394 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
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
A catalog of wide binary and multiple systems of bright stars from Gaia-DR2 and the Virtual Observatory
Binary and multiple stars have long provided an effective empirical method of
testing stellar formation and evolution theories. In particular, the existence
of wide binary systems (separations 20,000 au) is particularly challenging
to binary formation models as their physical separations are beyond the typical
size of a collapsing cloud core (5,00010,000 au). We mined the
recently published Gaia-DR2 catalog to identify bright comoving systems in the
five-dimensional space (sky position, parallax, and proper motion). We
identified 3,741 comoving binary and multiple stellar candidate systems, out of
which 575 have compatible RVs for all the members of the system. The candidate
systems have separations between 400 and 500,000 au. We used the analysis
tools of the Virtual Observatory to characterize the comoving system members
and to assess their reliability. The comparison with previous comoving systems
catalogs obtained from TGAS showed that these catalogs contain a large number
of false systems. In addition, we were not able to confirm the ultra-wide
binary population presented in these catalogs. The robustness of our
methodology is demonstrated by the identification of well known comoving star
clusters and by the low contamination rate for comoving binary systems with
projected physical separations 50,000 au. These last constitute a reliable
sample for further studies. The catalog is available online at the Spanish
Virtual Observatory portal
(http://svo2.cab.inta-csic.es/vocats/v2/comovingGaiaDR2/).Comment: Accepted in A
On the evolutionary connection between AGB stars and PNe
The `O-rich AGB sequence' is a sequence of colours describing the location of
O-rich AGB stars in the IRAS two-colour diagram [12]--[25] vs [25]--[60]. We
propose an evolutionary scenario for this sequence in which all stars,
independent of their progenitor mass, start the AGB phase in the blue part of
the `O-rich AGB sequence' and then evolve toward redder colors, although only
the more massive stars would reach the very end of the `O-rich AGB sequence'.
The sources located in the blue part of the sequence are mainly Mira variables,
whose mean period is increasing with the IRAS colours. Most of them will evolve
into O-rich Type II (and III) Planetary Nebulae. Part of the stars located in
the red part of the sequence will change their chemical composition from O-rich
to C-rich during their evolution in the AGB phase, and might evolve into C-rich
Type II Planetary Nebulae. Hot bottom burning may prevent the conversion to
carbon stars of the rest of sources located in the red part of the sequence and
they will end up as N-rich Type I Planetary Nebulae.Comment: 4 pages, 6 figures, proceedings of the conference 'Planetary Nebulae
as Astrophysical Tools', held in Gdansk, Poland (June 28 - July 2, 2005
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
Intermittent hypoxic training and cycling performance in triathletes
Los deportistas incorporan como complemento a su entrenamiento convencional, programas de entrenamiento en altitud para incrementar el rendimiento. El objetivo del estudio fue analizar los efectos sobre el umbral anaerĂłbico (Uan) producidos por un programa de entrenamiento en hipoxia intermitente (IHT) en triatletas.
Participaron 18 triatletas divididos en un grupo de entrenamiento en hipoxia (GIHT: n=9; Edad: 26 ± 6.73 años; Talla 173.33 ± 5.94 cm; Peso: 66.38 ± 5.91 kg) y un grupo control (GC: n=9; Edad: 29.27 ± 6.84 años; Talla 174.89 ± 4.59 cm; Peso: 71.59 ± 6.81 Kg). Se aplicó un programa de IHT, complementario al entrenamiento habitual de 7 semanas al 15-14.5% de FiO2, 2 sesiones semanales de 60 minutos en cicloergómetro a la intensidad del Uan. Se llevó a cabo un test de umbrales låcticos previo y otro posterior al programa. El tratamiento propuesto produce un incremento en la potencia y el esfuerzo percibido en el Uan y disminuye la frecuencia cardiaca en el umbral aeróbico (Uae) y el UanAthletes include altitude training as a complement to their conventional training to improve performance. The aim of the study was to analyze the effects on anaerobic threshold (AT) produced by an IHT program in triathletes.
