HL Tau Research Articles

Radio continuum observations of IRAS sources associated with dense cores

view Abstract Citations (61) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Radio Continuum Observations of IRAS Sources Associated with Dense Cores Rodriguez, L. F. ; Myers, P. C. ; Cruz-Gonzalez, I. ; Terebey, S. Abstract Using the VLA, the continuum emission associated with IRAS sources embedded in dense cores was searched for at 6 cm. Two new sources, 04016 + 2610 in L1489 and 19243 + 2350 in L778, were detected. The embedded sources have low luminosity (L less than about 10 solar luminosities). As in other similar sources, if the emission is free-free, the stellar radiation cannot account for the observed ionization rate. Two models that have been proposed to explain the radio continuum emission from low-luminosity stars are those of (partially) ionized winds and shock-induced ionization. For the two new sources and a previously reported one (HL Tau), the associated molecular outflow is of modest power. It is shown that, under these conditions, these models, at least in their simplest versions, do not provide sufficient ionized gas. The nature of the radio continuum emission from low-luminosity young stars remains unexplained. Publication: The Astrophysical Journal Pub Date: December 1989 DOI: 10.1086/168134 Bibcode: 1989ApJ...347..461R Keywords: Early Stars; Infrared Sources (Astronomy); Radio Emission; Star Formation; Infrared Astronomy Satellite; Stellar Luminosity; Stellar Radiation; Stellar Winds; Very Large Array (Vla); Astrophysics; INFRARED: SOURCES; RADIATION MECHANISMS; STARS: FORMATION; STARS: RADIO RADIATION full text sources ADS | data products SIMBAD (12)

Tomographic imaging of HL Tauri

A two-dimensional image of HL Tauri at 2.2 microns with 0.4-arcsec resolution is constructed from one-dimensional speckle-interferometric scans by means of tomographic back projection. The light distribution is dominated by scattered starlight above and below the midplane of the circumstellar disk of gas and dust. It is suggested that the scattering material is not associated directly with the disk but rather represents particles entrained in gas accreting onto the disk and star. The estimated mass accretion rate of 2 x 10 to the -6th solar mass/yr is in excellent accord with that expected from residual infall associated with the formation of the star. 27 refs.

Submillimeter measurements of T Tauri and FU Orionis stars

view Abstract Citations (192) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Submillimeter Measurements of T Tauri and FU Orionis Stars Weintraub, David A. ; Sandell, G. ; Duncan, W. D. Abstract Millimeter and submillimeter detections of 12 low-mass, premain-sequence stars are reported: nine T Tauri stars, one SU Aurigae star, and two FU Orionis stars. The submm spectra of T Tauri stars are found to be less steep than that expected from optically thin thermal dust emission. The dust emissivity index, beta, is found to range between 0 and 1.5 for the T Tauri stars. For the two FU Ori stars in our sample, beta is greater than 1 which is more similar to the beta index range 1-2 found for dust associated with molecular clouds and compact H II regions. The low values for beta indicate that column density and temperature gradients cannot be neglected for the dusty T Tauri environments and/or that the grains are large in the accretion disks surrounding T Tauri stars. Although most of the stars in the sample appear unresolved, the stars T Tau, DG Tau, and possibly HL Tau appear to have structure on 1000-2000 AU scales at 800 microns. Total circumstellar masses of a few times 0.01 solar masses for the T Tauri stars and greater than 0.1 solar masses for the FU Ori stars are estimated. Publication: The Astrophysical Journal Pub Date: May 1989 DOI: 10.1086/185441 Bibcode: 1989ApJ...340L..69W Keywords: Radio Emission; Stellar Envelopes; Stellar Spectra; T Tauri Stars; Cosmic Dust; Optical Thickness; Radiant Flux Density; Submillimeter Waves; Astrophysics; STARS: CIRCUMSTELLAR SHELLS; STARS: PRE--MAIN-SEQUENCE; STARS: RADIO RADIATION full text sources ADS | data products SIMBAD (16)

