Two hegemonies, one island: Cyprus as a "Middle Ground" between the Byzantines and the Arabs (650-850 A.D.)

This paper aims to assess the political and cultural status of the island of Cyprus as the only place within the Mediterranean where Christian heirs of Romans and Muslims shared the local tax revenue to create a buffer zone between two empires. Geographically isolated between the Constantinopolitan and Damascene hegemonies, and marginalized by emperors and caliphs alike, the development of Cyprus was destined to take a unique, perhaps problematic, trajectory. Detailed examination of archaeological material (seals, coins, ceramics and material artifacts) suggests a different interpretative scheme to the one traditionally adopted to interpret the declining fate of Cyprus after the Muslim raids and the occupation of Syria and Palestine. Instead, I propose, Cyprus and its cities were still active from late antiquity to the early middle ages, preserving a variable but still traceable degree of economic vitality (benefitting from the circulation of Byzantine and Arab coinage), which infers the maintenance of complex political, commercial and cultural relations (implicit in issues of imagery and prototypes of coins) between the Byzantine Empire and the Umayyad Caliphate

Triggered star formation on the borders of the Galactic HII region RCW 120

To investigate the process of star formation triggered by the expansion of an HII region, we present a multi-wavelength analysis of the Galactic HII region RCW 120 and its surroundings. The collect and collapse model predicts that the layer of gas and dust accumulated between the ionization and shock fronts during the expansion of the HII region collapses and forms dense fragments, giving rise to potential sites of massive-star formation. The aim of our study is to look for such massive fragments and massive young stars on the borders of RCW 120. We mapped the RCW 120 region in the cold dust continuum emission at 1.2 mm to search for these fragments. We supplemented this study with the available near- (2MASS) and mid-IR (GLIMPSE) data to locate the IR sources observed towards this region and to analyse their properties. We then compared the observational results with the predictions of Hosokawa & Inutsuka's model (2005, 2006). At 1.2 mm we detected eight fragments towards this region, five located on its borders. The largest fragment has a mass of about 370 Msun. Class I and Class II young stellar objects are detected all over the region, with some observed far from the ionization front. This result emphasises the possible importance distant interactions between the radiation, escaping from the ionized region, and the surrounding medium

Triggered massive-star formation on the borders of Galactic HII regions. II. Evidence for the collect and collapse process around RCW 79

We present SEST-SIMBA 1.2-mm continuum maps and ESO-NTT SOFI JHK images of the Galactic HII region RCW 79. The millimetre continuum data reveal the presence of massive fragments located in a dust emission ring surrounding the ionized gas. The two most massive fragments are diametrically opposite each other in the ring. The near-IR data, centred on the compact HII region located at the south-eastern border of RCW 79, show the presence of an IR-bright cluster containing massive stars along with young stellar objects with near-IR excesses. A bright near- and mid-IR source is detected towards maser emissions, 1.2 pc north-east of the compact HII region centre. Additional information, extracted from the Spitzer GLIMPSE survey, are used to discuss the nature of the bright IR sources observed towards RCW 79. Twelve luminous Class I sources are identified towards the most massive millimetre fragments. All these facts strongly indicate that the massive-star formation observed at the border of the HII region RCW 79 has been triggered by its expansion, most probably by the collect and collapse process.Comment: 14 pages, 15 figures. Accepted for publication in A&A. The images have been highly compressed for astro-ph. A version of this paper with higher-resolution figures is available at http://www.oamp.fr/matiere/rcw79.pd

Sequentially Triggered Star Formation in OB Associations

We discuss observational evidence for sequential and triggered star formation in OB associations. We first review the star formation process in the Scorpius-Centaurus OB association, the nearest OB association to the Sun, where several recent extensive studies have allowed us to reconstruct the star formation history in a rather detailed way. We then compare the observational results with those obtained for other OB associations and with recent models of rapid cloud and star formation in the turbulent interstellar medium. We conclude that the formation of whole OB subgroups (each consisting of several thousand stars) requires large-scale triggering mechanisms such as shocks from expanding wind and supernova driven superbubbles surrounding older subgroups. Other triggering mechanisms, like radiatively driven implosion of globules, also operate, but seem to be secondary processes, forming only small stellar groups rather than whole OB subgroups with thousands of stars.Comment: Invited talk at the IAU Symposium 237: "Triggered Star Formation in a Turbulent ISM", Prague, Czech Republic, August 200

Triggered massive-star formation on the borders of Galactic HII regions. III. Star formation at the periphery of Sh2-219

