A Multiwavelength Study of Evolved Massive Stars in the Galactic Center

The central region of the Milky Way provides a unique laboratory for a systematic, spatially-resolved population study of evolved massive stars of various types in a relatively high metallicity environment. We have conducted a multi-wavelength data analysis of 180 such stars or candidates, most of which were drawn from a recent large-scale HST/NICMOS narrow-band Pa-a survey, plus additional 14 Wolf-Rayet stars identified in earlier ground-based spectroscopic observations of the same field. The multi-wavelength data include broad-band IR photometry measurements from HST/NICMOS, SIRIUS, 2MASS, Spitzer/IRAC, and Chandra X-ray observations. We correct for extinctions toward individual stars, improve the Pa-a line equivalent width measurements, quantify the substantial mid-IR dust emission associated with WC stars, and find X-ray counterparts. In the process, we identify 10 foreground sources, some of which may be nearby cataclysmic variables. The WN stars in the Arches and Central clusters show correlations between the Pa-a equivalent width and the adjacent continuum emission. However, the WN stars in the latter cluster are systematically dimmer than those in the Arches cluster, presumably due to the different ages of the two clusters. In the EW-magnitude plot, WNL stars, WC stars and OB supergiants roughly fall into three distinct regions. We estimate that the dust mass associated with individual WC stars in the Quintuplet cluster can reach 1e-5 M, or more than one order of magnitude larger than previous estimates. Thus WC stars could be a significant source of dust in the galaxies of the early universe. Nearly half of the evolved massive stars in the GC are located outside the three known massive stellar clusters. The ionization of several compact HII regions can be accounted for by their enclosed individual evolved massive stars, which thus likely formed in isolation or in small groups.Comment: Accepted for publication in MNRA

X-RED: A Satellite Mission Concept To Detect Early Universe Gamma Ray Bursts

Gamma ray bursts (GRBs) are the most energetic eruptions known in the Universe. Instruments such as Compton-GRO/BATSE and the GRB monitor on BeppoSAX have detected more than 2700 GRBs and, although observational confirmation is still required, it is now generally accepted that many of these bursts are associated with the collapse of rapidly spinning massive stars to form black holes. Consequently, since first generation stars are expected to be very massive, GRBs are likely to have occurred in significant numbers at early epochs. X-red is a space mission concept designed to detect these extremely high redshifted GRBs, in order to probe the nature of the first generation of stars and hence the time of reionisation of the early Universe. We demonstrate that the gamma and x-ray luminosities of typical GRBs render them detectable up to extremely high redshifts (z~10-30), but that current missions such as HETE2 and SWIFT operate outside the observational range for detection of high redshift GRB afterglows. Therefore, to redress this, we present a complete mission design from the science case to the mission architecture and payload, the latter comprising three instruments, namely wide field x-ray cameras to detect high redshift gamma-rays, an x-ray focussing telescope to determine accurate coordinates and extract spectra, and an infrared spectrograph to observe the high redshift optical afterglow. The mission is expected to detect and identify for the first time GRBs with z > 10, thereby providing constraints on properties of the first generation of stars and the history of the early Universe.Comment: 14 pages, 10 figures, spie.cls neede

Моделирование уравнений проекционного осциллографирования на машине "ЭМУ-10"

The passive-alignment-packaging technique presented in this work provides a method for mounting tolerance-insensitive optical components e.g. non-linear crystals by means of mechanical stops. The requested tolerances for the angle deviation are ±100 µrad and for the position tolerance ±100 µm. Only the angle tolerances were investigated, because they are more critical. The measurements were carried out with an autocollimator. Fused silica components were used for test series. A solder investigation was carried out. Different types of solder were tested. Due to good solderability on air and low induced stress in optical components, Sn based solders were indicated as the most suitable solders. In addition several concepts of reflow soldering configuration were realized. In the first iteration a system with only the alignment of the yaw angle was implemented. The deviation for all materials after the thermal and mechanical cycling was within the tolerances. The solderability of BBO and LBO crystals was investigated and concepts for mounting were developed

О необходимости прослеживания Балейско-Дарасунского разлома в пределах Борщевочного кряжа

