Evaporation and Accretion of Extrasolar Comets Following White Dwarf Kicks

Several lines of observational evidence suggest that white dwarfs receive small birth kicks due to anisotropic mass loss. If other stars possess extrasolar analogues to the Solar Oort cloud, the orbits of comets in such clouds will be scrambled by white dwarf natal kicks. Although most comets will be unbound, some will be placed on low angular momentum orbits vulnerable to sublimation or tidal disruption. The dusty debris from these comets will manifest itself as an IR excess temporarily visible around newborn white dwarfs; examples of such disks may already have been seen in the Helix Nebula, and around several other young white dwarfs. Future observations with the James Webb Space Telescope may distinguish this hypothesis from alternatives such as a dynamically excited Kuiper Belt analogue. Although competing hypotheses exist, the observation that $\gtrsim 15\%$ of young white dwarfs possess such disks, if interpreted as indeed being cometary in origin, provides indirect evidence that low mass gas giants (thought necessary to produce an Oort cloud) are common in the outer regions of extrasolar planetary systems. Hydrogen abundances in the atmospheres of older white dwarfs can, if sufficiently low, also be used to place constraints on the joint parameter space of natal kicks and exo-Oort cloud models.Comment: 22 pages, 13 figures, published in MNRAS. Changes made to match published versio

VLA and ATCA Search for Natal Star Clusters in Nearby Star-Forming Galaxies

In order to investigate the relationship between the local environment and the properties of natal star clusters, we obtained radio observations of 25 star-forming galaxies within 20 Mpc using the Very Large Array (VLA) and the Australia Telescope Compact Array (ATCA). Natal star-forming regions can be identified by their characteristic thermal radio emission, which is manifest in their spectral index at centimeter wavelengths. The host galaxies in our sample were selected based upon their likelihood of harboring young star formation. In star-forming regions, the ionizing flux of massive embedded stars powers the dominant thermal free-free emission of those sources, resulting in a spectral index of {\alpha} {\gtrsim} -0.2 (where S{\nu} {\propto} {\nu}{\alpha}), which we compute. With the current sensitivity, we find that of the 25 galaxies in this sample only five have radio sources with spectral indices that are only consistent with a thermal origin; four have radio sources that are only consistent with a non-thermal origin; six have radio sources whose nature is ambiguous due to uncertainties in the spectral index; and sixteen have no detected radio sources. For those sources that appear to be dominated by thermal emission, we infer the ionizing flux of the star clusters and the number of equivalent O7.5 V stars that are required to produce the observed radio flux densities. The most radio-luminous clusters that we detect have an equivalent of ~7x103 O7.5 V stars, and the smallest only have an equivalent of ~102 O7.5 V stars; thus these star-forming regions span the range of large OB-associations to moderate "super star clusters" (SSCs). With the current detection limits, we also place upper limits on the masses of clusters that could have recently formed...Comment: Subject headings: galaxies: star clusters--galaxies: irregular--galaxies: starburst--stars: formation--HII regions 34 pages, 11 figures, accepted for publication in The Astronomical Journal (1 February 2011

Local Recruitment and Natal Dispersal Distances of American Kestrels

Variation in recruitment patterns and dispersal behavior can have important consequences for population viability, genetic structure, and rates of evolutionary change. From 1992 to 2006 we studied a marked population of American Kestrels (Falco sparverius) nesting in boxes in southwestern Idaho to identify factors that affect local recruitment and natal dispersal distances. A low proportion (4%) of locally produced kestrels (n = 2180) returned to nest in study area boxes. Offspring of locally produced individuals were 3.1 times more likely to return than offspring of parents that did not hatch in study area boxes and, independent of a parent’s origin, males were 1.8 times more likely than females to return. Kestrels that hatched earlier in the breeding season and those that hatched immediately prior to a mild winter were more likely to return. Local natal dispersal distances were best explained by sex and parental origin but not by hatching dates. Fifty-four males moved an average of 5.3 km from their natal box to the location of their first breeding in the study area, and 27 females moved an average of 9.8 km. Offspring of locally produced parents dispersed shorter distances within the study area than offspring of other parents, and local natal dispersal distances of locally produced parents correlated with those of their same-sex offspring. Patterns of natal dispersal of American Kestrels in southwestern Idaho appear to be driven by a combination of parental dispersal tendencies and ecological factors. The population consists of a mix of immigrants and philopatric birds

Helium in natal HII regions: the origin of the X-ray absorption in gamma-ray burst afterglows

Soft X-ray absorption in excess of Galactic is observed in the afterglows of most gamma-ray bursts (GRBs), but the correct solution to its origin has not been arrived at after more than a decade of work, preventing its use as a powerful diagnostic tool. We resolve this long-standing problem and find that He in the GRB's host HII region is responsible for most of the absorption. We show that the X-ray absorbing column density (N_Hx) is correlated with both the neutral gas column density and with the optical afterglow extinction (Av). This correlation explains the connection between dark bursts and bursts with high N_Hx values. From these correlations we exclude an origin of the X-ray absorption which is not related to the host galaxy, i.e. the intergalactic medium or intervening absorbers are not responsible. We find that the correlation with the dust column has a strong redshift evolution, whereas the correlation with the neutral gas does not. From this we conclude that the column density of the X-ray absorption is correlated with the total gas column density in the host galaxy rather than the metal column density, in spite of the fact that X-ray absorption is typically dominated by metals. The strong redshift evolution of N_Hx/Av is thus a reflection of the cosmic metallicity evolution of star-forming galaxies. We conclude that the absorption of X-rays in GRB afterglows is caused by He in the HII region hosting the GRB. While dust is destroyed and metals are stripped of all of their electrons by the GRB to great distances, the abundance of He saturates the He-ionising UV continuum much closer to the GRB, allowing it to remain in the neutral or singly-ionised state. Helium X-ray absorption explains the correlation with total gas, the lack of strong evolution with redshift as well as the absence of dust, metal or hydrogen absorption features in the optical-UV spectra.Comment: 10 pages, 4 figures, submitted to Ap

