2. Observations and data reduction
2.1. Sample of objects
We observed 22 fields containing 25 target objects (HAEBE and
FU Orionis stars) in the continuum at 1.3 mm wavelength. The target
stars are compiled in Table 1 together with the optical
positions, the spectral type, and the distances adopted from the
literature. In the case of different distance estimates, the bold
printed distances indicate the values used in this paper. In addition,
we list information about the multiplicity of sources as far as it is
known and the associated regions. In the case of dubious associations
we give the regions in parentheses. The target list includes objects
from our earlier pilot survey of southern HAEBE stars (Henning et al.
1994), from the list of Hillenbrand et al. (1992), and from the survey
of Mannings (1994). With the exception of
V 376 Cas/LkH 198, RNO 1B, MWC 137, HD 97048,
V 1686 Cyg/V 1685 Cyg, and LkH 234 all other
target sources are located inside the position error ellipse of the
associated IRAS point sources. Five objects (RNO 1B, Z CMa, Parsamian
(Par) 21, V 1515 Cyg, and V 1331 Cyg) were classified as FU Orionis
type objects (see, e.g., Kenyon et al. 1993, Hartmann et al. 1989,
Staude & Neckel 1992, Kenyon et al. 1991, Welin 1976). The objects
LkH 198, MWC 137, VY Mon,
CoD -42o 11721, MWC 297, LkH 234 and
MWC 1080 were found to be extended at 50 or 100 µm,
whereas AB Aur and Z CMa could not be resolved by KAO observations
(Natta et al. 1993, Di Francesco et al. 1994, Casey & Harper
1990). Millimetre interferometry observations were performed for
Elias 1, AB Aur, and HD 163296 (Di Francesco et al. 1997, Mannings
& Sargent 1997).
Table 1. Source list
Table 1. Source list (continued)
2.2. Millimeter continuum observations
The 1.3 mm continuum observations were performed in February 1995 and March 1997 at the 30-m IRAM telescope (MRT) on Pico Veleta, Spain, and in November 1995 and March 1997 at the 15-m SEST telescope on La Silla, Chile (ESO No 56.D-0510, ESO No 58.D-0213). The SEST observations were performed with the single-channel facility bolometer system. At the 30-m telescope, the MPIfR 7-channel and 19-channel bolometer arrays were used (Kreysa 1994, Kreysa et al. in prep.). The individual 3He-cooled bolometers are identical at both telescopes (Kreysa 1990, Thum et al. 1992). The equivalent bandwidth of the bolometers was 50 GHz centered on a frequency of 236 GHz (). The effective beam sizes (HPBW) at this wavelength amount to at the 30-m MRT and at the 15-m SEST, respectively. The maps were obtained with the "double-beam" technique described first by Emerson et al. (1979). The map rows were generated by scanning the telescope continuously along the direction of the beam separation (i.e., in azimuth) with scanning velocities and elevation spacings between adjacent scans of /sec and (MRT) and of /sec and (SEST), respectively. To generate the dual beams, a wobbling secondary operating at 2 Hz with a chopper throw of and a focal plane chopper operating at 6 Hz with a chopper throw of were used at the MRT and the SEST, respectively. Random jiggle maps with the 7-channel array at the MRT were obtained towards two objects (HD 250550, V 1331 Cyg). The map sizes, angular resolution (HPBW) and 1 noise levels (measured in empty fields within the maps) are listed in Table 2.
Table 2. Parameters of the millimetre continuum maps and NIR images
The planets Uranus and Mars were used as primary calibration standards, adopting brightness temperatures of 96 K and 203 K, respectively (Griffin & Orton 1993). Maps of these planets were obtained every day with the same technique and parameters as used for the target objects. The atmospheric transmission was usually measured by skydips every two hours. Telescope pointing and focus were checked more frequently. Pointing was found to be repeatable within at the MRT and at the SEST.
The data reduction was done with the software packages MARMAP, MAP, and MOPSI (written by R. Zylka, MPIfR Bonn) which use the NOD2 and GAG libraries. After correction of the atmospheric extinction, double-beam maps were created from the raw data scans. The double-beam maps were restored into single-beam maps using the Emerson-Klein-Haslam algorithm (Emerson et al. 1979). The individual maps were averaged and transformed from the horizontal into the equatorial coordinate system. The jiggle maps (HD 250550, V 1331 Cyg) were obtained by moving the telescope in small steps randomly around the target position.
The calibration factor was computed by integrating over the main antenna beam in the planet maps. The relative statistical error of the calibration was derived from all planet maps obtained between 1992 and 1995 at the 30-m MRT and is 6%. Due to the limited accuracy of the adopted planet temperatures and uncertainties in the flux integration procedure, the total relative uncertainty of the flux calibration is, however, derived to be 20%. Especially for weak and extended sources, the derived source size and the integrated flux density depend on the map size, the curvature of the extended flux density distribution and the method of baseline subtraction since the sources are mostly observed against a more extended background emission originating from the surrounding molecular cloud.
Of the 22 fields observed in total, 18 fields containing 21 target stars were mapped at the 30-m MRT with bolometer arrays and 4 fields (HD 97048, HD 100546, IRAS 12496-7650, CoD -42o11721) were mapped with the SEST single-channel bolometer.
2.3. Near-infrared camera observations
In order to compare the 1.3 mm dust continuum emission with the stellar positions and the location of near-infrared (NIR) nebulosities and to search for deeply embedded objects in the vicinity of the target stars, K band images of 20 fields containing 23 target objects were obtained between January 1994 and June 1996 at the 2.2-m telescope of ESO and at the 2.2-m and 3.5-m telescopes of the Calar Alto Observatory (Spain). Both the IRAC 2b camera of ESO and the BLUE/BLACK-MAGIC cameras of the MPIA use 256256 NICMOS3-HgCdTe arrays operating between 1.0 and 2.4m. The observing parameters for the individual objects are compiled in Table 2. The listed limiting magnitudes correspond to the 5 level per square arcseconds. Three to five individual images shifted against each other by 1/3 to 1/2 of the detector field of view were obtained from each object leading to small mosaics.
The individual images were corrected for the detector bias, bad pixels, and for sensitivity variations within the detector array by using flat field images of the sky. Since the NIR emission of the observed objects is not very extended, the sky background which was subtracted from the final images was obtained by applying a median filter to the individual images of each mosaic. The final images were obtained by combining the overlapping corrected images to one mosaic per object using a cross-correlation method.
In order to obtain reference coordinates, we compared the positions of the stars in the NIR images with their optical positions in the Digitized Sky Survey (Space Telescope Science Institute 1994). The absolute position accuracy of the presented NIR images is better than . We did not observe IRAS 12496-7650 and V 1331 Cyg. In the case of V 1331 Cyg, we use data from the literature (Hodapp 1994).
© European Southern Observatory (ESO) 1998
Online publication: July 20, 1998