C. Farina

The Onfp Class in the Magellanic Clouds

The Onfp class of rotationally broadened, hot spectra was defined some time ago in the Galaxy, where its membership to date numbers only eight. The principal defining characteristic is a broad, centrally reversed He II λ 4686 emission profile; other emission and absorption lines are also rotationally broadened. Recent surveys in the Magellanic Clouds (MCs) have brought the class membership there, including some related spectra, to 28. We present a survey of the spectral morphology and rotational velocities, as a first step toward elucidating the nature of this class. Evolved, rapidly rotating hot stars are not expected theoretically, because the stellar winds should brake the rotation. Luminosity classification of these spectra is not possible, because the principal criterion (He II λ4686) is peculiar; however, the MCs provide reliable absolute magnitudes, which show that they span the entire range from dwarfs to supergiants. The Onfp line-broadening distribution is distinct and shifted toward larger values from those of normal O dwarfs and supergiants with >99.99% confidence. All cases with multiple observations show line-profile variations, which even remove some objects from the class temporarily. Some of them are spectroscopic binaries; it is possible that the peculiar profiles may have multiple causes among different objects. The origin and future of these stars are intriguing; for instance, they could be stellar mergers and/or gamma-ray-burst progenitors.

SPECTROSCOPIC STUDY OF THE N159/N160 COMPLEX IN THE LARGE MAGELLANIC CLOUD

We present a spectroscopic study of the N159/N160 massive star-forming region south of 30 Doradus in the Large Magellanic Cloud, classifying a total of 189 stars in the field of the complex. Most of them belong to O and early B spectral classes; we have also found some uncommon and very interesting spectra, including members of the Onfp class, a Be P Cygni star, and some possible multiple systems. Using spectral types as broad indicators of evolutionary stages, we considered the evolutionary status of the region as a whole. We infer that massive stars at different evolutionary stages are present throughout the region, favoring the idea of a common time for the origin of recent star formation in the N159/N160 complex as a whole, while sequential star formation at different rates is probably present in several subregions.

A view of Large Magellanic Cloud H ii regions N159, N132, and N166 through the 345-GHz window

Fil: Paron, Sergio Ariel. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Astronomia y Fisica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomia y Fisica del Espacio; Argentina

Unveiling the circumstellar environment toward a massive young stellar object

Aims. As a continuation of a previous work, in which we found strong evidence of massive molecular outflows toward a massive starforming site, we present a new study of this region based on very high angular resolution observations with the aim of discovering the outflow-driven mechanism. Methods. Using near-IR data acquired with Gemini-NIRI at the broad H -a ndKs-bands, we studied a region of 22 �� × 22 �� around the UCHii region G045.47+0.05, a massive-star forming site at a distance of about 8 kpc. To image the source with the highest spatial resolution possible we employed the adaptative optics system ALTAIR, achieving an angular resolution of about 0. �� 15. Results. We discovered a cone shaped nebula that has an opening angle of about 90 ◦ and extends eastward of the IR source 2MASS J19142564+1109283, which is very likely a massive young stellar object (MYSO). This morphology suggests a cavity that was cleared in the circumstellar material, and its emission may arise from scattered continuum light, warm dust, and probably also from emission lines from shock-excited gas. The nebula, which presents arc-like features, is connected with the IR source through a jet-like structure, which is aligned with the blueshifted CO outflow found in a previous study. The near-IR structure lies ∼3 �� north of the radio continuum emission, revealing that it is not spatially coincident with the UCHii region. The observed morphology and structure of the near-IR nebula strongly suggest the presence of a precessing jet. We resolved the circumstellar environment (in scale of a thousand AU) of a distant MYSO, indeed one of the farthest currently known.

UNVEILING THE NEW GENERATION OF STARS IN NGC 604 WITH GEMINI-NIRI

We present a near infrared study focused on the detection and characterization of the youngest stellar component of the NGC 604 giant star-forming region, in the Triangulum galaxy (M 33). By means of color-color diagrams derived from the photometry of JHKs images taken with Gemini-NIRI, we have found 68 candidate massive young stellar objects. The spatial distribution of these sources matches the areas where previous studies suggested that star formation might be taking place, and the high spatial resolution of our deep NIRI imaging allows to pinpoint the star-forming knots. An analysis of the fraction of objects that show infrared excess suggests that the star formation is still active, supporting the presence of a second generation of stars being born, although the evidence for or against sequential star formation does not seem to be conclusive.

A Charge-Coupled Device Photometric Study of South Hemispheric Contact Binary AE Phoenicis

The complete charge-coupled device light curves in B, V, R, and I bands of the short-period binary system, AE Phe, are presented. It is found that the light curves of AE Phe belong to typical EW-type light variation. Photometric solutions were derived by using the 2003 version of the Wilson-Devinney code. It showed that AE Phe is a W-subtype shallow-contact system (f = 14.6%(+/- 0.5%)) with a mass ratio of q = 2.5491(+/- 0.0092). The temperature difference between the two components is 227 K. Analysis of the O-C curve suggests that the period of AE Phe shows a long-term continuous increase at a rate of dP/dt = + 6.17(+/- 0.44) x 10(-8) days year(-1). The long-term period increase, the marginal-contact configuration, and the astrophysical parameters of the binary system, all suggest that it is a shallow-contact binary undergoing a thermal relaxation oscillation evolving into a detached binary.

Near-IR imaging toward a puzzling young stellar object precessing jet

Aims. The study of jets that are related to stellar objects in formation is important because it enables us to understand the history of how the stars have built up their mass. Many studies currently examine jets towards low-mass young stellar objects, while equivalent studies toward massive or intermediate-mass young stellar objects are rare. In a previous study, based on 12 CO J = 3 2 and public near-IR data, we found highly misaligned molecular outflows toward the infrared point source UGPS J185808.46+010041.8 (IRS) and some infrared features suggesting the existence of a precessing jet. Methods. Using near-IR data acquired with Gemini-NIRI at the JHKs broad- and narrowbands centered on the emission lines of [FeII], H2 1 0 S(1), H2 2 1 S(1), Br , and CO 2 0 (bh), we studied the circumstellar environment of IRS with an angular resolution between 000: 35 and 000: 45. Results. The emission in the JHKs broadbands shows in great detail a cone-shaped nebula extending to the north-northeast of the point source, which appears to be attached to it by a jet-like structure. In the three bands the nebula is resolved in a twisted-shaped feature composed of two arc-like features and a bow-shock-like structure seen mainly in the Ks band, which strongly suggests the presence of a precessing jet. An analysis of proper motions based on our Gemini observations and UKIDSS data additionally supports the precession scenario. We present one of the best-resolved cone-like nebula that is most likely related to a precessing jet up to date. The analysis of the observed near-IR lines shows that the H2 is collisionally excited, and the spatially coincidence of the [FeII] and H2 emissions in the closer arc-like feature suggests that this region is a ected by a J shock. The second arc-like feature presents H2 emission without [FeII], which suggests a nondissociated C shock or a less energetic J shock. The H2 1-0 S(1) continuumsubtracted image reveals several knots and filaments at a larger spatial scale around IRS. These perfect match the distribution of the red- and blueshifted molecular outflows discovered in our previous work. An unresolved system of YSOs is suggested to explain the distribution of the analyzed near-IR features and the molecular outflows, which in turn explains the jet precession through tidal interactions.

Studying the molecular ambient towards the young stellar object EGO G35.04−0.47

Fil: Paron, Sergio Ariel. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Astronomia y Fisica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomia y Fisica del Espacio; Argentina