Tauri-type Stars Research Articles

Physical and Chemical Vertical Structure of Magnetostatic Accretion Disks of Young Stars

The vertical structure of the accretion disks of young stars with fossil large-scale magnetic field is studied. The equations of magnetostatic equilibrium of the disk are solved taking into account the stellar gravity, gas and magnetic pressure, turbulent heating, and heating by stellar radiation. The modelled physical structure of the disk is used to simulate its chemical structure, in particular, to study the spatial distribution of CN molecules. The disk of the typical T Tauri star is considered. Simulations show that the temperature within the disk in the region $r<50$ au decreases with height and density profiles are steeper than in the isothermal case. Outside the `dead' zone, vertical profiles of the azimuthal component of the magnetic field are nonmonotonic, and the magnetic field strength maximum is reached within the disk. The magnetic pressure gradient can cause an increase in the disk thickness in comparison with the hydrostatic one. The CN molecule concentration is maximum near the photosphere and in the disk atmosphere where the magnetic field strength at chosen parameters is $\sim 0.01$ G. Measurements of the Zeeman splitting of CN lines in the submm range can be used to determine the magnetic field strength in these regions of accretion disks.

Modulated accretion in the T Tauri star RY Tau – a stable MHD propeller or a planet at 0.2 au?

ABSTRACT Planets are thought to form at the early stage of stellar evolution when mass accretion is still ongoing. RY Tau is a T Tauri type star at the age of a few Myr, with an accretion disc seen at high inclination, so that the line of sight crosses both the wind and accretion gas flows. In a long series of spectroscopic monitoring of the star over the period 2013–2020, we detected variations in H$\, {\alpha }$ and Na i D absorptions at radial velocities of infall (accretion) and outflow (wind) with a period of about 22 d. The absorptions in the infalling and outflowing gas streams vary in antiphase: an increase of infall is accompanied by a decrease of outflow, and vice versa. These ‘flip-flop’ oscillations retain phase over several years of observations. We suggest that this may result from the magnetohydrodynamics processes at the disc–magnetosphere boundary in the propeller mode. Another possibility is that a massive planet is modulating some processes in the disc and is providing the observed effects. The period, if Keplerian, corresponds to a distance of 0.2 au, which is close to the dust sublimation radius in this star. The presence of the putative planet can be confirmed by radial velocity measurements: the expected amplitude is ≥90 m s−1 if the planet mass is ≥2 MJ.

Estimation of the Gould Belt Scale Height from T Tauri Type Stars in the Gaia DR2 Catalog

We analyze the spatial and kinematic properties of a large sample of young T Tauri type stars in a 500 pc radius solar neighborhood, closely related to the Gould belt. The following parameters of the exponential density distribution have been determined: the average $(z_G)_\odot=-25\pm5$ pc and scale height $h_G=56\pm6$ pc. We propose a method of excluding background stars from the samples, which are located at large heights with respect to the symmetry plane of the Gould belt. We discovered that the expansion effect for the entire star system, $K_G=6\pm1$ km s$^{-1}$ kpc$^{-1}$, is determined mainly by the dynamics of the Scorpius-Centaurus association. We show that the angular velocity of the residual intrinsic rotation of the Gould belt can reach $\Omega_G=6.9\pm0.2$ km s$^{-1}$ kpc$^{-1}$ and that this rotation is opposite to the galactic rotation.

Grain Growth in Newly Discovered Young Eruptive Stars*

Abstract FU Orionis–type stars are young stellar objects showing large outbursts due to highly enhanced accretion from the circumstellar disk onto the protostar. FU Orionis–type object (FUor) outbursts happen in a wide variety of sources from the very embedded ones to those with almost no sign of extended emission beyond the disk. The subsequent eruptions might gradually clear up the obscuring envelope material and drive the protostar on its way to become a disk-only T Tauri star. We used the Very Large Telescope (VLT)/VLT spectrometer and imager for the mid-infrared (VISIR) to obtain the first spectra that cover the 8–13 μm mid-infrared wavelength range in low resolution of five recently discovered FUors. Four objects from our sample show the 10 μm silicate feature in emission. We study the shape and strength of the silicate feature in these objects and find that they mostly contain large amorphous grains, suggesting that large grains are typically not settled to the midplane in FUor disks. This is a general characteristic of FUors, as opposed to regular T Tauri–type stars whose disks display anything from pristine small grains to significant grain growth. We classify our targets by determining whether the silicate feature is in emission or in absorption, and confront them with the evolutionary scenarios on the dispersal of the envelopes around young stars. In our sample, all Class II objects exhibit silicate emission, while for Class I objects, the appearance of the feature in emission or absorption depends on the viewing angle with respect to the outflow cavity. This highlights the importance of geometric effects when interpreting the silicate feature.

