58 research outputs found
The most recent burst of Star Formation in the Massive Elliptical Galaxy NGC 1052
High-spatial resolution near-infrared (NIR) images of the central 24 x 24
arcsec^2 (~ 2 x 2 kpc^2) of the elliptical galaxy NGC 1052 reveal a total of 25
compact sources randomly distributed in the region. Fifteen of them exhibit
Halpha luminosities an order of magnitude above the estimate for an evolved
population of extreme horizontal branch stars. Their Halpha equivalent widths
and optical-to-NIR spectral energy distributions are consistent with them being
young stellar clusters aged < 7 Myr. We consider this to be the first direct
observation of spatially resolved star-forming regions in the central
kiloparsecs of an elliptical galaxy. The sizes of these regions are ~< 11 pc
and their median reddening is E(B - V) ~ 1 mag. According to previous works,
NGC 1052 may have experienced a merger event about 1 Gyr ago. On the assumption
that these clusters are spreaded with similar density over the whole galaxy,
the fraction of galaxy mass (5 x 10^{-5}) and rate of star formation (0.01
Msun/yr) involved, suggest the merger event as the possible cause for the star
formation we see today.Comment: 5 pages, 3 figures. Accepted for publication in MNRAS Letter
How peculiar is the ‘peculiar variable’ DZ Crucis (Nova Cru 2003)?
The variable star DZ Cru was thought to be a nova when it was discovered in eruption in 2003 August. This explanation was later challenged, however, when the first spectra of the object were reported. We present near-infrared spectroscopy of DZ Cru obtained at the New Technology Telescope on three occasions, starting ∼1.5 yr after outburst, with the aim of establishing the nature of the object. The spectra display H i, O i, [N i] emission lines, together with He i P Cygni lines superposed on a dust continuum. These observations suggest the ‘peculiar variable in Crux’ is a classical nova
The Large Magellanic Cloud and the Distance Scale
The Magellanic Clouds, especially the Large Magellanic Cloud, are places
where multiple distance indicators can be compared with each other in a
straight-forward manner at considerable precision. We here review the distances
derived from Cepheids, Red Variables, RR Lyraes, Red Clump Stars and Eclipsing
Binaries, and show that the results from these distance indicators generally
agree to within their errors, and the distance modulus to the Large Magellanic
Cloud appears to be defined to 3% with a mean value of 18.48 mag, corresponding
to 49.7 Kpc. The utility of the Magellanic Clouds in constructing and testing
the distance scale will remain as we move into the era of Gaia.Comment: 23 pages, accepted for publication in Astrophysics and Space Science.
From a presentation at the conference The Fundamental Cosmic Distance Scale:
State of the Art and the Gaia Perspective, Naples, May 201
Fast X-ray transients in the Galactic bulge with the Rossi X-ray Timing Explorer
In X-ray binaries, rapid variability in X-ray flux of greater than an order
of magnitude on time-scales of a day or less appears to be a signature of wind
accretion from a supergiant companion. When the variability takes the form of
rare, brief, bright outbursts with only faint emission between them, the
systems are called Supergiant Fast X-ray Transients (SFXTs). We present data
from twice-weekly scans of the Galactic bulge by the Rossi X-ray Timing
Explorer (RXTE) that allow us to compare the behaviour of known SFXTs and
possible SFXT candidates with the persistently bright supergiant X-ray binary
4U 1700-377. We independently confirm the orbital periods reported by other
groups for SFXTs SAX J1818.6-1703 and IGR J17544-2619. The new data do not
independently reproduce the orbital period reported for XTE J1739-302, but
slightly improve the significance of the original result when the data are
combined. The bulge source XTE J1743-363 shows a combination of fast
variability and a long-term decline in activity, the latter behaviour not being
characteristic of supergiant X-ray binaries. A far-red spectrum of the
companion suggests that it is a symbiotic neutron star binary rather than a
high-mass binary, and the reddest known of this class: the spectral type is
approximately M8 III.Comment: 15 pages, 16 figures, 5 tables, accepted for publication in Monthly
Notices of the Royal Astronomical Societ
Investigation of Adhesion and Tribological Behavior of Borided AISI 310 Stainless Steel
In the present study, the effects of the boriding process on adhesion and tribological properties of AISI 310 steel were investigated. Boriding was performed in a solid medium consisting of Ekabor-II powders at 1123 and 1323K for 2 and 6 h. The boride layer was characterized by optical microscopy, the X-ray diffraction technique and the micro-Vickers hardness tester. The X-ray diffraction analysis of the boride layers on the surface of the steels revealed the existence of FexBy, CrxBy and NixBy compounds. Depending on the chemical composition of substrates, the boride layer thickness on the surface of the AISI 310 steel was found to be 56.74 μm. The hardness of the boride compounds formed on the surface of the AISI 310 steel ranged from 1658 to 2284 HV0,1, whereas the Vickers hardness value of the untreated steel AISI 310 was 276 HV0,1. The wear tests were carried out in a ball-disc arrangement under a dry friction condition at room temperature with an applied load of 10N and with a sliding speed of 0.3 m/s, at a sliding distance of 1000m. The wear surfaces of the steel were analyzed using an SEM microscopy and X-ray energy dispersive spectroscopy EDS. It was observed that the wear rate of unborided and borided AISI 310 steel ranged from 4.57 to 71.42 mm3/Nm
