We present the technical specifications and first results of the ESA-funded, lunar monitoring project “NELIOTA” (NEO Lunar Impacts and Optical TrAnsients) at the National Observatory of Athens, which ...aims to determine the size-frequency distribution of small near-Earth objects (NEOs) via detection of impact flashes on the surface of the Moon. For the purposes of this project a twin camera instrument was specially designed and installed at the 1.2 m Kryoneri telescope utilizing the fast-frame capabilities of scientific Complementary Metal-Oxide Semiconductor detectors (sCMOS). The system provides a wide field-of-view (17.0′ × 14.4′) and simultaneous observations in two photometric bands (R and I), reaching limiting magnitudes of 18.7 mag in 10 s in both bands at a 2.5 signal-to-noise ratio (S/N) level. This makes it a unique instrument that can be used for the detection of NEO impacts on the Moon, as well as for any astronomy projects that demand high-cadence multicolor observations. The wide field-of-view ensures that a large portion of the Moon is observed, while the simultaneous, high-cadence, monitoring in two photometric bands makes possible the determination of the temperatures of the impacts on the Moon’s surface and the validation of the impact flashes from a single site. Considering the varying background level on the Moon’s surface we demonstrate that the NELIOTA system can detect NEO impact flashes at a 2.5 S/N level of ∼12.4 mag in the I-band and R-band for observations made at low lunar phases (∼0.1). We report 31 NEO impact flashes detected during the first year of the NELIOTA campaign. The faintest flash was at 11.24 mag in the R-band (about two magnitudes fainter than ever observed before) at lunar phase 0.32. Our observations suggest a detection rate of 1.96 × 10−7 events km−2 h−1.
Context.
This paper contains results from the first 30 months of the NELIOTA project for near-Earth objects and meteoroids impacting the lunar surface. We present our analysis of the statistics ...concerning the efficiency of the campaign and the parameters of the projectiles and those of their impacts.
Aims.
The parameters of the lunar impact flashes are based on simultaneous observations in two wavelength bands. They are used to estimate the distributions of the masses, sizes, and frequency of the impactors. These statistics can have applications in both space engineering and science.
Methods.
The photometric fluxes of the flashes are measured using aperture photometry and their apparent magnitudes are calculated using standard stars. Assuming that the flashes follow a black body law of irradiation, the temperatures can be derived analytically, while the parameters of the projectiles are estimated using fair assumptions on their velocity and luminous efficiency of the impacts.
Results.
There have been 79 lunar impact flashes observed with the 1.2 m Kryoneri telescope in Greece. The masses of the meteoroids range between 0.7 g and 8 kg, and their respective sizes between 1 and 20 cm, depending on their assumed density, impact velocity, and luminous efficiency. We find a strong correlation between the observed magnitudes of the flashes and the masses of the meteoroids. Moreover, an empirical relation between the emitted energies of each band has been derived, allowing for an estimation of the physical parameters of the meteoroids that produce low energy impact flashes.
Conclusions.
The NELIOTA project has so far the highest detection rate and the faintest limiting magnitude for lunar impacts compared to other ongoing programs. Based on the impact frequency distribution on the Moon, we estimate that sporadic meteoroids with typical masses less than 100 g and sizes less than 5 cm enter the mesosphere of the Earth with a rate of ~108 meteoroids h
−1
and also impact Moon with a rate of ~8 meteoroids h
−1
.
We report the first scientific results from the NELIOTA (NEO Lunar Impacts and Optical TrAnsients) project, which has recently begun lunar monitoring observations with the 1.2-m Kryoneri telescope. ...NELIOTA aims to detect faint impact flashes produced by near-Earth meteoroids and asteroids and thereby help constrain the size-frequency distribution of near-Earth objects in the decimeter to meter range. The NELIOTA setup, consisting of two fast-frame cameras observing simultaneously in the R and I bands, enables – for the first time – direct analytical calculation of the flash temperatures. We present the first ten flashes detected, for which we find temperatures in the range ~1600 to 3100 K, in agreement with theoretical values. Two of these flashes were detected on multiple frames in both filters and therefore yield the first measurements of the temperature drop for lunar flashes. In addition, we compute the impactor masses, which range between ~100 g and ~50 kg.
Aims. The presence of small- and large-scale star formation structures in a sample of six spiral Hubble Space Telescope (HST) galaxies is investigated to identify small structures of young stars ...known as OB associations and to tell whether they are formed inside larger scale star forming stellar structures in a hierarchical form. Methods. This process was based on a friend-of-friend (FOF) algorithm applied to the bright, early type stars above a certain color cutoff limit in order to ensure that we include main sequence stars. A size criterion was introduced in order to apply the same algorithm to different types of stellar structures. Depending on their size, the structures were divided into the four categories of associations, aggregates, complexes, and supercomplexes. Results. Star forming structures of the four types mentioned above are found in all six galaxies of our sample. The majority of the associations and aggregates (the smaller structures) found are lying inside larger structures like complexes and supercomplexes, indicating a hierarchical star formation mechanism.
