Search

Aims. We present the spectra of 36 supernovae (SNe) of various types, obtained by the European Supernova Collaboration. Because of the spectral classification and the phase determination at their discovery the SNe did not warrant further study, and the spectra we present are the only ones available for the respective objects. In this paper we present and discuss this material using a new software for the automated classification of SNe spectra.

Context.Spectropolarimetry has been used to directly measure the asymmetries of Supernovae (SNe), Gamma-Ray Bursts (GRBs) and X-Ray Flashes (XRFs).

Aims.We study the optical spectroscopic properties of Type Ia Supernova (SN Ia) 2004dt, focusing our attention on the early epochs.

Context.The nature of the companion stars in type Ia Supernova (SNe) progenitor systems remains unclear. One possible way to discriminate between different scenarios is the presence (or absence) of circumstellar material, the left overs from the progenitor evolution that may be revealed by their interaction with the SN.

Aims.We present a study of the optical and near-infrared (NIR) properties of the Type Ia Supernova (SN Ia) 2003du.

Context.Twilight studies have proved to be important tools for analyzing the atmospheric structure with interesting consequences on the characterization of astronomical sites. Active discussions of this topic have started again recently in connection with the evaluation of Dome C, Antarctica, as a potential astronomical site and several site-testing experiments, including twilight brightness measurements, are being prepared.

We present an extensive set of optical spectroscopy of the nearby type Ia supernova, SN 2002er, with 24 epochs spanning -11 to +34 days. Its spectral evolution is fairly typical of a type Ia supernova although it suffers high extinction. Nevertheless, there are differences in the spectral evolution when compared to coeval spectra of other normal type Ia supernova with comparable decline-rate parameters. Modelling of the photospheric phase spectra using a homogeneous abundance distribution in the atmosphere provides a fair match to the observations, but only by pushing the adopted distance and risetime close to the observational limits. Future improvements here will require models with a more realistic stratified abundance distribution. From simple modelling of a nebular spectrum obtained at +215 d, we infer a 56Ni mass of 0.69 $M_\odot$, consistent with that derived from the light curve.

We report the first result of a supernova search program designed to measure the evolution of the supernova rate with redshift. To make the comparison with local rates more significant we copied, as much as possible, the same computation recipes as for the measurements of local rates. Moreover, we exploited the multicolor images and the photometric redshift technique to characterize the galaxy sample and accurately estimate the detection efficiency.
Combining our data with the recently published measurements of the SN Ia rate at different redshifts, we derived the first, direct measurement of the core collapse supernova rate at $z = 0.26$as $r_{\rm cc} = 1.45^{+0.55}_{-0.45} \, h^2$SNu [ $h=H_0$/75] . This is a factor of three (±50%) larger than the local estimate. The increase for a look back time of 2.8 Gyr is more rapid than predicted by most of the published models of SN rate evolution. Core-collapse SN rates measure the death rate of massive stars and, because of the short time scale of evolution, can be translated into a measurement of the ongoing SFR. Assuming a Salpeter IMF and the standard scenario for core-collapse progenitors we derived an estimate of the star formation rate at redshift $3.1^{+1.1}_{-1.0} \times 10^{-2}~h^3~{M}_\odot\,{\rm yr}^{-1}\,{\rm Mpc}^{-3 }$which compares very well with a recent estimate based on the measurement of the Hαluminosity density at the same redshift.

