92 research outputs found
The Astro-WISE approach to quality control for astronomical data
We present a novel approach to quality control during the processing of
astronomical data. Quality control in the Astro-WISE Information System is
integral to all aspects of data handing and provides transparent access to
quality estimators for all stages of data reduction from the raw image to the
final catalog. The implementation of quality control mechanisms relies on the
core features in this Astro-WISE Environment (AWE): an object-oriented
framework, full data lineage, and both forward and backward chaining. Quality
control information can be accessed via the command-line awe-prompt and the
web-based Quality-WISE service. The quality control system is described and
qualified using archive data from the 8-CCD Wide Field Imager (WFI) instrument
(http://www.eso.org/lasilla/instruments/wfi/) on the 2.2-m MPG/ESO telescope at
La Silla and (pre-)survey data from the 32-CCD OmegaCAM instrument
(http://www.astro-wise.org/~omegacam/) on the VST telescope at Paranal.Comment: Accepted for publication in topical issue of Experimental Astronomy
on Astro-WISE information syste
Infrared composition of the Large Magellanic Cloud
The evolution of galaxies and the history of star formation in the Universe
are among the most important topics in today's astrophysics. Especially, the
role of small, irregular galaxies in the star-formation history of the Universe
is not yet clear. Using the data from the AKARI IRC survey of the Large
Magellanic Cloud at 3.2, 7, 11, 15, and 24 {\mu}m wavelengths, i.e., at the
mid- and near-infrared, we have constructed a multiwavelength catalog
containing data from a cross-correlation with a number of other databases at
different wavelengths. We present the separation of different classes of stars
in the LMC in color-color, and color-magnitude, diagrams, and analyze their
contribution to the total LMC flux, related to point sources at different
infrared wavelengths
A single sub-km Kuiper Belt object from a stellar Occultation in archival data
The Kuiper belt is a remnant of the primordial Solar System. Measurements of
its size distribution constrain its accretion and collisional history, and the
importance of material strength of Kuiper belt objects (KBOs). Small, sub-km
sized, KBOs elude direct detection, but the signature of their occultations of
background stars should be detectable. Observations at both optical and X-ray
wavelengths claim to have detected such occultations, but their implied KBO
abundances are inconsistent with each other and far exceed theoretical
expectations. Here, we report an analysis of archival data that reveals an
occultation by a body with a 500 m radius at a distance of 45 AU. The
probability of this event to occur due to random statistical fluctuations
within our data set is about 2%. Our survey yields a surface density of KBOs
with radii larger than 250 m of 2.1^{+4.8}_{-1.7} x 10^7 deg^{-2}, ruling out
inferred surface densities from previous claimed detections by more than 5
sigma. The fact that we detected only one event, firmly shows a deficit of
sub-km sized KBOs compared to a population extrapolated from objects with r>50
km. This implies that sub-km sized KBOs are undergoing collisional erosion,
just like debris disks observed around other stars.Comment: To appear in Nature on December 17, 2009. Under press embargo until
1800 hours London time on 16 December. 19 pages; 7 figure
Surprising dissimilarities in a newly formed pair of 'identical twin' stars
The mass and chemical composition of a star are the primary determinants of
its basic physical properties--radius, temperature, luminosity--and how those
properties evolve with time. Thus, two stars born at the same time, from the
same natal material, and with the same mass are 'identical twins,' and as such
might be expected to possess identical physical attributes. We have discovered
in the Orion Nebula a pair of stellar twins in a newborn binary star system.
