Robert Estalella

FRAGMENTATION OF MASSIVE DENSE CORES DOWN TO ≲ 1000 AU: RELATION BETWEEN FRAGMENTATION AND DENSITY STRUCTURE*

In order to shed light on the main physical processes controlling fragmentation of massive dense cores, we present a uniform study of the density structure of 19 massive dense cores, selected to be at similar evolutionary stages, for which their relative fragmentation level was assessed in a previous work. We inferred the density structure of the 19 cores through a simultaneous fit of the radial intensity profiles at 450 and 850 μm (or 1.2 mm in two cases) and the spectral energy distribution, assuming spherical symmetry and that the density and temperature of the cores decrease with radius following power-laws. Even though the estimated fragmentation level is strictly speaking a lower limit, its relative value is significant and several trends could be explored with our data. We find a weak (inverse) trend of fragmentation level and density power-law index, with steeper density profiles tending to show lower fragmentation, and vice versa. In addition, we find a trend of fragmentation increasing with density within a given radius, which arises from a combination of flat density profile and high central density and is consistent with Jeans fragmentation. We considered the effects of rotational-to-gravitational energy ratio, non-thermal velocity dispersion, and turbulence mode on the density structure of the cores, and found that compressive turbulence seems to yield higher central densities. Finally, a possible explanation for the origin of cores with concentrated density profiles, which are the cores showing no fragmentation, could be related with a strong magnetic field, consistent with the outcome of radiation magnetohydrodynamic simulations.

VLBI multi-epoch water maser observations toward massive protostars

UB/IEEC, Barcelona (Spain)Abstract.VLBI multi-epoch water maser observations are a powerful tool to study the gas veryclose to the central engine responsible for the phenomena associated with the early evolutionof massive protostars. In this paper we present a summary of the main observational resultsobtained toward the massive star-forming regions of Cepheus A and W75N. These observa-tions revealed unexpected phenomena in the earliest stages of evolution of massive objects (e.g.,non-collimated “short-lived” pulsed ejections in different massive protostars), and provided newinsights in the study of the dynamic scenario of the formation of high-mass stars (e.g., simul-taneous presence of a jet and wide-angle outflow in the massive object Cep A HW2, similarto what is observed in low-mass protostars). In addition, with these observations it has beenpossible to identify new, previously unseen centers of high-mass star formation through outflowactivity.Keywords.ISM: general, stars: formation, ISM: jets and outflows

Investigation of stellar loop structures using VLBI

Abstract In this paper we discuss a set of three consecutive VLBI observations of the binary system UX Arietis. The most interesting result is the variation with time of the source structure. The usual interpretation in terms of gyrosynchrotron emission from relativistic electrons trapped in a magnetic loop and undergoing collisional and radiative losses is not able, alone, to explain the observed variations. By using optical, radio and X-ray information we have produced a model of two giant loops anchored on a rotating star. As the star rotates, the loops change their relative position and orientation with respect to the line of sight, causing the observed variation of the source structure. The qualitative agreement found is consistent with our hypothesis and makes these observations a sort of a pilot experiment for a new way of using VLBI to observe radio-stars. In order to quantitatively test our model of evolving electrons confined in loops anchored on a rotating star, we plan in the near future a set of several phase-reference VLBI observations fully covering the 6.4 day rotational period.

3D Spectroscopy of Herbig-Haro Objects

HH 110 and HH 262 are two Herbig-Haro jets with rather peculiar, chaotic morphology. In the two cases, no source suitable to power the jet has been detected along the outflow, at optical or radio wavelengths. Both, previous data and theoretical models, suggest that these objects are tracing an early stage of an HH jet/dense cloud interaction. We present the first results of the integral field spectroscopy observations made with the PMAS spectrophotometer (with the PPAK configuration) of these two turbulent jets. New data of the kinematics in several characteristic HH emission lines are shown. In addition, line-ratio maps have been made, suitable to explore the spatial excitation an density conditions of the jets as a function of their kinematics.

The spatial structure of the HH 30 jet

New, deep, wide-field [SII] images of the HL Tauri region show the extended spatial structure of the HH 30 jet and counter-jet. At an angular distance of ∼ 300 arcsec toward the NE, the HH 30 jet ends in a group of scattered condensations. This previously undetected structure might correspond to a broken-up working surface. Our images also include HH 262, which is shown to have a previously undetected extended emission region.

High Collimation and Low Collimation Winds in HH 34

We present preliminary results of VLA D-configuration observations of the high-density gas toward the HH 34 system exciting source (HH 34 IRS). We observed the (J,K) = (1,1) transition of the ammonia molecule. The brightest high-density condensation is a shell-like structure that surrounds the east side of the star HH 34 IRS, and coincides with the reflection nebula associated with HH 34 IRS5. If this condensation is part of a spherical shell dynamically related to HH 34 IRS, it should have been created at some stage by its stellar wind. This would imply that two kinds of stellar wind might have been present: an isotropic wind that has created the shell, and a highly collimated wind that is at the origin of the jet.

L723: One or Two Outflows?

The CO maps of the outflows in L723 and IRAS 16293-2422 show a complex structure, with four lobes disposed in two bipolar pairs. With our recent detection of a double radio source at the center of the L723 outflow, both outflows have a central double radio source. We suggest that this result favors the models in which these complexes are constituted by two independent outflows with two independent exciting sources.

CS observations of selected star-forming regions

Maps of the CS (J=1→0) emission at 49 GHz of L43 (RNO 91), NGC 2068 (HH 19-27) and L1524 (Haro 6-10) are presented. Physical parameters of these clouds are derived from the observations. The CS emission is compared with ammonia emission maps obtained with a similar angular resolution. Both CS and ammonia molecules are tracers of the high-density gas in molecular clouds. Thus, a similar distribution of the emission is expected. However, our observations show evidence of some remarkable morphological differences.