882 research outputs found
X-Shooter study of accretion in -Ophiucus: very low-mass stars and brown dwarfs
We present new VLT/X-Shooter optical and NIR spectra of a sample of 17
candidate young low-mass stars and BDs in the rho-Ophiucus cluster. We derived
SpT and Av for all the targets, and then we determined their physical
parameters. All the objects but one have M*<0.6 Msun, and 8 have mass below or
close to the hydrogen-burning limit. Using the intensity of various emission
lines present in their spectra, we determined the Lacc and Macc for all the
objects. When compared with previous works targeting the same sample, we find
that, in general, these objects are not as strongly accreting as previously
reported, and we suggest that the reason is our more accurate estimate of the
photospheric parameters. We also compare our findings with recent works in
other slightly older star-forming regions to investigate possible differences
in the accretion properties, but we find that the accretion properties for our
targets have the same dependence on the stellar and substellar parameters as in
the other regions. This leads us to conclude that we do not find evidence for a
different dependence of Macc with M* when comparing low-mass stars and BDs.
Moreover, we find a similar small (1 dex) scatter in the Macc-M* relation as in
some of our recent works in other star-forming regions, and no significant
differences in Macc due to different ages or properties of the regions. The
latter result suffers, however, from low statistics and sample selection biases
in the current studies. The small scatter in the Macc-M* correlation confirms
that Macc in the literature based on uncertain photospheric parameters and
single accretion indicators, such as the Ha width, can lead to a scatter that
is unphysically large. Our studies show that only broadband spectroscopic
surveys coupled with a detailed analysis of the photospheric and accretion
properties allows us to properly study the evolution of disk accretion rates.Comment: accepted for publication in Astronomy & Astrophysics. Abstract
shortened to fit arXiv constraint
The Chamaeleon II low-mass star-forming region: radial velocities, elemental abundances, and accretion properties
Radial velocities, elemental abundances, and accretion properties of members
of star-forming regions (SFRs) are important for understanding star and planet
formation. While infrared observations reveal the evolutionary status of the
disk, optical spectroscopy is fundamental to acquire information on the
properties of the central star and on the accretion characteristics. 2MASS
archive data and the Spitzer c2d survey of the Chamaeleon II dark cloud have
provided disk properties of a large number of young stars. We complement these
data with spectroscopy with the aim of providing physical stellar parameters
and accretion properties. We use FLAMES/UVES+GIRAFFE observations of 40 members
of Cha II to measure radial velocities through cross-correlation technique, Li
abundances by means of curves of growth, and for a suitable star elemental
abundances of Fe, Al, Si, Ca, Ti, and Ni using the code MOOG. From the
equivalent widths of the Halpha, Hbeta, and the HeI-5876, 6678, 7065 Angstrom
emission lines, we estimate the mass accretion rates, dMacc/dt, for all the
objects. We derive a radial velocity distribution for the Cha II stars
(=11.4+-2.0 km/s). We find dMacc/dt prop. to Mstar^1.3 and to Age^(-0.82)
in the 0.1-1.0 Msun mass regime, and a mean dMacc/dt for Cha II of ~7*10^(-10)
Msun/yr. We also establish a relationship between the HeI-7065 Angstrom line
emission and the accretion luminosity. The radial velocity distributions of
stars and gas in Cha II are consistent. The spread in dMacc/dt at a given
stellar mass is about one order of magnitude and can not be ascribed entirely
to short timescale variability. Analyzing the relation between dMacc/dt and the
colors in Spitzer and 2MASS bands, we find indications that the inner disk
changes from optically thick to optically thin at dMacc/dt~10^(-10) Msun/yr.
Finally, the disk fraction is consistent with the age of Cha II.Comment: 21 Pages, 15 Figures, 7 Tables. Accepted for publication in Astronomy
and Astrophysics. Abstract shortene
X-Shooter spectroscopy of young stellar objects: V - Slow winds in T Tauri stars
Disks around T Tauri stars are known to lose mass, as best shown by the
profiles of forbidden emission lines of low ionization species. At least two
separate kinematic components have been identified, one characterised by
velocity shifts of tens to hundreds km/s (HVC) and one with much lower velocity
of few km/s (LVC). The HVC are convincingly associated to the emission of jets,
but the origin of the LVC is still unknown. In this paper we analyze the
forbidden line spectrum of a sample of 44 mostly low mass young stars in Lupus
and -Ori observed with the X-Shooter ESO spectrometer. We detect
forbidden line emission of [OI], [OII], [SII], [NI], and [NII], and
characterize the line profiles as LVC, blue-shifted HVC and red-shifted HVC. We
focus our study on the LVC. We show that there is a good correlation between
line luminosity and both L and the accretion luminosity (or the
mass-accretion rate) over a large interval of values (L L; L L;
M/yr). The lines show the presence of a slow
wind ( cm), warm (T K), mostly neutral. We estimate the mass of the emitting gas and
provide a value for the maximum volume it occupies. Both quantities increase
steeply with the stellar mass, from M and
AU for M M, to
M and AU for M M, respectively.
