831 research outputs found
Near-infrared photometry of WISE J085510.74-071442.5
Indexación: Web of ScienceAims. We aim at obtaining near-infrared photometry and deriving the mass, age, temperature, and surface gravity of WISE J085510.74 071442.5 (J0855 0714), which is the coolest object beyond the solar system currently known.
Methods. We used publicly available data from the archives of the Hubble Space Telescope (HST) and the Very Large Telescope (VLT) to determine the emission of this source at 1.153 mu m (F110W) and 1.575 mu m (CH4-o ff). J0855 0714 was detected at both wavelengths with a signal-to-noise ratio of approximate to 10 (F110W) and approximate to 4 (CH4-off) at the peak of the corresponding point-spread-functions.
Results. This is the first detection of J0855 0714 in the H-band wavelengths. We measured 26.31 +/- 0.10 and 23.22 +/- 0.35 mag in F110W and CH4-o ff (Vega system). J0855 0714 remains unresolved in the HST images that have a spatial resolution of 0.22 0 0. Companions at separations of 0.5 AU (similar mass and brightness) and at similar to 1 AU approximate to 1 mag fainter in the F110W filter) are discarded. By combining the new data with published photometry, including non-detections, we build the spectral energy distribution of J0855 0714 from 0.89 through 22.09 mu m, and contrast it against current solar-metallicity models of planetary atmospheres. We determine that the best spectral fit yields a temperature of 225 250 K, a bolometric luminosity of log L/L-circle dot = 8 : 57, and a high surface gravity of log g = 5 : 0 (cm s(2)), which suggests an old age although a gravity this high is not fully compatible with evolutionary models. After comparing our data with the cooling theory for brown dwarfs and planets, we infer a mass in the interval 2 10 MJup for ages of 1 12 Gyr and high atmospheric gravities of log g greater than or similar to 3.5 (cm s(2)). If it had the age of the Sun, J0855 0714 would be a approximate to 5-M-Jup free-floating planetary-mass object.
Conclusions. J0855 0714 meets the mass values previously determined for free-floating planetary-mass objects discovered in starforming regions and young stellar clusters. Based on extrapolations of the substellar mass functions of young clusters to the field, as many J0855 0714-like objects as M5-L2 stars may be expected to populate the solar neighborhood.http://www.aanda.org/articles/aa/pdf/2016/08/aa28662-16.pd
2MASS J154043.42-510135.7: a new addition to the 5 pc population
The aim of the project is to find the stars nearest to the Sun and to
contribute to the completion of the stellar and substellar census of the solar
neighbourhood. We identified a new late-M dwarf within 5 pc, looking for high
proper motion sources in the 2MASS-WISE cross-match. We collected astrometric
and photometric data available from public large-scale surveys. We complemented
this information with low-resolution optical and near-infrared spectroscopy
with instrumentation on the ESO NTT to confirm the nature of our candidate. We
also present a high-quality medium-resolution VLT/X-shooter spectrum covering
the 400 to 2500 nm wavelength range. We classify this new neighbour as an
M7.00.5 dwarf using spectral templates from the Sloan Digital Sky Survey
and spectral indices. Lithium absorption at 670.8 nm is not detected in the
X-shooter spectrum, indicating that the M7 dwarf is older than 600 Myr and more
massive than 0.06 M. We also derive a trigonometric distance of 4.4
pc, in agreement with the spectroscopic distance estimate, making
2MASS\,J154043.42510135.7 the nearest M7 dwarf to the Sun. This
trigonometric distance is somewhat closer than the 6 pc distance reported
by the ALLWISE team, who independently identified this object recently. This
discovery represents an increase of 25\% in the number of M7--M8 dwarfs already
known at distances closer than 8\,pc from our Sun. We derive a density of
\,=\,1.90.910\,pc for M7 dwarfs in the 8 pc
volume, a value similar to those quoted in the literature. This new ultracool
dwarf is among the 50 nearest systems to the Sun, demonstrating that our
current knowledge of the stellar census within the 5 pc sample remains
incomplete. 2M1540 represents a unique opportunity to search for extrasolar
planets around ultracool dwarfs due to its proximity and brightness.Comment: 8 pages, 5 figures. Acepted in Astronomy & Astrophysics (15/05/2005
Discovery of a wide companion near the deuterium burning mass limit in the Upper Scorpius association
We present the discovery of a companion near the deuterium burning mass limit
located at a very wide distance, at an angular separation of 4.6+/-0.1 arcsec
(projected distance of ~ 670 AU) from UScoCTIO108, a brown dwarf of the very
young Upper Scorpius association. Optical and near-infrared photometry and
spectroscopy confirm the cool nature of both objects, with spectral types of M7
and M9.5, respectively, and that they are bona fide members of the association,
