The Dust Properties of Eight Debris Disk Candidates as Determined by Submillimeter Photometry

The nature of far-infrared dust emission toward main sequence stars, whether interstellar or circumstellar, can be deduced from submillimeter photometry. We present JCMT/SCUBA flux measurements at 850 microns toward 8 stars with large photospheric excesses at 60-100 microns. 5 sources were detected at 3-sigma or greater significance and one was marginally detected at 2.5-sigma. The inferred dust masses and temperatures range from 0.033 to 0.24 Earth masses and 43-65 K respectively. The frequency behavior of the opacity, tau_nu ~ nu^beta, is relatively shallow, beta < 1. These dust properties are characteristic of circumstellar material, most likely the debris from planetesimal collisions. The 2 non-detections have lower temperatures, 35-38 K and steeper opacity indices, beta > 1.5, that are more typical of interstellar cirrus. The confirmed disks all have inferred diameters > 2'', most lie near the upper envelope of the debris disk mass distribution, and 4 are bright enough to be feasible for high resolution imaging.Comment: accepted by Ap

A new archaic homodont toothed cetacean (Mammalia, Cetacea, Odontoceti) from the early Miocene of Peru

Apart from a few exceptions, extant odontocetes (toothed cetaceans) exhibit a roughly homodont dentition. The transition from basilosaurid-like double-rooted cheek teeth with accessory denticles to single-rooted conical teeth occurred during the late Oligocene-early Miocene. At that time, several clades of now extinct, homodont and predominantly long-snouted odontocetes appeared in the fossil record. Among them, members of the genera Argyrocetus Lydekker, 1893 and Macrodelphinus Wilson, 1935, from the early Miocene of the Northeast Pacific and Argentina, were tentatively attributed to the family Eurhinodelphinidae. However, due to the fragmentary state of the specimens, unambiguous apomorphies of the family could not be detected. Based on two well-preserved skulls with associated mandibular elements, discovered in early Miocene layers of the Chilcatay Formation (Pisco Basin, Peru), we report on a new genus and species of long-snouted homodont odontocete, Chilcacetus cavirhinus n. gen., n. sp. Characterized by, among others, the presence of alveoli on the anterior premaxillary portion of the rostrum, the lack of a lateral groove on the rostrum, anterodorsally elevated nasals, a possibly autapomorphic cavity between nasals and mesethmoid in the posterior wall of the bony nares, a high temporal fossa, and the absence of ankylosis along the mandibular symphysis, C. cavirhinus n. gen., n. sp. does not fit in any of the known odontocete families, but shares several morphological features with Argyrocetus spp. and Macrodelphinus. Our phylogenetic analysis, based on 77 characters for 35 odontocete taxa, suggests the existence of an early Miocene Eastern Pacific long-snouted homodont odontocete clade (with an hypothetical South Atlantic member, the poorly known Argyrocetus patagonicus Lydekker, 1893), distinct from the only superficially similar eoplatanistids and eurhinodelphinids. Furthermore, our consensus tree indicates an early branching of this new clade compared to other homodont odontocete lineages. Unfortunately, the results of the cladistic analysis presented here are not well supported; a reappraisal of Argyrocetus and Macrodelphinus is needed to more clearly define the new clade and bolster its phylogentic position

