F. J. Aceituno

Short-term variability of a sample of 29 trans-Neptunian objects and Centaurs

Aims. We attempt to increase the number of trans-Neptunian objects (TNOs) whose short-term variability has been studied and compile a high quality database with the least possible biases, which may be used to perform statistical analyses. Methods. We performed broadband CCD photometric observations using several telescopes (the 1.5 m telescope at Sierra Nevada Observatory, the 2.2 m Calar Alto telescope and the 2.5 m INT on La Palma). Results. We present the results of 6 years of observations, reduced and analyzed with the same tools in a systematic way. We report completely new data on 15 objects, for 5 objects we present a new analysis of previously published results plus additional data and for 9 objects we present a new analysis of data already published. Lightcurves, possible rotation periods, and photometric amplitudes are reported for all of them. The photometric variability is smaller than previously thought: the mean amplitude of our sample is 0.1 mag and only around 15% of our sample has a larger variability than 0.15 mag. The smaller variability seems to be caused by a bias of previous observations. We find a very weak trend of faster spinning objects towards smaller sizes, which appears to be consistent with the smaller objects being more collisionally evolved, but may also be a specific feature of the Centaurs, the smallest objects in our sample. We also find that the smaller the objects, the larger their amplitude, which is also consistent with the idea that small objects are more collisionally evolved and thus more deformed. Average rotation rates from our work are 7.5 h for the whole sample, 7.6 h for the TNOs alone and 7.3 h for the Centaurs. Maxwellian fits to the period distribution yield similar results.

Optical detection of meteoroidal impacts on the Moon

Impacts of meteoroids on the Moon should cause detectable optical flashes, but the population of objects that are big enough is very low, and hitherto no unambiguous impact flashes have been recorded. The flux of meteoroids associated with the Leonid meteor shower of 18 November 1999 was predicted to produce observable flashes on the night side of the Moon. Here we report the unambiguous detection of five such impact flashes, three of which were seen simultaneously by other observers. We also observed a possible impact flash on 16 July 1999. All of the flashes were of very brief duration (<0.02 s), as expected for high-speed impacts.

The dark nature of GRB 051022 and its host galaxy

Aims. We present multiwavelength (X-ray/optical/near-infrared/millimetre) observations of GRB 051022 between 2.5 h and ∼1.15 yr after the event. It is the most intense gamma-ray burst (∼10 −4 erg cm −2 ) detected by HETE-2, with the exception of the nearby GRB 030329. Methods. Optical and near infrared observations did not detect the afterglow despite a strong afterglow at X-ray wavelengths. Millimetre observations at Plateau de Bure (PdB) detected a source and a flare, confirming the association of this event with a moderately bright (R = 21.5) galaxy. Results. Spectroscopic observations of this galaxy show strong [O II], Hβ and [O III] emission lines at a redshift of 0.809. The spectral energy distribution (SED) of the galaxy implies AV (rest frame) = 1.0 and a starburst occuring ∼25 Myr ago, during which the star-forming-rate reached ∼50 M� /yr. In conjunction with the spatial extent (∼1 �� ) it suggests a very luminous (MV = −21.8) blue compact galaxy, for which we also find Z ∼ Z� . The X-ray spectrum shows evidence of considerable absorption by neutral gas with NH,X−ray = 3.47 +0.48 −0.47 × 10 22 cm −2 (rest frame). Absorption by dust in the host galaxy at z = 0.809 certainly cannot account for the non-detection of the optical afterglow, unless the dust-to-gas ratio is quite different than that seen in our Galaxy (i.e. large dust grains). Conclusions. It is likely that the afterglow of the dark GRB 051022 was extinguished along the line of sight by an obscured, dense star forming region in a molecular cloud within the parent host galaxy. This galaxy is different from most GRB hosts being brighter than L ∗ by a factor of 3. We have also derived a SFR ∼ 50 M� /yr and predict that this host galaxy will be detected at sub-mm wavelengths.