Brightness variations of young Sun-like stars from ground-based and space telescopes

AbstractYoung stellar objects often show photometric variability, which is well examined at optical wavelengths, but more and more infrared data are also available. The wavelength dependence of the variability carries information on the physical cause of the changing brightness. Here, we examine seven T Tauri-type stars known for their large amplitude variability selected from the Campaign 13 field of the Kepler K2 mission. We complemented the K2 light curves by multifilter optical monitoring observations made with the 90 cm Schmidt telescope of Konkoly Observatory, and by 3.6 and 4.5 μm infrared photometry with a 20 hours cadence using the Spitzer Space Telescope. We found that the wavelength dependence of the observed variability is not consistent with changing interstellar extinction. We suggest that the brightness changes are due to variable accretion, causing a variable illumination of the inner disk.

Periodicities of the RV Tauri-type pulsating star DF Cygni: A combination ofKeplerdata with ground-based observations

The RV Tauri stars constitute a small group of classical pulsating stars with some dozen known members in the Milky Way. The light variation is caused predominantly by pulsations, but these alone do not explain the full complexity of the light curves. High quality photometry of RV Tau-type stars is very rare. DF Cygni is the only member of this class of stars in the original Kepler field, hence allowing the most accurate photometric investigation of an RV Tauri star to date. The main goal is to analyse the periodicities of the RV Tauri-type star DF Cygni by combining four years of high-quality Kepler photometry with almost half a century of visual data collected by the American Association of Variable Star Observers. Kepler quarters of data have been stitched together to minimize the systematic effects of the space data. The mean levels have been matched with the AAVSO visual data. Both datasets have been submitted to Fourier and wavelet analyses, while the stability of the main pulsations has been studied with the O-C method and the analysis of the time-dependent amplitudes. DF Cygni shows a very rich behaviour on all time-scales. The slow variation has a period of 779.606 d and it has been remarkably coherent during the whole time-span of the combined data. On top of the long-term cycles the pulsations appear with a period of 24.925 d. Both types of light variation significantly fluctuate in time, with a constantly changing interplay of amplitude and phase modulations. The long-period change (i.e. the RVb signature) somewhat resembles the Long Secondary Period (LSP) phenomenon of the pulsating red giants, whereas the short-period pulsations are very similar to those of the Cepheid variables. Comparing the pulsation patterns with the latest models of Type-II Cepheids, we found evidence of strong non-linear effects directly observable in the Kepler light curve.

LIGHT CURVE TYPES OF CLASSIC T TAURI STARS

By using the archive photometric data’s obtained for a long time intervals we have carried out a master light curves of 28 classical T Tauri type stars. For the physical character of variability mainly 5 type light curves can be separated. We have proposed a new scheme of classification among the examined light curves. The proposed scheme suggests a qualitative interpretation in terms of interaction of the central star with its circumstellar accretion disk.

UX Ori Variables in the Cluster IC 348

Results are presented from many years of photometric (VR C I C ) observations of three variable T Tauri type stars in the cluster IC 348: V712 Per, V719 Per, and V909 Per. All three stars have photometric activity characteristic of UX Ori stars. The activity of V719 Per has increased significantly over the last 10 years: the amplitude of its Algol-like minima has increased by roughly a factor of 4 and has reached three stellar magnitudes in the I band. Periodograms of the light curves do not confirm the periods found previously by other authors on the basis of shorter series of observations. The slope of the color tracks on “color-magnitude” diagrams is used to determine the reddening law for these stars owing to selective absorption by circumstellar dust. Modelling of these parameters by the Mie theory shows that the maximum size a max of the dust particles in the protoplanetary disks of these stars is 1.5-2 times greater than in the interstellar medium. In V712 Per and V909 Per, the bulk of the mass of the dust particles is concentrated near a max , while in V719 Per the average mass of the dust particles is determined by the minimum size of the particles. It should be emphasized that these conclusions rely on an analysis of the optical variability of these stars.

