796 research outputs found
XMM-Newton imaging of V1818 Ori: a young stellar group on the eastern edge of the Kappa Ori ring
We present the results of a 40 ks XMM-Newton observation centered on the
variable star V1818 Ori. Using a combination of the XMM-Newton and AllWISE
catalog data, we identify a group of about 31 young stellar objects around
V1818 Ori. This group is coincident with the eastern edge of the dust ring
surrounding Kappa Ori. Previously, we concluded that the young stellar objects
on the western side of ring were formed in an episode of star formation that
started 3-5 Myr ago, and are at a distance similar to that of kappa Ori
(250-280 pc) and in the foreground to the Orion A cloud. Here we use the
XMM-Newton observation to calculate X-ray fluxes and luminosities of the young
stars around V1818 Ori. We find that their X-ray luminosity function (XLF),
calculated for a distance of ~270 pc, matches the XLF of the YSOs west of Kappa
Ori. We rule out that this group of young stars is associated to Mon R2 as
assumed in the literature, but rather they are part of the same Kappa Ori's
ring stellar population.Comment: 4 pages, 4 figures, 1 table. Accepted for publication to A&
Smooth X-ray variability from Ophiuchi A+B. A strongly magnetized primary B2 star?
X-rays from massive stars are ubiquitous yet not clearly understood. In an
XMM-Newton observation devoted to observe the first site of star formation in
the Ophiuchi dark cloud, we detect smoothly variable X-ray emission from
the B2IV+B2V system of Ophiuchi. Tentatively we assign the emission to
the primary component. The light curve of the pn camera shows a first phase of
low, almost steady rate, then a rise phase of duration of 10 ks, followed by a
high rate phase. The variability is seen primarily in the band 1.0-8.0 keV
while little variability is detected below 1 keV. The spectral analysis of the
three phases reveals the presence of a hot component at 3.0 keV that adds up to
two relatively cold components at 0.9 keV and 2.2 keV. We explain the smooth
variability with the emergence of an extended active region on the surface of
the primary star due to its fast rotation (v km/s). We estimate
that the region has diameter in the range R. The hard X-ray
emission and its variability hint a magnetic origin, as suggested for few other
late-Oearly-B type stars. We also discuss an alternative explanation based
on the emergence from occultation of a young (5-10 Myr) low mass companion
bright and hot in X-rays.Comment: 4 pages, 3 figures, 2 tables. Accepted for publication as a letter in
A&
The early B-type star Rho Oph A is an X-ray lighthouse
We present the results of a 140 ks XMM-Newton observation of the B2 star
Ophiuchi A. The star has exhibited strong X-ray variability: a
cusp-shaped increase of rate, similar to that which we partially observed in
2013, and a bright flare. These events are separated in time by about 104 ks,
which likely corresponds to the rotational period of the star (1.2 days). Time
resolved spectroscopy of the X-ray spectra shows that the first event is caused
by an increase of the plasma emission measure, while the second increase of
rate is a major flare with temperatures in excess of 60 MK ( keV).
