Jonathan Smoker

A giant outburst two years before the core-collapse of a massive star

The death of massive stars produces a variety of supernovae, which are linked to the structure of the exploding stars. The detection of several precursor stars of type II supernovae has been reported (see, for example, ref. 3), but we do not yet have direct information on the progenitors of the hydrogen-deficient type Ib and Ic supernovae. Here we report that the peculiar type Ib supernova SN 2006jc is spatially coincident with a bright optical transient that occurred in 2004. Spectroscopic and photometric monitoring of the supernova leads us to suggest that the progenitor was a carbon-oxygen Wolf–Rayet star embedded within a helium-rich circumstellar medium. There are different possible explanations for this pre-explosion transient. It appears similar to the giant outbursts of luminous blue variable stars (LBVs) of 60–100 solar masses, but the progenitor of SN 2006jc was helium- and hydrogen-deficient (unlike LBVs). An LBV-like outburst of a Wolf–Rayet star could be invoked, but this would be the first observational evidence of such a phenomenon. Alternatively, a massive binary system composed of an LBV that erupted in 2004, and a Wolf–Rayet star exploding as SN 2006jc, could explain the observations.

Optical atmospheric extinction over Cerro Paranal

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. Methods. The extinction curve of Paranal was obtained through low-resolution spectroscopy of 8 spectrophotometric standard stars observed with FORS1 mounted at the 8.2 m Very Large Telescope, covering a spectral range 3300–8000 A. A total of 600 spectra were collected on more than 40 nights distributed over six months, from October 2008 to March 2009. The average extinction curve was derived using a global fit algorithm, which allowed us to simultaneously combine all the available data. The main atmospheric parameters were retrieved using the LBLRTM radiative transfer code, which was also utilised to study the impact of variability of the main molecular bands of O2 ,O 3 ,a nd H 2O, and to estimate their column densities. Results. In general, the extinction curve of Paranal appears to conform to those derived for other astronomical sites in the Atacama desert, like La Silla and Cerro Tololo. However, a systematic deficit with respect to the extinction curve derived for Cerro Tololo before the El Chichon eruption is detected below 4000 A. We attribute this downturn to a non standard aerosol composition, probably revealing the presence of volcanic pollutants above the Atacama desert. An analysis of all spectroscopic extinction curves obtained since 1974 shows that the aerosol composition has been evolving during the last 35 years. The persistence of traces of non meteorologic haze suggests the effect of volcanic eruptions, like those of El Chichon and Pinatubo, lasts several decades. The usage of the standard CTIO and La Silla extinction curves implemented in IRAF and MIDAS produce systematic over/under-estimates of the absolute flux.

The extraordinarily bright optical afterglow of GRB 991208 and its host galaxy

Broad-band optical observations of the extraordi- narily bright optical afterglow of the intense gamma-ray burst GRB 991208 started � 2.1 days after the event and continued until 4 Apr 2000. The flux decay constant of the optical after- glow in the R-band is 2.30 ± 0.07 up to � 5 days, which

Early-type stars observed in the ESO UVES Paranal Observatory Project - I. Interstellar Na I UV, Ti II and Ca II K observations

We present an analysis of interstellar Na I (λair = 3302.37 and 3302.98 A), Ti II (λair = 3383.76 A) and Ca II K( λair = 3933.66 A) absorption features for 74 sightlines towards O- and B-type stars in the Galactic disc. The data were obtained from the Ultraviolet and Visual Echelle Spectrograph Paranal Observatory Project, at a spectral resolution of 3.75 km s −1 and with mean signal-to-noise ratios per pixel of 260, 300 and 430 for the Na I ,T iII and Ca II observations, respectively. Interstellar features were detected in all but one of the Ti II sightlines and all of the Ca II sightlines. The dependence of the column density of these three species with distance, height relative to the Galactic plane, H I column density, reddening and depletion relative to the solar abundance has been investigated. We also examine the accuracy of using the Na I column density as an indicator of that for H I. In general, we find similar strong correlations for both Ti and Ca, and weaker correlations for Na. Our results confirm the general belief that Ti and Ca occur in the same regions of the interstellar medium (ISM) and also that the Ti II/Ca II ratio is constant over all parameters. We hence conclude that the absorption properties of Ti and Ca are essentially constant under the general ISM conditions of the Galactic disc.

