Publications (22)85.03 Total impact
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Article: A new population of ultra-long duration gamma-ray bursts
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ABSTRACT: We present comprehensive multiwavelength observations of three gamma-ray bursts (GRBs) with durations of several thousand seconds. We demonstrate that these events are extragalactic transients; in particular we resolve the long-standing conundrum of the distance of GRB 101225A (the "Christmas-day burst"), finding it to have a redshift z=0.847, and showing that two apparently similar events (GRB 111209A and GRB 121027A) lie at z=0.677 and z=1.773 respectively. The systems show extremely unusual X-ray and optical lightcurves, very different from classical GRBs, with long lasting highly variable X-ray emission and optical light curves that exhibit little correlation with the behaviour seen in the X-ray. Their host galaxies are faint, compact, and highly star forming dwarf galaxies, typical of "blue compact galaxies". We propose that these bursts are the prototypes of a hitherto largely unrecognized population of ultra-long GRBs, that while observationally difficult to detect may be astrophysically relatively common. The long durations may naturally be explained by the engine driven explosions of stars of much larger radii than normally considered for GRB progenitors which are thought to have compact Wolf-Rayet progenitor stars. However, we cannot unambiguously identify supernova signatures within their light curves or spectra. We also consider the alternative possibility that they arise from the tidal disruption of stars by supermassive black holes.02/2013; -
Article: Mining the ESO WFI and INT WFC archives for known Near Earth Asteroids. Mega-Precovery software
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ABSTRACT: The ESO/MPG WFI and the INT WFC wide field archives comprising 330,000 images were mined to search for serendipitous encounters of known Near Earth Asteroids (NEAs) and Potentially Hazardous Asteroids (PHAs). A total of 152 asteroids (44 PHAs and 108 other NEAs) were identified using the PRECOVERY software, their astrometry being measured on 761 images and sent to the Minor Planet Centre. Both recoveries and precoveries were reported, including prolonged orbital arcs for 18 precovered objects and 10 recoveries. We analyze all new opposition data by comparing the orbits fitted before and after including our contributions. We conclude the paper presenting Mega-Precovery, a new online service focused on data mining of many instrument archives simultaneously for one or a few given asteroids. A total of 28 instrument archives have been made available for mining using this tool, adding together about 2.5 million images forming the Mega-Archive.01/2013; -
Article: Fundamentals of the Dwarf Fundamental Plane
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ABSTRACT: Star-forming dwarfs are studied to elucidate the physical underpinnings of their fundamental plane. It is confirmed that residuals in the Tully-Fisher relation are correlated with surface brightness, but that even after accommodating the surface brightness dependence through the dwarf fundamental plane, residuals in absolute magnitude are far larger than expected from observational errors. Rather, a more fundamental plane is identified which connects the potential to HI line width and surface brightness. Residuals correlate with the axis ratio in a way which can be accommodated by recognizing the galaxies to be oblate spheroids viewed at varying angles. Correction of surface brightnesses to face-on leads to a correlation among the potential, line width, and surface brightness for which residuals are entirely attributable to observational uncertainties. The mean mass-to-light ratio of the diffuse component of the galaxies is constrained to be 0.88 +/- 0.20 in Ks. Blue compact dwarfs lie in the same plane as dwarf irregulars. The dependence of the potential on line width is less strong than expected for virialized systems, but this may be because surface brightness is acting as a proxy for variations in the mass-to-light ratio from galaxy to galaxy. Altogether, the observations suggest that gas motions are predominantly disordered and isotropic, that they are a consequence of gravity, not turbulence, and that the mass and scale of dark matter haloes scale with the amount and distribution of luminous matter. The tight relationship between the potential and observables offers the promise of determining distances to unresolved star-forming dwarfs to an accuracy comparable to that provided by the Tully-Fisher relation for spirals.åp. 04/2012; 540. -