From the analysis of its rise, we infer a magnetic field of G and a
size of the flaring region of cm, which corresponds
to of the stellar radius. We speculate that either an intrinsic
magnetism that produces a hot spot on its surface or an unknown low mass
companion are the source of such X-rays and variability. A hot spot of magnetic
origin should be a stable structure over a time span of 2.5 years, and
suggests an overall large scale dipolar magnetic field that produces an
extended feature on the stellar surface. In the second scenario, a low mass
unknown companion is the emitter of X-rays and it should orbit extremely close
to the surface of the primary in a locked spin-orbit configuration, almost on
the verge of collapsing onto the primary. As such, the X-ray activity of the
secondary star would be enhanced by its young age, and the tight orbit as in RS
Cvn systems and Ophiuchi would constitute an extreme system that is
worthy of further investigation.Comment: 10 pages, 7 figures, 2 tables, A&A accepted, this is the version
after the language editor correction
No X-rays from WASP-18. Implications for its age, activity, and the influence of its massive hot Jupiter
About 20% out of the known exoplanets are Jupiter analogs orbiting
very close to their parent stars. It is still under debate to what detectable
level such hot Jupiters possibly affect the activity of the host stars through
tidal or magnetic star-planet interaction. In this paper we report on an 87 ks
Chandra observation of the hot Jupiter hosting star WASP-18. This system is
composed of an F6 type star and a hot Jupiter of mass orbiting
in less than 20 hr around the parent star. On the basis of an isochrone
fitting, WASP-18 is thought to be 600 Myr old and within the range of
uncertainty of 0.5-2 Gyr. The star is not detected in X-rays down to a
luminosity limit of erg/s, more than two orders of magnitude
lower than expected for a star of this age and mass. This value proves an
unusual lack of activity for a star with estimated age around 600 Myr. We argue
that the massive planet can play a crucial role in disrupting the stellar
magnetic dynamo created within its thin convective layers. Another additional
212 X-ray sources are detected in the Chandra image. We list them and briefly
discuss their nature.Comment: 8 pages, 7 figures, 5 tables. Accepted for publication in A&
The first stars of the Rho Ophiuchi Dark Cloud. XMM-Newton view of Rho Oph and its neighbors
Star formation in molecular clouds can be triggered by the dynamical action
of winds from massive stars. Furthermore, X-ray and UV fluxes from massive
stars can influence the life time of surrounding circumstellar disks. We
present the results of a 53 ks XMM-Newton observation centered on the Rho
Ophiuchi A+B binary system. Rho Ophiiuchi lies in the center of a ring of dust,
likely formed by the action of its winds. This region is different from the
dense core of the cloud (L1688 Core F) where star formation is at work. X-rays
are detected from Rho Ophiuchi as well as a group of surrounding X-ray sources.
We detected 89 X-ray sources, 47 of them have at least one counterpart in 2MASS
+ All-WISE catalogs. Based on IR and X-ray properties, we can distinguish
between young stellar objects (YSOs) belonging to the cloud and background
objects. Among the cloud members, we detect 3 debris disk objects and 22
disk-less / Class III young stars. We show that these stars have ages in
Myr, and are significantly older than the YSOs in L1688. We speculate that they
are the result of an early burst of star formation in the cloud. An X-ray
energy of ergs has been injected into the surrounding
medium during the past Myr, we discuss the effects of such energy budget in
relation to the cloud properties and dynamics.Comment: 17 pages, 9 figures, 7 tables. Accepted for publication to Astronomy
& Astrophysic
The stellar population of Sco OB2 revealed by Gaia DR2 data
Sco OB2 is the nearest OB association, extending over approximately 2000
sq.deg. on the sky. Only its brightest members are already known (from
Hipparcos) across its entire size, while studies of its lower-mass population
refer only to small portions of its extent. In this work we exploit the
capabilities of Gaia DR2 measurements to search for Sco OB2 members across its
entire size and down to the lowest stellar masses. We use both Gaia astrometric
and photometric data to select association members, using minimal assumptions
derived mostly from the Hipparcos studies. Gaia resolves small details in both
the kinematics of individual Sco OB2 subgroups and their distances from the
Sun. We develop methods to explore the 3D kinematics of stellar populations
covering large sky areas. We find ~11000 pre-main sequence (PMS) Sco OB2
members (with <3% contamination), plus ~3600 MS candidate members with a larger
(10-30%) field-star contamination. A higher-confidence subsample of ~9200 PMS
(and ~1340 MS) members is also selected (<1% contamination for the PMS),
affected however by larger (~15%) incompleteness. We classify separately stars
in compact and diffuse populations. Most members belong to a few kinematically
distinct diffuse populations, whose ensemble outlines the association shape.
