180,598 research outputs found
Faint galactic X-ray binaries
No full textWe present a short overview of the properties of faint Galactic X‐ray binaries. We place emphasis on current classification scenarios. One of the important parameters for the faint sources is their intrinsic luminosity. In the case of low‐mass X‐ray binaries it has recently been realised that besides a phase of radius expansion, the duration of type I X‐ray bursts can be used as a primer for the source luminosity in some cases. Further, we show that a very low equivalent width of hydrogen and helium emission lines in the optical spectrum alone is not a tell‐tale sign for an ultra‐compact system. Finally, we list and discuss some unusual sources that could be X‐ray binaries
Searching for managerial opportunism faint traces in French diversifying acquisitions
No full textWe are looking for traces of managerial opportunism in french diversifyingacquisitions. Indeed, following various theories, diversification is seeking by managers.Furthermore, recent empiric evidences show that corporate diversification is valuedestructive for shareholders. Using classical OLS methodology with diversification,management ownership and performance variables, we find some evidence of managerialopportunism. But classical methodology presents two shortages. First, it supposed a uniquesense of causality. In particular, firm diversification is supposed to impact firmperformance without considering the inverse relationship (from performance todiversification). This one-way analysis can create biases in the estimated results. Second,this OLS methodology doesn't permit to take simultaneously the relationship between ourvariables. Noticing that this classical methodology is not well adapted to the problem, wesubmit our data to a system of simultaneous equations. Using this system, according to usbetter adapted, the faint traces of managerial opportunism vanishes. This is the case inparticular because the negative impact of diversification on performance disappears whenwe consider a non recursive relation between the variables. We derive others surprisingresults from our simultaneaous equations framework. Management stake in the equity caninfluence or be influenced by the performance depending on wether the performance ismeasured at the firm or at the operation (acquisition) level. Together, these results suggestthat we have to be cautious when searching for managerial opportunism in sample andstatistical studies. If manager opportunist inclination can be suspected in this kind ofstudies, it has to be distinguished from manager opportunist behavior which is far moredifficult to exhibit.managerial opportunism;acquisition;corporate diversification;agence;performance
The development of a detector system for mint object spectroscopy on the Isaac Newton telescope
No full textThe work reported in this thesis describes the development of the CCD instrumentation for the Faint Object Spectrograph on the 2.5m Isaac Newton Telescope at the Observatorio del Roque de los Muchachos, more commonly known as the La Palma Observatory. The Faint Object Spectrograph is a highly efficient, fixed-format CCD spectrograph aimed at low resolution spectrophotometry (15-20 A FWHM) over a wide spectral range (400-1050 nm). Its high throughput, compared with that of more conventional spectrographs, is due to the small number of optical surfaces, and the minimum vignetting which results from, locating the CCD inside the spectrograph camera. A CCD camera system is described which was developed primarily to test and commission the Faint Object Spectrograph, but also to assess the characteristics of the GEC P8603 CCD used In the spectrograph, and optimize its performance for this application. The use of CCDs in astronomy is now commonplace but there still remains some uncertainty as to which aspects of their performance need to be most critically assessed when choosing a device for a particular application. It is argued that it is important to consider not only the obvious characteristics such as quantum efficiency, spectral coverage, readout noise and geometrical format, but also, and particularly at astronomically relevant low-light levels, the consequences of the more subtle properties such as charge transfer efficiency, threshold effects and chip defects. The CCD detector in the Faint Object Spectrograph is located inside the spectrograph camera and needs to be positioned to high accuracy within the optical path. A microprocessor system is described which enables the CCD detector to be aligned remotely from the observer's control console. Finally, the commissioning of the Faint Object Spectrograph on the Isaac Newton Telescope is described, and some of the first results obtained during commissioning are presented in order to illustrate its potential in the field of faint object spectroscopy
Faint lines in the arc spectrum of iron (FeI)
No full textA search for new faint iron lines has been made on spectrograms taken with an arc-in-air as source. The range of observations is from 2102 to 8679 A. The reciprocal dispersion of the spectrographs used for the various spectral regions varies from 1A/mm to 3A/mm. Twelve new energy levels have been found, resulting in a total of 121 classified lines. A table containing 698 classified lines includes many lines whose wavelengths had been predicted as combinations among the known energy levels, and found in the solar spectrum in earlier work. Their Reality has been confirmed in the present work. A list containing 1,102 newly measured unclassified lines is included. Many of the lines listed in the tables have been reported by other observers with varying degrees of accuracy. All such reference sources are indicated in the tables. As a result of the new measurements, these lines may safely be attributed to Fe I. A comparison of the new lines with the solar spectrum has resulted in the identification of 306 solar lines of Fe I unblended, and of 85 as blends to which Fe I is a contributor
Chemical abundances in the multiple sub-giant branch of 47 Tucanae: Insights on its faint sub-giant branch component