Article: Binary asteroid population. 2. Anisotropic distribution of orbit poles of small, inner main-belt binaries
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ABSTRACT: Our photometric observations of 18 main-belt binary systems in more than one apparition revealed a strikingly high number of 15 having positively re-observed mutual events in the return apparitions. Our simulations of the survey showed that it cannot be due to an observational selection effect and that the data strongly suggest that poles of mutual orbits between components of binary asteroids in the pri-mary size range 3–8 km are not distributed randomly: The null hypothesis of an isotropic distribution of the orbit poles is rejected at a confidence level greater than 99.99%. Binary orbit poles concentrate at high ecliptic latitudes, within 30° of the poles of the ecliptic. We propose that the binary orbit poles oriented preferentially up/down-right are due to either of the two processes: (i) the YORP tilt of spin axes of their 0019-1035/$ -see front matter ÓIcarus 01/2012; 218:125-143. · 3.38 Impact Factor -
Conference Proceeding: Activity in main-belt asteroid P/2010 A2
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ABSTRACT: The dust tail of Main-Belt Asteroid P/2010 A2 (LINEAR) has been observed with several telescopes at the at the Observatorio del Roque de los Muchachos on La Palma, Spain. Application of an inverse dust tail Monte Carlo method to the images of the dust ejecta from the object implies a sustained activity over some eight months. The onset of the activity occurred in late March 2009, with a peak dust mass loss rate of about 5 kg/s in early June 2009, decreasing afterwards to 0.1 kg/s near perihelion in early December 2009. The total amount of dust released is estimated to be 5x10^7 kg, which represents about 0.3% of the nucleus mass. The nucleus diameter is D=220 +/- 40 m, assuming a bulk albedo of p=0.11, typical of a S-type asteroid. The event could have been triggered by a collision, but this cannot be decided from this dataset alone.Highlights of Spanish Astrophysics VI; 11/2011 -
Article: Searching for star-forming galaxies in the Fornax and Hydra clusters
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ABSTRACT: The formation and evolution of dwarf galaxies is relatively difficult to understand because of their faint emission in all regimes that require large aperture telescopes. We intend to study the evolution of star forming dwarf galaxies in clusters. We selected Fornax and Hydra clusters to complement our previous study of Virgo. On the basis of available literature data, we selected ten star-forming candidates in Fornax and another ten objects in Hydra. We used Gemini South with GMOS to acquire H-alpha images necessary to detect star-forming regions in the two galaxy samples. We then performed long-slit spectroscopy for the brightest six candidates, to derive their chemical properties. Finally, we employed the VLT with HAWK-I to observe all galaxies in the K' band to derive their main physical properties. We studied the morphology of our two samples, finding five objects in Fornax and six in Hydra with structures consistent with those of star-forming dwarfs, i.e., dwarf irregulars (dIs) or blue compact dwarfs (BCDs). About four other objects are probably dwarf spirals, while three objects remained undetected in both visible and near infrared. On the basis of visible bright emission lines, we derived oxygen abundances for ten star-forming candidates with values between 8.00 and 8.78. Most fundamental properties of star-forming galaxies in Fornax and Hydra appear similar to corresponding properties of dIs and BCDs from Virgo and the Local Volume (LV). The luminosity-metallicity and metallicity-gas fraction relations in the LV and Virgo appear to be followed by Fornax and Hydra samples, suggesting that the chemical evolution of the two clusters seems consistent with the predictions from the closed box model, although larger samples are needed to investigate the role of possible environmental effects. (CONTINUED)08/2011; -
Article: EURONEAR - Recovery, Follow-up and Discovery of NEAs and MBAs using Large Field 1-2m Telescopes
