Planetary Nebulae with Ultra-Violet Imaging Telescope (UVIT): Far Ultra-violet halo around the Bow Tie nebula (NGC 40)

Context. NGC 40 is a planetary nebula with diffuse X-ray emission, suggesting an interaction of the high speed wind from WC8 central star (CS) with the nebula. It shows strong Civ 1550 {\AA} emission that cannot be explained by thermal processes alone. We present here the first map of this nebula in C IV emission, using broad band filters on the UVIT. Aims. To map the hot C IV emitting gas and its correspondence with soft X-ray (0.3-8 keV) emitting regions, in order to study the shock interaction with the nebula and the ISM. This also illustrates the potential of UVIT for nebular studies. Methods. Morphological study of images of the nebula obtained at an angular resolution of about 1.3" in four UVIT filter bands that include C IV 1550 {\AA} and C II] 2326 {\AA} lines and UV continuum. Comparisons with X-ray, optical, and IR images from literature. Results. The C II] 2326 {\AA} images show the core of the nebula with two lobes on either side of CS similar to [N II]. The C IV emission in the core shows similar morphology and extant as that of diffuse X-ray emission concentrated in nebular condensations. A surprising UVIT discovery is the presence of a large faint FUV halo in FUV Filter with {\lambda}eff of 1608 {\AA}. The UV halo is not present in any other UV filter. FUV halo is most likely due to UV fluorescence emission from the Lyman bands of H2 molecules. Unlike the optical and IR halo, FUV halo trails predominantly towards south-east side of the nebular core, opposite to the CS's proper motion direction. Conclusions. Morphological similarity of C IV 1550 {\AA} and X-ray emission in the core suggests that it results mostly from interaction of strong CS wind with the nebula. The FUV halo in NGC 40 highlights the existence of H2 molecules extensively in the regions even beyond the optical and IR halos.Comment: 4 pages, 5 figures, accepted for publication as a letter in Astronomy & Astrophysic

Planetary Nebulae with UVIT II: Revelations from FUV vision of Butterfly Nebula NGC 6302

The high excitation planetary nebula, NGC 6302, has been imaged in two far-ultraviolet (FUV) filters, F169M (Sapphire; {\lambda}$_{\rm eff}$: 1608 {\AA}) and F172M (Silica; {\lambda}$_{\rm eff}$: 1717 {\AA}) and two NUV filters, N219M (B15; {\lambda}$_{\rm eff}$: 2196 {\AA}) and N279N (N2; {\lambda}$_{\rm eff}$: 2792 {\AA}) with the Ultra Violet Imaging Telescope (UVIT). The FUV F169M image shows faint emission lobes that extend to about 5 arcmin on either side of the central source. Faint orthogonal collimated jet-like structures are present on either side of the FUV lobes through the central source. These structures are not present in the two NUV filters nor in the FUV F172M filter. Optical and IR images of NGC 6302 show bright emission bipolar lobes in the east-west direction with a massive torus of molecular gas and dust seen as a dark lane in the north-south direction. The FUV lobes are much more extended and oriented at a position angle of 113{\deg}. They and the jet-like structures might be remnants of an earlier evolutionary phase, prior to the dramatic explosive event that triggered the Hubble type bipolar flows approximately 2200 years ago. The source of the FUV lobe and jet emission is not known, but is likely due to fluorescent emission from H$_2$ molecules. The cause of the difference in orientation of optical and FUV lobes is not clear and, we speculate, could be related to two binary interactions.Comment: 9 pages, 5 figures, accepted for publication in Astronomy & Astrophysic

Asp-89: a critical residue in maintaining the oligomeric structure of sheep liver cytosolic serine hydroxymethyltransferase

