On C*-algebras generated by pairs of q-commuting isometries

We consider the C*-algebras O_2^q and A_2^q generated, respectively, by isometries s_1, s_2 satisfying the relation s_1^* s_2 = q s_2 s_1^* with |q| < 1 (the deformed Cuntz relation), and by isometries s_1, s_2 satisfying the relation s_2 s_1 = q s_1 s_2 with |q| = 1. We show that O_2^q is isomorphic to the Cuntz-Toeplitz C*-algebra O_2^0 for any |q| < 1. We further prove that A_2^{q_1} is isomorphic to A_2^{q_2} if and only if either q_1 = q_2 or q_1 = complex conjugate of q_2. In the second part of our paper, we discuss the complexity of the representation theory of A_2^q. We show that A_2^q is *-wild for any q in the circle |q| = 1, and hence that A_2^q is not nuclear for any q in the circle.Comment: 18 pages, LaTeX2e "article" document class; submitted. V2 clarifies the relationships between the various deformation systems treate

Atomic jet from SMM1 (FIRS1) in Serpens uncovers non-coeval binary companion

We report on the detection of an atomic jet associated with the protostellar source SMM1 (FIRS1) in Serpens. The jet is revealed in [FeII] and [NeII] line maps observed with Spitzer/IRS, and further confirmed in HiRes IRAC and MIPS images. It is traced very close to SMM1 and peaks at ~5 arcsec" from the source at a position angle of $\sim 125 degrees. In contrast, molecular hydrogen emission becomes prominent at distances > 5" from the protostar and extends at a position angle of 160 degrees. The morphological differences suggest that the atomic emission arises from a companion source, lying in the foreground of the envelope surrounding the embedded protostar SMM1. In addition the molecular and atomic Spitzer maps disentangle the large scale CO (3-2) emission observed in the region into two distinct bipolar outflows, giving further support to a proto-binary source setup. Analysis at the peaks of the [FeII] jet show that emission arises from warm and dense gas (T ~1000 K, n(electron) 10^5 - 10^6 cm^-3). The mass flux of the jet derived independently for the [FeII] and [NeII] lines is 10^7 M(sun)/yr, pointing to a more evolved Class~I/II protostar as the driving source. All existing evidence converge to the conclusion that SMM1 is a non-coeval proto-binary source.Comment: 10 pages, 7 figures, 1 table. Accepted for publication in Astronomy \& Astrophysic

An interferometric study of the low-mass protostar IRAS 16293-2422: small scale organic chemistry

Aims: To investigate the chemical relations between complex organics based on their spatial distributions and excitation conditions in the low-mass young stellar objects IRAS 16293-2422 A and B. Methods: Interferometric observations with the Submillimeter Array have been performed at 5''x3'' resolution revealing emission lines of HNCO, CH3CN, CH2CO, CH3CHO and C2H5OH. Rotational temperatures are determined from rotational diagrams when a sufficient number of lines are detected. Results: Compact emission is detected for all species studied here. For HNCO and CH3CN it mostly arises from source A, CH2CO and C2H5OH have comparable strength for both sources and CH3CHO arises exclusively from source B. HNCO, CH3CN and CH3CHO have rotational temperatures >200 K. The (u,v)-visibility data reveal that HNCO also has extended cold emission. Conclusions: The abundances of the molecules studied here are very similar within factors of a few to those found in high-mass YSOs. Thus the chemistry between high- and low-mass objects appears to be independent of luminosity and cloud mass. Bigger abundance differences are seen between the A and B source. The HNCO abundance relative to CH3OH is ~4 times higher toward A, which may be due to a higher initial OCN- ice abundances in source A compared to B. Furthermore, not all oxygen-bearing species are co-existent. The different spatial behavior of CH2CO and C2H5OH compared with CH3CHO suggests that hydrogenation reactions on grain-surfaces are not sufficient to explain the observed gas phase abundances. Selective destruction of CH3CHO may result in the anti-coincidence of these species in source A. These results illustrate the power of interferometric compared with single dish data in terms of testing chemical models.Comment: 11 pages, 15 figures, accepeted by A&

The effect of a strong external radiation field on protostellar envelopes in Orion

We discuss the effects of an enhanced interstellar radiation field (ISRF) on the observables of protostellar cores in the Orion cloud region. Dust radiative transfer is used to constrain the envelope physical structure by reproducing SCUBA 850 micron emission. Previously reported 13CO, C17O and H2CO line observations are reproduced through detailed Monte Carlo line radiative transfer models. It is found that the 13CO line emission is marginally optically thick and sensitive to the physical conditions in the outer envelope. An increased temperature in this region is needed in order to reproduce the 13CO line strengths and it is suggested to be caused by a strong heating from the exterior, corresponding to an ISRF in Orion 10^3 times stronger than the "standard" ISRF. The typical temperatures in the outer envelope are higher than the desorption temperature for CO. The C17O emission is less sensitive to this increased temperature but rather traces the bulk envelope material. The data are only fit by a model where CO is depleted, except in the inner and outermost regions where the temperature increases above 30-40 K. The fact that the temperatures do not drop below approximately 25 K in any of the envelopes whereas a significant fraction of CO is frozen-out suggest that the interstellar radiation field has changed through the evolution of the cores. The H2CO lines are successfully reproduced in the model of an increased ISRF with constant abundances of 3-5x10^{-10}.Comment: 11 pages, 10 figures. Accepted for publication in A&

