502 research outputs found
A cryogenic liquid-mirror telescope on the moon to study the early universe
We have studied the feasibility and scientific potential of zenith observing
liquid mirror telescopes having 20 to 100 m diameters located on the moon. They
would carry out deep infrared surveys to study the distant universe and follow
up discoveries made with the 6 m James Webb Space Telescope (JWST), with more
detailed images and spectroscopic studies. They could detect objects 100 times
fainter than JWST, observing the first, high-red shift stars in the early
universe and their assembly into galaxies. We explored the scientific
opportunities, key technologies and optimum location of such telescopes. We
have demonstrated critical technologies. For example, the primary mirror would
necessitate a high-reflectivity liquid that does not evaporate in the lunar
vacuum and remains liquid at less than 100K: We have made a crucial
demonstration by successfully coating an ionic liquid that has negligible vapor
pressure. We also successfully experimented with a liquid mirror spinning on a
superconducting bearing, as will be needed for the cryogenic, vacuum
environment of the telescope. We have investigated issues related to lunar
locations, concluding that locations within a few km of a pole are ideal for
deep sky cover and long integration times. We have located ridges and crater
rims within 0.5 degrees of the North Pole that are illuminated for at least
some sun angles during lunar winter, providing power and temperature control.
We also have identified potential problems, like lunar dust. Issues raised by
our preliminary study demand additional in-depth analyses. These issues must be
fully examined as part of a scientific debate we hope to start with the present
article.Comment: 35 pages, 11 figures. To appear in Astrophysical Journal June 20 200
The zenithal 4-m International Liquid Mirror Telescope: a unique facility for supernova studies
The 4-m International Liquid Mirror Telescope (ILMT) will soon become
operational at the newly developed Devasthal observatory near Nainital
(Uttarakhand, India). Coupled with a 4k 4k pixels CCD detector and TDI
optical corrector, it will reach approximately 22.8, 22.3 and 21.4 magnitude in
the , and spectral bands, respectively in a single scan. The
limiting magnitudes can be further improved by co-adding the consecutive night
images in particular filters. The uniqueness to observe the same sky region by
looking towards the zenith direction every night, makes the ILMT a unique
instrument to detect new supernovae (SNe) by applying the image subtraction
technique. High cadence (24 hours) observations will help to construct
dense sampling multi-band SNe light curves. We discuss the importance of the
ILMT facility in the context of SNe studies. Considering the various plausible
cosmological parameters and observational constraints, we perform detailed
calculations of the expected SNe rate that can be detected with the ILMT in
different spectral bands.Comment: 11 pages, 6 figures, 3 tables, accepted for publication in MNRA
Transcriptome analysis of Paspalum notatum and Paspalum vaginatum under water deficit condition.
Drought is one of the abiotic stresses that most affect plant growth and productivity. Grasses of the genus Paspalum are successfully used as turf and forage in Australia, Argentina, Brazil and United States. Paspalum notatum has good forage quality, and P. vaginatum, high tolerance to salinity. In addition, their potential to tolerate drought has been described previously, making them interesting for transcriptome studies under water deficit. The objective of this work was to analyze the gene expression profiles of both species in response to drought.Genética 2019
The Pro12Ala polymorphism of the PPAR gamma 2 gene is associated with hepatic glucose uptake during hyperinsulinemia in subjects with type 2 diabetes mellitus
Nanoengineered Astronomical Optics
We describe a technology for the fabrication of inexpensive and versatile
mirrors through the use of a new type of nanoengineered optical material
composed by the spreading of a self-assembling reflective colloidal film spread
at the surface of a liquid. These new reflecting liquids offer interesting
possibilities for astronomical instrumentation. For example, they can replace
mercury in conventional rotating liquid mirrors. The main advantages offered
include extremely low cost and, by coating a viscous liquid, the possibility of
tilting the mirror by a few tens of degrees. We also have coated ferromagnetic
liquids with these reflecting films. The resulting surfaces can be shaped by
the application of a magnetic field, yielding reflecting surfaces that can have
complicated shapes that can rapidly shift with time. These inexpensive and
versatile optical elements could have numerous scientific and technological
applications. Among possible astronomical applications, they could be used to
make large inexpensive adaptive mirrors exhibiting strokes ranging from
nanometers to several millimeters.Comment: Submitted to Astrophysical Journal Letters. 18 pages, 4 figure
Observations of radio pulses from CU Virginis
The magnetic chemically peculiar star CU Virginis is a unique astrophysical
laboratory for stellar magnetospheres and coherent emission processes. It is
the only known main sequence star to emit a radio pulse every rotation period.
