it is speculated that the TT phase represents the final stages of disk accretion driven by gravitational instabilities.
Hartmann, Lee W.↗
Three Weak-Lined T Tauri Stars in Orion
We have identified three new weak lined T Tauri stars in Orion using the Double Spectrograph and 5-m telescope at Palomar Observatory. One of these is a candidate for the X-ray source RX0535-0633. H(alpha) and H(beta) line emisison are detected and equivalent widths measured in all three stars, and in V942 Ori. We also searched without success for H(alpha) line variability in V942 Ari.
stars emission line be stars flare stars V942 Ori ↗
Circularly polarized radio emission from the T Tauri star Hubble 4
Multiwavelength VLA observations of the weak-lined T Tauri star (WTTS) Hubble 4, which is located in the nearby (about 140 pc) Taurus-Auriga star-forming region, are reported. The emission is characterized by a nearly flat spectral energy distribution with a spectral index of 0 (S sub nu varies as nu exp alpha). Right circular polarization was detected at both 3.6 and 6 cm at levels of 19 +/- 5 percent and 18 +/- 3 percent, respectively, with an upper limit of not more than 15 percent (3 sigma) at 20 cm. The star was in a state of low radio activity, with flux densities of 1.3-1.7 mJy and a radio luminosity of 10 exp 16.5 ergs/Hz s. The unambiguous detection of circularly polarized radio emission from Hubble 4 provides direct evidence for the existence of ordered magnetic fields in this WTTS.
Skinner, Stephen L.↗