The origin of Scorpius X-1

We have used multi-wavelength observations of high precision to derive the space velocity and compute the orbit around the Galactic Centre of the prototype X-ray binary Scorpius X-1. An origin in the local spiral arm of the Milky Way is ruled out. The galactocentric kinematics of Scorpius X-1 is similar to that of the most ancient stars and globular clusters of the inner Galactic halo. Most probably, this low-mass X-ray binary was formed by a close encounter in a globular cluster. However, it cannot be ruled out that a natal supernova explosion launched Scorpius X-1 into an orbit like this from a birth place in the galactic bulge. In any case, the Galactocentric orbit indicates that Scorpius X-1 was formed more than 30 Myrs ago.Comment: 4 pages, 1 figure. Animation and high resolution figures can be retrived from the NRAO press release: http://www.aoc.nrao.edu/epo/pr/2003/scox1

Travel and the Greek migrant youth residing in West Germany in the 1960s-1970s

Volume information: 'Between Leisure, Work, and Study: Tourism and Mobility in Europe from 1945-1989', Nikolaos Papadogiannis (U St. Andrews, UK) and Detlef Siegfried (U Kopenhagen, Denmark), eds., ISBN 978-3-86583-896-4.This article explores the travel patterns of young Greek migrants, both students and workers, who resided in the Federal Republic of Germany in the 1960s and 1970s. It draws on recent scholarly works that call into question a rigid distinction between migration and tourism. In this vein, the article claims that their joint examination contributes to a more nuanced understanding of both the migratory experience of Greeks who lived in West Germany and of the youth culture that emerged in Europe at that time. In particular, while a growing number of peer groups of young people from West Germany engaged in tourism, especially the cross-border variety, from the 1960s onwards, travel was hardly an age-specific pursuit for young Greek migrants at that point: by contrast, their travel revolved (or at least was expected to revolve) around visiting their natal areas and reinforcing their links with relatives. A diversification of their travel-related lifestyle norms, however, occured in the early 1970s as a result of the influx of Greek students at West German universities. Those youngsters, along with some young Greek migrant workers, began to travel as tourists beyond their country of origin as well as to acquaint themselves with aspects of the travel culture of local young people from West Germany, such as hitch-hiking. The article also challenges the argument that youth tourism in the second half of the 20th century helped forge a transnational European identity: for the young migrants in question, some of their tourism practices in the 1960s and 1970s reinforced the idea of a North–South divide.Peer reviewe

Nature's Starships II: Simulating the Synthesis of Amino Acids in Meteorite Parent Bodies

Carbonaceous chondrite meteorites are known for having high water and organic material contents, including amino acids. Here we address the origin of amino acids in the warm interiors of their parent bodies (planetesimals) within a few million years of their formation, and connect this with the astrochemistry of their natal protostellar disks. We compute both the total amino acid abundance pattern as well as the relative frequencies of amino acids within the CM2 (e.g. Murchison) and CR2 chondrite subclasses based on Strecker reactions within these bodies. We match the relative frequencies to well within an order of magnitude among both CM2 and CR2 meteorites for parent body temperatures $<$ 200$^{\circ}$C. These temperatures agree with 3D models of young planetesimal interiors. We find theoretical abundances of approximately 7x10$^5$ parts-per-billion (ppb), which is in agreement with the average observed abundance in CR2 meteorites of 4$\pm$7x10$^5$, but an order of magnitude higher than the average observed abundance in CM2 meteorites of 2$\pm$2x10$^4$. We find that the production of hydroxy acids could be favoured over the production of amino acids within certain meteorite parent bodies (e.g. CI1, CM2) but not others (e.g. CR2). This could be due to the relatively lower NH$_3$ abundances within CI1 and CM2 meteorite parent bodies, which leads to less amino acid synthesis. We also find that the water content in planetesimals is likely to be the main cause of variance between carbonaceous chondrites of the same subclass. We propose that amino acid abundances are primarily dependent on the ammonia and water content of planetesimals that are formed in chemically distinct regions within their natal protostellar disks.Comment: 19 pages, 11 figures, Accepted for publication in Ap

Dispersal of larval and juvenile seabream: Implications for Mediterranean marine protected areas

In the marine context, information about dispersal is essential for the design of networks of marine protected areas (MPAs). Generally, most of the dispersal of demersal fishes is thought to be driven by the transport of eggs and larvae in currents, with the potential contribution of dispersal in later life stages relatively minimal.Using otolith chemistry analyses, we estimate dispersal patterns across a spatial scale of approximately 180. km at both propagule (i.e. eggs and larvae) and juvenile (i.e. between settlement and recruitment) stages of a Mediterranean coastal fishery species, the two-banded seabream Diplodus vulgaris. We detected three major natal sources of propagules replenishing local populations in the entire study area, suggesting that propagule dispersal distance extends to at least 90. km. For the juvenile stage, we detected dispersal of up to 165. km. Our work highlights the surprising and significant role of dispersal during the juvenile life stages as an important mechanism connecting populations. Such new insights are crucial for creating effective management strategies (e.g. MPAs and MPA networks) and to gain support from policymakers and stakeholders, highlighting that MPA benefits can extend well beyond MPA borders, and not only via dispersal of eggs and larvae, but also through movement by juveniles