High-dispersion Spectroscopic Observations of the T Tauri-type Stars with Weak Emission Lines

By using the 2.16 m telescope of Xinglong Observing Station of National Astronomical Observatories and its high-dispersion spectrograph, the high-dispersion spectroscopic observations of six T Tauri-type stars with weak emission lines (i.e., weak-line T Tauri-type stars, abbreviated as WTTS) were carried out. The lithium abundances of these weak-line T Tauri-type stars are calculated and the relationships of the lithium abundances with the rotation periods as well as the amplitudes of light variations of these stars are discussed. It is found by this study that the lithium abundance for the weak-line T Tauri-type stars with fast rotations tends to be less than that of those with slow rotations. However, for all these weak-line T Tauri-type stars, the lithium abundances have no conspicuous correlation with the amplitudes of light variations of these stars in the V waveband.

Peculiarities and Variations in the Optical Spectrum of the RV Tauri-type Star R Sct

Abstract We analyzed some new high resolution optical spectra of the semiregular RV Tauri-type star R Sct. Fundamental parameters were found to be T eff = 4500 K, log g = 0.0 and ξ t = 4.0 km s−1. The results of chemical analysis show that R Sct is a metal-poor star with [Fe/H]≈ −0.5. The carbon content with respect to iron is significantly larger than in the Sun, [C/Fe]=0.84, but there is an evident deficiency of heavy elements. We found no tight correlation of the chemical abundances on the condensation temperatures of elements. This means that in R Sct the depletion by condensation into dust does not work, with possible exception of Ca and Sc. The luminosity derived from the Hipparcos parallax corresponds to a tip of the red-giant branch or slightly above it. Thus it is possible that R Sct evolved off the early-AGB when it has not yet experienced the third dredge-up in thermal pulses, or it is still located on AGB. The peculiarities of spectral features (emissions, line-splitting) and the complicated time-variable radial velocities were also studied.

UV and optical spectrum variability of T Tau and RY Tau

AbstractIn this report we have presented results of spectral observations of classical T Tauri type stars T Tau and RY Tau. Observational dates were obtained from following sources: spectrograms of the UV range from the IUE archive data, and spectrograms of the visual range obtained in the 2 m telescope of ShAO of the NAS of Azerbaijan (Ismailov et al. 2010). For both of stars on the Scargle method we have searched a periodicity of variations in equivalent widths of emission lines in the optical and UV ranges. In the RY Tau firstly was detected the periodic variability in MgII λ2800 Å emission doublet intensities with a period of 23 days. The observed period had also revealed with the equivalent widths and displacements of components of Hα and H+Hϵ and K CaII emission.The lines were found to be shifted to short wavelengths as the emission line intensities increased in both UV and optical spectral ranges. The lack of a correlation between the brightness variation and the emission line intensity also suggests that, on the whole, the contribution from the radiation in emission lines for the star RY Tau is insignificant.On the analysis of T Tau we conclude that there is a significant variation of spectral emission lines in the optical and UV on a time scale of about 33 days and that this variations is periodic. Both of stars shows the periodicity also for observed group of such lines as CIV λ1450 Å, HeII λ 1640 Å, SII λ1756 Å (Ismailov et al. 2010, Ismailov et al. 2011).Additionally we have carried out spectral energy distributions of this stars in the range 0.36-100 μm which have indicated the excess of spectral radiation in the IR range of spectrum. These excesses of radiations can be explained by the thermal radiation of still unformed bodies at the circumstellar environment. The periodic variability in the spectrum together with the excess of the spectral radiation may be occurred by protoplanets and/or protostars in these young systems. It is showed that possible, planet formation processes mainly to be completed at the time of the formation of classical T Tauri type stars.

Constraints on the Formation of the Planet in HD 188753

The claimed discovery of a Jupiter-mass planet in the close triple-star system HD 188753 poses a problem for planet formation theory. A circumstellar disk around the planet's parent star would be truncated close to the star, leaving little material available for planet formation. In this paper we attempt to model a protoplanetary disk around HD 188753A using a fairly simple α-disk model, exploring a range of parameters constrained by observations of T Tauri-type stars. The disk is truncated to within 1.5-2.7 AU, depending on model parameters. We find that the in situ formation of the planet around HD 188753A is implausible.

