A multiwavelength study of the remnant of nova GK Persei

We present new observations of the nebular remnant of the old nova GK Persei 1901, in the optical using the 2m HCT and at low radio frequencies using the GMRT. The evolution of the nova remnant indicates shock interaction with the ambient medium, especially in the southwest quadrant. Application of a simple model for the shock and its evolution to determine the time dependence of the radius of the shell in the southwest quadrant indicates that the shell is now expanding into an ambient medium that has a lower density compared to the density of the ambient medium ahead of the shock in 1987.There are indications of a recent interaction of the nova remnant with the ambient medium in the northeast quadrant also. The nova remnant of GK Per is detected at all the observed radio frequencies and is of similar extent as the optical remnant. Putting together our radio observations with VLA archival data on GK Per from 1997, we obtain three interesting results: 1. The spectrum above 1.4 GHz follows a power law with an index -0.7 and below 1.4 GHz follows a power law with an index ~ -0.85. This could be due to the presence of at least two populations of electrons dominating the global emission at different frequencies. 2. We record an annual secular decrease of 2.1% in the flux density of the nova remnant at 1.4 and 4.9 GHz between 1984 and 1997 which has left the spectral index unchanged at -0.7. No such decrease is observed in the flux densities below 1 GHz. 3. We record an increase in the flux density at 0.33 GHz compared to the previous estimate in 1987. We conclude that the remnant of nova GK Per is similar to supernova remnants and in particular, to the young supernova remnant Cas A.Comment: 10 pages; uses A&A style; figures 1, 2 & 6 are in JPEG format. Accepted for publication in Astronomy & Astrophysics. Full paper including Figures 1, 2 & 6 may be downloaded from http://www.iiap.res.in/personnel/gca/gca.htm

Evolution of the Cluster Correlation Function

We study the evolution of the cluster correlation function and its richness-dependence from z = 0 to z = 3 using large-scale cosmological simulations. A standard flat LCDM model with \Omega_m = 0.3 and, for comparison, a tilted \Omega_m = 1 model, TSCDM, are used. The evolutionary predictions are presented in a format suitable for direct comparisons with observations. We find that the cluster correlation strength increases with redshift: high redshift clusters are clustered more strongly (in comoving scale) than low redshift clusters of the same mass. The increased correlations with redshift, in spite of the decreasing mass correlation strength, is caused by the strong increase in cluster bias with redshift: clusters represent higher density peaks of the mass distribution as the redshift increases. The richness-dependent cluster correlation function, presented as the correlation-scale versus cluster mean separation relation, R_0 - d, is found to be, remarkably, independent of redshift to z <~ 2 for LCDM and z <~ 1 for TCDM (for a fixed correlation function slope and cluster mass within a fixed comoving radius). The non-evolving R_0 - d relation implies that both the comoving clustering scale and the cluster mean separation increase with redshift for the same mass clusters so that the R_0 - d relation remains essentially unchanged. The evolution of the R_0 - d relation from z ~ 0 to z ~ 3 provides an important new tool in cosmology; it can be used to break degeneracies that exist at z ~ 0 and provide precise determination of cosmological parameters.Comment: AASTeX, 15 pages, including 5 figures, accepted version for publication in ApJ, vol.603, March 200

GMRT Observations of the 2006 outburst of the Nova RS Ophiuchi: First detection of emission at radio frequencies < 1.4 GHz

The first low radio frequency (<1.4 GHz) detection of the outburst of the recurrent nova RS Ophiuchi is presented in this letter. Radio emission was detected at 0.61 GHz on day 20 with a flux density of ~48 mJy and at 0.325 GHz on day 38 with a flux density of ~ 44 mJy. This is in contrast with the 1985 outburst when it was not detected at 0.327 GHz even on day 66. The emission at low radio frequencies is clearly non-thermal and is well-explained by a synchrotron spectrum of index alpha ~ -0.8 (S propto nu^alpha) suffering foreground absorption due to the pre-existing, ionized, warm, clumpy red giant wind. The absence of low frequency radio emission in 1985 and the earlier turn-on of the radio flux in the current outburst are interpreted as being due to higher foreground absorption in 1985 compared to that in 2006, suggesting that the overlying wind densities in 2006 are only ~30% of those in 1985.Comment: 14 pages, 1 figure. Accepted for publication in ApJ

ZZE-Configuration of chromophore ß-153 in C-phycocyanin from Mastigocladus laminosus

The photochemistry of C-phycocyanin has been studied after denaturation in the dark. It shows an irreversible reaction which has characteristics of a Ζ,Ζ,Ε- to Z,Z,Z-isomerization of dihydrobilins. Its amplitude depends on the reaction conditions, with a maximum corresponding to 15% conversion of one of the three PC chromophores. This chromophore is suggested to be ß-153, for which recent X-ray data T. Schirmer, W. Bode, and R. Huber, J. Mol. Biol., submitted, show ring D being highly twisted out of the plane of the other rings. During unfolding, there is thus a probability of falling into the photochemically labile Z,Z,^-configuration

First experiences with HMC for dynamical overlap fermions

We describe an HMC algorithm for dynamical overlap fermions which makes use of their good chiral properties. We test the algorithm in the Schwinger model. Topological sectors are readily changed even in the massless case.Comment: 4 pages with 1 ps figure; crckapb.sty included; to appear in the proceedings of the workshop "Lattice Fermions and Structure of the Vacuum", Oct 5-9, Dubna, Russi

