1,723,312 research outputs found
CPD-41° 7742: an unusual wind interaction
No full textWe summarize the results of a multiwavelength observing campaign on the massive eclipsing binary CPD-41° 7742, another remarkable object in the young open cluster NGC 6231. Our campaign relies on high resolution echelle spectroscopy, narrow-band optical photometry, and XMM-Newton X-ray observations. Combined with the spectroscopic analysis, the light curve analysis provides a direct measurement of the masses and sizes of the system components. However, the most outstanding results come from the XMM observations. Our 180 ks campaign towards NGC 6231, and CPD-41° 7742, provides an unprecedented phase coverage of such a close early-type binary. The EPIC-MOS light curves almost fully cover the 2.4 day period of the system and the brightness of the object is sufficient to yield a time resolution as tight as 1 ks. The X-ray flux presents clear variations along the orbit, that we interpret as the signature of an unusual wind interaction. We indeed expect that, in this O+B system, the dominant primary wind crashes into the secondary surface, leading to a wind-photosphere interaction. As a strong support to our interpretation, we provide a geometrical model that associates an extra X-ray emission to the secondary inner surface. Though quite simple, the present model matches the main features of the X-ray light curve
EXTREMELY RAPID STAR CLUSTER DISRUPTION IN HIGH-SHEAR CIRCUMNUCLEAR STARBURST RINGS: THE UNUSUAL CASE OF NGC 7742
No full textAll known mass distributions of recently formed star cluster populations resemble a "universal" power-law function. Here we assess the impact of the extremely disruptive environment in NGC 7742's circumnuclear starburst ring on the early evolution of the galaxy's high-mass (similar to 10(5)-10(7) M-circle dot) star cluster population. Surprisingly, and contrary to expectations, at all ages-including the youngest, less than or similar to 15 Myr-the cluster mass functions are robustly and verifiably represented by lognormal distributions that resemble those commonly found only for old, evolved globular cluster systems in the local universe. This suggests that the high-shear conditions in the NGC 7742 starburst ring may significantly speed up dynamical star cluster destruction. This enhanced mass-dependent disruption rate at very young ages might be caused by a combination of the starburst ring's high density and the shear caused by the counterrotating gas disk.Astronomy & AstrophysicsSCI(E)3ARTICLE1null75
CPD-41° 7742: an unusual wind interaction
No full textWe summarize the results of a multiwavelength observing campaign on the massive eclipsing binary CPD-41° 7742, another remarkable object in the young open cluster NGC 6231. Our campaign relies on high resolution echelle spectroscopy, narrow-band optical photometry, and XMM-Newton X-ray observations. Combined with the spectroscopic analysis, the light curve analysis provides a direct measurement of the masses and sizes of the system components. However, the most outstanding results come from the XMM observations. Our 180 ks campaign towards NGC 6231, and CPD-41° 7742, provides an unprecedented phase coverage of such a close early-type binary. The EPIC-MOS light curves almost fully cover the 2.4 day period of the system and the brightness of the object is sufficient to yield a time resolution as tight as 1 ks. The X-ray flux presents clear variations along the orbit, that we interpret as the signature of an unusual wind interaction. We indeed expect that, in this O+B system, the dominant primary wind crashes into the secondary surface, leading to a wind-photosphere interaction. As a strong support to our interpretation, we provide a geometrical model that associates an extra X-ray emission to the secondary inner surface. Though quite simple, the present model matches the main features of the X-ray light curve.status: Publishe
Minor Merger Origin for the Circumnuclear Starburst in NGC 7742
No full textWe present an emission-line diagnostic analysis of integral-field spectroscopic observations that cover the central kiloparsec of NGC 7742. This Sa galaxy hosts a spectacular nuclear starburst ring and nuclear regions characterized by low-ionization emission. The gas in the ring rotates in the opposite sense to the stars in the galaxy, suggesting a recent merging or acquisition event. The combination of integral-field measurements for the H alpha+[N II] emission lines from DensePak and the H beta and [O 111] emission from SAURON allow the construction of diagnostic diagrams that highlight the transition from star formation in the nuclear ring to excitation by high-velocity shocks or by a central AGN towards the center. DensePak measurements for the [S II] line ratio reveal very low gas densities in the nuclear ring, N(sub e) less than 100 per cubic centimeters, characteristic of massive H II regions. Comparison with MAPPINGS III models for starbursts with low gas densities show that the ring is of roughly solar metallicity. This suggests that the gas in the nuclear ring originated in a stellar system capable of substantially enriching the gas metallicity through sustained star formation. We propose that NGC 7742 cannibalised a smaller galaxy rich in metal-poor gas, and that star formation episodes in the ring have since increased the metallicity to its present value. The techniques explored here can be widely used to study similar systems, including composite (AGN+starburst) galaxies
