We present BV RI observations of the optical counterpart to the Gamma-Ray Burst (GRB) 990510 obtained with the Las Campanas 1.0-m telescope between 15 and 48 hours after the burst. The temporal analysis of the data indicates steepening decay, independent of wavelength, approaching asymptotically t −0.76±0.01 at early times (t ≪ 1 day) and t −2.40±0.02 at late times, with the break time at t 0 = 1.57 ± 0.03 days. GRB 990510 is the most rapidly fading of the well-documented GRB afterglows. It is also the first observed example of broad-band break for a GRB optical counterpart. The optical spectral energy distribution, corrected for significant Galactic reddening, is well fitted by a single power-law with ν −0.61±0.12 . However, when the B-band point is dropped from the fit, the power-law becomes ν −0.46±0.08 , indicating a possible deviation from the power-law in the spectrum, either intrinsic or due to additional extinction near the source or from an intervening galaxy at z = 1.62. Broad-band break behavior broadly similar to that observed in GRB 990510 has been predicted in some jet models of GRB afterglows, thus supporting the idea that the GRB energy is beamed, at least in some cases.

We present results of a photometric survey for variable stars in the field of the globular cluster ω Centauri. The observed region was centered roughly on the cluster core and covered 644 arcmin 2 . The cluster was monitored on 59 nights in 1999 and 2000. A total of 117 new variables were identified. Among them there are 16 RR Lyr-type stars, 35 SX Phe variables and 26 eclipsing binaries. A comprehensive catalog including all variable stars so far reported from the cluster field is presented. We list basic photometric properties and provide finding charts for a total of 392 objects. For 313 of them new BV light curves were obtained. The presented sample includes several interesting variables, such as SX Phe stars with extremely short periods of pulsation and several candidates for pulsating K giants. Optical counterparts to 9 X-ray sources detected by XMM and Chandra telescopes were identified: all of them are likely to be foreground variables not related to the cluster.

We present u 0 g 0 r 0 i 0 BV photometry and optical spectroscopy of the Type Ib/Ic SN 2005bf covering the first $100 days following discovery. The u 0 g 0 BV light curves displayed an unprecedented morphology among Type Ib/Ic supernovae, with an initial maximum some 2 weeks after discovery and a second, main maximum about 25 days after that. The bolometric light curve indicates that SN 2005bf was a remarkably luminous event, radiating at least 6:3 ; 10 42 ergs s À1 at maximum light and a total of 2:1 ; 10 49 ergs during the first 75 days after the explosion. Spectroscopically, SN 2005bf underwent a unique transformation from a Type Ic-like event at early times to a typical Type Ib supernova at later phases. The initial maximum in u 0 g 0 BV was accompanied by the presence in the spectrum of high-velocity (>14,000 km s À1 ) absorption lines of Fe ii, Ca ii, and H i. The photospheric velocity derived from spectra at early epochs was below 10,000 km s À1 , which is unusually low compared with ordinary Type Ib supernovae. We describe one-dimensional computer simulations that attempt to account for these remarkable properties. The most favored model is that of a very energetic (2 ; 10 51 ergs), asymmetric explosion of a massive (8.3 M ) Wolf-Rayet WN star that had lost most of its hydrogen envelope. We speculate that an unobserved relativistic jet was launched producing a two-component explosion consisting of (1) a polar explosion containing a small fraction of the total mass and moving at high velocity and (2) the explosion of the rest of the star. At first, only the polar explosion is observed, producing the initial maximum and the high-velocity absorption-line spectrum resembling a Type Ic event. At late times, this fast-moving component becomes optically thin, revealing the more slowly moving explosion of the rest of the star and transforming the observed spectrum to that of a typical Type Ib supernova. If this scenario is correct, then SN 2005bf is the best example to date of a transition object between normal Type Ib/Ic supernovae and -ray bursts. Subject headingg s: gamma rays: bursts -supernovae: individual (SN 2005bf )

Abstract. We present the near infrared photometry of a new sample of 225 IRAS sources, many of them previously unidentified in the literature, selected because their far infrared colours are similar to those shown by known planetary nebulae. The results obtained are used to establish the main source of near infrared emission. Combining this information with the far infrared IRAS data and a few additional criteria we determine the nature and evolutionary stage of all the sources observed so far, including those for which near infrared photometry was previously reported in Papers I and II.Among the unidentified IRAS sources in our sample we find only a small percentage of planetary nebulae, many of them very young and dusty, showing peculiar near infrared colours. Most of the new objects observed in the near infrared are identified as transition objects in the previous stages of the stellar evolution. Among them, we find heavily obscured late-AGB stars, early post-AGB stars still obscured by thick circumstellar envelopes which are probably the true progenitors of planetary nebulae, and a significant fraction of stars with bright optical counterparts showing little or no near infrared excess, which we associate with highly evolved post-AGB stars with low mass progenitors, which may never become planetary nebulae. In addition, we also find a small percentage of young stellar objects, as well as a few Seyfert galaxies.We conclude that, in most cases, based on near infrared data alone, it is not possible to give a confident classification of the unidentified IRAS source. However, the near infrared is shown to be a powerful tool, specially when dealing with objects which are heavily obscured in Send offprint requests to: P. García-Lario Based on observations collected at the European Southern Observatory, La Silla (Chile) and at the Spanish Observatorio del Teide, Tenerife, Spain. Table 6 is only available electronically at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http: //cdsweb.u-strasbg.fr/Abstract.html the optical. In this case, the detection of the near infrared counterpart is the only way in which we can extend the study of these sources to other spectral ranges and may be crucial to understand the short-lived phase which precedes the formation of a new planetary nebula.

We present frequency analysis of RR Lyrae stars of globular cluster NGC 6362. 1 Observations and data analysis NGC 6362 is a nearby globular cluster of Oosterhoff I type. It has a mean metallicity of [Fe/H]= −0.95 and belongs to the old halo population ([1]). 35 RR Lyrae-type stars have been discovered in the cluster ([5]). We revisit these variables, taking advantage of the new CCD photometry accumulated by the Cluster AgeS Experiment (CASE). In our analysis we used 3200 V-band images collected with the 1-m Swope telescope of the Las Campanas Observatory between July 8th, 1999 and September 9th, 2009. The frequency analysis of the data was performed with the standard consecutive prewhitening technique. For full discussion of our results we refer the reader to [6]. 2 RR Lyrae variables of NGC 6362 16 RR Lyrae stars of NGC 6362 are fundamental mode pulsators (RRab variables) and 16 are first overtone pulsators (RRc variables). Two objects, previously identified as RRab stars, turned out to be double mode pulsators (RRd stars), with two lowest radial modes simultaneously excited. Finally, in V37 we detect two high-amplitude modes of close frequencies and with lightcurves significantly differing from those of RR Lyrae stars. The nature of V37 is a puzzle. It will not be discussed here. 2.1 Non-radial modes In 10 out of 16 RRc stars of NGC 6362 (63% of the sample) we detect a secondary short period variability, with the period ratio falling in the range of P x /P 1 = 0.60 − 0.65. The amplitudes of the secondary signals never exceed 6 mmag. Similar pulsators have recently been discovered in many stellar systems ([3], and references therein). Space observations indicate that this form of variability most likely occurs in almost all RRc and RRd stars ([4]). Detecting it in the ground-based data is difficult, however, because of the extremely low amplitude of the secondary periodicities. The incidence rate of 63%, that we report for NGC 6362, is the highest among all stellar systems observed