Comment on ‘Where are the halo stars?’

We comment briefly on a recent paper by Fuhrmann which claims that about half of the sample of halo stars in the solar neighbourhood presented by Fuchs and Jahreiß [A&A 329 (1998) 81] are actually thick disc stars. By referring to star counts in the CADIS survey we argue that this is rather unlikely.     

1–100 μm energy spectra and 2.3–4 μm spectrophotometry of MSC stars

The JHKL' photometry and 2.3–4 μm spectrophotometry of some M giants, S type stars and carbon stars are presented in this paper. It is found that in combination with IRAS data, the energy spectra in 1–100 μm of S type stars are intermediate between those of M giants and carbon stars, which are obviously different. The spectrophotometry in the near infrared shows that, besides carbon stars, which have HCN and C₂H₂ strong absorptions at 3.1 μm, some S type stars have the similar but weaker absorption in the same spectral region. However, no trace of any absorption at 3.1 μm can be seen in M giants. These results probably provide more evidence for the M-S-C sequence in the late stage of stellar evolution.     

On the maximal value of the turbulent α ‐parameter in accretion discs

In this short paper we show that making turbulence two‐rather than three‐dimensional may increase the effective turbulent viscosity by about 40 %. Dimensionless hydrodynamical viscosity parameters up to α_max = 0.25 M_t² may be obtained in this approach, which are in better agreement with the observational data on non‐stationary accretion than the values obtained in numerical simulations. However, the α ‐parameter values known from observations are still several times higher (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Measuring ΩM and ΩΛ with long‐duration gamma‐ray bursts

Gamma‐ray bursts (GRBs) are one of the most luminous events in the Universe. In addition, the Universe itself is almost transparent to γ ‐rays, making GRBs detectable up to very high redshifts. As a result, GRBs are very suitable to probe the cosmological parameters. This work shows the potential of long‐duration GRBs for measuring the cosmological parameters Ω_M and Ω_Λ by comparing the observed log N ‐log P distribution with the theoretical one. Provided that the GRBs rate and luminosity function are well determined, the best values and 1σ confidence intervals obtained are Ω_M = 0.22^+0.05_–0.03 and Ω_Λ = 1.06^+0.05_–0.10. Finally, a set of simulations show the ability of the method to measure Ω_M and Ω_Λ (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Interacting Galaxies — the X-ray View

We have selected a complete, flux-limited sample of bright point-like sources with absorbed X-ray spectra from the ROSAT All-Sky survey, the ROSAT Hard Survey (RHS). The sample is drawn from the high-galactic latitude sky, |b^II| > ±30°, and avoids the general direction of the Magellanic Clouds and the Virgo Cluster. It comprises a total of 182 objects of which 118 were previosly catalogued objects and 64 were new AGN candidates. Through optical follow-up studies at La Silla, Calar Alto and the 6m Zelentchuk telescope we could identify 56 of the new objects, thus achieving a spectrscopic completeness of 96% of the sample. The selection strategy turned out to be extremely useful. Out of the new identifications, 84% are indeed active galaxies or emission line galaxies. While 14 objects are new BL Lac candidates 33 of the new AGN are Seyfert galaxies with a redshift distribution in the range 0.021–0.63, peaking at around 0.06, i.e. relatively local. Surprisingly, about 40% of the X-ray selected Seyfert galaxies seem to reside in interacting systems. With smaller selection uncertainties this fraction exceeds the number of paired galaxies in optically selected samples and therefore gives strong support to the idea that AGN activity is triggered by interaction.     

Dwingeloo – the golden radio telescope

The Dwingeloo 25‐m telesope, inaugurated in 1956, has played a major role in research for half a century. We trace its history back to its conception in 1944, and summarize its main achievements. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Counts of galaxies in the region of the “intergalactic dark cloud” near ι microscopii

The distribution of the total numbers of galaxies down to about 18^TH magnitude on 84 squares is largely in agreement with the structure of the hypothetic intergalactic absorbing cloud near ι Microscopii found by C. HOFFMEISTER . The counts of galaxies were performed on the WHITEOAK prints covering that region.     

