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Dysphagia is a common functional outcome following treatment of laryngeal cancer. Despite curative advances in both nonsurgical and surgical approaches, preserving and optimizing swallowing function is critical. Understanding the nature and severity of dysphagia depending on initial tumor staging and treatment modality and intensity is crucial. This chapter explores current evidence on the acute and chronic impacts of treatments for laryngeal cancer on swallow function, as well as the medical and nonmedical management of dysphagia in this population.

IMPORTANCE: Understanding the preoperative, intraoperative, and postoperative risk factors of reoperation is the optimal way to approach decreasing its incidence. OBJECTIVE: To identify risk factors of unplanned reoperation following major operations of the head and neck. DESIGN, SETTING, AND PARTICIPANTS: This retrospective cohort study queried the American College of Surgeons National Surgical Quality Improvement Program database and identified 2475 cases of major operations of the head and neck performed between 2005 and 2014. Specific operations analyzed were glossectomy, mandibulectomy, laryngectomy, and pharyngectomy. Univariate and multivariate analyses were performed to compare demographic and clinical characteristics of patients with or without unplanned reoperation. Data were analyzed between September and November 2017. MAIN OUTCOMES AND MEASURES: The primary outcome was incidence of unplanned reoperation in patients with major operations in the head and neck region. An additional aim was to assess the risk factors associated with an increased likelihood of reoperation. RESULTS: In total, 1941 patients were included in this study (1298 [66.9%] males), with most patients (961 [49.5%]) between 61 and 80 years of age. The overall unplanned reoperation rate within 30 days after the principal operative procedure was 14.2% (275 patients). The operative procedure with the highest reoperation rate was pharyngectomy (8 of 46 [17.4%]), followed by glossectomy (95 of 632 [15.0%]), laryngectomy (53 of 399 [13.3%]), and mandibulectomy (25 of 240 [10.4%]). Among the unplanned reoperation patients, 516 patients (76.8%) underwent reoperation during their initial hospital admission and 156 patients (23.2%) after readmission. The mean (SD) number of days from the principal operative procedure to unplanned reoperation was 8.5 (3.6) days for initial-admission reoperations and 16.0 (4.8) days for readmission reoperations. The most common unplanned reoperation procedures overall included repair, surgical exploration, and revision procedures on arteries and veins (47 of 2475 [1.9%]), incision procedures on the soft tissue of the neck and thorax (37 of 1941 [1.9%]), and incision and drainage procedures on the skin, subcutaneous, and accessory structures (21 of 1941 [1.1%]). Multivariate analysis results indicated that the independent risk factors for unplanned reoperation following a major cancer operation of the head or neck included black race (odds ratio [OR], 1.72; 95% CI, 1.09-2.74), disseminated cancer (OR, 1.85; 95% CI, 1.14-3.00), greater total operation time (OR, 2.05; 95% CI, 1.49-2.82), superficial (OR, 2.56; 95% CI, 1.55-4.24) or deep (OR, 4.83; 95% CI, 2.60-8.95) surgical site infection, wound dehiscence (OR, 8.36; 95% CI, 5.10-13.69), and ventilator dependence up to 48 hours after surgery (OR, 2.95; 95% CI, 1.79-4.87). CONCLUSIONS AND RELEVANCE: The identification of a significant association of black race, disseminated cancer, total operation time, surgical site infection in either the superficial or deep spaces, wound dehiscence, or ventilator dependence for more than 48 hours after surgery with increased risk of reoperation in major head and neck surgery may guide the modification and adaptation of these risk factors to decrease the burden that unplanned reoperation places on patients, surgeons, and the health care system.

Aims. To better understand the phenomenon of colliding winds in massive binary stars, we study the X-ray lightcurve of a WR+O system of the Carina region, a system well known for the high mass of its primary.

Aims. We present the results obtained from a long-term spectroscopic campaign to study the multiplicity of O-type stars in both the young open cluster NGC 2244 and the Mon OB2 association.

Context. HD 152219 is a massive binary system with O9.5 III + B1-2 V/III components and a short orbital period of 4.2 d. Its primary component further displays clear line profile variability (LPV). The primary component being located within the pulsational instability domain predicted for high-luminosity stars, we previously suggested that the observed LPV could be associated with non-radial pulsations.

