499 research outputs found
Irradiated brown dwarfs
We have observed the post common envelope binary WD0137-349 in the near
infrared , and bands and have determined that the photometry varies
on the system period (116 min). The amplitude of the variability increases with
increasing wavelength, indicating that the brown dwarf in the system is likely
being irradiated by its 16500 K white dwarf companion. The effect of the
(primarily) UV irradiation on the brown dwarf atmosphere is unknown, but it is
possible that stratospheric hazes are formed. It is also possible that the
brown dwarf (an L-T transition object) itself is variable due to patchy cloud
cover. Both these scenarios are discussed, and suggestions for further study
are made.Comment: 5 pages, 2 figures. Proceedings from "Brown dwarfs come of age"
meeting in Fuerteventura 201
Reverse graded relaxed buffers for high Ge content SiGe virtual substrates
An innovative approach is proposed for epitaxial growth of high Ge content, relaxed Si1âxGex buffer layers on a Si(001) substrate. The advantages of the technique are demonstrated by growing such structures via chemical vapor deposition and their characterization. Relaxed Ge is first grown on the substrate followed by the reverse grading approach to reach a final buffer composition of 0.78. The optimized buffer structure is only 2.8 ”m thick and demonstrates a low surface threading dislocation density of 4Ă106 cmâ2, with a surface roughness of 2.6 nm. The buffers demonstrate a relaxation of up to 107%
PHL 5038: a spatially resolved white dwarf + brown dwarf binary
A near-infrared excess is detected at the white dwarf PHLâ5038 in UKIDSS photometry, consistent with the presence of a cool, substellar companion. We have obtained H- and K-grism spectra and images of PHLâ5038 using NIRI on Gemini North. The target is spatially and spectrally resolved into two components: an 8000 K DA white dwarf, and a likely L8 brown dwarf companion, separated by 0.94\arcsec. The spectral type of the secondary was determined using standard spectral indices for late L and T dwarfs. The projected orbital separation of the binary is 55 AU, so it becomes only the second known wide WD+dL binary to be found after GDâ165AB. This object could potentially be used as a benchmark for testing substellar evolutionary models at intermediate to older ages
New stellar members of the Coma Berenices open star cluster
We present the results of a survey of the Coma Berenices open star cluster
(Melotte 111), undertaken using proper motions from the USNO-B1.0 and
photometry from the 2MASS Point Source catalogues. We have identified 60 new
candidate members with masses in the range 1.007<M<$0.269M_solar. For each we
have estimated a membership probability by extracting control clusters from the
proper motion vector diagram. All 60 are found to have greater than 60 per cent
probability of being clusters more than doubling the number of known cluster
members. The new luminosity function for the cluster peaks at bright
magnitudes, but is rising at K~12, indicating that it is likely lower mass
members may exist. The mass function also supports this hypothesis.Comment: accepted for MNRA
Vaping for weight control: Findings from a qualitative study
Introduction: Smokers have expressed concern about weight gain once they stop smoking and weight gain is a risk factor associated with smoking relapse. Nicotine in e-cigarettes, as well as vaping behaviour, may support smoking cessation by reducing weight gain. This study explored the factors that influence attitudes towards, and awareness of, e-cigarettes and weight control post smoking cessation. Methods: Qualitative study involving focus groups with adults in the UK (n = 58) who were either exclusive vapers or dual users. Results: There was limited awareness and/or inclination to vape to prevent weight gain after stopping smoking. Reasons for this centred on: the health gains of stopping smoking outweighing any potential weight gain; a lack of understanding of the appetite supressing effects of nicotine; a belief that vaping could not suppress appetite like a cigarette and could result in craving for certain flavours; concerns about the longer-term effects of e-cigarettes on health and the ethics of promoting vaping as way to support smoking cessation by limiting weight gain, especially for young women. Conclusion: Participants in this study do not appear inclined to use e-cigarettes to prevent weight gain after smoking cessation. There is a lack of understanding about why nicotine might help prevent weight gain and a concern that e-cigarette flavours could provoke cravings and that vaping may be unsafe in the long-term
WD0837+185:the formation and evolution of an extreme mass ratio white dwarf-brown dwarf binary in Praesepe
There is a striking and unexplained dearth of brown dwarf companions in close
orbits (< 3AU) around stars more massive than the Sun, in stark contrast to the
frequency of stellar and planetary companions. Although rare and relatively
short-lived, these systems leave detectable evolutionary end points in the form
of white dwarf - brown dwarf binaries and these remnants can offer unique
insights into the births and deaths of their parent systems. We present the
discovery of a close (orbital separation ~ 0.006 AU) substellar companion to a
massive white dwarf member of the Praesepe star cluster. Using the cluster age
and the mass of the white dwarf we constrain the mass of the white dwarf
progenitor star to lie in the range 3.5 - 3.7 Msun (B9). The high mass of the
white dwarf means the substellar companion must have been engulfed by the B
star's envelope while it was on the late asymptotic giant branch (AGB). Hence,
the initial separation of the system was ~2 AU, with common envelope evolution
