Maria Teresa V. T. Lago

Non-axisymmetric accretion on the classical TTS RW Aur A

(Abridged) High-resolution spectroscopic monitoring of RW Aur A was carried out in 1996, 1998 and 1999 with simultaneous B, V photometry. A multicomponent spectrum is revealed with a veiled photospheric spectrum, broad emissions, narrow emission lines of helium, and accretion, wind and shell features. Periodic modulations in many spectral features were found. The photospheric absorption lines show sinusoidal variations in radial velocity with an amplitude of +-6 km/s and a period of about 2.77 days. The radial velocities of the narrow emission lines of He vary with the same period but in anti-phase to the photospheric lines. The equivalent widths of the narrow emissions vary with a phase-shift with respect to the velocity curve. The strength of the red-shifted accretion components of Na D and other lines is also modulated with the same period. The broad emission lines of metals vary mostly with the double period of about 5.5 days. One unexpected result is that no correlation was found between the veiling and the brightness, although both varied in wide ranges. This is partly due to a contribution of the shell absorption to the photospheric line profiles, which make them vary in width and depth thus simulating lower veiling. Most of the observed features can be interpreted in the framework of non-axisymmetric magnetospheric accretion. We consider two possible models. In the first the asymmetry is induced by orbital motion of an invisible, low mass secondary, which also influences the gasflows around the star, the second considers rotational modulation of a single star with an inclined or asymmetric magnetosphere.High{resolution spectroscopic monitoring of the exceptionally active classical T Tauri star (CTTS) RW Aur A was carried out in three seasons of 1996, 1998 and 1999 with simultaneous B, V photometry. The high quality spectra revealed a multicomponent structure of the spectrum, which includes: 1) a veiled photospheric spectrum of a K1{K4 star, 2) broad emission lines of neutrals and ions, 3) narrow emission lines of He i and He ii, 4) red{shifted accretion features of many lines, 5) shell lines at about the stellar velocity, 6) blue{shifted wind features and 7) forbidden lines. Periodic modulations in many spectral features were found. The photospheric absorption lines show sinusoidal variations in radial velocity with an amplitude of 6k m s 1 and a period of about 2: 77. The radial velocities of the narrow emission lines of He vary with the same period but in anti{phase to the photospheric lines. The equivalent widths of the narrow emissions vary with a phase{shift with respect to the velocity curve. The strength of the red{shifted accretion components of Na D and other lines is also modulated with the same period. The broad emission lines of metals vary mostly with the double period of about 5: d 5. One unexpected result is that no correlation was found between the veiling and the brightness, although both parameters varied in wide ranges. This is partly due to a contribution of the shell absorption to the photospheric line proles, which make them vary in width and depth thus simulating lower veiling. The spectral lines of the accreting gas show two distinct components: one is formed at low velocity at the beginning of the accretion column, and the other at high velocity near the stellar surface. The low velocity components are strong in low excitation lines of neutrals, while the high velocity components are strong in high excitation lines of ions, thus showing the gradients of temperature and density along the accretion column. Most of the observed features can be interpreted in the framework of non{axisymmetric magnetospheric accretion, but the origin of this asymmetry can be explained in dierent ways. We consider two possible models. The rst model suggests that RW Aur A is a binary with a brown dwarf secondary in a nearly circular orbit with a period of 2: d 77. The orbiting secondary generates a moving stream of enhanced accretion from one side of the disk towards the primary. The other model assumes that RW Aur A is a single star with a rotational period of 5: d 5a nd with two footpoints of channeled accretion streams within a global magnetosphere which is tilted relative to the rotational axis or otherwise non{axisymmetric. Both models can explain qualitatively and quantitatively most of the observed variations, but there are some details which are less well accounted for.