18 male trained triathletes were divided into intermittent hypoxic training group (GIHT: n=9; age: 26±6.73 years, height 173.33±5.94 cm, weight: 66.38±5.91 kg) and control group (GC: n=9; age: 29.27±6.84 years, height 174.89±4.59 cm, weight: 71.59±6.81 kg). The IHT program consisted of two 60-min sessions per week at intensities over the AT and atmospheric conditions between 14.5 and 15% FiO2. Before and after the program, cycling performance in a lactate thresholds test was determined. The treatment caused an improvement in the power output and perceived exertion in AT and enhanced cardiac performance in the aerobic threshold and AT
A white dwarf catalogue from Gaia-DR2 and the Virtual Observatory
We present a catalogue of 73Âż221 white dwarf candidates extracted from the astrometric and photometric data of the recently published Gaia-DR2 catalogue. White dwarfs were selected from the Gaia HertzsprungâRussell diagram with the aid of the most updated population synthesis simulator. Our analysis shows that Gaia has virtually identified all white dwarfs within 100Âżpc from the Sun. Hence, our sub-population of 8555 white dwarfs within this distance limit and the colour range considered, -0.52<(GBP-GRP)<0.80Âż, is the largest and most complete volume-limited sample of such objects to date. From this sub-sample, we identified 8343 CO-core and 212 ONe-core white dwarf candidates and derived a white dwarf space density of 4.9±0.4Ă10-3pc-3Âż. A bifurcation in the HertzsprungâRussell diagram for these sources, which our models do not predict, is clearly visible. We used the Virtual Observatory SED Analyzer tool to derive effective temperatures and luminosities for our sources by fitting their spectral energy distributions, that we built from the ultraviolet to the near-infrared using publicly available photometry through the Virtual Observatory. From these parameters, we derived the white dwarf radii. Interpolating the radii and effective temperatures in hydrogen-rich white dwarf cooling sequences, we derived the surface gravities and masses. The Gaia 100Âżpc white dwarf population is clearly dominated by cool (~8000ÂżK) objects and reveals a significant population of massive (ÂżM~0.8M¿¿) white dwarfs, of which no more than ~30--40 per cent can be attributed to hydrogen-deficient atmospheres, and whose origin remains uncertain.Peer ReviewedPreprin
Intermittent hypoxic training and cycling performance in triathletes
Athletes include altitude training as a complement to their conventional training to improve performance. The aim of the study was to analyze the effects on anaerobic threshold (AT) produced by an IHT program in triathletes. 18 male trained triathletes were divided into intermittent hypoxic training group (GIHT: n=9; age: 26±6.73 years, height 173.33±5.94 cm, weight: 66.38±5.91 kg) and control group (GC: n=9; age: 29.27±6.84 years, height 174.89±4.59 cm, weight: 71.59±6.81 kg). The IHT program consisted of two 60-min sessions per week at intensities over the AT and atmospheric conditions between 14.5 and 15% FiO2. Before and after the program, cycling performance in a lactate thresholds test was determined. The treatment caused an improvement in the power output and perceived exertion in AT and enhanced cardiac performance in the aerobic threshold and AT.Actividad FĂsica y Deport
Changes in electromyographic activity of latent trigger points after a dry needling intervention: a randomised controlled trial.
Objective
To analyse the effects of dry needling (DN) in upper trapezius latent trigger points (LTrPs) on pressure pain threshold (PPT) and surface electromyography (sEMG).
Design
Randomized, double-blind, placebo controlled clinical trial.
Settings
Sports Rehabilitation Laboratory, University of Castilla-La Mancha.
Participants
Forty-six participants (18â35 years old) with LTrP in the upper trapezius were divided into two groups: DN-group and Sham-DN-group.
Interventions
In the DN-group, the needle was inserted 10-times through the skin, and it was manipulated up and down using a "fast in and out" technique. In the Sham-DN-group, non-penetrating needles were used.
Main outcome measures
PPT, sEMG at rest, and sEMG in isometric contraction of the LTrP of the upper trapezius muscle were evaluated at baseline, 30âŻmin after treatment, and after 24âŻh, and 72âŻh of follow-up.
Results
The mean change in sEMG at rest between baseline and 30âŻmin was ââŻ0.38 (0.38) %refRMS for the DN group and ââŻ0.05 (0.31) %refRMS for the Sham-DN group (mean difference â0.34, 95% confidence interval (CI) of the difference: ââŻ0.54 to ââŻ0.13), and between baseline and 24âŻh was ââŻ0.35 (0.35) %refRMS for the DN group and ââŻ0.06 (0.58) %refRMS for the Sham-DN group (mean difference â0.29, 95% CI: â0.57 to â0.01). In addition, the DN-group showed higher values of PPT than the Sham-DN group at 72âŻh (5.22 (1.23) to 4.65 (1.03) kg/cm2; pâŻ<âŻ0.05).
Conclusions
A single session of DN intervention was effective in reducing the electromyographic activity, muscle fatigue and pain of the upper trapezius muscle in LTrP.pre-print542 K
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