CFHT MEGACAM Imaging Survey Proposal ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ MASS LOSS IN STAR FORMING REGIONS: A Complete Census of Jets and Outflows around Yound Stars PI: F. Menard, Canada-France-Hawaii Telescope, Hawaii, USA co-Is:J.L. Monin, Laboratoire d'Astrophysique, Obs. Grenoble, FRANCE C.Dougados, Laboratoire d'Astrophysique, Obs. Grenoble, FRANCE Abstract: We propose a complete census of outflows in two nearby molecular clouds through deep large-scale [SII] and/or Halpha imaging. GENERAL CONTEXT: ---------------- The disks and jets associated with Young Stellar Objects (YSOs) represent one of the most common examples of accretion phenomena in astrophysics. Yet, it is poorly understood. The bulk of accretion onto a YSO occurs from a surrounding disk and lasts about 10E5 years. During this phase, young stars drive powerful jets and bipolar outflows into the surrounding medium. These processes are important for star formation as they regulate the angular momentum evolution and the final stellar mass for example. There is now strong evidence that accretion and ejection are tightly linked, but the exact details of the connection are not known, although it is likely of MHD nature. The deep imaging survey we propose will help understand the jet frequency among YSOs as a function of age, as well as their variability and lifetimes. From infrared and millimeter observations, we now know that literally all Class I YSOs (the young and embedded sources) have circumstellar disks, while that fraction goes down to about 50% in class II (i.e, the classical T Tauri stars) and to nearly zero in class III (i.e., the weak-line T Tauri stars). Similarly, the fraction, and brightness, of jets decreases from Class I to Class III. Although these guidelines are well accepted, the exact frequency of the presence of jets/outflows around YSO's is not well known. This is due to the lack of an adequate and complete large-scale coverage of the star forming regions. Another aspect of our survey is to study the impact of the star formation process on the host giant molecular cloud. The recent discovery of parsec-scale jets, i.e., outflows from single low-mass young stars reaching distances of a parsec or so (about 20' in Orion, 1deg in Taurus) shed new lights on the impact of the mass-loss phenomenon. On one hand, the mass loss must have been going on for much longer than previously thought. On the other hand, the volume filling factor of the jets is larger than previously thought. As a consequence, their effect on the molecular environment may be important. For now, only a few (20) of these parsec-scale jets are known, and it is difficult to assess their universality, and therefore their impact on the molecular cloud for the support against collapse (via turbulence) or for the cloud dispersal. These questions remain open today because large format imagers with good resolution were not available. IMMEDIATE GOALS OF THE PROPOSAL: -------------------------------- We propose to map two (2) prototypical star forming regions, the Taurus and Orion molecular clouds in [SII], or Halpha if not available. These two clouds cover the range of expected conditions in which star formation occurs: low-mass distributed population for Taurus and high-mass stars surrounded by rich clusters for Orion. These should be the same fields that will be imaged by Dougados et al. (see MEGACAM proposal to search for low-mass stellar and sub-stellar objects in Taurus and Orion). The sensitivity and the large format of MEGACAM will give us the first large-scale, deep, brightness limited survey for jets done in any star forming region. From the statistics on the jet detection, we will be able to compare the frequency of occurence of the jets with respect to that of disks. The large surface covered uniformly by the survey will allow us to accurately evaluate the surface covering factor of the jets and hence estimate their effect on the stability and/or dispersal of the molecular cloud environment. The overall shape of the jets and the spacing between the shocks found along them are as many clues to understand the time- and direction variability of the jets. These parameters are fundamental to better constraint the accretion/ejection MHD models. Similarly, because magnetic fields are thought to play a key role in the collapse of molecular cores and in the accretion/ejection process, it has been claimed several times that jets align themselves with the ambient magnetic field direction (the disk being perpendicular). Although current observations suggest that it is not the case in Orion, the situation is still controversial, especially in Taurus. Our data set would offer the perfect tool to provide a definitive answer to that issue. Secondary by-products of this study include a large data base for: (1) stellar variability, (2) jet and bow-shock proper motion studies, (3) accurate star counts to map the extinction in the clouds, (4) discovery of new embedded sources by identification of previously unknown jets. TARGET SELECTION: ----------------- We propose to map the same field that Dougados et al. propose to map. Although BOTH PROGRAMS CAN BE PERFORMED INDEPENDENTLY AND WITHOUT THE OTHER, the two data sets would be complementary. Performing the two studies would allow to compare the jet and disk frequencies, and accurately assess the jet frequency with evolutionary status of the driving star (i.e., whether the star is a class I, II, or III). Dougados et al. propose a deep photometric survey of a region typically 30 deg^2 in the Taurus cloud. We propose to map the same region in [SII] to search for jets/outflows in the same sample of stars. The Taurus dark cloud is among the closest star-forming region to the sun at a distance of 140 pc. Its extension on the sky is 100 deg^2. The surface covered by current deep narrow-band imaging surveys is of the order of one square degree and the number of known jets and/or Herbig-Haro Objects is ~30. These number should be increased 100-fold by our survey. On the other hand, the Orion A and B molecular clouds are the closest giant molecular clouds (d =450 pc) and active massive star forming regions. They each extend over typically 30deg^2 with total gas mass of 10^5 msun. Their associated stellar population spans the whole spectrum of stellar masses up to 30msun. They probably represent the typical environment in which a galactic star forms. Again, we propose to map the same fields as Dougados et al. to search for jets/outflows, i.e., two times 30deg^2. Current surveys unveiled ~110 jets and HH objects in the whole Orion cloud complex. But new results obtained with other large imagers suggest that this number can also be increased by a large amount. OBSERVING STRATEGY: ------------------- The main body of the jets is brighter in the low-excitation [SII] lines at 6717 & 6731 A. We propose to perform our observations at this wavelength. Typical total exposure times of 60minutes (1h) on each field are necessary to image the faint jets and bow-shock. The bow-shock, i.e., the working surfaces of the jets, are also bright in Halpha. In the case where an [SII] filter would not be available, the present proposal could still be performed successfully in Halpha, although with a reduced detection efficiency. In both cases, the images need to be continuum-subtracted and a short exposure in the I-band (which does not contain bright emission lines) is sufficient. Typical exposure times of 5 minutes, depending on the width of the narrow-band filters, are expected. We propose to image 100 fields. 75 minutes are typically needed on each fields, i.e., 125 hours. SPECIFIC NEEDS: --------------- Filters: [SII] including both lines at 671.7 and 673.1 nm. (bandwidth of 3 to 5nm is sufficient). If unavailable, Halpha. NOTE: 1) We expect other co-investigators to join us during the course of this survey. Candidates are Karl Stapelfeldt (NASA/JPL), Bo Reipurth (CASA/Univ of Colorado), Sylvie Cabrit (DEMIRM), and possibly a few others. 2) Francois Menard would like to serve in the MEGACAM working group.