Aims.We present a spectroscopic analysis of four massive binary systems that are known or are good candidates to display the Struve-Sahade effect (defined as the apparent strengthening of the secondary spectrum of the binary when the star is approaching, and the corresponding weakening of the lines when it is receding).

Aims.We analyze INTEGRAL-ISGRI data in order to probe the hard X-ray emission (above 20 keV) from point sources in the Cyg OB2 region and to investigate the putative non-thermal high-energy emission from early-type stars (Wolf-Rayet and O-type stars). Among the targets located in the field of view, we focus on the still unidentified EGRET source 3EG 2033+4118 that may be related to massive stars known to produce non-thermal emission in the radio domain, and on the wide colliding-wind binary WR 140.

Aims.The properties of the early-type stars in the core of the Westerlund 2cluster are examined in order to establish a link between the cluster and the very massive Wolf-Rayet binary WR 20aas well as the H iicomplex RCW 49.

Context.Since the discovery, with the EINSTEIN satellite, of strong X-ray emission associated with HD 93162 (≡WR 25), this object has been predicted to be a colliding-wind binary system. However, radial-velocity variations that would prove the suspected binary nature have yet to be found.

This paper is the first of a series dedicated to the X-ray properties of the young open cluster NGC 6231. Our data set relies on an XMM-Newtoncampaign of a nominal duration of 180 ks and reveals that NGC 6231  is very rich in the X-ray domain too. Indeed, 610 X-ray sources are detected in the present field of view, centered on the cluster core. The limiting sensitivity of our survey is approximately 6 $\times$10-15erg cm-2s-1but clearly depends on the location in the field of view and on the source spectrum. Using different existing catalogues, over 85% of the X-ray sources could be associated with at least one optical and/or infrared counterpart within a limited cross-correlation radius of 3´´ at maximum. The surface density distribution of the X-ray sources presents a slight N-S elongation. Once corrected for the spatial sensitivity variation of the EPIC instruments, the radial profile of the source surface density is well described by a King profile with a central density of about 8 sources per arcmin2and a core radius close to 3.1 arcmin. The distribution of the X-ray sources seems closely related to the optical source distribution. The expected number of foreground and background sources should represent about 9% of the detected sources, thus strongly suggesting that most of the observed X-ray emitters are physically belonging to NGC 6231. Finally, beside a few bright but soft objects – corresponding to the early-type stars of the cluster – most of the sources are relatively faint (~5 $\times$10-15erg cm-2s-1) with an energy distribution peaked around 1.0–2.0 keV.

In the first paper of this series, we presented a detailed high-resolution spectroscopic study of CPD - 41° 7742, deriving for the first time an orbital solution for both components of the system. In this second paper, we focus on the analysis of the optical light curve and on recent XMM-NewtonX-ray observations. In the optical, the system presents two eclipses, yielding an inclination $i\sim77\degr$. Combining the constraints from the photometry with the results of our previous work, we derive the absolute parameters of the system. We confirm that the two components of CPD - 41° 7742are main sequence stars (O9 V + B1–1.5 V) with masses ($M_1\sim18$$M_{\odot}$and $M_2\sim10$$M_{\odot}$) and respective radii ($R_1\sim7.5$$R_{\odot}$and $R_2\sim5.4$$R_{\odot}$) close to the typical values expected for such stars.
We also report an unprecedented set of X-ray observations that almost uniformly cover the 2.44-day orbital cycle. The X-ray emission from CPD - 41° 7742is well described by a two-temperature thermal plasma model with energies close to 0.6 and 1.0 keV, thus slightly harder than typical early-type emission. The X-ray light curve shows clear signs of variability. The emission level is higher when the primary is in front of the secondary. During the high emission state, the system shows a drop of its X-ray emission that almost exactly matches the optical eclipse. We interpret the main features of the X-ray light curve as the signature of a wind-photosphere interaction, in which the overwhelming primary O9 star wind crashes into the secondary surface. Alternatively the light curve could result from a wind-wind interaction zone located near the secondary star surface. As a support to our interpretation, we provide a phenomenological geometric model that qualitatively reproduces the observed modulations of the X-ray emission.

