152 research outputs found
Chemical tracers of high-metallicity environments
We present for the first time a detailed study of the properties of molecular
gas in metal-rich environments such as early-type galaxies (ETGs). We have
explored Photon-Dominated Region (PDR) chemistry for a wide range of physical
conditions likely to be appropriate for these sources. We derive fractional
abundances of the 20 most chemically reactive species as a function of the
metallicity, as a function of the optical depth and for various volume number
gas densities, Far-Ultra Violet (FUV) radiation fields and cosmic ray
ionisation rates. We also investigate the response of the chemistry to the
changes in element enhancement as seen in ETGs. We find that the
fractional abundances of CS, HS, HCS, HO, HO,
HCO and HCN seem invariant to an increase of metallicity whereas
C, CO, CH, CN, HCN, HNC and OCS appear to be the species most
sensitive to this change. The most sensitive species to the change in the
fractional abundance of elements are C, C, CN, HCN, HNC, SO,
SO, HO and CS. Finally, we provide line brightness ratios for the
most abundant species, especially in the range observable with ALMA. Discussion
of favorable line ratios to use for the estimation of super-solar metallicities
and -elements are also provided.Comment: 15 pages, 6 figures, 4 tables, Accepted for publication into MNRA
K2 Discovers a Busy Bee: An Unusual Transiting Neptune Found in the Beehive Cluster
Open clusters have been the focus of several exoplanet surveys but only a few
planets have so far been discovered. The \emph{Kepler} spacecraft revealed an
abundance of small planets around small, cool stars, therefore, such cluster
members are prime targets for exoplanet transit searches. Kepler's new mission,
K2, is targeting several open clusters and star-forming regions around the
ecliptic to search for transiting planets around their low-mass constituents.
Here, we report the discovery of the first transiting planet in the
intermediate-age (800 Myr) Beehive cluster (Praesepe). K2-95 is a faint
() dwarf from K2's Campaign 5
with an effective temperature of , approximately
solar metallicity and a radius of . We
detected a transiting planet with a radius of and an orbital period of 10.134 days. We combined photometry,
medium/high-resolution spectroscopy, adaptive optics/speckle imaging and
archival survey images to rule out any false positive detection scenarios,
validate the planet, and further characterize the system. The planet's radius
is very unusual as M-dwarf field stars rarely have Neptune-sized transiting
planets. The comparatively large radius of K2-95b is consistent with the other
recently discovered cluster planets K2-25b (Hyades) and K2-33b (Upper
Scorpius), indicating systematic differences in their evolutionary states or
formation. These discoveries from K2 provide a snapshot of planet formation and
evolution in cluster environments and thus make excellent laboratories to test
differences between field-star and cluster planet populations.Comment: 14 pages, 8 figues. Accepted for publication in A
Analytic-Wavelet-Ridge-Based Detection of Dynamic Eccentricity in Brushless Direct Current (BLDC) Motors Functioning Under Dynamic Operating Conditions
Disk-Jet Connection in the Radio Galaxy 3C 120
We present the results of extensive multi-frequency monitoring of the radio
galaxy 3C 120 between 2002 and 2007 at X-ray, optical, and radio wave bands, as
well as imaging with the Very Long Baseline Array (VLBA). Over the 5 yr of
observation, significant dips in the X-ray light curve are followed by
ejections of bright superluminal knots in the VLBA images. Consistent with
this, the X-ray flux and 37 GHz flux are anti-correlated with X-ray leading the
radio variations. This implies that, in this radio galaxy, the radiative state
of accretion disk plus corona system, where the X-rays are produced, has a
direct effect on the events in the jet, where the radio emission originates.
