On the accuracy of the S/N estimates obtained with the exposure time calculator of the Wide Field Planetary Camera 2 on board the Hubble Space Telescope

We have studied the accuracy and reliability of the exposure time calculator (ETC) of the Wide Field Planetary Camera 2 (WFPC2) on board the Hubble Space Telescope (HST) with the objective of determining how well it represents actual observations and, therefore, how much confidence can be invested in it and in similar software tools. We have found, for example, that the ETC gives, in certain circumstances, very optimistic values for the signal-to-noise ratio (SNR) of point sources. These values overestimate by up to a factor of 2 the HST performance when simulations are needed to plan deep imaging observations, thus bearing serious implications on observing time allocation. For this particular case, we calculate the corrective factors to compute the appropriate SNR and detection limits and we show how these corrections vary with field crowding and sky background. We also compare the ETC of the WFPC2 with a more general ETC tool, which takes into account the real effects of pixel size and charge diffusion. Our analysis indicates that similar problems may afflict other ETCs in general showing the limits to which they are bound and the caution with which their results must be taken.Comment: 14 pages, 13 figures, to be published in PASP on July 200

REVISIONE PRELIMINARE DELLA BIODIVERSITÀ ENTOMOLOGICA DELL’ISOLA DI LAMPEDUSA (SICILIA - ITALIA) PRELIMINARY REVISION OF ENTOMOLOGICAL BIODIVERSITY IN THE LAMPEDUSA ISLAND (SICILY, ITALY)

Lampedusa è un'isola appartenente all'arcipelago delle Pelagie, che è particolarmente interessante per l'aspetto faunistico, in quanto crocevia tra la fauna Europea e Africana. Gli insetti, per la loro abbondanza e diversità in natura, rappresentano una classe nel regno animale particolarmente utile per studiare la biodiversità e i fenomeni di migrazione o emigrazione delle specie, e per valutare inoltre eventuali cambiamenti climatici. Allo stato attuale i dati sull'entomofauna non sono organici e sono riportati in modo spesso frammentario, e la check-list più completa disponibile è datata 1995, quasi venti anni fa. Lo scopo di questo lavoro è stato quello di impiegare nuove tecniche di ricerca, sia bibliografiche che sitografiche, impiegando differenti fonti quali: database e giornali scientifici di rilevanza internazionale, riviste internazionali e locali, banche dati nazionali ed europee, ma anche forum, Facebook ed altre risorse spesso utili per nuove segnalazioni. In questo caso i dati sono stati opportunamente controllati sia contattando direttamente la fonte sia richiedendo altro materiale di supporto. Rispetto alla check-list precedente si sono rilevate circa 71 specie precedentemente non segnalate. Oltre a ciò, si sono potuti analizzare circa 5000 individui catturati con campionamenti bimensili da aprile a maggio 2010, con l'ausilio di trappole Malaise collocate in due differenti e caratteristici habitat di Lampedusa. Si sono registrati in totale 9 ordini di esapodi, di cui 2 ordini (Thysanoptera e Psocoptera) e una sottoclasse (Collembola: Sottoclasse Symphypleona) mai segnalati in precedenza. Dai risultati del presente lavoro si evince l‟elevata biodiversità dell‟isola, nonostante le sue relativamente piccole dimensioni.Lampedusa is an island belonging to the Pelagian archipelago and particularly interesting for the fauna, because a crossroads between the Sothern Europea and Africa. Insects for their abundance and diversity in nature, represent a class in the animal kingdom particularly useful for studying biodiversity, migration or emigration of species, and assess potential climate change. At present the data on insects's biodiversity in Lampedusa are not organic and often fragmentary, and the only complete check-list-list is dated 1995. The purpose of this work was to employ new techniques of research using both traditional bibliographical sources (international, national and local journals) and all available in the Internet from scientifica data base to forum and Facebook. Forums and other resources were often useful for new reports that were always validate before considering in the new checklist. Compared with to the previous checklist we reported 71 new species. In addition, were studied approximately 5000 individuals. The sampling was carried out with Malaise traps bi- monthly rom April to July 2010. We recorded nine orders of hexapods: Orthoptera, Psocoptera, Thysanoptera, Hemiptera, Coleoptera, Lepidoptera, Diptera e Hymenoptera, e Collembola. The results of this first experimental analysis have revealed the presence of some taxa not previously reported as Thysanoptera, Psocoptera and Collembola (subclass Symphypleona). The results highlight the high biodiversity of the Lampedusa despite its small size

