102 research outputs found
A new bivalve fauna from the Permian-Triassic boundary section of southwestern China
A new marine bivalve fauna from the continuous Upper Permian Longtan Formation to Lower Triassic Yelang Formation of the Zhongzai section in southwestern China is documented. Four bivalve assemblages spanning the Permian–Triassic boundary are recognized and regionally correlated in South China. The bivalve assemblages changed from elements dominated by Palaeozoic types to those dominated by Mesozoic types. Three new species, Claraia zhongzaiensis sp. nov., Claraia sp. nov. 1 and Claraia sp. nov. 2, are described
New early Triassic Lingulidae (Brachiopoda) genera and species from South China
Two new genera, Sinolingularia gen. nov. and Sinoglottidia gen. nov., together with three new species, Sinolingularia huananensis gen. et sp. nov., Sinolingularia yini gen. et sp. nov. and Sinoglottidia archboldi gen. et sp. nov., are described on the basis of a large collection of well-preserved specimens from several sections straddling the Permian - Triassic boundary in South China. <br /
Secular Evolution in Mira Variable Pulsations
Stellar evolution theory predicts that asymptotic giant branch stars undergo
a series of short thermal pulses that significantly change their luminosity and
mass on timescales of hundreds to thousands of years. Secular changes in these
stars resulting from thermal pulses can be detected as measurable changes in
period if the star is undergoing Mira pulsations. The American Association of
Variable Star Observers (AAVSO) International Database currently contains
visual data for over 1500 Mira variables. Light curves for these stars span
nearly a century in some cases, making it possible to study the secular
evolution of the pulsation behavior on these timescales. In this paper, we
present the results of our study of period change in 547 Mira variables using
data from the AAVSO. We find non-zero rates of period change, dlnP/dt, at the
2-sigma significance level in 57 of the 547 stars, at the 3-sigma level in 21
stars, and at the level of 6-sigma or greater in eight of the 547. The latter
eight stars have been previously noted in the literature, and our derived rates
of period changes largely agree with published values. The largest and most
statistically significant dlnP/dt are consistent with the rates of period
change expected during thermal pulses on the AGB. A number of other stars
exhibit non-monotonic period changes on decades-long timescales, the cause of
which is not yet known.Comment: 37 pages, with 9 figures and 1 table. The complete electronic version
of Table 1 is available from the authors upon request. Accepted for
publication in The Astronomical Journa
A silicified Early Triassic marine assemblage from Svalbard
peerreview_statement: The publishing and review policy for this title is described in its Aims & Scope. aims_and_scope_url: http://www.tandfonline.com/action/journalInformation?show=aimsScope&journalCode=tjsp2
The First Post-Kepler Brightness Dips of KIC 8462852
We present a photometric detection of the first brightness dips of the unique variable star KIC 8462852 since the end of the Kepler space mission in 2013 May. Our regular photometric surveillance started in October 2015, and a sequence of dipping began in 2017 May continuing on through the end of 2017, when the star was no longer visible from Earth. We distinguish four main 1-2.5% dips, named "Elsie," "Celeste," "Skara Brae," and "Angkor", which persist on timescales from several days to weeks. Our main results so far are: (i) there are no apparent changes of the stellar spectrum or polarization during the dips; (ii) the multiband photometry of the dips shows differential reddening favoring non-grey extinction. Therefore, our data are inconsistent with dip models that invoke optically thick material, but rather they are in-line with predictions for an occulter consisting primarily of ordinary dust, where much of the material must be optically thin with a size scale <<1um, and may also be consistent with models invoking variations intrinsic to the stellar photosphere. Notably, our data do not place constraints on the color of the longer-term "secular" dimming, which may be caused by independent processes, or probe different regimes of a single process
Astrophysics in 2005
We bring you, as usual, the Sun and Moon and stars, plus some galaxies and a new section on astrobiology. Some highlights are short (the newly identified class of gamma-ray bursts, and the Deep Impact on Comet 9P/ Tempel 1), some long (the age of the universe, which will be found to have the Earth at its center), and a few metonymic, for instance the term "down-sizing" to describe the evolution of star formation rates with redshift
Palynostratigraphy at the Permian-Triassic boundary of the Amb section, Salt Range, Pakistan
- …