2,586 research outputs found
The young, wide and very low mass visual binary LOri167
We look for wide, faint companions around members of the 5 Myr Lambda Orionis
open cluster. We used optical, near-infrared, and Spitzer/IRAC photometry. We
report the discovery of a very wide very low mass visual binary, LOri167,
formed by a brown dwarf and a planetary-mass candidate located at 5 arcsec,
which seems to belong to the cluster. We derive Teff of 2125 and 1750 K. If
they are members, comparisons with theoretical models indicate masses of 17
(20-15) Mjup and 8 (13-7) Mjup, with a projected separation of 2000 AU. Such a
binary system would be difficult to explain in most models, particularly those
where substellar objects form in the disks surrounding higher mass stars.Comment: Astronomy & Astrophysics Letters, in pres
VOSA: Virtual Observatory SED Analyzer. An application to the Collinder 69 open cluster
The physical properties of almost any kind of astronomical object can be
derived by fitting synthetic spectra or photometry extracted from theoretical
models to observational data.
We want to develop an automatic procedure to perform this kind of fittings to
a relatively large sample of members of a stellar association and apply this
methodology to the case of Collinder 69.
We combine the multiwavelength data of our sources and follow a work-flow to
derive the physical parameters of the sources. The key step of the work-flow is
performed by a new VO-tool, VOSA. All the steps in this process are done in a
VO environment.
We present this new tool, and provide physical parameters such as T, gravity, luminosity, etc. for 170 candidate members to Collinder
69, and an upper-limit for the age of this stellar association.
This kind of studies of star forming regions, clusters, etc. produces a huge
amount of data, very tedious to analyse using the traditional methodology.
Thus, they are excellent examples where to apply the VO capabilities.Comment: Accepted for publication in A&
Singular Continuous Spectrum for the Laplacian on Certain Sparse Trees
We present examples of rooted tree graphs for which the Laplacian has
singular continuous spectral measures. For some of these examples we further
establish fractional Hausdorff dimensions. The singular continuous components,
in these models, have an interesting multiplicity structure. The results are
obtained via a decomposition of the Laplacian into a direct sum of Jacobi
matrices
Propagation of ultrahigh energy nuclei in clusters of galaxies: resulting composition and secondary emissions
We study the survival of ultrahigh energy nuclei injected in clusters of
galaxies, as well as their secondary neutrino and photon emissions, using a
complete numerical propagation method and a realistic modeling of the magnetic,
baryonic and photonic backgrounds. It is found that the survival of heavy
nuclei highly depends on the injection position and on the profile of the
magnetic field. Taking into account the limited lifetime of the central source
could also lead in some cases to the detection of a cosmic ray afterglow,
temporally decorrelated from neutrino and gamma ray emissions.
We calculate that the diffusive neutrino flux around 1 PeV coming from
clusters of galaxies may have a chance to be detected by current instruments.
The observation of single sources in neutrinos and in gamma rays produced by
ultrahigh energy cosmic rays will be more difficult. Signals coming from lower
energy cosmic rays (E < 1 PeV), if they exist, might however be detected by
Fermi, for reasonable sets of parameters.Comment: 19 pages, 15 figures, version to appear in ApJ (minor changes
The 0.4-Mo Eclipsing Binary CU Cancri: Absolute Dimensions, Comparison with Evolutionary Models and Possible Evidence for a Circumstellar Dust Disk
Photometric observations in the R and I bands of the detached M-type
double-lined eclipsing binary CU Cnc have been acquired and analysed. The
photometric elements obtained from the analysis of the light curves have been
combined with an existing spectroscopic solution to yield high-precision
(errors<2%) absolute dimensions: M_A=0.4333+/-0.0017 Mo, M_B=0.3980+/-0.0014
Mo, R_A=0.4317+/-0.0052 Ro, and R_B=0.3908+/-0.0094 Ro. The mean effective
temperature of the system has been estimated to be Teff=3140+/-150 K by
comparing multi-band photometry with synthetic colors computed from model
atmospheres. Additionally, we have been able to obtain an estimate for the age
(~320 Myr) and chemical composition ([Fe/H]~0.0) of the binary system through
its membership of the Castor moving group. With all these observational
constraints, we have carried out a critical test of recent stellar models for
low-mass stars. The comparison reveals that most evolutionary models
underestimate the radius of the stars by as much as 10%, thus confirming the
trend observed by Torres & Ribas (2002) for YY Gem and V818 Tau. In the
mass-absolute magnitude diagram, CU Cnc is observed to be dimmer than other
stars of the same mass. After ruling out a number of different scenarios, the
apparent faintness of CU Cnc can be explained if its components are some 10%
cooler than similar-mass stars or if there is some source of circumstellar dust
absorption. The latter could be a tantalizing indirect evidence for a coplanar
(Vega-like) dusty disk around this relatively young M-type binary.Comment: 14 pages, 5 figures, 6 tables. Accepted for publication in A&A.
Tables 1 and 2 available in electronic form at the CDS after publicatio
Metallicity, temperature, and gravity scales of M subdwarfs
The aim of the project is to define a metallicity/gravity/temperature scale
vs spectral types for metal-poor M dwarfs.
We obtained intermediate-resolution ultraviolet (R~3300), optical (R~5400),
and near-infrared (R~3900) spectra of 43 M subdwarfs (sdM), extreme subdwarfs
(esdM), and ultra-subdwarfs (usdM) with the X-shooter spectrograph on the
European Southern Observatory Very Large Telescope. We compared our atlas of
spectra to the latest BT-Settl synthetic spectral energy distribution over a
wide range of metallicities, gravities, and effective temperatures to infer the
physical properties for the whole M dwarf sequence (M0--M9.5) at sub-solar
metallicities and constrain the latest state-of-the-art atmospheric models.
The BT-Settl models reproduce well the observed spectra across the 450-2500
nm wavelength range except for a few regions. We find that the best fits are
obtained for gravities of log(g) = 5.0-5.5 dex for the three metal classes. We
infer metallicities of [Fe/H] = -0.5, -1.5, and -2.0+/-0.5 dex and effective
temperatures of 3700-2600 K, 3800-2900 K, and 3700-2900 K for subdwarfs,
extreme subdwarfs, and ultra-subdwarfs, respectively. Metal-poor M dwarfs tend
to be warmer by about 200+/-100 K and exhibit higher gravity than their
solar-metallicity counterparts. We derive abundances of several elements (Fe,
Na, K, Ca, Ti) for our sample but cannot describe their atmospheres with a
single metallicity parameter. Our metallicity scale expands the current scales
available for midly metal-poor planet-host low-mass stars. Our compendium of
moderate-resolution spectra covering the 0.45--2.5 micron range represents an
important legacy value for large-scale surveys and space missions to come.Comment: 31 pages, 4 pages, 4 tables + 1 appendix with 12 figures and 5
tables. Accepted for publication in A&A. Version prior to language editio
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