Age dependence of the Vega Phenomenon: Theory

In a separate paper (Decin et al 2003), we have re-examined the observations of IR excess obtained with the ISO satellite and discussed the ages of stars with excess. The amount of dust (measured by the luminosity fraction \fdust=L_\mathrm{IR}/L_{\star}) seen around main-sequence stars of different ages shows several interesting trends. To discuss these results in the context of a physical model, we develop in this paper an analytical model for the dust production in Vega-type systems. Previously it has been claimed that a powerlaw slope of about -2 in the diagram plotting amount of dust versus time could be explained by a simple collisional cascade. We show that such a cascade in fact results in a powerlaw \fdust\propto t^{-1} if the dust removal processes are dominated by collisions. A powerlaw \fdust\propto t^{-2} only results when the dust removal processes become dominated by Pointing-Robertson drag. This may be the case in the Kuiper Belt of our own solar system, but it is certainly not the case in any of the observed disks. A steeper slope can, however, be created by including continuous stirring into the models. We show that the existence of both young and old Vega-like systems with large amounts of dust (\fdust\simeq 10^{-3}) can be explained qualitatively by Kuiper-Belt-like structures with \emph{delayed stirring}. Finally, the absence of young stars with intermediate amounts of dust may be due to the fact that stirring due to planet formation may not be active in young low-mass disks. The considerations in this paper support the picture of simultaneous stirring and dust production proposed by Kenyon and Bromley (2002).Comment: 26 pages, 3 figures, accepted for Publication in Ap

Women labour supply and country specific institutions

In this thesis, I study the influence of country-specific institutions on the labour supply decision of prime-aged women. In chapter 1, I use reduced-form methods, to evaluate the impact of wide changes to the benefit system and childcare subsidies targeted at households with pre-school age children in France. I estimate strong responses to maternity leave type benefits, and a positive impact of childcare subsidies on mothers employment rates in the long-run. In chapter 2, I develop and estimate a static labour supply model with part-time wage equations as well as demand-side constraints. I can compare the elasticities estimates and predictions from tax reform simulations to those of models assuming a unique hourly productivity and the absence of any employment constraint. The structural model also enables me to clearly simulate the impact of each component of the wide policy reform studied in the first chapter. In chapter 3, I try to understand why the number of hours worked by British married women is lower than that of French married women. I find that in the presence of children, British mothers are far more responsive to financial incentives. Husbands’ earnings and their interaction with childcare prices seem to play an important role. Nevertheless, the fall in hours worked in the British households with children, despite facing lower taxes than in France, remains somewhat puzzling. It could be mainly attributed (in the framework used) to different preferences. In the final chapter, I study the impact of joint-taxation on the labour supply choices of married women with working husbands in France. I simulate a revenue-neutral reform that would cancel the tax penalty or gain associated with being married. I find that the overall labour supply of these women would increase by 1.2%

<i>Koristocetus pescei</i> gen. et sp. nov., a diminutive sperm whale (Cetacea: Odontoceti: Kogiidae) from the late Miocene of Peru

Among odontocetes, members of the family Kogiidae (pygmy and dwarf sperm whales) are known as small-sized and in many respects enigmatic relatives of the great sperm whale Physeter macrocephalus. Most of the still scanty fossil record of Kogiidae is represented by isolated skulls and ear bones from Neogene deposits of the Northern Hemisphere, with the significant exception of Scaphokogia, a highly autapomorphic genus from late Miocene deposits of the Pisco Formation exposed along the southern coast of Peru. Here we report on a new fossil kogiid from Aguada de Lomas, a site where the late Miocene beds of the Pisco Formation are exposed. This specimen consists of an almost complete cranium representing a new taxon of Kogiidae: Koristocetus pescei gen. et sp. nov. Koristocetus mainly differs from extant Kogia spp. by displaying a larger temporal fossa and well-individualized dental alveoli on the upper jaws. Coupled with a relatively elongated rostrum, these characters suggest that Koristocetus retained some degree of raptorial feeding abilities, contrasting with the strong suction feeding specialization seen in Recent kogiids. Our phylogenetic analysis recognizes Koristocetus as the earliest branching member of the subfamily Kogiinae. Interestingly, Koristocetus shared the southern coast of present-day Peru with members of the genus Scaphokogia, whose unique convex rostrum and unusual neurocranial morphology seemingly indicate a peculiar foraging specialization that has still to be understood. In conclusion, Koristocetus evokes a long history of high diversity, morphological disparity, and sympatric habits in fossil kogiids, thus suggesting that our comprehension of the evolutionary history of pygmy and dwarf sperm whales is still far from being exhaustive