1,721,043 research outputs found
Optical spectroscopy of the low-mass X-ray binary GX 9+9
Full text linkPhase-resolved medium-resolution VLT spectroscopy of the low-mass X-ray binary GX 9+9 has revealed narrow C ill emission lines that move in phase relative to our new estimate of the ephemeris, and show a velocity amplitude of 230 +/not superset of 35 km s(-1). We identify the origin of these lines as coming from the surface of the donor star, thereby providing the first estimate of the mass function of f(M-1) >= 0.22 M-circle dot. Rotational broadening estimates together with assumptions for the mass donor give 0.07 <= q <= 0.35 and 182 <= K-2 <= 406 km s(-1). Despite a low-mass ratio, there is no evidence for a superhump in our data set. Doppler maps of GX 9+9 show the presence of a stream overflow, either in the form of material flowing downward along the accretion disc rim or in a similar fashion as occurs in high mass transfer rate cataclysmic variables known as the SW Sex stars. Finally, we note that the Bowen region in GX 9+9 is dominated by C in instead of N III emission as has been the case for most other X-ray binaries
Dynamical evidence for a black hole in GX 339-4
No full textWe present outburst spectroscopy of GX 3394 that may reveal the motion of its elusive companion star.
N iii lines exhibit sharp emission components moving over ?300 km s1 in a single night. The most plausible
interpretation of these components is that they are formed by irradiation of the companion star and the velocities
indicate its orbital motion. We also detect motion of the wings of the He ii 4686 A° line and changes in its
morphology. No previously proposed period is consistent with periodic behavior of all of these measures. However,
consistent and sensible solutions are obtained for periods around 1.7 days. For the best period, 1.7557 days, we
estimate a mass function of M,. Even allowing for aliases, the 95% confidence lower limit on the 5.80.5
mass function is 2.0 M,. GX 3394 can therefore be added to the list of dynamical black hole candidates. This
is supported by the small motion in the wings of the He ii line; if the compact object velocity is not larger than
the observed motion, then the mass ratio is , similar to other systems harboring black holes. Finally, q 0.08
we note that the sharp components are not always present but do seem to occur within a repeating phase range.
This appears to migrate between our epochs of observation and may indicate shielding of the companion star
by a variable accretion geometry such as a warp
Halpha flares from V404 Cyg in quiescence
Full text linkWe present a spectrophotometric study of short-term optical variability in the quiescent black hole X-ray transient V404 Cyg. This includes two nights of high-time-resolution Ha spectroscopy with which we resolve much of the time variability, and a further six nights of archival spectroscopy with lower time resolution but higher spectral resolution. We find significant variability in most of the data considered, with both the Haline and the continuum often varying in a correlated way. This includes both dramatic flares lasting a few hours in which the line flux nearly doubles and lower-level flickering. The strongest flares involve development of asymmetry in the line profile, with the red wing usually strongest independent of orbital phase. It is unclear why this is the case, but we discuss several possible
explanations. We consider the energetics of the flares and compare with plausible models including chromospheric activity on the companion star, local magnetic reconnection events
within the disc and varying irradiation from close to the black hole. Based on the line profile changes during the flares, we conclude that the most likely origin for the variability is variable
photoionization by the central source, although local flares within the disc cannot be ruled out
Detection of the irradiated donor in the LMXBs 4U 1636-536 (=V801 Ara) and 4U 1735-444 (=V926 Sco)
Full text linkPhase-resolved VLT spectroscopy of the bursting low-mass X-ray binaries 4U 1636-536/V801 Ara and 4U 1735-444/V926 Sco is presented. Doppler images of the N iiiλ4640 Bowen transition reveal compact spots which we attribute to fluorescent emission from the donor star and enable us to define a new set of spectroscopic ephemerides. We measure Kem= 277 ± 22 and 226 ± 22 km s−1 from the N iii spots in V801 Ara and V926 Sco, respectively, which represent strict lower limits to the radial velocity semi-amplitude of the donor stars. Our new ephemerides provide confirmation that light-curve maxima in V801 Ara and likely V926 Sco occur at superior conjunction of the donor star and hence photometric modulation is caused by the visibility of the X-ray heated donor. The velocities of He iiλ4686 and the broad Bowen blend are strongly modulated with the orbital period, with phasing supporting emission dominated by the disc bulge. In addition, a reanalysis of burst oscillations in V801 Ara, using our spectroscopic T0, leads to K1= 90–113 km s−1. We also estimate the K-corrections for all possible disc flaring angles and present the first dynamical constraints on the masses of these X-ray bursters. These are K2= 360 ± 74 km s−1, f(M) = 0.76 ± 0.47 M⊙ and q= 0.21–0.34 for V801 Ara and K2= 298 ± 83 km s−1, f(M) = 0.53 ± 0.44 M⊙ and q= 0.05–0.41 for V926 Sco. Disc flaring angles α≥ 12° and q≃ 0.26–0.34 are favoured for V801 Ara whereas the lack of K1 constraint for V926 Sco prevents tight constraints on this system. Although both binaries seem to have intermediate inclinations, the larger equivalent width of the narrow N iii line in V801 Ara at phase 0.5 relative to phase 0 suggests that it has the higher inclination of the two
A detection of the donor star of Aquila X-1 during its 2004 outburst?
Full text linkPhase-resolved high-resolution optical spectroscopy has revealed narrow N iii and He ii emission lines from the soft X-ray transient Aquila X-1 during its 2004 outburst that move as a function of the orbit consistent with the phasing of the donor star. Under the assumption that these lines come from the irradiated side of the donor star, we can constrain its K2 velocity to ≥247 ± 8 km s−1 and derive a mass function of f(M1) ≥ 1.23 ± 0.12 M⊙. Estimates for the rotational broadening based on the emission components suggest a possible massive neutron star of ≥1.6 M⊙ (at 95 per cent confidence). However, an updated ephemeris and additional high-resolution spectroscopy of Aql X-1 during a future outburst are warranted in order to confirm that the narrow lines indeed originate on the donor star surface, and reliably characterize the system parameters of this important X-ray binary. Spectra taken during the end of the outburst show that the morphology of the emission lines changed dramatically. No donor star signature was present anymore, while the presence of narrow low-velocity emission lines became clear, making Aql X-1 a member of the slowly growing class of low-velocity emission-line sources
A signature of the donor star in the extra-galactic X-ray binary LMC X-2
Full text linkTwo nights of phase-resolved medium-resolution Very Large Telescope spectroscopy of the extra-galactic low-mass X-ray binary LMCX-2 have revealed a 0.32 +/- 0.02 d spectroscopic period in the radial velocity curve of the He II lambda 4686 emission line that we interpret as the orbital period. However, similar to previous findings, this radial velocity curve shows a longer term variation that is most likely due to the presence of a precessing accretion disc in LMCX-2. This is strengthened by He II lambda 4686 Doppler maps that show a bright spot that is moving from night to night. Furthermore, we detect narrow emission lines in the Bowen region of LMCX-2, with a velocity of K-em = 351 +/- 28 km s(-1), that we tentatively interpret as coming from the irradiated side of the donor star. Since K-em must be smaller than K-2, this leads to the first upper limit on the mass function of LMCX-2 of f(M-1) >= 0.86 M-circle dot (95 per cent confidence), and the first constraints on its system parameters
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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