Aspartate residues function as proton acceptors in catalysis and are involved in ionic interactions stabilizing subunit assembly. In an attempt to unravel the role of a conserved aspartate (D89) in sheep-liver tetrameric serine hydroxymethyltransferase (SHMT), it was converted into aspargine by site-directed mutagenesis. The purified D89N mutant enzyme had a lower specific activity compared with the wild-type enzyme. It was a mixture of dimers and tetramers with the proportion of tetramers increasing with an increase in the pyridoxal-5′-phosphate (PLP) concentration used during purification. The D89N mutant tetramer was as active as the wild-type enzyme and had similar kinetic and spectral properties in the presence of 500 μM PLP. The quinonoid spectral intermediate commonly seen in the case of SHMT was also seen in the case of D89N mutant tetramer, although the amount of intermediate formed was lower. Although the purified dimer exhibited visible absorbance at 425 nm, it had a negligible visible CD spectrum at 425 nm and was only 5% active. The apo-D89N mutant tetramer was a dimer unlike the apo-form of the wild-type enzyme which was present predominantly as a tetramer. Furthermore the apo mutant dimer could not be reconstituted to the holo-form by the addition of excess PLP, suggesting that dimer-dimer interactions are weak in this mutant. The recently published crystal structure of human liver cytosolic recombinant SHMT indicates that this residue (D90 in the human enzyme) is located at the N-terminal end of the fourth helix of one subunit and packs against K39 from the second N-terminal helix of the other symmetry related subunit forming the tight dimer. D89 is at the interface of tight dimers where the PLP 5'-phosphate is also bound. Mutation of D89 could lead to weakened ionic interactions in the tight dimer interface, resulting in decreased affinity of the enzyme for the cofactor

Distribution of sea weeds off Kattapadu - Tiruchendur coast, Tamil nadu

The present paper deals with the distribution of seaweeds and seagrasses during the deep sea survey conducted in the first sector from Kattapadu to Tiruchendur in Tamil Nadu coast between December 1986 and March 1987 covering an area of 650 sq.km. In thiS survey. 58 species of marine algae \\ere recorded. of which 7 belong to Chlorophyta. 12 to Phaeophyta and 39 to Rhodophyta. Three species of seagrasses vi z. Cymodocea serrl/lata. Halophila ovails and H. ovala were also recorded at the depths ranging from 5.5 to 21.5 III Halim eda macroloba, D,ClyOIO barlayresiana, D. Maxima, Gracliaria corl/cala var. corlicala, G. edulis, Sarcodia indica, Sarconema filiform e, Soliena rob"sla, flypnea esperi and H. "alenliae were found to be dominant and widely distributed. Hydrological data were also collected from area surveyed. The atmospheric and bottom water temperature varied from 25.0 to 36.8'C and 26.0 to 31.8'C respectively. The pH ranged from 8.3 to 8.6 and the salinity from 26.39 to 33.430/00 . The dissolved oxygen ranged from 3A2 to 6.47 mill. The phosphate content varied from 0.05 to 0. 15 I'g atm/ l, silicate from 4.00 to 12.00 I'g atmll, nitrate from 0.25 to 1.00 I'g at mil and nitrite from 1.05 to 3.99 I'g atml l

Non-singular radiation cosmological models

In this paper we analyse the possibility of constructing singularity-free inhomogeneous cosmological models with a pure radiation field as matter content. It is shown that the conditions for regularity are very easy to implement and therefore there is a huge number of such spacetimes.Comment: 13 pages, LaTex, ws-mpla, to appear in Modern Physics Letters

Observation of the Smectic C -- Smectic I Critical Point

We report the first observation of the smectic C--smectic I (C--I) critical point by Xray diffraction studies on a binary system. This is in confirmity with the theoretical idea of Nelson and Halperin that coupling to the molecular tilt should induce hexatic order even in the C phase and as such both C and I (a tilted hexatic phase) should have the same symmetry. The results provide evidence in support of the recent theory of Defontaines and Prost proposing a new universality class for critical points in layered systems.Comment: 9 pages Latex and 5 postscript figures available from [email protected] on request, Phys.Rev.Lett. (in press