H α variability in the quiescent spectrum of the recurrent nova T Coronae Borealis

The emission lines in the quiescent spectrum of the recurrent nova T Coronae Borealis are variable. Optical spectra recorded during the years 1985–90 show one full cycle of high and low states. After removing the slow variation, an orbital-phase-dependent variation becomes apparent in the H α line, with maxima around orbital phases 0 and 0.5. The slow variation indicates secular changes in the accretion disc possibly caused by a variable mass transfer rate. Orbital variations can be caused either by geometrical effects or a phase-modulated mass transfer rate. More detailed monitoring is needed to model the system

Embedded Clusters in Giant Extragalactic HII Regions III. Extinction and Star Formation

A study of star formation is carried out on 35 giant extragalactic HII regions (GEHRs) in seven galaxies using optical photometric data in BVR broad bands and in the emission line of H alpha. Interstellar extinction, metallicity and nebular contributions to the broad bands are estimated using spectroscopic data on these objects. Dimensionless diagrams involving B-V and V-R colors and the flux ratio of Balmer line to B band continuum are used to study star formation. The cluster colors indicate reduced extinction towards stellar continuum compared to the values derived from Balmer lines for the ionized gas. The frequency of detection of classical young (t < 3 Myr) regions with only one burst of star formation is found to be low as compared to young regions with an accompanying population rich in red supergiants from a previous burst (t ~ 10 Myr). Reduced extinction towards cluster stars, destruction of ionizing photons and the existence of older population, often spatially unresolvable from the younger population, all conspire to make the observed Balmer line equivalent widths low in a majority of the GEHRs. A scenario of star formation is suggested which explains many of the observed properties of GEHRs, including the core-halo structure, reduced extinction for the radiation from stars as compared to that from the nebular gas, non-detection of young single burst regions and the co-existence of two populations of different ages.Comment: 18 pages, AASTeX v4.0, 3 tables with aj_pt and 8 postscript figures. Figure 9 is available on request from [email protected] or at the URL http://tifrc3.tifr.res.in:2000/ydm/www/preprint.html To appear in Astronomical Journa

Spectroscopic results of the recurrent nova RS ophiuchi

The recurrent nova RS Ophiuchi has had five outbursts in 1898, 1933, 1958, 1967 and 1985. We present here in brief the spectroscopic results of the 1985 outburst and subsequent quiescence, based on data obtained at the Vainu Bappu Observatory (VBO), Kavalur. Detailed results of the 1985 outburst appear in Anupama and Prabhu (1989). Spectra were recorded in the range 6200-8900 A at dispersion of 194 A mm−1 at four epochs: 32, 59 and 60; 89 and 91 and 108 days since the 1985 outburst maximum on January 27.5. In addition, spectra were recorded in the range 4300-5600 and 5000-7600 A at dispersion of 132 A mm−1on day 60, and in the range 5700-8000 A, at dispersion of 194 A mm−1, on days 89, 91 and 108

The nebular remnant and quiescent spectrum of Nova GK Persei

CCD images of the nebular shell of the old nova GK Per in [N II] and [O III] emission lines, and also the quiescent spectrum in the optical region, are presented. Proper motion measurements of the knots in [N II] over the baseline 1984–90 give a mean expansion rate of 0.31 &#177; 0.07 arcsec yr-1. This value agrees with models of the expansion of the ejecta into the ambient circumstellar medium. A correction for projection effects indicates that the ratio of the mass of the shell to the density of the circumstellar medium is a factor of 2 – 3 higher than estimated previously. The optical spectrum is decomposed into those of the secondary and the accretion disc. The estimate of MV = + 4.9 for the accretion disc implies a mass transfer rate of 3.5 × 10-9 M&#9737; yr-1 in the steady state. The H and He emission-line fluxes are used to infer that (i) the line-emitting region has a high density, (ii) the He/H abundance is near-solar, and (iii) the ionizing source has a Zanstra temperature of 1.3 × 105 K and an effective radius of 0.01 R&#9737;, which are consistent with its being a white dwarf

