Marilia J. Sartori

Pre-main sequence star Proper Motion Catalogue

We measured the proper motions of 1250 pre-main sequence (PMS) stars and of 104 PMS candidates spread over all-sky major star-forming regions. This work is the continuation of a previous effort where we obtained proper motions for 213 PMS stars located in the major southern star-forming regions. These stars are now included in this present work with refined astrometry. The major upgrade presented here is the extension of proper motion measurements to other northern and southern star-forming regions including the well-studied Orion and Taurus-Auriga regions for objects as faint as V ≤ 16.5. We improve the precision of the proper motions which benefited from the inclusion of new observational material. In the PMS proper motion catalogue presented here, we provide for each star the mean position and proper motion as well as important photometric information when available. We provide also the most common identifier. The rms of proper motions vary from 2 to 5 mas/yr depending on the available sources of ancient positions and depending also on the embedding and binarity of the source. With this work, we present the first all-sky catalogue of proper motions of PMS stars.

ANALYSIS OF THE PICO DOS DIAS SURVEY HERBIG Ae/Be CANDIDATES ∗

A large sample of Herbig Ae/Be (HAeBe) candidates, distributed in different Galactic regions south to declination +30°, were identified by the Pico dos Dias Survey (a search for young stellar objects based on IRAS colors). Most of the candidates are nearby or associated with star-forming clouds, but several others are considered isolated objects. Aiming to verify the young nature of 93 HAeBe candidates, we searched for additional information that could be useful to confirm if they are pre-main-sequence (PMS) stars or evolved objects, which coincidentally show similar IRAS colors. By adopting a spectral index that is related to the amount of infrared excess and the shape of the spectral energy distribution, we have classified the sample according to three groups, which are analyzed on the basis of (1) circumstellar luminosity; (2) spatial distribution; (3) optical polarization; (4) near-infrared colors; (5) stellar parameters (mass, age, effective temperature); and (5) intensity of emission lines. Our analysis indicates that only 76% of the studied sample, mainly the group with intermediate to low levels of circumstellar emission, can be more confidently considered PMS stars. The nature of the remaining stars, which are in the other group that contains the highest levels of infrared excess, remains to be confirmed. They share the same characteristics of evolved objects, requiring complementary studies in order to correctly classify them. At least seven objects show characteristics typical of post-asymptotic giant branch or proto-planetary nebulae.

Optical Polarization and Near-Infrared Photometry of the Proto-planetary Nebula Henize 3-1475*

We present BVRI CCD aperture polarization and near-infrared photometry of the proto-planetary nebula Hen 3-1475. Its intrinsic polarization is high and shows a strong spectral dependence. The position angles in all bands are perpendicular to the axis of the observed bipolar structure. A Monte Carlo code is used to model the intrinsic polarization of Hen 3-1475. Using disk dimensions and other constraints suggested by previous works, we are able to reproduce the observations with an optically thick disk composed by grains with a power-law size distribution ranging from 0.06 to 0.22 μm. We also reliably estimate the foreground polarization from hundreds of stars contained in the CCD images. It is parallel to the intrinsic polarization of Hen 3-1475. Possible implications of this result are discussed. From IR observations, we estimate an interstellar reddening, AV, of about 3.2.

Classification of the Pico Dos Dias Survey Herbig Ae/Be Stars

In this work we analyzed the circumstellar matter distribution of a large sample of Herbig Ae/Be (HAeBe) stars identified by the Pico dos Dias Survey. We adopted a simple model to fit the spectral energy distribution (SED) of 99 PDS stars (80 candidates and 19 well-known HAeBe stars). From this model, we estimated Sc, the contribution of the circumstellar components (dust disk and/or envelope) to the total emitted flux. We classified the sample stars in 3 groups based on the shape of their SEDs. We analyzed this classification and Sc in relation to other properties of the these stars.

Polarization of Herbig Ae/Be candidates and their environment

We present the V band polarization of 81 Herbig Ae/Be (HAeBe) candidates from the Pico dos Dias Survey (PDS). A good estimate of the foreground polarization was possible for most stars. A large number of objects shows intrinsic polarization, which indicates that their circumstellar envelopes have some kind of non-spherical symmetry. In this work, however, we study these data focusing on their relation with the interstellar medium. Our data seem to indicate a correlation between the position angle of the HAeBe star polarization and that of the corresponding field stars. This may be an evidence that the ambient interstellar magnetic field can play a role in the development of asymmetries in the envelope of young stars of intermediate mass. The spatial distribution of the sample relative to neighboring star forming regions is also studied.

The Oph-Sco-Lup-Cen-Cru-Mus-Cha Star-formation Region

The origin of the extended group of OB associations and molecular clouds situated between about galactic longitudes 360° to 290°, from Ophiuchus to Chamaeleon, is discussed. We consider that a satisfactory model must be able to explain the main properties of these associations, like the spatial distribution of the stars, the geometry of the interstellar clouds, the space velocities and age distribution of the premain sequence (PMS) and OB stars. A brief review is presented of some of the conflicting models that have been proposed in the literature, like the Gould Belt model and sequential star formation. We argue that the presence of a spiral arm can explain most of the observations of that super-association.