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ABSTRACT: We report on the follow-up and recovery of 100 program NEAs, PHAs and VIs using the ESO/MPG 2.2m, Swope 1m and INT 2.5m telescopes equipped with large field cameras. The 127 fields observed during 11 nights covered 29 square degrees. Using these data, we present the incidental survey work which includes 558 known MBAs and 628 unknown moving objects mostly consistent with MBAs from which 58 objects became official discoveries. We planned the runs using six criteria and four servers which focus mostly on faint and poorly observed objects in need of confirmation, follow-up and recovery. We followed 62 faint NEAs within one month after discovery and we recovered 10 faint NEAs having big uncertainties at their second or later opposition. Using the INT we eliminated 4 PHA candidates and VIs. We observed in total 1,286 moving objects and we reported more than 10,000 positions. All data were reduced by the members of our network in a team effort, and reported promptly to the MPC. The positions of the program NEAs were published in 27 MPC and MPEC references and used to improve their orbits. The O-C residuals for known MBAs and program NEAs are smallest for the ESO/MPG and Swope and about four times larger for the INT whose field is more distorted. The incidental survey allowed us to study statistics of the MBA and NEA populations observable today with 1--2m facilities. We calculate preliminary orbits for all unknown objects, classifying them as official discoveries, later identifications and unknown outstanding objects. The orbital elements a, e, i calculated by FIND_ORB software for the official discoveries and later identified objects are very similar with the published elements which take into account longer observational arcs; thus preliminary orbits were used in statistics for the whole unknown dataset. (CONTINUED)08/2011; -
Article: (596) Scheila in Outburst: A Probable Collision Event in the Main Asteroid Belt
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ABSTRACT: Images of asteroid (596) Scheila have been acquired at various dates after the discovery of the 2010 outburst. Assuming a short-duration event scenario, as suggested by the quick vanishing of the dust tail brightness with time, and numerically integrating the equation of motion of individual particles ejected from the surface, we have developed a tail model from which we estimate the parameters associated with the geometry of the ejection, the size distribution, and the velocity distribution of the ejected particles, as well as the total mass ejected. We found a weak inverse power-law dependence of ejection velocity versus particle radius, with velocities ranging from 50 to 80 m s–1 for particle radii in the range from 5 cm to 8 × 10–5 cm, respectively. These velocities are very different from those expected from ice sublimation at the asteroid heliocentric distance (~3 AU) and suggest a collision scenario as a likely cause of the outburst. We found that the ejected particles are distributed in size following a power law of index -3, and, based on the ejecta mass and scaling laws, the impactor size is estimated at 30-90 m in radius, assuming an impact velocity of ~5 km s–1, and the same density (1500 kg m–3) for the asteroid as for the projectile. We have inferred an asymmetry in the ejecta along the axis normal to the asteroid orbit plane, a likely indicator of an oblique impact. The impact is estimated to have occurred on November 27, with an accuracy not better than ±3 days.The Astrophysical Journal 08/2011; 738(2):130. · 6.02 Impact Factor -
Article: Mining the CFHT Legacy Survey for known Near Earth Asteroids
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ABSTRACT: The Canada-France-Hawaii Legacy Survey (CFHTLS) comprising about 25 000 MegaCam images was data mined to search for serendipitous encounters of known Near Earth Asteroids (NEAs) and Potentially Hazardous Asteroids (PHAs). A total of 143 asteroids (109 NEAs and 34 PHAs) were found on 508 candidate images which were field corrected and measured carefully, and their astrometry was reported to Minor Planet Centre. Both recoveries and precoveries (apparitions before discovery) were reported, including data for 27 precovered asteroids (20 NEAs and 7 PHAs) and 116 recovered asteroids (89 NEAs and 27 PHAs). Our data prolonged arcs for 41 orbits at first or last opposition, refined 35 orbits by fitting data taken at one new opposition, recovered 6 NEAs at their second opposition and allowed us to ameliorate most orbits and their Minimal Orbital Intersection Distance (MOID), an important parameter to monitor for potential Earth impact hazard in the future.07/2011; -
Article: An extremely luminous panchromatic outburst from the nucleus of a distant galaxy.
