Suchergebnisse

The study of minor planets is motivated both by fundamental science of Solar system origins (some of these bodies contain the most pristine materials from the early ages of the planetary nebula) and by practical reasons concerning space exploration and impact frequency with Earth. Among minor bodies, near-Earth asteroids are a particularly important group: these objects are nearby the Earth's orbit and they represent both resources and hazards to humans. This is the case of 2014 JO 25. The encounter of this potentially hazardous asteroid with the Earth at 0.011 75 au on 2017 April 19 was a good opportunity to study its properties through photometric and spectral analyses. The work we present here has been carried out thanks to a worldwide observational campaign that included time-series photometry and spectroscopy in the visible and near-infrared wavelengths. The optical images for photometric analysis were collected at different phase angles using small telescopes (<0.5 m) and medium telescopes (from 0.6 to 1.5 m). Spectral analysis was performed by 2-4 m telescopes. The light curve of 2014 JO 25 indicates a synodic rotational period of 4.5286 ± 0.0004 h. Although rotational period had been previously obtained by other authors, this work confirms it with a better accuracy. The obtained reflectance spectrum of this asteroid indicates that it belongs to the S-complex and its surface is most likely composed of a mixture of pyroxenes and olivine. From the comparison of its spectrum to those of meteorite samples, as well as from the wavelength position of the first absorption band (close to 0.9 μm), we suggest that this asteroid might contain a large fraction of low-calcium pyroxene and, tentatively, some amounts of metal.© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. ; J. Licandro (JL), M. Serra-Ricart (MSR), O. Vaduvescu (OV), M. Popescu (MP), and J. de Leon (JdL) acknowledge support from the AYA2015-67772-R project (MINECO, Spain). JdL also acknowledges support from from MINECO under the 2015 Severo Ochoa Program SEV-2015-0548. The Isaac Newton Telescope and its service mode are operated on the island of La Palma by the Isaac Newton Group of Telescopes in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. The work of MP was also been supported by a grant of the Romanian National Authority for Scientific Research - UEFISCDI, project number PN-II-RU-TE-2014-4-2199. The research leading to these results has received funding from the European Union's Horizon 2020 Research and Innovation Programme, under Grant Agreement No. 687378. We thank E. Molinari for allocation of Director's Discretionary Time at the Telescopio Nazionale Galileo. The work by P. Pravec was supported by the Grant Agency of the Czech Republic, Grant 17-00774S. Observations at CS3 and continued support of the asteroid light-curve data base (LCDB; Warner et al. 2009) are supported by NASA grant 80NSSC18K0851. This paper is partially based on data taken at the 0.77 m La Hita telescope, which is jointly operated by the Instituto de Astrofisica de Andalucia-CSIC and Astrohita. Blue Mountains Observatory is supported by the 2015 Shoemaker NEO grant. ; Peer Reviewed

