ALBERT

Description: We performed spectroscopy of five luminous blue variable (LBV) candidates and two known LBV stars (AE And and Var A-1) in M31. We obtained the same-epoch near-infrared (NIR) and optical spectra of these stars. The NIR spectra were taken with the Triplespec spectrograph at the 3.5-m telescope at the Apache Point Observatory, and the optical spectroscopy was carried out using the SCORPIO focal reducer at the 6-m BTA telescope (Special Astrophysical Observatory of the Russian Academy of Science). The candidates demonstrate typical LBV features in their spectra: broad and strong hydrogen lines, and He i , Fe ii and [Fe ii ] lines. All our candidates show photometric variability. We develop a new approach to the estimation of LBV parameters based on the inherent property of LBVs to change their spectral type at constant bolometric luminosity. We compare the spectral energy distributions of the variable stars obtained in two or more different states, and we estimate the temperatures, reddening, radii and luminosities of the stars using this method. Two considered candidates (J004526.62+415006.3 and J004051.59+403303.0) have to be classified as new LBV stars. Two more candidates are, apparently, B[e] supergiants. The nature of one more star (J004350.50 + 414611.4) is not clear. It does not show obvious LBV-like variability and remains an LBV candidate.

Description: Fitness landscapes depict how genotypes manifest at the phenotypic level and form the basis of our understanding of many areas of biology, yet their properties remain elusive. Previous studies have analysed specific genes, often using their function as a proxy for fitness, experimentally assessing the effect on function of single mutations and their combinations in a specific sequence or in different sequences. However, systematic high-throughput studies of the local fitness landscape of an entire protein have not yet been reported. Here we visualize an extensive region of the local fitness landscape of the green fluorescent protein from Aequorea victoria (avGFP) by measuring the native function (fluorescence) of tens of thousands of derivative genotypes of avGFP. We show that the fitness landscape of avGFP is narrow, with 3/4 of the derivatives with a single mutation showing reduced fluorescence and half of the derivatives with four mutations being completely non-fluorescent. The narrowness is enhanced by epistasis, which was detected in up to 30% of genotypes with multiple mutations and mostly occurred through the cumulative effect of slightly deleterious mutations causing a threshold-like decrease in protein stability and a concomitant loss of fluorescence. A model of orthologous sequence divergence spanning hundreds of millions of years predicted the extent of epistasis in our data, indicating congruence between the fitness landscape properties at the local and global scales. The characterization of the local fitness landscape of avGFP has important implications for several fields including molecular evolution, population genetics and protein design.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Sarkisyan, Karen S -- Bolotin, Dmitry A -- Meer, Margarita V -- Usmanova, Dinara R -- Mishin, Alexander S -- Sharonov, George V -- Ivankov, Dmitry N -- Bozhanova, Nina G -- Baranov, Mikhail S -- Soylemez, Onuralp -- Bogatyreva, Natalya S -- Vlasov, Peter K -- Egorov, Evgeny S -- Logacheva, Maria D -- Kondrashov, Alexey S -- Chudakov, Dmitry M -- Putintseva, Ekaterina V -- Mamedov, Ilgar Z -- Tawfik, Dan S -- Lukyanov, Konstantin A -- Kondrashov, Fyodor A -- 55007424/Howard Hughes Medical Institute/ -- England -- Nature. 2016 May 11;533(7603):397-401. doi: 10.1038/nature17995.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Miklukho-Maklaya 16/10, 117997 Moscow, Russia. ; Nizhny Novgorod State Medical Academy, Minin Sq. 10/1, 603005 Nizhny Novgorod, Russia. ; Central European Institute of Technology, Masaryk University, Brno 62500, Czech Republic. ; Bioinformatics and Genomics Programme, Centre for Genomic Regulation (CRG), The Barcelona Institute of Science and Technology, 88 Dr. Aiguader, 08003 Barcelona, Spain. ; Universitat Pompeu Fabra (UPF), 08003 Barcelona, Spain. ; Moscow Institute of Physics and Technology, Institutskiy Pereulok 9, g.Dolgoprudny 141700, Russia. ; Faculty of Medicine, Moscow State University, Lomonosov Avenue 31/5, Moscow 119192, Russia. ; Laboratory of Protein Physics, Institute of Protein Research of the Russian Academy of Sciences, 4 Institutskaya Str., Pushchino, Moscow Region 142290, Russia. ; Pirogov Russian National Research Medical University, Ostrovitianov 1, Moscow 117997, Russia. ; A. A. Kharkevich Institute for Information Transmission Problems, Russian Academy of Sciences, Moscow 127051, Russia. ; Department of Bioinformatics and Bioengineering, Moscow State University, Moscow 119234, Russia. ; Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan 48109, USA. ; Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel. ; Institucio Catalana de Recerca i Estudis Avancats (ICREA), 23 Pg. Lluis Companys, 08010 Barcelona, Spain.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/27193686" target="_blank"〉PubMed〈/a〉