In this paper we present and analyze new CCD UBVRIphotometry down to $V\approx21$in the region of the young open cluster Collinder 232, located in the Carina spiral arm, and discuss its relationship to Trumpler 14 and Trumpler 16, the two most prominent young open clusters located in the core of NGC 3372 (the Carina Nebula). First of all we study the extinction pattern in the region. We find that the total to selective absorption ratio RVdiffers from cluster to cluster, being $3.48\pm0.11$, $4.16\pm0.07$and $3.73\pm0.01$for Trumpler 16, Trumpler 14 and Collinder 232, respectively. Then we derive individual reddenings and intrinsic colours and magnitudes using the method devised by Romaniello et al. ([CITE]). Ages, age spreads and distances are then estimated by comparing the Colour Magnitude Diagrams and the Hertzsprung-Russel diagram with post and pre-main sequence tracks and isochrones. We find that Trumpler 14 and Collinder 232 lie at the same distance from the Sun (about 2.5 kpc), whereas Trumpler 16 lies much further out, at about 4 kpc from the Sun. As for the age, we find that Trumpler 16 is older than both Trumpler 14 and Collinder 232. For all the clusters we indicate the existence of a significant age dispersion, whose precise value is hampered by our inability to properly distinguish members from non-members. We finally suggest that Collinder 232 is a physical aggregate and provide estimates of its basic parameters.

In this paper we present a non-interactive algorithm to estimate a representative value for the sky background on CCD images. The method we have devised uses the mode as a robust estimator of the background brightness in sub-windows distributed across the input frame. The presence of contaminating objects is detected through the study of the local intensity distribution function and the perturbed areas are rejected using a statistical criterion which was derived from numerical simulations. The technique has been extensively tested on a large number of images and it is suitable for fully automatic processing of large data volumes. The implementation we discuss here has been optimized for the ESO-FORS1 instrument, but it can be easily generalized to all CCD imagers with a sufficiently large field of view. The algorithm has been successfully used for the UBVRIESO-Paranal night sky brightness survey (Patat [CITE]).

In this paper we present and discuss for the first time a large data set of UBVRInight sky brightness measurements collected at ESO-Paranal from April 2000 to September 2001. A total of about 3900 images obtained on 174 different nights with FORS1 were analysed using an automatic algorithm specifically designed for this purpose. This led to the construction of an unprecedented database that allowed us to study in detail a number of effects such as differential zodiacal light contamination, airmass dependency, daily solar activity and moonlight contribution. Particular care was devoted to the investigation of short time scale variations and micro-auroral events. The typical dark time night sky brightness values found for Paranal are similar to those reported for other astronomical dark sites at a similar solar cycle phase. The zenith-corrected values averaged over the whole period are 22.3, 22.6, 21.6 20.9 and 19.7 mag arcsec-2in $U, B, V, R$and Irespectively. In particular, there is no evidence of light pollution either in the broadband photometry or in the high-airmass spectra we have analysed. Finally, possible applications for the exposure time calculators are discussed.

NGC 3628 is a well-studied starburst/low level AGN galaxy in the Leo Triplet noted for its extensive outgassed plumes of neutral hydrogen. QSOs are shown to be concentrated around NGC 3628 and aligned with the HI plumes. The closest high redshift quasar has $z=2.15$and is at the tip of an X–ray filament emerging along the minor axis HI plume.Location at this point has an accidental probability of ~$ 2\times10^{-4}$. In addition a coincident chain of optical objects coming out along the minor axis ends on this quasar.More recent measures on a pair of strong X–ray sources situated at 3.2 and 5.4 arcmin on either side of NGC 3628 along its minor axis, reveal that they have nearly identical redshifts of $z=0.995$and 0.981. The closer quasar lies directly in the same X–ray filament which extends from the nucleus out 4.1 arcmin to end on the quasar of $z=2.15$.The chain of objects SW along the minor axis of NGC 3628 has been imaged in four colours with the VLT. Images and spectra of individual objects within the filament are reported. It is suggested that material in various physical states and differing intrinsic redshifts is ejected out along the minor axis of this active, disturbed galaxy.

The probable association with GRB 980425immediately put SN 1998bwat the forefront of supernova research. Here, we present revised late-time BVRIlight curves of the supernova, based on template images taken at the VLT. To follow the supernova to the very last observable phases we have used HST/STIS. Deep images taken in June and November 2000 are compared to images taken in August 2001. The identification of the supernova is firmly established. This allows us to measure the light curve to ~1000 days past explosion. The main features are a rapid decline up to more than 500 days after explosion, with no sign of complete positron trapping from the $\element[][56]{Co}$decay. Thereafter, the light curve flattens out significantly. One possible explanation is powering by more long lived radioactive isotopes, if they are abundantly formed in this energetic supernova.