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ABSTRACT: Variable x-ray and γ-ray emission is characteristic of the most extreme physical processes in the universe. We present multiwavelength observations of a unique γ-ray-selected transient detected by the Swift satellite, accompanied by bright emission across the electromagnetic spectrum, and whose properties are unlike any previously observed source. We pinpoint the event to the center of a small, star-forming galaxy at redshift z = 0.3534. Its high-energy emission has lasted much longer than any γ-ray burst, whereas its peak luminosity was ∼100 times higher than bright active galactic nuclei. The association of the outburst with the center of its host galaxy suggests that this phenomenon has its origin in a rare mechanism involving the massive black hole in the nucleus of that galaxy.Science 06/2011; 333(6039):199-202. · 31.20 Impact Factor -
Article: A tale of two GRB-SNe at a common redshift of z = 0.54
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ABSTRACT: We present ground-based and HST optical observations of the optical transients (OTs) of long-duration Gamma Ray Bursts (GRBs) 060729 and 090618, both at a redshift of z = 0.54. For GRB 060729, bumps are seen in the optical light curves (LCs), and the late-time broadband spectral energy distributions (SEDs) of the OT resemble those of local type Ic supernovae (SNe). For GRB 090618, the dense sampling of our optical observations has allowed us to detect well-defined bumps in the optical LCs, as well as a change in colour, that are indicative of light coming from a core-collapse SN. The accompanying SNe for both events are individually compared with SN1998bw, a known GRB-supernova, and SN1994I, a typical type Ic supernova without a known GRB counterpart, and in both cases the brightness and temporal evolution more closely resemble SN1998bw. We also exploit our extensive optical and radio data for GRB 090618, as well as the publicly-available SWIFT -XRT data, and discuss the properties of the afterglow at early times. In the context of a simple jet-like model, the afterglow of GRB 090618 is best explained by the presence of a jet-break at t-to > 0.5 days. We then compare the rest-frame, peak V -band absolute magnitudes of all of the GRB and X-Ray Flash (XRF)-associated SNe with a large sample of local type Ibc SNe, concluding that, when host extinction is considered, the peak magnitudes of the GRB/XRF-SNe cannot be distinguished from the peak magnitudes of non-GRB/XRF SNe.12/2010; -
Article: Formation of asteroid pairs by rotational fission.
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ABSTRACT: Pairs of asteroids sharing similar heliocentric orbits, but not bound together, were found recently. Backward integrations of their orbits indicated that they separated gently with low relative velocities, but did not provide additional insight into their formation mechanism. A previously hypothesized rotational fission process may explain their formation-critical predictions are that the mass ratios are less than about 0.2 and, as the mass ratio approaches this upper limit, the spin period of the larger body becomes long. Here we report photometric observations of a sample of asteroid pairs, revealing that the primaries of pairs with mass ratios much less than 0.2 rotate rapidly, near their critical fission frequency. As the mass ratio approaches 0.2, the primary period grows long. This occurs as the total energy of the system approaches zero, requiring the asteroid pair to extract an increasing fraction of energy from the primary's spin in order to escape. We do not find asteroid pairs with mass ratios larger than 0.2. Rotationally fissioned systems beyond this limit have insufficient energy to disrupt. We conclude that asteroid pairs are formed by the rotational fission of a parent asteroid into a proto-binary system, which subsequently disrupts under its own internal system dynamics soon after formation.Nature 08/2010; 466(7310):1085-8. · 36.28 Impact Factor -
Article: Spectroscopic Observations of New Oort Cloud Comet 2006 VZ13 and Four Other Comets
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ABSTRACT: Spectral data are presented for comets 2006 VZ13 (LINEAR), 2006 K4 (NEAT), 2006 OF2 (Broughton), 2P/Encke, and 93P/Lovas I, obtained with the Cerro-Tololo Inter-American Observatory 1.5-m telescope in August 2007. Comet 2006 VZ13 is a new Oort cloud comet and shows strong lines of CN (3880 angstroms), the Swan band sequence for C_2 (4740, 5160, and 5630 angstroms), C_3 (4056 angstroms), and other faint species. Lines are also identified in the spectra of the other comets. Flux measurements of the CN, C_2 (Delta v = +1,0), and C_3 lines are recorded for each comet and production rates and ratios are derived. When considering the comets as a group, there is a correlation of C_2 and C_3 production with CN, but there is no conclusive evidence that the production rate ratios depend on heliocentric distance. The continuum is also measured, and the dust production and dust-to-gas ratios are calculated. There is a general trend, for the group of comets, between the dust-to-gas ratio and heliocentric distance, but it does not depend on dynamical age or class. Comet 2006 VZ13 is determined to be in the carbon-depleted (or Tempel 1 type) class. Comment: 8 pages, 6 figures, 6 tables; Accepted by MNRASMonthly Notices of the Royal Astronomical Society 10/2009; · 4.90 Impact Factor -