GRB 060121: Implications of a Short-/Intermediate-Duration γ-Ray Burst at High Redshift

Since the discovery of the first short-population γ-ray burst (GRB) afterglows in 2005, the handful of observed events have been found to be embedded in nearby (z 102). A photometric redshift for this event places the progenitor at a most probable redshift of z = 4.6, with a less probable scenario of z = 1.7. In either case, GRB 060121 could be the farthermost short-population GRB detected to date and implies an isotropic-equivalent energy release in gamma rays comparable to that seen in long-population bursts. We discuss the implications of the released energy on the nature of the progenitor. These results suggest that GRB 060121 may belong to a family of energetic short-population events, lying at z > 1 and whose optical afterglows would outshine their host galaxies, unlike the first short GRBs observed in 2005. The possibility of GRB 060121 being an intermediate-duration burst is also discussed.

Multiwavelength observations of the energetic GRB 080810: detailed mapping of the broad-band spectral evolution

GRB 080810 was one of the first bursts to trigger both Swift and the Fermi Gamma-ray Space Telescope. It was subsequently monitored over the X-ray and UV/optical bands by Swift, in the optical by Robotic Optical Transient Search Experiment (ROTSE) and a host of other telescopes, and was detected in the radio by the Very Large Array. The redshift of z = 3.355 ± 0.005 was determined by Keck/High Resolution Echelle Spectrometer (HIRES) and confirmed by RTT150 and NOT. The prompt gamma/X-ray emission, detected over 0.3–10 3 keV, systematically softens over time, with Epeak moving from ∼600 keV at the start to ∼40 keV around 100 s after the trigger; alternatively, this spectral evolution could be identified with the blackbody temperature of a quasi-thermal model shifting from ∼60 to ∼3 keV over the same time interval. The first optical detection was made at 38 s, but the smooth, featureless profile of the full optical coverage implies that this is originated from the afterglow component, not from the pulsed/flaring prompt emission.

The γ Doradus CoRoT target HD 49434: I. Results from the ground-based campaign

Context. We present an extensive ground-based photometric and spectroscopic campaign of the γ Dor CoRoT target HD 49434. This campaign was a preparatory step of the CoRoT satellite observations, which occurred between October 2007 and March 2008. Aims. With satellite data, detection of low-degree pulsation modes only is achievable, and, as no filters are available, with poor identification. Ground-based data promise eventually to identify additional modes and provide extra input for the identification: spectroscopic data allows the detection of high-degree modes and an estimate of the azimuthal number m. We attempt to detect and identify as many pulsation modes as possible from the ground-based dataset of the γ Dor star HD 49434, and anticipate the CoRoT results. Methods. We searched for frequencies in the multi-colour variations, the pixel-to-pixel variations across the line profiles, and the moments variations in a large dataset, consisting of both multi-colour photometric and spectroscopic data from different observatories, using different frequency analysis methods. We performed a tentative mode identification of the spectroscopic frequencies using the Moment Method and the Intensity Period Search Method. We also completed an abundance analysis. Results. The frequency analysis clearly indicates the presence of four frequencies in the 0.2−1.7 d −1 interval, as well as six frequencies in the 5−12 d −1 domain. The low frequencies are typical of γ Dor variables, while the high frequencies are common to δ Sct pulsators. We propose that the frequency 2.666 d −1 is the rotational frequency. All modes, for which an identification was possible, appear to be high-degree modes (3 ≤ � ≤ 8). We did not find evidence for a possible binary nature of the star HD 49434. The element abundances that we derived are consistent with values obtained in previous analyses. Conclusions. We classify the γ Dor star HD 49434 as a hybrid pulsator, which pulsates simultaneously in p -a ndg-modes. This implies that HD 49434 is an extremely interesting target for asteroseismic modelling.