In this paper we present the development of a compact, thermo-optically stable and vibration and mechanical shock resistant mounting technique by soldering of optical components. Based on this technique a new generation of laser sources for aerospace applications is designed. In these laser systems solder technique replaces the glued and bolted connections between optical component, mount and base plate. Alignment precision in the arc second range and realization of long term stability of every single part in the laser system is the main challenge. At the Fraunhofer Institute for Laser Technology ILT a soldering and mounting technique has been developed for high precision packaging. The specified environmental boundary conditions (e.g. a temperature range of -40 °C to +50 °C) and the required degrees of freedom for the alignment of the components have been taken into account for this technique. In general the advantage of soldering compared to gluing is that there is no outgassing. In addition no flux is needed in our special process. The joining process allows multiple alignments by remelting the solder. The alignment is done in the liquid phase of the solder by a 6 axis manipulator with a step width in the nm range and a tilt in the arc second range. In a next step the optical components have to pass the environmental tests. The total misalignment of the component to its adapter after the thermal cycle tests is less than 10 arc seconds. The mechanical stability tests regarding shear, vibration and shock behavior are well within the requirements

Некоторые результаты применения метода геометрического анализа дизъюнктов для поисков смещенного крыла пласта в Прокопьевском районе Кузбасса

In this paper we present the development of a compact, thermo-optically stable and vibration and mechanical shock resistant mounting technique by soldering of optical components. Based on this technique, new generations of laser pump sources for aerospace applications are designed. In these laser systems the used soldering technique replaces the glued connection between the optical component and its join partner. The main challenges are the alignment accuracy in the arc second range and the realization of the long term stability of every single part in the laser system (e.g. resonator mirrors)

Pressure-induced structural change in liquid GaIn eutectic alloy

Synchrotron x-ray diffraction reveals a pressure induced crystallization at about 3.4 GPa and apolymorphic transition near 10.3 GPa when compressed a liquid GaIn eutectic alloy up to ~13 GPa atroom temperature in a diamond anvil cell. Upon decompression, the high pressure crystalline phaseremains almost unchanged until it transforms to the liquid state at around 2.3 GPa. The ab initiomolecular dynamics calculations can reproduce the low pressure crystallization and give some hints onthe understanding of the transition between the liquid and the crystalline phase on the atomic level.The calculated pair correlation function g(r) shows a non-uniform contraction reflected by the differentcompressibility between the short (1st shell) and the intermediate (2nd to 4th shells). It is concludedthat the pressure-induced liquid-crystalline phase transformation likely arises from the changes in localatomic packing of the nearest neighbors as well as electronic structures at the transition pressure

Universal phase transitions of B1 structured stoichiometric transition-metal carbides

The high-pressure phase transitions of B1-structured stoichiometric transition metal carbides (TMCs, TM=Ti, Zr, Hf, V, Nb, and Ta) were systematically investigated using ab initio calculations. These carbides underwent universal phase transitions along two novel phase-transition routes, namely, B1\rightarrowdistorted TlI (TlI')\rightarrowTlI and/or B1\rightarrowdistorted TiB (TiB')\rightarrowTiB, when subjected to pressures. The two routes can coexist possibly because of the tiny enthalpy differences between the new phases under corresponding pressures. Four new phases result from atomic slips of the B1-structured parent phases under pressure. After completely releasing the pressure, taking TiC as a representative of TMCs, only its new TlI'-type phase is mechanically and dynamically stable, and may be recovered.Comment: [email protected]

Stellar Populations in the Galactic Center

We discuss the stellar content of the Galactic Center, and in particular, recent estimates of the star formation rate (SFR). We discuss pros and cons of the different stellar tracers and focus our attention on the SFR based on the three classical Cepheids recently discovered in the Galactic Center. We also discuss stellar populations in field and cluster stars and present some preliminary results based on near-infrared photometry of a field centered on the young massive cluster Arches. We also provide a new estimate of the true distance modulus to the Galactic Center and we found 14.49$\pm$0.02(standard)$\pm$0.10(systematic) mag (7.91$\pm0.08\pm0.40$ kpc). Current estimate agrees quite well with similar photometric and kinematic distance determinations available in the literature. We also discuss the metallicity gradient of the thin disk and the sharp change in the slope when moving across the edge of the inner disk, the Galactic Bar and the Galactic Center. The difference becomes even more compelling if we take into account that metal abundances are based on young stellar tracers (classical Cepheids, Red Supergiants, Luminous Blue Variables). Finally, we briefly outline the possible mechanisms that might account for current empirical evidence.Comment: To be published in the Astrophysics and Space Science Proceeding