We analyse the optical spectrum of the very massive binary system WR 20a (WN6ha + WN6ha). The most prominent emission lines, Hαand He iiλ4686, display strong phase-locked profile variability. From the variations of their equivalent widths and from a tomographic analysis, we find that part of the line emission probably arises in a wind interaction region between the stars. Our analysis of the optical spectrum of WR 20a indicates a reddening of $A_{\rm V} \simeq 6.0$mag and a distance of ~$ 7.9$kpc, suggesting that the star actually belongs to the open cluster Westerlund 2. The location of the system at ∼1.1 pc from the cluster core could indicate that WR 20a was gently ejected from the core via dynamical interactions. Using a non-LTE model atmosphere code, we derive the fundamental parameters of each component: $T_{\rm eff} = 43\,000 \pm 2000$K, $\log{L_{\rm bol}/{L_{\odot}}} \simeq 6.0$, ${\dot{M}} = 8.5 \times 10^{-6}$$M_{\odot}$yr-1(assuming a clumped wind with a volume filling factor $f = 0.1$). Nitrogen is enhanced in the atmospheres of the components of WR 20a, while carbon is definitely depleted. Finally, the position of the binary components in the Hertzsprung-Russell diagram suggests that they are core hydrogen burning stars in a pre-LBV stage and their current atmospheric chemical composition probably results from rotational mixing that might be enhanced in a close binary compared to a single star of same age.

We present the results of an XMM-Newtonobservation of the field of the Wolf-Rayet star WR 40. Despite a nominal exposure of 20 ks and the high sensitivity of the satellite, the star itself is not detected: we thus derive an upper limit on its X-ray flux and luminosity. Joining this result to recent reports of a non-detection of some WC stars, we suggest that the X-ray emission from single normal Wolf-Rayet stars could often be insignificant despite remarkable instabilities in the wind. On the basis of a simple modelling of the opacity of the Wolf-Rayet wind of WR 40, we show that any X-ray emission generated in the particular zone where the shocks are supposed to be numerous will indeed have little chance to emerge from the dense wind of the Wolf-Rayet star. We also report the non-detection of the ejecta nebula RCW 58 surrounding WR 40. Concerning the field around these objects, we detected 33 X-ray sources, most of them previously unknown: we establish a catalog of these sources and cross-correlate it with catalogs of optical/infrared sources.

We analyse spectroscopic observations of WR 20a revealing that this star is a massive early-type binary system with a most probable orbital period of ~3.675 days. Our spectra indicate that both components are most likely of WN6ha or O3If*/WN6ha spectral type. The orbital solution for a period of 3.675 days yields extremely large minimum masses of $70.7\,\pm\,4.0$and $68.8 \pm 3.8~M_{\odot}$for the two stars. These properties make WR 20a a cornerstone system for the study of massive star evolution.

We report the results of a multiwavelength study of the non-thermal radio emitter HD 168112 (O5.5III(f+)). The detailed analysis of two quasi-simultaneous XMM-Newtonand VLA observations reveals strong variability of this star both in the X-ray and radio ranges. The X-ray observations separated by five months reveal a decreaseof the X-ray flux of ~30%. The radio emission on the other hand increasesby a factor 5–7 between the two observations obtained roughly simultaneously with the XMM-Newtonpointings. The X-ray data reveal a hard emission that is most likely produced by a thermal plasma at kT~ 2–3 keV while the VLA data confirm the non-thermal status of this star in the radio waveband. Comparison with archive X-ray and radio data confirms the variability of this source in both wavelength ranges over a yet ill defined time scale. The properties of HD 168112 in the X-ray and radio domain point towards a binary system with a significant eccentricity and an orbital period of a few years. However, our optical spectra reveal no significant changes of the star's radial velocity suggesting that if HD 168112 is indeed a binary, it must be seen under a fairly low inclination.

