Recent Astronomical highlights from SuperCOSMOS

(most recent first)


Discovery of the nearest brown dwarf to the Sun (2003)

A team of European astronomers have been using SuperCOSMOS Sky Survey data to search for very nearby, low luminosity stars. Using the UKST I band data and the recently released two-micron all sky survey (2MASS) they found a common proper motion companion to the very nearby star Epsilon Indi (which is around 10 light-years away from the Sun).

This image from the UKST I band survey show the primary star Epsilon Indi A (very bright, central star) and it's newly discovered companion (B; arrowed). Components A and B share a common proper motion, and a spectrum of the much fainter brown dwarf shows that it is a member of an extremely rare class of very low luminosity star, the T dwarfs. Currently, Epsilon Indi B is the nearest known brown dwarf to the Sun.

For more information, see Scholz et al., A&A, 398, 29 (2003).

Note added later: After follow-up observations, it turns out that Epsilon Indi B is in fact a binary itself. The triple system Epsilon Indi is now known to consist of the primary plus a T1/T6 brown dwarf binary. This remarkable discovery will enable the direct mass measurement of two brown dwarfs within the next decade or so via astrometry of the orbiting pair. For much more detail concerning this discovery, see McCaughrean et al., A&A, 413, 1029 (2004) .

Measurement of intrinsic alignments in galaxy ellipticities (2002)

A team of Edinburgh astronomers have used the SuperCOSMOS Sky Survey to measure a very weak correlation signal between the alignment of galaxy ellipticites on small scales. In a tour-de-force of data processing and statistical estimation, the team (lead by Michael Brown and Andy Taylor) measured the alignment of 2 million galaxy ellipticities in the local Universe over a range of scales, and found for a magnitude cut of Bj=20.5, corresponding to a median galaxy redshift of z around 0.1, that the galaxy ellipticities exhibit a non-zero correlation over a range of scales between 1 and 100 arcmin. Considering the low median redshift of the galaxies in the sample and hence the relatively low effective cross-section for lensing of these galaxies by the large-scale structure of the Universe, they propose that they have detected an intrinsic alignment of galaxy ellipticities. Comparison with recent analytical and numerical predictions made for intrinsic galaxy alignment found good agreement.

For much more detail concerning this discovery, see Brown et al., MNRAS, 333, 501 (2002) .

The UK Schmidt Panoramic Deep Fields (2001)

A team of Australian astronomers have used SuperCOSMOS scans of UK Schmidt photographic plates to create a deep, coadded stack of data that rivals intermediate sized, large format CCD cameras in terms of depth, but that out-performs them in terms of field-of-view. The Panoramic Deep Fields consist of a multicolor survey of two 5x5 degree Schmidt fields with limiting magnitude of Bj=23.5. The data have been used to measure the clustering of AGN and galaxies at intermediate redshift; the evolution of radio galaxies at intermediate redshift; and the clustering of colour-selected galaxies.

For much more detail concerning the Panoramic Deep Fields and astronomical applications of the data, see the following papers by lead author M.J.I. Brown: AJ 122 26 (2001); AJ 121 2381 (2001); and MNRAS 317 782 (2000).

The SuperCOSMOS Sky Survey goes live (1999)

The first release of the online SuperCOSMOS Sky Survey was announced in June 1999. The first installment of data consisted of around 4000 square degrees of data in three colours (BRI), one colour being available at two epochs. The ambitious sky survey program ultimately aims to cover the entire sky by using the UKST/ESO collections in the southern hemisphere and the POSS-I E and POSS-II BRI collections in the north.

For more information, consult the SuperCOSMOS Sky Survey homepage.

Precision astrometry from SuperCOSMOS (1998)

The SuperCOSMOS team have completed a detailed analysis of the system for the purpose of ascertaining the accuracy of SuperCOSMOS for precision astrometry, and in particular for proper motion studies. They demonstrate that the system has intrinsic machine repeatability and absolute positional accuracy having single co-ordinate, single measurement errors of sigma less than 0.1 microns and sigma~0.15 microns respectively. In addition, measurement errors from the system are shown to be small relative to emulsion noise dominated errors from measurements of different plates of the same field.

For the purposes of relative astrometry of stars, this will enable, for example, the determination of relative proper motions to an accuracy of ~ a few milliarcseconds per year using the first and second epoch survey Schmidt plate material in both the northern and southern hemispheres. There is now a great potential for studies in, for example, stellar kinematics; Galactic formation, structure and evolution; and mean space motions of satellite galaxies and globular clusters, to name but a few topical research area.

For more details, see Hambly et al., MNRAS, 298, 897 (1998).

Coolest known degenerate star detected? (1997)

A team of astronomers from the ROE, ING and Leicester University have detected (from its high proper motion - 1.3 arcsecs yr-1) a star which, from follow-up photometry and spectroscopy, reveal it to be an extremely cool degenerate (T ~ 3900 degrees Kelvin), and is possibly the coolest degenerate star currently known.

These images are digitised scans of photographic plates showing the motion of WD0346+246 over 43 years. The epochs of the three images are (from left to right) 1951.91, 1987.92 and 1994.99. The first image uses the Red (0.7 microns) passband, while the last two are in the I (0.8 microns) passband.

For more information, see Hambly, Smartt & Hodgkin, ApJL, 489, 157 (1997).

Note added later: As it turned out, this star was the first of a new class of ultracool white dwarfs to be discovered. For more information about this fascinating object, see Hodgkin et al., Nature, 403, 57 (2000).

Another large group of quasars discovered - evidence for cellular structure and voids as far back as z~1.5?

In recent years, quasars being typically much brighter than galaxies have been used to probe the structure of the Universe at early times, between the smooth beginning and the highly structured present (clusters, superclusters, filaments, sheets, voids and quasi-periodic spacings). These observations have revealed rare instances of extremely large structures - the large quasar groups - with sizes ~100-200h^-1 Mpc, making them the largest structures known in the early universe.

The largest of the large quasar groups is that discovered by a group of astronomers from the Universtity of Central Lancashire and the University of Chile: it has a size of ~200h^-1 Mpc and redshift z~1.3. To investigate this large scale structure in more detail and to investigate large-scale structure in general at early times, the group have recently been using SuperCOSMOS for a new, wide-angle quasar survey - the Chile-UK quasar survey.

The Chile-UK survey selects candidates for quasars as UV-excess objects, using SuperCOSMOS scans of U,B plates from the UKST. All candidates are subsequently observed spectroscopically. A preliminary analysis of the survey so far suggests very strongly that a new group, of size ~150h^-1 Mpc and redshift z~1.5 is emerging. Part of it is directly behind the previously detected large group at z~1.3, suggesting that parallel sheets or cellular structure and voids existed by z~1.5.