Circumstellar gas associated with HL Tauri - Evidence for a remnant infalling envelope

view Abstract Citations (25) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Circumstellar Gas Associated with HL Tauri: Evidence for a Remnant Infalling Envelope Grasdalen, Gary L. ; Sloan, Gregory ; Stout, Natalie ; Strom, Stephen E. ; Welty, Alan D. Abstract Molecular carbon absorption lines in the spectrum of HL Tau has been discovered near 8775 A. These C2 lines have a heliocentric radial velocity of 43 + or - 3 km/s, redshifted by 23 + or - 3 km/s relative to the star and the associated molecular cloud. This velocity difference suggests that the molecular carbon absorption arises in an infalling envelope. Since KI and diffuse interstellar bands are much weaker than expected, the chemical composition and/or excitation conditions in the HL Tau envelope appear to differ substantially from those in the interstellar medium. Publication: The Astrophysical Journal Pub Date: April 1989 DOI: 10.1086/185414 Bibcode: 1989ApJ...339L..37G Keywords: Cosmic Gases; Pre-Main Sequence Stars; Stellar Envelopes; Molecular Clouds; Radial Velocity; Stellar Composition; Stellar Spectra; Astrophysics; STARS: CIRCUMSTELLAR SHELLS; STARS: PRE--MAIN-SEQUENCE full text sources ADS | data products SIMBAD (5)

Extremely high-velocity molecular flows in young stellar objects

view Abstract Citations (62) References (39) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Extremely High-Velocity Molecular Flows in Young Stellar Objects Koo, Bon-Chul Abstract Very sensitive, wideband CO J = 1-0, J = 2-1, and HCO+ J = 1-0 spectra of several young stellar objects are presented. Extremely weak and very broad extremely high velocity (EHV) wings are found in GL 4909, HH 7-11, S140, and MWC 1080. The line profiles of EHV wings are smooth or flat, quite different from steep HV wings. In L551 and HL Tau, EHV wings as broad as other sources are not found, which would be due to the inclination of the bipolar flows to the line of sight. From the excitation temperature of about 10 K derived for the EHV flows, the estimated column density of CO yields a number density too small to explain the observed ratio of CO J = 2-1 to J = 1-0 intensity. It is concluded that either EHV flows are composed of small dense clumps or most of the carbon in the flow is atomic carbon, unless the kinetic temperature of the flow is much higher than 100 K. Publication: The Astrophysical Journal Pub Date: February 1989 DOI: 10.1086/167105 Bibcode: 1989ApJ...337..318K Keywords: Molecular Flow; Pre-Main Sequence Stars; Stellar Spectra; Stellar Winds; Carbon Monoxide; Formyl Ions; Line Spectra; Molecular Spectra; Astrophysics; INTERSTELLAR: MOLECULES; LINE PROFILES; STARS: PRE--MAIN-SEQUENCE; STARS: WINDS full text sources ADS | data products SIMBAD (11)

A Remarkable Bipolar Flow in the Center of the Rho Ophiuchi Cloud

Using the IRAM 30-m telescope in August and December 1988, we have discovered the first molecular outflow in the central part (L1688) of the nearby ρ Ophiuchi dark cloud. This outflow, found in the J = 2 — 1 line of 12CO near the cloud core A, is an extreme case, weak (outflow mass-loss rate ≈ 5 x 10−8M⊙yr−1) and highly collimated (lenght to width ratio > 14), which explains why it has escaped previous detections with smaller telescopes. The high-velocity molecular gas is hot and optically thin, making the J = 2 — 1 line of 12CO ≈ 3-4 times stronger than the J = 1 — 0 line. Unexpectedly, this outflow does not appears to be driven by any of the embedded near-IR sources known in this region previous deep VLA surveys of the cloud (André, Montmerle, and Feigelson, 1987; Stine et al., 1988; André et al., in prep.). The outflow exciting source is thus probably a very low-luminosity ((L < 0.1L⊙) young stellar object. Using the 30-m equipped with the MPIfIR bolometer, we have very recently found (March 1989) that this object is the strongest continuum point source of L1688 at 1.3 mm. By analogy with L1551-IRS5 and HL Tau, the radio properties of this source suggest that it possesses a weak, possibly collimated, ionized wind and a relatively massive, cold circumstellar disk (Mdisk ≈0.1M⊙).