We present the results of a spectroscopic campaign on the early-type binary CPD?-?41°?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 ($e=0.027\pm0.006$) despite the short period ($P=2.44070\pm0.00043$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 $P=2.44062\pm0.00005$?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 NGC?6231 rather indicate lower luminosity classes. We show that the equivalent widths of well isolated primary lines display variations that suggest that CPD?-?41°?7742 is an eclipsing binary. This makes CPD?-?41°?7742 the second known SB2 eclipsing early-type binary of the NGC?6231 cluster. We approximately constrain the inclination of the system $i_\mathrm{min}\approx60\degr$. 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.

We report the results of a multi-wavelength investigation of the O4 V star 9 Sgr (= HD 164794). Our data include observations in the X-ray domain with XMM-Newton, in the radio domain with the VLA as well as optical spectroscopy. 9 Sgr is one of a few presumably single OB stars that display non-thermal radio emission. This phenomenon is attributed to synchrotron emission by relativistic electrons accelerated in strong hydrodynamic shocks in the stellar wind. Given the enormous supply of photospheric UV photons in the wind of 9 Sgr, inverse Compton scattering by these relativistic electrons is a priori expected to generate a non-thermal power law tail in the X-ray spectrum. Our EPIC and RGS spectra of 9 Sgr reveal a more complex situation than expected from this simple theoretical picture. While the bulk of the thermal X-ray emission from 9 Sgr arises most probably in a plasma at temperature ~$3 \times 10^6$K distributed throughout the wind, the nature of the hard emission in the X-ray spectrum is less clear. Assuming a non-thermal origin, our best fitting model yields a photon index of ≥2.9 for the power law component which would imply a low compression ratio of ≤1.79 for the shocks responsible for the electron acceleration. However, the hard emission can also be explained by a thermal plasma at a temperature ≥$2 \times 10^7$K. Our VLA data indicate that the radio emission of 9 Sgr was clearly non-thermal at the time of the XMM-Newtonobservation. Again, we derive a low compression ratio (1.7) for the shocks that accelerate the electrons responsible for the synchrotron radio emission. Finally, our optical spectra reveal long-term radial velocity variations suggesting that 9 Sgr could be a long-period spectroscopic binary.

We report the first results of a campaign aimed at the study of early-type binaries with the XMM-Newtonobservatory. Phase-resolved EPIC spectroscopy of the eccentric binary HD 93403 reveals a clear orbital modulation of the X-ray luminosity as a function of the orbital phase. Below 1.0 keV, the observed X-ray flux is modulated by the opacity of the primary wind. Above 1.0 keV, the observed variation of the X-ray flux is roughly consistent with a $1/r$dependence expected for an adiabatic colliding wind interaction. HD 93403 appears less overluminuous in X-rays than previously thought and a significant fraction of the total X-ray emission arises probably within the winds of the individual components of the binary. Optical monitoring of the system reveals strong variability of the He iiλ4686 and Hαline profiles. The He iiλ4686 line displays a broad asymmetrical emission component which is found to be significantly stronger between phases 0.80 and 0.15 than around apastron. This suggests that part of the emission arises in the interaction region and most probably in the trailing arm of a shock cone wrapped around the secondary. Some absorption lines of the secondary's spectrum display equivalent width variations reminiscent of the so-called Struve-Sahade effect. The differences in behaviour between individual lines suggest that the temperature may not be the only relevant parameter that controls this effect.

We present the results of a four year spectroscopic campaign on the early-type binary system HD152248. Our analysis yields a new classification as O7.5III(f) + O7III(f), in contradiction with previous classifications of the components as supergiants. We derive improved orbital elements and the corresponding masses ($M_1=29.6 M_{\odot}$and $M_2=29.9 M_{\odot}$) are somewhat larger than previously reported in the literature, although they are still significantly lower than the ones expected from evolutionary tracks. Both components of the system are close to filling their Roche lobe at periastron passage. We also investigate the equivalent width variations of the lines of the two components and we discuss their relation to the Struve-Sahadeeffect. Finally, we show that the line profile variability of the Heiił4686 and Hαlines is consistent with a strong wind interaction between the two stars, quite as predicted by current colliding wind models.

