I report observations of the triple system BD +62 2296 showing that all its components are early-type stars, most likely physically related. The faintest component BD +62 2296B is a hitherto uncatalogued Wolf-Rayet star. The brightest component, star A, is shown to be a seemingly normal B2.5Ia supergiant. Long-slit spectroscopy of BD +62 2296B shows it to be a narrow-lined WN4 star. Given the spatial separation, the two objects are unlikely to form a physical binary. Spectra of the third visual component, BD +62 2296C, allow its classification as a B0III star. Such concentration of massive stars strongly suggests that BD +62 2296 is in reality a very compact young open cluster in the area of the OB association Cas OB5.

Ignacio Negueruela

We present observations of the massive transitional star W243 in Westerlund 1. We find an apparent spectral type of early-mid A from our data, in contrast to an earlier classification of B2I, made from data obtained in 1981. The concurrent development of a rich emission line spectrum suggests a very high mass loss rate; the continued presence of HeI emission suggesting that the underlying star remains significantly hotter than implied by its apparent spectral type. We suggest that W243 is a Luminous Blue Variable undergoing an eruptive phase, leading to an extreme mass loss rate and the formation of a pseudo photosphere.

J. Simon Clark Ignacio Negueruela

We present high-quality spectra of the majority of stars that have been classified as Oe and find that their published spectral types are generally too early, most likely due to infilling of HeI lines. As a matter of fact, all stars classified as Oe actually fall inside the range O9-B0 with the important exception of HD155806 (O7.5III) and perhaps HD39680 (difficult to classify, but likely O8.5V). Observations of a sample of objects with published spectral types in the O9-B0 range previously classified as peculiar or emission-line stars fail to reveal any new Oe star with spectral type earlier than O9.5. Most objects classified as peculiar in ``classical'' literature show signs of binarity in our spectra, but no spectral anomalies. We conclude that there is likely a real decline in the fraction of Be stars for spectral types earlier than B0, not due to observational bias. The few Oe stars with spectral types earlier than O9.5 deserve detailed investigation in order to provide constraints on the physical reasons of the Be phenomenon.

Ignacio Negueruela Iain A. Steele Guillem Bernabeu

The study of massive X-ray binaries provides important observational diagnostics for a number of fundamental astrophysical issues, such as the evolution of massive stars, the stellar winds of massive stars, the formation of compact objects and accretion processes. More than three decades of study have led to a coherent picture of their formation and evolution and some understanding of the physical mechanisms involved. As more and more systems are discovered, this picture grows in complexity. Over the last two years, INTEGRAL has discovered a new population of massive X-ray binaries, characterised by absorbed spectra, which challenges some of our previous assumptions and guarantees that this will be a major subject of research for the near future.

Ignacio Negueruela

We present new low and intermediate-resolution spectroscopic observations of the Wolf Rayet (WR) star population in the massive starburst cluster Westerlund 1. Finding charts are presented for five new WRs - four WNL and one WCL - raising the current total of known WRs in the cluster to 19. We also present new spectra and correct identifications for the majority of the 14 WR stars previously known, notably confirming the presence of two WNVL stars. Finally we briefly discuss the massive star population of Westerlund 1 in comparison to other massive young galactic clusters.

Ignacio Negueruela J. Simon Clark

The weak X-ray transient XTE J1739-302, characterized by extremely short outbursts, has recently been identified with a reddened star. Here we present spectroscopy and photometry of the counterpart, identifying it as a O8Iab(f) supergiant at a distance of ~2.3 kpc. XTE J1739-302 becomes thus characterized as the prototype of the new class of Supergiant Fast X-ray Transients. The optical and infrared spectra of the counterpart to XTE J1739-302 do not reveal any obvious characteristics setting it apart from other X-ray binaries with supergiant companions, which display a very different type of X-ray lightcurve.

Ignacio Negueruela David M. Smith Thomas E. Harrison Jose Miguel Torrejon

INTEGRAL monitoring of the Galactic Plane is revealing a growing number of recurrent X-ray transients, characterised by short outbursts with very fast rise times (~ tens of minutes) and typical durations of a few hours. Here we show that several of these transients are associated with OB supergiants and hence define a new class of massive X-ray binaries which we call Supergiant Fast X-ray Transients (SFXTs). Many other transient X-ray sources display similar X-ray characteristics, suggesting that they belong to the same class. Since they are difficult to detect and their number is growing fast and steadily, they could represent a major class of X-ray binaries.

Ignacio Negueruela David M. Smith Pablo Reig Sylvain Chaty Jose Miguel Torrejon

Combination of high-precision photometry and spectroscopy allows the detailed study of the upper main sequence in open clusters. We are carrying out a comprehensive study of a number of clusters containing Be stars in order to evaluate the likelihood that a significant number of Be stars form through mass exchange in a binary. Our first results show that most young open clusters contain blue stragglers. In spite of the small number of clusters so far analysed, some trends are beginning to emerge. In younger open clusters, such as NGC 869 and NGC 663, there are many blue stragglers, most of which are not Be stars. In older clusters, such as IC 4725, the fraction of Be stars among blue stragglers is very high. Two Be blue stragglers are moderately strong X-ray sources, one of them being a confirmed X-ray binary. Such objects must have formed through binary evolution. We discuss the contribution of mass transfer in a close binary to the formation of both blue stragglers and Be stars

Amparo Marco Ignacio Negueruela Christian Motch

There are obvious and direct ways in which the presence of binary companions may affect activity in OB stars through tidal interactions. In this review, however, I consider a more fundamental role for multiplicity and explore claims that the Be phenomenon may be intimately linked to binarity. I describe the binary channel for the formation of Be stars and the ongoing discussion about the relative contribution of this channel to the population of Be stars. I also present evidence suggesting that some environments are more favourable for the appearance of Be stars and explore whether this may be connected to initial conditions, such as the chemical composition or the distribution of rotational velocities on the ZAMS.

Ignacio Negueruela

Supergiant Fast X-ray Transients are obviously related to persistent Supergiant X-ray Binaries. Any convincing explanation for their behaviour must consistently take into account all types of X-ray sources powered by wind accretion. Here we present a common framework for wind accreting sources, within the context of clumpy wind models, that allows a coherent interpretation of their different behaviours as an immediate consequence of diverse orbital geometries.

Ignacio Negueruela Jose Miguel Torrejon Pablo Reig Marc Ribo David M. Smith