Microvariability of line profiles in the spectrum of the star ι Her

We present the results of a search for and analysis of line-profile variations in the spectrum of the star ι Her. The observations were acquired with the 1.8 m telescope of the Bohyunsan Optical Astronomy Observatory (Republic of Korea) in May–June 2004. We obtained 69 spectra of the star with signal-to-noise ratios ≈300 and a time resolution of 5–7 min. Profile variability was revealed for six lines of HI, HeI, and SiIII, in the central parts of the lines. The variability amplitude is ≈(1–2)% in units of the intensity of the adjacent continuum. Evidence was found for cyclic variations of the lines, with periods from ≈7^h to ≈2.9^d. We conclude that ι Her belongs to the group of slowly pulsating stars.     

Super-Fast Line-Profile Variability in the Spectra of OBA-Stars: B1-Star <Emphasis Type="Italic">ρ</Emphasis> Leo

This study continues our investigation of the super-fast variability of line profiles in the spectra of early-type stars. We have investigated the line-profile variability in spectra of OBA-stars with the SCORPIO multi-mode focal reducer mounted at the 6-m SAO RAS telescope. Regular short-period variations of the H and He lines in the spectra of the B1I star ρ Leo were detected with periods ranging from 2 to 90 minutes, as well as irregular line-profile variations on time intervals less than 1 minute. A possible origin of rapid spectral variations is discussed.     

SPEXTRA: Optimal extraction code for long-slit spectra in crowded fields

We present a code for the optimal extraction of long-slit 2D spectra in crowded stellar fields. Its main advantage and difference from the existing spectrum extraction codes is the presence of a graphical user interface (GUI) and a convenient visualization system of data and extraction parameters. On the whole, the package is designed to study stars in crowded fields of nearby galaxies and star clusters in galaxies. Apart from the spectrum extraction for several stars which are closely located or superimposed, it allows the spectra of objects to be extracted with subtraction of superimposed nebulae of different shapes and different degrees of ionization. The package can also be used to study single stars in the case of a strong background. In the current version, the optimal extraction of 2D spectra with an aperture and the Gaussian function as PSF (point spread function) is proposed. In the future, the package will be supplemented with the possibility to build a PSF based on a Moffat function. We present the details of GUI, illustrate main features of the package, and show results of extraction of the several interesting spectra of objects from different telescopes.     

A summary of sulfur dioxide emission rate measuremnts from Guatemalan volcanoes

Measurements of the sulfur dioxide (SO₂) emission rate from three Guatemalan volcanoes provide data which are consistent with theoretical and laboratory studies of eruptive and shallow magma chamber processes. In particular, unerupted magma makes a major contribution to the measured SO₂ emission rates at Santiaguito, a continuously erupting dacitic volcanic dome. Varying shallow magma convection rates can explain the variations in SO₂ emission rates at Santiaguito. At Fuego, a basaltic volcano currently in repose, SO₂ emission rate measurements are consistent with a high level magma body that is crystallizing and releasing volatiles. At Pacaya, a continuously erupting basaltic volcano, recent SO₂ emission rate measurements support laboratory simulation studies of strombolian eruptions; these studies indicate that the majority of gas escapes during eruptions and little gas escapes between eruptions.Average SO₂ emission rates over the last 20 years for Santiaguito, Fuego and Pacaya are 80, 160 and 260 Mg/d, respectively. On a global scale, these three volcanoes account for 1% of the annual global volcanic output of SO₂. Santiaguito and Pacaya, together, emit 6% of the total annual SO₂ emitted by continuously erupting volcanoes.Even though SO₂ measurements at these volcanoes have been made infrequently and by different investigators, the collective data help to establish a useful baseline by which to judge future changes. A more complete record of SO₂ emission rates from these volcanoes could lead to a better understanding of their eruption mechanisms and reduce the impact of their future eruptions on Guatemalan society.     

Statistics of magnetic fields for OB stars

Based on an analysis of the catalog of magnetic fields, we have investigated the statistical properties of the mean magnetic fields for OB stars. We show that the mean effective magnetic field B of a star can be used as a statistically significant characteristic of its magnetic field. No correlation has been found between the mean magnetic field strength B and projected rotational velocity of OB stars, which is consistent with the hypothesis about a fossil origin of the magnetic field. We have constructed the magnetic field distribution function for B stars, F(B), that has a power-law dependence on B with an exponent of ≈−1.82. We have found a sharp decrease in the function F(B) for B ⩽ 400 G that may be related to rapid dissipation of weak stellar surface magnetic fields.     

