We present new observations of projected rotational velocities of main sequence B stars in the galactic clusters NGC 2439, NGC 3293, NGC 3766, NGC 4755, NGC 7160 and h & χ Persei. 257 stars have been observed with three instruments, 207 of which are presented here. Projected rotational velocities have been determined by least-squares fit to synthetic spectra. Our v sin i scale is compared with that of Slettebak et al. (1975).

We discuss the v sin i distributions of main sequence B stars in galactic clusters in relation to stellar luminosity and to cluster metallicity. We show that evolutionary effects and/or dependence of initial v sin i distribution on stellar mass are important, so that a much larger sample and a wider metallicity range are required to detect any possible metallicity effect beyond doubt.

The actual characteristic average surface angular velocity ratio of the Be phenomenon may be higher than Ω/Ωc = 0.8 ± 0.1 derived from v sin i values not corrected from gravity darkening effects. Late Be Stars need not only higher values of Ω/Ωc, but also larger main sequence age ratios τ/τMS than early Be Stars to display the Be phenomenon. Galactic field Be Stars appear at any MS phase, but their frequency is higher for τ/τMS ≳ 0.5. Be Stars are probably neat differential rotators, i.e. they rotate with energy ratios kinetic/|gravitational| larger than withstood by critical rigid rotators. Initial formation conditions must favor the existence of fast rotators, while only a small fraction of them could be accounted for by mass transfer in close binary systems. Bn stars could perhaps represent a pre-Be phase.

Allowing for systematic differences in the counting of Be Stars due to their overluminosity, changes produced by their fast rotation on spectral types and time spent in the main sequence, a difference between the IMF (Be) and IMF(B) appears, which indicates that the appearance of the Be phenomenon may relay on differences in the initial star formation conditions.

Rough indications that v sin i is correlated with peculiar velocities exist only in the range of early-type Be Stars. Further corrections of space velocities of Be Stars for systematic movements of stellar groups to which they belong, as well as identifications of coeval stars have to be performed in order to decide whether the high rotation of some of them could be the consequence of gravitational encounters.

BCD (λ1, D) parameters of 49 “field” Be Stars are used to show that the Be phenomenon may appear over the whole main sequence evolutionary span. Models of rotating B stars are used to estimate the incidence of the fast rotation in the (λ1, D) parameters.

Distributions of true rotational velocities as a function of spectral type for different luminosity class groups of B and Be Stars are compared. While the distributions for B stars differ clearly from one luminosity class to another, those of Be Stars differ less, which indicates that due to rotational effects many Be Stars are considered more evolved than they actually are. Be Stars ‘select’ a narrow range of true rotational velocities to display the Be phenomenon and those of latter spectral types rotate only marginally faster than the early ones.

A series of intensive high-resolution spectroscopic observations of 7 Be Stars conducted over 5 years strongly indicates that the source of mass loss in these stars is to be found in magnetic activity coupled with rapid rotation. Magnetic centrifugal acceleration of ionized H and He along open field lines produce the circumstellar disk, while gas trapped in closed magnetic loops are responsible for the periodic variations.

v sin i was determined by applying the Fourier transform method to the line profiles of two classical Be Stars. A variation is observed in the apparent v sin i which corresponds to the main frequencies associated to nrp modes. Rotational modulation is observed in wind sensitive UV lines of the Be star ω Ori and is associated with an oblique magnetic dipole which is discovered for the first time in a classical Be star.

Satellite absorptions are identified as a general feature of Be binaries. In addition, Be + sdO binaries seem to show a characteristic short-term emission variability and short-lived shell events. The identification of such features can ease the search for further Be binaries with hot companions to allow an estimate of the fraction of Be Stars, possibly spun-up through binary evolution.

A brief review of the observational properties of evolved massive stars is presented. In the pursuit of clues for their rotation, formidable difficulties are encountered. At the same time, common features emerge between B[e] supergiants, Luminous Blue Variables and Wolf-Rayet stars. Several indications of rapid rotation are found, mostly indirect ones, in each class. It is shown that fast rotation can probably survive the mass loss events which characterize the late evolution of massive stars.

The non-spherically symmetric winds of B[e] supergiants are investigated. An empirical density distribution is chosen that accounts for the density concentrations and ratios derived from observations, and our model winds are assumed to contain only H and He. We calculate the Strömgren radii and the more accurate ionization fractions for H and He and find that in equatorial direction the winds of B[e] supergiants can become neutral very near the stellar surface. A neutral disk therefore exists around these stars in which molecules and dust can form which are shielded from the photodissociating stellar radiation field.

