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We report $I$-band photometric observations of the radio-detected M9.5 dwarf BRI 0021-0214, obtained with the Galway Ultra Fast Imager (GUFI) on the 1.8m Vatican Advanced Technology Telescope VATT at Mt. Graham International Observatory, Arizona. In total, 19 hours of observations over a 73 day baseline were obtained. BRI 0021-0214 was shown to exhibit modulated emission with a period of $ 3.052 \pm 0.004$ hours with a mean amplitude variability of 0.0044 mag. When combined with rotational velocity data obtained from previous work, our newly discovered rotation period gives an inclination angle of 51.7$^{+5.0}_{-4.5}$ degrees for the rotation axis of BRI 0021-0214 relative to our line of sight. Previous studies have reported that the most plausible cause for optical variability from this dwarf is a consequence of suspended co-rotating dust clouds in its atmosphere. However reports of enhanced H$_{\alpha}$ and intermittent coherent radio emission suggest the possibility of auroral activity in its magnetosphere. Further, more coordinated multiwavlength observations of this dwarf could fully resolve the nature of this elusive rapid-rotator object's observational properties.

Virtual observatories allow the means by which an astronomer is able to discover, access, and process data seamlessly, regardless of its physical location. However, steep learning curves are often required to become proficient in the software employed to access, analyse and visualise this trove of data. It would be desirable, for both research and educational purposes, to have applications which allow users to visualise data at the click of a button. Therefore, we have developed a standalone application (written in Python) for plotting photometric Colour Magnitude Diagrams (CMDs) - one of the most widely used tools for studying and teaching about astronomical populations. The CMD Plot Tool application functions "out of the box" without the need for the user to install code interpreters, additional libraries and modules, or to modify system paths; and it is available on multiple platforms. Interacting via a graphical user interface (GUI), users can quickly and easily generate high quality plots, annotated and labelled as desired, from various data sources. This paper describes how CMD Plot Tool was developed using Object Orientated Programming and a formal software design lifecycle (SDLC). We highlight the need for the astronomical software development culture to identify appropriate programming paradigms and SDLCs. We outline the functionality and uses of CMD Plot Tool, with examples of star cluster photometry. All results plots were created using CMD Plot Tool on data readily available from various online virtual observatories, or acquired from observations and reduced with IRAF/PyRAF.

We find periodic I-band variability in two ultracool dwarfs, TVLM 513-46546 and 2MASS J00361617+1821104, on either side of the M/L dwarf boundary. Both of these targets are short-period radio transients, with the detected I-band periods matching those found at radio wavelengths (P=1.96 hr for TVLM 513-46546, and P=3 hr for 2MASS J00361617+1821104). We attribute the detected I-band periodicities to the periods of rotation of the dwarfs, supported by radius estimates and measured $v$ sin $i$ values for the objects. Based on the detected period of rotation of TVLM 513-46546 (M9) in the I-band, along with confirmation of strong magnetic fields from recent radio observations, we argue for magnetically induced spots as the cause of this periodic variability. The I-band rotational modulation of L3.5 dwarf 2MASS J00361617+1821104 appeared to vary in amplitude with time. We conclude that the most likely cause of the I-band variability for this object is magnetic spots, possibly coupled with time-evolving features such as dust clouds., Comment: 11 pages, 2 figures, accepted for publication in ApJ Letters

In an investigative 16 hour L band observation using the MERLIN radio interferometric array, we have resolved both the pulsar PSR B1951+32 and structure within the flat spectral radio continuum region, believed to be the synchrotron nebula associated with the interaction of the pulsar and its `host' supernova remnant CTB 80. The extended structure we see, significant at $\sim$ 4.5 $\sigma$, is of dimensions 2.5" $\times$ 0.75", and suggests a sharp bow shaped arc of shocked emission, which is correlated with similar structure observed in lower resolution radio maps and X-ray images. Using this MERLIN data as a new astrometric reference for other multiwavelength data we can place the pulsar at one edge of the HST reported optical synchrotron knot, ruling out previous suggested optical counterparts, and allowing an elementary analysis of the optical synchrotron emission which appears to trail the pulsar. The latter is possibly a consequence of pulsar wind replenishment, and we suggest that the knot is a result of magnetohydrodynamic (MHD) instabilities. These being so, it suggests a dynamical nature to the optical knot, which will require high resolution optical observations to confirm., Comment: 12 pages, 2 figures. Accepted for publication in ApJL

There remain several definitive gamma-ray pulsars that are as yet undetected in the optical regime. A classic case is the pulsar PSR B1951+32, associated with the complex CTB 80 SNR. Previous ground based high speed 2-d optical studies have ruled out candidates to m_V ~ 24. Hester (2000) has reported an analysis of archival HST/WFPC2 observations of the CTB 80 complex which suggest a compact synchrotron nebula coincident with the pulsar's radio position. Performing a similar analysis, we have identified a possible optical counterpart within this synchrotron nebula at m_V ~ 25.5, and another optical counterpart candidate nearby at m_V ~ 24.2. PSR J0537-6910 is a young (canonical age ~ 5000 years), 16ms pulsar in the LMC. We report a search for optical pulsations from the region around the X-ray position. We see no obvious candidate exhibiting optical pulsations at the X-ray period, with a 3 sigma upper limit of m_V ~ 23.6. We have also examined recent Chandra results (Wang et al. 2001) and show that their X-ray-Optical astrometry is in error by about 7''., Comment: 4 pages, 4 figures, 2 tables. To appear in the Proceedings of the 270. WE-Heraeus Seminar on Neutron Stars, Pulsars and Supernova Remnants, Jan. 21-25, 2002, Physikzentrum Bad Honnef, eds W.Becker, H.Lesch & J.Truemper. Proceedings are available as MPE-Report 278

There remain several definitive gamma-ray pulsars that are as yet undetected in the optical regime. A classic case is the pulsar PSR B1951+32, associated with the complex CTB 80 SNR. Previous ground based high speed 2-d optical studies have ruled out candidates to V ~ 24. Hester (2000a) has reported an analysis of archival HST/WFPC2 observations of the CTB 80 complex which suggest a compact synchrotron nebula coincident with the pulsar's radio position. Performing a similar analysis, we have identified a possible optical counterpart within this synchrotron nebula at V ~ 25.5 - 26, and another optical counterpart candidate nearby at V ~ 24.5. We assess the reality of these counterpart candidates in the context of existing models of pulsar emission., Comment: 7 pages, 5 figures, Accepted for publication in Astronomy & Astrophysics

The theory of superparamagnetic (SP) threshold calculations and single-domain (SD) to nonuniform spin threshold calculations is considered. The SD upper grain size limit and the SP-to-SD threshold size are calculated. The size and shape criteria for the stable SD behavior of metallic iron have implications for lunar magnetism and the mechanism of iron-silicate fractionation in the solar nebula.

Improved values of critical grain-size thresholds for magnetite and Fe have been obtained using a rigorous theoretical approach. The temperature dependence of these thresholds is interesting in that it indicates the existence of certain grains which, when cooled from above their blocking temperature, pass sequentially through the following magnetization states: superparamagnetic to single-domain to nonuniform magnetization. Such grains will yield correct paleointensities by the Wilson (1961) or Shaw (1974) method but not by the well-known method due to Thellier and Thellier (1959).