311 research outputs found
Open clusters with Hipparcos I. Mean astrometric parameters
New memberships, mean parallaxes and proper motions of all 9 open clusters
closer than 300 pc (except the Hyades) and 9 rich clusters between 300 and 500
pc have been computed using Hipparcos data. Precisions, ranging from 0.2 to 0.5
mas for parallaxes and 0.1 to 0.5 mas/yr for proper motions, are of great
interest for calibrating photometric parallaxes as well as for kinematical
studies. Careful investigations of possible biases have been performed and no
evidence of significant systematic errors on the mean cluster parallaxes has
been found. The distances and proper motions of 32 more distant clusters, which
may be used statistically, are also indicated.Comment: 15 pages, A&A in pres
On the Radii of Extrasolar Giant Planets
We have computed evolutionary models for extrasolar planets which range in
mass from 0.1 to 3.0 Jovian Masses, and which range in equilibrium temperature
from 113 K to 2000 K. We present four sequences of models, designed to show the
structural effects of a solid core and of internal heating due to the
conversion of kinetic to thermal energy at pressures of tens of bars. The model
planetary radii are intended for comparisons with radii derived from
observations of transiting extrasolar planets. To provide such comparisons, we
expect that of order 10 transiting planets with orbital periods less than 200
days can be detected around bright (V<10) main-sequence stars for which
accurate, well-sampled radial velocity measurements can be readily accumulated.
Through these observations, structural properties of the planets will be
derivable, particularly for low-mass, high-temperature planets. Implications
regarding the transiting companion to OGLE-TR-56 recently announced by Konacki
et al. are discussed.
With regard to the confirmed transiting planet, HD 209458b, we find, in
accordance with other recent calculations, that models without internal heating
predict a radius that is 35 percent smaller than the observed radius. We
explore the possibility that HD 209458b owes its large size to dissipation of
energy arising from ongoing tidal circularization of the orbit. We show that
residual scatter in the current radial velocity data set for HD 209458b is
consistent with the presence of an as-of-yet undetected second companion, and
that further radial velocity monitoring of the star is indicated.Comment: 23 pages, 3 figures, accepted by Astrophysical Journa
Discovery of high proper motion ancient white dwarfs: nearby massive compact halo objects?
We present the discovery and spectroscopic identification of two very high
proper motion ancient white dwarf stars, found in a systematic proper motion
survey. Their kinematics and apparent magnitude clearly indicate that they are
halo members, while their optical spectra are almost identical to the recently
identified cool Halo white dwarf WD0346+246. Canonical stellar halo models
predict a white dwarf volume density of two orders of magnitude less than the
approx 7*10^{-4} Solar masses per pc^{-3} inferred from this survey. With the
caveat that the sample size is very small, it appears that a significant
fraction, about 10%, of the local dark matter halo is in the form of very old,
cool, white dwarfs.Comment: 8 pages, 2 figures, accepted for publication in ApJL; references
adde
Regulation of ABCA1 expression and cholesterol efflux during adipose differentiation of 3T3-L1 cells.
Adipose cells specialized in energy storage, contain large intracellular triglyceride-rich lipid droplets, are enriched with free cholesterol, and express sterol-regulated transcription factors such as liver X receptor (LXR). The recent identification of the LXR-dependent ATP binding cassette transporter A1 (ABCA1) pathway for cholesterol release from peripheral cells has led us to address the question of the expression and function of ABCA1 in adipocytes. In 3T3-L1 adipose cells, we observed a strong induction of ABCA1 mRNA during adipose differentiation, but only limited variations in ABCA1 protein. Lipid efflux onto apolipoprotein A-I (apoA-I), which depends on ABCA1, was comparable in adipocytes and preadipocytes, demonstrating a differential regulation of ABCA1 mRNA and cholesterol efflux. We also found that total cell cholesterol remained stable during differentiation of 3T3-L1 cells, but membrane cholesterol was lower in adipocytes than in preadipocytes, suggesting redistribution of cholesterol to the lipid droplet. Finally, we show that under standard lipolytic stimulation, 3T3-L1 adipocytes do not release cholesterol onto apoA-I, a process that required long exposures to lipolytic agents (24 h). In conclusion, despite large induction of ABCA1 mRNA during differentiation, cholesterol efflux through the ABCA1 pathway remains limited in adipocytes and requires prolonged lipolysis. This is consistent with the view of the adipocyte behaving as a cholesterol sink, with plasma cholesterol-buffering properties
The HARPS search for southern extra-solar planets. XX. Planets around the active star BD-08:2823
We report the detection of a planetary system around BD-08:2823, that
includes at least one Uranus-mass planet and one Saturn-mass planet. This
discovery serendipitously originates from a search for planetary transits in
the Hipparcos photometry database. This program preferentially selected active
stars and did not allow the detection of new transiting planets. It allowed
however the identification of the K3V star BD-08:2823 as a target harboring a
multiplanet system, that we secured and characterized thanks to an intensive
monitoring with the HARPS spectrograph at the 3.6-m ESO telescope in La Silla.