These results provide quite stringent constraints to wind models in low mass
young stars, that need to be explored further
Detection of delta Scuti-like pulsation in H254, a pre-main sequence F-type star in IC 348
We present time series observations of intermediate mass PMS stars belonging
to the young star cluster IC 348. The new data reveal that a young member of
the cluster, H254, undergoes periodic light variations with delta Scuti-like
characteristics. This occurrence provides an unambiguous evidence confirming
the prediction that intermediate-mass pre-main sequence (PMS) stars should
experience this transient instability during their approach to the
main-sequence. On the basis of the measured frequency f=7.406 c/d, we are able
to constrain the intrinsic stellar parameters of H254 by means of linear, non
adiabatic, radial pulsation models. The range of the resulting luminosity and
effective temperature permitted by the models is narrower than the
observational values. In particular, the pulsation analysis allows to derive an
independent estimate of the distance to IC 348 of about 320 pc. Further
observations could either confirm the monoperiodic nature of H254 or reveal the
presence of other frequencies.Comment: 7 pages, including 7 postscript figures, accepted for publication on
A&
Fast Food Sovereignty: Contradiction in Terms or Logical Next Step?
The growing academic literature on ‘food sovereignty’ has elaborated a food producer-
driven vision of an alternative, more ecological food system rooted in greater
democratic control over food production and distribution. Given that the food sovereignty
developed with and within producer associations, a rural setting and production-
side concerns have overshadowed issues of distribution and urban consumption.
Yet, ideal types such as direct marketing, time-intensive food preparation and the
‘family shared meal’ are hard to transcribe into the life realities in many non-rural,
non-farming households, and it is unclear, in turn, how such realities can fit into
models of food sovereignty. A particular practical and research gap exists in how to
engage the overwhelming need for food options served under time constraints and
(often) outside of the home or a full-service restaurant. The over-generalized vilification
of ‘fast food’ should be replaced by a framework that allows us to distinguish
between unhealthy, corporate fast foods and both traditional and emerging alternatives
that can serve to extend the tenets of food sovereignty further into food processing,
distribution and consumption. This article analyzes existing conceptualizations
of fast food, explores fast food historically, and studies how food sovereignty
can operationalize its tenets and priorities in situations where fast food is an unquestionable
necessity
The VISTA Orion mini-survey: star formation in the Lynds 1630 North cloud
The Orion cloud complex presents a variety of star formation mechanisms and
properties and it is still one of the most intriguing targets for star
formation studies. We present VISTA/VIRCAM near-infrared observations of the
L1630N star forming region, including the stellar clusters NGC 2068 and NGC
2071, in the Orion molecular cloud B and discuss them in combination with
Spitzer data. We select 186 young stellar object (YSO) candidates in the region
on the basis of multi-colour criteria, confirm the YSO nature of the majority
of them using published spectroscopy from the literature, and use this sample
to investigate the overall star formation properties in L1630N. The K-band
luminosity function of L1630N is remarkably similar to that of the Trapezium
cluster, i.e., it presents a broad peak in the range 0.3-0.7 M and a
fraction of sub-stellar objects of 20%. The fraction of YSOs still
surrounded by disk/envelopes is very high (85%) compared to other star
forming regions of similar age (1-2 Myr), but includes some uncertain
corrections for diskless YSOs. Yet, a possibly high disk fraction together with
the fact that 1/3 of the cloud mass has a gas surface density above the
threshold for star formation (129 M pc), points towards a
still on-going star formation activity in L1630N. The star formation efficiency
(SFE), star formation rate (SFR) and density of star formation of L1630N are
within the ranges estimated for galactic star forming regions by the Spitzer
"core to disk" and "Gould's Belt" surveys. However, the SFE and SFR are lower
than the average value measured in the Orion A cloud and, in particular, lower
than that in the southern regions of L1630. This might suggest different star
formation mechanisms within the L1630 cloud complex.Comment: 22 pages, 9 figure
A WFI survey in the Chamaeleon II dark cloud
We present the results of an optical multi-band survey for low-mass Pre-Main
Sequence (PMS) stars and young Brown Dwarfs (BDs) in the Chamaeleon II (Cha II)
dark cloud. This survey constitutes the complementary optical data to the c2d
Spitzer Legacy survey in Cha II.
