1,497 research outputs found
Metal-rich T-dwarfs in the Hyades cluster
We present the results of a search for brown dwarfs (BDs) and very low mass
(VLM) stars in the 625 Myr-old, metal-rich ([Fe/H]=0.14) Hyades cluster. We
performed a deep (I=23, z=22.5) photometric survey over 16 deg around the
cluster center. We report the discovery of the first 2 BDs in the Hyades
cluster, with a spectral type T1 and T2, respectively. Their optical and
near-IR photometry, as well as their proper motion, are consistent with them
being cluster members. According to models, their mass is about 50 Jupiter
masses at an age of 625 Myr. We also report the discovery of 3 new very low
mass stellar members and confirm the membership of 15 others
Herschel observations of the circumstellar environment of the two Herbig Be stars R Mon and PDS27
We report and analyse FIR observations of two Herbig Be stars, R Mon and PDS
27, obtained with Herschel's instruments PACS and SPIRE. We construct SEDs and
derive the infrared excess. We extract line fluxes from the PACS and SPIRE
spectra and construct rotational diagrams in order to estimate the excitation
temperature of the gas. We derive CO, [OI] and [CI] luminosities to determine
physical conditions of the gas, as well as the dominant cooling mechanism. We
confirm that the Herbig Be stars are surrounded by remnants from their parental
clouds, with an IR excess that mainly originates in a disc. In R Mon we detect
[OI], [CI], [CII], CO (26 transitions), water and OH, while in PDS 27 we only
detect [CI] and CO (8 transitions). We attribute the absence of OH and water in
PDS 27 to UV photo-dissociation and photo-evaporation. From the rotational
diagrams, we find several components for CO: we derive 94990 K,
35820 K & 7712 K for R Mon, 9612 K & 314 K for PDS 27 and
258 K & 276 K for their respective compact neighbours. The forsterite
feature at 69m was not detected in either of the sources, probably due to
the lack of (warm) crystalline dust in a flat disc. We find that cooling by
molecules is dominant in the Herbig Be stars, while this is not the case in
Herbig Ae stars where cooling by [OI] dominates. Moreover, we show that in the
Herbig Be star R Mon, outflow shocks are the dominant gas heating mechanism,
while in Herbig Ae stars this is stellar. The outflow of R Mon contributes to
the observed line emission by heating the gas, both in the central spaxel/beam
covering the disc and the immediate surroundings, as well as in those
spaxels/beams covering the parabolic shell around it. PDS 27, a B2 star, has
dispersed a large part of its gas content and/or destroyed molecules; this is
likely given its intense UV field.Comment: Accepted for publication in Astronomy & Astrophysic
The absence of the 10 um silicate feature in the isolated Herbig Ae star HD 100453
We analyse the optical and IR spectra, as well as the spectral energy
distribution (UV to mm) of the candidate Herbig Ae star HD100453. This star is
particular, as it shows an energy distribution similar to that of other
isolated Herbig Ae/Be stars (HAEBEs), but unlike most of them, it does not have
a silicate emission feature at 10 um, as is shown in Meeus (2001). We confirm
the HAEBE nature of HD100453 through an analysis of its optical spectrum and
derived location in the H-R diagram. The IR spectrum of HD100453 is modelled by
an optically thin radiative transfer code, from which we derive constraints on
the composition, grain-size and temperature distribution of the circumstellar
dust. We show that it is both possible to explain the lack of the silicate
feature as (1) a grain-size effect - lack of small silicate grains, and (2) a
temperature effect - lack of small, hot silicates, as proposed by Dullemond
(2001), and discuss both possibilities.Comment: 9 pages, 7 figures; accepted by A&
Sectoral patterns of interactive learning : an empirical exploration using an extended resource based model
This paper pursues the development of a theoretical framework that explains interactive learning between innovating firms and external actors in the knowledge infrastructure and the production chain. The research question is: what kinds of factors explain interactive learning of innovating firms with external actors? In our theoretical framework we augment the resource-based perspective predominant in network theory with an activity based account and a structural account of interactive learning. We contend basically: that higher technological dynamics induce innovative activities with a higher complexity. More complex innovative activities increase the probability of internal resource deficits/shortages in the innovating firms. The higher the resource deficits/shortages and the lower the alignment of innovative activities the more likely the search for complementary resources externally, which increases the likeliness of external relationships. In order to test the generality of our theoretical claims we analyse our models within four sectors with different technological dynamics as distinguished by Pavitt. Furthermore we estimate four models within each sector predicting: 1) the level of interactive learning of innovating firms with the public knowledge infrastructure (difficult to access, demands high internal competences to utilise scientific knowledge), 2) the level of interactive learning of innovating firms with the production chain (easy to access), 3) the level of interactive learning of innovating firms with their users (here the innovating firms are the producers), 4) the level of interactive learning of innovating firms with their suppliers (here the innovating firms are the users), 5) the level of interactive learning with competitors. These analyses allow for a comparison between interactive learning with different external actors and give deeper insights into the differentiated interaction patterns governing innovation. Our fmdings show that patterns of interactive learning between sectors differ. Some are more resource based and others are more affected by the complexity of innovative activities. Particularly the interactive learning with the knowledge infrastructure differs from that with actors in the production chain