In this paper we present and analyze CCD UBVRIphotometry in the region of the three young open clusters NGC 3114, Collinder 228, and vdB-Hagen 99, located in the Carina spiral feature. NGC 3114 lies in the outskirts of the Carina nebula. We found 7 star members in a severely contaminated field, and obtain a distance of 950 pc and an age less than $3 \times 10^{8}$yrs. Collinder 228 is a younger cluster (8$\times 10^{6}$yrs), located in front of the Carina nebula complex, for which we identify 11 new members and suggest that 30% of the stars are probably binaries. As for vdB-Hagen 99, we add 4 new members, confirming that it is a nearby cluster located at 500 pc from the Sun and projected toward the direction of the Carina spiral arm.

We report on UBVRIphotometry of two $5^{\prime} \times 5^{\prime}$fields in the region of the young open cluster NGC 3324. One of our fields covers the core region, while the other is closer to the tidal radius of the cluster. Our study provides the first CCD photometry of NGC 3324. We find that the cluster is very young and probably contains several pre Main Sequence (MS) stars. 25 members are identified on the basis of their position in the $(U-B)$vs. $(B-V)$diagram. We investigate the relation of the red super-giant HD 92207 with NGC 3324, suggesting that it probably does not belong to the cluster. Our second field is close to Loden 165, a possible cluster of stars that has never been studied so far. We show that this object is a probable open cluster, much older than NGC 3324 and much closer to the Sun.

Aims. The main goal of this study is to probe the ejecta geometry and to get otherwise unobtainable information about the explosion mechanism of type?Ia Supernovae (SNe). Methods. Using VLT-FORS1 we performed optical spectropolarimetric observations of the type?Ia SN?2006X on 7?pre-maximum epochs (day -10 to day -1) and one post-maximum epoch (+39?days).Results. The SN shows strong continuum interstellar polarization reaching about?8% at 4000??, characterized by a wavelength dependency that is substantially different from that of the Milky-Way dust mixture. Several SN features, like Si?II?6355??and the Ca?II?IR triplet, present a marked evolution. The Ca?II near-IR triplet shows a pronounced polarization (~1.4%) already on day -10 in correspondence with a strong high-velocity feature (HVF). The Si?II polarization peaks on day -6 at about?1.1% and decreases to?0.8% on day -1. By day +39 no polarization signal is detected for the Si?II line, while the Ca?II?IR triplet shows a marked re-polarization at the level of?1.2%. As in the case of another strongly polarized?SN (2004dt), no polarization was detected across the O?I?7774??absorption. Conclusions. The fast-expanding SN?2006X lies on the upper edge of the relation between peak polarization and decline rate, and it confirms previous speculations about a correlation between degree of polarization, expansion velocity, and HVF strength. The polarization of Ca?II detected in our last epoch, the most advanced ever obtained for a type?Ia SN, coincides in velocity with the outer boundary of the Ca synthesized during the explosion (15?000?17?000?km?s-1) in delayed-detonation models. This suggests a large scale chemical inhomogeneity as produced by off-center detonations, a rather small amount of mixing, or a combination of both effects. In contrast, the absence of polarization at the inner edge of the Ca-rich layer (8000?10?000?km?s-1) implies a substantial amount of mixing in these deeper regions.

