VLA 3.5 cm continuum sources in the Serpens cloud core

We present VLA 3.5 cm continuum observations of the Serpens cloud core. 22 radio continuum sources are detected. 16 out of the 22 cm sources are suggested to be associated with young stellar objects (Class 0, Class I, flat-spectrum, and Class II) of the young Serpens cluster. The rest of the VLA sources plausibly are background objects. Most of the Serpens cm sources likely represent thermal radio jets; on the other hand, the radio continuum emission of some sources could be due to a gyrosynchroton mechanism arising from coronally active young stars. The Serpens VLA sources are spatially distributed into two groups; one of them located towards the NW clump of the Serpens core, where only Class 0 and Class I protostars are found to present cm emission, and a second group located towards the SE clump, where radio continuum sources are associated with objects in evolutionary classes from Class 0 to Class II. This subgrouping is similar to that found in the near IR, mid-IR and mm wavelength regimes.Comment: 2 figures, accepted by Astronomical journa

Thin-shell wormholes with a generalized Chaplygin gas in Einstein-Born-Infeld theory

We construct spherically symmetric thin-shell wormholes supported by a generalized Chaplygin gas in Born-Infeld electrodynamics coupled to Einstein gravity, and we analyze their stability under radial perturbations. For different values of the Born-Infeld parameter and the charge, we compare the results with those obtained in a previous work for Maxwell electrodynamics. The stability region in the parameter space reduces and then disappears as the value of the Born-Infeld parameter is modified in the sense of a larger departure from Maxwell theory.Comment: 9 pages, 6 figures; v2: improved versio

Brans-Dicke cylindrical wormholes

Static axisymmetric thin-shell wormholes are constructed within the framework of the Brans-Dicke scalar-tensor theory of gravity. Examples of wormholes associated with vacuum and electromagnetic fields are studied. All constructions must be threaded by exotic matter, except in the case of geometries with a singularity of finite radius, associated with an electric field, which can have a throat supported by ordinary matter. These results are achieved with any of the two definitions of the flare-out condition considered.Comment: 11 pages, 3 figures; v3: corrected version, conclusions unchange

Dilaton thin-shell wormholes supported by a generalized Chaplygin gas

In this article, we construct spherical thin-shell wormholes with charge in dilaton gravity. The exotic matter required for the construction is provided by a generalized Chaplygin gas. We study the stability under perturbations preserving the symmetry. We find that the increase of the coupling between the dilaton and the electromagnetic fields reduces the range of the parameters for which stable configurations are possible.Comment: 14 pages, 6 figures. v3: typos correcte

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

Addemdum to: ''The Mathematical Structure of Quantum Superspace as a Consequence of Time Asymmetry''

In this paper we improve the results of sec. VI of paper [M. Castagnino, Phys. Rev. D 57, 750 (1998)] by considering that the main source of entropy production are the photospheres of the stars

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

Thin-shell wormholes with a generalized Chaplygin gas

In this article, spherically symmetric thin-shell wormholes supported by a generalized Chaplygin gas are constructed and their stability under perturbations preserving the symmetry is studied. Wormholes with charge and with a cosmological constant are analyzed and the results are compared with those obtained for the original Chaplygin gas, which was considered in a previous work. For some values of the parameters, one stable configuration is also present and a new extra unstable solution is found.Comment: 14 pages, 6 figures; v2: typos corrected and minor rewordin

Envelope structure of deeply embedded young stellar objects in the Serpens Molecular Cloud

Aperture synthesis and single-dish (sub) millimeter molecular lines and continuum observations reveal in great detail the envelope structure of deeply embedded young stellar objects (SMM1, SMM2, SMM3, SMM4) in the densely star-forming Serpens Molecular Cloud. Resolved millimeter continuum emission constrains the density structure to a radial power law with index -2.0 +/- 0.5, and envelope masses of 8.7, 3.0, and 5.3 M_sol for SMM1, SMM3, and SMM4. The core SMM2 does not seem to have a central condensation and may not have formed a star yet. The molecular line observations can be described by the same envelope model, if an additional, small amount of warm (100 K) material is included. This probably corresponds to the inner few hundred AU of the envelope were the temperature is high. In the interferometer beam, the molecular lines reveal the inner regions of the envelopes, as well as interaction of the outflow with the surrounding envelope. Bright HCO+ and HCN emission outlines the cavities, while SiO and SO trace the direct impact of the outflow on ambient gas. Taken together, these observations provide a first comprehensive view of the physical and chemical structure of the envelopes of deeply embedded young stellar objects in a clustered environment on scales between 1000 and 10,000 AU.Comment: 46 pages, incl. 12 postscript figures, uses ApJ latex and psfig macro

Strong Gravitational Lensing in a Charged Squashed Kaluza- Klein Black hole

In this paper we investigate the strong gravitational lensing in a charged squashed Kaluza-Klein black hole. We suppose that the supermassive black hole in the galaxy center can be considered by a charged squashed Kaluza-Klein black hole and then we study the strong gravitational lensing theory and estimate the numerical values for parameters and observables of it. We explore the effects of the scale of extra dimension $\rho_0$ and the charge of black hole $\rho_q$ on these parameters and observables.Comment: 17 pages, 10 figure