73 research outputs found

    Near Infrared polarimetry of a sample of YSOs

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    Our goal is to study the physical properties of the circumstellar environment of young stellar objetcs (YSOs). In particular, the determination of the scattering mechanism can help to constrain the optical depth of the disk and/or envelope in the near infrared. We used the IAGPOL imaging polarimeter along with the CamIV infrared camera at the LNA observatory to obtain near infrared polarimetry measurements at the H band of a sample of optically visible YSOs, namely, eleven T Tauri stars and eight Herbig Ae/Be stars. An independent determination of the disk (or jet) orientation was obtained for twelve objects from the literature. The circumstellar optical depth could be then estimated comparing the integrated polarization position angle (PA) with the direction of the major axis of the disk projected in the plane of the sky. In general, optically thin disks have polarization PA perpendicular to the disk plane. In contrast, optically thick disks produce polarization PA parallel to the disks. Among the T Tauri stars, three are consistent with optically thin disks (AS 353A, RY Tau and UY Aur) and five with optically thick disks (V536 Aql, DG Tau, DO Tau, HL Tau and LkHalpha 358). Among the Herbig Ae/Be stars, two stars show evidence of optically thin disk (Hen 3-1191 and VV Ser) and two of optically thick disks (PDS 453 and MWC 297). Our results seem consistent with the fact that optically thick disks at near infrared bands are associated more likely with younger YSOs. Marginal evidence of polarization reversal is found in RY Tau, RY Ori, WW Vul, and UY Aur. On the first three cases this feature can be associated to the UXOR phenomenon. Correlations with the IRAS colours and the spectral index yielded evidence of an evolutionary segregation with the disks tend to be optically thin when they are older.Comment: 15 pages, 15 figures, accepted in Astronomy and Astrophysic

    Challenges in outdoor tourism explorations: an embodied approach

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    Methodological challenges are rarely discussed in depth among outdoor adventure tourism scholars. Despite the prevailing quali- tative approaches in this field, and the recognition that the fleet- ingness of the human experience and the non-linearity and unpredictability of the more-than-human world have the power to influence the research process, the messy, negotiated and often contested researcher’s role has been less considered. In addressing this, the aim here is to critically discuss the methodo- logical approach to explorations of the outdoor experiences through deconstructing the researcher’s role. Through renderings of the existentialist propositions of being in the world and a post- structuralist philosophy of fluidity and flux, the attention is granted to embodied experiences as a way of generating knowl- edges. Being situated in the research setting, space is created for interrogation of the processual dimensions of commodified out- door journeys from an emic, researcher-as-tourist perspective. Research in the outdoor scenaria is by no means a linear process but rather a messy, complex and often ruptured journey, further complicated by the ethical concerns, struggles and idiosyncrasies of the researcher. I thus discuss the nuances and complexities of doing the embodied research and the haphazard ways of data collection. In shifting attention to more existential aspects of being in the outdoors through the process of post-experiential reflections, discomfort emerged as a critical quality of the outdoor experience. I thus illuminate the significance of embodied research and epiphenomenal discoveries in the production of new knowledges, to which greater attention, both in theoretical and methodological conversations, should be paid in the future

    Star-forming cores embedded in a massive cold clump: Fragmentation, collapse and energetic outflows

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    The fate of massive cold clumps, their internal structure and collapse need to be characterised to understand the initial conditions for the formation of high-mass stars, stellar systems, and the origin of associations and clusters. We explore the onset of star formation in the 75 M_sun SMM1 clump in the region ISOSS J18364-0221 using infrared and (sub-)millimetre observations including interferometry. This contracting clump has fragmented into two compact cores SMM1 North and South of 0.05 pc radius, having masses of 15 and 10 M_sun, and luminosities of 20 and 180 L_sun. SMM1 South harbours a source traced at 24 and 70um, drives an energetic molecular outflow, and appears supersonically turbulent at the core centre. SMM1 North has no infrared counterparts and shows lower levels of turbulence, but also drives an outflow. Both outflows appear collimated and parsec-scale near-infrared features probably trace the outflow-powering jets. We derived mass outflow rates of at least 4E-5 M_sun/yr and outflow timescales of less than 1E4 yr. Our HCN(1-0) modelling for SMM1 South yielded an infall velocity of 0.14 km/s and an estimated mass infall rate of 3E-5 M_sun/yr. Both cores may harbour seeds of intermediate- or high-mass stars. We compare the derived core properties with recent simulations of massive core collapse. They are consistent with the very early stages dominated by accretion luminosity.Comment: Accepted for publication in ApJ, 14 pages, 7 figure

    The Herschel-SPIRE Legacy Survey (HSLS): the scientific goals of a shallow and wide submillimeter imaging survey with SPIRE

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    A large sub-mm survey with Herschel will enable many exciting science opportunities, especially in an era of wide-field optical and radio surveys and high resolution cosmic microwave background experiments. The Herschel-SPIRE Legacy Survey (HSLS), will lead to imaging data over 4000 sq. degrees at 250, 350, and 500 micron. Major Goals of HSLS are: (a) produce a catalog of 2.5 to 3 million galaxies down to 26, 27 and 33 mJy (50% completeness; 5 sigma confusion noise) at 250, 350 and 500 micron, respectively, in the southern hemisphere (3000 sq. degrees) and in an equatorial strip (1000 sq. degrees), areas which have extensive multi-wavelength coverage and are easily accessible from ALMA. Two thirds of the of the sources are expected to be at z > 1, one third at z > 2 and about a 1000 at z > 5. (b) Remove point source confusion in secondary anisotropy studies with Planck and ground-based CMB data. (c) Find at least 1200 strongly lensed bright sub-mm sources leading to a 2% test of general relativity. (d) Identify 200 proto-cluster regions at z of 2 and perform an unbiased study of the environmental dependence of star formation. (e) Perform an unbiased survey for star formation and dust at high Galactic latitude and make a census of debris disks and dust around AGB stars and white dwarfs

    EFSA BIOHAZ Panel (EFSA Panel on Biological Hazards, 2013. Scientific Opinion on the public health hazards to be covered by inspection of meat from sheep and goats.

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