The 1985 outburst of RS Ophiuchi: spectroscopic results

Optical spectroscopic data on the recurrent nova RS Ophiuchi obtained between 32 and 108 days after its last outburst on 1985 January 27 are presented. RS Oph was in the coronal-line phase at that time. The widths of the permitted as well as coronal-lines decreased continuously. Assuming that the ejected envelope decelerated due to its interaction with circum stellar matter, its size is deduced as a function of time. Observed fluxes in permitted lines would then imply that the electron density decreased from 3 × 10 9 cm #x2212;3 on day 32 to 1.8 × 108 cm-3 on day 108, for an assumed filling factor of 0.01. The helium abundance in the ejecta is estimated to be n(He)/n(H) ∼ 0.16. The mass of the unshocked ejecta was 3 × 10-6 (&#934;/0.01)1/2M&#9737;, (at this stage, where f is the filling factor. Observed fluxes in coronal-lines imply that the temperature of coronal-line region decreased from 1.5 × 106 K on day 32 to 1.1 × 106 K on day 108. Most of the coronal line emission, as well as He n emission arises in shocked and cooling ejecta. This region is not isothermal, but contains material at a wide range of temperatures. Mass of the shocked ejecta is estimated to be in the range 10−7−10-6M&#9737; Based on the number of H- and He-ionizing photons, we estimate that the ionizing source evolved from a radius and temperature of (2 × l012 cm, 3 × 104 K) on day 32 to (6 × l09 cm, 3.6 × 105K) on day 204. We also present the spectra of RS Oph recorded in quiescent phase, 2 and 3 years after outburst, for comparison. The spectrum is dominated by that of M2 giant secondary, with superposed emission lines of H and He I

Chemical Compositions of Four Metal-poor Giants

We present the chemical compositions of four K giants CS 22877-1, CS 22166-16, CS22169-35 and BS 16085 - 0050 that have [Fe/H] in the range -2.4 to -3.1. Metal-poor stars with [Fe/H] < -2.5 are known to exhibit considerable star - to - star variations of many elements. This quartet confirms this conclusion. CS 22877-1 and CS 22166-16 are carbon-rich. There is significant spread for [$\alpha$/Fe] within our sample where [$\alpha$/Fe] is computed from the mean of the [Mg/Fe], and [Ca/Fe] ratios. BS 16085 - 0050 is remarkably $\alpha$ enriched with a mean [$\alpha$/Fe] of $+$0.7 but CS 22169-35 is $\alpha$-poor. The aluminium abundance also shows a significant variation over the sample. A parallel and unsuccessful search among high-velocity late-type stars for metal-poor stars is described.Comment: 14 pages (text), 4 tables, 3 figures, Accepted for publication in PAS

The AGN and Gas Disk in the Low Surface Brightness Galaxy PGC045080

We present radio observations and optical spectroscopy of the giant low surface brightness (LSB) galaxy PGC 045080 (or 1300+0144). PGC 045080 is a moderately distant galaxy having a highly inclined optical disk and massive HI gas content. Radio continuum observations of the galaxy were carried out at 320 MHz, 610 MHz and 1.4 GHz. Continuum emission was detected and mapped in the galaxy. The emission appears extended over the inner disk at all three frequencies. At 1.4 GHz and 610 MHz it appears to have two distinct lobes. We also did optical spectroscopy of the galaxy nucleus; the spectrum did not show any strong emission lines associated with AGN activity but the presence of a weak AGN cannot be ruled out. Furthermore, comparison of the H$\alpha$ flux and radio continuum at 1.4 GHz suggests that a significant fraction of the emission is non-thermal in nature. Hence we conclude that a weak or hidden AGN may be present in PGC 045080. The extended radio emission represents lobes/jets from the AGN. These observations show that although LSB galaxies are metal poor and have very little star formation, their centers can host significant AGN activity. We also mapped the HI gas disk and velocity field in PGC 045080. The HI disk extends well beyond the optical disk and appears warped. In the HI intensity maps, the disk appears distinctly lopsided. The velocity field is disturbed on the lopsided side of the disk but is fairly uniform in the other half. We derived the HI rotation curve for the galaxy from the velocity field. The rotation curve has a flat rotation speed of ~ 190 km/s.Comment: Paper contains 14 figures and 4 tables. Figures 8, 10 (color) and 13 supplied separately. Accepted for publication in MNRA