Jessy Jose

Type Ia supernova SN 2003du: Optical observations

UBVRI photometry and optical spectra of type Ia supernova SN 2003du obtained at the Indian Astronomical Observatory for nearly a year since discovery are presented. The apparent magnitude at maximum was B = 13.53 ± 0.02 mag, and the colour (B − V) = −0.08 ± 0.03 mag. The luminosity decline rate, ∆m15(B) = 1.04 ± 0.04 mag indicates an absolute B magnitude at maximum of M max = −19.34 ± 0.3 mag and the distance modulus to the parent galaxy as µ = 32.89 ± 0.4. The light curve shapes are similar, though not identical, to those of SNe 1998bu and 1990N, both of which had luminosity decline rates similar to that of SN 2003du and occurred in spiral galaxies. The peak bolometric luminosity indicates that ∼0.9 Mmass of 56 Ni was ejected by the supernova. The spectral evolution and the evolution of the Si II and Ca II absorption velocities closely follows that of SN 1998bu, and in general, is within the scatter of the velocities observed in normal type Ia supernovae. The spectroscopic and photometric behaviour of SN 2003du is quite typical for SNe Ia in spirals. A high velocity absorption component in the Ca II (H and K) and IR-triplet features, with absorption velocities of ∼20 000 km s −1 and ∼22 000 km s −1 respectively, is detected in the pre-maximum spectra of days −11 and −7.

NGC 1624-2: a slowly rotating, X-ray luminous Of?cp star with an extraordinarily strong magnetic field

This paper presents a first observational investigation of t he faint Of?p star NGC 1624-2, yielding important new constraints on its spectral and physical characteristics, rotation, magnetic field strength, X-ray emission and magnetospheric pro perties. Modeling the spectrum and spectral energy distribution, we conclude that NGC 1624-2 is a main sequence star of mass M≃ 30 M⊙, and infer an effective temperature of 35± 2 kK and log g = 4.0± 0.2. Based on an extensive time series of optical spectral observation s we report significant variability of a large number of spectral lines, and infer a unique period of 157.99± 0.94 d which we interpret as the rotational period of the star. We report the detec tion of a very strong - 5.35± 0.5 kG - longitudinal magnetic field h Bzi , coupled with probable Zeeman splitting of Stokes I profiles of metal lines confirming a surface field modulus h Bi of 14± 1 kG, consistent with a surface dipole of polar strength ∼ 20 kG. This is the largest magnetic field ever detected in an O-type star, and the first report of Zeeman splitting of Stoke s I profiles in such an object. We also report the detection of reversed Stokes V profiles associated with weak, high-excitation emission lines of Oiii, which we propose may form in the close magnetosphere of the star. We analyze archival Chandra ACIS-I X-ray data, inferring a very hard spectrum with an X-ray effi ciency log Lx/Lbol =−6.4, a factor of 4 larger than the canonical value for O-type sta rs and comparable to that of the young magnetic O-type starθ 1 Ori C and other Of?p stars. Finally, we examine the probable magnetospheric properties of the star, reporting in particular very strong magnetic confinement of the stellar wind, with η∗≃ 1.5× 10 4 , and a very large Alfven radius, RAlf = 11.4 R∗.

Probing the physics of narrow-line regions of Seyfert galaxies - I. The case of NGC 5427

Context. The spectra of the extended narrow-line regions (ENLRs) of Seyfert 2 galaxies probe the physics of the central active galaxy nucleus (AGN), since they encode the energy distribution of the ionising photons, the radiative flux and radiation pressure, nuclear chemical abundances and the mechanical energy input of the (unseen) central AGN. Aims. We aim to constrain the chemical abundance in the interstellar medium of the ENLR by measuring the abundance gradient in the circum-nuclear H ii regions to determine the nuclear chemical abundances, and to use these to in turn determine the EUV spectral energy distribution for comparison with theoretical models. Methods. We have used the Wide Field Spectrograph (WiFeS) on the ANU 2.3 m telescope at Siding Spring to observe the nearby, nearly face-on, Seyfert 2 galaxy, NGC 5427. We have obtained integral field spectroscopy of both the nuclear regions and the H ii regions in the spiral arms. The observed spectra have been modelled using the MAPPINGS IV photoionisation code, both to derive the chemical abundances in the H ii regions and the Seyfert nucleus, and to constrain the EUV spectral energy distribution of the AGN illuminating the ENLR. Results. We find a very high nuclear abundance, 3.0 times solar, with clear evidence of a nuclear enhancement of N and He, possibly caused by massive star formation in the extended (∼100 pc) central disk structure. The circum-nuclear narrow-line region spectrum is fit by a radiation pressure dominated photoionisation model model with an input EUV spectrum from a Black – .

Young stellar population of bright-rimmed clouds BRC 5, BRC 7 and BRC 39

Bright-rimmed clouds (BRCs), illuminated and shaped by nearby OB stars, are potential sites of recent/ongoing star formation. Here we present an optical and infrared photometric study of three BRCs: BRC 5, BRC 7 and BRC 39 to obtain a census of the young stellar population, thereby inferring the star formation scenario, in these regions. In each BRC, the Class I sources are found to be located mostly near the bright rim or inside the cloud, whereas the Class II sources are preferentially outside, with younger sources closer to the rim. This provides strong support to sequential star formation triggered by radiation-driven implosion due to the ultraviolet radiation. Moreover, each BRC contains a small group of young stars being revealed at its head, as the next-generation stars. In particular, the young stars at the heads of BRC 5 and BRC 7 are found to be intermediate-/high-mass stars, which, under proper conditions, may themselves trigger further star birth, thereby propagating star formation out to long distances.

PROBING THE PHYSICS OF NARROW-LINE REGIONS IN ACTIVE GALAXIES. III. ACCRETION AND COCOON SHOCKS IN THE LINER NGC 1052

M.A.D. and L.K. acknowledge the support of the Australian Research Council (ARC) through Discovery project DP130103925.

Probing the Physics of Narrow Line Regions in Active Galaxies. II. The Siding Spring Southern Seyfert Spectroscopic Snapshot Survey (S7)

Here we describe the \emph{Siding Spring Southern Seyfert Spectroscopic Snapshot Survey} (S7) and present results on 64 galaxies drawn from the first data release. The S7 uses the Wide Field Spectrograph (WiFeS) mounted on the ANU 2.3m telescope located at the Siding Spring Observatory to deliver an integral field of

Young stellar population and ongoing star formation in the H ii complex Sh2-252

38\times25

Placing the spotted T Tauri star LkCa 4 on an HR diagram

~ arcsec at a spectral resolution of

A study of the starless dark cloud LDN 1570: Distance, dust properties, and magnetic field geometry

R=7000

The ASAS-SN bright supernova catalogue – I. 2013–2014

in the red (