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
Variations on the Author
No full text“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
The massive binary CPD-41°7742 - I. High-resolution optical spectroscopy
No full textpeer reviewedWe present the results of a spectroscopic campaign on the early-type binary CPD-41degrees 7742. For the first time, we unambiguously detect the secondary's spectral signature and derive an accurate orbital solution for both components of the system. We confirm that the orbit displays a slight but definite eccentricity (e=0.027+/-0.006) despite the short period (P=2.44070+/-0.00043 days). Previous radial velocity measurements available in the literature constitute together with our new observations a data set that spans more than 30 years. The combined primary orbital solution inferred is in excellent agreement with our solution and gives a period P=2.44062+/-0.00005 days. Based on spectroscopic criteria, we derive a spectral and luminosity classification of O9 III + B1 III. However, the luminosities and radii inferred from the membership of NGC6231 rather indicate lower luminosity classes. We show that the equivalent widths of well isolated primary lines display variations that suggest that CPD-41degrees 7742 is an eclipsing binary. This makes CPD-41degrees 7742 the second known SB2 eclipsing early-type binary of the NGC 6231 cluster. We approximately constrain the inclination of the system i(min) approximate to 60degrees. This may indicate that the system does not offer enough room for two stars with radii typical of giant stars and lends further support to a less evolved luminosity classification for at least one of the objects
Apsidal motion in massive eccentric binaries: The case of CPD-41°7742, and HD 152218 revisited
No full textpeer reviewedContext. This paper is part of a study of the apsidal motion in close eccentric massive binary systems, which aims to constrain the internal structure of the stars. We focus on the binary CPD-41° 7742 and briefly revisit the case of HD 152218.
Aims. Independent studies of CPD-41° 7742 in the past showed large discrepancies in the longitude of periastron of the orbit, hinting at the presence of apsidal motion. We here perform a consistent analysis of all observational data, explicitly accounting for the rate of change of the longitude of periastron.
Methods. We make use of the extensive set of spectroscopic and photometric observations of CPD-41° 7742 to infer values for the fundamental parameters of the stars and of the binary. Applying a disentangling method to the spectra allows us to simultaneously derive the radial velocities (RVs) at the times of observation and reconstruct the individual spectra of the stars. The spectra are analysed by means of the CMFGEN model atmosphere code to determine the stellar properties. We determine the apsidal motion rate in two ways: First, we complement our RVs with those reported in the literature, and, second, we use the phase shifts between the primary and secondary eclipses. The light curves are further analysed by means of the Nightfall code to constrain the orbital inclination and, thereby, the stellar masses. Stellar structure and evolution models are then constructed with the Clés code for the two stars with the constraints provided by the observations. Different prescriptions for the mixing inside the stars are adopted in the models. Newly available photometric data of HD 152218 are analysed, and stellar structure and evolution models are built for the system as for CPD-41° 7742.
Results. The binary system CPD-41° 7742, made of an O9.5 V primary (M_P = 17.8 ± 0.5 M⊙, R_P = 7.57 ± 0.09 R⊙, Teff,P = 31 800 ± 1000 K, Lbol,P = 5.28+0.67-0.68 × 10^4 L⊙) and a B1–2 V secondary (M_S = 10.0 ± 0.3 M⊙, R_S = 4.29+0.04-0.06 R⊙, Teff,S = 24 098 ± 1000 K, Lbol,S = 5.58+0.93−0.94 × 10^3 L⊙), displays apsidal motion at a rate of (15.38+0.42−0.51)° yr-1 . Initial masses of 18.0 ± 0.5 M⊙ and 9.9 ± 0.3 M⊙ are deduced for the primary and secondary stars, respectively, and the binary’s age is estimated to be 6.8 ± 1.4 Myr. Regarding HD 152218, initial masses of 20.6 ± 1.5 and 15.5 ± 1.1 M⊙ are deduced for the primary and secondary stars, respectively, and the binary’s age of 5.2 ± 0.8 Myr is inferred.
Conclusions. Our analysis of the observational data of CPD-41° 7742 that explicitly accounts for the apsidal motion allows us to explain the discrepancy in periastron longitudes pointed out in past studies of this binary system. The age estimates are in good agreement with estimates obtained for other massive binaries in NGC 6231. This study confirms the need for enhanced mixing in the stellar evolution models of the most massive stars to reproduce the observational stellar properties; this points towards larger convective cores than usually considered
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