A search for shock-excited molecular hydrogen knots in Chamaeleon I very low mass YSOs^*

¹ Observatorio Astronómico de Córdoba, Laprida 854, 5000 Córdoba, Argentina e-mail: mercedes@oac.uncor.edu
² Istituto Astrofisica Spaziale e Fisica Cosmica, CNR, Via del Fosso del Cavaliere, 00133 Roma, Italia e-mail: [persi ;marenzi]@rm.iasf.cnr.it
³ Las Campanas Observatory, Carnegie Institution of Washington, Casilla 601, La Serena, Chile e-mail: miguel@lco.cl
⁴ Instituto de Astronomía, UNAM, Apartado Postal 877, Ensenada, Baja California, CP 22830, Mexico e-mail: mt@astrosen.unam.mx

Received: 30 January 2004
Accepted: 3 May 2004

Abstract

We have obtained narrow-band images of three selected areas of the Chamaeleon I dark cloud which harbor very low mass young stars, centered on the H₂ and Brγ lines and neighboring continuum as well as on the broad band K_s. One region is located in the northern part of the cloud, roughly coinciding with the densest area. The other two regions are in the southern section of the cloud. Our aim is to search for H₂ outflows associated with these objects. In the northern region, we found seven new H₂ knots, five of which are aligned in the direction of a previously known ¹²CO molecular bipolar outflow. Further evidence that the class I low mass stellar object ISO-ChaI 192 is the driving source of the molecular flow is given by the presence of a 960 AU long elongated structure at 2.2 μm emanating from this star and oriented parallel to the bipolar structure. Another pair of H₂ knots, although lying relatively nearby, is not aligned with the outflow direction. They are located on opposite sides of C1–6, a low mass class II object in the northern part of the Chamaeleon I dark cloud. In contrast, we fail to detect any H₂ emission object brighter than our sensitivity limit (~ W/m² Hz arcsec²) in the two southern areas of the cloud that also harbor several very low mass stars, including two transition stellar/sub-stellar objects. This negative result is probably not surprising in view of the extremely low accretion rates measured for brown dwarfs ( yr^-1). Deeper H₂ observations are required to better constraint the outflow event in sub-stellar objects.