The X-ray power spectral density of 3C 120 shows a break, with steeper slope at
shorter timescale and the break timescale is commensurate with the mass of the
central black hole based on observations of Seyfert galaxies and black hole
X-ray binaries. These findings provide support for the paradigm that black hole
X-ray binaries and active galactic nuclei are fundamentally similar systems,
with characteristic time and size scales linearly proportional to the mass of
the central black hole. The X-ray and optical variations are strongly
correlated in 3C 120, which implies that the optical emission in this object
arises from the same general region as the X-rays, i.e., in the accretion
disk-corona system. We numerically model multi-wavelength light curves of 3C
120 from such a system with the optical-UV emission produced in the disk and
the X-rays generated by scattering of thermal photons by hot electrons in the
corona. From the comparison of the temporal properties of the model light
curves to that of the observed variability, we constrain the physical size of
the corona and the distances of the emitting regions from the central BH.Comment: Accepted for publication in the Astrophysical Journal. 28 pages, 21
figures, 2 table
Modelling element abundances in semi-analytic models of galaxy formation
We update the treatment of chemical evolution in the Munich semi-analytic model, L-GALAXIES. Our new implementation includes delayed enrichment from stellar winds, supernovae type II (SNe-II) and supernovae type Ia (SNe-Ia), as well as metallicity-dependent yields and a reformulation of the associated supernova feedback. Two different sets of SN-II yields and three different SN-Ia delay-time distributions (DTDs) are considered, and eleven heavy elements (including O, Mg and Fe) are self-consistently tracked. We compare the results of this new implementation with data on a) local, star-forming galaxies, b) Milky Way disc G dwarfs, and c) local, elliptical galaxies. We find that the z=0 gas-phase mass-metallicity relation is very well reproduced for all forms of DTD considered, as is the [Fe/H] distribution in the Milky Way disc. The [O/Fe] distribution in the Milky Way disc is best reproduced when using a DTD with less than or equal to 50 per cent of SNe-Ia exploding within ~400 Myrs. Positive slopes in the mass-[alpha/Fe] relations of local ellipticals are also obtained when using a DTD with such a minor `prompt' component. Alternatively, metal-rich winds that drive light alpha elements directly out into the circumgalactic medium also produce positive slopes for all forms of DTD and SN-II yields considered. Overall, we find that the best model for matching the wide range of observational data considered here should include a power-law SN-Ia DTD, SN-II yields that take account of prior mass loss through stellar winds, and some direct ejection of light alpha elements out of galaxies
IMI – Clinical Management Guidelines Report
Best practice clinical guidelines for myopia control involve an understanding of the epidemiology of myopia, risk factors, visual environment interventions, and optical and pharmacologic treatments, as well as skills to translate the risks and benefits of a given myopia control treatment into lay language for both the patient and their parent or caregiver. This report details evidence-based best practice management of the pre-, stable, and the progressing myope, including risk factor identification, examination, selection of treatment strategies, and guidelines for ongoing management. Practitioner considerations such as informed consent, prescribing off-label treatment, and guides for patient and parent communication are detailed. The future research directions of myopia interventions and treatments are discussed, along with the provision of clinical references, resources, and recommendations for continuing professional education in this growing area of clinical practice
Sequential Star Formation in RCW 34: A Spectroscopic Census of the Stellar Content of High-mass Star-forming Regions
We present VLT/SINFONI integral field spectroscopy of RCW 34 along with
Spitzer/IRAC photometry of the surroundings. RCW 34 consists of three different
regions. A large bubble has been detected on the IRAC images in which a cluster
of intermediate- and low-mass class II objects is found. At the northern edge
of this bubble, an HII region is located, ionized by 3 OB stars. Intermediate
mass stars (2 - 3 Msun) are detected of G- and K- spectral type. These stars
are still in the pre-main sequence (PMS) phase. North of the HII region, a
photon-dominated region is present, marking the edge of a dense molecular cloud
traced by H2 emission. Several class 0/I objects are associated with this
cloud, indicating that star formation is still taking place. The distance to
RCW 34 is revised to 2.5 +- 0.2 kpc and an age estimate of 2 - 1 Myrs is
derived from the properties of the PMS stars inside the HII region. The most