Metallicity and Physical Conditions in the Magellanic Bridge

Wepresent a new analysis of the diffuse gas in the Magellanic Bridge (R.A.k3 h ) based onHST STIS E140M and FUSE spectra of two early-type stars lying within the Bridge and a QSO behind it. We derive the column densities of theHi(fromLy� ),Ni,Oi,Ari,Siii,Sii,andFeiiof thegasintheBridge.Usingtheatomicspecies,wedeterminethe first gas-phase metallicity of the Magellanic Bridge, ½Z/H �¼� 1:02 � 0:07 toward one sight lineand � 1:7 < ½Z/H� < � 0:9 toward the other, a factor of 2 or more smaller than the present-day SMC metallicity. Using the metallicity and N(Hi), we show that the Bridge gas along our three lines of sight is � 70%‐90% ionized, despite high H i columns, logN(Hi) ’19:6 20:1.Possible sources for theongoing ionization are certainly thehot stars within theBridge, hot gas(revealedbyOviabsorption),andleakingphotonsfromtheSMCandLMC.Fromtheanalysisof Cii � ,wededuce thattheoveralldensityof theBridgemustbelow(<0.03‐0.1cm � 3 ).Wearguethatourfindingscombinedwithother recent observational results should motivate new models of the evolution of the SMC-LMC-Galaxy system. Subject headingg galaxies: abundances — ISM: structure — Magellanic Clouds — ultraviolet: ISM

The Birth Place of the Type Ic Supernova 2007gr

We report our attempts to locate the progenitor of the peculiar Type Ic SN 2007gr in Hubble Space Telescope (HST) preexplosion images of the host galaxy, NGC 1058. Aligning adaptive optics Altair/NIRI imaging of SN 2007gr from the Gemini (North) Telescope with the preexplosion HST WFPC2 images, we identify the supernova (SN) position on the HST frames with an accuracy of 20 mas. Although nothing is detected at the SN position, we show that it lies on the edge of a bright source, 134 ± 23mas (6.9 pc) from its nominal center. On the basis of its luminosity, we suggest that this object is possibly an unresolved, compact, and coeval cluster and that the SN progenitor was a cluster member, although we note that model profile fitting favors a single bright star. We find two solutions for the age of this assumed cluster: 7 0.5 Myr and 20-30 Myr, with turnoff masses of 28 ± 4 M☉ and 12-9 M☉, respectively. Preexplosion ground-based K-band images marginally favor the younger cluster age/higher turnoff mass. Assuming the SN progenitor was a cluster member, the turnoff mass provides the best estimate for its initial mass. More detailed observations, after the SN has faded, should determine whether the progenitor was indeed part of a cluster and, if so, allow an age estimate to within ~2 Myr, thereby favoring either a high-mass single star or lower-mass interacting binary progenitor.

The yellow hypergiant HR 5171 A: Resolving a massive interacting binary in the common envelope phase

We initiated long-term optical interferometry monitoring of the diameters of unstable yellow hypergiants (YHG) with the goal of detecting both the long-term evolution of their radius and shorter term formation related to large mass-loss events. We observed HR5171 A with AMBER/VLTI. We also examined archival photometric data in the visual and near-IR spanning more than 60 years, as well as sparse spectroscopic data. HR5171A exhibits a complex appearance. Our AMBER data reveal a surprisingly large star for a YHG R*=1315+/-260Rsun\ (~6.1AU) at the distance of 3.6+/-0.5kpc. The source is surrounded by an extended nebulosity, and these data also show a large level of asymmetry in the brightness distribution of the system, which we attribute to a newly discovered companion star located in front of the primary star. The companions signature is also detected in the visual photometry, which indicates an orbital period of Porb=1304+/-6d. Modeling the light curve with the NIGHTFALL program provides clear evidence that the system is a contact or possibly over-contact eclipsing binary. A total current system mass of 39^{+40}_{-22} solar mass and a high mass ratio q>10 is inferred for the system. The low-mass companion of HR5171 A is very close to the primary star that is embedded within its dense wind. Tight constraints on the inclination and vsini of the primary are lacking, which prevents us from determining its influence precisely on the mass-loss phenomenon, but the system is probably experiencing a wind Roche-Lobe overflow. Depending on the amount of angular momentum that can be transferred to the stellar envelope, HR5171 A may become a fast-rotating B[e]/Luminous Blue Variable (LBV)/Wolf-Rayet star. In any case, HR5171 A highlights the possible importance of binaries for interpreting the unstable YHGs and for massive star evolution in general.