New CP-violation and preferred-frame tests with polarized electrons
We used a torsion pendulum containing polarized
electrons to search for CP-violating interactions between the pendulum's
electrons and unpolarized matter in the laboratory's surroundings or the sun,
and to test for preferred-frame effects that would precess the electrons about
a direction fixed in inertial space. We find and for AU. Our preferred-frame constraints, interpreted in
the Kosteleck\'y framework, set an upper limit on the parameter eV that should be compared to the benchmark
value eV.Comment: 4 figures, accepted for publication in Physical Review Letter
ISO spectroscopy of circumstellar dust in 14 Herbig Ae/Be systems: towards an understanding of dust processing
We present Infrared Space Observatory (ISO) spectra of fourteen isolated
Herbig Ae/Be (HAEBE) stars, to study the characteristics of their circumstellar
dust. These spectra show large star-to-star differences, in the emission
features of both carbon-rich and oxygen-rich dust grains. The IR spectra were
combined with photometric data ranging from the UV through the optical into the
sub-mm region. We defined two key groups, based upon the spectral shape of the
infrared region. The derived results can be summarized as follows: (1) the
continuum of the IR to sub-mm region of all stars can be reconstructed by the
sum of a power-law and a cool component, which can be represented by a black
body. Possible locations for these components are an optically thick,
geometrically thin disc (power-law component) and an optically thin flared
region (black body); (2) all stars have a substantial amount of cold dust
around them, independent of the amount of mid-IR excess they show; (3) also the
near-IR excess is unrelated to the mid-IR excess, indicating different
composition/location of the emitting material; (4) remarkably, some sources
lack the silicate bands; (5) apart from amorphous silicates, we find evidence
for crystalline silicates in several stars, some of which are new detections;
(6) PAH bands are present in at least 50% of our sample, and their appearance
is slightly different from PAHs in the ISM; (7) PAH bands are, with one
exception, not present in sources which only show a power-law continuum in the
IR; their presence is unrelated to the presence of the silicate bands; (8) the
dust in HAEBE stars shows strong evidence for coagulation; this dust processing
is unrelated to any of the central star properties (such as age, spectral type
and activity).Comment: 15 pages, accepted by A&
Contradictory yet coherent? Inconsistency in performance feedback and R&D investment change
This paper is based upon doctoral research of the first author
conducted while at the Center for Innovation Research, Tilburg University.
The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.In this paper, we study to what extent inconsistent feedback signals about performance affect firm adaptive behavior in terms of changes made to research-and-development (R&D) investments. We argue that inconsistency in performance feedbackâbased on discrepancies between two distinct performance signalsâaffects the degree to which such investments will be changed. Our aim is to show that accounting for inconsistent performance feedback is necessary as predictions for the direction of change in R&D investments based on the individual performance feedback signals are contradictory. Furthermore, we contribute by proposing a holistic consideration mechanism as an alternative to the selective attention mechanism previously applied to inconsistent performance feedback. Our findings show that the impact of inconsistency depends on the exact configuration of the underlying performance feedback signal discrepancies. While consistently negative performance feedback signals would amplify their impact in stimulating increased R&D investments, inconsistent performance feedback signals created more nuanced effects. Having lower performance compared to an industry-based peer groupâdespite doing well compared to the previous yearâmade firms decrease their R&D investments. For the opposite case of inconsistent performance feedback, we did not find an effect on change in R&D investments. These findings support to a degree our contention that explaining the effects of inconsistent performance feedback requires a holistic consideration theoretical mechanism instead of one involving selective attention. In sum, these findings suggest future research should take into account the differences between distinct instances of inconsistent performance feedback
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