The Sizes of Kuiper Belt Objects

One of the most fundamental problems in the study of Kuiper belt objects (KBOs) is to know their true physical size. Without knowledge of their albedos we are not able to distinguish large and dark from small and bright KBOs. Spitzer produced rough estimates of the sizes and albedos of about 20 KBOs, and the Herschel space telescope will improve on those initial measurements by extending the sample to the ~150 brightest KBOs. SPICA's higher sensitivity instruments should allow us not only to broaden the sample to smaller KBOs but also to achieve a statistically significant sample of KBO thermal light curves (Herschel will measure only six objects). A large sample covering a broad range of sizes will be key to identify meaningful correlations between size and other physical and surface properties that constrain the processes of formation and evolution of the solar system.Comment: 6 pages, 6 figures, Proc. Workshop "The Space Infrared Telescope for Cosmology and Astrophysics: Revealing the Origins of Planets and Galaxies

Extinction in the Coma of Comet 17P/Holmes

On 2007 October 29 the outbursting comet 17P/Holmes passed within 0.79 arcsec of a background star. We recorded the event using optical, narrowband photometry and detect a 3% to 4% dip in stellar brightness bracketing the time of closest approach to the comet nucleus. The detected dimming implies an optical depth tau~0.04 at 1.5 arcsec from the nucleus and an optical depth towards the nucleus center tau_n<13.3. At the time of our observations, the coma was optically thick only within rho<~0.01 arcsec from the nucleus. By combining the measured extinction and the scattered light from the coma we estimate a dust red geometric albedo p_d=0.006+/-0.002 at 16 deg phase angle. Our measurements place the most stringent constraints on the extinction optical depth of any cometary coma.Comment: 5 pages, 3 figures, 2 table. Accepted for publication in ApJ

Outer solar system possibly shaped by a stellar fly-by

The planets of our solar system formed from a gas-dust disk. However, there are some properties of the solar system that are peculiar in this context. First, the cumulative mass of all objects beyond Neptune (TNOs) is only a fraction of what one would expect. Second, unlike the planets themselves, the TNOs do not orbit on coplanar, circular orbits around the Sun, but move mostly on inclined, eccentric orbits and are distributed in a complex way. This implies that some process restructured the outer solar system after its formation. However, some of TNOs, referred to as Sednoids, move outside the zone of influence of the planets. Thus external forces must have played an important part in the restructuring of the outer solar system. The study presented here shows that a close fly-by of a neighbouring star can simultaneously lead to the observed lower mass density outside 30 AU and excite the TNOs onto eccentric, inclined orbits, including the family of Sednoids. In the past it was estimated that such close fly-bys are rare during the relevant development stage. However, our numerical simulations show that such a scenario is much more likely than previously anticipated. A fly-by also naturally explains the puzzling fact that Neptune has a higher mass than Uranus. Our simulations suggest that many additional Sednoids at high inclinations still await discovery, perhaps including bodies like the postulated planet X.Comment: 16 pages, 7 figures, accepted by Ap

Time-Resolved Near-Infrared Photometry of Extreme Kuiper Belt Object Haumea

We present time-resolved near-infrared (J and H) photometry of the extreme Kuiper belt object (136108) Haumea (formerly 2003 EL61) taken to further investigate rotational variability of this object. The new data show that the near-infrared peak-to-peak photometric range is similar to the value at visible wavelengths, \Delta m_R = 0.30+/-0.02 mag. Detailed analysis of the new and previous data reveals subtle visible/near-infrared color variations across the surface of Haumea. The color variations are spatially correlated with a previously identified surface region, redder in B-R and darker than the mean surface. Our photometry indicates that the J-H colors of Haumea (J-H=-0.057+/-0.016 mag) and its brightest satellite Hi'iaka (J-H=-0.399+/-0.034 mag) are significantly (>9 sigma) different. The satellite Hi'iaka is unusually blue in J-H, consistent with strong 1.5 micron water-ice absorption. The phase coefficient of Haumea in the J-band is found to increase monotonically with wavelength in the range 0.4<lambda<1.3. We compare our findings with other Solar system objects and discuss implications regarding the surface of Haumea.Comment: 10 pages, 10 figures, 6 tables. Accepted for publication in The Astronomical Journal (2008 November 28

O mercado de aluguel de imóveis comerciais e de serviços em centros históricos brasileiros: implicações da conservação inovadora e da destruição aniquiladora nos preços dos bens patrimoniais