For certain security-sensitive wireless sensor network (WSN) applications, physical location information of the sensor nodes must not be disclosed to any unauthorised entity. During the localisation phase for such applications the physical locations of sensor nodes are kept secret. Globally, a number of secure location estimation schemes have been proposed from various perspectives, but some important constraints of sensor nodes are often ignored. The considered limitations during design of those schemes vary with respect to varying research perspective. In this study, we propose a novel security framework for secure location estimation of sensor nodes suitable for security-sensitive WSN applications. The proposed framework aims to provide security, scalability, adaptability and optimise power consumption during the secure location estimation phase of a wireless sensor network. The designed framework consists of a two-way authentication scheme, a light-weight encryption mechanism and a novel secure key generation algorithm. The study discusses strengths of the components if used for secure localisation individually, as well as when used together as interactive parts of a security framework for WSN applications.

Aims. To better understand the phenomenon of colliding winds in massive binary stars, we study the X-ray lightcurve of a WR+O?system of the Carina region, a system well known for the high mass of its primary.Methods. Phase-resolved X-ray observations of the massive WR+O binary system WR?22 were performed with the XMM-Newton facility. We observed the object at seven different phases from near apastron to near periastron.Results. The X-ray spectrum can be represented by a two-component, optically thin, thermal plasma model with a first one at a typical temperature of 0.6?keV and a second hotter one in the range 2.0?4.5?keV. The hot component is indicative of a colliding wind phenomenon, but its flux is remarkably constant with time despite the high eccentricity of the orbit. Although surprising at first, this actually does not contradict the results of the hydrodynamical simulations of the wind collision that we performed. When the system goes from apastron to periastron, the soft part of the X-ray flux is progressively lowered by an increasing intervening absorbing column. This behaviour can be interpreted in terms of an X-ray emitting plasma located near the O?star, but not fully intrinsic to it, and accompanying the star when it dives into the wind of the WR?component. A model is presented that interprets most of the observational constraints. This model suggests that the mass-loss rate of MWR~ 1.6 ? 10-5? M??yr-1assumed for the WR could still be slightly too high, whereas it is already lower than other published values. From the comparison of the observed and the expected absorptions at phases near periastron, we deduce that the hard X-ray emitting collision zone should at least have a typical size of 50?60?R?, but that the size for the soft X-ray emitting region could reach 244?R?if the assumed mass-loss rate is correct. We also present an upper limit to the X-ray luminosity of the WR?component that further questions the existence of intrinsic X-ray emission from single WN?stars.

Context. Plaskett's star (HD?47?129) is a very massive O?+?O binary that belongs to the Mon OB2 association. Previous work suggests that this system displays the Struve-Sahade effect although the measurements of the secondary radial velocities are very difficult and give controversial results. Both components have powerful stellar winds that collide and produce a strong X-ray emission.Aims. Our aim is to study the physical parameters of this system in detail and to investigate the relation between its spectral properties and its evolutionary status.Methods. We present here analysis of an extensive set of high-resolution optical spectra of HD?47?129. We used a disentangling method to separate the individual spectra of each star. We derived a new orbital solution and discuss the spectral classification of both components. A Doppler tomography technique applied to the emission lines H? and Heii???4686 yields a Doppler map that illustrates the wind interactions in the system. Finally, an atmosphere code is used to determine the different chemical abundances of the system components and the wind parameters.Results. HD?47?129 appears to be an O8?III/I?+?O7.5?III binary system in a post RLOF evolutionary stage, where matter has been transferred from the primary to the secondary star. The He overabundance of the secondary supports this scenario. In addition, the N overabundance and C underabundance of the primary component confirm previous results based on X-ray spectroscopy and indicate that the primary is an evolved massive star. We also determined a new orbital solution, with MPsin3i = 45.4 ?2.4?M?and MSsin3i = 47.3 ?0.3?M?. Furthermore, the secondary star has a high rotational velocity (vsini ?300?km?s-1) that deforms its surface, leading to a non-uniform distribution in effective temperature. This could explain the variations in the equivalent widths of the secondary lines with phase. We suggest that the wind of the secondary star is confined near the equatorial plane because of its high rotational velocity, affecting the ram pressure equilibrium in the wind interaction zone.