The spectra of stars with the B[e] phenomenon are dominated by features that are related to physical conditions of circumstellar material around these objects and are not intrinsic to the stars. Previous studies have shown that emission lines present in the optical spectra of these objects are formed in an equatorial rotating disk. The analysis of high and low resolution spectra, obtained by us with 1.52 telescope in ESO for some Southern Galactic B[e] Stars, can give us information about the structure and velocity of the disk. We will describe the analysis of the unclassified B[e] star Hen 2-90.

We present evidence suggesting that the star that erupted in 1994 in the SMC multiple system HD 5980 has v sin i ~230 km s–1, which is close to the breakup velocity for this star.

Major photometric monitoring campaigns of star-forming regions in the past decade have provided rich rotation period distributions of pre-main-sequence stars. The rotation periods span more than an order of magnitude in period, with most falling between 1 and 10 days. Thus the broad rotation period distributions found in 100 Myr clusters are already established by an age of 1 Myr. The most rapidly rotating stars are within a factor of 2-3 of their critical velocities; if angular momentum is conserved as they evolve to the ZAMS, these stars may come to exceed their critical velocities. Extensive efforts have been made to find connections between stellar rotation and the presence of protostellar disks; at best only a weak correlation has been found in the largest samples. Magnetic disk-locking is a theoretically attractive mechanism for angular momentum evolution of young stars, but the links between theoretical predictions and observational evidence remain ambiguous. Detailed observational and theoretical studies of the magnetospheric environments will provide better insight into the processes of pre-main-sequence stellar angular momentum evolution.

We have compiled data from the literature on rotational velocities and/or periods for > 1000 K & M stars in 10 young clusters ranging in age from Orion to the IC 1391/2602. These data show that most PMS stars < 3 Myr do not appear to spin up in response to contraction, but there is a suggestion of slight spinup by ~8 Myr. These results extend and reinforce our earlier study (Rebull et al. 2002), based on observations of ~300 stars in the Orion Flanking Fields, NGC 2264, and the Orion Nebula Cluster (ONC), which showed that the majority of PMS stars in these three groups apparently do not conserve stellar angular momentum as they contract, but instead evolve at nearly constant angular velocity. This result applies both to stars with and without near-IR I – K excesses indicative of disks.

We present the results of a photometric monitoring program of pre-main sequence (PMS) stars in the young (2-4 Myr) open cluster NGC 2264 (d=700 pc). We find that the rotation periods are mass dependent and show a bimodal distribution for higher mass stars with M ≳ 0.3 M⊙ and a unimodal distribution for lower mass stars with M ≲ 0.3 M⊙.

Bob Kraft (1967) showed that there is a break in the mean rotational velocity of stars at about spectral type F5, with more massive stars generally being rapid rotators and less massive stars generally being slow rotators. He also showed that in the late F spectral range at least, there is an evolution with time on the main sequence, with younger F stars being more rapidly rotating. Kraft's observational database extended only to about one solar mass due to the sensitivy limitations of photographic plates. Modern observations of low mass stars in open clusters, extending down in mass to nearly the hydrogen burning mass limit in a few clusters, have since been used to show that rotational spindown is the common feature of stars less massive than the sun but that there is a wide spread in rotational velocities when stars arrive on the ZAMS. I will review what is known empirically concerning the rotational velocities of intermediate and low mass field stars, using the open cluster data to place the field star observations in context.

v sin i has been measured from high-resolution (λ/Δλ~50000) infrared spectra of ~30 M and L dwarfs. The spectral region observed covers approximately 0.01 μm centered at 2.312 μm in the CO 2-0 band. v sin i, measured from the CO lines, increases dramatically from the M to L dwarfs. In extreme cases the rotational periods are a few hours.

We have obtained high resolution (R ≈ 220000) - high signal-to-noise (S/N > 500) spectra of 142 field dwarfs of spectral types F–K and v sin i ≤ 45 km s–1. Using the Fourier Transform Method (FTM) we precisely determined rotational velocities (Δ v sin i < 1.0 km s–1). For stars with v sin i ≥ 12.0 km s–1 this method allows the detection of deviations from solid body rotation. In the case of symmetric profiles the differential rotation parameter α = (ωequator – ωpole) / ωequator can be determined. This was possible for 32 of our sample stars; ten stars show evidence for solar-like differential rotation with α > 0.0. Thus it becomes possible to search for connections between differential rotation, rotational velocities and other stellar parameters. Signatures of differential rotation could be found on stars rotating as fast as v sin i = 42 km s–1. Particularly the Li-depleted stars turned out to show strong signatures of differential rotation. Our measurements support the idea, that Li-depletion in fast rotators (v sin i > 15 km s–1) is closely connected to differential rotation.