Two new LBV candidates in the M 33 galaxy

We present two new luminous blue variable (LBV) candidate stars discovered in the M33 galaxy. We identified these stars as massive star candidates at the final stages of evolution, presumably with a notable interstellar extinction. The candidates were selected from the Massey et al. catalog based on the following criteria: emission in H _α , V<18^./m 5 and 0_.^m 35 < (B - V) < 1_.^m 2. The spectra of both stars reveal a broad and strong H _α emission with extended wings (770 and 1000 kms⁻¹). Based on the spectra we estimated the main parameters of the stars. Object N45901 has a bolometric luminosity log(L/L_⊙) = 6.0–6.2 with the value of interstellar extinction A _V = 2.3 ± 0.1. The temperature of the star’s photosphere is estimated as T⋆ ∼ 13000–15000 K, its probable mass on the Zero Age Main Sequence is M∼ 60–80 M_⊙. The infrared excess in N 45901 corresponds to the emission of warm dust with the temperature Twarm ∼ 1000 K, and amounts to 0.1%of the bolometric luminosity. A comparison of stellar magnitude estimates from different catalogs points to the probable variability of the object N45901. Bolometric luminosity of the second object, N125093, is log(L/L_⊙) = 6.3 − 6.6, the value of interstellar extinction is A _V = 2.75 ± 0.15. We estimate its photosphere’s temperature as T⋆∼ 13000–16000K, the initial mass as M ∼ 90–120 M_⊙. The infrared excess in N125093 amounts to 5–6% of the bolometric luminosity. Its spectral energy distribution reveals two thermal components with the temperatures T_warm ∼ 1000K and T_cold ∼ 480 K. The [Ca II] λλ7291, 7323 lines, observed in LBV-like stars Var A and N93351 in M33 are also present in the spectrum of N 125093. These lines indicate relatively recent gas eruptions and dust activity linked with them. High bolometric luminosity of these stars and broad H α emissions allow classifying the studied objects as LBV candidates.     

Optical observations of type-IIP supernova 2004dj: Evidence for asymmetry of the <Superscript>56</Superscript>Ni ejecta

Photometric and spectroscopic observations of the nearby type-IIP supernova 2004dj are presented. The ⁵⁶Ni mass in the envelope of SN 2004dj was estimated from the light curve to be ≈0.02M_⊙. This estimate is confirmed by modeling the Hα luminosity. The Hα emission line exhibits a strong asymmetry characterized by the presence of a blue component in the line with a shift of ?1600 km s^?1 at the early nebular phase. A similar asymmetry was found in the Hβ, [O I], and [Ca II] lines. The line asymmetry is interpreted as being the result of asymmetric ⁵⁶Ni ejecta. The Hα profile and its evolution are reproduced in the model of an asymmetric bipolar ⁵⁶Ni structure for a spherical hydrogen distribution. The mass of the front ⁵⁶Ni jet is comparable to that of the central component and twice that of the rear ⁵⁶Ni jet. We point out that the asymmetric bipolar structure of ⁵⁶Ni ejecta is also present in SN 1999em, a normal type-IIP supernova.     

Ultra-luminous X-ray sources as supercritical accretion disks: Spectral energy distributions

We describe a model of spectral energy distribution in supercritical accretion disks (SCAD) based on the conception by Shakura and Sunyaev. We apply this model to five ultra-luminous X-ray sources (ULXs). In this approach, the disk becomes thick at distances to the center less than the spherization radius, and the temperature dependence is T ∝ r ^?1/2. In this region the disk luminosity is L _bol ～ L _Edd $\ln \left( {{{\dot M} \mathord{\left/ {\vphantom {{\dot M} {\dot M_{Edd} }}} \right. \kern-0em} {\dot M_{Edd} }}} \right)$ , and strong wind arises forming a wind funnel above the disk. Outside the spherization radius, the disk is thin and its total luminosity is Eddington, L _Edd. The thin disk heats the wind from below. From the inner side of the funnel the wind is heated by the supercritical disk. In this paper we do not consider Comptonization in the inner hot winds which must cover the deep supercritical disk regions. Our model is technically similar to the DISKIR model of Gierlinski et al. The models differ in disk type (standard—supercritical) and irradiation (disk—wind).We propose to distinguish between these two models in the X-ray region of about 0.3–1 keV, where the SCAD model has a flat νF _ν spectrum, and the DISKIR model never has a flat part, as it is based on the standard α-disk. An important difference between the models can be found in their resulting black hole masses. In application to the ULX spectra, the DISKIR model yields black hole masses of a few hundred solar masses, whereas the SCAD model produces stellar-mass (about 10M_⊙) black holes.     

Monitoring the recovery of a previously exploited surf-zone fish community in the St Lucia Marine Reserve,South Africa,using a no-take sanctuary area as a benchmark

Limiting accessibility to a fishing area can reduce fishing effort effectively and may therefore promote local recovery of depleted stocks. In January 2002, beach driving was banned in South Africa, thereby reducing angler access to large areas of the coastline, particularly in less-developed areas. In November 2001 a project had been established in the St Lucia Marine Reserve, on the east coast of South Africa, to compare surf-zone fish populations inside a no-take sanctuary zone with those in an adjacent exploited area. Subsequent to the ban, the aim of the project was adapted such that surf-zone fish populations were monitored for potential recovery in what had been the exploited area, located to the north of Cape Vidal, which anglers could no longer access easily, because of the prohibition on beach driving. Standardised research fishing was conducted at two sites in the previously exploited area and two sites in the no-take sanctuary. Conventional stock-status indicators showed evidence of recovery in the four most common species caught in the previously exploited area, in terms of both abundance and biomass. Generalised additive mixed models were used to account for the influence of targeting specific species; however, subtle differences in habitat between the sampling sites, improved angling skill over time, variability in recruitment, and differential species-specific responses complicated interpretation of results. The implications of the findings are discussed in terms of the future monitoring and management of marine protected areas both within the St Lucia Marine Reserve and farther afield.