Context.The distance of the very young open cluster Westerlund 2, which contains the very massive binary system WR 20aand is likely associated with a TeV source, has been the subject of much debate.

VFTS 682 is located in an active star-forming region, at a projected distance of 29 pc from the young massive cluster R136 in the Tarantula Nebula of the Large Magellanic Cloud. It was previously reported as a candidate young stellar object, and more recently spectroscopically revealed as a hydrogen-rich Wolf-Rayet (WN5h) star. Our aim is to obtain the stellar properties, such as its intrinsic luminosity, and to investigate the origin of VFTS 682. To this purpose, we model optical spectra from the VLT-FLAMES Tarantula Survey with the non-LTE stellar atmosphere code cmfgen, as well as the spectral energy distribution from complementary optical and infrared photometry. We find the extinction properties to be highly peculiar (RV~ 4.7), and obtain a surprisingly high luminosity log (L/L⊙) = 6.5 ± 0.2, corresponding to a present-day mass of  ~150 M⊙. The high effective temperature of 52.2 ± 2.5 kK might be explained by chemically homogeneous evolution – suggested to be the key process in the path towards long gamma-ray bursts. Lightcurves of the object show variability at the 10% level on a timescale of years. Such changes are unprecedented for classical Wolf-Rayet stars, and are more reminiscent of Luminous Blue Variables. Finally, we discuss two possibilities for the origin of VFTS 682: (i) the star either formed in situ, which would have profound implications for the formation mechanism of massive stars, or (ii) VFTS 682 is a slow runaway star that originated from the dense cluster R136, which would make it the mostmassive runaway known to date.

Aims.The present study was conducted to determine the optical extinction curve for Cerro Paranal under typical clear-sky observing conditions, with the purpose of providing the community with a function to be used to correct the observed spectra, with an accuracy of 0.01 mag airmass-1. Additionally, this work was meant to analyze the variability of the various components, to derive the main atmospheric parameters, and to set a term of reference for future studies, especially in view of the construction of the Extremely Large Telescope on the nearby Cerro Armazones.

We present adaptive optics (AO) near-infrared observations of the core of the Tr 14 cluster in the Carina region obtained with the ESO multi-conjugate AO demonstrator, MAD. Our campaign yields AO-corrected observations with an image quality of about 0.2´´ across the 2´ field of view, which is the widest AO mosaic ever obtained. We detected almost 2000 sources spanning a dynamic range of 10 mag. The pre-main sequence (PMS) locus in the colour-magnitude diagram is well reproduced by Palla & Stahler isochrones with an age of 3 to 5×105yr, confirming the very young age of the cluster. We derive a very high (deprojected) central density n0~ 4.5(±0.5)×104pc-3and estimate the total mass of the cluster to be about ~$4.3^{+3.3}_{-1.5}$×103$M_\odot$, although contamination of the field of view might have a significant impact on the derived mass. We show that the pairing process is largely dominated by chance alignment so that physical pairs are difficult to disentangle from spurious ones based on our single epoch observation. Yet, we identify 150 likely bound pairs, 30% of these with a separation smaller than 0.5´´ (~1300 AU). We further show that at the 2σlevel massive stars have more companions than lower-mass stars and that those companions are respectively brighter on average, thus more massive. Finally, we find some hints of mass segregation for stars heavier than about 10 $M_\odot$. If confirmed, the observed degree of mass segregation could be explained by dynamical evolution, despite the young age of the cluster.

