220 research outputs found
Exteme Variables in Star Forming Regions
The notion that low- to intermediate-mass young stellar objects (YSOs) gain mass at a
constant rate during the early stages of their evolution appears to be challenged by observations of YSOs suffering sudden increases of the rate at which they gain mass from their circumstellar discs. Also, this idea that stars spend most of their lifetime with a low accretion rate and gain most of their final mass during short-lived episodes of high accretion bursts, helps to solve some long-standing problems in stellar evolution.
The original classification of eruptive variables divides them in two separate subclasses
known as FU Orionis stars (FUors) and EX Lupi stars (EXors). In this classical view FUors
are at an early evolutionary stage and are still gaining mass from their parent envelopes, whilst EXors are thought to be older objects only surrounded by an accretion disc. The problem with this classical view is that it excludes younger protostars which have higher accretion rates but are too deeply embedded in circumstellar matter to be observed at optical wavelengths. Optically invisible protostars have been observed to display large variability in the near-infrared. These and some recent discoveries of new eruptive variables, show characteristics that can be attributed to both of the optically-defined subclasses of eruptive variables. The new objects have been proposed to be part of a new class of eruptive variables. However, a more accepted scenario is that in fact the original classes only represent two extremes of the same phenomena. In this sense eruptive variability could be explained as arising from one physical mechanism, i.e. unsteady accretion, where a variation in the parameters of such mechanism can cause the different characteristics observed in the members of this class. With the aim of studying the incidence of episodic accretion among young stellar objects, and to characterize the nature of these eruptive variables we searched for high amplitude variability in two multi-epoch infrared surveys: the UKIDSS Galactic Plane Survey (GPS) and the Vista Variables in the Via Lactea (VVV). In order to further investigate the nature of the selected variable stars, we use photometric information arising from public surveys at near- to farinfrared wavelengths. In addition we have performed spectroscopic and photometric follow-up for a large subset of the samples arising from GPS and VVV.
We analyse the widely separated two-epoch K-band photometry in the 5th, 7th and 8th data
releases of the UKIDSS Galactic Plane Survey. We find 71 stars with _K > 1 mag, including
2 previously known OH/IR stars and a Nova. Even though the mid-plane is mostly excluded
from the dataset, we find the majority (66%) of our sample to be within known star forming
regions (SFRs), with two large concentrations in the Serpens OB2 association (11 stars) and the Cygnus-X complex (27 stars). The analysis of the multi-epoch K-band photometry of 2010-2012 data from VVV covering the Galactic disc at |b| < 1⊠yields 816 high amplitude variables, which include known variables of different classes such as high mass X-ray binaries, Novae and eclipsing binaries among others. Remarkably, 65% of the sample are found concentrated towards areas of star formation, similar to the results from GPS. In both surveys, sources in SFRs show spectral energy distributions (SEDs) that support classification as YSOs. This indicates that YSOs dominate the Galactic population of high amplitude infrared variable stars at low luminosities and therefore likely dominate the total high amplitude population. Spectroscopic follow-up allows us to confirm the pre-main sequence nature of several GPS and VVV Objects. Most objects in both samples show spectroscopic signatures that can be attributed to YSOs undergoing high states of accretion, such as veiling of photospheric features and CO emission, or show FUor-like spectra. We also find a large fraction of objects with 2.12 Όm H2 emission that can be explained as arising from shock-excited emission caused by molecular outflows. Whether these molecular outflows are related to outbursts events cannot be confirmed from our data.
Adding the GPS and VVV spectroscopic results, we find that between 6 and 14 objects
are new additions to the FUor class from their close resemblance to the near-infrared spectra of FUors, and at least 23 more objects are new additions to the eruptive variable class. For most of these we are unable to classify them into any of the original definitions for this variable class. In any case, we are adding up to 37 new stars to the eruptive variable class which would double the current number of known objects. We note that most objects are found to be deeply embedded optically invisible stars, thus increasing the number of objects belonging to this subclass by a much larger factor. In general, objects in our samples which are found to be likely eruptive variable stars show a mixture of characteristics that can be attributed to both of the optically-defined classes. This agrees well with the recent discoveries in the literature.