Aims. Supernovae offer the unique possibility to probe diffuse extra-galactic sightlines via observation of the optical transitions of atoms, molecules and the diffuse interstellar bands?(DIBs). Through optical spectroscopy the presence of (complex) molecules in distant galaxies can be established and used to derive local physical conditions of the interstellar medium?(ISM). Methods. High resolution optical (3300?6800??) spectra of?SN2006X?at different phase obtained with?UVES on the?VLT were reduced and analysed. Results. In addition to previously detected atomic (Na?I and Ca?II) and molecular?(CN) transitions we present detections of?DIBs (??6196, 6283), diatomic molecules (CH, CH+) and neutral atoms (Ca?I) in the spectra of SN2006X?taken at different phases (at 2?days before and?14 and 61?days after the brightness maximum). An analysis of the absorption profiles shows no variation between phases in the abundance, nor the central velocities (within?3? error bars) of the (dense) gas tracers (CH, CH+and Ca?I) and the?DIBs. This is consistent with the conclusion in the literature that SN2006X?exploded behind a dense interstellar cloud (inferred from strong atomic sodium and calcium lines and CN?transitions) which caused strong photometric reddening but whose material was not directly affected by the supernova explosion. The?CH and CN?column densities correspond to a reddening of one magnitude following the Galactic correlation derived previously. The ??6196 and 6283?lines detected in the M?100 ISM are under-abundant by factor of?2.5 to?3.5 (assuming a visual extinction of ~2?mag) compared to the average Galactic?ISM relationship. Upper limits for ??6379 and?6613 show that these are at least a factor of seven weaker. Therefore, the Galactic DIB-reddening relation does not seem to hold in M?100, although the lower gas-to-dust ratio may further reduce this discrepancy.

Aims. This work provides the results of the first six years of operation by the systematic night-sky monitoring at ESO-Paranal (Chile).Methods. The UBVRI night-sky brightness was estimated on about 10?000 VLT-FORS1 archival images, obtained on more than 650 separate nights, distributed over 6 years, and covering the descent from maximum to minimum of sunspot cycle n. 23. Additionally, a set of about 1000 low-resolution, optical, night-sky spectra were extracted and analysed.Results. The unprecedented database discussed in this paper has led to detecting a clear seasonal variation of the broad-band night-sky brightness in the VRI passbands, similar to the well-known semi-annual oscillation of the Na?I?D doublet. The spectroscopic data demonstrate that this seasonality is common to all spectral features, with the remarkable exception of the OH rotational-vibrational bands. A clear dependency on the solar activity is detected in all passbands and is particularly pronounced in the U band, where the sky brightness decreased by ~0.6?mag arcsec-2from maximum to minimum of solar cycle n.?23. No correlation is found between solar activity and the intensity of the Na?I?D doublet and the OH bands. A strong correlation between the intensity of N?I 5200???and [OI]6300, 6364???is reported here for the first time. The paper also addresses the determination of the correlation time-scales with solar activity and the possible connection with the flux of charged particles emitted by the Sun.

Aims.To measure the supernova (SN) rates at intermediate redshift we performed a search, the Southern inTermediate Redshift ESO Supernova Search (STRESS). Unlike most of the current high redshift SN searches, this survey was specifically designed to estimate the rate for both type?Ia and core collapse (CC) SNe.Methods.We counted the SNe discovered in a selected galaxy sample measuring SN?rate per unit blue band luminosity. Our analysis is based on a sample of ~43000?galaxies and on 25 spectroscopically confirmed SNe plus 64 selected SN?candidates. Our approach is aimed at obtaining a direct comparison of the high redshift and local rates and at investigating the dependence of the rates on specific galaxy properties, most notably their colour.Results.The type?Ia SN rate, at mean redshift z=0.3, is 0.22+0.10 +0.16-0.08 -0.14?h702?SNu, while the CC SN?rate, at z=0.21, is 0.82+0.31 +0.30-0.24 -0.26?h702?SNu. The quoted errors are the statistical and systematic uncertainties. Conclusions.With respect to the local value, the CC SN rate at z=0.2 is higher by a factor of ~2, whereas the type?Ia SN?rate remains almost constant. This implies that a significant fraction of SN?Ia?progenitors has a lifetime longer than 2-3?Gyr. We also measured the SN?rates in the red and blue galaxies and found that the SN?Ia?rate seems to be constant in galaxies of different colour, whereas the CC?SN?rate seems to peak in blue galaxies, as in the local Universe.?SN rates per unit volume were found to be consistent with other measurements showing a steeper evolution with redshift for CC?SNe than SNe?Ia.?We have exploited the link between SFH and SN rates to predict the evolutionary behaviour of the SN?rates and compare it with the path indicated by observations. We conclude that in order to constrain the mass range of CC SN?progenitors and SN?Ia?progenitor models it is necessary to reduce the uncertainties in the cosmic?SFH. In addition it is important to apply a consistent dust extinction correction both to SF and to CC SN?rate and to measure the SN?Ia?rate in star forming and in passively evolving galaxies over a wide redshift range.

