Astron. Astrophys. 364, L13-L18 (2000)

2. Observations and data reduction

2.1. VLT/ISAAC imaging

2.1.1. Observations

Near-infrared J [1.11-1.39 µm], H [1.50-1.80 µm], and Ks [2.03-2.30 µm] broad-band images of young stellar sources in southern star forming regions were obtained on 28 April 1999 with the ESO VLT/UT1 ("Antu") and the facility Infrared Spectrometer And Array Camera (ISAAC, Moorwood et al. 1998). The observations were carried out with the short-wavelength channel of ISAAC, which is equipped with a 10241024 Hawaii Rockwell HgCdTe array. The pixel scale was pixel^-1 and the seeing was (FWHM) in Ks. Two fields were centered between Elias 29 and WL 19, and between WLY 43 and 44, respectively. Total exposure times were 240s in H and 120s in Ks for the Elias 29/WL 19 field, and 640s in J, 320s in H, and 150s in Ks for the WLY 43/44 field. Fig. 1 illustrates the location of the two ISAAC pointings.

Fig. 1. K-band finding chart based on 2MASS atlas images. The dashed lines indicate the area covered by the two VLT/ISAAC pointings, and the solid lines mark the area imaged by SUBARU/CISCO. The edge-on disk sources are located in the center of the black circles.

2.1.2. Data reduction and analysis

Two bipolar reflection nebulosities intersected by dark lanes were detected. The objects closely resemble edge-on circumstellar disk sources in Taurus and Orion, and in the following we refer to them as "disk 1" and "disk 2". A close-up of the two new edge-on disk sources, and a comparison to edge-on disks in Taurus is presented in Fig. 2. Absolute positions were determined using 2MASS data products and relative offsets measured on the ISAAC frames. The photometric calibration is based on the observations of infrared standard stars, and photometric measurements from the 2MASS point source catalog. Coordinates and near-infrared photometry of the disk sources are summarized in Table 1.

Fig. 2. Edge-on circumstellar disk sources in Ophiuchus and Taurus. In comparison to isolated disks in Taurus, the Ophiuchus disks and their reflection nebulosities are more compact. For the disk sources in the Ophiuchus region, North is up and East is to the left.

Table 1. Coordinates and near infrared photometry (in the 2MASS photometric system) of the edge-on circumstellar disks.
Notes:
a) Comerón et al. 1993

2.2. SUBARU/CISCO imaging and spectroscopy

2.2.1. Observations

Long-slit K-band spectra were obtained on 18 June 2000 ("disk 2") and 16 July 2000 ("disk 1") with the SUBARU telescope and the Cooled Infrared Spectrograph and Camera for OH suppression (CISCO, Motohara et al. 1998). CISCO is equipped with a 10241024 Hawaii Rockwell HgCdTe array and has a pixel scale of pixel^-1. The slit-width was 1" and the slit was oriented north-south. Individual exposure times were 60s and 100s, yielding a total integration time of 240s and 400s for "disk 2" and "disk 1", respectively. Deep dithered K'-band [1.96-2.30 µm] imaging data of disk 1 were obtained on 16 July 2000 (Fig. 3). The seeing on the coadded 800s exposure is .

Fig. 3. Deep K' band imaging of disk 1 (OphE-MM3) reveals that the bipolar reflection nebulosity stretches out for 5" above and below the plane of the disk. LFAM 26 (CRBR 2403.7-2948) is associated with a bipolar reflection nebulosity intersected by a central dust lane as well. Unlike disk 1 and 2, however, a central point source is visible. North is up and East is to the left.

2.2.2. Data reduction and analysis

The data reduction included sky subtraction, and a removal of the geometrical distortion of the 2D spectra. Telluric features were removed by dividing the spectrum of each disk by the spectrum of the standard star. As the observations were obtained under a relatively high airmass of 1.6 to 2.0, the removal of the telluric features was not perfect. The instrumental response was removed by applying an appropriate library spectrum (Pickles 1998). The resulting spectra are shown in Fig. 4. No variation in the spectra across the objects was seen, giving further evidence that the objects are indeed reflection nebulosities.

Fig. 4. K-band spectra of disk 1, disk 2, and LFAM26 obtained with SUBARU/CISCO. All three sources exhibit a featureless continuum and show no signs of underlying stellar photospheres, or accretion and outflow signatures (e.g., H2 or Br emission).

2.3. ISO observations

The Ophiuchus region has been observed multiple times by ISO (Kessler et al. 1996). The regions including disks 1 and 2 were covered by pointed ISOCAM (Césarsky et al. 1996) observations and by larger scale raster scans with ISOCAM and ISOPHOT (Lemke et al. 1996). HH 30 was also observed by ISOCAM and ISOPHOT (PI: K.R. Stapelfeldt, see Stapelfeldt & Moneti 1999). Basic science data were retrieved from the ISO archive and reprocessed using the latest versions (as of June 2000) of the CIA and PIA software packages.

Disk 2 is detected in several ISOCAM observations towards WLY 2-43 at wavelengths between 4.5 µm and 11.3 µm. Large area raster scans of the regions including disk 1 and disk 2 (Abergel et al. 1996) suffer from memory effects due to brighter sources in the vicinity of the disk sources. It was therefore not possible to derive precise flux values from the large area scans. The ISOCAM fluxes of disk 2 and HH 30 are summarized in Table 2.

Table 2. ISOCAM fluxes of edge-on disk sources.

ISOPHOT maps at 60 and 100 µm detect and resolve Elias 2-29 and WLY 2-43. Disks 1 and 2, however, are located in the wings of the point spread function of the much brighter sources (FWHM for ISO is 20" and 35" at wavelengths of 60 µm and 100 µm, respectively), and were not detected as individual sources.

2.4. HST/NICMOS observations

HST/NICMOS observations of HH 30 were retrieved from the HST archive. The data had been obtained as part of GTO 7228 (PI E. Young). IRAS 04302+2247 was studied by Padgett et al. (1999). The NICMOS data were processed using the standard IRAF/STSDAS data reduction pipeline, and the most current calibration files.

© European Southern Observatory (ESO) 2000

Online publication: December 15, 2000
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