showing low gravity and features of youth. Their masses, estimated from the
comparison of their bolometric luminosities and theoretical models for the age
range of the association, are 60+/-20 and 14^{+2}_{-8} MJup, respectively. The
existence of this object around a brown dwarf at this wide orbit suggests that
the companion is unlikely to have formed in a disk based on current planet
formation models. Because this system is rather weakly bound, they did not
probably form through dynamical ejection of stellar embryos.Comment: 10 pages, including 4 figures and 2 table
Spin-polarized current oscillations in diluted magnetic semiconductor multiple quantum wells
We study the spin and charge dynamics of electrons in n-doped II--VI
semiconductor multiple quantum wells when one or more quantum wells are doped
with Mn. The interplay between strongly nonlinear inter-well charge transport
and the large tunable spin-splitting induced by exchange interactions with
spin-polarized Mn ions produces interesting new spin dependent features. The
tunneling current between quantum wells can be strongly spin polarized and,
under certain conditions, can develop self sustained oscillations under a
finite dc voltage. The spin polarization oscillates in both magnetic and
nonmagnetic quantum wells and the time average in magnetic wells can differ
from its zero-voltage value. Our numerical simulations demonstrate that the
amplitude of the spin polarization oscillations depends on the distribution of
magnetic wells within the sample. We discuss how the spin polarized current and
the spin polarization of the quantum wells can be tailored experimentally.Comment: 5 pages, 5 figures; to be published in Phys. Rev.
Electric dipole rovibrational transitions in HD molecule
The rovibrational electric dipole transitions in the ground electronic state
of the HD molecule are studied. A simple, yet rigorous formula is derived for
the transition rates in terms of the electric dipole moment function ,
which is calculated in a wide range of . Our numerical results for
transition rates are in moderate agreement with experiments and previous
calculations, but are at least an order of magnitude more accurate.Comment: 7 pages, 1 figur
Recommended from our members
A pragmatic patient-reported outcome strategy for rare disease clinical trials: application of the EORTC item library to myelodysplastic syndromes, chronic myelomonocytic leukemia, and acute myeloid leukemia.
BackgroundNovel, pragmatic, patient-centered strategies are needed to ensure fit-for-purpose patient-reported outcomes (PRO) instruments in clinical trial research for rare diseases such as myelodysplastic syndromes (MDS), acute myeloid leukemia (AML), and chronic myelomonocytic leukemia (CMML). The objective of the current study was to select supplemental items to add to the European Organization for Research and Treatment of Cancer (EORTC) Quality of Life-Core 30 (QLQ-C30) to ensure content coverage of all important clinical concepts in patients with higher-risk (HR) MDS, low-blast count (LB) AML, and CMML, thus, improving the instrument's ability to detect clinically meaningful treatment benefit for this context of use.MethodsOur mixed methods approach comprised literature review, clinician consultation (n = 3), and qualitative and quantitative analysis of two stages of patient interview data (n = 14, n = 18) to select library bank items to supplement a generic cancer PRO, the EORTC QLQ-C30.ResultsUnique symptom (n = 54) and impact (n = 72) concepts were organized into conceptual frameworks of treatment benefit, compared with EORTC QLQ-C30 items and conceptual gaps identified. Supplemental items (n = 13) addressing those gaps were selected from the EORTC Item Library and tested with patients. Supplemental item endorsement frequencies met World Health Organization Quality of Life criteria, suggesting good targeting and relevance for this sample. However, three supplemental items were confirmed as problematic based upon cognitive debriefing results, and expert clinical consultations. Ultimately, 10 supplemental items (n = 7 symptom; n = 3 impact) were selected for the MDS/AML/CMML context.ConclusionSupplemental items were selected to enhance the conceptual coverage of the EORTC QLQ-C30 in the areas of fatigue, shortness of breath, and functioning
Temporal changes of the flare activity of Proxima Cen
We study temporal variations of the emission lines of Halpha, Hepsilon, H and
K Ca II, D1 and D2 Na I, 4026 and 5876 A He I in the HARPS spectra of Proxima
Centauri across an extended time of 13.2 years, from May 27, 2004, to September
30, 2017.
Aims. We analyse the common behaviour and differences in the intensities and
profiles of different emission lines in flare and quiet modes of Proxima
activity.
Methods. We compare the pseudo-equivalent widths (pEW) and profiles of the
emission lines in the HARPS high-resolution (R ~ 115,000) spectra observed at
the same epochs.