Spectral, Photometric, and Polarimetric Study of Visual Binary COU 14

Slit spectra of visual binary COU 14 (HD 207652) in the range 3750-5400 A are studied. In total, 53 absorption lines have been identified in the spectrum reclassified as F2 IV. No spectral features of the secondary component, which is estimated to be an early G-type dwarf, have been detected. The equivalent widths of the strongest lines of the Balmer series, G band, Ca I, Ca II, Mg I, Mg II, Fe I, Fe II, Cr I, Sr II, and other metallic lines are given. No spectral variability has been detected for 2 weeks of spectral observations. Two flares of amplitude more than 03 each in B and V colors and another four of lesser amplitude in the U band have been detected during photometric and polarimetric monitoring lasting 50 hr. Irregular long-term brightness and color variations have also been registered, while no significant polarization signal has been detected. Because of its relative brightness, the spectral features of the secondary component are too faint and unseen in the composite spectrum of COU 14, which practically represents the spectrum of its nonvariable primary star. All detected brightness variations are attributed to the secondary component, whose photometric properties are similar to those of T Tauri-type stars. For the first time a T Tauri type-star has been found to be a member of a nearby visual binary system with well-determined orbital parameters.

The search of rotational modulation of the T Tauri-type stars in the ophiuchus dark clouds

Abstract We present some results of the long-term photometric program ROTOR being carryed out at the Mt. Maidanak observatory. The program seeks for a periodic components in the emission of the non-stationary T Tauri-type stars (TTS), HAEBE, FUORs and related objects. In this paper we analyse the results concerning TTS in Rho Oph dark clouds and vicinity. Our sample of stars includes 6 weak-emission TTS (WTTS) and 11 classical TTS (CTTS).

Molecular Clouds in Cepheus and Cassiopeia

A large-scale 13CO(J = 1-0) survey for nearby molecular clouds was performed toward the Cepheus and Cassiopeia regions (100° < l < 130° and -10° < b < 20°) with the velocity coverage of -40 < VLSR < +20 km s-1 by using the two 4 m millimeter-wave telescopes at Nagoya University. An area of 866 square degrees was covered at an 8' grid spacing with a 27 beam, and 48,750 positions were observed. Significant 13CO emission (≥1.8 K km s-1 = 3 σ) is detected at 1015 positions. On the basis of the 13CO data, 188 distinct 13CO clouds are identified whose total mass is 1.0 × 105 M☉. Physical properties of the 13CO clouds such as molecular column densities, sizes, and masses are derived for each cloud. Astronomical objects associated with the 13CO clouds were searched for in the literature: 10 H II regions, eight reflection nebulae, 23 T Tauri type stars, 28 molecular outflows, and 125 IRAS point sources selected as candidates for protostars are likely to be associated with the 13CO clouds. Statistical studies on the 13CO clouds detected in this survey have been made. The mass spectra of the 13CO clouds in Cepheus and Cassiopeia are well represented by a power law, dNcloud/dMcloud ∝ Mcloud−α, with α = 1.7 ± 0.3 in a cloud mass range 101-105 M☉, which is similar to previously observed other regions like Cygnus. We also investigated the relation between the line width and the size of the 13CO clouds and found that there is no significant correlation among them in the cloud mass range 101-104 M☉. A virial analysis made for the 13CO clouds indicates that the relation between the virial mass Mvir and the mass measured in 13CO Mcloud is approximated well by (Mvir/M☉) = 2.8 × 101(Mcloud/M☉)0.62, suggesting that smaller clouds tend to be more weakly bound than larger clouds gravitationally or are dispersing if the possible external pressure is disregarded. It is found that the 13CO clouds associated with IRAS point sources, which are regarded as ongoing star-forming clouds, tend to be more massive and larger in size, and to have higher column densities than those without any signs of star formation. There seems to be a threshold value in the peak H2 column density of N(H2) = 2.5 × 1021 cm-2 for stars to form in a13CO cloud. In order to study star formation activities in the 13CO clouds, we investigated the global luminosity distribution of the IRAS point sources and attempted to determine the distribution as a function of the parent molecular cloud mass. The IRAS luminosity function in a given cloud with mass Mcloud is found to be well approximated by a power law dnstar/dLstar = 6 × 10−3(Mcloud/M☉)0.8(Lstar/L☉)−1.5 L☉−1 for the IRAS luminosity range 1 < Lstar/L☉ < 105 and the cloud mass range 101 < Mcloud/M☉ < 105. The luminosity function does not depend significantly on the cloud mass, the regions sampled, and the existence of H II regions. The luminosity of the most luminous IRAS point source in a given molecular cloud Lstar,max increases systematically with the mass of the associated cloud, which is fitted by the power law (Lstar,max/L☉) = 0.098 × (Mcloud/M☉)1.43. These relations are found to be consistent with those derived in Cygnus by Dobashi, Bernard, & Fukui, suggesting that they may represent general relations between the maximum IRAS luminosity and the molecular clouds. We finally demonstrate that the slope of the initial mass function estimated from the IRAS luminosity function derived here is consistent with the stellar initial mass function for a stellar mass to luminosity relation of (Lstar/L☉) = (Mstar/M☉)3.45.

