Subarcsecond images of CW-Tauri - constraints on disk size and jet formation

Subarcsecond spatial resolution images in the [S II] and [N II] + Halpha emission lines of the T Tauri star (TTS) CW Tau are presented. It is shown that CW Tau has a jet that extends up to 2.2'' (300 AU) from the star in the direction P.A. = 144-degrees. The jet emits strongly in [S II], and it is already collimated at 1.3'' (176 AU) from the star. The images also indicate that CW Tau is extended in the east-west direction and that the jet is slightly shifted to the east. This suggests that CW Tau may be a binary with the two components separated 0.20'' (28 AU). The observations are compared with the theoretical models proposed for the production of forbidden line emission regions (FLERs) and protostellar jets

An optical and infrared study of the reflection nebulae GGD-30 and GGD-31

CCD images and near-IR observations of the nebular objects GGD 30 and GGD 31 are presented. The data have been used to study the morphology and physical nature of the nebulosities. GGD 30 is a reflection nebula illuminated by a low mass PMS star of estimated luminosity almost-equal-to 2.3 L.. The CCD images reveal that the illuminating star is likely to be double with a separation between components of 4", corresponding to a projected linear separation of 2000 AU. A stream arises from one of the stellar components; our data do not show, however, evidence of shock-excited material. GGD 31 is a reflection nebula showing a rather complex morphology. It has a dark cavity within the nebulosity and there are two nebular streams arising from the illuminating star and surrounding the cavity. The estimated luminosity of the star is almost-equal-to 10 L.. In addition, the region around GGD 30 has been surveyed in the near-IR and also searched for IRAS point sources. A further PMS object is present in the GGD 30 region. Finally, a peculiar near-IR object has been detected. The object seems to be a late type oxygen-rich star with very extreme colours, H - K = 4.47, K - L' = 4.49, and L' - M' = 1.19 mag

Accretion and UV variability in BP Tauri

BP Tau is one of the few classical T Tauri stars for which the presence of a hot spot in the surface has been reported without ambiguity. The most likely source of heating is gravitational energy released by the accreting material as it shocks with the stellar surface. This energy is expected to be radiated mainly at UV wavelengths. In this work we report the variations of the UV spectrum of BP Tau for 1992 January 5-19, when the star was monitored with IUE during two rotation periods. Our data indicate that lines that can be excited by recombination processes, such as those from O I and He II, have periodic-like light curves, whereas lines that are only collisionally excited do not follow a periodic-like trend. These results agree with the expectations of the magnetically channeled accretion models. The kinetic energy released in the accretion shocks is expected to heat the gas to temperatures of similar to 10(6) K, which henceforth produces ionizing radiation. The UV (Balmer) continuum and the O I and He II lines are direct outputs of the recombination process. However, the C IV, Si II, and Mg II lines are collisionally excited not only in the shock region but also in inhomogeneous accretion events and in the active (and flaring) magnetosphere, and therefore their light curves are expected to be blurred by these irregular processes. We also report the detection of warm infalling gas from the presence of redshifted (81 km s(-1)) absorption components in some of the high-resolution Mg II profiles available in the IUE and Hubble Space Telescope archives

Resolving the forbidden-line emission regions of young stellar objects - DD Tauri

We present high spatial resolution, narrow-band images of the T Tauri star, DD Tau, obtained with the High-Resolution Camera of CFHT. We have resolved the forbidden line emission region (FLER) of this source, on a spatial scale 0".5 in both [N II] and [S II]. The bulk of the continuum emission is concentrated in two knots that are separated by 0".55 (77 AU) and oriented in the direction P.A. = 6.4-degrees. The forbidden-line morphology is distinctly different from that of the continuum. The [N II] emission appears to be a "jetlike" extension connecting the two continuum knots. The [S II] emission seems to be confined to the northern knot. The southern knot (DD Tau B) is extended in the direction P.A. congruent-to 130-degrees. The orientation of the disk as defined by IR polarization measurements is P.A. congruent-to 125-degrees. We compare our observations with the existing theoretical models for the origin of FLERs