We present adaptive optics (AO) near-infrared observations of the core of the Tr 14 cluster in the Carina region obtained with the ESO multi-conjugate AO demonstrator, MAD. Our campaign yields AO-corrected observations with an image quality of about 0.2´´ across the 2´ field of view, which is the widest AO mosaic ever obtained. We detected almost 2000 sources spanning a dynamic range of 10 mag. The pre-main sequence (PMS) locus in the colour-magnitude diagram is well reproduced by Palla & Stahler isochrones with an age of 3 to 5×105yr, confirming the very young age of the cluster. We derive a very high (deprojected) central density n0~ 4.5(±0.5)×104pc-3and estimate the total mass of the cluster to be about ~$4.3^{+3.3}_{-1.5}$×103$M_\odot$, although contamination of the field of view might have a significant impact on the derived mass. We show that the pairing process is largely dominated by chance alignment so that physical pairs are difficult to disentangle from spurious ones based on our single epoch observation. Yet, we identify 150 likely bound pairs, 30% of these with a separation smaller than 0.5´´ (~1300 AU). We further show that at the 2σlevel massive stars have more companions than lower-mass stars and that those companions are respectively brighter on average, thus more massive. Finally, we find some hints of mass segregation for stars heavier than about 10 $M_\odot$. If confirmed, the observed degree of mass segregation could be explained by dynamical evolution, despite the young age of the cluster.

Context. The Bulge is the least understood major stellar population of the Milky Way. Most of what we know about the formation and evolution of the Bulge comes from bright giant stars. The underlying assumption that giants represent all the stars, and accurately trace the chemical evolution of a stellar population, is under debate. In particular, recent observations of a few microlensed dwarf stars give a very different picture of the evolution of the Bulge from that given by the giant stars. Aims. We aim to resolve the apparent discrepancy between Bulge metallicity distributions derived from microlensed dwarf stars and giant stars. Additionally, we aim to put observational constraints on the elemental abundance trends and chemical evolution of the Bulge. Methods. We perform a detailed elemental abundance analysis of dwarf stars in the Galactic bulge, based on high-resolution spectra that were obtained while the stars were optically magnified during gravitational microlensing events. The analysis method is the same as for a large sample of F and G dwarf stars in the Solar neighbourhood, enabling a fully differential comparison between the Bulge and the local stellar populations in the Galactic disc. Results. We present detailed elemental abundances and stellar ages for six new dwarf stars in the Galactic bulge. Combining these with previous events, here re-analysed with the same methods, we study a homogeneous sample of 15 stars, which constitute the largest sample to date of microlensed dwarf stars in the Galactic bulge. We find that the stars span the full range of metallicities from [Fe/H] = -0.72 to +0.54, and an average metallicity of $\langle$[Fe/H]$\rangle$= -0.08 ±0.47, close to the average metallicity based on giant stars in the Bulge. Furthermore, the stars follow well-defined abundance trends, that for [Fe/H]<0 are very similar to those of the local Galactic thick disc. This suggests that the Bulge and the thick disc have had, at least partially, comparable chemical histories. At sub-solar metallicities we find the Bulge dwarf stars to have consistently old ages, while at super-solar metallicities we find a wide range of ages. Using the new age and abundance results from the microlensed dwarf stars we investigate possible formation scenarios for the Bulge.

Context. The Bulge is the least understood major stellar population of the Milky Way. Most of what we know about the formation and evolution of the Bulge comes from bright giant stars. The underlying assumption that giants represent all the stars, and accurately trace the chemical evolution of a stellar population, is under debate. In particular, recent observations of a few microlensed dwarf stars give a very different picture of the evolution of the Bulge from that given by the giant stars.

We report on the composition of the Halley-family comet (HFC) 8P/Tuttle investigated with high-dispersion near-infrared spectroscopic observations. The observations were carried out at the ESO VLT (Very Large Telescope) with the CRIRES instrument as part of a multi-wavelength observation campaign of 8P/Tuttle performed in late January and early February 2008. Radar observations suggested that 8P/Tuttle is a contact binary, and it was proposed that these components might be heterogeneous in chemistry. We determined mixing ratios of organic volatiles with respect to H2O and found that mixing ratios were consistent with previous near infrared spectroscopic observations obtained in late December 2007 and in late January 2008. It has been suggested that because 8P/Tuttle is a contact binary, it might be chemically heterogeneous. However, we find no evidence for chemical heterogeneity within the nucleus of 8P/Tuttle. We also compared the mixing ratios of organic molecules in 8P/Tuttle with those of both other HFCs and long period comets (LPCs) and found that HCN, C2H2, and C2H6are depleted whereas CH4and CH3OH have normal abundances. This may indicate that 8P/Tuttle was formed in a different region of the early solar nebula than other HFCs and LPCs. We estimated the conversion efficiency from C2H2to C2H6by hydrogen addition reactions on cold grains by employing the C2H6/(C2H6+C2H$_{2})$ratio. The C2H6/(C2H6+C2H$_{2})$ratio in 8P/Tuttle is consistent with the ratios found in other HFCs and LPCs within the error bars. We also discuss the source of C2and CN based on our observations and conclude that the abundances of C2H2and C2H6are insufficient to explain the C2abundances in comet 8P/Tuttle and that the abundance of HCN is insufficient to explain the CN abundances in the comet, so at least one additional parent is needed for each species, as pointed out in previous study.

