Gaia Early Data Release 3: The celestial reference frame (Gaia-CRF3)

Context. Gaia-CRF3 is the celestial reference frame for positions and proper motions in the third release of data from the Gaia mission, Gaia DR3 (and for the early third release, Gaia EDR3, which contains identical astrometric results). The reference frame is defined by the positions and proper motions at epoch 2016.0 for a specific set of extragalactic sources in the (E)DR3 catalogue. Aims. We describe the construction of Gaia-CRF3 and its properties in terms of the distributions in magnitude, colour, and astrometric quality. Methods. Compact extragalactic sources in Gaia DR3 were identified by positional cross-matching with 17 external catalogues of quasi-stellar objects (QSO) and active galactic nuclei (AGN), followed by astrometric filtering designed to remove stellar contaminants. Selecting a clean sample was favoured over including a higher number of extragalactic sources. For the final sample, the random and systematic errors in the proper motions are analysed, as well as the radio-optical offsets in position for sources in the third realisation of the International Celestial Reference Frame (ICRF3). Results. Gaia-CRF3 comprises about 1.6 million QSO-like sources, of which 1.2 million have five-parameter astrometric solutions in Gaia DR3 and 0.4 million have six-parameter solutions. The sources span the magnitude range G = 13-21 with a peak density at 20.6 mag, at which the typical positional uncertainty is about 1 mas. The proper motions show systematic errors on the level of 12 μas yr-1 on angular scales greater than 15 deg. For the 3142 optical counterparts of ICRF3 sources in the S/X frequency bands, the median offset from the radio positions is about 0.5 mas, but it exceeds 4 mas in either coordinate for 127 sources. We outline the future of Gaia-CRF in the next Gaia data releases. Appendices give further details on the external catalogues used, how to extract information about the Gaia-CRF3 sources, potential (Galactic) confusion sources, and the estimation of the spin and orientation of an astrometric solution

Spatialities of skin: the chafing of skin, ego and second skins in T. E. Lawrence's <i>Seven Pillars of Wisdom</i>

This paper explores the relationship between skin, ego and second skins. It does so conceptually by re-examining Freud's suggestion, in The Ego and the Id (1923), that the ego is first and foremost a bodily entity, while also being a projection of a surface (i.e. skin). Drawing upon Anzieu, a dynamic model of inter-weaving surfaces can be seen to underpin an understanding of the ego – and skin ego. This model is fundamentally spatialized. Even so, an appreciation of the spatialities of skin and ego can be developed further. To illuminate these, this paper examines two key experiences of T. E. Lawrence during his military service in Arabia (c.1917), as he describes them in his autobiographical account Seven Pillars of Wisdom (1926). In a meeting with British military police, and in the notorious Deraa rape incident, what is at stake is Lawrence of Arabia's skins. Reading these experiences using Freud and Anzieu, the paper argues that these events re-present an ongoing chafing of Lawrence's skin, ego and second skins, which can be called his 'skin of suffering'