The long-term evolution of the X-ray pulsar XTE J1814-338: a receding jet contribution to the quiescent optical emission?

We present a study of the quiescent optical counterpart of the Accreting Millisecond X-ray Pulsar XTE J1814-338, carrying out multiband (BVR) orbital phase-resolved photometry using the ESO VLT/FORS2. The optical light curves are consistent with a sinusoidal variability modulated with the orbital period, showing evidence for a strongly irradiated companion star, in agreement with previous findings. The observed colours cannot be accounted for by the companion star alone, suggesting the presence of an accretion disc during quiescence. The system is fainter in all analysed bands compared to previous observations. The R band light curve displays a possible phase offset with respect to the B and V band. Through a combined fit of the multi-band light curves we derive constraints on the companion star and disc fluxes, on the system distance and on the companion star mass. The irradiation luminosity required to account for the observed day-side temperature of the companion star is consistent with the spin-down luminosity of a millisecond radio pulsar. The flux decrease and spectral evolution of the quiescent optical emission observed comparing our data with previous observations, collected over 5 years, cannot be well explained with the contribution of an irradiated companion star and an accretion disc alone. The progressive flux decrease as the system gets bluer could be due to a continuum component evolving towards a lower, bluer spectrum. While most of the continuum component is likely due to the disc, we do not expect it to become bluer in quiescence. Hence we hypothesize that an additional component, such as synchrotron emission from a jet was contributing significantly in the earlier data obtained during quiescence and then progressively fading or moving its break frequency toward longer wavelengths.Comment: 7 pages, 8 figures, accepted for publication in Section 7. Stellar structure and evolution of Astronomy and Astrophysic

Substructure around M31 : Evolution and Effects

We investigate the evolution of a population of 100 dark matter satellites orbiting in the gravitational potential of a realistic model of M31. We find that after 10 Gyr, seven subhalos are completely disrupted by the tidal field of the host galaxy. The remaining satellites suffer heavy mass loss and overall, 75% of the mass initially in the subhalo system is tidally stripped. Not surprisingly, satellites with pericentric radius less than 30 kpc suffer the greatest stripping and leave a complex structure of tails and streams of debris around the host galaxy. Assuming that the most bound particles in each subhalo are kinematic tracers of stars, we find that the halo stellar population resulting from the tidal debris follows an r^{-3.5} density profile at large radii. We construct B-band photometric maps of stars coming from disrupted satellites and find conspicuous features similar both in morphology and brightness to the observed Giant Stream around Andromeda. An assumed star formation efficiency of 5-10% in the simulated satellite galaxies results in good agreement with the number of M31 satellites, the V-band surface brightness distribution, and the brightness of the Giant Stream. During the first 5 Gyr, the bombardment of the satellites heats and thickens the disk by a small amount. At about 5 Gyr, satellite interations induce the formation of a strong bar which, in turn, leads to a significant increase in the velocity dispersion of the disk.Comment: 45 pages, 18 figures. To be submitted to the Astrophysical Journal, version 2.0 : scale height value corrected, references added, and some figures have been modifie

The Biodiversity of Macroalgae in the Coastal Waters of Kora-Kora, East Lembean Sub-District, Minahasa Regency

Penelitian ini dilakukan di perairan pesisir Kora-Kora, Kecamatan Lembean Timur, Kabupaten Minahasa dengan tujuan untuk mengetahui komposisi taksa makroalga melalui pendekatan morfologi. Pengambilan data dilakukan dengan menggunakan metode survei jelajah. Hasil penelitian menemukan 10 spesies, yang terdiri dari 1 spesies alga merah (Rhodophyta), 6 spesies alga cokelat (Phaeophyta)) dan 3 spesies alga hijau (Chlorophyta)

Observations of Doppler Boosting in Kepler Lightcurves

Among the initial results from Kepler were two striking lightcurves, for KOI 74 and KOI 81, in which the relative depths of the primary and secondary eclipses showed that the more compact, less luminous object was hotter than its stellar host. That result became particularly intriguing because a substellar mass had been derived for the secondary in KOI 74, which would make the high temperature challenging to explain; in KOI 81, the mass range for the companion was also reported to be consistent with a substellar object. We re-analyze the Kepler data and demonstrate that both companions are likely to be white dwarfs. We also find that the photometric data for KOI 74 show a modulation in brightness as the more luminous star orbits, due to Doppler boosting. The magnitude of the effect is sufficiently large that we can use it to infer a radial velocity amplitude accurate to 1 km/s. As far as we are aware, this is the first time a radial-velocity curve has been measured photometrically. Combining our velocity amplitude with the inclination and primary mass derived from the eclipses and primary spectral type, we infer a secondary mass of 0.22+/-0.03 Msun. We use our estimates to consider the likely evolutionary paths and mass-transfer episodes of these binary systems.Comment: 8 pages, 4 figures, ApJ 715, 51 (v4 is updated to match the published version, including a note added in proof with measured projected rotational velocities)