We report on the composition of the Halley-family comet (HFC) 8P/Tuttle investigated with high-dispersion near-infrared spectroscopic observations. The observations were carried out at the ESO VLT (Very Large Telescope) with the CRIRES instrument as part of a multi-wavelength observation campaign of 8P/Tuttle performed in late January and early February 2008. Radar observations suggested that 8P/Tuttle is a contact binary, and it was proposed that these components might be heterogeneous in chemistry. We determined mixing ratios of organic volatiles with respect to H2O and found that mixing ratios were consistent with previous near infrared spectroscopic observations obtained in late December 2007 and in late January 2008. It has been suggested that because 8P/Tuttle is a contact binary, it might be chemically heterogeneous. However, we find no evidence for chemical heterogeneity within the nucleus of 8P/Tuttle. We also compared the mixing ratios of organic molecules in 8P/Tuttle with those of both other HFCs and long period comets (LPCs) and found that HCN, C2H2, and C2H6are depleted whereas CH4and CH3OH have normal abundances. This may indicate that 8P/Tuttle was formed in a different region of the early solar nebula than other HFCs and LPCs. We estimated the conversion efficiency from C2H2to C2H6by hydrogen addition reactions on cold grains by employing the C2H6/(C2H6+C2H$_{2})$ratio. The C2H6/(C2H6+C2H$_{2})$ratio in 8P/Tuttle is consistent with the ratios found in other HFCs and LPCs within the error bars. We also discuss the source of C2and CN based on our observations and conclude that the abundances of C2H2and C2H6are insufficient to explain the C2abundances in comet 8P/Tuttle and that the abundance of HCN is insufficient to explain the CN abundances in the comet, so at least one additional parent is needed for each species, as pointed out in previous study.

We report on the composition of the Halley-family comet (HFC) 8P/Tuttle investigated with high-dispersion near-infrared spectroscopic observations. The observations were carried out at the ESO VLT (Very Large Telescope) with the CRIRES instrument as part of a multi-wavelength observation campaign of 8P/Tuttle performed in late January and early February 2008. Radar observations suggested that 8P/Tuttle is a contact binary, and it was proposed that these components might be heterogeneous in chemistry. We determined mixing ratios of organic volatiles with respect to H2O and found that mixing ratios were consistent with previous near infrared spectroscopic observations obtained in late December 2007 and in late January 2008. It has been suggested that because 8P/Tuttle is a contact binary, it might be chemically heterogeneous. However, we find no evidence for chemical heterogeneity within the nucleus of 8P/Tuttle. We also compared the mixing ratios of organic molecules in 8P/Tuttle with those of both other HFCs and long period comets (LPCs) and found that HCN, C2H2, and C2H6are depleted whereas CH4and CH3OH have normal abundances. This may indicate that 8P/Tuttle was formed in a different region of the early solar nebula than other HFCs and LPCs. We estimated the conversion efficiency from C2H2to C2H6by hydrogen addition reactions on cold grains by employing the C2H6/(C2H6+C2H$_{2})$ratio. The C2H6/(C2H6+C2H$_{2})$ratio in 8P/Tuttle is consistent with the ratios found in other HFCs and LPCs within the error bars. We also discuss the source of C2and CN based on our observations and conclude that the abundances of C2H2and C2H6are insufficient to explain the C2abundances in comet 8P/Tuttle and that the abundance of HCN is insufficient to explain the CN abundances in the comet, so at least one additional parent is needed for each species, as pointed out in previous study.