199 research outputs found
Sex-Specific Relationships of Physical Activity and Sedentary Behaviour with Oxidative Stress and Inflammatory Markers in Young Adults
This study aims to analyse sex-specific associations of physical activity and sedentary behaviour with oxidative stress and inflammatory markers in a young-adult population. Sixty participants (21 women, 22.63 ± 4.62 years old) wore a hip accelerometer for 7 consecutive days to estimate their physical activity and sedentarism. Oxidative stress (catalase, superoxide dismutase, glutathione peroxidase, glutathione, malondialdehyde, and advanced oxidation protein products) and inflammatory (tumour necrosis factor-alpha and interleukin-6) markers were measured. Student t-tests and single linear regressions were applied. The women presented higher catalase activity and glutathione concentrations, and lower levels of advanced protein-oxidation products, tumour necrosis factor-alpha, and interleukin-6 than the men (p < 0.05). In the men, longer sedentary time was associated with lower catalase activity (β = −0.315, p = 0.04), and longer sedentary breaks and higher physical-activity expenditures were associated with malondialdehyde (β = −0.308, p = 0.04). Vigorous physical activity was related to inflammatory markers in the women (tumour necrosis factor-alpha, β = 0.437, p = 0.02) and men (interleukin−6, β = 0.528, p < 0.01). In conclusion, the women presented a better redox and inflammatory status than the men; however, oxidative-stress markers were associated with physical activity and sedentary behaviours only in the men. In light of this, women could have better protection against the deleterious effect of sedentarism but a worse adaptation to daily physical activity.This work was partly supported by Universidad de Cádiz (grant number PR2016-051 and PR2019-054), by Instituto de Investigación e Innovación Biomédica de Cádiz (LI19/21IN-CO09), and by the Spanish Ministry of Science and Innovation (Ministerio de Ciencia e Innovación) (MCIN/AEI/ 10.13039/501100011033), grants PID2019-110063RA-I00 and PID2020-120034RA-I00. J.C.-P. is supported by a predoctoral grant from the Spanish Ministry of Education (Ministerio de Educación) (grant number FPU19/02326). D.V.-D is funded by the Margarita Salas Postdoctoral Program from European Union Next GenerationEU and University of Cádiz. Partial funding for open access charge: Universidad de Málag
An empirical criterion to classify T Tauri stars and substellar analogs using low-resolution optical spectroscopy
We have compiled and studied photometric and spectroscopic data published in
the literature of several star forming regions and young open clusters (Orion,
Taurus, IC348, Sco-Cen Complex, Chamaeleon I, TW Hya association, sigma Orionis
cluster, IC2391, alpha Per cluster and the Pleiades). Our goal was to seek the
definition of a simple empirical criterion to classify stars or brown dwarfs
which are accreting matter from a disk on the sole basis of low-resolution
optical spectroscopic data. We show that using Halpha equivalent widths and
spectral types we can statistically classify very young stars and brown dwarfs
as classical T Tauri stars and substellar analogs. As a boundary between
accreting and non accreting objects, we use the saturation limit of
chromospheric activity at Log L(Halpha)/L(bol)=-3.3 (determined in the open
clusters). We discuss the uncertainties in the classification scheme due to the
occurrence of flares. We have used this spectroscopic empirical criterion to
classify objects found in the literature, and we compute the fraction of
accreting objects in several star forming regions. The fraction of accreting
objects appears to decrease from about 50% to about 5% from 1 Myr to 10 Myr for
both stars and brown dwarfs.Comment: Astronomical Journal, accepte
Antioxidants and Oxidative Stress: Focus in Obese Pregnancies
The prevalence of obesity in women of childbearing age around the globe has dramatically increased in the last decades. Obesity is characterized by a low-state chronic inflammation, metabolism impairment and oxidative stress, among other pathological changes. Getting pregnant in this situation involves that gestation will occur in an unhealthy environment, that can potentially jeopardize both maternal and fetal health. In this review, we analyze the role of maternal obesity-induced oxidative stress as a risk factor to develop adverse outcomes during gestation, including reduced fertility, spontaneous abortion, teratogenesis, preeclampsia, and intrauterine growth restriction. Evidences of macromolecule oxidation increase in reactive oxygen species generation and antioxidant defense alterations are commonly described in maternal and fetal tissues. Thus, antioxidant supplementation become an interesting prophylactic and therapeutic tool, that yields positive results in cellular, and animal models. However, the results from most meta-analysis studying the effect of these therapies in complicated gestations in humans are not really encouraging. It is still to be analyzed whether these therapies could work if applied to cohorts of patients at a high risk, such as those with low concentration of antioxidants or obese pregnant women