Using the Wide-Field Imager (WFI) at the ESO 2.2m telescope, we surveyed a
sky area of about 1.75 square degrees in Cha II. The region was observed in the
Rc, Ic and z broad-bands, in H-alpha and in two medium-band filters centered at
856 and 914 nm. We select PMS star and young BD candidates using
colour-magnitude diagrams (CMDs) and theoretical isochrones reproduced ad-hoc
for the WFI at the ESO2.2m telescope system. The selection criteria are also
reinforced by using the previously known PMS stars in Cha II to define the PMS
locus on the CMDs and by investigating the infrared (IR) colours of the
candidates. By exploiting the WFI intermediate-band photometry we also estimate
the effective temperature and the level of H-alpha emission of the candidates.
Our survey, which is one of the largest and deepest optical surveys conducted
so far in Cha II, recovered the majority of the PMS stars and 10 member
candidates of the cloud from previous IR surveys. In addition, the survey
revealed 10 new potential members. From our photometric characterisation, we
estimate that some 50% of the 20 candidates will result in true Cha II members.
Based on our temperature estimates, we conclude that several of these objects
are expected to be sub-stellar and give a first estimate of the fraction of
sub-stellar objects.Comment: 26 pages, 18 figure
Stability of a lyophilized milk enriched with microbial CLA/CLNA
Conjugated linoleic (CLA) and conjugated linolenic (CLNA) acids have been described with potential bioactive properties. Due limited availability in their natural sources (e.g. ruminants’ milk and meat or vegetable oils), in situ microbial production in dairy products may potentially improve CLA/CLNA daily intake. Several probiotic strains have been reported to produce CLA/CLNA isomers using linoleic (LA) and alpha-linolenic (α-LNA) acids as precursor substrates, respectively. Previous work by this research team led to the formulation of a CLA/CLNA-enriched lyophilized milk, using Bifidobacterium breve DSM 20091 and hydrolysed flaxseed oil (FSO; rich in α-LNA). Since CLA, CLNA, LA and α-LNA are polyunsaturated and prone to oxidation, this research aimed to investigate if this new functional milk product is stable at conditions mimicking shelf-life. Pasteurized cow milk (100 mL) inoculated with B. breve DSM 20091 and hydrolysed FSO or not (control) was fermented for 22 h at 37 ºC under anaerobic conditions. Afterwards, samples were lyophilized and stored at room temperature in an exicator, being air- and light-protected. Samples were taken at the beginning (T0wk) and every 4 weeks until the end of the assay (T12wk) for further microbial counting and fatty acid (FA) analysis. Concerning to B. breve DSM 20091 viable cell counting, counts remained below the countable range during the entire study, so as total microbial counting. As for FA analysis, in the non-esterified fraction, the CLA and CLNA contents in the enriched milk product increased after 4 weeks (up to 1.80 and 11.12 mg/g, respectively) and, thereafter, no significant differences were detected. The same was observed for total polyunsaturated FA, but, in the esterified fraction, its level increased significantly after 8 weeks (up to 6.01 mg/g) and then reduced to 5.18 mg/g at the end of the study. In conclusion, a lyophilised milk enriched with microbial CLA/CLNA is not entirely stable, including its CLA/CLNA content, which was inclusively enhanced.info:eu-repo/semantics/publishedVersio
Access to Care and Cardiovascular Disease Prevention: A Cross-Sectional Study in 2 Latino Communities.
Cardiovascular disease (CVD) is the leading killer of Americans. CVD is understudied among Latinos, who have high levels of CVD risk factors. This study aimed to determine whether access to health care (ie, insurance status and having a usual source of care) is associated with 4 CVD prevention factors (ie, health care utilization, CVD screening, information received from health care providers, and lifestyle factors) among Latino adults and to evaluate whether the associations depended on CVD clinical risk/disease.Data were collected as part of a community-engaged food environment intervention study in East Los Angeles and Boyle Heights, CA. Logistic regressions were fitted with insurance status and usual source of care as predictors of the 4 CVD prevention factors while controlling for demographics. Analyses were repeated with interactions between self-reported CVD clinical risk/disease and access to care measures.Access to health care significantly increased the odds of CVD prevention. Having a usual source of care was associated with all factors of prevention, whereas being insured was only associated with some factors of prevention. CVD clinical risk/disease did not moderate any associations.Although efforts to reduce CVD risk among Latinos through the Affordable Care Act could be impactful, they might have limited impact in curbing CVD among Latinos, via the law's expansion of insurance coverage. CVD prevention efforts must expand beyond the provision of insurance to effectively lower CVD rates
Stability of a lyophilized milk enriched with microbial CLA/CLNA
info:eu-repo/semantics/publishedVersio
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