On the nature of the galactic early-B hypergiants

Despite their importance to a number of astrophysical fields, the lifecycles of very massive stars are still poorly defined. In order to address this shortcoming, we present a detailed quantitative study of the physical properties of four early-B hypergiants (BHGs); Cyg OB2 #12, zeta Sco, HD190603 and BP Cru. These are combined with an analysis of their long-term spectroscopic and photometric behaviour in order to determine their evolutionary status. The long-term datasets revealed that they are remarkably stable over long periods (>40yr), with the possible exception of zeta Sco prior to the 20th century, in contrast to the typical excursions that characterise luminous blue variables (LBVs). Zeta Sco, HD190603 and BP Cru possess physical properties intermediate between B supergiants and LBVs; we therefore suggest that BHGs are the immediate descendants and progenitors (respectively) of such stars (for initial masses in the range ~30-60Msun). In contrast, while the wind properties of Cyg OB2 #12 are consistent with this hypothesis, the combination of extreme luminosity and spectroscopic mass (~110Msun) and comparatively low temperature means it cannot be accommodated in such a scheme. Likewise, despite its co-location with several LBVs above the Humphreys-Davidson (HD) limit, the lack of long term variability and its unevolved chemistry apparently excludes such an identification. Since such massive stars are not expected to evolve to such cool temperatures, the properties of Cyg OB2 #12 are difficult to understand under current evolutionary paradigms. [ABRIDGED]Comment: 36 pages, 19 figures (of which 17 pages are online supplemental material). Accepted for publication in Astronomy and Astrophysic

Pargasite at high pressure and temperature

The P-T phase stability field, the thermoelastic behavior and the P-induced deformation mechanisms at the atomic scale of pargasite crystals, from the "phlogopite peridotite unit" of the Finero mafic-ultramafic complex (Ivrea-Verbano Formation, Italy), have been investigated by a series of in situ experiments: (a) at high pressure (up to 20.1 GPa), by single-crystal synchrotron X-ray diffraction with a diamond anvil cell, (b) at high temperature (up to 823 K), by powder synchrotron X-ray diffraction using a hot air blower device, and (c) at simultaneous HP-HT conditions, by single-crystal synchrotron X-ray diffraction with a resistive-heated diamond anvil cell (Pmax = 16.5 GPa, Tmax = 1200 K). No phase transition has been observed within the P-T range investigated. At ambient T, the refined compressional parameters, calculated by fitting a second-order Birch-Murnaghan Equation of State (BM-EoS), are: V0 = 915.2(8) \uc53 and KP0,T0 = 95(2) GPa (\u3b2P0,T0 = 0.0121(2) GPa-1) for the unit-cell volume; a0 = 9.909(4) \uc5 and K(a)P0,T0 = 76(2) GPa for the a-axis; b0 = 18.066(7) \uc5 and K(b)P0,T0 = 111(2) GPa for the b-axis; c0 = 5.299(5) \uc5 and K(c)P0,T0 = 122(12) GPa for the c-axis [K(c)P0,T0 ~ K(b)P0,T0 > K(a)P0,T0]. The high-pressure structure refinements (at ambient T) show a moderate contraction of the TO4 double chain and a decrease of its bending in response to the hydrostatic compression, along with a pronounced compressibility of the A- and M(4)-polyhedra [KP0,T0(A) = 38(2) GPa, KP0,T0(M4) = 79(5) GPa] if compared to the M(1)-, M(2)-, M(3)-octahedra [KP0,T0(M1,2,3) 64 120 GPa] and to the rigid tetrahedra [KP0,T0(T1,T2) ~ 300 GPa]. The thermal behavior, at ambient pressure up to 823 K, was modelled with Berman's formalism, which gives: V0 = 909.1(2) \uc53, \u3b10 = 2.7(2)*10-5 K-1 and \u3b11 = 1.4(6)*10-9 K-2 [with \u3b10(a) = 0.47(6)*10-5 K-1, \u3b10(b) = 1.07(4)*10-5 K-1, and \u3b10(c) = 0.97(7)*10-5 K-1]. The petrological implications for the experimental findings of this study are discussed