Astron. Astrophys. 363, 755-766 (2000)

2. Input data

2.1. Optical data

Schmidt Observations: We have obtained objective prism images of Kh 15 using the 60/90/180 cm Schmidt telescope of the Konkoly Observatory. The diameter of the field was and it was centered at , . A UV transparent objective prism with a refracting angle of and dispersion of 580 Å/mm at was used. The spectra were recorded on Kodak 103aO emulsion with 2mm widening. Two sets of images were taken with exposures of minutes and minutes. The observations were carried out in 1995, January 31. in the UT time interval 18:40-20:16 and in 1995, August 23. in the UT time interval 0:33-0:41, respectively. Visual magnitudes of all the classified stars (see Sect. 3) have been taken from the HST Guide Star Catalogue CD-ROM Version 1.1 ¹. We identified the stars in the GSC using the SKYMAP software (version 2.7, by Doug Mink ²).

Star count data: Coordinates, B and R magnitudes of stars within 11^o and 3.5 deg² fields (both centered at , , the reference position of the radio measurements) were obtained from the electronic version of the USNO A2.0 catalogue  ³.

2.2. IRAS data

The distribution of the FIR radiation at 12, 25, 60 and 100 µm wavelength was studied using ISSA images (Wheelock et al. 1994) with angular resolution of 1´ to 4´ and a uniform pixel size of . Far-infrared (FIR) point sources within the Kh 15 area were searched in the IRAS Point Source Catalogue ⁴. We also analysed 12, 25, 60 and 100 µm high resolution (HIRES) IRAS images provided by the Infrared Processing and Analysis Center (IPAC).

COBE-DIRBE annual average maps (AAM) at 60 and 100 µm were used in order to calibrate ISSA and HIRES maps. AAM maps have been obtained from the NASA Gothard Space Flight Center ftp site ⁵.

2.3. CO data

Nagoya-4m observations:

We observed Kh 15 in the ¹³CO (J=1-0) line, using the 4m millimeter-wave telescope at Nagoya University in 1991 January and December as part of mapping observations of the Cepheus molecular cloud complex. The half-power beamwidth of the telescope was with a main beam efficiency of 0.7 at 110 GHz. The front-end of the receiver consisted of a 4 K cooled SIS mixer operated in the single-sideband (SSB) mode with the image sideband suppressed by more than 10 dB (Ogawa et al. 1990). The system noise temperature was 150 K (SSB) toward the zenith. An ambient-temperature chopper wheel was used to determine the antenna temperature scale. To estimate the excitation temperature of the CO gas, we observed in April 1992 the centre of the CO cloud in the ¹²CO (J=1-0) line with the same equipment. The observations were made by using frequency switching over 13 MHz (corresponding to kms^-1 at 110 GHz). We used an acousto-optical spectrometer (AOS) as a backend. The bandwidth of the AOS is 40 MHz, divided into 1024 channels. The effective frequency resolution was 40 kHz, equivalent to a velocity resolution of 0.11 at 110 GHz. In reducing the spectral data, we subtracted baselines of third-order polynomials.

An area of 0.13 deg² was mapped in the ¹³CO line covering the main part of Kh 15 cloud with a grid spacing of in galactic coordinates. The number of observed points was 124. The integration time per point was typically 20-30 s in 1991 January, while it was 80 s in 1991 December due to the poor weather conditions. The resulting r.m.s. noise level was typically 0.2 K. For ¹²CO (J=1-0) an r.m.s. noise level of 0.29 K was obtained after an integration of 7 min. Sample spectra are given in Fig. 2 (see also Sect. 3.3).

In order to monitor the system performance and calibrate the antenna temperature, we observed the source S 140 at about hourly intervals. Its adopted radiation temperatures, , were 20 K and 9 K for the ¹²CO and ¹³CO (J=1-0) lines, respectively. They include the coupling of the antenna beam pattern with the brightness distribution in the source.

Onsala-20m observations:

We observed the ¹³CO (=1-0) and the C¹⁸O (=1-0) lines using the Onsala Space Observatory (OSO) 20-m telescope in March, 1998. The receiver was an SIS mixer with a typical =100 K (SSB) in the used frequency range. We used a 1600-channel autocorrelator with 40MHz bandwidth corresponding to a velocity resolution of 0.068 . At 110 GHz the telescope has a HPBW of 35", with a beam efficiency of 0.8. The pointing was checked by observing the SiO maser source T Cep and we estimated the pointing uncertainty to be about 3" r.m.s. in Az. and El. The observations were made in a frequency switching observing mode, with frequency throw. The chopper-wheel method was used for the calibration, and the intensity scale is given in terms of . We mapped the central region of Kh 15 (see Fig. 6) with a variable 1´ and spacing in the ¹³CO (J=1-0) (129 positions) and the C¹⁸O (J=1-0) (99 positions) transitions. The r.m.s. noise was typically 0.4 K for ¹³CO and 0.15 K for C¹⁸O. We subtracted linear baselines.

KOSMA-3m observations: ¹²CO (J=2-1) and (J=3-2) spectra were measured with the old University of Cologne 3m telescope. (J=2-1) data were obtained at two positions in December, 1995. The half-power beam width of the antenna at the CO (2-1) and CO (3-2) transitions was 125" and 70" respectively. The telescope and the instrumentation are described in detail in Winnewisser et al. (1990). Spectra obtained at the position of Nagoya's ¹²CO (1-0) measurement are shown in Fig. 2. The velocity resolution was 0.22 and 0.14 for the ¹²CO (2-1) and ¹²CO (3-2) transitions, respectively. A small (5 pos. 5 pos.) map was made in the ¹²CO (J=3-2) line in March, 1998, using the new KOSMA telescope (after refurbishing), centered at the same sky position as in 1995 (the telescope and the instrumentation are described in detail in Kramer et al. 1998). Using the new KOSMA telescope we have made a measurement of LDN 1308 in the ¹²CO (2-1) transition in September 1999. The measurement were made at three positions ((l, b) = (, ), (, ), (, )) in position switching mode, using the 230/345 GHz dual channel SIS receiver, with a velocity resolution of 0.21 kms^-1. The r.m.s. noise was about 0.2 K at the scale.

© European Southern Observatory (ESO) 2000

Online publication: December 11, 2000
helpdesk.link@springer.de