A long-lasting quiescence phase of the eruptive variable V1118 Ori

V1118 Ori is an eruptive variable belonging to the EXor class of Pre-Main Sequence stars whose episodic outbursts are attributed to disk accretion events. Since 2006, V1118 Ori is in the longest quiescence stage ever observed between two subsequent outbursts of its recent history. We present near-infrared photometry of V1118 Ori carried out during the last eight years, along with a complete spectroscopic coverage from 0.35 to 2.5 um. A longterm sampling of V1118 Ori in quiescence has never been done, hence we can benefit from the current circumstance to determine the lowest values (i.e. the zeroes) of the parameters to be used as a reference for evaluating the physical changes typical of more active phases. A quiescence mass accretion rate between 1--3 $\times$ 10$^{-9}$ M_{\sun} yr$^{-1}$ can be derived and the difference with previous determinations is discussed. From line emission and IR colors analysis a visual extinction of 1-2 mag is consistently derived, confirming that V1118 Ori (at least in quiescence) is a low-extinction T Tauri star with a bolometric luminosity of about 2.1 L_{\sun}. An anti-correlation exists between the equivalent width of the emission lines and the underlying continuum. We searched the literature for evaluating whether or not such a behaviour is a common feature of the whole class. The anti-correlation is clearly recognizable for all the available EXors in the optical range (H$\beta$ and H$\alpha$ lines), while it is not as much evident in the infrared (Pa$\beta$ and Br$\gamma$ lines). The observed anti-correlation supports the accretion-driven mechanism as the most likely to account for continuum variations.Comment: 6 figures, 5 tables, accepted on Ap

Recent outburst of the young star V1180 Cas

We report on the ongoing outburst of the young variable V1180 Cas, which is known to display characteristics in common with EXor eruptive variables. We present results that support the scenario of an accretion-driven nature of the brightness variations of the object and provide the first evidence of jet structures around the source. We monitored the recent flux variations of the target in the Rc, J, H, and K bands. New optical and near-IR spectra taken during the current high state of V1180 Cas are presented, in conjunction with H2 narrow-band imaging of the source. Observed near-IR colour variations are analogous to those observed in EXors and consistent with excess emission originating from an accretion event. The spectra show numerous emission lines, which indicates accretion, ejection of matter, and an active disc. Using optical and near-IR emission features we derive a mass accretion rate of ~3 E-8 Msun/yr, which is an order of magnitude lower than previous estimates. In addition, a mass loss rate of ~4 E-9 and ~4 E-10 Msun/yr are estimated from atomic forbidden lines and H2, respectively. Our H2 imaging reveals two bright knots of emission around the source and the nearby optically invisible star V1180 Cas B, clearly indicative of mass-loss phenomena. Higher resolution observations of the detected jet will help to clarify whether V1180 Cas is the driving source and to determine the relation between the observed knots.Comment: Accepted as Letter in A&A; 4 pages, 3 figure

GOHSS: current status and technical aspects

Abstract. We describe the current status and technical aspects of the GOHSS (Galileo OH Subtracted Spectrograph) project. In particular, we stress the most critical points and we address the innovative technical solutions implemented to fulfill the compelling requirements imposed by both the optical tolerances and the demand of a high sensitivity. The commissioning phase at the telescope is expected to begin at the end of year 2002

Supervised machine learning on Galactic filaments. Revealing the filamentary structure of the Galactic interstellar medium

Context. Filaments are ubiquitous in the Galaxy, and they host star formation. Detecting them in a reliable way is therefore key towards our understanding of the star formation process. Aims: We explore whether supervised machine learning can identify filamentary structures on the whole Galactic plane. Methods: We used two versions of UNet-based networks for image segmentation. We used H2 column density images of the Galactic plane obtained with Herschel Hi-GAL data as input data. We trained the UNet-based networks with skeletons (spine plus branches) of filaments that were extracted from these images, together with background and missing data masks that we produced. We tested eight training scenarios to determine the best scenario for our astrophysical purpose of classifying pixels as filaments. Results: The training of the UNets allows us to create a new image of the Galactic plane by segmentation in which pixels belonging to filamentary structures are identified. With this new method, we classify more pixels (more by a factor of 2 to 7, depending on the classification threshold used) as belonging to filaments than the spine plus branches structures we used as input. New structures are revealed, which are mainly low-contrast filaments that were not detected before. We use standard metrics to evaluate the performances of the different training scenarios. This allows us to demonstrate the robustness of the method and to determine an optimal threshold value that maximizes the recovery of the input labelled pixel classification. Conclusions: This proof-of-concept study shows that supervised machine learning can reveal filamentary structures that are present throughout the Galactic plane. The detection of these structures, including low-density and low-contrast structures that have never been seen before, offers important perspectives for the study of these filaments

Optical and infrared observations of the supernova SN 1999el

Optical and near-infrared light curves of the Type IIn supernova 1999el in NGC 6951 are presented. A period of 220 days (416 days in the near-infrared) is covered from the first observation obtained a few days before maximum light. Spectroscopic observations are also discussed. Using as a distance calibrator the Type Ia SN 2000E, which occurred some months later in the same galaxy, and fitting a blackbody law to the photometric data we obtain a maximum bolometric luminosity for SN 1999el of $\sim 10^{44}$ erg s$^{-1}$. In general, the photometric properties of SN 1999el are very similar to those of SN 1998S, a bright and well studied Type IIn SN, showing a fast decline in all observed bands similar to those of Type II-L SNe. The differences with SN 1998S are analyzed and ascribed to the differences in a pre-existing circumstellar envelope in which dust was already present at the moment of the SN outburst. We infer that light echoes may play a possibly significant role in affecting the observed properties of the light curves, although improved theoretical models are needed to account for the data. We conclude that mass loss in the progenitor RG stars is episodic and occurs in an asymmetric way. This implies that collapsing massive stars appear as normal Type II SN if this occurs far from major mass loss episodes, whereas they appear as Type IIn SNe if a large mass loss episode is in progress.Comment: 30 pages, 8 figures, figure 1 available as jpeg file, ApJ in pres