Microturbulent velocity from stellar spectra: a comparison between different approaches (Research Note)

Context --- The classical method to infer microturbulent velocity in stellar spectra requires that the abundances of the iron lines are not correlated with the observed equivalent widths. An alternative method, requiring the use of the expected line strength, is often used to by-pass the risk of spurious slopes due to the correlation between the errors in abundance and equivalent width. Aims --- To compare the two methods and identify pros and cons and applicability to the typical practical cases. Methods --- I performed a test with a grid of synthetic spectra, including instrumental broadening and Poissonian noise. For all these spectra, microturbulent velocity has been derived by using the two approaches and compared with the original value with which the synthetic spectra have been generated. Results --- The two methods provide similar results for spectra with SNR$ > 70, while for lower SNR both approaches underestimate the true microturbulent velocity, depending of the SNR and the possible selection of the lines based on the equivalent width errors. Basically, the values inferred by using the observed equivalent widths better agree with those of the synthetic spectra. In fact, the method based on the expected line strength is not totally free from a bias that can heavily affect the determination of microturbulent velocity. Finally, I recommend to use the classical approach (based on the observed equivalent widths) to infer this parameter. In cases of full spectroscopical determination of all the atmospherical parameters, the difference between the two approaches is reduced, leading to an absolute difference in the derived iron abundances of less than 0.1 dex.Comment: Accepted for publication in Astronomy and Astrophysic

Transfer of Company’s Registered Office and Forum-Shopping in International Insolvency Cases: an Important Decision from Italy

The Italian Supreme Court (Corte di Cassazione) has issued an important decision on companies’ freedom of establishment in the European Union (EU) and on jurisdiction over insolvency proceedings. It was a typical forum-shopping case in insolvency situations, in which a company decides to shift its registered office abroad before a court from its original country declares the insolvency. The Cassazione did not apply EC-Regulation 1346/2000 on cross-border insolvency, but declared the company as liquidated because of the transfer of the registered office. This solution leaves many questions unclear, both under EC-freedom of establishment and under jurisdiction rules for cross-border insolvenc

Detailed Chemical Abundances of Globular Clusters in Local Group Dwarf Galaxies

We present detailed chemical abundances of Fe, Ca and Ba for 17 globular clusters (GCs) in 5 Local Group dwarf galaxies: NGC 205, NGC 6822, WLM, the SMC and LMC. These abundances are part of a larger sample of over 20 individual elements measured in GCs in these galaxies using a new analysis method for high resolution, integrated light spectra. Our analysis also provides age and stellar population constraints. The existence of GCs in dwarf galaxies with a range of ages implies that there were episodes of rapid star formation throughout the history of these galaxies; the abundance ratios of these clusters suggest that the duration of these burst varied considerably from galaxy to galaxy. We find evolution of Fe, Ca, and Ba with age in the LMC, SMC, and NGC 6822 that is consistent with extended, lower-efficiency SF between bursts, with an increasing contribution of low-metallicity AGB ejecta at late times. Our sample of GCs in NGC 205 and WLM are predominantly old and metal-poor with high [Ca/Fe] ratios, implying that the early history of these galaxies was marked by consistently high SF rates.Comment: 2 pages, To appear in the proceedings of the conference "A Universe of Dwarf Galaxies" (Lyon, June 14-18, 2010

Optical variability of the ultraluminous X-ray source NGC 1313 X-2

We analyzed the longest phase-connected photometric dataset available for NGC 1313 X-2, looking for the ~6 day modulation reported by Liu et al. (2009). The folded B band light curve shows a 6 days periodicity with a significance slightly larger than 3 sigma. The low statistical significance of this modulation, along with the lack of detection in the V band, make its identification uncertain.Comment: 4 pages, 2 figures. Accepted for publication in the Astronomische Nachrichten (Astronomical Notes), to appear in the proceedings of the conference "Ultra-Luminous X-ray sources and Middle Weight Black Holes" (Madrid, May 24-26, 2010

The Potassium abundance in the globular clusters NGC104, NGC6752 and NGC6809

We derived Potassium abundances in red giant branch stars in the Galactic globular clusters NGC104 (144 stars), NGC6752 (134 stars) and NGC6809 (151 stars) using high-resolution spectra collected with FLAMES at the ESO - Very Large Telescope. In the considered samples we do not find significant intrinsic spreads in [K/Fe] (confirming the previous findings by Carretta et al.), at variance with the cases of the massive clusters NGC2419 and NGC2808. Additionally, marginally significant [K/Fe]-[O/Fe] anti-correlations are found in NGC104 and NGC6809, and [K/Fe]-[Na/Fe] correlations are found in NGC104 and NGC6752. No evidence of [K/Fe]-[Mg/Fe] anti-correlation are found. The results of our analysis are consistent with a scenario in which the process leading to the multi-populations in globular clusters implies also enrichment in the K abundance, the amplitude of the associated [K/Fe] enhancement becoming measurable only in stars showing the most extreme effects of O and Mg depletion. Stars enhanced in [K/Fe] have been found so far only in clusters harbouring some Mg-poor stars, while the other globulars, without a Mg-poor sub-population, show small or null [K/Fe] spreads.Comment: 9 pages, 7 figures, 3 tables, accepted for publication in A&

XMM-Newton detects the beginning of the X-ray decline of SN 1995N

We present the results of a new XMM-Newton observation of the interacting supernova 1995N, performed on July 27, 2003. We find that the 0.2-10.0 keV flux has dropt at a level of 1.44e-13 erg cm^-2 s^-1, about one order of magnitude lower than that of a previous ASCA observation performed on January 1998. The X-ray spectral analysis shows statistically significant evidence for the presence of two distinct components, that can be modeled with emission from optically thin, thermal plasmas at different temperatures. From these temperatures we derive that the exponent of the ejecta density distribution is n ~ 6.5.Comment: 3 pages, 2 figures. To appear in proceedings of the International Conference "1604-2004: Supernovae as Cosmological Lighthouses" (Padova, Italy, June 16-19, 2004), eds. M. Turatto, W. Shea, S. Benetti and L. Zampieri, ASP conference Serie