2,071 research outputs found
The multiplicity of massive stars
Binaries are excellent astrophysical laboratories that provide us with direct
measurements of fundamental stellar parameters. Compared to single isolated
star, multiplicity induces new processes, offering the opportunity to confront
our understanding of a broad range of physics under the extreme conditions
found in, and close to, astrophysical objects. In this contribution, we will
discuss the parameter space occupied by massive binaries, and the observational
means to investigate it. We will review the multiplicity fraction of OB stars
within each regime, and in different astrophysical environments. In particular
we will compare the O star spectroscopic binary fraction in nearby open
clusters and we will show that the current data are adequately described by an
homogeneous fraction of f~0.44. We will also summarize our current
understanding of the observed parameter distributions of O+OB spectroscopic
binaries. We will show that the period distribution is overabundant in short
period binaries and that it can be described by a bi-modal Oepik law with a
break point around P~10d. The distribution of the mass-ratios shows no
indication for a twin population of equal mass binaries and seems rather
uniform in the range 0.2< q=M_2/M_1<1.0.Comment: 12 pages, 4 figures, IAU272: Active OB stars: structure, evolution,
mass los
An exceptional X-ray view of the young open cluster NGC 6231: what XMM-Newton has taught us
Considered as the core of the Sco OB1 association, the young open cluster NGC
6231 harbours a rich O-type star population. In 2001, the XMM-Newton satellite
targeted the cluster for a nominal duration of about 180 ks. Thanks to the
detector sensitivity, the EPIC cameras provided an unprecedented X-ray view of
NGC 6231, revealing about 600 point-like sources. In this contribution, we
review the main results that have been obtained thanks to this unprecedented
data set. Concerning the O-type stars, we present the latest developments
related to the so-called 'canonical' Lx-Lbol relation. The dispersion around
this relation might actually be much smaller than previously thought. In our
data set, the sole mechanism that yields a significant deviation from this
scheme is wind interaction. It is also the sole mechanism that induces a
significant variation of the early-type star X-ray flux. In a second part of
this contribution, we probe the properties of the optically faint X-ray
sources. Most of them are believed to be low mass pre-main sequence stars.
Their analysis provides direct insight into the star formation history of the
cluster.Comment: 6 pages, 5 figures, to appear in "The X-Ray Universe 2005", ESA
Symposium held at El Escorial, Madrid (Spain), 26-30 Sep 200
The massive star binary fraction in young open clusters - II. NGC 6611 (Eagle Nebula)
Based on a set of over 100 medium- to high-resolution optical spectra
collected from 2003 to 2009, we investigate the properties of the O-type star
population in NGC6611 in the core of the Eagle Nebula (M16). Using a much more
extended data set than previously available, we revise the spectral
classification and multiplicity status of the nine O-type stars in our sample.
We confirm two suspected binaries and derive the first SB2 orbital solutions
for two systems. We further report that two other objects are displaying a
composite spectrum, suggesting possible long-period binaries. Our analysis is
supported by a set of Monte-Carlo simulations, allowing us to estimate the
detection biases of our campaign and showing that the latter do not affect our
conclusions. The absolute minimal binary fraction in our sample is f_min=0.44
but could be as high as 0.67 if all the binary candidates are confirmed. As in
NGC6231 (see Paper I), up to 75% of the O star population in NGC6611 are found
in an O+OB system, thus implicitly excluding random pairing from a classical
IMF as a process to describe the companion association in massive binaries. No
statistical difference could be further identified in the binary fraction,
mass-ratio and period distributions between NGC6231 and NGC6611, despite the
difference in age and environment of the two clusters.Comment: Accepted by MNRAS; 15 pages, 17 fi
An XMM-Newton view of the young open cluster NGC 6231 -- II. The OB star population
In this second paper, we pursue the analysis of the 180 ks XMM-Newton
campaign towards the young open cluster NGC 6231 and we focus on its rich OB
star population. We present a literature-based census of the OB stars in the
field of view with more than one hundred objects, among which 30% can be
associated with an X-ray source. All the O-type stars are detected in the X-ray
domain as soft and reasonably strong emitters. In the 0.5-10.0 keV band, their
X-ray luminosities scale with their bolometric luminosities as . Such a scaling law holds in
the soft (0.5-1.0 keV) and intermediate (1.0-2.5 keV) bands but breaks down in
the hard band. While the two colliding wind binaries in our sample clearly
deviate from this scheme, the remaining O-type objects show a very limited
dispersion (40% or 20% according to whether `cool' dwarfs are included or not),
much smaller than that obtained from previous studies. At our detection
threshold and within our sample, the sole identified mechanism that produces
significant modulations in the O star X-ray emission is related to wind
interaction. The intrinsic X-ray emission of non-peculiar O-type stars seems
thus constant for a given star and the level of its X-ray emission is
accurately related to the its luminosity or, equivalently, to its wind
properties. Among B-type stars, the detection rate is only about 25% in the
sub-type range B0-B4 and remains mostly uniform throughout the different
sub-populations while it drops significantly at later sub-types. The associated
X-ray spectra are harder than those of O-type stars. Our analysis points
towards the detected emission being associated with a physical PMS companion
>... [see paper for the complete abstract]Comment: 21 pages, 14 figures, Table 2 and Figs 2 to 5 will be available
through the CDS only, accepted for publication by MNRAS, Fig 1 not included
in the present preprint because of size limitation
The long period eccentric orbit of the particle accelerator HD167971 revealed by long baseline interferometry
Using optical long baseline interferometry, we resolved for the first time
the two wide components of HD167971, a candidate hierarchical triple system
known to efficiently accelerate particles. Our multi-epoch VLTI observations
provide direct evidence for a gravitational link between the O8 supergiant and
the close eclipsing O + O binary. The separation varies from 8 to 15 mas over