The stellar activity level of BD-08:2823 complicates the analysis but does not
prohibit the detection of two planets around this star. BD-08:2823b has a
minimum mass of 14.4+/-2.1 M_Earth and an orbital period of 5.60 days, whereas
BD-08:2823c has a minimum mass of 0.33+/-0.03 M_Jup and an orbital period of
237.6 days. This new system strengthens the fact that low-mass planets are
preferentially found in multiplanetary systems, but not around high-metallicity
stars as this is the case for massive planets. It also supports the belief that
active stars should not be neglected in exoplanet searches, even when searching
for low-mass planets.Comment: 10 pages, 8 figures, 3 tables, accepted for publication in A&
WISE Circumstellar Disks in the Young Sco-Cen Association
We present an analysis of the WISE photometric data for 829 stars in the
Sco-Cen OB2 association, using the latest high-mass membership probabilities.
We detect infrared excesses associated with 135 BAF-type stars, 99 of which are
secure Sco-Cen members. There is a clear increase in excess fraction with
membership probability, which can be fitted linearly. We infer that 41+-5% of
Sco-Cen OB2 BAF stars to have excesses, while the field star excess fraction is
consistent with zero. This is the first time that the probability of
non-membership has been used in the calculation of excess fractions for young
stars. We do not observe any significant change in excess fraction between the
three subgroups. Within our sample, we have observed that B-type association
members have a significantly smaller excess fraction than A and F-type
association members.Comment: 5 Pages, 3 figure, 4 tables. Complete table 1 included. Accepted to
MNRAS Letter
A Constraint on brown dwarf formation via ejection: radial variation of the stellar and substellar mass function of the young open cluster IC2391
Using the Wide Field Imager (WFI) at the ESO 2.2m telescope at La Silla and
the CPAPIR camera at the CTIO 1.5m telescope at Cerro Tololo, we have performed
an extensive, multiband photometric survey of the open cluster IC2391 (D~146pc,
age~50Myr, solar metallicity). Here we present the results from our photometric
survey and from a spectroscopic follow-up of the central part of the survey.Comment: 4 pages, 3 figures, to appear in the proceedings of the Cool Stars 15
conferenc
Nalfurafine Reduces Neuroinflammation and Drives Remyelination in Models of CNS Demyelinating Disease
Objectives: Multiple sclerosis (MS) is a neurodegenerative disease characterised by inflammation and damage to the myelin sheath, resulting in physical and cognitive disability. There is currently no cure for MS, and finding effective treatments to prevent disease progression has been challenging. Recent evidence suggests that activating kappa opioid receptors (KOR) has a beneficial effect on the progression of MS. Although many KOR agonists like U50,488 are not suitable for clinical use because of a poor side-effect profile, nalfurafine is a potent, clinically used KOR agonist with a favorable side-effect profile.
Methods: Using the experimental autoimmune encephalomyelitis (EAE) model, the effect of therapeutically administered nalfurafine or U50,488 on remyelination, CNS infiltration and peripheral immune responses were compared. Additionally, the cuprizone model was used to compare the effects on non-immune demyelination.
Results: Nalfurafine enabled recovery and remyelination during EAE. Additionally, it was more effective than U50,488 and promoted disease reduction when administered after chronic demyelination. Blocking KOR with the antagonist, nor‐BNI, impaired full recovery by nalfurafine, indicating that nalfurafine mediates recovery from EAE in a KOR‐dependent fashion. Furthermore, nalfurafine treatment reduced CNS infiltration (especially CD4+ and CD8+ T cells) and promoted a more immunoregulatory environment by decreasing Th17 responses. Finally, nalfurafine was able to promote remyelination in the cuprizone demyelination model, supporting the direct effect on remyelination in the absence of peripheral immune cell invasion.
Conclusions: Overall, our findings support the potential of nalfurafine to promote recovery and remyelination and highlight its promise for clinical use in MS
A Hubble Space Telescope ACS Search for Brown Dwarf Binaries in the Pleiades Open Cluster
We present the results of a high-resolution imaging survey for brown dwarf
binaries in the Pleiades open cluster. The observations were carried out with
the Advance Camera for Surveys onboard the Hubble Space Telescope. Our sample
consists of 15 bona-fide brown dwarfs. We confirm 2 binaries and detect their
orbital motion, but we did not resolve any new binary candidates in the
separation range between 5.4AU and 1700AU and masses in the range
0.035--0.065~Msun. Together with the results of our previous study (Martin et
al., 2003), we can derive a visual binary frequency of 13.3\%
for separations greater than 7~AU masses between 0.055--0.065~M_{\sun} and
mass ratios between 0.45--0.91.0. The other observed properties of
Pleiades brown dwarf binaries (distributions of separation and mass ratio)
appear to be similar to their older counterparts in the field.Comment: 29 pages, 7 figures, 6 tables, accepted for publication in Ap
- …