2,035 research outputs found
Study of extremely reddened AGB stars in the Galactic bulge
Context. Extremely reddened AGB stars lose mass at high rates of >10^-5
Msun/yr. This is the very last stage of AGB evolution, in which stars in the
mass range 2.0--4.0 Msun (for solar metallicity) should have been converted to
C stars already. The extremely reddened AGB stars in the Galactic bulge are
however predominantly O-rich, implying that they might be either low-mass stars
or stars at the upper end of the AGB mass range. Aims. To determine the mass
range of the most reddened AGB stars in the Galactic bulge. Methods. Using
Virtual Observatory tools, we constructed spectral energy distributions of a
sample of 37 evolved stars in the Galactic bulge with extremely red IRAS
colours. We fitted DUSTY models to the observational data to infer the
bolometric fluxes. Applying individual corrections for interstellar extinction
and adopting a common distance, we determined luminosities and mass-loss rates,
and inferred the progenitor mass range from comparisons with AGB evolutionary
models. Results. The observed spectral energy distributions are consistent with
a classification as reddened AGB stars, except for two stars, which are
proto-planetary nebula candidates. For the AGB stars, we found luminosities in
the range 3000--30,000 Lsun and mass-loss rates 10^-5--3x10^-4 Msun/yr. The
corresponding mass range is 1.1--6.0 Msun assuming solar metallicity.
Conclusions. Contrary to the predictions of the evolutionary models, the
luminosity distribution is continuous, with many O-rich AGB stars in the mass
range in which they should have been converted into C stars already. We suspect
that bulge AGB stars have higher than solar metallicity and therefore may avoid
the conversion to C-rich. The presence of low-mass stars in the sample shows
that their termination of the AGB evolution also occurs during a final phase of
very high mass-loss rate, leading to optically thick circumstellar shells
Development of an Emergency Radio Beacon for Small Unmanned Aerial Vehicles
Emergency locator transmitters (ELTs) used to locate manned aircrafts are not well suited to find and recover small crashed unmanned aerial vehicles (UAVs). ELTs utilize an international satellite system for search and rescue (Cospas-Sarsat System), which should leverage its expensive resources to save lives as a priority. Besides, ELTs are too big and heavy to be used within small UAVs. Some of the existing solutions for this problem are based on receivers that detect signal strength, which may be a long and tedious process not suitable for user needs. Others do not have enough range or require radio license and expensive amateur radio receivers. This paper presents an emergency radio beacon specifically designed to locate small UAVs. It is triggered automatically in the event of a crash and allows finding and recovering a crashed UAV in a fast and simple way. It meets not only the required specifications of user-friendliness, size and weight of this kind of application, but also it is a high precision and low cost device. Besides, it has enough range and endurance. The experiments carried out show the operation of the proposed system
An infrared study of galactic OH/IR stars. I. An optical/near-IR atlas of the Arecibo sample
In this paper we present optical and near-infrared finding charts, accurate
astrometry (~1") and single-epoch near-infrared photometry for 371 IRAS
sources, 96% of those included in the so-called Arecibo sample of OH/IR stars
(Eder et al. 1988; Lewis et al. 1990a; Chengalur et al. 1993). The main
photometric properties of the stars in the sample are presented and discussed
as well as the problems found during the process of identification of the
optical/near-infrared counterparts. In addition, we also identify suitable
reference stars in each field to be used for differential photometry purposes
in the future.
We find that 39% of the sources (144 in number) have no optical counterpart,
8 of them being invisible even at near infrared wavelengths. The relative
distribution of sources with and without optical counterpart in the IRAS
two-colour diagram and their characteristic near infrared colours are
interpreted as the consequence of the increasing thickness of their
circumstellar shells. Among the objects not detected at near infrared
wavelengths four non-variable sources are proposed to be heavily obscured
post-AGB stars which have just very recently left the AGB. Eight additional
objects with unusually bright and/or blue near-infrared colours are identified
as candidate post-AGB stars and/or proto-planetary nebulae.Comment: 28 pages, 9 figures, for associated finding charts see:
http://www.edpsciences.org/articles/aa/full/2005/08/aa1709/FINDING_CHARTS/are
cibo_index.htm
Limiting the Abundance of LIGO/Virgo Black Holes with Microlensing Observations of Quasars of Finite Size
We thank the anonymous referee for ideas and comments, which greatly contributed to enhancing the scope of our paper. This research was supported by the Spanish Ministry of Economy and Competitiveness (MINECO) with the grants AYA2016-79104-C3-1-P and AYA2016-79104-C3-3-P. J.J.V. is supported by the project AYA2017-84897-P financed by MINECO and by the Fondo Europeo de Desarrollo Regional (FEDER), and by projects FQM-108, P20_00334, and A-FQM-510-UGR20/FEDER financed by Junta de Andalucia. A.E.G. thanks the support from grant FPI-SO from MINECO (research project SEV-2015-0548-17-4 and predoctoral contract BES-2017-082319).We present a simple but general argument that strongly limits the abundance of primordial black holes (PBHs) (or
other unknown population of compact objects) with masses similar to those determined by LIGO/Virgo from BH
binary mergers. We show that quasar microlensing can be very sensitive to the mass of the lenses, and that it is able
to distinguish between stars and BHs of high mass, when the finite size of the source is taken into account. A
significant presence of massive BHs would produce frequent high-flux magnifications (except for unrealistically
