199 research outputs found
Light propagation through optical media using metric contact geometry
In this work, we show that the orthogonality between rays and fronts of light
propagation in a medium is expressed in terms of a suitable metric contact
structure of the optical medium without boundaries. Moreover, we show that
considering interfaces (modeled as boundaries) orthogonality is no longer
fulfilled, leading to optical aberrations and in some cases total internal
reflection. We present some illustrative examples of this latter point.Comment: 8 pages, 7 figure
A proto brown dwarf candidate in Taurus
Aims. We search for brown dwarfs at the Class 0/I evolutionary stage, or proto brown dwarfs.
Methods. We present a multi wavelength study, ranging from optical at 0.8 μm to radio wavelengths at 6 cm, of a cool, very faint, and red multiple object, SSTB213 J041757, detected by Spitzer toward the Barnard 213 dark cloud, in Taurus.
Results. The SED of SSTB213 J041757 displays a clear excess at long wavelengths resembling that of a Class I object. The mid-IR source has two possible counterparts, A and B, in the near-IR and optical images, and the 350 μm observations detect clear extended emission, presumably from an envelope around the two sources. The position of A & B in the (Ic− J) versus (J − [3.6]) colour-colour diagram is consistent with them being Galactic sources and not extragalactic contaminants. A proper-motion study confirms this result for A, while it is inconclusive for B. The temperature and mass of the two possible central objects, according to COND evolutionary models, range between 1550−1750 K and 3−4 M_(Jupiter), and 950−1300 K and 1−2 M_(Jupiter), for A and B, respectively. The integrated SED provides bolometric temperatures and luminosities of 280 K and 0.0034 L_⊙, assuming that the emission at wavelengths > 5 μm is associated with component A, and 150 K and 0.0033 L_⊙, assuming that the emission at wavelengths > 5 μm is associated with component B, which would imply the SSTB213 J041757 object has a luminosity well below the luminosity of other very low luminosity objects discovered up to date.
Conclusions. With these characteristics, SSTB213 J041757 seems to be a promising, and perhaps double, proto brown dwarf candidate
A submillimeter search for pre- and proto-brown dwarfs in Chamaeleon II
Context. Chamaeleon II molecular cloud is an active star forming region that
offers an excellent opportunity for studying the formation of brown dwarfs in
the southern hemisphere. Aims. Our aims are to identify a population of pre-
and proto- brown dwarfs (5 sigma mass limit threshold of ~0.015 Msun) and
provide information on the formation mechanisms of substellar objects. Methods.
We performed high sensitivity observations at 870 microns using the LABOCA
bolometer at the APEX telescope towards an active star forming region in
Chamaeleon II. The data are complemented with an extensive multiwavelength
catalogue of sources from the optical to the far-infrared to study the nature
of the LABOCA detections. Results. We detect fifteen cores at 870 microns, and
eleven of them show masses in the substellar regime. The most intense objects
in the surveyed field correspond to the submillimeter counterparts of the well
known young stellar objects DK Cha and IRAS 12500-7658. We identify a possible
proto-brown dwarf candidate (ChaII-APEX-L) with IRAC emission at 3.6 and 4.5
microns. Conclusions. Our analysis indicates that most of the spatially
resolved cores are transient, and that the point-like starless cores in the
sub-stellar regime (with masses between 0.016 Msun and 0.066 Msun) could be
pre-brown dwarfs cores gravitationally unstable if they have radii smaller than
220 AU to 907 AU (1.2" to 5" at 178 pc) respectively for different masses. ALMA
observations will be the key to reveal the energetic state of these pre-brown
dwarfs candidates.Comment: 11 pages, 6 figure
TORRIJOS-CASTRILLEJO, DAVID, Anaxágoras y su recepción en Aristóteles, Dissertationes. Series Philosophica XLIII, EDUSC, Roma, 2014, 528 pp. [Reseña]
Trascendencia e inmanencia del Intelecto. Los casos de Anaxágoras y Giordano Bruno
The article presents and compares the perspectives of Anaxagoras and Giordano Bruno on the intellect as an efficient cause of the world. It is shown that while both concepts indicate the transcendence and the immanence of the intellect, neither manages to establish either transcendence or immanence in a categorical manner. This ambivalence shows that the intelligent cause of the world is detectable in nature because of its actions, but not because of its being.El artÃculo presenta y relaciona los planteamientos de Anaxágoras y de Giordano Bruno acerca de un intelecto comprendido como la causa eficiente del mundo. Se muestra que ambas concepciones indican ya la trascendencia, ya la inmanencia del intelecto; sin embargo, ninguna termina por afirmar su ser trascendente o inmanente de manera categórica. Esta ambivalencia compartida pone de manifiesto que la causa inteligente es perceptible en la naturaleza por su acción, pero no por su ser
A collimated, ionized bipolar structure and a high density torus in the young planetary nebula IRAS 17347-3139
We present observations of continuum (lambda = 0.7, 1.3, 3.6 and 18 cm) and
OH maser (lambda = 18 cm) emission toward the young planetary nebula IRAS
17347-3139, which is one of the three planetary nebulae that are known to
harbor water maser emission. From the continuum observations we show that the
ionized shell of IRAS 17347-3139 consists of two main structures: one extended
(size ~1". 5) with bipolar morphology along PA=-30 degrees, elongated in the
same direction as the lobes observed in the near-infrared images, and a central
compact structure (size ~0". 25) elongated in the direction perpendicular to
the bipolar axis, coinciding with the equatorial dark lane observed in the
near-infrared images. Our image at 1.3 cm suggests the presence of dense walls
in the ionized bipolar lobes. We estimate for the central compact structure a
value of the electron density at least ~5 times higher than in the lobes. A
high resolution image of this structure at 0.7 cm shows two peaks separated by
about 0". 13 (corresponding to 100-780 AU, using a distance range of 0.8-6
kpc). This emission is interpreted as originating in an ionized equatorial
torus-like structure, from whose edges the water maser emission might be
arising. We have detected weak OH 1612 MHz maser emission at VLSR ~ -70 km/s
associated with IRAS 17347-3139. We derive a 3 sigma upper limit of < 35% for
the percentage of circularly polarized emission. Within our primary beam, we
detected additional OH 1612 MHz maser emission in the LSR velocity ranges -5 to
-24 and -90 to -123 km/s, associated with the sources 2MASS J17380406-3138387
and OH 356.65-0.15, respectively.Comment: 26 pages, 8 figures. Accepted for publication in Ap
- …