High-resolution spectroscopy of globular cluster post-Asymptotic Giant Branch stars

We present model atmosphere analyses of high resolution Keck and VLT optical spectra for three evolved stars in globular clusters, viz. ZNG-1 in M 10, ZNG-1 in M 15 and ZNG-1 in NGC 6712. The derived atmospheric parameters and chemical compositions confirm the programme stars to be in the post-Asymptotic Giant Branch (post-AGB) evolutionary phase. Differential abundance analyses reveal CNO abundance patterns in M 10 ZNG-1, and possibly M 15 ZNG-1, which suggest that both objects may have evolved off the AGB before the third dredge-up occurred. The abundance pattern of these stars is similar to the third class of optically, bright post-AGB objects discussed by van Winckel (1997). Furthermore, M 10 ZNG-1 exhibits a large C underabundance (with � (C/O) ∼− 1.6 dex), typical of other hot post-AGB objects. Differential � (α/Fe) abundance ratios in both M 10 ZNG-1 and NGC 6712 ZNG-1 are found to be approximately 0.0 dex, with the Fe abundance of the former being in disagreement with the cluster metallicity of M 10. Given that the Fe absorption features in both M 10 ZNG-1 and NGC 6712 ZNG-1 are well observed and reliably modelled, we believe that these differential Fe abundance estimates to be secure. However, our Fe abundance is difficult to explain in terms of previous evolutionary processes that occur on both the Horizontal Branch and the AGB.

Performance of FLAMES at the VLT: one year of operation

Four years after its announcement at SPIE, FLAMES, the VLT fibre facility, has been completed, integrated into the VLT observatory and commissioned. It has been in operation since February 2003. More than 250000 scientific (single) spectra have been obtained, which have enabled the on-sky performance of the instrument to be compared to the predictions. We show that in several relevant aspects the real instrument significantly outperforms the specified astronomical performance. Some of the early scientific results are finally presented.

Multiwavelength observations of the M15 intermediate-velocity cloud

We present Westerbork Synthesis Radio Telescope H I images, Lovell telescope multibeam H I wide-field mapping, William Herschel Telescope long-slit echelle Can observations, Wisconsin Ha Mapper (WHAM) facility images, andIRAS ISSA 60- and 100-μm co-added images towards the intermediate-velocity cloud (IVC) at +70 km s - 1 , located in the general direction of the M1 5 globular cluster. When combined with previously published Arecibo data, the HI gas in the IVC is found to be clumpy, with a peak HI column density of ∼ 1.5 × 10 2 0 cm - 2 , inferred volume density (assuming spherical symmetry) of ∼ 24 cm - 3 /D (kpc) and a maximum brightness temperature at a resolution of 81 x 14 arcsec 2 of ∼14 K. The major axis of this part of the IVC lies approximately parallel to the Galactic plane, as does the low-velocity H I gas and IRAS emission. The H I gas in the cloud is warm, with a minimum value of the full width at half-maximum velocity width of 5 km s - 1 corresponding to a kinetic temperature, in the absence of turbulence, of ∼540 K. From the H I data, there are indications of two-component velocity structure. Similarly, the Ca II spectra, of resolution 7 km s - 1 , also show tentative evidence of velocity structure, perhaps indicative of cloudlets. Assuming that there are no unresolved narrow-velocity components, the mean values of log 1 0 [N(Ca II K) cm - 2 ] ∼ 12.0 and Ca II/HI ∼2.5 x 10 - 8 are typical of observations of high Galactic latitude clouds. This compares with a value of Ca II/HI>10 - 6 for IVC absorption towards HD 203664, a halo star of distance 3 kpc, some 3°.1 from the main M15 IVC condensation. The main IVC condensation is detected by WHAM in Ha with central local-standard-of-rest velocities of ∼60-70 km s - 1 , and intensities uncorrected for Galactic extinction of up to 1.3 R, indicating that the gas is partially ionized. The FWHM values of the Ha IVC component, at a resolution of 1°, exceed 30 km s - 1 . This is some 10 km s - 1 larger than the corresponding H I value at a similar resolution, and indicates that the two components may not be mixed. However, the spatial and velocity coincidence of the Ha and HI peaks in emission towards the main IVC component is qualitatively good. If the Ha emission is caused solely by photoionization, the Lyman continuum flux towards the main IVC condensation is ∼2.7 x 10 6 photon cm - 2 s - 1 . There is not a corresponding IVC Hα detection towards the halo star HD 203664 at velocities exceeding ∼60 km s - 1 . Finally, both the 60- and 100-μm IRAS images show spatial coincidence, over a 0.675 x 0.625 deg 2 field, with both low- and intermediate-velocity H I gas (previously observed with the Arecibo telescope), indicating that the IVC may contain dust. Both the Ha and tentative IRAS detections discriminate this IVC from high-velocity clouds, although the HI properties do not. When combined with the HI and optical results, these data point to a Galactic origin for at least parts of this IVC.