S. Muneer

Photometric and spectroscopic evolution of the Type IIP supernova SN 2004et

We present optical photometry and spectroscopy of the normal type IIP supernova SN2004A, which was discovered in the galaxy NGC 6207 on 2004 January 9.84UT. Early observations indicated that the supernova was discovered at about two weeks since explosion. We estimate the distance to NGC 6207 to be 20.35 \pm 4.5 Mpc using the Standard Candle method. Using this distance, we estimate the ejected nickel mass in the explosion to be 0.032 \pm 0.02M\odo\cdot. The plateau luminosity, its duration (about 80 days) and the expansion velocity of the supernova ejecta at the middle of the plateau indicate an explosion energy of 4.7 \pm 2.7 x 10^50 ergs and an ejected envelope mass of 7.2 \pm 2.2M\odot\cdot . The ejected envelope mass implies a main sequence mass of 10 2.5\pm M\odot\cdot for the progenitor.

Orbital period modulation and spot activity in the RS CVn binary V711 Tauri

Aims. We attempt to establish the real nature of the orbital period variation and its relation to the spot activity of V711 Tau, and determine why the (B −V) colour of the star appears to be nearly independent of its V magnitude. We wish to verify whether existing predictions in the literature for the long-term spot activity of the star are true or not by making extended photometric observations, and whether the broad component of Hα emission originates in more localised active regions, as suggested by some chromospheric models, by searching for any correlation between the base-line width of the emission and the light modulation. Methods. We obtained new radial velocities of the G-type component of V711 Tau on 42 nights during 2004−09, and BV photometry of V711 Tau on 202 nights during the years 1993−2009. We measured the equivalent widths of two well resolved lines of the G-type component from 13 of the spectra obtained by us. We also measured the equivalent widths and base-line widths of Hα emission from 21 spectra obtained during 2008−09. We analyse these along with relevant information available in the literature. Results. The available radial velocity data of V 711 Tau are consistent with a sinusoidal modulation of its orbital period; the period of modulation is found to be 36.3 ± 1.9 yr. The fractional light-loss over a photometric cycle is found to vary with an average period of 14.1 ± 0.3 yr. It appears that physical processes linked to the magnetic activity of the spotted star are responsible for the variation in the orbital period. The excess reduction in the B band flux relative to that in V band caused by spot activity is almost compensated for by the fractional increase in the contribution by the hotter companion to the total light in the blue spectral region, and thereby makes the (B − V) colour of the binary system nearly independent of its V magnitude. We find that the ratio of the radii of the components derived from their v sin i values, which is usually quoted in the literature, is substantially larger than that implied by the ratio of their brightnesses in V band. There is a slight indication from the V band data that the spot activity in V711 Tau has a component that is fixed in the orbital frame of reference. The equivalent width and base-line width of Hα emission do not show any obvious correlation with the V band light curve.

Identification of metal-poor stars using the artificial neural network

Context. Identification of metal-poor stars among field stars is extremely useful for studying the structure and evolution of the Galaxy and of external galaxies. Aims. We search for metal-poor stars using the artificial neural network (ANN) and extend its usage to determine absolute magnitudes. Methods. We have constructed a library of 167 medium-resolution stellar spectra (R ∼ 1200) covering the stellar temperature range of 4200 to 8000 K, log g range of 0.5 to 5.0, and [Fe/H] range of −3.0 to +0.3 dex. This empirical spectral library was used to train ANNs, yielding an accuracy of 0.3 dex in [Fe/H], 200 K in temperature, and 0.3 dex in log g. We found that the independent calibrations of near-solar metallicity stars and metal-poor stars decreases the errors in Teff and log g by nearly a factor of two. Results. We calculated Teff ,l ogg ,a nd [Fe/H] on a consistent scale for a large number of field stars and candidate metal-poor stars. We extended the application of this method to the calibration of absolute magnitudes using nearby stars with well-estimated parallaxes. A better calibration accuracy for MV could be obtained by training separate ANNs for cool, warm, and metal-poor stars. The current accuracy of MV calibration is ±0.3 mag. Conclusions. A list of newly identified metal-poor stars is presented. The MV calibration procedure developed here is reddeningindependent and hence may serve as a powerful tool in studying galactic structure.

Unveiling Vela – time variability of Na i D lines in the direction of the Vela supernova remnant

High-resolution spectral profiles of Na I D lines from the interstellar medium towards 64 stars in the direction of the Vela supernova remnant are presented. This survey conducted mostly between 2011-12 complements an earlier survey of the same stars by Cha & Sembach done in the 1993-96 period. The interval of 15 to 18 years provides a base line to search for changes in the interstellar profiles. Dramatic disappearance of strong absorption components at low radial velocity is seen towards three stars - HD 63578, HD 68217, HD 76161 - over 15-18 years; HD 68217 and HD 76161 are associated with the Vela SNR but HD 63578 is likely associated with the wind bubble of g2 Velorum. The vanishing of these cold neutral clouds in the short time of 15 to 18 years needs some explanation. Other changes are seen in high-velocity Na D components.

Period changes in the RR Lyrae stars of NGC 6171 (M107)

1 Instituto de Astronomı́a, Universidad Nacional Autónoma de México. Ciudad Universitaria, CP 04510, México: (armando@astro.unam.mx) 2 Grupo de Astrof́ısica Teórica, Facultad de Ciencias, Universidad de Los Andes, Venezuela. 3 Indian Institute of Astrophysics, Koramangala, 560034, Bangalore, India 4 Observatorio Astronómico Nacional, Instituto de Astronomı́a Universidad Nacional Autónoma de México, Ap. P. 877, Ensenada, BC 22860, México

Unveiling Vela: time variability of interstellar lines in the direction of the Vela supernova remnant – II. Na D and Ca ii

High-resolution optical spectra were obtained in 2017-2019 with The Southern African Large Telescope of fifteen stars in the direction of the Vela supernova remnant. Interstellar Ca ii H and K and Na i D lines are discussed in this paper. In particular, the line profiles are compared with profiles at a comparable spectral resolution obtained in 1993-1996 by Cha & Sembach. Ten of the lines of sight show changes to one or more of the components in that line of sight. Changes include small changes (1-2 km/s) in radial velocity and/or increases/decreases in equivalent width over the two decades between the periods of observation. Changes are more obvious in the Ca K line than in the Na D lines. These changes are attributed to gas disturbed by interactions between the supernova ejecta and the surrounding interstellar medium. A representative timescale may be 20-50 years. Small-scale variations in line profiles across the face of the remnant suggest, as previously remarked, that a linear scale for interactions is a small fraction of the 40 pc size of the present remnant.