A Census of the Chamaeleon I Star-Forming Region
Optical spectroscopy has been obtained for 179 objects that have been
previously identified as possible members of the cluster, that lack either
accurate spectral types or clear evidence of membership, and that are optically
visible (I<18). I have used these spectroscopic data and all other available
constraints to evaluate the spectral classifications and membership status of a
total sample of 288 candidate members of Chamaeleon I that have appeared in
published studies of the cluster. The latest census of Chamaeleon I now
contains 158 members, 8 of which are later than M6 and thus are likely to be
brown dwarfs. I find that many of the objects identified as members of
Chamaeleon I in recent surveys are actually field stars. Meanwhile, 7 of 9
candidates discovered by Carpenter and coworkers are confirmed as members, one
of which is the coolest known member of Chamaeleon I at a spectral type of M8
(~0.03 M_sun). I have estimated extinctions, luminosities, and effective
temperatures for the members and used these data to construct an H-R diagram
for the cluster. Chamaeleon I has a median age of ~2 Myr according to
evolutionary models, and hence is similar in age to IC 348 and is slightly
older than Taurus (~1 Myr). The measurement of an IMF for Chamaeleon I from
this census is not possible because of the disparate methods with which the
known members were originally selected, and must await an unbiased,
magnitude-limited survey of the cluster.Comment: 59 pages, 22 figure
The Spitzer c2d Survey of Weak-line T Tauri Stars II: New Constraints on the Timescale for Planet Building
One of the central goals of the Spitzer Legacy Project ``From Molecular Cores
to Planet-forming Disks'' (c2d) is to determine the frequency of remnant
circumstellar disks around weak-line T Tauri stars (wTTs) and to study the
properties and evolutionary status of these disks. Here we present a census of
disks for a sample of over 230 spectroscopically identified wTTs located in the
c2d IRAC (3.6, 4.5, 4.8, and 8.0 um) and MIPS (24 um) maps of the Ophiuchus,
Lupus, and Perseus Molecular Clouds. We find that ~20% of the wTTs in a
magnitude limited subsample have noticeable IR-excesses at IRAC wavelengths
indicating the presence of a circumstellar disk. The disk frequencies we find
in these 3 regions are ~3-6 times larger than that recently found for a sample
of 83 relatively isolated wTTs located, for the most part, outside the highest
extinction regions covered by the c2d IRAC and MIPS maps. The disk fractions we
find are more consistent with those obtained in recent Spitzer studies of wTTs
in young clusters such as IC 348 and Tr 37. From their location in the H-R
diagram, we find that, in our sample, the wTTs with excesses are among the
younger part of the age distribution. Still, up to ~50% of the apparently
youngest stars in the sample show no evidence of IR excess, suggesting that the
circumstellar disks of a sizable fraction of pre-main-sequence stars dissipate
in a timescale of ~1 Myr. We also find that none of the stars in our sample
apparently older than ~10 Myrs have detectable circumstellar disks at
wavelengths < 24 um. Also, we find that the wTTs disks in our sample exhibit a
wide range of properties (SED morphology, inner radius, L_DISK/L*, etc) which
bridge the gaps observed between the cTTs and the debris disk regimes.Comment: 54 pages, 13 figures, Accepted by Ap
A Search for Very Low-mass Stars and Brown Dwarfs in the Young sigma Orionis Cluster
We present a CCD-based photometric survey covering 870 sq. arcmin in a young
stellar cluster around the young multiple star sigma Orionis. Our survey
limiting R, I, and Z magnitudes are 23.2, 21.8, and 21.0, respectively. From
our colour-magnitude diagrams, we have selected 49 faint objects, which
smoothly extrapolate the photometric sequence defined by more massive known
members. Adopting the currently accepted age interval of 2-10 Myr for the Orion
1b association and considering recent evolutionary models, our objects may span
a mass range from 0.1 down to 0.02 Msun, well within the substellar regime.