Article: EURONEAR - Data Mining of Asteroids and Near Earth Asteroids
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ABSTRACT: Besides new observations, mining old photographic plates and CCD image archives represents an opportunity to recover and secure newly discovered asteroids, also to improve the orbits of Near Earth Asteroids (NEAs), Potentially Hazardous Asteroids (PHAs) and Virtual Impactors (VIs). These are the main research aims of the EURONEAR network. As stated by the IAU, the vast collection of image archives stored worldwide is still insufficiently explored, and could be mined for known NEAs and other asteroids appearing occasionally in their fields. This data mining could be eased using a server to search and classify findings based on the asteroid class and the discovery date as "precoveries" or "recoveries". We built PRECOVERY, a public facility which uses the Virtual Observatory SkyBoT webservice of IMCCE to search for all known Solar System objects in a given observation. To datamine an entire archive, PRECOVERY requires the observing log in a standard format and outputs a database listing the sorted encounters of NEAs, PHAs, numbered and un-numbered asteroids classified as precoveries or recoveries based on the daily updated IAUMPC database. As a first application, we considered an archive including about 13,000 photographic plates exposed between 1930 and 2005 at the Astronomical Observatory in Bucharest, Romania. PRECOVERY can be applied to other archives, being intended as a public facility offered to the community by the EURONEAR project. This is the first of a series of papers aimed to improve orbits of PHAs and NEAs using precovered data derived from archives of images to be data mined in collaboration with students and amateurs. In the next paper we will search the CFHT Legacy Survey, while data mining of other archives is planned for the near future. Comment: Accepted in Astronomische Nachrichten (Feb 2009)06/2009; -
Article: Photometric and astrometric analysis of a mutual event between the Uranian satellites Miranda and Oberon
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ABSTRACT: Observations of the predicted occultation between the satellites Miranda and Oberon were performed on 2007 July 30. Data analysis reveals that the predicted magnitude drop for this phenomenon was overestimated and we establish an upper limit of 0m. 05 for the phenomenon, perhaps due to a non-lambertian limb scattering. The new astrometry obtained from this run is in good agreement with the LA06 numerical model and these new data will improve the dynamical models of the Uranus system. The paper concludes with an uncertainty analysis on the parameters for the event, determined by the uncertainty of the magnitude drop of about 0.04 mag, and the difficulty to observe mutual phenomena between satellites in the Uranian system. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)Astronomische Nachrichten 06/2008; 329(6):567 - 572. · 1.01 Impact Factor -
Article: Photometric and astrometric analysis of a mutual event between the Uranian satellites Miranda and Oberon
01/2008; 329:567-572. -
Article: Chemical Properties of Star Forming Dwarf Galaxies
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ABSTRACT: Recent studies of the near-infrared (NIR) properties of dwarf irregular galaxies (dIs) and blue compact dwarfs (BCDs) have provided improved estimates for the NIR luminosity of old stellar populations in these galaxies. These can be used to derive gas fractions, and thereby to evaluate how BCDs have evolved with respect to dIs. Oxygen abundances have been derived for four BCDs in the Virgo Cluster from a run at Gemini-North in 2003. Combining these new abundances with published values, we study the correlations among the metallicity, Ks luminosity, gas mass, baryonic mass, and gas fraction. Within errors, the two types of dwarfs appear to share a common relation between the oxygen abundance and the luminosity in Ks. The correlation between metallicity and the gas fraction is the same for BCDs as for dIs, indicating that BCD evolution has been similar to dIs. Since dIs appear to have evolved as isolated systems, the BCD bursts are unlikely to be a consequence of gas infall or merging. Comment: Accepted in AJ (Aug 2007)04/2007; -
Article: Infrared Properties of Star Forming Dwarf Galaxies: Blue Compact Dwarfs in the Virgo Cluster