Bar imprints on the inner gas kinematics of M33

We present measurements of the stellar and gaseous velocities in the central 5' of the Local Group spiral M33. The data were obtained with the ARC 3.5m telescope. Blue and red spectra with resolutions from 2 to 4\AA covering the principal gaseous emission and stellar absorption lines were obtained along the major and minor axes and six other position angles. The observed radial velocities of the ionized gas along the photometric major axis of M33 remain flat at ~22 km s^{-1} all the way into the center, while the stellar velocities show a gradual rise from zero to 22 km s^{-1} over that same region. The central star cluster is at or very close to the dynamical center, with a velocity that is in accordance with M33's systemic velocity to within our uncertainties. Velocities on the minor axis are non-zero out to about 1' from the center in both the stars and gas. Together with the major axis velocities, they point at significant deviations from circular rotation. The most likely explanation for the bulk of the velocity patterns are streaming motions along a weak inner bar with a PA close to that of the minor axis, as suggested by previously published IR photometric images. The presence of bar imprints in M33 implies that all major Local Group galaxies are barred. The non-circular motions over the inner 200 pc make it difficult to constrain the shape of M33's inner dark matter halo profile. If the non-circular motions we find in this nearby Sc galaxy are present in other more distant late-type galaxies, they might be difficult to recognize.Comment: 20 pages, 12 figures, ApJ in pres

Discovery of the Optical Counterparts to Four Energetic Fermi Millisecond Pulsars

In the last few years, over 43 millisecond radio pulsars have been discovered by targeted searches of unidentified gamma-ray sources found by the Fermi Gamma-Ray Space Telescope. A large fraction of these millisecond pulsars are in compact binaries with low-mass companions. These systems often show eclipses of the pulsar signal and are commonly known as black widows and redbacks because the pulsar is gradually destroying its companion. In this paper, we report on the optical discovery of four strongly irradiated millisecond pulsar companions. All four sources show modulations of their color and luminosity at the known orbital periods from radio timing. Light curve modelling of our exploratory data shows that the equilibrium temperature reached on the companion's dayside with respect to their nightside is consistent with about 10-30% of the available spin-down energy from the pulsar being reprocessed to increase the companion's dayside temperature. This value compares well with the range observed in other irradiated pulsar binaries and offers insights about the energetics of the pulsar wind and the production of gamma-ray emission. In addition, this provides a simple way of estimating the brightness of irradiated pulsar companions given the pulsar spin-down luminosity. Our analysis also suggests that two of the four new irradiated pulsar companions are only partially filling their Roche lobe. Some of these sources are relatively bright and represent good targets for spectroscopic follow-up. These measurements could enable, among other things, mass determination of the neutron stars in these systems.Comment: 11 pages, 5 tables, 1 figure, 4 online tables. ApJ submitted and referee

Steady- and transient-state operation of a two-stage bioreactor for the treatment of a gaseous mixture of hydrogen sulphide, methanol and α-pinene

A two-stage bioreactor, comprising a biotrickling filter (BTF) as the first stage and a biofilter (BF) as the second stage, operated under steady- and transient-state conditions, was tested to remove gas-phase hydrogen sulphide, methanol and α-pinene. RESULTS: Hydrogen sulphide and methanol were removed in the first stage, while α-pinene, was removed predominantly in the second-stage fungal BF. The effect of the liquid trickling rate was evaluated in the BTF, while concentration-dependent synergistic and antagonistic interactions in both reactors were assessed by varying the concentration of one pollutant, and by maintaining 100% removal of other pollutants. Increasing the liquid trickling rate decreased methanol removal significantly, from > 93% to 40%. Increasing the concentration of hydrogen sulphide from low to high loading rates did not affect the removal of volatile organic compounds (VOCs), however, the reverse occurred. Under all the conditions tested, α-pinene removal in the second-stage biofilter still remained higher than 80%. CONCLUSIONS: The results show the maximum elimination capacities achievable for this complex ternary mixture, under a wide range of operating conditions

Performance of a fungal monolith bioreactor for the removal of styrene from polluted air

Gas-phase styrene removal using the fungus, Sporothrix variecibatus was evaluated in a novel monolith bioreactor, receiving a continuous supply of nutrients from the trickling liquid phase. During the start-up process, the monolith reactor was operated for 22 days with relatively low styrene concentrations in the gas-phase (<0.4 g m−3). Afterwards, continuous experiments were carried out at different inlet styrene concentrations, ranging between 0.06 and 2.5 g m−3, and at two different flow rates corresponding to empty bed residence times (EBRTs) of 77 and 19 s, respectively. A maximum elimination capacity of 67.4 g m−3 h−1 was observed at an inlet styrene load of 73.5 g m−3 h−1. However, it was observed that the critical loading rates to the monolith bioreactor were a strong function of the gas residence time. The critical load, with greater than 95% styrene removal was 74 g m−3 h−1 at an EBRT of 77 s, while it was only 37.2 g m−3 h−1 for an EBRT of 19 s. After 92 days of continuous operation, due to excess biomass growth on the surface of the monolith, the biodegradation efficiency decreased significantly. To ascertain the instantaneous response of the attached fungus, to withstand fluctuations in loading conditions, two dynamic shock loads were conducted, at EBRTs of 77 and 19 s, respectively. It was observed that, the performance of the monolith bioreactor decreased significantly at low residence times, when subjected to high shock loads. The recovery times for high performance, in both cases, did not exceed more than 1 h