Each star in the binary has a mass of 0.41 +/- 0.01 solar masses, identical to
within 2 percent. Here we report that these twin stars have surface
temperatures that differ by ~300K (~10%), and luminosities that differ by ~50%,
both at high confidence level. Preliminary results indicate that the stars'
radii also differ, by 5-10%. These surprising dissimilarities suggest that one
of the twins may have been delayed by several hundred thousand years in its
formation relative to its sibling. Such a delay could only have been detected
in a very young, definitively equal-mass binary system3 such as that reported
here. Our findings reveal cosmic limits on the age synchronisation of young
binary stars, often used as tests for the age calibrations of star-formation
models.Comment: Published in Nature, 19 June 200
Reddening-free Q indices to identify Be star candidates
Astronomical databases currently provide high-volume spectroscopic and
photometric data. While spectroscopic data is better suited to the analysis of
many astronomical objects, photometric data is relatively easier to obtain due
to shorter telescope usage time. Therefore, there is a growing need to use
photometric information to automatically identify objects for further detailed
studies, specially H{\alpha} emission line stars such as Be stars. Photometric
color-color diagrams (CCDs) are commonly used to identify this kind of objects.
However, their identification in CCDs is further complicated by the reddening
effect caused by both the circumstellar and interstellar gas. This effect
prevents the generalization of candidate identification systems. Therefore, in
this work we evaluate the use of neural networks to identify Be star candidates
from a set of OB-type stars. The networks are trained using a labeled subset of
the VPHAS+ and 2MASS databases, with filters u, g, r, H{\alpha}, i, J, H, and
K. In order to avoid the reddening effect, we propose and evaluate the use of
reddening-free Q indices to enhance the generalization of the model to other
databases and objects. To test the validity of the approach, we manually
labeled a subset of the database, and use it to evaluate candidate
identification models. We also labeled an independent dataset for cross dataset
evaluation. We evaluate the recall of the models at a 99% precision level on
both test sets. Our results show that the proposed features provide a
significant improvement over the original filter magnitudes.Comment: 14 pages, 4 figures, Accepted for inclusion in the JCC-BD&ET 2020
minutes book, which will be published in the Springer series CCIS -
Communications in Computer and Information Scienc
A single low-energy, iron-poor supernova as the source of metals in the star SMSS J 031300.36-670839.3
The element abundance ratios of four low-mass stars with extremely low
metallicities indicate that the gas out of which the stars formed was enriched
in each case by at most a few, and potentially only one low-energy, supernova.
Such supernovae yield large quantities of light elements such as carbon but
very little iron. The dominance of low-energy supernovae is surprising, because
it has been expected that the first stars were extremely massive, and that they
disintegrated in pair-instability explosions that would rapidly enrich galaxies
in iron. What has remained unclear is the yield of iron from the first
supernovae, because hitherto no star is unambiguously interpreted as
encapsulating the yield of a single supernova. Here we report the optical
spectrum of SMSS J031300.36- 670839.3, which shows no evidence of iron (with an
upper limit of 10^-7.1 times solar abundance). Based on a comparison of its
abundance pattern with those of models, we conclude that the star was seeded
with material from a single supernova with an original mass of ~60 Mo (and that
the supernova left behind a black hole). Taken together with the previously
mentioned low-metallicity stars, we conclude that low-energy supernovae were
common in the early Universe, and that such supernovae yield light element
enrichment with insignificant iron. Reduced stellar feedback both chemically
and mechanically from low-energy supernovae would have enabled first-generation
stars to form over an extended period. We speculate that such stars may perhaps
have had an important role in the epoch of cosmic reionization and the chemical
evolution of early galaxies.Comment: 28 pages, 6 figures, Natur
Accreting Protoplanets in the LkCa 15 Transition Disk
Exoplanet detections have revolutionized astronomy, offering new insights
into solar system architecture and planet demographics. While nearly 1900
exoplanets have now been discovered and confirmed, none are still in the
process of formation. Transition discs, protoplanetary disks with inner
clearings best explained by the influence of accreting planets, are natural
laboratories for the study of planet formation. Some transition discs show
evidence for the presence of young planets in the form of disc asymmetries or
infrared sources detected within their clearings, as in the case of LkCa 15.