Follow-up low-resolution optical spectroscopy (635-920 nm) for eight of our
candidates (I=16-19.5) shows that they have spectral types M6-M8.5 which are
consistent with the expectations for true members. Compared with their Pleiades
counterparts of similar types, Halpha emission is generally stronger, while NaI
and KI absorption lines appear weaker, as expected for lower surface gravities
and younger ages. Additionally, TiO bands and in particular VO bands appear
clearly enhanced in our candidate with the latest spectral type, SOri 45 (M8.5,
I=19.5), compared to objects of similar types in older clusters and the field.
We have estimated the mass of this candidate at only 0.020-0.040 Msun, hence it
is one of the least massive brown dwarfs yet discovered. We also discuss in
this paper the potential role of deuterium as a tracer of both substellar
nature and age in very young clusters.Comment: Accepted for publication in ApJ Main Journal. 32 pages of text and
tables + 9 pages of figures. Figures 3a and 3b (gif format) provided
separatel
Spectroscopic binaries in a sample of ROSAT X-ray sources south of the Taurus molecular clouds
We report the results of our radial-velocity monitoring of spectroscopic
binary systems in a sample of X-ray sources from the ROSAT All Sky Survey south
of the Taurus-Auriga star-forming region. The original sample of approximately
120 sources by Neuhaeuser et al. was selected on the basis of their X-ray
properties and the visual magnitude of the nearest optical counterpart, in such
a way as to promote the inclusion of young objects. Roughly 20% of those
sources have previously been confirmed to be very young. We focus here on the
subset of the original sample that shows variable radial velocities (43
objects), a few of which have also been flagged previously as being young. New
spectroscopic orbits are presented for 42 of those systems. Two of the
binaries, RXJ0528.9+1046 and RXJ0529.3+1210, are indeed weak-lined T Tauri
stars likely to be associated with the Lambda Orionis region. Most of the other
binaries are active objects of the RS CVn-type, including several W UMa and
Algol systems. We detect a strong excess of short-period binaries compared to
the field, and an unusually large fraction of double-lined systems, as well as
an overall high frequency of binaries out of the original sample. These results
can be understood as selection effects. A short description of the physical
properties of each binary is provided, and a comparison with evolutionary
tracks is made using the stellar density as a distance-independent measure of
evolution (abridged).Comment: 36 pages, 10 figures, 7 tables, to appear in The Astronomical
Journal, March 200
The Eta Chamaeleontis Cluster: Origin in the Sco-Cen OB Association
A young, nearby compact aggregate of X-ray emitting pre-main sequence stars
was recently discovered in the vicinity of eta Cha (B8V). In this paper, we
further investigate this cluster: its membership, its environs and origins.
ROSAT HRI X-ray data for the cluster's T Tauri stars show high levels of
magnetic activity and variability. The cluster has an anomalous X-ray
luminosity function compared to other young clusters, deficient in stars with
low, but detectable X-ray luminosities. This suggests that many low-mass
members have escaped the surveyed core region. Photographic photometry from the
USNO-A2.0 catalog indicates that additional, X-ray-quiet members exist in the
cluster core region. The components of the eclipsing binary RS Cha, previously
modeled in the literature as post-MS with discordant ages, are shown to be
consistent with being coeval pre-MS stars. We compute the Galactic motion of
the cluster from Hipparcos data, and compare it to other young stars and
associations in the fourth Galactic quadrant. The kinematic study shows that
the eta Cha cluster, the TW Hya association, and a new group near epsilon Cha,
probably originated near the giant molecular cloud complex that formed the two
oldest subgroups of the Sco-Cen OB association roughly 10-15 Myr ago. Their
dispersal is consistent with the velocity dispersions seen in giant molecular
clouds. A large H I filament and dust lane located near eta Cha has been
identified as part of a superbubble formed by Sco-Cen OB winds and supernova
remnants. The passage of the superbubble may have terminated star-formation in
the eta Cha cluster and dispersed its natal molecular gas.Comment: 26 pages, 9 figures, LaTex2.09, ApJ, in press,
http://etacha.as.arizona.edu/~eem/etacha/MLF00/index.htm
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