Observation and Interpretation of Leonid Impact Flashes on the Moon in 2001

We present observations of lunar Leonid impact flashes recorded in 2001 November from Spain. Four impact flashes were detected on November 18. Another flash was also recorded on the same night, which appears to be impact related, and two more on that night are possibly, but not unambiguously, of impact nature. On November 19 another flash was detected, which very likely resulted from an impact. The brightest impact flash reached a peak brightness of 5.2 ± 0.3 mag in V; it had a very dim precursor just 0.02 s prior to peak brightness and had a very long lasting afterglow that remained visible for more than 600 ms with oscillations in brightness; this unique and unexpected behavior challenges current models of impact flashes. The other flashes did not show such a behavior and remained visible for a few tens of milliseconds. Adopting the luminous efficiency derived for the 1999 lunar Leonids (2 × 10-3), our observations can be used to estimate meteoroid fluxes. The observations are compatible with a flux of 0.1 meteoroids of mass larger than 2 × 10-8 kg km-2 hr-1 on November 18 at 18:15 UT, provided that a mass index of 1.69 is used. Both the flux and the mass index agree with meteor observations carried out in 2001 from several locations on Earth.

Flares from a candidate Galactic magnetar suggest a missing link to dim isolated neutron stars

Magnetars are young neutron stars with very strong magnetic fields of the order of 1014–1015 G. They are detected in our Galaxy either as soft γ-ray repeaters or anomalous X-ray pulsars. Soft γ-ray repeaters are a rare type of γ-ray transient sources that are occasionally detected as bursters in the high-energy sky. No optical counterpart to the γ-ray flares or the quiescent source has yet been identified. Here we report multi-wavelength observations of a puzzling source, SWIFT J195509+261406. We detected more than 40 flaring episodes in the optical band over a time span of three days, and a faint infrared flare 11 days later, after which the source returned to quiescence. Our radio observations confirm a Galactic nature and establish a lower distance limit of ∼3.7 kpc. We suggest that SWIFT J195509+261406 could be an isolated magnetar whose bursting activity has been detected at optical wavelengths, and for which the long-term X-ray emission is short-lived. In this case, a new manifestation of magnetar activity has been recorded and we can consider SWIFT J195509+261406 to be a link between the ‘persistent’ soft γ-ray repeaters/anomalous X-ray pulsars and dim isolated neutron stars.A. J. Castro-Tirado, A. de Ugarte Postigo, J. Gorosabel, M. Jeĺınek, T. A. Fatkhullin, V. V. Sokolov, P. Ferrero, D. A. Kann, S. Klose, D. Sluse, M. Bremer, J. M. Winters, D. Nuernberger, D. Pérez-Ramı́rez, M. A. Guerrero, J. French, G. Melady, L. Hanlon, B. McBreen, F. J. Aceituno, R. Cunniffe, P. Kubánek, S. Vitek, S. Schulze, A. C. Wilson, R. Hudec, J. M. González-Pérez, T. Shahbaz, S. Guziy, S. B. Pandey L. Pavlenko, E. Sonbas, S. A. Trushkin, N. N. Bursov, N. A. Nizhelskij and L. Sabau-Graziati

The planetary system host HR 8799: on its λ Bootis nature

HR8799 is a λ Bootis, γ Doradus star hosting a planetary system and a debris disk with two rings. This makes this system a very interesting target for asteroseismic studies. This work is devoted to the determination of the internal metallicity of this star, linked with its λ Bootis nature (i.e., solar surface abundances of light elements, and subsolar surface abundances of heavy elements), taking advantage of its γ Doradus pulsations. This is the most accurate way to obtain this information, and this is the first time such a study is performed for a planetary-system-host star. We have used the equilibrium code CESAM and the non-adiabatic pulsational code GraCo. We have applied the Frequency Ratio Method (FRM) and the Time Dependent Convec

PlanetCam UPV/EHU: a two-channel lucky imaging camera for solar system studies in the spectral range 0.38-1.7 µm

This is an author-created, un-copyedited version of an article published in Publications of the Astronomical Society of the Pacific. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it.