We present the results of a large multiwavelength follow-up campaign of the tidal disruption event (TDE) AT 2019dsg, focusing on low to high resolution optical spectroscopy, X-ray, and radio observations. The galaxy hosts a super massive black hole of mass (5.4±3.2)×106M⊙ and careful analysis finds no evidence for the presence of an active galactic nucleus, instead the TDE host galaxy shows narrow optical emission lines that likely arise from star formation activity. The transient is luminous in the X-rays, radio, UV, and optical. The X-ray emission becomes undetected after ∼100 d, and the radio luminosity density starts to decay at frequencies above 5.4 GHz by ∼160 d. Optical emission line signatures of the TDE are present up to ∼200 d after the light-curve peak. The medium to high resolution spectra show traces of absorption lines that we propose originate in the self-gravitating debris streams. At late times, after ∼200 d, narrow Fe lines appear in the spectra. The TDE was previously classified as N-strong, but after careful subtraction of the host galaxy's stellar contribution, we find no evidence for these N lines in the TDE spectrum, even though O Bowen lines are detected. The observed properties of the X-ray emission are fully consistent with the detection of the inner regions of a cooling accretion disc. The optical and radio properties are consistent with this central engine seen at a low inclination (i.e. seen from the poles). © 2021 The Author(s). ; GC and PGJ acknowledge support from European Research Council (ERC) Consolidator Grant 647208. TW is funded by ERC grant 320360 and by European Commission grant 730980. This research was made possible through the use of the AAVSO Photometric All-Sky Survey (APASS), funded by the Robert Martin Ayers Sciences Fund and NSFAST-1412587. We acknowledge the use of public data from the Swift data archive. We thank P. M. Vreeswijk for the data reduction of the UVES spectrum. This paper includes data obtained with the William Herschel Telescope (proposal IDs: W19B/P7, W19A/N3) as well as observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Isaac Newton Group of Telescopes and the Fundación Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programmes 1103.D-0328 "advanced Public ESO Spectroscopic Survey for Transient Objects" (ePESSTO+). GL was supported by a research grant (19054) from VILLUM FONDEN. D.M.-S. acknowledges support from the ERC under the European Union's Horizon 2020 research and innovation programme (grant agreement no. 715051; Spiders). JM acknowledges financial support from the State Agency for Research of the Spanish MICIU through the "Center of Excellence Severo Ochoa" award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709) and from the grant RTI2018-096228-B-C31 (MICIU/FEDER, EU). IA is a CIFAR Azrieli Global Scholar in the Gravity and the Extreme Universe Program and acknowledges support from that program, from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement number 852097), from the Israel Science Foundation (grant numbers 2108/18 and 2752/19), from the United States – Israel Binational Science Foundation (BSF), and from the Israeli Council for Higher Education Alon Fellowship. TWC acknowledges the EU Funding under Marie Skłodowska-Curie grant H2020-MSCA-IF-2018-842471. TMB was funded by the CONICYT PFCHA / DOCTORADOBECAS CHILE/2017-72180113. MN is supported by a Royal Astronomical Society Research Fellowship. FO acknowledges the support of the GRAWITA/PRIN-MIUR project: The new frontier of the Multi-Messenger Astrophysics: follow-up of electromagnetic transient counterparts of gravitational wave sources. ; Peer reviewed

Context. One-opposition near-Earth asteroids (NEAs) are growing in number, and they must be recovered to prevent loss and mismatch risk, and to improve their orbits, as they are likely to be too faint for detection in shallow surveys at future apparitions. Aims. We aimed to recover more than half of the one-opposition NEAs recommended for observations by the Minor Planet Center (MPC) using the Isaac Newton Telescope (INT) in soft-override mode and some fractions of available D-nights. During about 130 h in total between 2013 and 2016, we targeted 368 NEAs, among which 56 potentially hazardous asteroids (PHAs), observing 437 INT Wide Field Camera (WFC) fields and recovering 280 NEAs (76% of all targets). Methods. Engaging a core team of about ten students and amateurs, we used the THELI, Astrometrica, and the FindOrb software to identify all moving objects using the blink and track-And-stack method for the faintest targets and plotting the positional uncertainty ellipse from NEODyS. Results. Most targets and recovered objects had apparent magnitudes centered around V ~ 22.8 mag, with some becoming as faint as V ~ 24 mag. One hundred and three objects (representing 28% of all targets) were recovered by EURONEAR alone by Aug. 2017. Orbital arcs were prolonged typically from a few weeks to a few years; our oldest recoveries reach 16 years. The O-C residuals for our 1854 NEA astrometric positions show that most measurements cluster closely around the origin. In addition to the recovered NEAs, 22 000 positions of about 3500 known minor planets and another 10 000 observations of about 1500 unknown objects (mostly main-belt objects) were promptly reported to the MPC by our team. Four new NEAs were discovered serendipitously in the analyzed fields and were promptly secured with the INT and other telescopes, while two more NEAs were lost due to extremely fast motion and lack of rapid follow-up time. They increase the counting to nine NEAs discovered by the EURONEAR in 2014 and 2015. Conclusions. Targeted projects to recover one-opposition NEAs are efficient in override access, especially using at least two-meter class and preferably larger field telescopes located in good sites, which appear even more efficient than the existing surveys.© ESO, 2018. ; I.O. acknowledges support from the European Research Council (ERC) in the form of Advanced Grant, cosmicism. R.T. acknowledges funding for her La Palma trip to Armagh Observatory, which is core-funded by the Northern Ireland Government. The research led by BTG, CJM, and NPGF has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013) / ERC Grant Agreement No. 320964 (WDTracer). ; Peer Reviewed