Abstract. We present photometry and spectroscopy of the afterglow of GRB 030323. VLT spectra of the afterglow show damped Lyα (DLA) absorption and low-and high-ionization lines at a redshift z = 3.3718 ± 0.0005. The inferred neutral hydrogen column density, log N(H i) = 21.90 ± 0.07, is larger than any (GRB-or QSO-) DLA H  column density inferred directly from Lyα in absorption. From the afterglow photometry, we derive a conservative upper limit to the host-galaxy extinction: A V < 0.5 mag. The iron abundance is [Fe/H] = −1.47 ± 0.11, while the metallicity of the gas as measured from sulphur is [S/H] = −1.26 ± 0.20. We derive an upper limit on the H 2 molecular fraction of 2N(H 2 )/(2N(H 2 ) + N(H i)) < ∼ 10 −6 . In the Lyα trough, a Lyα emission line is detected, which corresponds to a star-formation rate (not corrected for dust extinction) of roughly 1 M yr −1 . All these results are consistent with the host galaxy of GRB 030323 consisting of a low metallicity gas with a low dust content. We detect fine-structure lines of silicon, Si *, which have never been clearly detected in QSO-DLAs; this suggests that these lines are produced in the vicinity of the GRB explosion site. Under the assumption that these fine-structure levels are populated by particle collisions, we estimate the H  volume density to be n H i = 10 2 −10 4 cm −3 . HST/ACS imaging 4 months after the burst shows an extended AB(F606W) = 28.0 ± 0.3 mag object at a distance of 0. 14 (1 kpc) from the early afterglow location, which presumably is the host galaxy of GRB 030323.

This paper describes a new Heterodyne Array Receiver Program (HARP) and Auto‐Correlation Spectral Imaging System (ACSIS) that have recently been installed and commissioned on the James Clerk Maxwell Telescope. The 16‐element focal‐plane array receiver, operating in the submillimetre from 325 to 375 GHz, offers high (three‐dimensional) mapping speeds, along with significant improvements over single‐detector counterparts in calibration and image quality. Receiver temperatures are ∼120 K across the whole band, and system temperatures of ∼300 K are reached routinely under good weather conditions. The system includes a single‐sideband (SSB) filter so these are SSB values. Used in conjunction with ACSIS, the system can produce large‐scale maps rapidly, in one or more frequency settings, at high spatial and spectral resolution. Fully sampled maps of size can be observed in under 1 h. The scientific need for array receivers arises from the requirement for programmes to study samples of objects of statistically significant size, in large‐scale unbiased surveys of galactic and extra‐galactic regions. Along with morphological information, the new spectral imaging system can be used to study the physical and chemical properties of regions of interest. Its three‐dimensional imaging capabilities are critical for research into turbulence and dynamics. In addition, HARP/ACSIS will provide highly complementary science programmes to wide‐field continuum studies and produce the essential preparatory work for submillimetre interferometers such as the Submillimeter Array (SMA) and Atacama Large Millimeter/Submillimeter Array (ALMA).

In this paper we present the first observations of the Ophiuchus molecular cloud performed as part of the James Clerk Maxwell Telescope (JCMT) Gould Belt Survey (GBS) with the SCUBA-2 instrument. We demonstrate methods for combining these data with previous HARP CO, Herschel, and IRAM N 2 H + observations in order to accurately quantify the properties of the SCUBA-2 sources in Ophiuchus. We produce a catalogue of all of the sources found by SCUBA-2. We separate these into protostars and starless cores. We list all of the starless cores and perform a full virial analysis, including external pressure. This is the first time that external pressure has been included in this level of detail. We find that the majority of our cores are either bound or virialised. Gravitational energy and external pressure are on average of a similar order of magnitude, but with some variation from region to region. We find that cores in the Oph A region are gravitationally bound prestellar cores, while cores in the Oph C and E regions are pressure-confined. We determine that N 2 H + is a good tracer of the bound material of prestellar cores, although we find some evidence for N 2 H + freezeout at the very highest core densities. We find that non-thermal linewidths decrease substantially between the gas traced by C 18 O and that traced by N 2 H + , indicating the dissipation of turbulence at higher densities. We find that the critical Bonnor-Ebert stability criterion is not a good indicator of the boundedness of our cores. We detect the pre-brown dwarf candidate Oph B-11 and find a flux density and mass consistent with previous work. We discuss regional variations in the nature of the cores and find further support for our previous hypothesis of a global evolutionary gradient across the cloud from southwest to northeast, indicating sequential star formation across the region.

