ISOCAM observations of the L1551 star formation region

Abstract

Abstract. 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.

A Pre‐Protostellar Core in L1551

“…4 in Gålfalk et al 2004). Sources 23 and 29 are consistent with dust-reddened stars with no infrared excess.…”

“…Given these considerations we conclude that L1551 MC is starless. A plot of the Gålfalk et al (2004), 2MASS, and SIMBAD sources can be seen in Figure 2 The dense, inner regions of cores are traced well with NH 3 emission because of a high abundance under these conditions and a tendency to avoid depletion onto grains (Aikawa et al 2003). In this section the primary morphological features of L1551 MC are characterized based on the NH 3 emission in the region.…”

“…Several single-pointing spectra taken at 23 GHz within the larger L1551 cloud reveal that NH 3 emission is not widespread but rather confined to the regions around L1551 NE and -Velocity-integrated NH 3 emission in gray scale with C 2 S contours at 30%, 50%, 70%, and 90% of the 0.623 K km s À1 maximum overlaid. Boxes signify the point sources from Gålfalk et al (2004), crosses are point sources from the 2MASS catalog, and the asterisks are SIMBAD objects. IRS 5 in addition to the region mapped in this paper (see Fig.…”

Entrainment Mechanisms for Outflows in the L1551 Star‐forming Region

“…These two miniclusters are clearly undergoing active star formation characterized by HH objects and optical and nearinfrared jets. In addition, multiwavelength surveys in mid-IR (Gålfalk et al 2004), X-ray ( Favata et al 2003), optical and near-IR (Briceño et al 1998), optical spectra (Gomez et al 1992), and H (Garnavich et al 1992) have shown that the whole L1551 molecular core is surrounded by a halo of young stars in the Class II stage or older, indicating that star formation activity has been ongoing in this region for at least a few million years. Here we explore the possibility that the current epoch of star formation activity in L1551 may be the result of sequential star formation induced by the effects of the multiple outflows in the system.…”

A detailed study of the L1641N star formation region

“…Our ISOCAM circular aperture photometry uses well tested routines which have been used in several previous papers Olofsson et al 1999;Persi et al 2000;Bontemps et al 2001;Kaas et al 2004;Gålfalk et al 2004), our Spitzer photometry uses another set of routines that we wrote especially for the Spitzer data. That fact that they agree very well with each other, although using different routines and calibrations (not done by the same people), indicates that both our ISO and Spitzer photometry are reliable.…”