Finally, we are able to derive a first rough estimate on the incidence of episodic accretion
among class I YSOs in the star-forming complex G305. We find that _ 9% of such objects
are in a state of high accretion. This number is in agreement with previous theoretical and
observational estimates among class I YSOs
On the incidence of episodic accretion in Class I YSOs from VVV
© 2024 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/Episodic accretion is one of the competing models to explain the observed luminosity spread in young stellar clusters. These short-lived high accretion events could also have a strong impact on planet formation. Observations of high-amplitude variability in young stellar objects (YSOs) due to large changes in the accretion rate provide direct observational evidence for episodic accretion. However, there are still uncertainties in the frequency of these events and if episodic accretion is universal among YSOs. To determine the frequency of outbursts in Class I YSOs, we built a large and robust sample of objects at this evolutionary stage, and searched for high-amplitude near-infrared (ÎKS > 2 mag) variability in the VIRAC2 database of the Vista Variables in the Via Lactea survey. By complementing with near-IR (2MASS and DENIS) and mid-IR (WISE/Neo-WISE) data, we find that from âŒ7000 Class I YSOs, 97 objects can be classified as eruptive variable YSOs. The duration of the outbursts vary from a few months to longer than 9 yr, and cover a similar range of amplitudes. Values of ÎKS > 5 mag, however, are only observed in outbursts with duration longer than 9 yr. When considering different effects of completeness and contamination, we estimate that the incidence of episodic accretion in Class I YSOs is between 2 and 3 per cent. Finally, we determine a recurrence time-scale of long-term outbursts (a.k.a FUors) of kyr. The latter value agrees with previous estimates and is in line with the expectations of higher frequency of FUor outbursts during younger stages of evolution.Peer reviewe
Evaluating Metabolite-Based Biomarkers for Early Diagnosis of Pancreatic Cancer: A Systematic Review
Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest cancers, with five-year
survival rates around 10%. The only curative option remains complete surgical resection, but due
to the delay in diagnosis, less than 20% of patients are eligible for surgery. Therefore, discovering
diagnostic biomarkers for early detection is crucial for improving clinical outcomes. Metabolomics
has become a powerful technology for biomarker discovery, and several metabolomic-based panels
have been proposed for PDAC diagnosis, but these advances have not yet been translated into the
clinic. Therefore, this review focused on summarizing metabolites identified for the early diagnosis
of PDAC in the last five years. Bibliographic searches were performed in the PubMed, Scopus and
WOS databases, using the terms âBiomarkers, Tumorâ, âPancreatic Neoplasmsâ, âEarly Diagnosisâ,
âMetabolomicsâ and âLipidomeâ (January 2018âMarch 2023), and resulted in the selection of fourteen
original studies that compared PDAC patients with subjects with other pancreatic diseases. These
investigations showed amino acid and lipid metabolic pathways as the most commonly altered,
reflecting their potential for biomarker research. Furthermore, other relevant metabolites such as
glucose and lactate were detected in the pancreas tissue and body fluids from PDAC patients. Our
results suggest that the use of metabolomics remains a robust approach to improve the early diagnosis
of PDAC. However, these studies showed heterogeneity with respect to the metabolomics techniques
used and further studies will be needed to validate the clinical utility of these biomarkersB-TIC-414-UGR18 (Junta deAndalucĂa 2020) (FEDER
The relationship between mid-infrared and sub-millimetre variability of deeply embedded protostars
Funding: The contribution of CCP was funded by a Leverhulme Trust Research Project Grant. AS is supported by the STFC grant no. ST/R000824/1. GJH is supported by general grant 11773002 awarded by the National Science Foundation of China. DJ is supported by NRC Canada and by an NSERC Discovery Grant. J-EL and GB are supported by the Basic Science Research Program through the National Research Foundation of Korea (grant no. NRF-2018R1A2B6003423) and the Korea Astronomy and Space Science Institute under the R&D program supervised by the Ministry of Science, ICT and Future Planning. G.B. was also supported by the National Research Foundation of Korea (NRF) grant funded by the Korean Government (NRF-2017H1A2A1043046-Global Ph.D.Fellowship Program).We study the relationship between the mid-infrared (mid-IR) and sub-millimetre (sub-mm) variability of deeply embedded protostars using the multi-epoch data from the Wide-field Infrared Survey Explorer (WISE/NEOWISE) and the ongoing James Clerk Maxwell Telescope (JCMT) Transient Survey. Our search for signs of stochastic (random) and/or secular (roughly monotonic in time) variability in a sample of 59 young stellar objects (YSOs) revealed that 35 are variable in at least one of the two surveys. This variability is dominated by secular changes. Of those objects with secular variability, 14 objects (â 22 per cent of the sample) show correlated secular variability over mid-IR and sub-mm wavelengths. Variable accretion is the likely mechanism responsible for this type of variability. Fluxes of YSOs that vary in both wavelengths follow a relation of log10F4.6(t) = ηlog10F850(t) between the mid-IR and sub-mm, with η = 5.53 ± 0.29. This relationship arises from the fact that sub-mm fluxes respond to the dust temperature in the larger envelope whereas the mid-IR emissivity is more directly proportional to the accretion luminosity. The exact scaling relation, however, depends on the structure of the envelope, the importance of viscous heating in the disc, and dust opacity laws.Publisher PDFPeer reviewe
New Eruptive YSOs from SPICY and WISE