Upper Sco is the densest part of Sco OB2, with a complex spatial and
kinematical structure, and no global pattern of motion. Other dense subclusters
are found in Upper Centaurus-Lupus and in Lower Centaurus-Crux. Most clustered
stars appear to be younger than the diffuse PMS population, suggesting star
formation in small groups which rapidly disperse and dilute, while keeping
memory of their original kinematics. We also find that the open cluster IC 2602
has a similar dynamics to Sco OB2, and its PMS members are evaporating and
forming a ~10 deg halo around its double-peaked core.Comment: 27 pages, 37 figures. Accepted for publication in Astronomy and
Astrophysic
Screening for Diabetes in At-Risk Populations in Primary Care: A Practice Guide
Diabetes mellitus (DM), a disease with far-reaching cardiovascular and physiological consequences, continues to grow at epidemic proportions despite efforts by the medical community to manage the disease, placing an enormous financial burden on the healthcare system. The Centers for Disease Control and Prevention released a report in 2014 reporting 29.1 million people in the United States have diabetes including 8.1 million undiagnosed cases. Colorado is one of eight states with the most significant increases in DM diagnoses, nearly doubling between 2003 and 2014. An estimated 300,000 adults have diabetes in Colorado and an estimated 110,000 more are undiagnosed (Colorado Department of Public Health and Environment, 2015). In the last three years, the American Diabetes Association (ADA; 2017), the World Health Organization (WHO; 2011b) and the U.S. Preventative Services Task Force (USPSTF; 2017) have released new recommendations on screening and diagnosing DM--all with nearly identical criteria; yet, these recommendations are rarely referenced or utilized. Glycosylated hemoglobin A1c (A1c) and fasting glucose levels are the most widely recognized tests for screening and managing diabetes and are included in the screening recommendations for the three largest organizations. To enhance the quality and consistency of diabetes screening practices in adults in the primary care setting, the purpose of this capstone project was to create a simple yet comprehensive clinical practice guideline utilizing fasting glucose levels and A1c as screening tests to aid providers at Park Avenue Medical Group in Ft. Lupton, Colorado. Two rounds of Delphi surveys were completed by expert provider participants to provide the foundation for the development of a clinical practice guideline in conjunction with current literature supported by the ADA (2017), WHO (2011b), and USPSTF (2017) and a retrospective study conducted as part of this research project. Five providers responded to the first round of surveys and four responded to the second round to elicit over an 80% response rate on the utility, comprehensiveness, and practical use of a diabetes screening guideline and algorithm. The results indicated a strong need for a discrete and comprehensive practice guideline. Data extracted from the retrospective study, literature review, and Delphi surveys were aggregated to develop the clinical practice guideline; through the use of the second Delphi survey, the guideline was refined to accommodate the provider participants’ recommendations. In addition to the creation of a written guideline, an algorithm was designed that offered two clinical pathways depending on age to screen with an informal risk assessment and A1c at different intervals. Additional recommendations outside the scope of this capstone project were included to conduct a second post-implementation retrospective study after an initial pilot period. The Stetler (2001) model was used to translate the research for this project into practice utilizing a clinical practice guideline
Symbiotic stars in X-rays II: faint sources detected with XMM-Newton and Chandra
We report the detection, with and XMM-, of
faint, soft X-ray emission from four symbiotics stars that were not known to be
X-ray sources. These four object show a -type X-ray spectrum, i.e. their
spectra can be modeled with an absorbed optically thin thermal emission with
temperatures of a few million degrees. Photometric series obtained with the
Optical Monitor on board XMM- from V2416 Sgr and NSV 25735
support the proposed scenario where the X-ray emission is produced in a
shock-heated region inside the symbiotic nebulae.Comment: 5 pages, 1 figure, 2 tables; A&A publishe
Detection of magnetic field in the B2 star Oph A with ESO FORS2
Circumstantial evidence suggests that magnetism and enhanced X-ray emission
are likely correlated in early B-type stars: similar fractions of them (
10 %) are strong and hard X-ray sources and possess strong magnetic fields. It
is also known that some B-type stars have spots on their surface. Yet up to now
no X-ray activity associated with spots on early-type stars was detected. In
this Letter we report the detection of a magnetic field on the B2V star
Oph A. Previously, we assessed that the X-ray activity of this star is
associated with a surface spot, herewith we establish its magnetic origin. We
analyzed FORS2 ESO VLT spectra of Oph A taken at two epochs and detected
a longitudinal component of the magnetic field of order of G in one
of the datasets. The detection of the magnetic field only at one epoch can be
explained by stellar rotation which is also invoked to explain observed
periodic X-ray activity. From archival HARPS ESO VLT high resolution spectra we
derived the fundamental stellar parameters of Oph A and further
constrained its age. We conclude that Oph A provides strong evidence for
the presence of active X-ray emitting regions on young magnetized early type
stars.Comment: 4 pages, 1 figure, 2 tables, accepted as a "Letter to the Editor" to
Astronomy & Astrophysic
- …