A close association of five jet and outflow sources in the HL Tauri region

view Abstract Citations (79) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Close Association of Five Jet and Outflow Sources in the HL Tauri Region Mundt, Reinhard ; Ray, Thomas P. ; Buehrke, Thomas Abstract The discovery of a high degree of outflow activity in the HL Tau/HH 30 region, with five out of six known young stars showing outflows within a region of 0.05 x 0.1 pc, is reported. CCD images reveal not only hitherto unseen features in the known bipolar jets associated with the HH 30 star and VLA 1-HL Tau source, but also show jets emanating directly from HL Tau and a source southeast of XZ Tau. Elongated Herbig-Harolike emission is also found centered on XZ Tau. If these outflows are somehow caused by mass accretion, this high degree of activity may be due to mutual gravitational disturbances (and subsequent mass infall) increasing the degree and duration of the outflow over that expected for an'isolated star'. Publication: The Astrophysical Journal Pub Date: October 1988 DOI: 10.1086/185283 Bibcode: 1988ApJ...333L..69M Keywords: Charge Coupled Devices; Early Stars; Pre-Main Sequence Stars; Stellar Coronas; Stellar Mass Ejection; Taurus Constellation; Emission Spectra; Herbig-Haro Objects; Image Processing; Line Spectra; Very Large Array (Vla); Astrophysics; NEBULAE: GENERAL; STARS: MASS LOSS; STARS: PRE--MAIN-SEQUENCE full text sources ADS | data products SIMBAD (13)

Dust discs around low-mass main-sequence stars

Current understanding of the formation of circumstellar discs as a natural accompaniment to the process of low-mass star formation is briefly reviewed. Models of the thermal emission from the dust discs around the prototype stars a Lyr, a PsA, P Pic and 8 Eri are discussed, which indicate that the central regions of three of these discs are almost devoid of dust within radii ranging between 17 and 26 AU, with the temperature of the hottest dust lying between about 115 and 210 K. One possible explanation of the dust-free zones is the presence of a planet at the inner boundary of each cloud that sweeps up grains crossing its orbit. The discs have outer radii that range between about 250 and 800 AU and have dust masses that are unlikely to exceed about 300 Earth masses. Assuming a gas: dust ratio of 100:1 for the pre-mainsequence disc this corresponds to a mass of ca. 0.1 M Q comparable to that of the premain-sequence star HL Tau. The colour, diameter and thickness of the optical image of P Pic, obtained by coronagraphic techniques, have provided further information on the size, radial distribution of number density and orbital inclination of the grains. The difference in surface brightness on the two sides of the disc is puzzling, but might be explained if the grains are elongated and aligned by the combined effects of a stellar wind and a magnetic field of spiral configuration. Finally, we discuss the orbital evolution and lifetimes of particles in these discs, which are governed primarily by radiation pressure, Poynting-Robertson drag and grain-grain collisions. Although replenishment of these discs may be occurring, for example by grains ejected from comets, discs of initial radius ca. 1000 AU can survive Poynting-Robertson depletion over the stellar age and there is no prima facie evidence as yet in favour of a balance between sources and sinks of dust.

The disks of T Tauri stars with flat infrared spectra

The authors model the energy distributions of T Tauri stars with flat infrared spectra by assuming that they have spatially thin disks with unorthodox radial gradients of temperature. These sources differ from more common T Tauri stars in that the extreme shallowness of their spectral slope cannot be plausibly explained by conventinal ideas (e.g., Keplerian accretion or reprocessing of starlight by a slightly flared disk). 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 one possible source for this activity - the spectral limits and estimates of the disk masses derived for three systems (T Tau, DG Tau, and HL Tau) are close to the theoretical values that would make the self-gravity of the disks dynamically important.