reducing the separation to its current value. The initial and final orbital
separations allow us to constrain the combination of the common envelope
efficiency (alpha) and binding energy parameters (lambda) for the AGB star to
alpha lambda ~3. We examine the various formation scenarios and conclude that
the substellar object was most likely to have been captured by the white dwarf
progenitor early in the life of the cluster, rather than forming in situ.Comment: Accepted for publication in ApJ
The Power of Product Innovation: Smokers' Perceptions of Capsule Cigarettes
Introduction Since being brought to market in 2007, cigarettes with capsules in the filter that can be burst to change the flavor have had remarkable global success, highlighting the importance of product innovation for tobacco companies. Very few studies have explored how these products are perceived by smokers however. This paper sought to address this gap by exploring smokersâ awareness of cigarettes with one or two flavor-changing capsules in the filter and the appeal of these products. Methods Twenty focus groups were conducted in Glasgow and Edinburgh in 2015 with current smokers (N= 120), segmented by age (16â17, 18â24, 25â35, 36â50, >50), gender, and social grade. Results Awareness, use and appeal of capsule cigarettes was greater among younger adults (16â35 years), who showed most interest in these products. Those who perceived capsules positively mentioned multiple benefits: the ability to burst the capsule, convenience of being able to share cigarettes among menthol and nonmenthol smokers, better taste, fresher breath, reduced smell, and greater discretion. It was suggested that capsule cigarettes, particularly the double capsule cigarette (which had two differently flavored capsules in the filter), would encourage nonsmokers to experiment with smoking and discourage smokers from quitting. Conclusions The findings offer some reasons behind the global growth of the capsule cigarette segment. Implications Cigarettes with flavor-changing capsules in the filter have been one of the most successful product innovations of the last decade for tobacco companies. They have received very little academic attention however. Employing focus groups with 120 smokers aged 16 and over, we found that capsule cigarettes held most appeal to, and were considered to be targeted at, younger people, with it suggested that these products would encourage initiation and discourage cessation. This study provides some understanding of how these products are viewed by smokers
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Representing time-dependent freezing behaviour in immersion mode ice nucleation
In order to understand the impact of ice formation in clouds, a quantitative understanding of ice nucleation is required, along with an accurate and efficient representation for use in cloud resolving models. Ice nucleation by atmospherically relevant particle types is complicated by interparticle variability in nucleating ability, as well as a stochastic, time-dependent, nature inherent to nucleation. Here we present a new and computationally efficient Framework for Reconciling Observable Stochastic Time-dependence (FROST) in immersion mode ice nucleation. This framework is underpinned by the finding that the temperature dependence of the nucleation-rate coefficient controls the residence-time and cooling-rate dependence of freezing. It is shown that this framework can be used to reconcile experimental data obtained on different timescales with different experimental systems, and it also provides a simple way of representing the complexities of ice nucleation in cloud resolving models. The routine testing and reporting of time-dependent behaviour in future experimental studies is recommended, along with the practice of presenting normalised data sets following the methods outlined here
A wide deep infrared look at the Pleiades with UKIDSS: new constraints on the substellar binary fraction and the low mass IMF
We present the results of a deep wide-field near-infrared survey of 12 square
degrees of the Pleiades conducted as part of the UKIDSS Deep Infrared Sky
Survey (UKIDSS) Galactic Cluster Survey (GCS). We have extracted over 340 high
probability proper motion members down to 0.03 solar masses using a combination
of UKIDSS photometry and proper motion measurements obtained by
cross-correlating the GCS with data from the Two Micron All Sky Survey (2MASS),
the Isaac Newton (INT) and the Canada-France-Hawai'i (CFHT) telescopes.
Additionally, we have unearthed 73 new candidate brown dwarf members on the
basis of five band UKIDSS photometry alone. We have identified 23 substellar
multiple system candidates out of 63 candidate brown dwarfs from the (Y-K,Y)
and (J-K,J) colour-magnitude diagrams, yielding a binary frequency of 28-44% in
the 0.075-0.030 Msun mass range. Our estimate is three times larger than the
binary fractions reported from high-resolution imaging surveys of field
ultracool dwarfs and Pleiades brown dwarfs. However, it is marginally
consistent with our earlier ``peculiar'' photometric binary fraction of
50+/-10% presented in Pinfield et al. (2003), in good agreement with the 32-45%
binary fraction derived from the recent Monte-Carlo simulations of Maxted &
Jeffries (2005) and compatible with the 26+/-10% frequency recently estimated
by Basri & Reiners (2006). A tentative estimate of the mass ratios from
photometry alone seems to support the hypothesis that binary brown dwarfs tend
to reside in near equal-mass ratio systems. (abridged)Comment: 21 pages, 8 figures, 6 tables, 1 electronic table, 6 appendices with
tables, accepted to MNRA
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