In view of the importance of the rental real estate property sector intended for tertiary activities in historic centers in Brazil, the intention of this article to draw an interpretative schema of the manner in which this market functions, based on the historic center of Recife, in the state of Pernambuco. This has been undertaken through an investigation into the conduct of its agents, who, at times, acted as though driven to preserve the historical values of heritage assets (innovative conservation), while at others, to destroy them and, thus, annihilate the values contained within them (annihilating destruction). For this, a need was perceived to analyze the relevance of land rent; the characteristics of the goods traded regarding heterogeneity and the prospects for increasing supply; the profile and level of information held by the agents, and their conduct in relation to these real assets and the rent prices offered on the market.Diante da importância do parque imobiliário de locação destinado às atividades terciárias nos centros históricos brasileiros, este artigo pretende desenhar um esquema interpretativo do funcionamento desse mercado, tendo como fundamento o centro histórico recifense, em Pernambuco, com base na averiguação dos comportamentos dos seus agentes, os quais agem ora impulsionados a conservar os valores históricos dos bens patrimoniais (conservação inovadora), ora a destruí-los e, assim, aniquilar os valores neles presentes (destruição aniquiladora). Para isso, foi necessário analisar a relevância do rentismo imobiliário; as características dos bens transacionados quanto à heterogeneidade e às perspectivas de aumento da oferta; o perfil e o grau de informação dos agentes; suas condutas em face desses ativos reais e os preços de aluguéis ofertados no mercado

How do people perceive new ways of sustainable mobility? : the case of electric scooters : San Francisco vs Lisbon

Nowadays, mobility is a crucial factor in our society, we use it almost every day. However, it is important to think about the consequences of our actions, it is important to be sustainable and adopt sustainable means of transport. The purpose of the present dissertation is to understand how people perceive new ways of sustainable mobility, specifically the electric scooters and to compare the results between Lisbon and San Francisco. In order to conduct this study, literature was revised to get a clear vision on strategies, sustainability and consumer behavior related with mobility and the electric scooters. As for retrieving data, mixed methods methodology was used, an online survey with 345 participants and three interviews with two representatives of mobility companies and one representative of the city hall of Lisbon. The results show that there is a difference in usage between people from San Francisco and from Lisbon (more for San Francisco), however no differences in perceptions between both cities. After the data analysis it was possible to conclude that people perceive technology, sustainability and safety as the most important characteristics on a transport. Further analysis indicated that measures must be taken in order to increase the perception of safety regarding the electric scooters, such as safer places to ride and safer designs. To summarize, the advantages of using electric scooters surpass the disadvantages, nevertheless it is necessary to take measures, both companies and the government, to face the disadvantages.Hoje em dia, a mobilidade é um fator crucial na nossa sociedade, usamo-la quase todos os dias. No entanto, é importante pensar nas consequências das nossas ações, é importante sermos sustentáveis e adotarmos meios de transporte sustentáveis. O objetivo da presente dissertação é perceber como as pessoas percecionam novas formas de mobilidade sustentável, nomeadamente as scooters elétricas, e comparar os resultados entre Lisboa e São Francisco. Para realizar este estudo, a literatura foi revista para obter uma visão clara sobre estratégias, sustentabilidade e comportamento do consumidor relacionados com a mobilidade e as scooters elétricas. Quanto à obtenção de dados, foi utilizada metodologia de métodos mistos, um inquérito online com 345 participantes e três entrevistas com dois representantes de empresas de mobilidade e um representante da câmara municipal de Lisboa. Os resultados mostram que há uma diferença de utilização entre pessoas de São Francisco e de Lisboa (mais para São Francisco), no entanto não há diferenças de perceção entre ambas as cidades. Após a análise de dados, foi possível concluir que as pessoas veem a tecnologia, a sustentabilidade e a segurança como as características mais importantes num transporte. Uma análise mais aprofundada indicou que devem ser tomadas medidas para aumentar a perceção de segurança no que diz respeito às trotinetes elétricas, tais como locais mais seguros para andar e designs mais seguros. Resumindo, as vantagens de utilizar trotinetes elétricas superam as desvantagens, no entanto, é necessário tomar medidas, tanto as empresas como o governo, para fazer face às desvantagens

A Change in the Lightcurve of Kuiper Belt Contact Binary (139775) 2001 QG298

New observations show that the lightcurve of Kuiper belt contact binary (139775) 2001 QG298 has changed substantially since the first observations in 2003. The 2010 lightcurve has a peak-to-peak photometric of range \Deltam{2010}=0.7\pm0.1 mag, significantly lower than in 2003, \Deltam{2003}=1.14\pm0.04 mag. This change is most simply interpreted if 2001 QG298 has an obliquity near 90 deg. The observed decrease in \Deltam is caused by a change in viewing geometry, from equator-on in 2003 to nearly 16 deg (the orbital angular distance covered by the object between the observations) off the equator in 2010. The 2003 and 2010 lightcurves have the same rotation period and appear in phase when shifted by an integer number of full rotations, also consistent with high obliquity. Based on the new 2010 lightcurve data, we find that 2001 QG298 has an obliquity {\epsilon}=90\pm30 deg. Current estimates of the intrinsic fraction of contact binaries in the Kuiper belt are debiased assuming that these objects have randomly oriented spins. If, as 2001 QG298, KBO contact binaries tend to have large obliquities, a larger correction is required. As a result, the abundance of contact binaries may be larger than previously believed.Comment: 28 pages, 10 figures, 5 tables. Accepted for publication in The Astronomical Journal (2011 July 18