Molecular Signatures in the Near Infrared Dayside Spectrum of HD 189733b

We have measured the dayside spectrum of HD 189733b between 1.5 and 2.5 microns using the NICMOS instrument on the Hubble Space Telescope. The emergent spectrum contains significant modulation, which we attribute to the presence of molecular bands seen in absorption. We find that water (H2O), carbon monoxide (CO), and carbon dioxide (CO2) are needed to explain the observations, and we are able to estimate the mixing ratios for these molecules. We also find temperature decreases with altitude in the ~0.01 < P < ~1 bar region of the dayside near-infrared photosphere and set an upper limit to the dayside abundance of methane (CH4) at these pressures.Comment: 13 pages, 3 figures. accepted in Astrophysical Journal Letter

X-ray Variability from the Compact Source in the Supernova Remnant RCW 103

A new ASCA observation of 1E 161348-5055, the central compact X-ray source in the supernova remnant RCW 103, reveals an order-of-magnitude decrease in its 3 - 10 keV flux since the previous ASCA measurement four years earlier. This result is hard to reconcile with suggestions that the bulk of the emission is simple quasi-blackbody, cooling radiation from an isolated neutron star. Furthermore, archived EINSTEIN and ROSAT datasets spanning 18 years confirm that this source manifests long-term variability, to a lesser degree. This provides a natural explanation for difficulties encountered in reproducing the original EINSTEIN detection of 1E 161348-5055. Spectra from the new data are consistent with no significant spectral change despite the decline in luminosity. We find no evidence for a pulsed component in any of the data sets, with a best upper limit on the pulsed modulation of 13 percent. We discuss the phenomenology of this remarkable source.Comment: 5 pages with 2 embedded figures, LaTex, emulateapj.sty. To appear in the Astrophysical Journal Letter

Astrometry with the VLTI: calibration of the Fringe Sensor Unit for the PRIMA astrometric camera

The future PRIMA facility at the Very Large Telescope Interferometer (VLTI) in astrometric mode offers the possibility to perform relative narrow-angle astrometry with 10 micro-arcsecond accuracy. This is achieved with a dual-beam interferometer concept, where a reference star and the scientific target, confined in a 60 arcsecond field, are observed simultaneously. The angular separation of the two stellar objects gives rise to an optical delay in the interferometer, which is measured by the Fringe Sensor Unit (FSU) and an internal laser metrology. PRIMA is using two FSU fringe detectors, each observing the interference of stellar beams coming from one of the two objects and measuring the corresponding phase and group delay. The astrometric observable, yielding the angular separation, is deduced from the group delay difference observed between the two objects. In addition, the FSU phase delay estimate is used as error signal for the fringe stabilisation loop of the VLTI. Both functions of the FSU require high precision fringe phase measurements with a goal of 1 nm rms (corresponding to λ/2000). These can only be achieved by applying a calibration procedure prior to the observing run. We discuss the FSU measurement principle and the applied algorithms. The calibration strategy and the methods used to derive the calibration parameters are presented. Special attention is given to the achieved measurement linearity and repeatability. The quality of the FSU calibration is crucial in order to achieve the ultimate accuracy and to fulfill the primary objective of PRIMA astrometry: the detection and characterisation of extrasolar planetary system

Discovery of a 7 Second Anomalous X-ray Pulsar in the Distant Milky Way

We report the serendipitous discovery of a 7-s X-ray pulsar using data acquired with the Advanced Satellite for Cosmology and Astrophysics. The pulsar is detected as an unresolved source located towards a region of the Galactic plane (l,b ~ 29.5, 0.08) that coincides with an overdensity of star-formation tracers. The signal suffers tremendous foreground absorption, equivalent to N_H ~ 10E23 cm^-2; the absorption correlates well with a line-of-sight that is tangential to the inner spiral arms and the 4-kpc molecular ring. The pulsar is not associated with any known supernova remnants or other cataloged objects in that direction. The near sinusoidal pulse (period P ~ 6.9712) is modulated at 35% pulsed amplitude, and the steep spectrum is characteristic of hot black-body emission with temperature kT ~ 0.65 keV. We characterize the source as an anomalous X-ray pulsar (AXP).Comment: 8 pages, latex, 4 figures, Accepted for publication in New Astronom

Neutron Star Crust in Strong Magnetic Fields

We discuss the effects of strong magnetic fields through Landau quantization of electrons on the structure and stability of nuclei in neutron star crust. In strong magnetic fields, this leads to the enhancement of the electron number density with respect to the zero field case. We obtain the sequence of equilibrium nuclei of the outer crust in the presence of strong magnetic fields adopting most recent versions of the experimental and theoretical nuclear mass tables. For $B\sim 10^{16}$G, it is found that some new nuclei appear in the sequence and some nuclei disappear from the sequence compared with the zero field case. Further we investigate the stability of nuclei in the inner crust in the presence of strong magnetic fields using the Thomas-Fermi model. The coexistence of two phases of nuclear matter - liquid and gas, is considered in this case. The proton number density is significantly enhanced in strong magnetic fields $B\sim 10^{17}$G through the charge neutrality. We find nuclei with larger mass number in the presence of strong magnetic fields than those of the zero field. These results might have important implications for the transport properties of the crust in magnetars.Comment: 6 pages including 3 figures; based on the talk presented at INPC2010, Vancouver; Submitted to the Proceedings of the conference in J. Phys. Conf. Se