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ABSTRACT: A sample of 16 blue compact dwarf galaxies (BCDs) in the Virgo Cluster has been imaged in the near-infrared (NIR) in $J$ and $K_s$ on the 2.1m telescope at OAN-SPM in Mexico. Isophotes as faint as $\mu_J$ = 24 mag arcsec$^{-2}$ and $\mu_{K_s}$ = 23 mag arcsec$^{-2}$ have been reached in most of the targets. Surface brightness profiles can be fitted across the whole range of radii by the sum of two components: a hyperbolic secant (sech) function, which is known to fit the light profiles of dIs, and a Gaussian component, which quantifies the starburst near the centre. Isophotal and total fitted NIR magnitudes have been calculated, along with semimajor axes at $\mu_J$ = 23 mag arcsec$^{-2}$ and $\mu_{K_s}$ = 22 mag arcsec$^{-2}$. The diffuse underlying component and the young starburst have been quantified using the profile fitting. Most color profiles show a constant color, between $J-K_s$=0.7 to 0.9 mag. The diffuse component represents the overwhelming majority of the NIR light for most BCDs, the starburst enhancing the flux by less than about 0.3 mag. Linear correlations were found between the sech scale length and the sech magnitude, and between the sech semimajor axis and the sech magnitude. Overall, galaxies with more luminous diffuse components are larger and brighter in the centre. The central burst correlates with the diffuse component, with brighter BCDs having stronger star-bursts, suggesting that more massive objects are forming stars more efficiently. BCDs lie on the ``fundamental plane'' defined by dwarf irregulars (dISs) in Paper I, following the same relation between sech absolute magnitude, sech central surface brightness, and the hydrogen line-width $W_{20}$, although the scatter is larger than for the dIs. [one sentence cut]11/2005; -
Article: More than 160 Near Earth Asteroids observed in the EURONEAR network
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ABSTRACT: Astrometry is mandatory in order to acquire the positional information necessary to define and improve orbits of NEAs and PHAs and to study their trajectories through the solar system, especially in the vicinity of Earth. Photometry is required to derive some physical information about NEAs and PHAs. In order to achieve these objectives, the main method of research of the EURONEAR is the follow-up programme of objects selected by a few criteria, carried out mostly at 1m-class telescopes endowed with medium and large field cameras. 162 NEAs summing more than 1,500 individual positions were observed for a total time of 55 nights in both visiting mode and regular runs using nine telescopes located in four countries. The observations were reduced promptly and reported to the Minor Planet Centre (MPC) which validated and included them in the MPC and NEODyS databases following the improvement of their orbital elements. For one binary NEA we acquired photometry and were able to determine its orbital and rotational periods. Complementary to the follow-up work, as many as 500 unknown moving objects consistent with new Main Belt asteroids and one possible NEA were discovered in the analyzed fields. Our positions present 1′′ precision with an accuracy of 0.2-0.4′′ , sufficient for achieving our immediate main goals. The observations and data reduction were conducted by our network members, which included some students and amateurs supervised by professional astronomers. In most cases, we increased the observational arcs decreasing the uncertainties in the orbits, while in some cases the new positions allowed us to recover some bodies endangered to be lost, defining their orbits. -
Article: The fundamental plane of dwarf irregular galaxies
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ABSTRACT: Aims. Near-IR photometry of dwarf irregular galaxies (dIs) has been acquired to expand the sample of objects suitable for investigating the fundamental plane (FP) discovered previously by us. Data for blue compact dwarfs (BCDs), dwarf ellipticals (dEs), and dwarf spheroidal galaxies (dSphs) are amalgamated to evaluate how closely these classes of galaxies are related to dIs. Methods. Surface brightness profiles for dIs are modeled using a hyperbolic secant function (sech), which has been shown to sample the old galaxy component observed in the NIR ($K_{\rm s}$). Also, profiles for BCDs are modeled using a sech function, but to this is added a Gaussian burst. Kinematics for dIs and BCDs are constrained by the width $W_{20}$ of integrated HI line profiles, and motions within dEs and dSphs are judged from stellar velocity dispersions. Results. The existence of a FP for dIs is confirmed. Omitting extreme deviants, the scatter of dIs about the plane is 0.43 mag, somewhat higher than expected from observational errors alone. Corrections of line widths for tilt do not reduce the residuals, so motions must be predominantly random. Corrections of surface brightnesses for tilt have no effect either. BCDs and dEs lie precisely on the FP defined by dIs, suggesting strong underlying connections among dIs, BCDs, and dEs.http://dx.doi.org/10.1051/0004-6361:200809706.
Top co-authors
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Institutions
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2011
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Instituto de Astrofísica de Canarias
La Laguna, Canary Islands, Spain
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2009–2011
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Universidad Católica del Norte (Chile)
- Instituto de Astronomía
Antofagasta, Region de Antofagasta, Chile -
Isaac Newton Group of Telescopes
La Palma del Condado, Andalusia, Spain
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