This paper presents Australia Telescope Compact Array H I synthesis observations of the weak blue compact dwarf (BCD) galaxy NGC 2915. It is shown that NGC 2915 has the H I properties of a late type spiral galaxy (Sd -Sm), including a double horn global profile, and H I spiral arms. The H I extends out to over five times the Holmberg radius, and 22 times the exponential scale length in the B band. The optical counterpart corresponds to a central H I bar. The H I distribution and kinematics are discussed in detail. A rotation curve is derived and fitted with a mass model consisting of a stellar disk, a neutral gas disk, and a dark matter (DM) halo. The DM halo dominates at nearly all radii. The total mass to blue light ratio, M T /L B = 76 within the last measured point. Thus NGC 2915 is one of the darkest disk galaxies known. The complex H I dynamics of the central region results in a high uncertainty of many of the fitted 1 parameters. Nevertheless it is clear that the core of the DM halo is unusually dense (ρ 0 ≈ 0.1 M ⊙ pc −3 ) and compact (R c ≈ 1 kpc). The neutral gas component, with mass M g = 1.27×10 9 M ⊙ is probably more massive than the stellar disk. Split and broad H I lines (velocity dispersion ≈ 35 km s −1 ) are seen in the central region. Pressure support is probably significant, and it is not clear whether the core is in equilibrium. Beyond the optical disk the average H I line of sight velocity dispersion is 8 km s −1 , which is normal for disk galaxies. NGC 2915 does not obey the Tully-Fisher (1977) relation, being underluminous for its V rot = 88 km s −1 by a factor of nine. It also does not obey the star formation threshold model of Kennicutt (1989), when only the neutral gas is considered. A simple H I surface density threshold of Σ HI,crit ≈ 10 21 cm −2 adequately describes the location of current star formation. Although the H I properties of NGC2915 are extreme relative to normal galaxies they appear less extreme in comparison to other BCDS, which have similar radial profiles of H I density and velocity dispersion, and H I extending well beyond the optical disk.

We present the Macquarie/AAO/Strasbourg Hα Planetary Nebula Catalogue (MASH) of over 900 true, likely and possible new Galactic planetary nebulae (PNe) discovered from the AAO/UKST Hα survey of the southern Galactic plane. The combination of depth, resolution, uniformity and areal coverage of the Hα survey has opened up a hitherto unexplored region of parameter space permitting the detection of this significant new PN sample. Away from the Galactic bulge the new PNe are typically more evolved, of larger angular extent, of lower surface brightness and more obscured (i.e. extinguished) than those in most previous surveys. We have also doubled the number of PNe in the Galactic bulge itself and although most are compact, we have also found more evolved examples. The MASH catalogue represents the culmination of a seven-year programme of identification and confirmatory spectroscopy.A key strength is that the entire sample has been derived from the same, uniform observational data. The 60 per cent increase in known Galactic PNe represents the largest ever incremental sample of such discoveries and will have a significant impact on many aspects of PN research. This is especially important for studies at the faint end of the PN luminosity function which was previously poorly represented.

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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.

We present analysis of MACHO Alert 95-30, a dramatic gravitational microlensing event towards the Galactic bulge whose peak magnification departs significantly from the standard point-source microlensing model. Alert 95-30 was observed in real-time by the Global Microlensing Alert Network (GMAN), which obtained densely sampled photometric and spectroscopic data throughout the event. We interpret the light-curve "fine structure" as indicating transit of the lens across the extended face of the source star. This signifies resolution of a star several kpc distant.We find a lens angular impact parameter θ min /θ source = 0.715 ± 0.003. This information, along with the radius and distance of the source, provides an additional constraint on the lensing system. Spectroscopic and photometric data indicate the source is an M4 III star of radius 61 ± 12R ⊙ , located on the far side of the bulge at ∼ 9 kpc. We derive a lens angular velocity, relative to the source, of 21.5 ± 4.9 km s −1 kpc −1 , where the error is dominated by uncertainty in the source radius. Likelihood analysis yields a median lens mass of 0.67 +2.53 −0.46 M ⊙ , located with 80% probability in the Galactic bulge at a distance of 6.93 +1.56 −2.25 kpc. If the lens is a main-sequence star, we can include constraints on the lens luminosity. This modifies our estimates to M lens = 0.53 +0.52 −0.35 M ⊙ and D lens = 6.57 +0.99 −2.25 kpc. Spectra taken during the event show that the absorption line equivalent widths of Hα and the TiO bands near 6700Å vary, as predicted for microlensing of an extended source. This is most likely due to center-to-limb variation in the stellar spectral lines. The observed spectral changes further support our microlensing interpretation. These data demonstrate the feasibility of using microlensing limb crossings as a tool to probe stellar atmospheres directly.Subject headings: dark matter -gravitational lensing -stars: low-mass, brown dwarfsstars: late-type -stars: atmospheres Table 4. Photometry of the source star in MACHO 95-30Observed Extinction Dereddened Abs Mag, 8 kpc Abs Mag, 9 kpc V = 16.21 A V = 1.35 V 0 = 14.86 M V = +0.34 M V = +0.59 K = 9.98 A K = 0.15 K 0 = 9.83 M K = −4.69 M K = −4.45 V − R = 1.39 E(V − R) = 0.34 V − R 0 = 1.05 J − K = 1.12 E(J − K) = 0.23 J − K 0 = 0.89 H − K = 0.26 E(H − K) = 0.08 H − K 0 = 0.18 V − K = 6.23 E(V − K) = 1.21 V − K 0 = 5.03 Bolometric BC K = −2.7 ± 0.1 M bol = −2.0 M bol = −2.25

Neutral hydrogen (H I ) has been detected in the Local Group dwarf spheroidal galaxy Sculptor with the 64 m Parkes single dish and mapped with the Australia Telescope synthesis array. Most of the detected H I is in two clouds ∼ 15 ′ − 20 ′ away from the optical center. The gas is observed at the same systemic velocity than the stars but at ≥ 125 km s −1 away from the Magellanic Stream components in that region. A lower limit to the H I mass of 3.0 × 10 4 M ⊙ is derived from the synthesis observation for an (M HI /L B ) ≃ 0.02. This amount of H I is compatible with mass loss expected from normal giants even if only 10% of the gas is retained by the galaxy in its neutral form.

We present deep photometry (V≲26) in V and I bands obtained with the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope for 7 fields ∼5° away from the Large Magellanic Cloud centre. The fields contain, typically, 2000 stars each. Isochrones were fitted to the colour–magnitude diagrams in order to identify different star populations in these fields. An old population (τ>10 Gyr) has been found in all fields. Some events of enhanced star formation, with ages between 2 and 4 Gyr, were identified in the fields localized in the north to north‐west regions. Luminosity functions of low‐mass stars were also obtained for all fields. Kolmogorov Smirnov test results suggest differences smaller than 30 per cent in the mixture of stellar populations contributing to the fields. Finally, density profiles were derived for old and intermediate‐age stars. The former shows a slightly steeper decline than the latter.