No full textThe globular cluster 47 Tuc exhibits a complex sub-giant branch (SGB) with a faint-SGB comprising only about the 10 per cent of the cluster mass and a bright-SGB hosting at least two distinct populations. We present a spectroscopic analysis of 62 SGB stars including 21 faint-SGB stars. We thus provide the first chemical analysis of the intriguing faint-SGB population and compare its abundances with those of the dominant populations. We have inferred abundances of Fe, representative light elements C, N, Na, and Al, alpha elements Mg and Si for individual stars. Oxygen has been obtained by co-adding spectra of stars on different sequences. In addition, we have analysed 12 stars along the two main RGBs of 47 Tuc. Our principal results are (i) star-to-star variations in C/N/Na among RGB and bright-SGB stars; (ii) substantial N and Na enhancements for the minor population corresponding to the faint-SGB; (iii) no high enrichment in C+N+O for faint-SGB stars. Specifically, the C+N+O of the faint-SGB is a factor of 1.1 higher than the bright-SGB, which, considering random (+/- 1.3) plus systematic errors (+/- 0.3), means that their C+N+O is consistent within observational uncertainties. However, a small C+N+O enrichment for the faint-SGB, similar to what predicted on theoretical ground, cannot be excluded. The N and Na enrichment of the faint-SGB qualitatively agrees with this population possibly being He-enhanced, as suggested by theory. The iron abundance of the bright and faint-SGB is the same to a level of similar to 0.10 dex, and no other significant difference for the analysed elements has been detected
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Hot DAVs: a probable new class of pulsating white dwarf stars
No full textWe have discovered a pulsating DA white dwarf at the lower end of the temperature range 45 000–30 000 K where a few helium atmosphere white dwarfs are known. There are now three such pulsators known, suggesting that a new class of theoretically predicted pulsating white dwarf stars exists. We name them the hot DAV stars. From high-speed photometric observations with the ULTRACAM photometer on the 4.2-m William Herschel Telescope, we show that the hydrogen atmosphere white dwarf star WD1017−138 pulsates in at least one mode with a frequency of 1.62 mHz (a period of 624 s). The amplitude of that mode was near 1 mmag at a 10σ confidence level on one night of observation and an 8.4σ confidence level on a second night. The combined data have a confidence level of 11.8σ. This supports the two other detections of hot DAV stars previously reported. From three Very Large Telescope Ultraviolet and Visual Echelle Spectrograph spectra we confirm also that WD1017−138 is a hydrogen atmosphere white dwarf with no trace of helium or metals with Teff = 32 600 K, log g = 7.8 (cgs) and M = 0.55 M⊙. The existence of pulsations in these DA white dwarfs at the cool edge of the 45 000–30 000 K temperature range supports the thin hydrogen layer model for the deficit of helium atmosphere white dwarfs in this range. DA white dwarfs with thick hydrogen layers do not have the superadiabatic, chemically inhomogeneous (μ-gradient) zone that drives pulsation in this temperature range. The potential for higher amplitude hot DAV stars exists; their discovery would open the possibility of a direct test of the explanation for the deficit of helium atmosphere white dwarfs at these temperatures by asteroseismic probing of the atmospheric layers of the hot DAV stars. A search for pulsation in a further 22 candidates with ULTRACAM on the European Southern Observatory New Technology Telescope gave null results for pulsation at precisions in the range 0.5–3 mmag, suggesting that the pulsation amplitudes in such stars are relatively low, hence near the detection limit with the ground-based telescopes used in the survey
The GLARE Survey - II. Faint z 6 Ly line emitters in the HUDF
No full textThe galaxy population at z≈ 6 has been the subject of intense study in recent years, culminating in the Hubble Ultra Deep Field (HUDF) – the deepest imaging survey yet. A large number of high-redshift galaxy candidates have been identified within the HUDF, but until now analysis of their properties has been hampered by the difficulty of obtaining spectroscopic redshifts for these faint galaxies. Our ‘Gemini Lyman-Alpha at Reionization Era’ (GLARE) project has been designed to undertake spectroscopic follow-up of faint (z′ 5.5, and a further nine possible line emitters with detections at lower significance. We also place tight constraints on the equivalent width of Lyα emission for a further ten i′-drop galaxies and examine the equivalent width distribution of this faint spectroscopic sample of z≈ 6 galaxies. We find that the fraction of galaxies with little or no emission is similar to that at z≈ 3, but that the z≈ 6 population has a tail of sources with high rest-frame equivalent widths. Possible explanations for this effect include a tendency towards stronger line emission in faint sources, which may arise from extreme youth or low metallicity in the Lyman-break population at high redshift, or possibly a top-heavy initial mass function
Probabilistic stability assessment of rock excavations
No full textL M Faint, L T Ljubicic, S M Thomson, J R Veale, C Xu, M Karakus and N Melkoumia
The fight for accretion : discovery of intermittent mass transfer in BB Doradus in the low state
No full textOur long-term photometric monitoring of southern nova-like cataclysmic variables with the 1.3-m Small and Moderate Aperture Research Telescope System (SMARTS) telescope found BB Doradus fading from V∼ 14.3 towards a deep low state at V∼ 19.3 in 2008 April. Here we present time-resolved optical spectroscopy of BB Dor in this faint state in 2009. The optical spectrum in quiescence is a composite of a hot white dwarf with Teff= 30 000 ± 5000 K and a M3–M4 secondary star with narrow emission lines (mainly of the Balmer series and He i) superposed. We associate these narrow profiles with an origin on the donor star. An analysis of the radial velocity curve of the Hα emission from the donor star allowed the measurement of an orbital period of 0.154 095 ± 0.000 003 d (3.698 28 ± 0.000 07 h), different from all previous estimates. We detected episodic accretion events which veiled the spectra of both stars and radically changed the line profiles within a time-scale of tens of minutes. This shows that accretion is not completely quenched in the low state. During these accretion episodes the line wings are stronger and their radial velocity curve is delayed by ∼0.2 cycle, similar to that observed in SW Sex and AM Her stars in the high state, with respect to the motion of the white dwarf. Two scenarios are proposed to explain the extra emission: impact of the material on the outer edge of a cold, remnant accretion disc, or the combined action of a moderately magnetic white dwarf (B1≲ 5 MG) and the magnetic activity of the donor star
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