Description: MN112 is a Galactic luminous blue variable (LBV) candidate with a circumstellar nebula. P Cygni was the first LBV discovered, and was recorded during major eruptions in the 17th century. The stars have similar spectra with strong emission hydrogen lines, He i, N ii, Si ii, and Fe iii lines. We present the results of spectroscopic analysis and modelling of MN112 spectra. We obtained the main stellar parameters and chemical abundances of MN112 and compared them with those of P Cygni. Atmosphere models were calculated using the non-local thermodynamic equilibrium radiative transfer code cmfgen. We have used spectra of MN112 obtained with the 3.5-m telescope at the Observatory of Calar Alto and 3.5-m ARC telescope at the Apache Point Observatory. P Cygni spectra were taken with the 6-m BTA telescope. We have found the best fit of the observed spectrum with the model at temperature $T_{ext{eff}}= 15, 200$ K, clumping-corrected mass-loss rate $dot{M}f^{-0.5}=5.74 imes 10^{-5}, mathrm{M}_{odot }ext{yr}^{-1}$, filling factor f = 0.1, luminosity $L=5.77 imes 10^5, mathrm{L}_{odot }$ for MN112. The ratio of helium to hydrogen He/H is 0.27 (by the number of atoms) with nitrogen overabundance (XN/X⊙ = 6.8) and an underabundance of carbon (XC/X⊙ 〈 0.1).

Description: We study five luminous blue variable (LBV) candidates in the Andromeda galaxy and one more (MN112) in the Milky Way. We obtain the same-epoch near-infrared (NIR) and optical spectra on the 3.5-m telescope at the Apache Point Observatory and on the 6-m telescope of the SAO RAS. The candidates show typical LBV features in their spectra: broad and strong hydrogen lines, He i, Fe ii, and [Fe ii] lines. We estimate the temperatures, reddening, radii and luminosities of the stars using their spectral energy distributions. Bolometric luminosities of the candidates are similar to those of known LBV stars in the Andromeda galaxy. One candidate, J004341.84+411112.0, demonstrates photometric variability (about 0.27 mag in the V band), which allows us to classify it as an LBV. The star J004415.04+420156.2 shows characteristics typical of B[e] supergiants. The star J004411.36+413257.2 is classified as a Fe ii star. We confirm that the stars J004621.08+421308.2 and J004507.65+413740.8 are warm hypergiants. We obtain for the first time the NIR spectrum of the Galactic LBV candidate MN112. We use both optical and NIR spectra of MN112 for comparison with similar stars in M31 and notice identical spectra and the same temperature in J004341.84+411112.0. This allows us to confirm that MN112 is an LBV, which should show its brightness variability in longer time span observations.

Description: We search for luminous blue variable (LBV) stars in galaxies outside the Local Group. Here we present a study of two bright Hα sources in the NGC 247 galaxy. Object j004703.27–204708.4 (MV = −9.08 ± 0.15 mag) shows the spectral lines typical for well-studied LBV stars: broad and bright emission lines of hydrogen and helium He i with P Cyg profiles, emission lines of iron Fe ii, silicon Si ii, nitrogen N ii and carbon C ii, forbidden iron [Fe ii] and nitrogen [N ii] lines. The variability of the object is ΔB = 0.74 ± 0.09 mag and ΔV = 0.88 ± 0.09 mag, which makes it a reliable LBV candidate. The star j004702.18–204739.93 (MV = −9.66 ± 0.23 mag) shows many emission lines of iron Fe ii, forbidden iron lines [Fe ii], bright hydrogen lines with broad wings, and also forbidden lines of oxygen [O i] and calcium [Ca ii] formed in the circumstellar matter. The study of the light curve of this star did not reveal significant variations in brightness (ΔV = 0.29 ± 0.09 mag). We obtained estimates of interstellar absorption, the photosphere temperature, as well as bolometric magnitudes $M_ext{bol}=-10.5^{+0.5}_{-0.4}$ and $M_ext{bol}=-10.8^{+0.5}_{-0.6}$, which correspond to bolometric luminosities $log (L_ext{bol}/{ m L}_{odot })=6.11^{+0.20}_{-0.16}$ and $6.24^{+0.20}_{-0.25}$ for j004703.27–204708.4 and j004702.18–204739.93, respectively. Thus, the object j004703.27–204708.4 remains a reliable LBV candidate, while the object j004702.18–204739.93 can be classified as a B[e]-supergiant.

Description: We continue to search for LBV stars in galaxies outside the Local Group. In this work, we have investigated four luminous stars in NGC 4449. Multiple spectral observations carried out for J122810.94+440540.6, J122811.70+440550.9, and J122809.72+440514.8 revealed the emission features in their spectra that are characteristic of LBVs. Photometry showed noticeable brightness changes of J122809.72+440514.8 (ΔI = 0.69 ± 0.13m) and J122817.83+440630.8 (ΔR = 2.15 ± 0.13m), while the variability of J122810.94+440540.6 and J122811.70+440550.9 does not exceed 0.3m regardless of the filter. We have obtained estimates of the interstellar reddening, photosphere temperatures, and bolometric luminosities log (LBol/L⊙) ≈ 5.24–6.42. Using the cmfgen code, we have modelled the spectrum of the cold state of J122809.72+440514.8 ($T_{ext{eff}}=9300,$ K) and have obtained possible value of the mass-loss rate $dot{M} = 5.2imes 10^{-3}, mathrm{M}_{odot }, mathrm{yr}^{-1}$. Based on the observational properties, J122809.72+440514.8 and J122817.83+440630.8 were classified as LBVs, while the other two stars were classified as LBV candidates or B[e]-supergiants candidates.