Context. Massive-star formation triggered by the expansion of HII regions. Aims. To understand if sequential star formation is taking place at the periphery of the HII region Sh2-219. Methods. We present 12CO(2-1) line observations of this region, obtained at the IRAM 30-m telescope (Pico Veleta, Spain). Results. In the optical, Sh2-219 is spherically symmetric around its exciting star; furthermore it is surrounded along three quarters of its periphery by a ring of atomic hydrogen. This spherical symmetry breaks down at infrared and millimetre wavelengths. A molecular cloud of about 2000\msol lies at the southwestern border of Sh2-219, in the HI gap. Two molecular condensations, elongated along the ionization front, probably result from the interaction between the expanding HII region and the molecular cloud. In this region of interaction there lies a cluster containing many highly reddened stars, as well as a massive star exciting an ultracompact HII region. More surprisingly, the brightest parts of the molecular cloud form a `chimney', perpendicular to the ionization front. This chimney is closed at its south-west extremity by H-alpha walls, thus forming a cavity. The whole structure is 7.5 pc long. A luminous H-alpha emission-line star, lying at one end of the chimney near the ionization front, may be responsible for this structure. Confrontation of the observations with models of HII region evolution shows that Sh2-219 is probably 10^5 yr old. The age and origin of the near-IR cluster observed on the border of Sh2-219 remain unknown.Comment: 11 pages, 10 figures. To be published in A&

Spatial distribution of unidentified infrared bands and extended red emission in the compact galactic HII region Sh 152

We present visible and near IR images of the compact HII region Sh 152. Some of these images reveal the presence of Extended Red Emission (ERE) around 698 nm and emission from Unidentified Infra Red Bands (UIRBs) at 3.3 and 6.2 micron. Other images show the near infrared (7-12 micron) continuous emission of the nebula. The ERE emission is found to coincide with the ionized region and significantly differ from the UIRBs location. Also some evidence is found in favor of grains as carriers for ERE.Comment: 3 pages, 4 figures, to be published in the proceedings of the colloquium "The universe as seen by ISO" help in Paris, October 20-23, 1998 ; available in html format at http://www.obs-hp.fr/preprints.htm

The influence of physical illumination on lightness perception in simultaneous contrast displays

Three experiments investigated the role of physical illumination on lightness perception in simultaneous lightness contrast (SLC). Four configurations were employed: the classic textbook version of the illusion and three configurations that produced either enhanced or reduced SLC. Experiment 1 tested the effect of ambient illumination on lightness perception. It simulated very dark environmental conditions that nevertheless still allowed perception of different shades of gray. Experiment 2 tested the effect of the intensity of Gelb lighting on lightness perception. Experiment 3 presented two conditions that integrated illumination conditions from Experiments 1 and 2. Our results demonstrated an illumination effect on both lightness matching and perceived SLC contrast: As the intensity of illumination increased, the target on the black background appeared lighter, while the target on the white background was little affected. We hypothesize the existence of two illumination ranges that affect lightness perception differently: low and normal. In the low range, the SLC contrast was reduced and targets appeared darker. In the normal range, the SLC contrast and lightness matchings for each background were little changed across illumination intensities

Et Facta Est Lux: Experiencing Luminosity in Art and in the Real World

The experience of light determined some of the most intriguing cultural universals, yet it is an underrepresented problem in vision sciences. In their attempt to represent cultural universals, artists adopted empirical solutions to the representation of light sources. We believe that such graphic solutions are showcases of visual indexes related to the phenomenology of light, and therefore they already constitute a level of explanation for luminosity perception. This claim is supported by psychophysical experiments on the ‘glare effect’, an illusion that generates a vivid impression of self-luminosity only by means of quasi-linear luminance ramps. Recent studies show that a similar illusion can be obtained in absence of physically continuous luminance ramps. Results from several experiments suggest that: 1) the key features for luminosity perception lie within the photo-geometric structure of the proximal stimulus; 2) the processes involved in luminosity perception are intrinsically different from those involved in surface color perception

San Lorenzo and the Poggendorff illusion in Ravenna

In the Mausoleum of Galla Placidia (Ravenna, Italy), the San Lorenzo lunette shows two peculiar visual effects: a transparency effect of gold seen through gold and perceptual collinearity between two parts of a cross which are physically misaligned. Both effects are found within the area of the halo surrounding the saint’s head. In this work we addressed the problem posed by the physical misalignment of the cross. Our hypothesis is that the physical misalignment went unnoticed throughout history because the artist produced a perceptual alignment to correct for the Poggendorff illusion. Hence, we asked observers to align two ends of a cross in a reproduction showing the silhouette of San Lorenzo’s torso holding the cross. Results support our hypothesis: both direction and magnitude of adjustments comply with the alignment in the original mosaic