Estimate of the spectral classes of the T Tau type stars HL Tau and DG Tau

Estimates have been made of the fundamental physical characteristics of two stars in the stage of evolution to the main sequence. The revised spectral classification for the star HL Tau has made it possible to achieve agreement with the published physical characteristics. The results of the estimates by two independent methods of the fundamental physical characteristics of the two stars in the stage of evolution to the main sequence have given consistent results. For the star HL Tau the revised spectral classification has made it possible to establish agreement for the published physical characteristics of the star. It is probable that HL Tau is a star of early spectral class and of the Ae/Be Herbig type.

Kinematics of the circumstellar gas of HL Tauri and R Monocerotis

Kinematics of the circumstellar gas of HL Tauri and R Monocerotis

Observations of jets from low-luminosity stars. II - SVS 12, HH 30, near HL Tauri, and HH 34

Spatially resolved spectral scans were obtained for four Herbig-Haro jets emanating from low-luminosity premain-sequence stars. There appears to be a general tendency for the excitation and electron density to diminish along these jets. For three jets, the electron density dependence is close to 1/r. HH 30's scattered stellar continuum showed much weaker Fe II lines in 1985 than in 1979, indicative of variable stellar activity. The most distant knot in HH 34's jet has the lowest excitation of any known HH object, with S II-line/H-alpha = 12.

Interferometric images of 13CO emission toward HL Tau

Millimeter wave interferometric images of HL Tau show a clear disk morphology with a nearly keplerian velocity curve. A few a few tenths of a solar mass are in orbit around the star.

Small-scale structure of the circumstellar gas of HL Tauri and R Monocerotis

Small-scale structure of the circumstellar gas of HL Tauri and R Monocerotis

JHKL photometry of three Herbig-Haro jet sources and a nebulous T Tauri star

Infrared sources have been detected at the positions of the Herbig-Haro jet sources HH 30, DG Tau B, and Haro 6-5 B in the Taurus dark cloud complex. The colors of these Herbig-Haro jet sources in the 1-4 micron wavelength range are comparable to those of the dustiest T Tauri stars, while the K magnitudes corrected for likely interstellar extinction are actually somewhat fainter than those oftypical T Tauri stars in this region. These observations are consistent with the view that these Herbig-Haro jet sources are low-mass premain-sequence stars. The nebulous T Tauri star Haro 6-5 was also observed and found to show both a large infrared excess and an intrinsic-polarization of about 3 percent in visible light. Thus this star seems to resemble HL Tau and DG Tau, which have been suggested as examples of young stars with circumstellar disks. 17 references.

Discovery of solar system-size halos around young stars

Near-infrared speckle interferometric observations of five pre-main-sequence stars reveal a core-halo structure around two of these stars: HL Tau and R Mon. The halo light distribution is shown to arise from scattered light from small circumstellar particles. Halo sizes of 320 x 200 AU (alpha x delta FWHM) and 1300 x 1300 AU are deduced for HL Tau and R Mon, respectively, and the halo light is substantially bluer than the stellar light. The minimum mass of small particles in the scattering regions is comparable to the earth's mass in HL Tau and ten times greater in R Mon. Mass loss from the stars is almost certainly insufficient to produce the halo matter. The halos probably consist of relatively slowly moving matter bound gravitationally to the stars. From the size and mass of the circumstellar matter, it appears likely that these halos are in the early stage in the formation of planet-forming disks around the young stars.

Narrow-band imaging and velocity maps of young stellar objects - Initial results

The first trials of a new technique, designed to map low-excitation ionized gas surrounding young stellar objects, are reported. The region surrounding the T Tau stars HL Tau and XZ Tau, that near HH 101, and that near IRS 5 in L1551 have been imaged through a narrow-band (4.7 A FWHM) forbidden S II filter; three-phase CCD chip was used as the detector. By tilting the narrow-band filter, it is possible to vary the wavelength of peak transmission and thus to detect high-velocity radial flows as well as map the morphology of the excited gas near these young stars. Evidence of an apparently helical outflow is found for HH 101. Redshifted gas appears to extend southward from HL Tau toward HH 30; a blueshifted jet extends northeastward of HL Tau. A series of forbidden S II knots is seen to extend along a jet directed southwestward from the infrared source IRS 5; the knot chain appears to delineate a blueshifted outflow that decelerates as it recedes from IRS 5.

