At LAEFF, we study the phenomena that take place during the processes of star formation, and the mutual influence between these phenomena and the environment of young stars.
It is currently believed that stars form from the collapse of clumps of dense gas within molecular clouds. We study these denser areas by means of spectroscopy observations of the emission from some particular molecules, whose transitions are only excited in high-density gas (like ammonia or CCS). Determining enhancements of density, temperature and turbulence in these areas, we can identify the location of newborn stars.
Contour map of the ammonia lines J,K=1,1 (left) and 2,2 (right) in NGC 2264G. Crosses and triangle in the map represent possible young stellar objects. The (2,2) line traces warmer gas, and it is coincident with a radiocontinuum source (marked with a triangle). Taken from Gómez et al (1994)
Since angular momentum has to be conserved, it is usually not possible to form a star directly from gravitational collapse. A centrifugal barrier makes the material to lie on a rotating disk of gas and dust around the protostar. From these protoplanetary disks, new solar systems could arise.
The star grows by getting matter from the disk, in a process called accretion. For this accretion to be possible, some angular momentum has to be released, in the form of collimated jets, ejected perpendicular to the disks. We study these jets from young stars, and in some cases, we have evidence of the presence of a protoplanetary disk in the same sources.
For the star to continue growing, it takes matter from the disk, in a process called accretion. For this accretion to be possible, some angular momentum has to be released, in the form of collimated jets, ejected perpendicular to the disks. We study these jets from young stars, and in some cases, we have evidence of the presence of a protoplanetary disk in the same sources.
Jet (in color), traced by radio continuum emission, and protoplanetary disk (white circles), traced by water maser lines, in a young star in the NGC 2071 region. Note that the size of the disk is similar to that of our Solar System. From Torrelles et al (1998).
We also work on the prediction of the observational properties of molecular lines from protoplanetary disks when they can be observed with the new submillimeter interferometers, such as the Atacama Large Millimiter Array (ALMA).
The figure on the right shows the expected carbon monoxide emission at 0.85 mm from a protoplanetary disk, when observed with a resolution of 0.4" (Gómez & D'Alessio 2000).
Although the ejection of material is usually seen in the form of collimated jets, sometimes we see more or less spherical ejections, which are difficult to explain with current models of star formation. This is the case, for instance, of the Cepheus A region, in which an almost perfectly spherical bubble of gas (bottom left), traced by water masers (blue dots), is being expelled from a young star (Torrelles et al. 2001).
Jets from young stellar objects pushes the molecular gas around them, producing molecular outflows, which can be detected as high-velocity wings in the spectra of molecular lines, such as CO or HCO+. They usually show a bipolar distribution, with the redshifted and blueshifted lobes on oposite sides from the young stellar objects.
The contours in the previous figure show the blue and redshifted lobes of a molecular outflow in Cepheus A, traced by the wings of the HCO+ molecule, superposed on an optical image of the region (From Gómez et al 1999).
These mass-loss phenomena yield energy and momentum on the surrounding molecular cloud. All subsequent star-formation processes are therefore influenced by jets and molecular outflows.
This figure shows the mean velocity (coded in colors from red- to blueshifted) of the dense gas around B1-IRS, traced by the CCS molecule. The obvious velocity gradients could be the result of interaction between dense gas and a molecular outflow (de Gregorio-Monsalvo 2004).
All maps shown in this page have been obtained with radio interferometers (such as the VLA or OVRO), which provide a high angular resolution. We are also undergoing several single-dish surveys of molecular lines, searching for emission of high-density tracers (ammonia and CCS) and water masers in regions of star formation. In this work, we are using the 70 m antenna at NASA's DSN station in Robledo de Chavela (Madrid, Spain).
These surveys will allow us to study large samples of sources in an homogeneous way, and to identify interesting objects to be observed later with radio interferometers.