Chemistry of a newly detected circumbinary disk in Ophiuchus

(Abridged) Astronomers recently started discovering exoplanets around binary systems. Therefore, understanding the formation and evolution of circumbinary disks is crucial for a complete scenario of planet formation. The aim of this paper is to present the detection of a circumbinary disk around Oph-IRS67 and analyse its structure. We present high-angular-resolution (0.4", 60 AU) observations of C17O, H13CO+ , C34S, SO2, C2H and c-C3H2 molecular transitions with ALMA at 0.8 mm. The spectrally and spatially resolved maps reveal the kinematics of the circumbinary disk as well as its chemistry. Molecular abundances are estimated using RADEX. The continuum emission reveals the presence of a circumbinary disk around the two sources. This disk has a diameter of ~620 AU and is well traced by C17O and H13CO+ emission. C2H and c-C3H2 trace a higher-density region which is spatially offset from the sources (~430 AU). Finally, SO2 shows compact emission around one of the sources, Oph-IRS67 B. The molecular transitions which trace the circumbinary disk are consistent with a Keplerian profile on disk scales (< 200 AU) and an infalling profile for envelope scales (> 200 AU). The Keplerian fit leads to a mass of 2.2 Msun. Inferred CO abundances w.r.t. H2 are comparable to the canonical ISM value of 2.7e-4. This study proves the first detection of the circumbinary disk associated with Oph-IRS67. The disk is chemically differentiated from the nearby high-density region. The lack of methanol emission suggests the extended disk dominates the mass budget in the inner- most regions of the protostellar envelope, generating a flat density profile where less material is exposed to high temperatures. Thus, complex organic molecules would be associated with lower column densities. Finally, Oph-IRS67 is a promising candidate for the detection of both circumstellar disks with higher-angular-resolution observations.Comment: 19 pages, 14 figures, 6 table

Physical and chemical fingerprint of protostellar disc formation

(Abridged) The purpose of this paper is to explore and compare the physical and chemical structure of Class I low-mass protostellar sources on protoplanetary disc scales. We present a study of the dust and gas emission towards a representative sample of 12 Class I protostars from the Ophiuchus molecular cloud with the Atacama Large Millimeter/submillimeter Array (ALMA). The continuum at 0.87 mm and molecular transitions from C17O, C34S, H13CO+, CH3OH, SO2 , and C2H were observed at high angular resolution (0.4", ~60 au diameter) towards each source. Disc and stellar masses are estimated from the continuum flux and position-velocity diagrams, and six of the sources show disc-like structures. Towards the more luminous sources, compact emission and large line widths are seen for transitions of SO2 that probe warm gas (Eu ~200 K). In contrast, C17O emission is detected towards the least evolved and less luminous systems. No emission of CH3OH is detected towards any of the continuum peaks, indicating an absence of warm CH3OH gas towards these sources. A power-law relation is seen between the stellar mass and the bolometric luminosity, corresponding to a mass accretion rate of (2.4 +/- 0.6) x 10^-7 Msun/year for the Class I sources. This mass accretion rate is lower than the expected value if the accretion is constant in time and rather points to a scenario of accretion occurring in bursts. The differentiation between C17O and SO2 suggests that they trace different physical components: C17O traces the densest and colder regions of the disc-envelope system, while SO2 may be associated with regions of higher temperature, such as accretion shocks. The lack of warm CH3OH emission suggests that there is no hot-core-like region around any of the sources and that the CH3OH column density averaged over the disc is low.Comment: 20 pages, 16 figures, 8 table

The LOFT (Large Observatory for X-ray Timing) background simulations

The Large Observatory For X-ray Timing (LOFT) is an innovative medium-class mission selected for an assessment phase in the framework of the ESA M3 Cosmic Vision call. LOFT is intended to answer fundamental questions about the behaviour of matter in the very strong gravitational and magnetic fields around compact objects. With an effective area of ~10 m^2 LOFT will be able to measure very fast variability in the X-ray fluxes and spectra. A good knowledge of the in-orbit background environment is essential to assess the scientific performance of the mission and to optimize the instrument design. The two main contributions to the background are cosmic diffuse X-rays and high energy cosmic rays; also, albedo emission from the Earth is significant. These contributions to the background for both the Large Area Detector and the Wide Field Monitor are discussed, on the basis of extensive Geant-4 simulations of a simplified instrumental mass model.Comment: Proceedings of SPIE, Vol. 8443, Paper No. 8443-209, 201

Superconductivity-enhanced bias spectroscopy in carbon nanotube quantum dots

We study low-temperature transport through carbon nanotube quantum dots in the Coulomb blockade regime coupled to niobium-based superconducting leads. We observe pronounced conductance peaks at finite source-drain bias, which we ascribe to elastic and inelastic cotunneling processes enhanced by the coherence peaks in the density of states of the superconducting leads. The inelastic cotunneling lines display a marked dependence on the applied gate voltage which we relate to different tunneling-renormalizations of the two subbands in the nanotube. Finally, we discuss the origin of an especially pronounced sub-gap structure observed in every fourth Coulomb diamond