Performing ground-based submillimetre observations is a difficult task as the measurements are subject to absorption and emission from water vapour in the Earth's atmosphere and time variation in weather and instrument stability. Removing these features and other artifacts from the data is a vital process which affects the characteristics of the recovered astronomical structure we seek to study. In this paper, we explore two data reduction methods for data taken with the Submillimetre Common-User Bolometer Array-2 (SCUBA-2) at the James Clerk Maxwell Telescope (JCMT). The JCMT Legacy Reduction 1 (JCMT LR1) and The Gould Belt Legacy Survey Legacy Release 1 (GBS LR1) reduction both use the same software (Starlink ) but differ in their choice of data reduction parameters. We find that the JCMT LR1 reduction is suitable for determining whether or not compact emission is present in a given region and the GBS LR1 reduction is tuned in a robust way to uncover more extended emission, which better serves more in-depth physical analyses of star-forming regions. Using the GBS LR1 method, we find that compact sources are recovered well, even at a peak brightness of only 3 times the noise, whereas the reconstruction of larger objects requires much care when drawing boundaries around the expected astronomical signal in the data reduction process. Incorrect boundaries can lead to false structure identification or it can cause structure to be missed. In the JCMT LR1 reduction, the extent of the true structure of objects larger than a point source is never fully recovered.

JHK photometry in the Mauna Kea Observatories (MKO) near‐infrared system is presented for 115 stars. Of these stars, 79 are United Kingdom Infrared Telescope (UKIRT) standards from Hawarden et al., and 42 are Las Campanas Observatory (LCO, or NICMOS) standards from Persson et al. The average brightness of the sample in all three bandpasses is 11.5 mag, with a range between 10 and 15. The average number of nights each star was observed is 4, and the average of the internal error of the final results is 0.011 mag. These JHK data agree with those reported by other groups to 0.02 mag, for stars in common, which is consistent with the uncertainties. The measurements are used to derive colour transformations between the MKO JHK photometric system and the UKIRT, LCO and Two Micron All‐Sky Survey (2MASS) systems. The 2MASS–MKO data scatter by 0.05 mag for redder stars, which is consistent with a dependence on stellar luminosity: the 2MASS J bandpass includes H2O features in dwarfs and the MKO K bandpass includes CO features in giants. We stress that colour transformations derived for stars whose spectra contain only weak features cannot give accurate transformations for objects with strong absorption features within one, but not both, of the filter bandpasses. We find evidence of systematic effects at the 0.02 mag level in the photometry of stars with J < 11 and H, K < 10.5 presented here and in Hawarden et al. This is due to an underestimate of the linearity correction for stars observed with the shortest exposure times; very accurate photometry of stars approaching the saturation limits of infrared detectors which are operated in double‐read mode is difficult to obtain. There are indications that four stars in the sample, GSPC S705‐D, FS 116 (B216‐b7), FS 144 (Ser‐EC84) and FS 32 (Feige 108), may be variable. There are 84 stars in the sample presented here that have 11 < J < 15 and 10.5 < H, K < 15, are not suspected to be variable, and have magnitudes with an estimated error ≤0.027 mag; 79 of these have an error of ≤0.020 mag. These represent the first published high‐accuracy JHK stellar photometry in the MKO near‐infrared photometric system; we recommend these objects be employed as primary standards for that system.