Attempts to observe directly signatures of accretion onto protoplanets have
hitherto proven unsuccessful. Here we report adaptive optics observations of
LkCa 15 that probe within the disc clearing. With accurate source positions
over multiple epochs spanning 2009 - 2015, we infer the presence of multiple
companions on Keplerian orbits. We directly detect H{\alpha} emission from the
innermost companion, LkCa 15 b, evincing hot (~10,000 K) gas falling deep into
the potential well of an accreting protoplanet.Comment: 35 pages, 3 figures, 1 table, 9 extended data item
The Expanding Fireball of Nova Delphini 2013
A classical nova occurs when material accreting onto the surface of a white
dwarf in a close binary system ignites in a thermonuclear runaway. Complex
structures observed in the ejecta at late stages could result from interactions
with the companion during the common envelope phase. Alternatively, the
explosion could be intrinsically bipolar, resulting from a localized ignition
on the surface of the white dwarf or as a consequence of rotational distortion.
Studying the structure of novae during the earliest phases is challenging
because of the high spatial resolution needed to measure their small sizes.
Here we report near-infrared interferometric measurements of the angular size
of Nova Delphini 2013, starting from one day after the explosion and continuing
with extensive time coverage during the first 43 days. Changes in the apparent
expansion rate can be explained by an explosion model consisting of an
optically thick core surrounded by a diffuse envelope. The optical depth of the
ejected material changes as it expands. We detect an ellipticity in the light
distribution, suggesting a prolate or bipolar structure that develops as early
as the second day. Combining the angular expansion rate with radial velocity
measurements, we derive a geometric distance to the nova of 4.54 +/- 0.59 kpc
from the Sun.Comment: Published in Nature. 32 pages. Final version available at
http://www.nature.com/nature/journal/v515/n7526/full/nature13834.htm
COMPANIONS TO APOGEE STARS. I. A MILKY WAY-SPANNING CATALOG OF STELLAR AND SUBSTELLAR COMPANION CANDIDATES AND THEIR DIVERSE HOSTS
In its three years of operation, the Sloan Digital Sky Survey Apache Point Observatory Galactic Evolution Experiment (APOGEE-1) observed >14,000 stars with enough epochs over a sufficient temporal baseline for the fitting of Keplerian orbits. We present the custom orbit-fitting pipeline used to create this catalog, which includes novel quality metrics that account for the phase and velocity coverage of a fitted Keplerian orbit. With a typical radial velocity precision of similar to 100-200 m s(-1), APOGEE can probe systems with small separation companions down to a few Jupiter masses. Here we present initial results from a catalog of 382 of the most compelling stellar and substellar companion candidates detected by APOGEE, which orbit a variety of host stars in diverse Galactic environments. Of these, 376 have no previously known small separation companion. The distribution of companion candidates in this catalog shows evidence for an extremely truncated brown dwarf (BD) desert with a paucity of BD companions only for systems with a 10M(Jup). Finally, we find all types of companions are ubiquitous throughout the Galactic disk with candidate planetary-mass and BD companions to distances of similar to 6 and similar to 16 kpc, respectively
A rocky planet transiting a nearby low-mass star
M-dwarf stars -- hydrogen-burning stars that are smaller than 60 per cent of
the size of the Sun -- are the most common class of star in our Galaxy and
outnumber Sun-like stars by a ratio of 12:1. Recent results have shown that M
dwarfs host Earth-sized planets in great numbers: the average number of M-dwarf
planets that are between 0.5 to 1.5 times the size of Earth is at least 1.4 per
star. The nearest such planets known to transit their star are 39 parsecs away,
too distant for detailed follow-up observations to measure the planetary masses
or to study their atmospheres. Here we report observations of GJ 1132b, a
planet with a size of 1.2 Earth radii that is transiting a small star 12
parsecs away. Our Doppler mass measurement of GJ 1132b yields a density
consistent with an Earth-like bulk composition, similar to the compositions of
the six known exoplanets with masses less than six times that of the Earth and
precisely measured densities. Receiving 19 times more stellar radiation than
the Earth, the planet is too hot to be habitable but is cool enough to support
a substantial atmosphere, one that has probably been considerably depleted of
hydrogen. Because the host star is nearby and only 21 per cent the radius of
the Sun, existing and upcoming telescopes will be able to observe the
composition and dynamics of the planetary atmosphere.Comment: Published in Nature on 12 November 2015, available at
http://dx.doi.org/10.1038/nature15762. This is the authors' version of the
manuscrip
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