Determination of the Her-2/neu gene amplification status in cytologic breast cancer specimens using automated silver-enhanced in-situ hybridization (SISH)

Silver-enhanced in-situ hybridization (SISH) is an emerging tool for the determination of the Her-2/neu amplification status in breast cancer. SISH is technically comparable to fluorescence in-situ hybridization (FISH) but does not require a fluorescence microscope for its interpretation. Although recent studies on histologic evaluations of SISH are promising, we aimed to evaluate its performance on 71 cytologic breast cancer specimens with the new combined Her-2/Chr17 probe. Her-2/neu status as routinely determined by FISH was available for all patients. We found SISH signals in cytologic cell blocks and smear specimens easy to evaluate in most cases. Small numbers of tumor cells and difficulties in identifying tumor cells in lymphocyte-rich backgrounds were limiting factors. Her-2/neu status, as determined by Her-2/Chr17 SISH, was basically identical to the results of the corresponding FISH. The discrepancies were mainly owing to the heterogeneity of Her-2/neu amplification in the tumor tissue. Interobserver agreement for the SISH evaluation was high (kappa value: 0.972). We conclude that Her-2/Chr17 SISH is a useful and accurate method for the evaluation of the Her-2/neu gene amplification status in cytologic breast cancer specimens, particularly in metastatic breast cancer lesions. The advantages of signal permanency and bright-field microscopic result interpretation make this technique an attractive alternative to the current FISH-based gold standard

Chandra detection of extended X-ray emission from the recurrent nova RS Ophiuchi

Radio, infrared, and optical observations of the 2006 eruption of the symbiotic recurrent nova RS Ophiuchi (RS Oph) showed that the explosion produced non-spherical ejecta. Some of this ejected material was in the form of bipolar jets to the east and west of the central source. Here we describe Xray observations taken with the Chandra X-ray Observatory one and a half years after the beginning of the outburst that reveal narrow, extended structure with a position angle of approximately 300 degrees (east of north). Although the orientation of the extended feature in the X-ray image is consistent with the readout direction of the CCD detector, extensive testing suggests that the feature is not an artifact. Assuming it is not an instrumental effect, the extended X-ray structure shows hot plasma stretching more than 1,900 AU from the central binary (taking a distance of 1.6 kpc). The X-ray emission is elongated in the northwest direction - in line with the extended infrared emission and some minor features in the published radio image. It is less consistent with the orientation of the radio jets and the main bipolar optical structure. Most of the photons in the extended X-ray structure have energies of less than 0.8 keV. If the extended X-ray feature was produced when the nova explosion occurred, then its 1".2 length as of 2007 August implies that it expanded at an average rate of more than 2 mas/d, which corresponds to a flow speed of greater than 6,000 km/s (d/1.6 kpc) in the plane of the sky. This expansion rate is similar to the earliest measured expansion rates for the radio jets.Comment: accepted in Ap

Topology with Dynamical Overlap Fermions

We perform dynamical QCD simulations with $n_f=2$ overlap fermions by hybrid Monte-Carlo method on $6^4$ to $8^3\times 16$ lattices. We study the problem of topological sector changing. A new method is proposed which works without topological sector changes. We use this new method to determine the topological susceptibility at various quark masses.Comment: 15 pages, 3 figure

New issues for Numerical Stochastic Perturbation Theory

First attempts in the application of Numerical Stochastic Perturbation Theory (NSPT) to the problem of pushing one loop further the computation of SU(3) (SU(2)) pertubative beta function (in different schemes) are reviewed and the relevance of such a computation is discussed. Other issues include the proposal of a different strategy for gauge-fixed NSPT computations in lattice QCD.Comment: 3 pages, Latex, LATTICE98(algorithms

A very luminous, highly extinguished, very fast nova - V1721 Aquilae

Fast novae are primarily located within the plane of the Galaxy, slow novae are found within its bulge. Because of high interstellar extinction along the line of sight many novae lying close to the plane are missed and only the brightest seen. One nova lying very close to the Galactic plane is V1721 Aquilae, discovered in outburst on 2008 September 22. Spectra obtained 2.69 days after outburst revealed very high expansion velocities (FWHM ~6450 km/s). In this paper we have used available pre- and post-outburst photometry and post-outburst spectroscopy to conclude that the object is a very fast, luminous, and highly extinguished A_V=11.6+/-0.2) nova system with an average ejection velocity of ~3400 km/s. Pre-outburst near-IR colours from 2MASS indicate that at quiescence the object is similar to many quiescent CNe and appears to have a main sequence/sub-giant secondary rather than a giant. Based on the speed of decline of the nova and its emission line profiles we hypothesise that the axis ratio of the nova ejecta is ~1.4 and that its inclination is such that the central binary accretion disc is face-on to the observer. The accretion disc's blue contribution to the system's near-IR quiescent colours may be significant. Simple models of the nova ejecta have been constructed using the morphological modelling code XS5, and the results support the above hypothesis. Spectral classification of this object has been difficult owing to low S/N levels and high extinction, which has eliminated all evidence of any He/N or FeII emission within the spectra. We suggest two possibilities for the nature of V1721 Aql: that it is a U Sco type RN with a sub-giant secondary or, less likely, that it is a highly energetic bright and fast classical nova with a main sequence secondary. Future monitoring of the object for possible RN episodes may be worthwhile, as would archival searches for previous outbursts.Comment: 9 pages 10 figures, accepted for publication in A&A. Abstract has been slightly shortened from published versio