Here we report on new observations of the CU Virginis pulse profile in the 13
and 20\,cm radio bands. The profile is known to be characterised by two peaks
of 100 circularly polarised emission that are thought to arise in an
electron-cyclotron maser mechanism. We find that the trailing peak is stable at
both 13 and 20\,cm, whereas the leading peak is intermittent at 13\,cm. Our
measured pulse arrival times confirm the discrepancy previously reported
between the putative stellar rotation rates measured with optical data and with
radio observations. We suggest that this period discrepancy might be caused by
an unknown companion or by instabilities in the emission region. Regular
long-term pulse timing and simultaneous multi-wavelength observations are
essential to clarify the behaviour of this emerging class of transient radio
source.Comment: Accepted by MNRAS Letters; 5 pages, 2 figures, 3 table
Doppler imaging of the helium-variable star a Cen
The helium-peculiar star a Cen exhibits line profile variations of elements
such as iron, nitrogen and oxygen in addition to its well-known extreme helium
variability. New high S/N, high-resolution spectra are used to perform a
quantitative measurement of the abundances of the star and determine the
relation of the concentrations of the heavier elements on the surface of the
star to the helium concentration and the magnetic field orientation. Doppler
images have been created using programs described in earlier papers by Rice and
others. An alternative surface abundance mapping code has been used to model
the helium line variations after our Doppler imaging of certain individual
helium lines produced mediocre results. We confirm the long-known existence of
helium-rich and helium-poor hemispheres on a Cen and we measure a difference of
more than two orders of magnitude in helium abundance from one side of the star
to the other. Helium is overabundant by a factor of about 5 over much of the
helium-rich hemisphere. Of particular note is our discovery that the
helium-poor hemisphere has a very high abundance of helium-3, approximately
equal to the helium-4 abundance. a Cen is therefore a new member of the small
group of helium-3 stars and the first well-established magnetic member of the
class. For the three metals investigated here, there are two strong
concentrations of abundance near the equator consistent with the positive
magnetic maximum and two somewhat weaker concentrations of abundance where the
helium concentration is centered and roughly where the negative peak of the
magnetic field would be found. Another strong concentration is found near the
equator and this is not explainable in terms of any simple symmetry with the
helium abundance or the apparent magnetic field main polar locations.Comment: 9 pages, 9 figure
Characterisation of the magnetic field of the Herbig Be star HD 200775
After our recent discovery of four magnetic Herbig stars, we have decided to
study in detail one of them, HD 200775, to determine if its magnetic topology
is similar to that of the main sequence magnetic stars. With this aim, we
monitored this star in Stokes I and V over more than two years, using the new
spectropolarimeters ESPaDOnS at CFHT, and Narval at TBL. Using our data, we
find that HD 200775 is a double-lined spectroscopic binary system, whose
secondary seems similar, in temperature, to the primary. We determine the
luminosity ratio of the system, and using the luminosity of the system found in
literature, we derive the luminosity of both stars. From our measurements of
the radial velocities of both stars we determine the ephemeris and the orbital
parameters of the system. We have fitted 30 Stokes V profiles simultaneously,
using a chi2 minimisation method, with a decentered-dipole model. The best-fit
model provides a rotation period of 4.3281 d an inclination angle of 60
degrees, and a magnetic obliquity angle of 125 degrees. The polar strength of
the magnetic dipole field is 1000 G, which is decentered by 0.05 R* from the
center of the star. The derived magnetic field model is qualitatively identical
to those commonly observed in the Ap/Bp stars, which bring strong argument in
favour of the fossil field hypothesis, to explain the origin of the magnetic
fields in the main sequence Ap/Bp stars. Our determination of the inclination
of the rotation axis leads to a radius of the primary which is smaller than
that derived from the HR diagram position. This can be explained by a larger
intrinsic luminosity of the secondary relative to the primary, due to a larger
circumstellar extinction of the secondary relative to the primary.Comment: Accepted for publication in MNRAS, 14 pages, 10 figure
The magnetic Bp star 36 Lyncis, I. Magnetic and photospheric properties
This paper reports the photospheric, magnetic and circumstellar gas
characteristics of the magnetic B8p star 36 Lyncis (HD 79158). Using archival
data and new polarised and unpolarised high-resolution spectra, we redetermine
the basic physical properties, the rotational period and the geometry of the
magnetic field, and the photospheric abundances of various elements.}{Based on
magnetic and spectroscopic measurements, we infer an improved rotational period
of d. We determine a current epoch of the longitudinal
magnetic field positive extremum (HJD 2452246.033), and provide constraints on
the geometry of the dipole magnetic field (i\geq 56\degr, G, unconstrained). We redetermine the effective
temperature and surface gravity using the optical and UV energy distributions,
optical photometry and Balmer line profiles ( K,
), and based on the Hipparcos parallax we redetermine the
luminosity, mass, radius and true rotational speed ( \kms). We
measure photospheric abundances for 21 elements using optical and UV spectra,
and constrain the presence of vertical stratification of these elements. We
perform preliminary Doppler Imaging of the surface distribution of Fe, finding
that Fe is distributed in a patchy belt near the rotational equator. Most
remarkably, we confirm strong variations of the H line core which we
interpret as due to occultations of the star by magnetically-confined
circumstellar gas.Comment: Accepted by Astronomy and Astrophysic
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