Gölcük Gölü (Isparta) Kuşları
Türkiye floristik ve faunistik açıdan zengin bir ülkedir. Ülkemizin bu zenginliği; dört farklı denizle (Karadeniz, Ege Denizi, Marmara Denizi ve Akdeniz) çevrelenmesi, iklimsel çeşitliliğin görülmesi, önemli iki kuş göç yolu üzerinde bulunması, bazı türlerin gen merkezi olması, sulak alanların fazla oluşu, farklı topoğrafik özelliklere sahip olmasından kaynaklanmaktadır. Ülkemiz, yaklaşık 1.000.000 hektar ve 250'nin üzerinde farklı sulak alana sahiptir. Göller Bölgesi; Beyşehir, Burdur, Eğirdir ve Kovada gölleri başta olmak üzere bir çok göl ve sulak alan barındırmaktadır. Göller Bölgesinde yer alan Gölcük Gölü ise flora, fauna ve peyzaj özelliği nedeniyle 1991 yılında Tabiat Parkı (6684 ha) haline getirilmiştir. 2001-2002 yılları arasında Gölcük Gölü'nde gerçekleştirilen bu çalışmada 12 takım ve 29 familyaya ait 90 kuş türü tespit edilmiştir. Türlerin 37'si yerli, 30'u yaz göçmeni, 10'i kış göçmeni ve 13'ü transit göçerdir. Uluslararası koruma statüsüne (the International Union for the Conservation of Nature=IUCN) göre tehlike altında tür bulunmamaktadır. Ayrıca Kiziroğlu'na [1] göre; büyük tehlike altında 1, ciddi tehlike altında 6, tehlike altında 10 ve potansiyel tehlike altında olan 14 tür yer almaktadır
Cytogenetic and molecular responses of ammonium sulphate application for tolerance to extreme temperatures in Vicia faba L.
Effects of ammonium sulphate [(NH4)(2)SO4] on mitosis, cell cycle and chromosomes in Vicia faba L. seeds exposed to extreme temperatures were investigated using flowcytometric and cytogenetic analysis. Seeds germinated at high and low temperatures showed a significant decrease in mitotic index as compared to those of optimum temperature conditions. Application of 50 and 1000 mu M (NH4)(2)SO4 were successful in alleviating the negative effects of low and high temperature on mitotic activity, respectively. 50 mu M (NH4)(2)SO4 showed the most positive effect on cell cycle at the extreme temperatures. This concentration increased the cell division removing or decreasing the negative effects of temperature stress. Namely, the highest G2/M and S phase percentages under stress conditions were obtained with application of 50 mu M (NH4)(2)SO4. Chromosomal aberrations were not observed in cells of seeds germinated in distilled water and also at any temperatures. However, the frequency of chromosomal aberrations increased significantly by increasing (NH4)(2)SO4 concentration. The highest aberration frequency in all temperature degree tested was found at 1000 mu M (NH4)(2)SO4 concentration.Department of Scientific Research Project Management of Suleyman Demirel University (SDUBAP)Suleyman Demirel University [1636-YL-08]The authors thank the Department of Scientific Research Project Management of Suleyman Demirel University (SDUBAP) for the financial support of the project SDUBAP (1636-YL-08). Thanks also to Dr. Gulderen Yanikkaya DEMIREL and Mehtap OZDEMIR (Istanbul Centro Laboratory Flowcytometry Department, Istanbul, Turkey) for its help in flow cytometric study
Cytogenetic and molecular responses of ammonium sulphate application for tolerance to extreme temperatures in Vicia faba L.
Effects of ammonium sulphate [(NH4)(2)SO4] on mitosis, cell cycle and chromosomes in Vicia faba L. seeds exposed to extreme temperatures were investigated using flowcytometric and cytogenetic analysis. Seeds germinated at high and low temperatures showed a significant decrease in mitotic index as compared to those of optimum temperature conditions. Application of 50 and 1000 mu M (NH4)(2)SO4 were successful in alleviating the negative effects of low and high temperature on mitotic activity, respectively. 50 mu M (NH4)(2)SO4 showed the most positive effect on cell cycle at the extreme temperatures. This concentration increased the cell division removing or decreasing the negative effects of temperature stress. Namely, the highest G2/M and S phase percentages under stress conditions were obtained with application of 50 mu M (NH4)(2)SO4. Chromosomal aberrations were not observed in cells of seeds germinated in distilled water and also at any temperatures. However, the frequency of chromosomal aberrations increased significantly by increasing (NH4)(2)SO4 concentration. The highest aberration frequency in all temperature degree tested was found at 1000 mu M (NH4)(2)SO4 concentration.Department of Scientific Research Project Management of Suleyman Demirel University (SDUBAP)Suleyman Demirel University [1636-YL-08]The authors thank the Department of Scientific Research Project Management of Suleyman Demirel University (SDUBAP) for the financial support of the project SDUBAP (1636-YL-08). Thanks also to Dr. Gulderen Yanikkaya DEMIREL and Mehtap OZDEMIR (Istanbul Centro Laboratory Flowcytometry Department, Istanbul, Turkey) for its help in flow cytometric study
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