Molecular clouds in Cygnus. 1: A large-scale (13)CO survey

view Abstract Citations (100) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Molecular Clouds in Cygnus. I. A Large-Scale 13CO Survey Dobashi, Kazuhito ; Bernard, Jean-Phillipe ; Yonekura, Yoshinori ; Fukui, Yasuo Abstract A large-scale (13)CO (J = 1-0) survey was performed with a 2.7 min angular resolution toward the Cygnus region, using the two 4 m millimeter telescopes at Nagoya University. An area of 432 sq deg was covered with an 8 min grid spacing, and 24,300 positions were observed. Significant (13)CO emission (greater than 1.2 Kkm/s = 3 sigma) is detected at 2191 positions, corresponding to a detection rate of 9%. On the basis of the (13)CO data, 159 distinct clouds are identified. Physical properties of these clouds such as molecular column densities, sizes, and masses are derived for the individual clouds. Astronomical objects associated with the molecular clouds were searched for in the literature. Seven H II regions, three supernova remnants ((SNRs) 45 T Tauri-type stars, 18 molecular outflows, and 215 IRAS point sources selected as candidates for protostars are likely to be associated with the molecular clouds. This paper presents the observational technique used for this survey and a complete list of the detected molecular clouds in Cygnus. Publication: The Astrophysical Journal Supplement Series Pub Date: December 1994 DOI: 10.1086/192106 Bibcode: 1994ApJS...95..419D Keywords: Astronomical Catalogs; Carbon Monoxide; Cygnus Constellation; Interstellar Gas; Molecular Clouds; Molecular Spectra; Radio Astronomy; Radio Spectra; Sky Surveys (Astronomy); Carbon 13; H Ii Regions; Infrared Astronomy Satellite; Line Spectra; Millimeter Waves; Radio Telescopes; Supernova Remnants; T Tauri Stars; Astronomy; CATALOGS; ISM: CLOUDS; ISM: MOLECULES full text sources ADS | data products SIMBAD (342) CDS (2) Related Materials (2) Catalog: 1997yCat..20950419D Part 2: 1996ApJ...466..282D

Periodical variations of the brightness of T Tauri

T Tauri-type stars are characterized by the fast irregular variability. It is possible to select several components in brightness variations: slow components with timescales of years and fast ones with timescales of days and tens of days. Besides, up to 1 mag flares in the ultraviolet part of the spectrum occur during some nights. The overall change of the brightness may reach 2-3 mag.

A search for young stellar objects in southern dark clouds

The IRAS Point Source Catalog has been used to search 482 southern dark clouds for evidence of young stellar objects. Only 6 percent of the selected dark clouds have associated IRAS sources with IRAS colors typical of pre-main-sequence stars. A study of the energy distributions obtained from JHKLM photometry and IRAS flux densities give an identification of these IRAS sources. Thirteen sources have been classified as new low-mass protostellar objects and T Tauri-type stars with nebular surrounding material disks, while four IRAS sources have no evidence of near-IR excesses and appear to be similar to post T Tauri stars in which the nebular disks are probably absent or optically thin. 17 refs.

The stochastical approach to the modelling of the line profiles in T Tauri stellar winds

Line profiles calculations were carried out for spherically-symmetrical stellar wind models with discrete structure. It is shown the possibility to explain two-component emission profiles typical for T Tauri-type stars in the framework of such stochastical approach.

Linear polarization of T Tauri stars

Linear polarization observations over the wavelength range 0.44−2.2 µm are presented for six T Tauri type stars. All of the stars studied show substantial polarization in the infrared, while T Tau itself (and probably SU Aur) show a 90° change in position angle in the infrared. The data are discussed in terms of scattering from circumstellar dust grains with a component of large (∼ 1 µm) grains being required to fit the observed spectral dependence.