the three-year baseline of our observations, suggesting that the components
evolve on a wide and very eccentric orbit (most probably e>0.5). These results
provide evidence that the wide orbit revealed by our study is not coplanar with
the orbit of the inner eclipsing binary. From our measurements of the
near-infrared luminosity ratio, we constrain the spectral classification of the
components in the close binary to be O6-O7, and confirm that these stars are
likely main-sequence objects. Our results are discussed in the context of the
bright non-thermal radio emission already reported for this system, and we
provide arguments in favour of a maximum radio emission coincident with
periastron passage. HD167971 turns out to be an efficient O-type particle
accelerator that constitutes a valuable target for future high angular
resolution radio imaging using VLBI facilities.Comment: 8 pages, including 4 figures, accepted by Monthly Notices of the
Royal Astronomical Societ
Sher 25: pulsating but apparently alone
The blue supergiant Sher25 is surrounded by an asymmetric, hourglass-shaped
circumstellar nebula, which shows similarities to the triple-ring structure
seen around SN1987A. From optical spectroscopy over six consecutive nights, we
detect periodic radial velocity variations in the stellar spectrum of Sher25
with a peak-to-peak amplitude of ~12 km/s on a timescale of about 6 days,
confirming the tentative detec-tion of similar variations by Hendry et al. From
consideration of the amplitude and timescale of the signal, coupled with
observed line profile variations, we propose that the physical origin of these
variations is related to pulsations in the stellar atmosphere, rejecting the
previous hypothesis of a massive, short-period binary companion. The radial
velocities of two other blue supergiants with similar bipolar nebulae, SBW1 and
HD 168625, were also monitored over the course of six nights, but these did not
display any significant radial velocity variations.Comment: 9 pages, 7 figures. Accepted for publication in MNRA
The VLT-FLAMES Tarantula Survey
We present a number of notable results from the VLT-FLAMES Tarantula Survey
(VFTS), an ESO Large Program during which we obtained multi-epoch
medium-resolution optical spectroscopy of a very large sample of over 800
massive stars in the 30 Doradus region of the Large Magellanic Cloud (LMC).
This unprecedented data-set has enabled us to address some key questions
regarding atmospheres and winds, as well as the evolution of (very) massive
stars. Here we focus on O-type runaways, the width of the main sequence, and
the mass-loss rates for (very) massive stars. We also provide indications for
the presence of a top-heavy initial mass function (IMF) in 30 Dor.Comment: 7 Figures, 8 pages. Invited talk: IAUS 329: "The Lives and
Death-Throes of Massive Stars
Investigating the lack of main-sequence companions to massive Be stars
About 20% of all B-type stars are classical Be stars. The Be phenomenon is
strongly correlated with rapid rotation, the origin of which remains unclear.
It may be rooted in single- or binary-star evolution. In the framework of the
binary channel, the initially more massive star transfers mass and angular
momentum to the original secondary, which becomes a Be star. The system then
evolves into a Be binary with a post-main-sequence companion, which may later
be disrupted in a supernova event. Hence, if the binary channel dominates the
formation of Be stars, one may expect a strong lack of close Be binaries with
main sequence (MS) companions. Through an extensive, star-by-star review of the
literature of a magnitude-limited sample of Galactic early-type Be stars, we
investigate whether Be binaries with MS companions are known to exist. Our
sample is constructed from the BeSS database and cross-matched with all
available literature on the individual stars. Out of an initial list of 505 Be
stars, we compile a final sample of 287 Galactic Be stars earlier than B1.5
with V<=12 mag. Out of those, 13 objects were reported as Be binaries with
known post-MS companions and 11 as binaries with unknown, uncertain or debated
companions. We find no confirmed reports of Be binaries with MS companions. For
the remaining 263 targets, no significant reports of multiplicity exist in the
literature, implying that they are either Be binaries with faint companions, or
truly single. The clear lack of reported MS companions to Be stars, which
stands in contrast to the high number of detected B+B MS binaries, strongly
supports the hypothesis that early-type Be stars are binary interaction
products that spun up after mass and angular momentum transfer from a companion
star. Taken at face value, our results may suggest that a large majority of the
early-type Be stars have formed through binary mass-transfer.Comment: 15 pages (incl. appendix), 6 figures, 3 tables, accepted for
publication in A&
The Language of Creativity: Validating Linguistic Analysis to Assess Creative Scientists and Artists
The purpose of this study was twofold: first, to be among the first attempts to validate linguistic analysis as a method of creativity assessment and second, to differentiate between individuals in varying scientific and artistic creativity levels using personality language patterns. Creativity is most commonly assessed through methods such as questionnaires and specific tasks, the validity of which can be weakened by scorer or experimenter error, subjective and response biases, and self-knowledge constraints. Linguistic analysis may provide researchers with an automatic, objective method of assessing creativity, and free from human error and bias. The current study used 419 creativity text samples from a wide range of creative individuals mostly in science (and some in the arts and humanities) to investigate whether linguistic analysis can, in fact, distinguish between creativity levels and creativity domains using creativity dictionaries and personality dimension language patterns, from the linguistic inquiry and word count (LIWC) text analysis program. Creative individuals tended to use more words on the creativity keyword dictionaries as well as more introversion and openness to experience language pattern words than less creative individuals. Regarding creativity domains, eminent scientists used fewer introversion, and openness to experience language pattern words than eminent artists. Text analysis through LIWC was able to partially distinguish between the three creativity levels, in some cases, and the two creativity domains (science and art). These findings lend support to the use of linguistic analysis as a partially valid assessment of scientific and artistic creative achievement
- …