Upper Limit of Iodine Oxide in the Lower Stratosphere

It has been suggested that iodine oxides, IOx, could play a significant role in the ozone destruction in the lower stratosphere. To investigate this suggestion, spectra from nine SAOZ uv-visible spectrometer balloon flights were examined for the IO absorption signature between 405 and 450 nm. IO was not detected, either at mid- or high latitude, in the morning or the evening, in summer or winter. An upper limit of 0.2 parts per trillion by volume (pptv) at 20 km and 0.1 pptv at 15 km at the 95% confidence level (2), was derived from the best measurements at 90° SZA at sunset and sunrise. Since a photochemical model shows that 70% of inorganic iodine should be in the form IO at that time, it is concluded that unless iodine chemistry is different from that assumed at the moment, the role of iodine in stratospheric ozone depletion is small.     

Intercomparison of Tropospheric OH Measurements by Different Laser Techniques during the POPCORN Campaign 1994

In-situ OH measurements by laser-induced fluorescence (LIF) spectroscopy and folded long-path differential optical absorption spectroscopy (DOAS) were carried out in a rural environment in North-East Germany as part of the field experiment POPCORN in August 1994. The large set of OH data obtained allowed an intercomparison of both techniques based on relative diurnal profiles and simultaneously measured absolute concentrations. Most of the time the two OH instruments encountered the same air and agreed well in the measured relative diurnal variations. Only on a few occasions the measurements significantly disagreed due to a perturbation of the DOAS measurements by a local OH source in the north-western wind sector. Excluding data from this wind direction, the statistical analysis of 137 data pairs yields a correlation coefficient of r = 0.90 and a weighted linear fit with a slope of 1.09 ± 0.12. The correlations are carefully analyzed. The comparison of both instruments is discussed in the light of newly published effective absorption cross-sections for H2O and O2 that affect the calibration of LIF.     

Intrinsic spectra of the AXPs

Using direct measurements of photo-electric absorption edges, I derive the intrinsic spectra for the Anomalous X-ray Pulsars. In the past, the hydrogen column density, N _H had been found by fitting the X-ray spectra with a variety of simple continuum models. Since different models fit equally well, with different values of N _H, little is learned about the true column density or intrinsic spectra. Here, I measure the column densities in a model-independent way, and thus derive intrinsic spectra without first assuming what those spectra ought to look like. Particularly for the brightest source, 4U 0142+61, the column density can be determined accurately, and is a factor of 1.4 smaller that the typically N _H quoted. With this new value, the new intrinsic spectrum can be investigated anew, and shows a slight hint of a feature around 13 Å. To be emphasised, this is an empirical method with the minimum of assumptions, as is appropriate for these beguiling sources, the behaviour of which has mystifies astronomers for over a decade. This paper summarises the methods and conclusions to be published in the Astrophysical Journal by Durant and Van Kerkwijk (2006; see astro-ph/0606604).     

Kinematics and stellar populations of the dwarf elliptical galaxy IC 3653

We present the first 3D observations of a diffuse elliptical galaxy (dE). The good quality data (S/N up to 40) reveal the kinematical signature of an embedded stellar disc, reminiscent of what is commonly observed in elliptical galaxies, though similarity of their origins is questionable. Colour map built from Hubble Space Telescope Advanced Camera for Surveys (ACS) images confirms the presence of this disc. Its characteristic scale (about 3 arcsec =250 pc) is about a half of galaxy's effective radius, and its metallicity is 0.1–0.2 dex larger than the underlying population. Fitting the spectra with synthetic single stellar populations (SSP), we found an SSP-equivalent age of 5 Gyr and nearly solar metallicity [Fe/H]  =−0.06  dex. We checked that these determinations are consistent with those based on Lick indices, but have smaller error bars. The kinematical discovery of a stellar disc in dE gives additional support to an evolutionary link from dwarf irregular galaxies due to stripping of the gas against the intracluster medium.     

Searching for hidden Wolf–Rayet stars in the Galactic plane – 15 new Wolf–Rayet stars

We report the discovery of 15 previously unknown Wolf–Rayet (WR) stars found as part of an infrared (IR) broad-band study of candidate WR stars in the Galaxy. We have derived an empirically based selection algorithm which has selected ∼5000 WR candidate stars located within the Galactic plane drawn from the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (mid-IR) and Two-Micron All-Sky Survey (near-IR) catalogues. Spectroscopic follow-up of 184 of these reveals 11 nitrogen-rich (WN) and four carbon-rich (WC) WR stars. Early WC subtypes are absent from our sample and none shows evidence for circumstellar dust emission. Of the candidates which are not WR stars, ∼120 displayed hydrogen emission-line features in their spectra. Spectral features suggest that the majority of these are in fact B supergiants/hypergiants, ∼40 of these are identified Be/B[e] candidates.
Here, we present the optical spectra for six of the newly detected WR stars, and the near-IR spectra for the remaining nine of our sample. With a WR yield rate of ∼7 per cent and a massive star detection rate of ∼65 per cent, initial results suggest that this method is one of the most successful means for locating evolved, massive stars in the Galaxy.     

Structure of the inner regions of the circumstellar gas envelopes around young hot stars. II. The new cycle of spectral activity of the Herbig Ae star HD 31648

The results of the high-resolution long-term spectral monitoring of the Herbig Ae star HD 31648 in the regions of emission Hα line, Na I D resonance lines and OI 7774 lines are presented. We confirmed the conclusion, made in previous papers, that the spectral variability of the star in the region of Hα line have a cyclic character. It is manifested itself as the changing of the equivalent width and intensity of Hα line of the time scale of about 1200d. It is shown, that the stellar wind is non-homogeneous and consists of several components, which are differed each other by their velocities. They are observed as in the H line as in Na I D resonance lines. The component’s parameters are changed during the cycle of stellar activity (in the maximum of activity the velocity and density of the wind are taken the largest values and then they are gradually decreased). The investigation of rapid variability of the He I 5876 line on the time scale of a few hours allows find the correlation between the variability of the blue and the red wings of the line. It points at the connection between the accretion and the outflows. Such connection, in particularly, is predicted by the modeling of the wind from young stars made in the frame of the magneto-centrifugal model, the accordance of which for the HD 31648 was shown in the previous papers. In the present work we confirmed this conclusion on the basis of the new data. We found the weak variability of the stellar brightness (about 0.2m), which is agree with the spectral variability (the brightness of the star becomes lower in the maximum of the activity). These changes are well explained by the process of the dust transfer from CS disk by the stellar wind. This process is likely to be more effective in the maximum of activity. An analysis of the variability of other spectral lines shows the agreement between the changing of the Hα line, the Na I D resonance doublet lines and KI 7698 line. The weak connection between the He I 5876 and the Na I D lines is also found. Since the formation regions of He I 5876 and Na I D lines are essentially different, we can conclude that the phenomena, responsible for the observed cyclic variability, take place in a spacious region of the CS envelope. We believe that the most plausible reason of found cyclic variability is the reconstruction of the inner structure of the CS gas envelope, caused by the presence around the star a low mass companion or planet. __________ Translated from Astrofizika, Vol. 50, No. 4, pp. 565–588 (November 2007).