An anthropogenic origin of the “Sirente crater,” Abruzzi,Italy

Abstract— In this paper, we review the recent hypothesis, based mostly on geomorphological features, that a ～130 m‐wide sag pond, surrounded by a saddle‐shaped rim from the Sirente plain (Abruzzi, Italy), is the first‐discovered meteoritic crater of Italy. Sub‐circular depressions (hosting ponds), with geomorphological features and size very similar to those exhibited by the main Sirente sag, are exposed in other neighboring intermountain karstic plains from Abruzzi. We have sampled present‐day soils from these sag ponds and from the Sirente sags (both the main “crater” and some smaller ones, recently interpreted as a crater field) and various Abruzzi paleosols from excavated trenches with an age range encompassing the estimated age of the “Sirente crater.” For all samples, we measured the magnetic susceptibility and determined the Ni and Cr contents of selected specimens. The results show that the magnetic susceptibility values and the geochemical composition are similar for all samples (from Sirente and other Abruzzi sags) and are both significantly different from the values reported for soils contaminated by meteoritic dust. No solid evidence pointing at an impact origin exists, besides the circular shape and rim of the main sag. The available observations and data suggest that the “Sirente crater,” together with analogous large sags in the Abruzzi intermountain plains, have to be attributed to the historical phenomenon of “transumanza” (seasonal migration of sheep and shepherds), a custom that for centuries characterized the basic social‐economical system of the Abruzzi region. Such sags were excavated to provide water for millions of sheep, which spent summers in the Abruzzi karstic high pasture lands, on carbonatic massifs deprived of natural superficial fresh water. Conversely, the distribution of the smaller sags from the Sirente plain correlates with the local pattern of the calcareous bedrock and, together with the characteristics of their internal structure, are best interpreted as natural dolines. In fact, reported radiocarbon ages for the formation of the main sag pond and of the smaller sags differ (significantly) by more than two millennia, thus excluding that they were all contemporaneously formed by a meteoritic impact.     

The iron emission line complex of MCG‐5‐23‐16: the long XMMNewton look

We present the results of the simultaneous XMM‐Newton and Chandra observations of the bright Seyfert 1.9 galaxy MCG–5‐23‐16, which is one of the best known examples of a relativistically broadened iron Kα line. We find that: a) the soft X‐ray emission is likely to be dominated by photoionized gas, b) the complex iron emission line is best modelled with a narrow and a broad component with a FWHM ∼44000 km/s. This latter component has an EW ∼50 eV and its profile is well described with an emission line mainly originating from the accretion disk a few tens of gravitational radii from the central black hole and viewed with an inclination angle ∼40°. We found evidence of a possible sporadic absorption line at ∼7.7 keV which, if associated with Fe XXVI Kα resonance absorption, is indicative of a possible high velocity (v ∼ 0.1c) outflow. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the variability of the “blue objects”

The reality of the high percentage of variability among Blue Objects which was found in previous investigations was examined on 170 Tautenburg Schmidt plates of two test fields near M 31. The high percentage could not be confirmed. Spurious amplitudes can be explained by the large probable errors of the photometry (especially near the plate limit) and by bad suitability of good-looking plates. Out of 37 Blue Objects examined, only two (van den Bergh 5 and 12) are distinctly variable, but the final examination of Blue Objects which are suspected of variability can only be done by photoelectric photometry.     

Gemini J ‐band observations of RX J0806.4–4123

The detection of near‐infrared (NIR) excess at the position of a star can indicate either a substellar companion or a disk around the respective star. In this work we probed whether a 2.5σ H ‐band flux enhancement at the position of the isolated neutron star RX J0806.4–4123 can be confirmed at another NIR wavelength. We observed RXJ0806.4–4123 in the J ‐band with Gemini South equipped with FLAMINGOS‐2. There was no significant detection of a J ‐band source at the neutron star position. However, similarly to the H ‐band we found a very faint (1.4σ) flux enhancement with a nominal magnitude of J = 24.8 ± 0.5. The overall NIR‐detection significance is 3.1σ. If real, this emission is too bright to come from the neutron star alone. Deeper near‐infrared observations are necessary to confirm or refute the potential NIR excess. The confirmation of such NIR excess could imply that there is a substellar companion or a disk around RXJ0806.4–4123. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Atlas of the airglow spectrum 3000–12400 Å

An atlas of airglow spectrograms obtained in the USSR during the IGY is presented.