ISOCAM observations of the L1551 star formation region

Gålfalk, M., Olofsson, G., Kaas, A. A., Olofsson, S., Bontemps, S., Nordh, L., Abergel, A., André, P., Boulanger, F., Burgdorf, M., Casali, M. M., Cesarsky, C. J., Davies, J., Falgarone, E., Montmerle, T., Perault, M., Persi, P., Prusti, T., Puget, J. L., and Sibille, F.
Astronomy and Astrophysics, v.420, p.945-955 (2004)


The results of a deep mid-IR ISOCAM survey of the L1551 dark molecular cloud are presented. The aim of this survey is a search for new YSO (Young Stellar Object) candidates, using two broad-band filters centred at 6.7 and 14.3 μm. Although two regions close to the centre of L1551 had to be avoided due to saturation problems, 96 sources were detected in total (76 sources at 6.7 μm and 44 sources at 14.3 μm). Using the 24 sources detected in both filters, 14 were found to have intrinsic mid-IR excess at 14.3 μm and were therefore classified as YSO candidates. Using additional observations in B, V, I, J, H and K obtained from the ground, most candidates detected at these wavelengths were confirmed to have mid-IR excess at 6.7 μm as well, and three additional YSO candidates were found. Prior to this survey only three YSOs were known in the observed region (avoiding L1551 IRS 5/NE and HL/XZ Tau). This survey reveals 15 new YSO candidates, although several of these are uncertain due to their extended nature either in the mid-IR or in the optical/near-IR observations. Two of the sources with mid-IR excess are previously known YSOs, one is a brown dwarf (MHO 5) and the other is the well known T Tauri star HH 30, consisting of an outflow and an optically thick disk seen edge on.

Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA.

Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias.

Table 2 is only available in electronic form at the CDS via anonymous ftp to ( or via