likely scenario for the formation of the three regions is that star formation
propagates from South to North. First the bubble is formed, produced by
intermediate- and low-mass stars only, after that, the HII region is formed
from a dense core at the edge of the molecular cloud, resulting in the
expansion as a champagne flow. More recently, star formation occurred in the
rest of the molecular cloud. Two different formation scenarios are possible:
(a) The bubble with the cluster of low- and intermediate mass stars triggered
the formation of the O star at the edge of the molecular cloud which in turn
induces the current star-formation in the molecular cloud. (b) An external
triggering is responsible for the star-formation propagating from South to
North. [abridged]Comment: 19 pages, 11 figures, accepted by Ap
Radio source calibration for the VSA and other CMB instruments at around 30 GHz
Accurate calibration of data is essential for the current generation of CMB
experiments. Using data from the Very Small Array (VSA), we describe procedures
which will lead to an accuracy of 1 percent or better for experiments such as
the VSA and CBI. Particular attention is paid to the stability of the receiver
systems, the quality of the site and frequent observations of reference
sources. At 30 GHz the careful correction for atmospheric emission and
absorption is shown to be essential for achieving 1 percent precision. The
sources for which a 1 percent relative flux density calibration was achieved
included Cas A, Cyg A, Tau A and NGC7027 and the planets Venus, Jupiter and
Saturn. A flux density, or brightness temperature in the case of the planets,
was derived at 33 GHz relative to Jupiter which was adopted as the fundamental
calibrator. A spectral index at ~30 GHz is given for each. Cas A,Tau A, NGC7027
and Venus were examined for variability. Cas A was found to be decreasing at
percent per year over the period March 2001 to August 2004.
In the same period Tau A was decreasing at percent per year. A
survey of the published data showed that the planetary nebula NGC7027 decreased
at percent per year over the period 1967 to 2003. Venus showed
an insignificant ( percent) variation with Venusian illumination.
The integrated polarization of Tau A at 33 GHz was found to be
percent at pa .}Comment: 13 pages, 15 figures, submitted to MNRA
Optical Spectra of SNR Candidates in NGC 300
We present moderate-resolution (<5A) long-slit optical spectra of 51 nebular
objects in the nearby Sculptor Group galaxy NGC 300 obtained with the 2.3 meter
Advanced Technology Telescope at Siding Spring Observatory, Australia. Adopting
the criterion of [SII]/Ha>=0.4 to confirm supernova remnants (SNRs) from
optical spectra, we find that of 28 objects previously proposed as SNRs from
optical observations, 22 meet this criterion with six showing [SII]/Ha of less
than 0.4. Of 27 objects suggested as SNRs from radio data, four are associated
with the 28 previously proposed SNRs. Of these four, three (included in the 22
above) meet the criterion. In all, 22 of the 51 nebular objects meet the
[SII]/Ha criterion as SNRs while the nature of the remaining 29 objects remains
undetermined by these observations.Comment: Accepted for publication in Astrophysics & Space Scienc
K2 discovers a busy bee: an unusual transiting Neptune found in the beehive cluster
Open clusters have been the focus of several exoplanet surveys, but only a few planets have so far been discovered. The Kepler spacecraft revealed an abundance of small planets around small cool stars, therefore, such cluster members are prime targets for exoplanet transit searches. Kepler's new mission, K2, is targeting several open clusters and star-forming regions around the ecliptic to search for transiting planets around their low-mass constituents. Here, we report the discovery of the first transiting planet in the intermediate-age (800 Myr) Beehive cluster (Praesepe). K2-95 is a faint (Kp = 15.5 mag) dwarf from K2's Campaign 5 with an effective temperature of 3471 ±124 K, approximately solar metallicity and a radius of 0.402± 0.050.R⊕ We detected a transiting planet with a radius of3.47+0.78 -0.53R⊕ and an orbital period of 10.134 days. We combined photometry, medium/high-resolution spectroscopy, adaptive optics/speckle imaging, and archival survey images to rule out any false-positive detection scenarios, validate the planet, and further characterize the system. The planet's radius is very unusual as M-dwarf field stars rarely have Neptune-sized transiting planets. The comparatively large radius of K2-95b is consistent with the other recently discovered cluster planets K2-25b (Hyades) and K2-33b (Upper Scorpius), indicating systematic differences in their evolutionary states or formation. These discoveries from K2 provide a snapshot of planet formation and evolution in cluster environments and thus make excellent laboratories to test differences between field-star and cluster planet populations
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