large sources), which have been very rarely observed. On the contrary, a typical stellar population would induce
flux magnifications consistent with the observations. This result excludes PBHs (or any type of compact object) in
the mass range determined by LIGO/Virgo as the main dark matter constituents in the lens galaxies.Spanish Government AYA2016-79104-C3-1-P
AYA2016-79104-C3-3-P
AYA2017-84897-PEuropean CommissionSpanish GovernmentJunta de Andalucia FQM-108
P20_00334
A-FQM-510-UGR20/FEDERgrant FPI-SO from MINECO SEV-2015-0548-17-4
BES-2017-08231
Abundance of LIGO/Virgo Black Holes from Microlensing Observations of Quasars with Reverberation Mapping Size Estimates
We thank the anonymous referees for ideas and comments that greatly contributed to enhancing the scope of our paper. This research was supported by the Spanish Ministry of Economy and Competitiveness (MINECO) with grants AYA2016-79104-C3-1-P and AYA2016-79104-C3-3-P and projects PID2020-118687GB-C33, PID2020-118687GB-C32, and PID2020-118687GB-C31, financed by MCIN/AEI/10.13039/501100011033. J.J.V. is supported by project AYA2017-84897-P, financed by the Spanish MINECO and by the Fondo Europeo de Desarrollo Regional (FEDER), and by projects FQM-108, P20_00334 and A-FQM-510-UGR20/FEDER, financed by Junta de Andalucia. A.E.G. is grateful for the support from grant FPI-SO from the Spanish MINECO (research project SEV-2015-0548-17-4 and predoctoral contract BES-2017-082319).Assuming a population of black holes (BHs) with masses in the range inferred by LIGO/Virgo from BH mergers, we use quasar microlensing observations to estimate their abundances. We consider a mixed population of stars and BHs and the presence of a smooth dark matter component. We adopt reverberation mapping estimates of the quasar size. According to a Bayesian analysis of the measured microlensing magnifications, a population of BHs with masses similar to 30M (circle dot) constitutes less than 0.4% of the total matter at the 68% confidence level (less than 0.9% at the 90% confidence level). We have explored the whole mass range of LIGO/Virgo BHs, finding that this upper limit ranges from 0.5% to 0.4% at the 68% confidence level (from 1.1% to 0.9% at the 90% confidence level) when the BH masses change from 10 to 60M (circle dot). We estimate a 16% contribution from the stars, in agreement with previous studies based on a single-mass population that do not explicitly consider the presence of BHs. These results are consistent with the estimates of BH abundances from the statistics of LIGO/Virgo mergers, and rule out primordial BHs (or any other types of compact object) in this mass range constituting a significant fraction of the dark matter.Spanish Ministry of Economy and Competitiveness (MINECO) - MCIN/AEI AYA2016-79104-C3-1-P
AYA2016-79104-C3-3-P
PID2020-118687GB-C33
PID2020-118687GB-C32
PID2020-118687GB-C31Spanish Government AYA2017-84897-P
SEV-2015-0548-17-4
BES-2017-082319European CommissionSpanish Government AYA2017-84897-PJunta de Andalucia FQM-108
P20_00334
A-FQM-510-UGR20/FEDE
Lifetime of OH masers at the tip of the asymptotic giant branch
Context: A large fraction of otherwise similar asymptotic giant branch stars
(AGB) do not show OH maser emission. As shown recently, a restricted lifetime
may give a natural explanation as to why only part of any sample emits maser
emission at a given epoch.
Aims: We wish to probe the lifetime of 1612 MHz OH masers in circumstellar
shells of AGB stars.
Methods: We reobserved a sample of OH/IR stars discovered more than 28 years
ago to determine the number of stars that may have since lost their masers.
Results: We redetected all 114 OH masers. The minimum lifetime inferred is
2800 years (1 sigma). This maser lifetime applies to AGB stars with strong mass
loss leading to very red infrared colors. The velocities and mean flux density
levels have not changed since their discovery. As the minimum lifetime is of
the same order as the wind crossing time, strong variations in the mass-loss
process affecting the excitation conditions on timescales of ~3000 years or
less are unlikely.
Keywords: OH masers -- Stars: AGB and post-AGB -- circumstellar matterComment: 8 pages, 5 figures, accepted for publication in Astronomy &
Astrophysic
Proper motions of young stars in Chamaeleon. I. A Virtual Observatory study of spectroscopically confirmed members
(abridged) We want to provide further evidence of the origin of the proposed
stellar members of Chamaeleon and to identify interlopers from the foreground
\epsilon Cha and \eta Cha associations. To this aim, we compile lists of
spectroscopically confirmed members of Chamaeleon I and II, \epsilon Cha and
\eta Cha, and of background objects in the same line of sight. Using Virtual
Observatory tools, we cross-match these lists with the UCAC3 catalogue to get
the proper motions of the objects. In the vector point diagram, we identify the
different moving groups, and use this information to study the membership of
proposed candidate members of the associations from the literature. For those
objects with available radial velocities, we compute their Galactic space
velocities. We look for correlations between the known properties of the
objects and their proper motions. The members of the dark clouds exhibit
clearly different proper motions from those of the foreground associations and
of the background stars. The data suggest that Chamaeleon II could have
different dynamical properties from Chamaeleon I. Although the two foreground
clusters \epsilon and \eta Chamaeleontis constitute two different proper motion
groups, they have similar spatial motions, which are different from the spatial
motion of Chamaeleon I. On the other hand, the space motions of the Chamaeleon
II stars look more similar to those of the foreground clusters than to the
Chamaeleon I stars, but the numbers are low. Hence, with the available data it
is unclear to what extent the stellar populations in both clouds are physically
connected to each other. We find no correlations between the proper motions and
the properties of the objects in either of the clouds
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