Aims. We study small open star clusters, using Strömgren photometry to investigate a possible dependence between age and metallicity in the Magellanic Clouds (MCs). Our goals are to trace evidence of ...an age metallicity relation (AMR) and correlate it with the mutual interactions of the two MCs and to correlate the AMR with the spatial distribution of the clusters. In the Large Magellanic Cloud (LMC), the majority of the selected clusters are young (up to 1 Gyr), and we search for an AMR at this epoch, which has not been much studied. Methods. We report results for 15 LMC and 8 Small Magellanic Cloud (SMC) clusters, scattered all over the area of these galaxies, to cover a wide spatial distribution and metallicity range. The selected LMC clusters were observed with the 1.54 m Danish Telescope in Chile, using the Danish Faint Object Spectrograph and Camera (DFOSC) with a single 2k × 2k CCD. The SMC clusters were observed with the ESO 3.6 m Telescope, also in Chile, using the ESO Faint Object Spectrograph and Camera (EFOSC). The obtained frames were analysed with the conventional DAOPHOT and IRAF software. We used Strömgren filters in order to achieve reliable metallicities from photometry. Isochrone fitting was used to determine the ages and metallicities. Results. The AMR for the LMC displays a metallicity gradient, with higher metallicities for the younger ages. The AMR for LMC-SMC star clusters shows a possible jump in metallicity and a considerable increase at about 6 × 108 yr. It is possible that this is connected to the latest LMC-SMC interaction. The AMR for the LMC also displays a metallicity gradient with distance from the centre. The metallicities in SMC are lower, as expected for a metal-poor host galaxy.
There are 509 expanding neutral hydrogen shells catalogued in the Small Magellanic Cloud (SMC), all apparently very young, with dynamical ages of a few Myr. To examine their relationship with young ...stellar objects, we cross-correlated the shell catalogue with various catalogues of OB associations, supergiants, Cepheids, Wolf-Rayet stars, supernova remnants and star clusters. The incidence of chance line-ups was estimated via Monte Carlo simulations, and found to be high. However, it is important that there are 1.5 times more shells that are not spatially correlated to an OB association, than shells that are. Moreover, 59 of the 509 shells lie mainly in low stellar density fields and have no young stellar objects associated with them, and therefore no obvious energy source. It is shown that, on the whole, the properties of these ‘empty’ shells are very similar to the properties of the rest of the shells, once selection biases are taken into account. In both cases, the shell radius and expansion velocity distribution functions are consistent with the standard model, according to which shells are created by stellar winds and supernova explosions, as long as all shells were created in a single burst and with a power-law distribution of the input mechanical luminosity. This would indicate a burst of star formation. This interpretation, however, cannot explain why the 59 shells, with no young stellar counterparts, show almost exactly the same behaviour as shells with OB associations within their radius. Gamma-ray bursts could account for some but certainly not for the majority of the ‘empty’ shells. Many ‘empty’ shells, including most of the high-luminosity ones, are located in the north-western outer regions of the SMC, and may be associated with a chimney-like feature that is known to exist in that area. Finally, it is noted that turbulence is a promising mechanism for the formation of the shell-like structures, but direct comparison with the observations was not possible at this stage, due to lack of detailed models.
Aims.The Gaia astrometric survey mission will, as a consequence of its scanning law, obtain low resolution optical (330–1000 nm) spectrophotometry of several million unresolved galaxies brighter than ...$V = 22$. We present the first steps in a project to design and implement a classification system for these data. The goal is both to determine morphological classes and to estimate intrinsic astrophysical parameters via synthetic templates. Here we describe (1) a new library of synthetic galaxy spectra, and (2) first results of classification and parametrization experiments using simulated Gaia spectrophotometry of this library. Methods.We have created a large grid of synthetic galaxy spectra using the PÉGASE.2 code, which is based on galaxy evolution models that take into account metallicity evolution, extinction correction, emission lines (with stellar spectra based on the BaSeL library). Our classification and regression models are Support Vector Machines (SVMs), which are kernel-based nonlinear estimators. Results.We produce a basic library of about 3600 zero redshift galaxy spectra covering the main Hubble types over wavelength range 250 to 1050 nm at a sampling of 1 nm or less. It is computed on a regular grid of four key astrophysical parameters for each type and for intermediate random values of the same parameters. An extended library reproduces this at a series of redshifts. Initial results from the SVM classifiers and parametrizers are promising, indicating that Hubble types can be reliably predicted and several parameters estimated with low bias and variance. Comparing the colours of our synthetic library with Sloan Digital Sky Survey (SDSS) spectra we find good agreement over the full range of Hubble types and parameters.
A Catalogue of carbon stars in the LMC Kontizas, E.; Dapergolas, A.; Morgan, D. H. ...
Astronomy & astrophysics,
04/2001, Letnik:
369, Številka:
3
Journal Article
Recenzirano
Odprti dostop
A catalogue of 7760 carbon stars in the Large Magellenic Cloud is presented. The stars were identified during a systematic survey of objective-prism plates taken with the UK 1.2 m Schmidt Telescope. ...The catalogue is compared with other lists of carbon stars and the distribution of the carbon stars is discussed.
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