X-shooter is the first 2nd generation instrument of the ESO Very Large Telescope (VLT). It is a very efficient, single-target, intermediate-resolution spectrograph that was installed at the Cassegrain focus of UT2 in 2009. The instrument covers, in a single exposure, the spectral range from 300 to 2500 nm. It is designed to maximize the sensitivity in this spectral range through dichroic splitting in three arms with optimized optics, coatings, dispersive elements and detectors. It operates at intermediate spectral resolution (R~ 4000−17 000, depending on wavelength and slit width) with fixed échelle spectral format (prism cross-dispersers) in the three arms. It includes a 1.8″ × 4″ integral field unit as an alternative to the 11′′ long slits. A dedicated data reduction package delivers fully calibrated two-dimensional and extracted spectra over the full wavelength range. We describe the main characteristics of the instrument and present its performance as measured during commissioning, science verification and the first months of science operations.

Context.Supernova 1987A (SN 1987A) exploded in the Large Magellanic Cloud (LMC). Its proximity and rapid evolution makes it a unique case study of the early phases in the development of a supernova remnant. One particular aspect of interest is the possible formation of dust in SN 1987A, as SNe could contribute significantly to the dust seen at high redshifts.

Aims.Recurrent nova systems like RS Oph have been proposed as a possible channel for type Ia supernova (SN) explosions based on the high mass of the accreting white dwarf. Additional support for this hypothesis has recently been provided by the detection of circumstellar material around SN 2006X and SN 2007le, showing a structure compatible with that expected for recurrent nova outbursts. We investigate the circumstellar environment of RS Oph and its structure with the aim of establishing a firmer and independent link between this class of objects and type Ia SN progenitors.Methods.We study the time evolution of Ca ii, Na i, and K i absorption features in RS Oph before, during, and after the last outburst, using multi-epoch, high-resolution spectroscopy and applying the same method as was adopted for SN 2006X and SN 2007le.Results.A number of components are detected , that are blue-shifted with respect to the systemic velocity of RS Oph. In particular, one feature strongly weakens in the first two weeks after the outburst, at the same time that the very narrow P-Cyg profiles disappear, which are overimposed on the much wider nova emission lines of H, He, Fe ii, and other elements.Conclusions.We interpret this as the signature of density enhancements in the circumstellar material, suggesting that the recurrent eruptions might indeed create complex structures within the material lost by the donor star. This establishes a strong link between RS Oph and the progenitor system of the type Ia SN 2006X, for which similar features have been detected.

Aims.We present a full analysis of the CAFOS polarimeter mounted at the Calar Alto 2.2 m telescope. This provides future users of this mode with all necessary information to properly correct for instrumental effects in polarization data obtained with this instrument.

Aims.The present study was conducted to determine the optical extinction curve for Cerro Paranal under typical clear-sky observing conditions, with the purpose of providing the community with a function to be used to correct the observed spectra, with an accuracy of 0.01 mag airmass-1. Additionally, this work was meant to analyze the variability of the various components, to derive the main atmospheric parameters, and to set a term of reference for future studies, especially in view of the construction of the Extremely Large Telescope on the nearby Cerro Armazones.

Aims.We study possible signs of asymmetry in the luminous type IIn SN 2010jl, to obtain independent information about its explosion geometry.