No evidence of mass segregation in massive young clusters

Aims. We investigate the validity of the mass segregation indicators commonly used in analysing young stellar clusters. Methods. We simulate observations by constructing synthetic seeing-limited images of a 1000 massive clusters (10 4 M� ) with a standard IMF and a King-density distribution function. Results. We find that commonly used indicators are highly sensitive to sample incompleteness in observational data and that radial completeness determinations do not provide satisfactory corrections, rendering the studies of radial properties highly uncertain. On the other hand, we find that, under certain conditions, the global completeness can be estimated accurately, allowing for the correction of the global luminosity and mass functions of the cluster. Conclusions. We argue that there is currently no observational evidence of mass segregation in young compact clusters since there is no robust way to differentiate between true mass segregation and sample incompleteness effects. Caution should then be exercised when interpreting results from observations as evidence of mass segregation.

Gender and propensity to risk in advanced countries: Comparison between entrepreneurs and non-entrepreneurs

Purpose The purpose of this paper is to compare the way in which gender and propensity to risk are associated in two samples, one of entrepreneurs and the other of non-entrepreneurs, while controlling for other factors, namely, national cultures. Design/methodology/approach On the basis of data from 19 advanced countries, and by using two different samples, one of entrepreneurs and the other of non-entrepreneurs, the authors have used logistical regression analysis to analyse the relation between gender and propensity to risk has been used. Findings Findings suggest that gender and culture are much stronger in influencing risk propensity among non-entrepreneurs than among entrepreneurs. Originality/value Instead of analysing the effects of propensity to risk in entrepreneurship, as is usually done, the authors study some of its determinants, highlighting the differences between men and women.

No evidence for mass segregation in young clusters

Aims. We investigate the validity of mass segregation indicators commonly used in the analysis of young stellar clusters. Methods. We simulate observations by constructing synthetic seeing limited images of a 1000 massive clusters (10 M ) with a standard IMF and a King density distribution function. Results. We find that commonly used indicators are highly sensitive to sample incompleteness in observational data, and that radial completeness determinations do not provide satisfactory corrections, rendering the studies of radial properties highly uncertain. On the other hand, we find that under certain conditions, the global completeness can be estimated accurately, allowing for the correction of the global luminosity and mass functions of the cluster. Conclusions. We argue that there is currently no observational evidence for mass segregation in young compact clusters since there is not a robust way to differentiate between true mass segregation and sample incompleteness effects. Caution should then be exercised when interpreting results from observations as evidence for mass segregation.

Spectral Variability of T Tauri Stars in the Optical

We present the results of time variability analysis of the Hα, He I (λ5876 A) and Na D (λ5890, 5896 A) lines in two active T Tauri stars, DL Tau and DR Tau. The aim is the study of time behaviour of these lines, during one week, as well as possible correlations among them. The observed profiles of some lines are very complex, often showing characteristics of outflow and accretion.

T Tauri Stars: The X-Ray Connection

The launch of ROSAT opened a new era in the study of T Tauri stars. Prompted by the IUE results, the new X-ray data confirms the existence of extremely high levels of activity in these young stars, very likely of magnetic nature. We address a detailed analysis of the star TW Hya in the X-ray spectral range. A summary of its properties in the UV will also be included in order to grasp an overall picture of the activity in this star.

The Signatures of Structured Winds in T Tauri Stars

The identification of He I lines λ 4471.5 A, λ 5875.6 A, λ 6678.1 Aand He II lines λ 4685.7 Ain emission in the optical spectra of T Tauri stars (e.g. Penston & Keavey 1977, Lago & Penston 1982) was the first clear indication for a temperature structure in the outer layers of these stars. Yet no immediate explanation was proposed for the presence of those high temperature regions in the atmosphere of late type stars.

Models in T Tauri Stars Tested Through Hα

Since the pioneering works of Joy(1945) and Herbig(1970), the knowledge of T Tauri stars (TTS) has been steadily building up. It is now well established that these stars are young, with ages not exceeding 3×106 yrs, low mass, variable, with a late type spectrum with emission lines superimposed.

A T Tauri Star Database

A T Tauri Star Database was set up with the purpose of designing a user-friendly, graphical database which would provide a quick look into the properties of T Tauri stars.