Accretion shocks in T Tauri stars: diagnosis via semiforbidden UV lines ratios

Numerical calculations of the structure of accretion shocks in T Tauri stars (TTSs) indicate that the C III]1909, O III]1661+1666 and Si III]1892 ultraviolet lines should have comparable intensities. We show how the density and the velocity of the accreted gas can be derived from these line ratios. We also indicate how these parameters can be used, together with other less reliable parameters such as the distance and the extinction, to derive the accretion rate and the accretion luminosity. It is shown that the line ratios as well as their absolute fluxes [as measured with the International Ultraviolet Explorer (IUE)] are in agreement with the predictions of the accretion-shock model. However, this method is best suited for the analysis of high-resolution data [such as those obtained with the Hubble Space Telescope (HST)] from which accurate fluxes can be determined and blended components (stellar atmosphere, winds) can also be properly subtracted out.Peer reviewe

The T Tauri stars (TTSs) physics as studied with the IUE: From activity to accretion

The International Ultraviolet Explorer (IUE) has been contemporary to the rapid development of the research on star formation. The IUE has contributed significantly to the understanding of the atmospheres of the T Tauri stars (TTSs) as well as to the study of the accretion physics in pre-main sequence stars; the main findings in these two fields are summarized in this contribution. A brief summary of the contains of the IUE Final Archive on TTSs is also provided

Accretion shocks and winds in T Tauri stars

The dynamics of accretion and outflow in the T Tauri stars (TTSs) is expected to be associated with the production of shocks. Accretion shocks are expected to occur at the locations on the stellar surface where the kinetic energy of the infalling material is released into heating. Wind shocks are expected to be generated in the wind, at the base of the high velocity jets. Both types of shocks are expected to occur at velocities of some few hundreths of km/s and high densities (> 10(6) cm(-3)) producing strong semiforbidden lines of O III], C III] and Si III] in the ultraviolet range. High resolution profiles of the Si III](1892) and C III](1908) lines are available for three pre-main sequence stars (AB Dor, RY Tau, RU Lup) in the IUE and BST Archives. In this contribution, evidence for shocks in the circumstellar environment of these sources is presented. In two out of the three cases studied, the shock is observed to occur in the wind, at the base of the optical jet. This is estimated to be at 0.2 AU from the base of the wind for RY Tau

AK Sco: a tidally induced atmospheric dynamo in a pre-main sequence binary?

AK Sco is a unique source: a 10-30 Myrs old pre-main sequence spectroscopic binary composed by two nearly equal F5 stars that at periastron are separated by barely eleven stellar radii so, the stellar magnetospheres fill the Roche lobe at periastron. The orbit is not yet circularized (e=0.47) and very strong tides are expected. This makes of AK Sco, the ideal laboratory to study the effect of gravitational tides in the stellar magnetic field building up during pre-main sequence evolution. Evidence of this effect is reported in this contribution

Constraints for Use of Ultraviolet Spectropolarimetry to Detect Chiral Amino Acids from Comets

Life is pervasive on planet Earth, but whether life is ubiquitous in the Galaxy and sustainable over timescales comparable to stellar evolution is unknown. Evidence suggests that life first appeared on Earth more than 3.77 Gyr ago, during a period of heavy meteoric bombardment. Amino acids, the building blocks of proteins, have been demonstrated to exist in interstellar ice. As such, the contribution of space-generated amino acids to those existing on Earth should be considered. However, detection of space amino acids is challenging. In this study, we used analytical data from several meteorites and in situ measurements of the comet 67P/Churyumov-Gerasimenko collected by the Rosetta probe to evaluate the detectability of alanine by ultraviolet spectropolarimetry. Alanine is the second-most abundant amino acid after glycine and is optically active. This chirality produces a unique signature that enables reliable identification of this amino acid using the imprint of optical rotatory dispersion (ORD) and circular dichroism (CD) in the ultraviolet spectrum (130–230 nm). Here, we show that the ORD signature could be detected in comets by using ultraviolet spectropolarimetric observations conducted at middle size space observatories. These observations can also provide crucial information for the study of sources of enantiomeric imbalance on Earth

The UV high-resolution spectrum of A-type supergiants

Unidad Deptal. de Astronomía y GeodesiaFac. de Ciencias MatemáticasTRUEpu