Results. All emission lines show variability with a timescale of at least 10
min. The strength of all lines except He I 4026 A correlate with \Halpha.
During strong flares the `red asymmetry' appears in the Halpha emission line
indicating the infall of hot condensed matter into the chromosphere with
velocities greater than 100 km/s disturbing chromospheric layers. As a result,
the strength of the Ca II lines anti-correlates with Halpha during strong
flares. The He I lines at 4026 and 5876 A appear in the strong flares. The
cores of D1 and D2 Na I lines are also seen in emission. During the minimum
activity of Proxima Centauri, Ca II lines and Hepsilon almost disappear while
the blue part of the Na I emission lines is affected by the absorption in the
extending and condensing flows.
Conclusions. We see different behaviour of emission lines formed in the flare
regions and chromosphere. Chromosphere layers of Proxima Cen are likely heated
by the flare events; these layers are cooled in the `non-flare' mode. The
self-absorption structures in cores of our emission lines vary with time due to
the presence of a complicated system of inward and outward matter flows in the
absorbing layers.Comment: 22 pages, 12 Figures, accepted by A
Optical Linear Polarization of Late M- and L-Type Dwarfs
(Abridged). We report on the linear polarimetric observations in the Johnson
I filter of 44 M6-L7.5 ultracool dwarfs (2800-1400 K). Eleven (10 L and 1 M)
dwarfs appear to have significant linear polarization (P = 0.2-2.5%). We have
compared the M- and L-dwarf populations finding evidence for a larger frequency
of high I-band polarization in the coolest objects, supporting the presence of
significant amounts of dust in L-dwarfs. The probable polarizing mechanism is
related to the presence of heterogeneous dust clouds nonuniformly distributed
across the visible photospheres and the asymmetric shape of the objects. In
some young ultracool dwarfs, surrounding dusty disks may also yield
polarization. For polarimetric detections, a trend for slightly larger
polarization from L0 to L6.5 may be present in our data, suggesting changes in
the distribution of the grain properties, vertical height of the clouds,
metallicity, age, and rotation speed. One of our targets is the peculiar brown
dwarf (BD) 2MASS J2244+20 (L6.5), which shows the largest I-band polarization
degree. Its origin may lie in a surrounding dusty disk or rather large
photospheric dust grains. The M7 young BD CFHT-BD-Tau 4 and the L3.5 field
dwarf 2MASS J0036+18 were also observed in the Johnson R filter. Our data
support the presence of a circum(sub)stellar disk around the young accreting
BD. Our data also support a grain growth in the submicron regime in the visible
photosphere of J0036+18 (1900 K). The polarimetric data do not obviously
correlate with activity or projected rotational velocity. Three polarized
early- to mid-L dwarfs display I-band light curves with amplitudes below 10
mmag.Comment: Accepted for publication in ApJ (March 2005), 35 pages, 5 figure
The CARMENES search for exoplanets around M dwarfs - Photospheric parameters of target stars from high-resolution spectroscopy
The new CARMENES instrument comprises two high-resolution and high-stability
spectrographs that are used to search for habitable planets around M dwarfs in
the visible and near-infrared regime via the Doppler technique. Characterising
our target sample is important for constraining the physical properties of any
planetary systems that are detected. The aim of this paper is to determine the
fundamental stellar parameters of the CARMENES M-dwarf target sample from
high-resolution spectra observed with CARMENES. We also include several M-dwarf
spectra observed with other high-resolution spectrographs, that is CAFE, FEROS,
and HRS, for completeness. We used a {chi}^2 method to derive the stellar
parameters effective temperature T_eff, surface gravity log g, and metallicity
[Fe/H] of the target stars by fitting the most recent version of the
PHOENIX-ACES models to high-resolution spectroscopic data. These stellar
atmosphere models incorporate a new equation of state to describe spectral
features of low-temperature stellar atmospheres. Since T_eff, log g, and [Fe/H]
show degeneracies, the surface gravity is determined independently using
stellar evolutionary models. We derive the stellar parameters for a total of
300 stars. The fits achieve very good agreement between the PHOENIX models and
observed spectra. We estimate that our method provides parameters with
uncertainties of {sigma} T_eff = 51 K, {sigma} log g = 0.07, and {sigma} [Fe/H]
= 0.16, and show that atmosphere models for low-mass stars have significantly
improved in the last years. Our work also provides an independent test of the
new PHOENIX-ACES models, and a comparison for other methods using
low-resolution spectra. In particular, our effective temperatures agree well
with literature values, while metallicities determined with our method exhibit
a larger spread when compared to literature results
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