High spatial resolution IR observations of young stellar objects - A possible disk surrounding HL Tauri

view Abstract Citations (98) References (10) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS High spatial resolution IR observations of young stellar objects : a possible disk surrounding HL Tauri. Grasdalen, G. L. ; Strom, S. E. ; Strom, K. M. ; Capps, R. W. ; Thompson, D. ; Castelaz, M. Abstract High spatial resolution images of the T Tauri star HL Tau were obtained at 1.6 microns and 2.2 microns. The original images as well as maximum entropy image reconstructions reveal a circumstellar envelope structure, similar at both wavelenghts, and extended along P.A. = 112 deg; the 10 percent width of the structure is 1.9 sec (300 AU at 160 pc). The extended structure is interpreted as light scattered toward earth by dust in a disk surrounding this young stellar object. Polarization measurements made at 2.2 microns support this hypothesis. The total solid particle mass is, at minimum, 5 x 10 to the -7th solar mass. Publication: The Astrophysical Journal Pub Date: August 1984 DOI: 10.1086/184333 Bibcode: 1984ApJ...283L..57G Keywords: Infrared Astronomy; Pre-Main Sequence Stars; Stellar Envelopes; T Tauri Stars; Maximum Entropy Method; Spatial Resolution; Spectral Energy Distribution; Astrophysics full text sources ADS | data products SIMBAD (2)

Dense cores in dark clouds - Young embedded stars at 2 micrometers

view Abstract Citations (56) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Dense cores in dark clouds : young embedded stars at 2 micrometers. Benson, P. J. ; Myers, P. C. ; Wright, E. L. Abstract Twenty-five visually opaque regions which contain strong sources of NH3 (1,1) line emission (dense cores) have been surveyed for evidence of associated stars at two microns. Five such stars have been found, of which three - in B5, L1489, and L1582 - are optically invisible and probably embedded in their associated cores. The stars in B5 and L1489 have 2-100 micron spectra and luminosity similar to those of HL Tau, a very young T Tauri star. These stars probably formed in the cores where they are now seen. These results tend to confirm earlier suggestions that low-mass stars form in dense cores. Publication: The Astrophysical Journal Pub Date: April 1984 DOI: 10.1086/184248 Bibcode: 1984ApJ...279L..27B Keywords: Early Stars; Pre-Main Sequence Stars; Stellar Cores; Stellar Evolution; Stellar Spectra; Density Distribution; Infrared Astronomy; Micrometers; Molecular Clouds; Astrophysics full text sources ADS | data products SIMBAD (8)

New solar systems?

A team of astronomers from UCLA, Cornell University, and the University of Hawaii have discovered what may be two new planetary systems aborning around young stars in the constellations Taurus and Monoceros. The team's ground‐based infrared observations of HL Tau and R Mon reveal features similar to those seen around Vega and Fomalhaut last year by NASA's Infrared Astronomical Satellite (IRAS)—disks of very fine dust particles extending outward from a central star. If current theories about solar system formation are correct, then those disks most likely represent an early evolutionary step in the formation of planets.Using the technique of speckle interferometry to counter the effects of atmospheric distortion, Steven Beckwith of Cornell, Benjamin Zuckerman of UCLA, Melvin Dyck of the University of Hawaii, and Cornell graduate student Michael Skrutskie were able to make the observations using telescopes on Mauna Kea in Hawaii and Kitt Peak in Arizona. What they saw in both cases was short‐wavelength infrared starlight being scattered by dust particles surrounding the star. In the case of HL Tau, the dusty “cloud” appears to extend out about 160 Astronomical Units from the star (4 times as wide as our solar system) in the east‐west direction, but only half that far in the north‐south direction. The explanation, according to Beckwith, is that “we're looking at a tilted disk rather than an oblate spheroid.” The cloud, in other words, is neither exactly edge‐on nor face‐on as seen from earth.