© Published under Creative Commons license CC BY-SA 4.0.This work presents four high-amplitude variable YSOs (â3 mag at near-or mid-IR wavelengths) arising from the SPICY catalog. Three outbursts show a duration that is longer than 1 year, and are still ongoing. And additional YSO brightened over the last two epochs of NEOWISE observations and the duration of the outburst is thus unclear. Analysis of the spectra of the four sources confirms them as new members of the eruptive variable class. We find two YSOs that can be firmly classified as bona fide FUors and one object that falls in the V1647 Ori-like class. Given the uncertainty in the duration of its outburst, an additional YSO can only be classified as a candidate FUor. Continued monitoring and follow-up of these particular sources is important to better understand the accretion process of YSOs.Peer reviewe
Preventive effects of Brassicaceae family for colon cancer prevention: A focus on in vitro studies
The emergence of adverse effects and resistance to colorectal cancer (CRC) current therapies calls for the
development of new strategies aimed at both preventing and treating. In this context, functional extracts from
Brassicaceae family contains abundant bioactive compounds directly related to a positive effect on human health
including cancer. The main objective of this systematic review is to compile all recent studies that analyzed the in
vitro antiproliferative activity of functional extracts or isolated molecules from the Brassicaceae family against
CRC. A total of 711 articles published between January 2011 and May 2021 were identified. Of them, 68 met our
inclusion criteria. Different standardized protocols using variable parts of plants of the Brassicaceae family
resulted in diverse bioactive extracts and/or compounds. Most of them were related to isothiocyanates, which
showed significant antitumor activity against CRC. These in vitro studies provide an excellent guide to direct
research on the applications of plants of the Brassicaceae family to the prevention of this type of tumor. The
extracts and molecules with demonstrated activity against CRC should be tested in vivo and in clinical trials to
determine their usefulness in the prevention of this cancer to reduce its global incidence.Spanish Government RTC2019-006870-1Junta de Andalucia P18-TP-1420Granada UniversityCELLBITEC S.L.FPU2019 grant from the Ministerio de Universidades (Spain) FPU19/06170Spanish Government DIN2018009995B04847216Andalusian Government AGR145
CTS-10
Photometric and Spectroscopic monitoring of YSOs in nearby star forming regions. I. Eruptive YSOs
Mid-infrared (mid-IR) variability in young stellar objects (YSOs) is driven
by several physical mechanisms, which produce a variety of amplitudes and light
curve shapes. One of these mechanisms, variable disk accretion is predicted by
models of episodic accretion to drive secular variability, including in the
mid-IR. Because the largest accretion bursts are rare, adding new objects to
the YSO eruptive variable class aids our understanding of the episodic
accretion phenomenon and its possible impact on stellar and planetary
formation. A previous analysis of 6.5 yr of NeoWISE light curves (3-5 m)
of ~7000 nearby YSOs found an increase in the fraction of variability and
variability amplitude for objects at younger stages of evolution. To help
interpret these light curves, we have obtained low- and high-resolution near-IR
spectra of 78 objects from this sample of YSOs. In this work, we present the
analysis of nine nearby YSOs (d1 kpc) that show the characteristics of known
classes of eruptive variable YSOs. We find one FUor-like source, one EX
Lupi-type object, and six YSOs with mixed characteristics, or V1647 Ori-like
objects. The varied characteristics observed in our sample are consistent with
recent discoveries of eruptive YSOs. We discuss how a wide range in YSO
outburst parameters (central mass, maximum accretion rate during outburst,
evolutionary stage and/or instability leading to the outburst) may play a
significant role in the observed spectro-photometric properties of YSO
outbursts.Comment: 17 pages, 7 figures, accepted for publication in MNRAS on 14 March
202
Diagnosing FUor-like Sources: The Parameter Space of Viscously Heated Disks in the Optical and Near-IR
FU Ori type objects (FUors) are decades-long outbursts of accretion onto
young stars that are strong enough to viscously heat disks so that the disk
outshines the central star. We construct models for FUor objects by calculating
emission components from a steady-state viscous accretion disk, a
passively-heated dusty disk, magnetospheric accretion columns, and the stellar
photosphere. We explore the parameter space of the accretion rate and stellar
mass to investigate implications on the optical and near-infrared spectral
energy distribution and spectral lines. The models are validated by fitting to
multi-wavelength photometry of three confirmed FUor objects, FU Ori, V883 Ori
and HBC 722 and then comparing the predicted spectrum to observed optical and
infrared spectra. The brightness ratio between the viscous disk and the stellar
photosphere, , provides an important guide for identifying viscous
accretion disks, with ("transition line") and ("sufficient
dominance line") marking turning points in diagnostics, evaluated here in the
near-infrared. These turning points indicate the emergence and complete
development of FUor-characteristic strong CO absorption, weak metallic
absorption, the triangular spectral continuum shape in the -band, and
location in color-magnitude diagrams. Lower stellar mass and higher
accretion rate lead to larger ; for ,
corresponds to yr and
to yr. The sufficient dominance line
also coincides with the expected accretion rate where accreting material
directly reaches the star. We discuss implications of the models on extinction
diagnostics, FUor brightening timescales, viscous disks during initial
protostellar growth, and eruptive young stellar objects (YSO) associated with
FUors.Comment: 32 pages, 23 figures, accepted for publication in Ap
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